“ Serpentine outcrops occur in areas of tectonic activity, where ultramafic minerals high in iron and magnesium but low in calcium have intruded or displaced overlying sedimentary rocks” Serpentine outcrops associated with faulting are abundant in this area (approx 60) Some of the outcrops support native grassland, so provide potential habitat Other outcrops support chaparral or grasslands dominated by introduced species or have been developed in 1986 (preliminary survey), adults were found on 8 of the small patches that were 1.4-4.4 km from MH No adults on 15 suitable habitat patches 4.9-20.8 km from MH
S/SW slopes have high winter and spring incident solar radiation Pre diapause larvae must complete development to 4th instar before the Plantago erecta senesces- this is the primary determinant of population size changes Normally, P. erecta senesces early on these slopes so larvae die In wet years, plant senescence is delayed, larvae on S/SW slopes contribute disproportionately because greater incident solar radiation causes these larvae to develop faster so that they emerge sooner and lay eggs sooner-- their progeny will have a head start in the next year’s race against senescence patch to patch plant resources differ due to land use: heavily grazed areas have lower proportions of native host and nectar plants - if in high enough densities, Orthocarpus (which senesces later) can aid in the survival of the butterfly (can help prevent extinction during the dry years when P. erecta senesces early - abundant nectar may allow females to produce more egg masses, so they can build up pop sizes during wet years to “buffer” them against extinction during poor years
frequency of severe droughts in the past in CA have occurred approx every 50 years
Systematically searched for potential habitat Jan/Feb 1987 Patches with adults found during flight season (Mar/Apr)= occupied patches Looked at the 8 sites found in 1986 were checked for larvae, which would indicate breeding
Measured from patch to nearest edge Warm, moderate, and cool slopes were defined in terms of aspect and tilt angle (gives a measure of incident solar radiation) Used transects (3-10, depending on patch size) to measure densities - started from one edge where first P. erecta found to the other -every 10 paces, presence and absence of each plant within 1/2 m radius was noted Used logistic regression to test influence of the habitat quality measurements on the presence or absence of butterflies on the 59 patches)
Used Fisher-Ford technique to estimate population sizes and their variances Mentioned in results: The authors wanted to make sure that the distance of a patch from MH did not have a significant impact on the quality of that patch, so they repeated the regression using only the patches within 4.4 km of MH (b/c within this radius, distance has no relation to occupancy)
here, the 6 variables are % warm, % moderate, % cool, 2 host plants, and 1 nectar plant There was a significant correlation between the amount of warm area and the amount of (moderate + cool area), so the moderate and cool area terms were combined (this was significant at P < 0.05) No readily available biological explanation of the negative coefficient term for warm area (believed to be a by-product of combining the moderate and cool area terms)
Table 2 lists the 27 patches that were determined suitable using the quality regression equation Distance from MH, area, quality, and observed and expected population sizes are given Lowest quality patch that was occupied had a pop estimated at 12 +- 5.47 SD, so used that patch as a minimum standard for a habitable patch
This indicates that the suitable patches in the study area remain unoccupied because they are too far from a source of colonists -A metapopulation with a “Mainland-Island” structure!
This rate was determined assuming that the 3 populations went completely extinct in 1975-1977 (so that the presence of butterflies in 1987 indicates recolonization) AND that All/nearly all colonization of the small patches has come from MH These rates were assumed to be continuous Best fit value of D’ = 1.7 Since the lowest rate of extinction is assumed to be once every 50 years and the colonization rate is known, the maximum predicted occupancy after 50 years can be predicted (it is the sum of all the colonization probabilities of the patches)- 16.72 Patches -Therefore, the radius of the MH metapopulation would need to be 7-8 km -Patches outside this radius are unlikely to be colonized
-Jasper Ridge, San Mateo Co Significant stepping stone effects seem unlikely because of the size difference between MH and the small populations Unlikely that several small populations will add greatly to the net rates of colonization in the system
If extinctions only occur to major droughts (as seen 1975-1977), they are probably 1)infrequent, 2)correlated between all patches, and 3)independent of pop size Other studies suggest that 1 and 2 are unlikely true. When this paper was written, no known data existed to address #3 Factors affecting local populations: local environment change, weather interactions with vegetation and topography Took data from the Jasper Ridge site and determined changes in population sizes (delta Ns) Then, calculated mean times to extinction of populations of different initial sizes randomly selecting delta Ns via simulation
Patches with equilibrium probabilities above 50% are those that are most likely to support populations So, it is predicted that the populations in the MH metapopulation will wink in and out around an equilibrium occupancy of 8-11 patches Even with this, the absolute threshold of distance/quality suggests that the catastrophe scenario is supported because if there were continuous extinction a more random pattern of occupancy would be expected. However, it is likely that both modes of extinction have played a role in this metapop
![Euphydryas editha bayensis: Evidence for a Metapopulation Model ,[object Object],http://www.calacademy.org/science_now/headline_science/ AM. NAT. 1988. VOL. 132, PP. 360-382.](https://image.slidesharecdn.com/checkerspotbutterflypresentation-091108200946-phpapp02/85/Checkerspot-Butterfly-Presentation-1-320.jpg)
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