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Ähnlich wie BriefAvian Host Diversity and Landscape Characteristics as Predictors_Split
Ähnlich wie BriefAvian Host Diversity and Landscape Characteristics as Predictors_Split (20)
BriefAvian Host Diversity and Landscape Characteristics as Predictors_Split
- 1. AVIAN DIVERSITY AND LANDSCAPEAVIAN DIVERSITY AND LANDSCAPE RISK FACTORS FOR WEST NILE VIRUSRISK FACTORS FOR WEST NILE VIRUS INFECTION IN HOUSE SPARROWSINFECTION IN HOUSE SPARROWS ByBy Lara M. JuliussonLara M. Juliusson An Honors ThesisAn Honors Thesis Submitted to the Department of Ecology and Evolutionary BiologySubmitted to the Department of Ecology and Evolutionary Biology in partial fulfillment for departmental honors for the degree ofin partial fulfillment for departmental honors for the degree of BACHELOR OF ARTSBACHELOR OF ARTS University of Colorado, BoulderUniversity of Colorado, Boulder
- 2. – WNV Emerging zoonosis in North and South America – Exotic pathogen – Example, Yellow-billed magpie (Pica nuttalli) IntroductionIntroduction www.mcssb.com/photos/birds.htm Koenig et al., 2007 % WNV prevalence Conservation Implications of West Nile Virus for American Birds
- 3. Culex tarsalis Breeding habitats: – wetlands – flood-irrigated crops – hoof prints – new water sources with high nutrient content Host seeking: – elevated canopy cover IntroductionIntroduction WNV Transmission Dynamics – Focal Vector www.smcmad.org
- 4. – Predominant WNV host in rural CO – resident all-year in study foci – moderately high reservoir competence – sometimes open- cup nester (trees & hedges) IntroductionIntroduction WNV Transmission Dynamics – Focal Host House sparrow (Passer domesticus)
- 5. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 6. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: 1) perennial water, wetlands, and intermittent water Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 7. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: 1) perennial water, wetlands, and intermittent water 2) sod, corn, and vegetable crop production (highly inorganic N fertilized crops) Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 8. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: 1) perennial water, wetlands, and intermittent water 2) sod, corn, and vegetable crop production (highly inorganic N fertilized crops) 3) flood irrigated crops Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 9. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: 1) perennial water, wetlands, and intermittent water 2) sod, corn, and vegetable crop production (highly inorganic N fertilized crops) 3) flood irrigated crops 4) highly fertilized crops in Interaction with flood irrigated crops Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 10. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: 1) perennial water, wetlands, and intermittent water 2) sod, corn, and vegetable crop production (highly inorganic N fertilized crops) 3) flood irrigated crops 4) highly fertilized crops in Interaction with flood irrigated crops 5) high total nitrogen input from all crops, and Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 11. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: 1) perennial water, wetlands, and intermittent water 2) sod, corn, and vegetable crop production (highly inorganic N fertilized crops) 3) flood irrigated crops 4) highly fertilized crops in Interaction with flood irrigated crops 5) high total nitrogen input from all crops, and 6) tree canopy Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 12. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: 1) perennial water, wetlands, and intermittent water 2) sod, corn, and vegetable crop production (highly inorganic N fertilized crops) 3) flood irrigated crops 4) highly fertilized crops in Interaction with flood irrigated crops 5) high total nitrogen input from all crops, and 6) tree canopy II. WNV infection is predicted to be positively associated with greater numbers of : Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 13. I. WNV infection is predicted to be positively associated with greater percent surrounding area covered by: 1) perennial water, wetlands, and intermittent water 2) sod, corn, and vegetable crop production (highly inorganic N fertilized crops) 3) flood irrigated crops 4) highly fertilized crops in Interaction with flood irrigated crops 5) high total nitrogen input from all crops, and 6) tree canopy II. WNV infection is predicted to be positively associated with greater numbers of : 1) livestock confinement areas Vector feeding preference IntroductionIntroductionHypotheses: LandscapeHypotheses: Landscape
- 14. III. WNV infection is predicted to be negatively associated with: Vector feeding preference IntroductionIntroductionHypotheses: Avian DiversityHypotheses: Avian Diversity
- 15. III. WNV infection is predicted to be negatively associated with: 1) high relative abundance, species richness, and diversity of a group of low reservoir-competent avian orders: Columbiform, Piciform, and Anseriform, Vector feeding preference IntroductionIntroductionHypotheses: Avian DiversityHypotheses: Avian Diversity Reservoir competence = Low: Diluters, e.g. Mallard Mourning dove Rock dove Northern flicker
- 16. III. WNV infection is predicted to be negatively associated with: 1) high relative abundance, species richness, and diversity of a group of low reservoir-competent avian orders: Columbiform, Piciform, and Anseriform, 2) higher density proportions of diluter orders to a group of all Passeriform species. Vector feeding preference IntroductionIntroductionHypotheses: Avian DiversityHypotheses: Avian Diversity Reservoir competence = High: Spreaders, e.g. Low: Diluters, e.g. Mallard Mourning dove Rock dove Northern flicker Blue jay House sparrow
- 17. IV. WNV infection is predicted to be: Vector feeding preference IntroductionIntroductionHypotheses: ControlsHypotheses: Controls
- 18. IV. WNV infection is predicted to be: 1) Positively associated with high vector densities, Vector feeding preference IntroductionIntroductionHypotheses: ControlsHypotheses: Controls Vector density (+)
- 19. IV. WNV infection is predicted to be: 1) Positively associated with high vector densities, 2) Negatively associated with application of adulticide and larvacide control measures, and Vector feeding preference IntroductionIntroductionHypotheses: ControlsHypotheses: Controls Adulticide & Larvacide (-) Vector density (+)
- 20. IV. WNV infection is predicted to be: 1) Positively associated with high vector densities, 2) Negatively associated with application of adulticide and larvacide control measures, and 3) Negatively associated with high preepizotic House sparrow immunity. Vector feeding preference IntroductionIntroductionHypotheses: ControlsHypotheses: Controls Adulticide & Larvacide (-) Vector density (+) Immunity (-)
- 21. Study Area • 23 small, agricultural town cores, in Weld County, CO • 2-kilometer surrounding regions provide independent land cover / land use context for 22 sites MethodsMethods I-25
- 22. • The Centers for Disease Control and Prevention provided raw WNV seroprevalence data • Collected all season • Infection rate from HY sparrow seroprevalence and AHY birds negative in spring, but positive in fall • N=23 for each year MethodsMethods Outcome Variable: 2004 and 2005 house sparrow infection rate at each study site
- 23. • 2004 Model Land Cover: – Perennial water – Intermittent water – Wetlands – Tree canopy – From the National Land Cover Dataset, 2001 GIS grid • 2005 Model Land Use: – Crop type – Irrigation type – From the Colorado Department of Water Resources, 2005 GIS layer – Derived flood-irrigated acreage of corn, sod, and vegetable crops – Estimated pounds of inorganic nitrogen applied to corn, sod, and vegetable crops which were flood-irrigated MethodsMethods Predictor Variables: Land Cover / Land Use Estimated N for 2005 Example Gilcrest: 12 acres F-I Sod x 125 lbs / acre = 1,486 lbs
- 24. • 2005 Model Land Use: – Livestock Confinement Operations (LCOs) – Uses requiring special permits GIS layer from Weld Co. permitting – Verified and improved with digitized LCOs from 2004 aerials, and online business databases MethodsMethods Predictor Variables: Land Cover / Land Use
- 25. • 2005 Model Land Use: – Livestock Confinement Operations (LCOs) – Uses requiring special permits GIS layer from Weld Co. permitting – Verified and improved with digitized LCOs from 2004 aerials, and online business databases MethodsMethods Predictor Variables: Land Cover / Land Use
- 26. • 2004 Model: – CDC provided in-town bird survey of all birds seen or heard during four 1-minute observation intervals – Program MARK closed capture models used to estimate population abundance and density for: 1. Group of diluter orders – Species richness – Shannon’s diversity 2. Group of Passeriformes, and 3. Proportion of diluter density / hectare per 100,000 Passeriformes per hectare MethodsMethods Predictor Variables: Avian Diversity
- 27. • 2004 Model: – CDC provided in-town bird survey of all birds seen or heard during four 1-minute observation intervals – Program MARK closed capture models used to estimate population abundance and density for: 1. Group of diluter orders – Species richness – Shannon’s diversity 2. Group of Passeriformes, and 3. Proportion of diluter density / hectare per 100,000 Passeriformes per hectare Percent of Each Order in the Diluter Group 98% 1% 1% Columbiform Anseriform Piciform MethodsMethods Predictor Variables: Avian Diversity
- 28. • 2004 and 2005 Models: – Cx. tarsalis density data collected by the CDC, 2004 and 2005. – Mosquito control measures for each town (Y/N) provided by CMC, 2004, 2005 – Immunity rate: spring seroprevalence data for AHY sparrows collected by the CDC, 2004 and 2005 MethodsMethods Predictor Variables: Controls http://www.chesapeake.va.us/
- 29. • Poisson single variable regression • Akaike Information Criterion (AICc) model ranking – Screened for best predictors from: • Land Cover predictors (2004 model) • Avian diversity metrics (2004 model) • Land Use predictors (2005 model) • Two separate regression models (ranked by AICc): – 2004: Land cover, avian diversity, and control predictors, plus global model multiple regression – 2005: Land use, and control predictors, plus global model multiple regression • Used “R” statistical software MethodsMethods Statistical Analyses
- 30. Results: Variable ScreeningResults: Variable Screening Land Cover Candidates Akaike Weight Avian Diversity Candidates Akaike Weight Land Use Candidates Akaike Weight Percent perennial water (-) 0.307 Diluter group density (+) 0.636 Estimated N application for flood irrigated sod crops (-) 0.696 Percent wetland (+) 0.288 Proportion diluters to Passeriformes (+) 0.237 Estimated N application for flood irrigated corn crops (-) 0.159 Percent intermittent water (-) 0.285 Diluter species richness (+) 0.060 Total estimated N application for all flood irrigated crops (-) 0.135 Percent canopy (-) 0.095 Passeriform density (+) 0.034 Number of LCOs within 2 km (+) 0.006 Diluter group Shannon's Diversity Index (+) 0.029 Index of distance and size of LCOs within 2 km (+) 0.002 Estimated N application for flood irrigated vegetable crops (+) 0.001
- 31. Results: Variable ScreeningResults: Variable Screening Land Cover Candidates Akaike Weight Avian Diversity Candidates Akaike Weight Land Use Candidates Akaike Weight Percent perennial water (-) 0.307 Diluter group density (+) 0.636 Estimated N application for flood irrigated sod crops (-) 0.696 Percent wetland (+) 0.288 Proportion diluters to Passeriformes (+) 0.237 Estimated N application for flood irrigated corn crops (-) 0.159 Percent intermittent water (-) 0.285 Diluter species richness (+) 0.060 Total estimated N application for all flood irrigated crops (-) 0.135 Percent canopy (-) 0.095 Passeriform density (+) 0.034 Number of LCOs within 2 km (+) 0.006 Diluter group Shannon's Diversity Index (+) 0.029 Index of distance and size of LCOs within 2 km (+) 0.002 Estimated N application for flood irrigated vegetable crops (+) 0.001
- 32. Results: Variable ScreeningResults: Variable Screening Land Cover Candidates Akaike Weight Avian Diversity Candidates Akaike Weight Land Use Candidates Akaike Weight Percent perennial water (-) 0.307 Diluter group density (+) 0.636 Estimated N application for flood irrigated sod crops (-) 0.696 Percent wetland (+) 0.288 Proportion diluters to Passeriformes (+) 0.237 Estimated N application for flood irrigated corn crops (-) 0.159 Percent intermittent water (-) 0.285 Diluter species richness (+) 0.060 Total estimated N application for all flood irrigated crops (-) 0.135 Percent canopy (-) 0.095 Passeriform density (+) 0.034 Number of LCOs within 2 km (+) 0.006 Diluter group Shannon's Diversity Index (+) 0.029 Index of distance and size of LCOs within 2 km (+) 0.002 Estimated N application for flood irrigated vegetable crops (+) 0.001
- 33. Results: Variable ScreeningResults: Variable Screening Land Cover Candidates Akaike Weight Avian Diversity Candidates Akaike Weight Land Use Candidates Akaike Weight Percent perennial water (-) 0.307 Diluter group density (+) 0.636 Estimated N application for flood irrigated sod crops (-) 0.696 Percent wetland (+) 0.288 Proportion diluters to Passeriformes (+) 0.237 Estimated N application for flood irrigated corn crops (-) 0.159 Percent intermittent water (-) 0.285 Diluter species richness (+) 0.060 Total estimated N application for all flood irrigated crops (-) 0.135 Percent canopy (-) 0.095 Passeriform density (+) 0.034 Number of LCOs within 2 km (+) 0.006 Diluter group Shannon's Diversity Index (+) 0.029 Index of distance and size of LCOs within 2 km (+) 0.002 Estimated N application for flood irrigated vegetable crops (+) 0.001
- 34. Results: 2004 ModelResults: 2004 Model Land Cover, Avian Diversity, and Controls Land Cover, best candidate predictor: • Perennial water, 31% likelihood best model • Wetland, 29% • Intermittent water, 29% Avian Diversity, best candidate predictor: • Diluter group density, 64% likelihood best model • Proportion diluters to Passeriformes, 24% Candidate screening:
- 35. Results: 2004 ModelResults: 2004 Model Land Cover, Avian Diversity, and Controls Land Cover, best candidate predictor: • Perennial water, 31% likelihood best model • Wetland, 29% • Intermittent water, 29% Avian Diversity, best candidate predictor: • Diluter group density, 64% likelihood best model • Proportion diluters to Passeriformes, 24% Poisson Model of Infection Rate & Direction of Association Hypothesized Direction Akaike Weight Diluter group density (+) - 0.649 Percent perennial water (-) + 0.095 Immunity rate (+) - 0.083 Global model: diluter group density (+), percent perennial water (-), immunity rate (+), mosquito control (-), mosquito density (+) 0.064 Mosquito control (-) - 0.064 Mosquito density (+) + 0.046 Final model ranking:
- 36. Results: 2004 ModelResults: 2004 Model Land Cover, Avian Diversity, and Controls Land Cover, best candidate predictor: • Perennial water, 31% likelihood best model • Wetland, 29% • Intermittent water, 29% Avian Diversity, best candidate predictor: • Diluter group density, 64% likelihood best model • Proportion diluters to Passeriformes, 24% Poisson Model of Infection Rate & Direction of Association Hypothesized Direction Akaike Weight Diluter group density (+) - 0.649 Percent perennial water (-) + 0.095 Immunity rate (+) - 0.083 Global model: diluter group density (+), percent perennial water (-), immunity rate (+), mosquito control (-), mosquito density (+) 0.064 Mosquito control (-) - 0.064 Mosquito density (+) + 0.046 Final model ranking:
- 37. Results: 2004 ModelResults: 2004 Model Land Cover, Avian Diversity, and Controls
- 38. Results: 2004 ModelResults: 2004 Model Land Cover, Avian Diversity, and Controls
- 39. Results: 2005 ModelResults: 2005 Model Land Use and Controls Variable screening: Land use, best candidate predictor: • N application from flood-irrigated sod crops, 70% likelihood best model • N application from flood-irrigated corn crops, 16% • N application from all flood-irrigated sod 14%
- 40. Results: 2005 ModelResults: 2005 Model Land Use and Controls Land use, best candidate predictor: • N application from flood-irrigated sod crops, 70% likelihood best model • N application from flood-irrigated corn crops, 16% • N application from all flood-irrigated sod 14% Final model ranking: Poisson Model of Infection Rate & Direction of Association Hypothesized Direction Akaike Weight Estimated N application for flood-irrigated sod crops (-) + 0.954 Global Model: N sod (-), LCO count (+), mosquito density (-), immunity rate (+), mosquito control (+) 0.030 Number of LCOs within 2 km (+) + 0.008 Immunity rate (+) - 0.005 Mosquito density (-) + 0.001 Mosquito control (+) - 0.001
- 41. Results: 2005 ModelResults: 2005 Model Land Use and Controls
- 42. DiscussionDiscussion Avian Diversity 2004 Model: Diluter density a 65% likelihood of being the best model: associated with increasing house sparrow WNV infection.
- 43. DiscussionDiscussion Avian Diversity 2004 Model: Diluter density a 65% likelihood of being the best model: associated with increasing house sparrow WNV infection. • Are nestling Columbids competent WNV hosts?
- 44. DiscussionDiscussion Avian Diversity 2004 Model: Diluter density a 65% likelihood of being the best model: associated with increasing house sparrow WNV infection. • Are nestling Columbids competent WNV hosts? o Possibly, Mahmood et al. (2004), found nestling mourning doves competent hosts for St. Louis Encephalitis
- 45. DiscussionDiscussion Avian Diversity 2004 Model: Diluter density a 65% likelihood of being the best model: associated with increasing house sparrow WNV infection. • Are nestling Columbids competent WNV hosts? o Possibly, Mahmood et al. (2004), found nestling mourning doves competent hosts for St. Louis Encephalitis o Columbids are multiple brooders throughout a long breeding season
- 46. DiscussionDiscussion Avian Diversity 2004 Model: Diluter density a 65% likelihood of being the best model: associated with increasing house sparrow WNV infection. • Are nestling Columbids competent WNV hosts? o Possibly, Mahmood et al. (2004), found nestling mourning doves competent hosts for St. Louis Encephalitis o Columbids are multiple brooders throughout a long breeding season o Long breeding season overlaps with WNV transmission season
- 47. DiscussionDiscussion Avian Diversity 2004 Model: Diluter density a 65% likelihood of being the best model: associated with increasing house sparrow WNV infection. • Are nestling Columbids competent WNV hosts? o Possibly, Mahmood et al. (2004), found nestling mourning doves competent hosts for St. Louis Encephalitis o Columbids are multiple brooders throughout a long breeding season o Long breeding season overlaps with WNV transmission season • Are eurasian collared-dove adults competent WNV hosts?
- 48. DiscussionDiscussion Perennial Water 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection.
- 49. DiscussionDiscussion Perennial Water 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. • Is there a threshold effect with increasing percent water cover?
- 50. DiscussionDiscussion Perennial Water 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. • Is there a threshold effect with increasing percent water cover? o The Lowess curves suggest that this is possible.
- 51. DiscussionDiscussion 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. Perennial Water - Continued -
- 52. DiscussionDiscussion 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. • Does water body size, and not just total % area in 2-km matter? Perennial Water
- 53. DiscussionDiscussion 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. • Does water body size, and not just total % area in 2-km matter? Perennial Water Windsor Wellington Severance Berthoud Fort Lupton
- 54. DiscussionDiscussion 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. • Does water body size, and not just total % area in 2-km matter? Perennial Water Windsor Wellington Severance Berthoud Fort Lupton
- 55. DiscussionDiscussion 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. • Does water body size, and not just total % area in 2-km matter? o Visual review suggests that this is possible. Perennial Water Windsor Wellington Severance Berthoud Fort Lupton
- 56. DiscussionDiscussion 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. • Does water body size, and not just total % area in 2-km matter? o Visual review suggests that this is possible. • Indicative of a “dilution effect”? Perennial Water Windsor Wellington Severance Berthoud Fort Lupton
- 57. DiscussionDiscussion 2004 Model: % surrounding perennial water had a 10% likelihood of being the best model: associated with decreasing sparrow infection. • Does water body size, and not just total % area in 2-km matter? o Visual review suggests that this is possible. • Indicative of a “dilution effect”? o Additional bird surveys within 2-km region will be conducted. Perennial Water Windsor Wellington Severance Berthoud Fort Lupton
- 58. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection.
- 59. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection. • Lowess lines suggest a non-linear relationship
- 60. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection. • Lowess lines suggest a non-linear relationship • Are less female cx. tarsalis emerging due to toxins associated with nitrogenous fertilizer?
- 61. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection. • Lowess lines suggest a non-linear relationship • Are less female cx. tarsalis emerging due to toxins associated with nitrogenous fertilizer? o 2005 data do not support this.
- 62. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection. • Lowess lines suggest a non-linear relationship • Are less female cx. tarsalis emerging due to toxins associated with nitrogenous fertilizer? o 2005 data do not support this. • Are smaller females emerging due to larval crowding?
- 63. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection. • Lowess lines suggest a non-linear relationship • Are less female cx. tarsalis emerging due to toxins associated with nitrogenous fertilizer? o 2005 data do not support this. • Are smaller females emerging due to larval crowding? o Reisen (1984)
- 64. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection. • Lowess lines suggest a non-linear relationship • Are less female cx. tarsalis emerging due to toxins associated with nitrogenous fertilizer? o 2005 data do not support this. • Are smaller females emerging due to larval crowding? o Reisen (1984) • Are there changes in vector competence due to larval crowding?
- 65. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection. • Lowess lines suggest a non-linear relationship • Are less female cx. tarsalis emerging due to toxins associated with nitrogenous fertilizer? o 2005 data do not support this. • Are smaller females emerging due to larval crowding? o Reisen (1984) • Are there changes in vector competence due to larval crowding? o Alto et al. (2005)
- 66. DiscussionDiscussion Nitrogen Application 2005 Model: Inorganic nitrogen application due to flood-irrigated sod crops had a 95% likelihood of being the best model: associated with a decrease in house sparrow WNV infection. • Lowess lines suggest a non-linear relationship • Are less female cx. tarsalis emerging due to toxins associated with nitrogenous fertilizer? o 2005 data do not support this. • Are smaller females emerging due to larval crowding? o Reisen (1984) • Are there changes in vector competence due to larval crowding? o Alto et al. (2005) • Why was sod more important than other highly fertilized crops?
- 67. DiscussionDiscussion Controls 2004 and 2005 Models: House sparrow immunity rate in 2004 had an 8% likelihood of being the best model: associated with an increase in house sparrow WNV infection.
- 68. DiscussionDiscussion Controls 2004 and 2005 Models: House sparrow immunity rate in 2004 had an 8% likelihood of being the best model: associated with an increase in house sparrow WNV infection. • Are there increased vector feeding rates due to improved sparrow defense mechanisms?
- 69. DiscussionDiscussion Controls 2004 and 2005 Models: House sparrow immunity rate in 2004 had an 8% likelihood of being the best model: associated with an increase in house sparrow WNV infection. • Are there increased vector feeding rates due to improved sparrow defense mechanisms? •Edman and Scott (1987), Darbro and Harrington (2007)
- 70. DiscussionDiscussion Controls 2004 and 2005 Models: House sparrow immunity rate in 2004 had an 8% likelihood of being the best model: associated with an increase in house sparrow WNV infection. • Are there increased vector feeding rates due to improved sparrow defense mechanisms? •Edman and Scott (1987), Darbro and Harrington (2007) • Effects of other host species not considered.
- 71. DiscussionDiscussion Controls 2004 and 2005 Models: House sparrow immunity rate in 2004 had an 8% likelihood of being the best model: associated with an increase in house sparrow WNV infection. • Are there increased vector feeding rates due to improved sparrow defense mechanisms? •Edman and Scott (1987), Darbro and Harrington (2007) • Effects of other host species not considered. • Effects of nestlings not considered.
- 73. ConclusionsConclusions • Avian diversity and Landscape characteristics have complex interactions and non-linear relationships with WNV infection rate and transmission risk in house sparrows
- 74. ConclusionsConclusions • Avian diversity and Landscape characteristics have complex interactions and non-linear relationships with WNV infection rate and transmission risk in house sparrows • Columbid nestlings are likely to be important amplifiers of WNV infection
- 75. ConclusionsConclusions • Avian diversity and Landscape characteristics have complex interactions and non-linear relationships with WNV infection rate and transmission risk in house sparrows • Columbid nestlings are likely to be important amplifiers of WNV infection • Size-dependent water body thresholds were suggested for perennial water cover effects
- 76. ConclusionsConclusions • Avian diversity and Landscape characteristics have complex interactions and non-linear relationships with WNV infection rate and transmission risk in house sparrows • Columbid nestlings are likely to be important amplifiers of WNV infection • Size-dependent water body thresholds were suggested for perennial water cover effects • Certain flood-irrigated crops with high nitrogen fertilizer application rates showed important associations with infection rate
- 77. ConclusionsConclusions • Avian diversity and Landscape characteristics have complex interactions and non-linear relationships with WNV infection rate and transmission risk in house sparrows • Columbid nestlings are likely to be important amplifiers of WNV infection • Size-dependent water body thresholds were suggested for perennial water cover effects • Certain flood-irrigated crops with high nitrogen fertilizer application rates showed important associations with infection rate • Often assumed predictors of WNV transmission showed few important associations with house sparrow infection
- 78. AcknowledgementsAcknowledgements I thank Dr. Nicholas Komar of the Centers for Disease Control and Prevention for the wonderful opportunity to work on this project, and the support he provided while undertaking it. I also thank my committee members, Drs. Sharon Collinge, Alexander Cruz, and Barbara Demmig-Adams, who provided advice to me on subject content, relevant disease ecology questions, and writing and revision. I also thank GIS personnel from several agencies who provided data to me for free, or before it was available to the public. I additionally thank the CDC staff who collected the data I used. I give special thanks to the Fort Collins Audubon Society for their generous grant that provided gas money for field studies that will extend this research. Lastly, I thank my friends, family, and pets for putting up with me, and Carmen for her love and support.
Hinweis der Redaktion
- So WHY CARE ABOUT WNV TRANSMISSION RISK in HOSP. Well in addition to the implications for human health, as a biologist, I’m interested in the Conservation Implications of WNV transmission. The spread of exotic pathogens into the ranges of naïve populations of native species is a major threat to the conservation of biodiversity on earth. For example, the introduction of avian malaria into Hawaii in the early 1900s is believed to have resulted in the extinction of several native bird species. The emergence of WNv in North and South American may present a similar threat to our native bird species. For example, a study of California breeding birds found that the Yellow-billed Magpie (Pica nuttalli), an endemic species limited to the Central Valley and Central Coastal Ranges of California, had population declines at 60% of California Breeding Bird Survey (BBS) routes between the 2004 and 2005 BBS seasons (Koenig, et al., 2007).
- Now I’m going to go into a little more detail on the specifics of WNV transmission with regard to my study system. C. tarsalis, is the focal vector for this study, and is considered to be the primary vector of WNv in rural areas of Colorado. The larval habitats for C. tarsalis include wetlands, and irrigation overflow areas. C. tarsalis are opportunistic and seek out and will utilize ephemeral water sources such as hoof prints filled with water. Therefore, the species has a high association with livestock watering areas. Additionally, fertilized fields and constructed wetlands with high nitrogen content have been associated with increases in C. tarsalis mosquito abundance. With regard to feeding, C. tarsalis likes to seek out hosts in areas of canopy cover in the evening.
- Next, is my focal host, the House sparrow. House sparrows (P. domesticus) were chosen as the host study species because they are the predominant WNv host in the study’s focal towns, they are resident year-round in the towns, and have been shown to have moderately high reservoir competence for WNv, which I’ll talk about more in just a bit. Also, house sparrows are secondary open cup nesters, preferring cavities, but sometimes nesting in trees and hedges.
- So now I’ll go through the study’s hypotheses more formally.
- So now I’ll go through the study’s hypotheses more formally.
- So now I’ll go through the study’s hypotheses more formally.
- So now I’ll go through the study’s hypotheses more formally.
- So now I’ll go through the study’s hypotheses more formally.
- So now I’ll go through the study’s hypotheses more formally.
- So now I’ll go through the study’s hypotheses more formally.
- So now I’ll go through the study’s hypotheses more formally.
- So now I’ll go through the study’s hypotheses more formally.
- Avian diversity effects.
- Avian diversity effects.
- Avian diversity effects.
- And other Common predictors
- And other Common predictors
- And other Common predictors
- And other Common predictors
- The study area encompassed 1,500 square miles of agricultural land interspersed with small agricultural towns in western Weld County, Colorado. I selected twenty-three study towns within this area based on their small core-area size, and distance from each other, and large urban areas. The study site core was defined as the extent of the town covered with mature landscaping containing large trees, excluding new development. I digitized these areas using GIS from 2004 aerial photos, and then created zones around them to a distance of two kilometers. The distance from each other of at least 4 kilometers provided a closed transmission foci for the house sparrow population, and an independent population of vector mosquitoes, as well as an independent landscape matrix. The study sites had relatively heterogeneous landscapes with regard to the landscape characteristics I was interested in, despite being fairly similar in size. and defined the “within town” (core) area of each town, and then created zones around them at a distance of two and four kilometers.
- I received raw WNV seroprevalence data for house sparrows for two study years from the Centers for Disease Control and Prevention. The data included a spreadsheet with WNV testing results from individual house sparrows that were captured in mist nets and had blood samples taken at several locations in each site’s core over the course of the season. Infection rate for each year was calculated using the WNV seroprevalence of house sparrows who could only have become infected with the virus that year. This included hatch year sparrows, who had just been born that spring, and any after hatch year birds that were sampled in the spring and found to be negative, but then resampled and found to be positive. In addition to this basic seroprevalence calculation, the lab determined mortality rate of house sparrows was included in the calculation using a formula derived by Nick Komar, et al.
- For the landscape characteristics I wanted to investigate I had two sources of data from different years. For land cover variables, GIS grid data was available from the 2001 National Land Cover dataset. Because the study sites are rural and not undergoing large changes, I considered the 2001 snapshot of perennial water, intermittent water, wetlands, and canopy cover to be valid for the 2001 outcome data. However, for land cover, which involved looking at crop and irrigation types, which change annually, I needed to have the corresponding year’s data for comparison with the outcome variable. Luckily, the division of water resources was putting together a 2005 GIS layer of crop type and irrigation type that I could use. Using a GIS tool that derives different metrics from Grid data, I computed the percentages of each of my study variables within the study zones. For example, here you see corn, sod, and vegetable crops in several of my study zones. Using GIS I derived the area in each zone where each crop type was flood-irrigated, which provided my interaction variable of crop type with flood-irrigated crops. Finally, I collected average annual application rates (pounds per acre) of nitrogen by crop type from the “EPA Background Report on Fertilizer Use, Contaminants and Regulations” (Battele, 1999), and multiplied this by the flood-irrigated crop area output from the GIS to calculate the estimated number of pounds of N that would be applied to the crops immediately surrounding each town.
- Another land use characteristic I wanted to investigate was Livestock Confinement Operations, or feedlots. I was able to get a GIS layer from Weld County that included properties that required special permits due to the large densities of animals they were housing, but I found that this data was not complete. In order to enhance the data. I was able to use 2004 aerial photographs, combined with Weld county’s online accessor records and online databases to find high density animal operations within 2 kilometers of my study sites. For example, here you can see the general pattern a feedlot has on an aerial photograph, and when you zoom in, you can actually see the cows milling around.
- Another land use characteristic I wanted to investigate was Livestock Confinement Operations, or feedlots. I was able to get a GIS layer from Weld County that included properties that required special permits due to the large densities of animals they were housing, but I found that this data was not complete. In order to enhance the data. I was able to use 2004 aerial photographs, combined with Weld county’s online accessor records and online databases to find high density animal operations within 2 kilometers of my study sites. For example, here you can see the general pattern a feedlot has on an aerial photograph, and when you zoom in, you can actually see the cows milling around.
- So I could investigate avian diversity, the Centers for Disease Control and Prevention provided me a database of the results of a bird survey conducted at all study sites in 2004. For this study, point counts were conducted at 20 study locations in each site. A record was recorded of all birds seen or heard during four one-minute intervals. I used Program Mark software to calculate population abundance, and population density at each site for a group of all species observed in my three diluter orders, and in the order Passeriformes. Additionally, I calculated species richness and Shannon’s diversity index for the diluter species. And finally, as you can see here in this map, I calculated the proportion of diluter density per 100,000 passeriformes. One thing is important to point out about this data set. Because it was collected in each town, it is not highly diverse with regard to the three diluter orders I was interested in investigating. Because of this, this aspect of the study ends up being mostly about Columbiformes.
- So I could investigate avian diversity, the Centers for Disease Control and Prevention provided me a database of the results of a bird survey conducted at all study sites in 2004. For this study, point counts were conducted at 20 study locations in each site. A record was recorded of all birds seen or heard during four one-minute intervals. I used Program Mark software to calculate population abundance, and population density at each site for a group of all species observed in my three diluter orders, and in the order Passeriformes. Additionally, I calculated species richness and Shannon’s diversity index for the diluter species. And finally, as you can see here in this map, I calculated the proportion of diluter density per 100,000 passeriformes. One thing is important to point out about this data set. Because it was collected in each town, it is not highly diverse with regard to the three diluter orders I was interested in investigating. Because of this, this aspect of the study ends up being mostly about Columbiformes.
- The CDC also provided me with Culex tarsalis density data from the number of mosquitoes captured per trap night using four CO2-baited CDC light traps like the one shown here per study site. Each site was trapped a total of 12 nights from late July to mid-August. Colorado Mosquito Control, the predominant municiple and county mosquito control company in the area provide data from their larvacide and adulticide activities in Weld county. Unfortunately, they provided data that was inconsistent for each year, so I had to use a simple measure of Yes or No for any control activities at each site. Immunity of house sparrows was calculated for each year using the CDC provided house sparrow seroprevelence data. For immunity rate, the metric used was the seroprevalence of after hatch year sparrows sampled in the spring.
- Okay, so I’ve gone through the outcome and predictor variables I used in my study, now I’ll tell you about how I conducted my statistical analyses. First, I used Poisson single variable regression to compare my outcome variable to my predictor variables. Poisson regression is an alternative to linear regression that is used for count outcome data that does not fit the normal distribution. The seroprevalence data I had was count data, and it definitely did not fit the normal distribution. I used Poisson regression to rank the predictors from the land cover, land use, and avian diversity variables, and determine which variable from each of these categories was the best predictor. Once I had determined the strongest variable from each of these categories, I built models for each of my study years, and ranked these against each other to determine their relative strength using Akaike Information Criterion model ranking. I programmed routines in R statistical software to make all this calculations and create my results tables and graphics. For my predictor variables, I used data from two different years. My outcome variable was HOSP infection rate adjusted by mortality rate using this equation. I used Poisson multiple regression and Akaike Information Criterion (AICc) model ranking to find the candidate models that best fit the data.
- First, here are the Akaike rankings from screening the candidate predictor variables from each of my three main predictor categories. The Akaike weight given here indicates the probability that the model is the best among the whole set of candidate models. For instance, an Akaike weight of 0.307 for the % perennial water model, indicates that given the data, it has a 31% chance of being the best one among those considered in the set of candidate models. So we can see that for the land cover variables, % perennial water was found to be the most supported predictor variable of the land cover variables given the 2004 data. For the avian diversity variables, diluter group density was found to be the most supported predictor variable given the 2004 data. And finally, for the land use variables, nitrogen application due to flood-irrigated sod crops was found to be the most supported variable given the 2005 data.
- First, here are the Akaike rankings from screening the candidate predictor variables from each of my three main predictor categories. The Akaike weight given here indicates the probability that the model is the best among the whole set of candidate models. For instance, an Akaike weight of 0.307 for the % perennial water model, indicates that given the data, it has a 31% chance of being the best one among those considered in the set of candidate models. So we can see that for the land cover variables, % perennial water was found to be the most supported predictor variable of the land cover variables given the 2004 data. For the avian diversity variables, diluter group density was found to be the most supported predictor variable given the 2004 data. And finally, for the land use variables, nitrogen application due to flood-irrigated sod crops was found to be the most supported variable given the 2005 data.
- First, here are the Akaike rankings from screening the candidate predictor variables from each of my three main predictor categories. The Akaike weight given here indicates the probability that the model is the best among the whole set of candidate models. For instance, an Akaike weight of 0.307 for the % perennial water model, indicates that given the data, it has a 31% chance of being the best one among those considered in the set of candidate models. So we can see that for the land cover variables, % perennial water was found to be the most supported predictor variable of the land cover variables given the 2004 data. For the avian diversity variables, diluter group density was found to be the most supported predictor variable given the 2004 data. And finally, for the land use variables, nitrogen application due to flood-irrigated sod crops was found to be the most supported variable given the 2005 data.
- First, here are the Akaike rankings from screening the candidate predictor variables from each of my three main predictor categories. The Akaike weight given here indicates the probability that the model is the best among the whole set of candidate models. For instance, an Akaike weight of 0.307 for the % perennial water model, indicates that given the data, it has a 31% chance of being the best one among those considered in the set of candidate models. So we can see that for the land cover variables, % perennial water was found to be the most supported predictor variable of the land cover variables given the 2004 data. For the avian diversity variables, diluter group density was found to be the most supported predictor variable given the 2004 data. And finally, for the land use variables, nitrogen application due to flood-irrigated sod crops was found to be the most supported variable given the 2005 data.
- Well, what did I find when I looked at my predictor categories together? Here are the results from my 2004 model, which included the highest ranked land cover variable, percent perennial water, the highest ranked avian diversity metric, diluter group density, and all the control variables. First I’ll show you the set of models that were ranked using Akaike Information Criterion to be strong possible models because they are within ten percent of the best possible model, diluter group density. Here is the direction Poisson regression found the association to be in, and here is the direction I hypothesized for reference. As you can see, for all of the models within the 10% confidence range of the best model, regression results found exactly the opposite direction. The rest of the models, including the global model with the additive effects of all predictors, were all quite weakly supported, although they did fit the hypothesized directions.
- Well, what did I find when I looked at my predictor categories together? Here are the results from my 2004 model, which included the highest ranked land cover variable, percent perennial water, the highest ranked avian diversity metric, diluter group density, and all the control variables. First I’ll show you the set of models that were ranked using Akaike Information Criterion to be strong possible models because they are within ten percent of the best possible model, diluter group density. Here is the direction Poisson regression found the association to be in, and here is the direction I hypothesized for reference. As you can see, for all of the models within the 10% confidence range of the best model, regression results found exactly the opposite direction. The rest of the models, including the global model with the additive effects of all predictors, were all quite weakly supported, although they did fit the hypothesized directions.
- Well, what did I find when I looked at my predictor categories together? Here are the results from my 2004 model, which included the highest ranked land cover variable, percent perennial water, the highest ranked avian diversity metric, diluter group density, and all the control variables. First I’ll show you the set of models that were ranked using Akaike Information Criterion to be strong possible models because they are within ten percent of the best possible model, diluter group density. Here is the direction Poisson regression found the association to be in, and here is the direction I hypothesized for reference. As you can see, for all of the models within the 10% confidence range of the best model, regression results found exactly the opposite direction. The rest of the models, including the global model with the additive effects of all predictors, were all quite weakly supported, although they did fit the hypothesized directions.
- Here are plots of infection rate against the candidate predictors with Lowess lines superimposed. These trend lines suggest that most predictors are non-linearly related to infection rate. Diluter density is the closest to having a linear relationship, while percent perennial water seems to first be positively associated with infection rate, and then negatively associated. Infection rate first curves down, then upward with preepizootic immunity of House sparrows. I’d like to point out something with regard to these trend lines. While these lines might seem suspect, because of what seem to be outliers that draw the trend lines to them, in fact Lowess lines are outlier resistant, because they assign the Y value at each X weighted higher for nearer values.
- Here are plots of infection rate against the candidate predictors with Lowess lines superimposed. These trend lines suggest that most predictors are non-linearly related to infection rate. Diluter density is the closest to having a linear relationship, while percent perennial water seems to first be positively associated with infection rate, and then negatively associated. Infection rate first curves down, then upward with preepizootic immunity of House sparrows. I’d like to point out something with regard to these trend lines. While these lines might seem suspect, because of what seem to be outliers that draw the trend lines to them, in fact Lowess lines are outlier resistant, because they assign the Y value at each X weighted higher for nearer values.
- Now I’ll move on to the results from the 2005 model, which included land use and control variables. To review, variable screening of all the potential land use variables found nitrogen application for flood-irrigated sod crops to have a 70% likelihood of being the best model. The results with the global model and all control variables included showed that this model was best 95% of the time, although with a direction opposite what I hypothesized. All of the other models were very weak in relation to this model, and none met the 10% confidence range.
- Now I’ll move on to the results from the 2005 model, which included land use and control variables. To review, variable screening of all the potential land use variables found nitrogen application for flood-irrigated sod crops to have a 70% likelihood of being the best model. The results with the global model and all control variables included showed that this model was best 95% of the time, although with a direction opposite what I hypothesized. All of the other models were very weak in relation to this model, and none met the 10% confidence range.
- Plots and lowess regression lines for the 2005 models suggest that nitrogen application due to sod farming is somewhat linearly, negatively associated with infection rate. However, total nitrogen application for all crops, which was not ranked important as a model, but is shown last in this figure for comparison, shows that nitrogen application may first be positively associated and then negatively associated with House sparrow infection rate. The rest of the scatter plots were all for weak models, but I’d just like to point out that they are at least suggesting some complex relationships that seem to indicate that there are changes in directions of association when certain thresholds are met.
- And now on to my discussion. Instead of finding evidence for a dilution effect with increasing abundance species with low reservoir competence at the study sites, I found the reverse effect as a 65% likely model for WNV infection rate. However, as I pointed out the bird data which was for in-town areas only, effectively only tested avian diversity for Columbid species. Well, we have reservoir competence studies that show that Columbid adults have low WNV competence, but what about nestlings? Possibly. In 2004 Mahmood et al. looked at the role nestling Mourning doves have in amplifying St. Louis Encephalitis (SLE); a virus in the same family as West Nile Virus. They showed that nestling Mourning doves are competent hosts for SLE, and noted that they are frequently fed upon by Cx. tarsalis in California. Mourning doves made up 12% of Columbids surveyed in my study sites. Mourning doves are known to be multiple brooders, and have even been called the “champion of multiple brooding” due to their often three to six clutch attempts per breeding season. Although Mourning dove clutches are small, regularly two eggs, the long breeding season of these birds overlaps with the WNV transmission season. Additionally, Mourning doves often nest in the type of canopy cover favorable for host-seeking Cx. tarsalis. Therefore, my results suggest that Mourning dove nestlings may be important for amplification of the virus, if it is shown that they are reservoir competent for WNV. Eurasian collarded-dove (Streptopelia decaocto) made up 44% of the Columbids found within the study sites. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area, and also has multiple broods that overlap with the WNV season, research in this area would prove valuable. ; with equal proportions of each. Both of these species are multiple brooders, and have long breeding seasons that overlap with WNV epizootic activity (Burley, 1980; Robertson, 1990). During experimental infections with SLE, it was found that Rock dove nestlings did not to develop viremias consistently, and when they did, it was at levels probably too low to infect mosquitoes (Reisen, 1992). Research into the reservoir competence of these nestlings for WNV specifically would be beneficial, in order to clarify their role in its transmission. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area (IBID-Beckett, 2007), and has multiple broods that overlap with the WNV season, research in this area would prove valuable. Additionally, because many species of doves and pigeons exist in Central and South America, future research should be done to determine the reservoir competence of their nestlings, as they are possible amplifiers of WNV and may impact the spread of this disease to susceptible avian populations in their respective ranges.
- And now on to my discussion. Instead of finding evidence for a dilution effect with increasing abundance species with low reservoir competence at the study sites, I found the reverse effect as a 65% likely model for WNV infection rate. However, as I pointed out the bird data which was for in-town areas only, effectively only tested avian diversity for Columbid species. Well, we have reservoir competence studies that show that Columbid adults have low WNV competence, but what about nestlings? Possibly. In 2004 Mahmood et al. looked at the role nestling Mourning doves have in amplifying St. Louis Encephalitis (SLE); a virus in the same family as West Nile Virus. They showed that nestling Mourning doves are competent hosts for SLE, and noted that they are frequently fed upon by Cx. tarsalis in California. Mourning doves made up 12% of Columbids surveyed in my study sites. Mourning doves are known to be multiple brooders, and have even been called the “champion of multiple brooding” due to their often three to six clutch attempts per breeding season. Although Mourning dove clutches are small, regularly two eggs, the long breeding season of these birds overlaps with the WNV transmission season. Additionally, Mourning doves often nest in the type of canopy cover favorable for host-seeking Cx. tarsalis. Therefore, my results suggest that Mourning dove nestlings may be important for amplification of the virus, if it is shown that they are reservoir competent for WNV. Eurasian collarded-dove (Streptopelia decaocto) made up 44% of the Columbids found within the study sites. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area, and also has multiple broods that overlap with the WNV season, research in this area would prove valuable. ; with equal proportions of each. Both of these species are multiple brooders, and have long breeding seasons that overlap with WNV epizootic activity (Burley, 1980; Robertson, 1990). During experimental infections with SLE, it was found that Rock dove nestlings did not to develop viremias consistently, and when they did, it was at levels probably too low to infect mosquitoes (Reisen, 1992). Research into the reservoir competence of these nestlings for WNV specifically would be beneficial, in order to clarify their role in its transmission. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area (IBID-Beckett, 2007), and has multiple broods that overlap with the WNV season, research in this area would prove valuable. Additionally, because many species of doves and pigeons exist in Central and South America, future research should be done to determine the reservoir competence of their nestlings, as they are possible amplifiers of WNV and may impact the spread of this disease to susceptible avian populations in their respective ranges.
- And now on to my discussion. Instead of finding evidence for a dilution effect with increasing abundance species with low reservoir competence at the study sites, I found the reverse effect as a 65% likely model for WNV infection rate. However, as I pointed out the bird data which was for in-town areas only, effectively only tested avian diversity for Columbid species. Well, we have reservoir competence studies that show that Columbid adults have low WNV competence, but what about nestlings? Possibly. In 2004 Mahmood et al. looked at the role nestling Mourning doves have in amplifying St. Louis Encephalitis (SLE); a virus in the same family as West Nile Virus. They showed that nestling Mourning doves are competent hosts for SLE, and noted that they are frequently fed upon by Cx. tarsalis in California. Mourning doves made up 12% of Columbids surveyed in my study sites. Mourning doves are known to be multiple brooders, and have even been called the “champion of multiple brooding” due to their often three to six clutch attempts per breeding season. Although Mourning dove clutches are small, regularly two eggs, the long breeding season of these birds overlaps with the WNV transmission season. Additionally, Mourning doves often nest in the type of canopy cover favorable for host-seeking Cx. tarsalis. Therefore, my results suggest that Mourning dove nestlings may be important for amplification of the virus, if it is shown that they are reservoir competent for WNV. Eurasian collarded-dove (Streptopelia decaocto) made up 44% of the Columbids found within the study sites. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area, and also has multiple broods that overlap with the WNV season, research in this area would prove valuable. ; with equal proportions of each. Both of these species are multiple brooders, and have long breeding seasons that overlap with WNV epizootic activity (Burley, 1980; Robertson, 1990). During experimental infections with SLE, it was found that Rock dove nestlings did not to develop viremias consistently, and when they did, it was at levels probably too low to infect mosquitoes (Reisen, 1992). Research into the reservoir competence of these nestlings for WNV specifically would be beneficial, in order to clarify their role in its transmission. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area (IBID-Beckett, 2007), and has multiple broods that overlap with the WNV season, research in this area would prove valuable. Additionally, because many species of doves and pigeons exist in Central and South America, future research should be done to determine the reservoir competence of their nestlings, as they are possible amplifiers of WNV and may impact the spread of this disease to susceptible avian populations in their respective ranges.
- And now on to my discussion. Instead of finding evidence for a dilution effect with increasing abundance species with low reservoir competence at the study sites, I found the reverse effect as a 65% likely model for WNV infection rate. However, as I pointed out the bird data which was for in-town areas only, effectively only tested avian diversity for Columbid species. Well, we have reservoir competence studies that show that Columbid adults have low WNV competence, but what about nestlings? Possibly. In 2004 Mahmood et al. looked at the role nestling Mourning doves have in amplifying St. Louis Encephalitis (SLE); a virus in the same family as West Nile Virus. They showed that nestling Mourning doves are competent hosts for SLE, and noted that they are frequently fed upon by Cx. tarsalis in California. Mourning doves made up 12% of Columbids surveyed in my study sites. Mourning doves are known to be multiple brooders, and have even been called the “champion of multiple brooding” due to their often three to six clutch attempts per breeding season. Although Mourning dove clutches are small, regularly two eggs, the long breeding season of these birds overlaps with the WNV transmission season. Additionally, Mourning doves often nest in the type of canopy cover favorable for host-seeking Cx. tarsalis. Therefore, my results suggest that Mourning dove nestlings may be important for amplification of the virus, if it is shown that they are reservoir competent for WNV. Eurasian collarded-dove (Streptopelia decaocto) made up 44% of the Columbids found within the study sites. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area, and also has multiple broods that overlap with the WNV season, research in this area would prove valuable. ; with equal proportions of each. Both of these species are multiple brooders, and have long breeding seasons that overlap with WNV epizootic activity (Burley, 1980; Robertson, 1990). During experimental infections with SLE, it was found that Rock dove nestlings did not to develop viremias consistently, and when they did, it was at levels probably too low to infect mosquitoes (Reisen, 1992). Research into the reservoir competence of these nestlings for WNV specifically would be beneficial, in order to clarify their role in its transmission. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area (IBID-Beckett, 2007), and has multiple broods that overlap with the WNV season, research in this area would prove valuable. Additionally, because many species of doves and pigeons exist in Central and South America, future research should be done to determine the reservoir competence of their nestlings, as they are possible amplifiers of WNV and may impact the spread of this disease to susceptible avian populations in their respective ranges.
- And now on to my discussion. Instead of finding evidence for a dilution effect with increasing abundance species with low reservoir competence at the study sites, I found the reverse effect as a 65% likely model for WNV infection rate. However, as I pointed out the bird data which was for in-town areas only, effectively only tested avian diversity for Columbid species. Well, we have reservoir competence studies that show that Columbid adults have low WNV competence, but what about nestlings? Possibly. In 2004 Mahmood et al. looked at the role nestling Mourning doves have in amplifying St. Louis Encephalitis (SLE); a virus in the same family as West Nile Virus. They showed that nestling Mourning doves are competent hosts for SLE, and noted that they are frequently fed upon by Cx. tarsalis in California. Mourning doves made up 12% of Columbids surveyed in my study sites. Mourning doves are known to be multiple brooders, and have even been called the “champion of multiple brooding” due to their often three to six clutch attempts per breeding season. Although Mourning dove clutches are small, regularly two eggs, the long breeding season of these birds overlaps with the WNV transmission season. Additionally, Mourning doves often nest in the type of canopy cover favorable for host-seeking Cx. tarsalis. Therefore, my results suggest that Mourning dove nestlings may be important for amplification of the virus, if it is shown that they are reservoir competent for WNV. Eurasian collarded-dove (Streptopelia decaocto) made up 44% of the Columbids found within the study sites. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area, and also has multiple broods that overlap with the WNV season, research in this area would prove valuable. ; with equal proportions of each. Both of these species are multiple brooders, and have long breeding seasons that overlap with WNV epizootic activity (Burley, 1980; Robertson, 1990). During experimental infections with SLE, it was found that Rock dove nestlings did not to develop viremias consistently, and when they did, it was at levels probably too low to infect mosquitoes (Reisen, 1992). Research into the reservoir competence of these nestlings for WNV specifically would be beneficial, in order to clarify their role in its transmission. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area (IBID-Beckett, 2007), and has multiple broods that overlap with the WNV season, research in this area would prove valuable. Additionally, because many species of doves and pigeons exist in Central and South America, future research should be done to determine the reservoir competence of their nestlings, as they are possible amplifiers of WNV and may impact the spread of this disease to susceptible avian populations in their respective ranges.
- And now on to my discussion. Instead of finding evidence for a dilution effect with increasing abundance species with low reservoir competence at the study sites, I found the reverse effect as a 65% likely model for WNV infection rate. However, as I pointed out the bird data which was for in-town areas only, effectively only tested avian diversity for Columbid species. Well, we have reservoir competence studies that show that Columbid adults have low WNV competence, but what about nestlings? Possibly. In 2004 Mahmood et al. looked at the role nestling Mourning doves have in amplifying St. Louis Encephalitis (SLE); a virus in the same family as West Nile Virus. They showed that nestling Mourning doves are competent hosts for SLE, and noted that they are frequently fed upon by Cx. tarsalis in California. Mourning doves made up 12% of Columbids surveyed in my study sites. Mourning doves are known to be multiple brooders, and have even been called the “champion of multiple brooding” due to their often three to six clutch attempts per breeding season. Although Mourning dove clutches are small, regularly two eggs, the long breeding season of these birds overlaps with the WNV transmission season. Additionally, Mourning doves often nest in the type of canopy cover favorable for host-seeking Cx. tarsalis. Therefore, my results suggest that Mourning dove nestlings may be important for amplification of the virus, if it is shown that they are reservoir competent for WNV. Eurasian collarded-dove (Streptopelia decaocto) made up 44% of the Columbids found within the study sites. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area, and also has multiple broods that overlap with the WNV season, research in this area would prove valuable. ; with equal proportions of each. Both of these species are multiple brooders, and have long breeding seasons that overlap with WNV epizootic activity (Burley, 1980; Robertson, 1990). During experimental infections with SLE, it was found that Rock dove nestlings did not to develop viremias consistently, and when they did, it was at levels probably too low to infect mosquitoes (Reisen, 1992). Research into the reservoir competence of these nestlings for WNV specifically would be beneficial, in order to clarify their role in its transmission. No research has yet been published on the WNV reservoir competence of either adult, or nestling Eurasian collared-doves. Because the species has shown expanding populations in my study area (IBID-Beckett, 2007), and has multiple broods that overlap with the WNV season, research in this area would prove valuable. Additionally, because many species of doves and pigeons exist in Central and South America, future research should be done to determine the reservoir competence of their nestlings, as they are possible amplifiers of WNV and may impact the spread of this disease to susceptible avian populations in their respective ranges.
- Next, % perennial water was the best predictor of infection rate for land cover, and was also within the confidence range of likely models. However, overall the direction of association with infection rate for perennial water was found to be decreasing, which was opposite to what I hypothesized. Why is this, is it possible that the relationship is more complex? Well when looking at the Lowess curves of the there is support for a threshold effect, with actually increasing infection rate until a certain percent threshold is met, and then a downturn in infection rate.
- Next, % perennial water was the best predictor of infection rate for land cover, and was also within the confidence range of likely models. However, overall the direction of association with infection rate for perennial water was found to be decreasing, which was opposite to what I hypothesized. Why is this, is it possible that the relationship is more complex? Well when looking at the Lowess curves of the there is support for a threshold effect, with actually increasing infection rate until a certain percent threshold is met, and then a downturn in infection rate.
- Next, % perennial water was the best predictor of infection rate for land cover, and was also within the confidence range of likely models. However, overall the direction of association with infection rate for perennial water was found to be decreasing, which was opposite to what I hypothesized. Why is this, is it possible that the relationship is more complex? Well when looking at the Lowess curves of the there is support for a threshold effect, with actually increasing infection rate until a certain percent threshold is met, and then a downturn in infection rate.
- A second question that came to mind when reviewing these results was Does water body size, and not just total % area of perennial water in 2-km matter? Well let’s look at this with the results found. I’ve drawn a red line here at the inflection point between increasing infection rate and decreasing infection rate as percent water area increases, and labeled the individual sites found where infection rate decreases. Now looking at a map showing water bodies, a water body of this size is about 70 hectares, we can see that these same towns, in comparison with the others, have relatively large water bodies near them. So I would say that visual review suggests that this could be. Now is this indicative of a dilution effect, because one would expect large numbers of Anseriform species to be at these large bodies of water, along with other water birds. Additional bird surveys will be necessary to determine this. The percent area covered by perennial water in and within 2-km of the study sites was selected from the study variables as the most important land cover characteristic associated with WNV infection in House sparrows. Both intermittent water and wetland cover also appeared to be relatively important. However, while wetland area was positively associated, in contrast to their hypothesized effects, perennial and intermittent water areas were both negatively associated with infection rate. To understand these relationships better, these predictor variables were compared with mosquito density, which is typically assumed to increase infection rate. Only wetland area was positively associated, though not significantly, with mosquito density. The Lowess curves of mosquito density and House sparrow infection rate against perennial and intermittent water both show an initial increase with increasing percent area. Intriguingly, both curves turn downward at about the same percent area; between 2% and 3% for perennial water, and 0.09% and 0.1% for intermittent water (see Figures 3b and 3f). While this could be by chance alone, it also may be indication of threshold patterns for these two types of water cover with mosquito density, and infection rate. For example, for perennial water (but not intermittent water), there is a significant positive relationship of larvacide application with water body area. However, larvacide application was not found to be significantly associated with either mosquito density, or infection rate. A biological explanation for the parabolic pattern of water area with infection rate could be that, in addition to total water area, there are variations in average water body size surrounding the various sites that have interaction effects. A preliminary review of the data reveals that of the sites exhibiting a trend toward decreasing infection rate with higher perennial water area, most (Berthoud, Severance, Wellington and Windsor, but not Fort Lupton) were sites that have large lakes near them. An interesting conjecture is that these larger water bodies might allow for a greater abundance of Anseriformes, which could generate a dilution effect. Ezenwa et al. (2007), found that wetland area had a negative effect on WNV prevalence in Culex mosquitoes sampled, while at the same time having a positive effect on mosquito density. Although my results also show a positive effect of wetland area on mosquito density, this is not a significant relationship, and I did find a positive association with infection rate. The differences in the results of our studies may be due to variations in our study methodologies, including: 1.) the size of the area examined, 2.) the vector versus host focus for prevalence data, and 3.)
- A second question that came to mind when reviewing these results was Does water body size, and not just total % area of perennial water in 2-km matter? Well let’s look at this with the results found. I’ve drawn a red line here at the inflection point between increasing infection rate and decreasing infection rate as percent water area increases, and labeled the individual sites found where infection rate decreases. Now looking at a map showing water bodies, a water body of this size is about 70 hectares, we can see that these same towns, in comparison with the others, have relatively large water bodies near them. So I would say that visual review suggests that this could be. Now is this indicative of a dilution effect, because one would expect large numbers of Anseriform species to be at these large bodies of water, along with other water birds. Additional bird surveys will be necessary to determine this. The percent area covered by perennial water in and within 2-km of the study sites was selected from the study variables as the most important land cover characteristic associated with WNV infection in House sparrows. Both intermittent water and wetland cover also appeared to be relatively important. However, while wetland area was positively associated, in contrast to their hypothesized effects, perennial and intermittent water areas were both negatively associated with infection rate. To understand these relationships better, these predictor variables were compared with mosquito density, which is typically assumed to increase infection rate. Only wetland area was positively associated, though not significantly, with mosquito density. The Lowess curves of mosquito density and House sparrow infection rate against perennial and intermittent water both show an initial increase with increasing percent area. Intriguingly, both curves turn downward at about the same percent area; between 2% and 3% for perennial water, and 0.09% and 0.1% for intermittent water (see Figures 3b and 3f). While this could be by chance alone, it also may be indication of threshold patterns for these two types of water cover with mosquito density, and infection rate. For example, for perennial water (but not intermittent water), there is a significant positive relationship of larvacide application with water body area. However, larvacide application was not found to be significantly associated with either mosquito density, or infection rate. A biological explanation for the parabolic pattern of water area with infection rate could be that, in addition to total water area, there are variations in average water body size surrounding the various sites that have interaction effects. A preliminary review of the data reveals that of the sites exhibiting a trend toward decreasing infection rate with higher perennial water area, most (Berthoud, Severance, Wellington and Windsor, but not Fort Lupton) were sites that have large lakes near them. An interesting conjecture is that these larger water bodies might allow for a greater abundance of Anseriformes, which could generate a dilution effect. Ezenwa et al. (2007), found that wetland area had a negative effect on WNV prevalence in Culex mosquitoes sampled, while at the same time having a positive effect on mosquito density. Although my results also show a positive effect of wetland area on mosquito density, this is not a significant relationship, and I did find a positive association with infection rate. The differences in the results of our studies may be due to variations in our study methodologies, including: 1.) the size of the area examined, 2.) the vector versus host focus for prevalence data, and 3.)
- A second question that came to mind when reviewing these results was Does water body size, and not just total % area of perennial water in 2-km matter? Well let’s look at this with the results found. I’ve drawn a red line here at the inflection point between increasing infection rate and decreasing infection rate as percent water area increases, and labeled the individual sites found where infection rate decreases. Now looking at a map showing water bodies, a water body of this size is about 70 hectares, we can see that these same towns, in comparison with the others, have relatively large water bodies near them. So I would say that visual review suggests that this could be. Now is this indicative of a dilution effect, because one would expect large numbers of Anseriform species to be at these large bodies of water, along with other water birds. Additional bird surveys will be necessary to determine this. The percent area covered by perennial water in and within 2-km of the study sites was selected from the study variables as the most important land cover characteristic associated with WNV infection in House sparrows. Both intermittent water and wetland cover also appeared to be relatively important. However, while wetland area was positively associated, in contrast to their hypothesized effects, perennial and intermittent water areas were both negatively associated with infection rate. To understand these relationships better, these predictor variables were compared with mosquito density, which is typically assumed to increase infection rate. Only wetland area was positively associated, though not significantly, with mosquito density. The Lowess curves of mosquito density and House sparrow infection rate against perennial and intermittent water both show an initial increase with increasing percent area. Intriguingly, both curves turn downward at about the same percent area; between 2% and 3% for perennial water, and 0.09% and 0.1% for intermittent water (see Figures 3b and 3f). While this could be by chance alone, it also may be indication of threshold patterns for these two types of water cover with mosquito density, and infection rate. For example, for perennial water (but not intermittent water), there is a significant positive relationship of larvacide application with water body area. However, larvacide application was not found to be significantly associated with either mosquito density, or infection rate. A biological explanation for the parabolic pattern of water area with infection rate could be that, in addition to total water area, there are variations in average water body size surrounding the various sites that have interaction effects. A preliminary review of the data reveals that of the sites exhibiting a trend toward decreasing infection rate with higher perennial water area, most (Berthoud, Severance, Wellington and Windsor, but not Fort Lupton) were sites that have large lakes near them. An interesting conjecture is that these larger water bodies might allow for a greater abundance of Anseriformes, which could generate a dilution effect. Ezenwa et al. (2007), found that wetland area had a negative effect on WNV prevalence in Culex mosquitoes sampled, while at the same time having a positive effect on mosquito density. Although my results also show a positive effect of wetland area on mosquito density, this is not a significant relationship, and I did find a positive association with infection rate. The differences in the results of our studies may be due to variations in our study methodologies, including: 1.) the size of the area examined, 2.) the vector versus host focus for prevalence data, and 3.)
- A second question that came to mind when reviewing these results was Does water body size, and not just total % area of perennial water in 2-km matter? Well let’s look at this with the results found. I’ve drawn a red line here at the inflection point between increasing infection rate and decreasing infection rate as percent water area increases, and labeled the individual sites found where infection rate decreases. Now looking at a map showing water bodies, a water body of this size is about 70 hectares, we can see that these same towns, in comparison with the others, have relatively large water bodies near them. So I would say that visual review suggests that this could be. Now is this indicative of a dilution effect, because one would expect large numbers of Anseriform species to be at these large bodies of water, along with other water birds. Additional bird surveys will be necessary to determine this. The percent area covered by perennial water in and within 2-km of the study sites was selected from the study variables as the most important land cover characteristic associated with WNV infection in House sparrows. Both intermittent water and wetland cover also appeared to be relatively important. However, while wetland area was positively associated, in contrast to their hypothesized effects, perennial and intermittent water areas were both negatively associated with infection rate. To understand these relationships better, these predictor variables were compared with mosquito density, which is typically assumed to increase infection rate. Only wetland area was positively associated, though not significantly, with mosquito density. The Lowess curves of mosquito density and House sparrow infection rate against perennial and intermittent water both show an initial increase with increasing percent area. Intriguingly, both curves turn downward at about the same percent area; between 2% and 3% for perennial water, and 0.09% and 0.1% for intermittent water (see Figures 3b and 3f). While this could be by chance alone, it also may be indication of threshold patterns for these two types of water cover with mosquito density, and infection rate. For example, for perennial water (but not intermittent water), there is a significant positive relationship of larvacide application with water body area. However, larvacide application was not found to be significantly associated with either mosquito density, or infection rate. A biological explanation for the parabolic pattern of water area with infection rate could be that, in addition to total water area, there are variations in average water body size surrounding the various sites that have interaction effects. A preliminary review of the data reveals that of the sites exhibiting a trend toward decreasing infection rate with higher perennial water area, most (Berthoud, Severance, Wellington and Windsor, but not Fort Lupton) were sites that have large lakes near them. An interesting conjecture is that these larger water bodies might allow for a greater abundance of Anseriformes, which could generate a dilution effect. Ezenwa et al. (2007), found that wetland area had a negative effect on WNV prevalence in Culex mosquitoes sampled, while at the same time having a positive effect on mosquito density. Although my results also show a positive effect of wetland area on mosquito density, this is not a significant relationship, and I did find a positive association with infection rate. The differences in the results of our studies may be due to variations in our study methodologies, including: 1.) the size of the area examined, 2.) the vector versus host focus for prevalence data, and 3.)
- A second question that came to mind when reviewing these results was Does water body size, and not just total % area of perennial water in 2-km matter? Well let’s look at this with the results found. I’ve drawn a red line here at the inflection point between increasing infection rate and decreasing infection rate as percent water area increases, and labeled the individual sites found where infection rate decreases. Now looking at a map showing water bodies, a water body of this size is about 70 hectares, we can see that these same towns, in comparison with the others, have relatively large water bodies near them. So I would say that visual review suggests that this could be. Now is this indicative of a dilution effect, because one would expect large numbers of Anseriform species to be at these large bodies of water, along with other water birds. Additional bird surveys will be necessary to determine this. The percent area covered by perennial water in and within 2-km of the study sites was selected from the study variables as the most important land cover characteristic associated with WNV infection in House sparrows. Both intermittent water and wetland cover also appeared to be relatively important. However, while wetland area was positively associated, in contrast to their hypothesized effects, perennial and intermittent water areas were both negatively associated with infection rate. To understand these relationships better, these predictor variables were compared with mosquito density, which is typically assumed to increase infection rate. Only wetland area was positively associated, though not significantly, with mosquito density. The Lowess curves of mosquito density and House sparrow infection rate against perennial and intermittent water both show an initial increase with increasing percent area. Intriguingly, both curves turn downward at about the same percent area; between 2% and 3% for perennial water, and 0.09% and 0.1% for intermittent water (see Figures 3b and 3f). While this could be by chance alone, it also may be indication of threshold patterns for these two types of water cover with mosquito density, and infection rate. For example, for perennial water (but not intermittent water), there is a significant positive relationship of larvacide application with water body area. However, larvacide application was not found to be significantly associated with either mosquito density, or infection rate. A biological explanation for the parabolic pattern of water area with infection rate could be that, in addition to total water area, there are variations in average water body size surrounding the various sites that have interaction effects. A preliminary review of the data reveals that of the sites exhibiting a trend toward decreasing infection rate with higher perennial water area, most (Berthoud, Severance, Wellington and Windsor, but not Fort Lupton) were sites that have large lakes near them. An interesting conjecture is that these larger water bodies might allow for a greater abundance of Anseriformes, which could generate a dilution effect. Ezenwa et al. (2007), found that wetland area had a negative effect on WNV prevalence in Culex mosquitoes sampled, while at the same time having a positive effect on mosquito density. Although my results also show a positive effect of wetland area on mosquito density, this is not a significant relationship, and I did find a positive association with infection rate. The differences in the results of our studies may be due to variations in our study methodologies, including: 1.) the size of the area examined, 2.) the vector versus host focus for prevalence data, and 3.)
- A second question that came to mind when reviewing these results was Does water body size, and not just total % area of perennial water in 2-km matter? Well let’s look at this with the results found. I’ve drawn a red line here at the inflection point between increasing infection rate and decreasing infection rate as percent water area increases, and labeled the individual sites found where infection rate decreases. Now looking at a map showing water bodies, a water body of this size is about 70 hectares, we can see that these same towns, in comparison with the others, have relatively large water bodies near them. So I would say that visual review suggests that this could be. Now is this indicative of a dilution effect, because one would expect large numbers of Anseriform species to be at these large bodies of water, along with other water birds. Additional bird surveys will be necessary to determine this. The percent area covered by perennial water in and within 2-km of the study sites was selected from the study variables as the most important land cover characteristic associated with WNV infection in House sparrows. Both intermittent water and wetland cover also appeared to be relatively important. However, while wetland area was positively associated, in contrast to their hypothesized effects, perennial and intermittent water areas were both negatively associated with infection rate. To understand these relationships better, these predictor variables were compared with mosquito density, which is typically assumed to increase infection rate. Only wetland area was positively associated, though not significantly, with mosquito density. The Lowess curves of mosquito density and House sparrow infection rate against perennial and intermittent water both show an initial increase with increasing percent area. Intriguingly, both curves turn downward at about the same percent area; between 2% and 3% for perennial water, and 0.09% and 0.1% for intermittent water (see Figures 3b and 3f). While this could be by chance alone, it also may be indication of threshold patterns for these two types of water cover with mosquito density, and infection rate. For example, for perennial water (but not intermittent water), there is a significant positive relationship of larvacide application with water body area. However, larvacide application was not found to be significantly associated with either mosquito density, or infection rate. A biological explanation for the parabolic pattern of water area with infection rate could be that, in addition to total water area, there are variations in average water body size surrounding the various sites that have interaction effects. A preliminary review of the data reveals that of the sites exhibiting a trend toward decreasing infection rate with higher perennial water area, most (Berthoud, Severance, Wellington and Windsor, but not Fort Lupton) were sites that have large lakes near them. An interesting conjecture is that these larger water bodies might allow for a greater abundance of Anseriformes, which could generate a dilution effect. Ezenwa et al. (2007), found that wetland area had a negative effect on WNV prevalence in Culex mosquitoes sampled, while at the same time having a positive effect on mosquito density. Although my results also show a positive effect of wetland area on mosquito density, this is not a significant relationship, and I did find a positive association with infection rate. The differences in the results of our studies may be due to variations in our study methodologies, including: 1.) the size of the area examined, 2.) the vector versus host focus for prevalence data, and 3.)
- A second question that came to mind when reviewing these results was Does water body size, and not just total % area of perennial water in 2-km matter? Well let’s look at this with the results found. I’ve drawn a red line here at the inflection point between increasing infection rate and decreasing infection rate as percent water area increases, and labeled the individual sites found where infection rate decreases. Now looking at a map showing water bodies, a water body of this size is about 70 hectares, we can see that these same towns, in comparison with the others, have relatively large water bodies near them. So I would say that visual review suggests that this could be. Now is this indicative of a dilution effect, because one would expect large numbers of Anseriform species to be at these large bodies of water, along with other water birds. Additional bird surveys will be necessary to determine this. The percent area covered by perennial water in and within 2-km of the study sites was selected from the study variables as the most important land cover characteristic associated with WNV infection in House sparrows. Both intermittent water and wetland cover also appeared to be relatively important. However, while wetland area was positively associated, in contrast to their hypothesized effects, perennial and intermittent water areas were both negatively associated with infection rate. To understand these relationships better, these predictor variables were compared with mosquito density, which is typically assumed to increase infection rate. Only wetland area was positively associated, though not significantly, with mosquito density. The Lowess curves of mosquito density and House sparrow infection rate against perennial and intermittent water both show an initial increase with increasing percent area. Intriguingly, both curves turn downward at about the same percent area; between 2% and 3% for perennial water, and 0.09% and 0.1% for intermittent water (see Figures 3b and 3f). While this could be by chance alone, it also may be indication of threshold patterns for these two types of water cover with mosquito density, and infection rate. For example, for perennial water (but not intermittent water), there is a significant positive relationship of larvacide application with water body area. However, larvacide application was not found to be significantly associated with either mosquito density, or infection rate. A biological explanation for the parabolic pattern of water area with infection rate could be that, in addition to total water area, there are variations in average water body size surrounding the various sites that have interaction effects. A preliminary review of the data reveals that of the sites exhibiting a trend toward decreasing infection rate with higher perennial water area, most (Berthoud, Severance, Wellington and Windsor, but not Fort Lupton) were sites that have large lakes near them. An interesting conjecture is that these larger water bodies might allow for a greater abundance of Anseriformes, which could generate a dilution effect. Ezenwa et al. (2007), found that wetland area had a negative effect on WNV prevalence in Culex mosquitoes sampled, while at the same time having a positive effect on mosquito density. Although my results also show a positive effect of wetland area on mosquito density, this is not a significant relationship, and I did find a positive association with infection rate. The differences in the results of our studies may be due to variations in our study methodologies, including: 1.) the size of the area examined, 2.) the vector versus host focus for prevalence data, and 3.)
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. The lowess lines did suggest a non-linear relationship of house sparrow infection with nitrogen application. So what are some possible reasons for this? 2005 data showed no association of mosquito density with nitrogen application. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. Alto, the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005).
- Of the control data I looked at, mosquito density, vector control, and house sparrow immunity, only house sparrow immunity was found to be a somewhat likely model for house sparrow infection. Again, the direction found was opposite what I predicted, and what is commonly thought to be the effect of immunity on susceptible populations. One possibility might be that previously fed on, and infected house sparrows might have increased defenses against mosquitoes that pushed feeding mosquitoes to other birds, perhaps juveniles. There are conflicting studies that begin to address this. Edman and Scott (1987) found that Cx. tarsalis had decreased feeding success when house sparrows had experienced feeding mosquitoes compared to inexperienced sparrows. Darbro and Harrington 2007 examined the blood-feeding success of Cx. pipiens allowed to feed on house sparrows in captivity, as well as the defensive mechanisms used by the lab hosts. They found no evidence of a decrease in blood-feeding success due to a concomitant increase in defensive movements within the three exposures to feeding mosquitoes the sparrows experienced.
- Of the control data I looked at, mosquito density, vector control, and house sparrow immunity, only house sparrow immunity was found to be a somewhat likely model for house sparrow infection. Again, the direction found was opposite what I predicted, and what is commonly thought to be the effect of immunity on susceptible populations. One possibility might be that previously fed on, and infected house sparrows might have increased defenses against mosquitoes that pushed feeding mosquitoes to other birds, perhaps juveniles. There are conflicting studies that begin to address this. Edman and Scott (1987) found that Cx. tarsalis had decreased feeding success when house sparrows had experienced feeding mosquitoes compared to inexperienced sparrows. Darbro and Harrington 2007 examined the blood-feeding success of Cx. pipiens allowed to feed on house sparrows in captivity, as well as the defensive mechanisms used by the lab hosts. They found no evidence of a decrease in blood-feeding success due to a concomitant increase in defensive movements within the three exposures to feeding mosquitoes the sparrows experienced.
- Of the control data I looked at, mosquito density, vector control, and house sparrow immunity, only house sparrow immunity was found to be a somewhat likely model for house sparrow infection. Again, the direction found was opposite what I predicted, and what is commonly thought to be the effect of immunity on susceptible populations. One possibility might be that previously fed on, and infected house sparrows might have increased defenses against mosquitoes that pushed feeding mosquitoes to other birds, perhaps juveniles. There are conflicting studies that begin to address this. Edman and Scott (1987) found that Cx. tarsalis had decreased feeding success when house sparrows had experienced feeding mosquitoes compared to inexperienced sparrows. Darbro and Harrington 2007 examined the blood-feeding success of Cx. pipiens allowed to feed on house sparrows in captivity, as well as the defensive mechanisms used by the lab hosts. They found no evidence of a decrease in blood-feeding success due to a concomitant increase in defensive movements within the three exposures to feeding mosquitoes the sparrows experienced.
- Of the control data I looked at, mosquito density, vector control, and house sparrow immunity, only house sparrow immunity was found to be a somewhat likely model for house sparrow infection. Again, the direction found was opposite what I predicted, and what is commonly thought to be the effect of immunity on susceptible populations. One possibility might be that previously fed on, and infected house sparrows might have increased defenses against mosquitoes that pushed feeding mosquitoes to other birds, perhaps juveniles. There are conflicting studies that begin to address this. Edman and Scott (1987) found that Cx. tarsalis had decreased feeding success when house sparrows had experienced feeding mosquitoes compared to inexperienced sparrows. Darbro and Harrington 2007 examined the blood-feeding success of Cx. pipiens allowed to feed on house sparrows in captivity, as well as the defensive mechanisms used by the lab hosts. They found no evidence of a decrease in blood-feeding success due to a concomitant increase in defensive movements within the three exposures to feeding mosquitoes the sparrows experienced.
- Of the control data I looked at, mosquito density, vector control, and house sparrow immunity, only house sparrow immunity was found to be a somewhat likely model for house sparrow infection. Again, the direction found was opposite what I predicted, and what is commonly thought to be the effect of immunity on susceptible populations. One possibility might be that previously fed on, and infected house sparrows might have increased defenses against mosquitoes that pushed feeding mosquitoes to other birds, perhaps juveniles. There are conflicting studies that begin to address this. Edman and Scott (1987) found that Cx. tarsalis had decreased feeding success when house sparrows had experienced feeding mosquitoes compared to inexperienced sparrows. Darbro and Harrington 2007 examined the blood-feeding success of Cx. pipiens allowed to feed on house sparrows in captivity, as well as the defensive mechanisms used by the lab hosts. They found no evidence of a decrease in blood-feeding success due to a concomitant increase in defensive movements within the three exposures to feeding mosquitoes the sparrows experienced.
- So in conclusion, I’d like to offer the following. My study definitely supported the fact that avian diversity and landscape characteristics have complex associations with WNV infection in house sparrows, and that many of these relationships are non-linear. These findings suggest that Columbids, thought to be unimportant as WNV hosts, may have significant amplification roles during their nestling stage. Of critical importance will be determining the reservoir competence of local South American Columbid species, both adult and nestling, for their abilities to spread the virus within their home ranges. The non-linear findings for perennial water cover suggest threshold effects, which were suggested to include the actual size of water bodies. The strong association of host infection with the application of inorganic nitrogen to flood-irrigated sod crops implies that the risk of WNV infection may change annually. The relationships of nitrogen application to vector development, and ultimately to disease spread is highly complex, and would also benefit from additional studies. The often assumed associates of host infection (vector density, vector control measures, immunity) were not found to be strongly predictive of infection risk. Prior immunity did not dampen infection in house sparrows, but increased it in a non-linear fashion.
- So in conclusion, I’d like to offer the following. My study definitely supported the fact that avian diversity and landscape characteristics have complex associations with WNV infection in house sparrows, and that many of these relationships are non-linear. These findings suggest that Columbids, thought to be unimportant as WNV hosts, may have significant amplification roles during their nestling stage. Of critical importance will be determining the reservoir competence of local South American Columbid species, both adult and nestling, for their abilities to spread the virus within their home ranges. The non-linear findings for perennial water cover suggest threshold effects, which were suggested to include the actual size of water bodies. The strong association of host infection with the application of inorganic nitrogen to flood-irrigated sod crops implies that the risk of WNV infection may change annually. The relationships of nitrogen application to vector development, and ultimately to disease spread is highly complex, and would also benefit from additional studies. The often assumed associates of host infection (vector density, vector control measures, immunity) were not found to be strongly predictive of infection risk. Prior immunity did not dampen infection in house sparrows, but increased it in a non-linear fashion.
- So in conclusion, I’d like to offer the following. My study definitely supported the fact that avian diversity and landscape characteristics have complex associations with WNV infection in house sparrows, and that many of these relationships are non-linear. These findings suggest that Columbids, thought to be unimportant as WNV hosts, may have significant amplification roles during their nestling stage. Of critical importance will be determining the reservoir competence of local South American Columbid species, both adult and nestling, for their abilities to spread the virus within their home ranges. The non-linear findings for perennial water cover suggest threshold effects, which were suggested to include the actual size of water bodies. The strong association of host infection with the application of inorganic nitrogen to flood-irrigated sod crops implies that the risk of WNV infection may change annually. The relationships of nitrogen application to vector development, and ultimately to disease spread is highly complex, and would also benefit from additional studies. The often assumed associates of host infection (vector density, vector control measures, immunity) were not found to be strongly predictive of infection risk. Prior immunity did not dampen infection in house sparrows, but increased it in a non-linear fashion.
- So in conclusion, I’d like to offer the following. My study definitely supported the fact that avian diversity and landscape characteristics have complex associations with WNV infection in house sparrows, and that many of these relationships are non-linear. These findings suggest that Columbids, thought to be unimportant as WNV hosts, may have significant amplification roles during their nestling stage. Of critical importance will be determining the reservoir competence of local South American Columbid species, both adult and nestling, for their abilities to spread the virus within their home ranges. The non-linear findings for perennial water cover suggest threshold effects, which were suggested to include the actual size of water bodies. The strong association of host infection with the application of inorganic nitrogen to flood-irrigated sod crops implies that the risk of WNV infection may change annually. The relationships of nitrogen application to vector development, and ultimately to disease spread is highly complex, and would also benefit from additional studies. The often assumed associates of host infection (vector density, vector control measures, immunity) were not found to be strongly predictive of infection risk. Prior immunity did not dampen infection in house sparrows, but increased it in a non-linear fashion.
- So in conclusion, I’d like to offer the following. My study definitely supported the fact that avian diversity and landscape characteristics have complex associations with WNV infection in house sparrows, and that many of these relationships are non-linear. These findings suggest that Columbids, thought to be unimportant as WNV hosts, may have significant amplification roles during their nestling stage. Of critical importance will be determining the reservoir competence of local South American Columbid species, both adult and nestling, for their abilities to spread the virus within their home ranges. The non-linear findings for perennial water cover suggest threshold effects, which were suggested to include the actual size of water bodies. The strong association of host infection with the application of inorganic nitrogen to flood-irrigated sod crops implies that the risk of WNV infection may change annually. The relationships of nitrogen application to vector development, and ultimately to disease spread is highly complex, and would also benefit from additional studies. The often assumed associates of host infection (vector density, vector control measures, immunity) were not found to be strongly predictive of infection risk. Prior immunity did not dampen infection in house sparrows, but increased it in a non-linear fashion.
- So in conclusion, I’d like to offer the following. My study definitely supported the fact that avian diversity and landscape characteristics have complex associations with WNV infection in house sparrows, and that many of these relationships are non-linear. These findings suggest that Columbids, thought to be unimportant as WNV hosts, may have significant amplification roles during their nestling stage. Of critical importance will be determining the reservoir competence of local South American Columbid species, both adult and nestling, for their abilities to spread the virus within their home ranges. The non-linear findings for perennial water cover suggest threshold effects, which were suggested to include the actual size of water bodies. The strong association of host infection with the application of inorganic nitrogen to flood-irrigated sod crops implies that the risk of WNV infection may change annually. The relationships of nitrogen application to vector development, and ultimately to disease spread is highly complex, and would also benefit from additional studies. The often assumed associates of host infection (vector density, vector control measures, immunity) were not found to be strongly predictive of infection risk. Prior immunity did not dampen infection in house sparrows, but increased it in a non-linear fashion.
- Nitrogen application due to flood irrigated sod crops was the most predictive model of all land use models evaluated. However, it was associated with a decrease in House sparrow infection rate; a direct contrast to the hypothesized relationship of increasing infection due to presumed increases in Culex larval and pupal abundance. Victor and Reuben (2000) found that rice fields in India treated with inorganic fertilizers had significantly higher population densities of local Culex mosquito larva than untreated fields. Likewise, Schaefer et al. (1982), found that Cx. tarsalis had higher breeding rates in California rice fields irrigated with sewage effluent, compared with standard canal water. However, a third study found that concentrated N enrichment from dairy water (2.77 μmoles mL-1) decreased the number of Cx. tarsalis females emerging by a factor of 2.5 when compared with diluted (1:10) dairy water. The females that emerged though were larger in overall mass, and eclosed earlier. In the study, the authors proposed that the reduction in adults emerging from undiluted dairy water might have been due to unknown pollutants in the water, but that the surviving mosquitoes gained from the extra particulate density, and C, N, and P content in the concentrated water. Interestingly, in my study, Lowess curves of Cx. tarsalis density compared with total N application, and N application due to corn, sod, and vegetables all show the same pattern; first a decrease in mosquito density, then a short increase, followed by another decrease (Figure 5), which suggests that a complex set of natural thresholds may be involved in this relationship. Although potentially increasing mosquito densities, inorganic N application at certain levels might also negatively impact future female mosquito populations by increasing density dependent competition, while not providing sustained nutrient enrichment in such ephemeral habitats as flood irrigation runoff pools. Higher larval populations of Cx. tarsalis have been shown to be associated with increased competition, and have resulted in density dependent growth patterns in adult mosquitoes. For example, in lab experiments, crowding of first instar larva significantly decreased adult survival and increased development time of male and female Cx. tarsalis (Reisen et al. 1984). Additionally, Reisen found that wing length of adult females was significantly reduced with increasing larval densities, and he proposed that this could result in a decrease in capacity for arbovirus transmission. While this idea may help to explain the overall decrease in infection rates associated with increasing N application by my study, this is an unanswered matter, and additional research would prove quite valuable. Illustrative of the need for this type of research is a study on larval competition, and its effect on the ability of Aedes mosquitoes to become infected with Sindbis virus. This study found that larval crowding actually increased adult Aedes albopictus infection, titer, and virus dissemination rates. However, this was not the case for the related species, Aedes aegypti, indicating that larval densities may have species-specific implications for arbovirus transmission (Alto et al., 2005). Finally, unlike land cover and avian diversity, which will generally have relatively slow changes in their spatial structure, N application potentially changes seasonally when crop types are rotated to different fields. Because this research shows a strong association of host infection with different crop types, it implies that the risk of WNV infection may change annually across the agricultural landscape.