Elements of Ecology

1. CHAPTERS 8-11
PRESENTED BY: LEANDRO MICHAEL C. DE LOS SANTOS, JR.

2. CHAPTER 8
PROPERTIES OF POPULATIONS

3. 1. Discuss the three distribution patterns
of individuals within a population and
explain the condition that give rise to
each pattern.

4. 3 Distribution Patterns of Individuals
Source: https://www.boundless.com/biology/population-and-community-
ecology/population-demography/species-distribution

5. Random- individuals are distributed
randomly if each individual position is
independent of those of the others.
Plants that have wind-dispersed
seeds such as dandelions exhibit
random distribution as they
germinate wherever they happen to
fall in a favorable environment.
Source: https://www.boundless.com/biology/population-and-community-
ecology/population-demography/species-distribution

6. Uniform- individuals are more or less
evenly spaced. A uniform distribution
usually results from some form of
negative interaction among individuals
such as competition, which functions to
maintain minimum distance among
members of the population.

7. In animals- uniform distribution is
common where individuals defend an
area for their exclusive use
(territoriality)
In plants- uniform distribution is
common where severe competition
exists for belowground resources such
as water or nutrients
Source: Elements of Ecology, 8th Edition

8. Clump- most common distribution
which individuals occur in groups.
Clumping of individuals happen when
suitable habitat or other resources
may be distributed as patches on the
larger landscape, forming of social
groups among individuals and asexual
reproduction
Source: Elements of Ecology, 8th Edition

9. 2. Provide the mark-recapture
equation used for estimating
population size and define the
terms of the equation.Why is the
mark-recapture such a popular &
effective method for determining
animal population densities?

10. MARK-RECAPTURE EQUATION
- A method based on trapping,
marking, and releasing a known
number of marked animals into
the population.
*This procedure was first used by C.J.G.
Petersen in studies of marine fishes & F.C
Lincoln in studies of waterfowl populations.

11. Source: http://www.radford.edu

12. This technique is commonly used by
fish and wildlife managers to estimate
population sizes before fishing or
hunting seasons. Ecologists also find
that a measure of relative density or
abundance is sufficient and by using
mark-recapture method trends in
abundance is depicted thus this
method is popular and effective.
Source: http://www.radford.edu

13. 3. Describe several approaches
used by ecologists to establish age
structure for plant and animal
populations

14. Some approaches used by ecologists
to establish age structure
Animals:
• Marking young individuals in a population
& following their survival through time
• Examining sample of individual carcasses
to determine age at death
• Morphological changes such as wear &
replacement of teeth among deers or
counting rings deposited annually in fish

15. Some approaches used by ecologists
to establish age structure
Plants:
• Marking young individuals in a population
& following their survival through time
• Determining size of diameter (assumption
that diameter increases with age)
• Attempts to age non-woody plants have
not been successful
Source: Elements of Ecology, 8th Edition

16. 4. Some animals migrate daily
while others migrate seasonally.
Give an example of each migration
pattern and explain the benefit of
this lifestyle to the organisms that
you present.

18. 5. Using examples, discuss the
impact of increased human
travel in the 20th century on
long-distance dispersal of
plants & animals. Describe how
& why introduced species
typically alter native
ecosystems

19. In human-dominated landscapes, people have
a major influence not only on the distribution,
but also on the dispersal of plant & animal
species . Human-mediated dispersal in these
environments can be either intentional or
unintentional-A. Auffret & S. Cousins
(Humans as Long-Distance Dispersers of
Rural Plant Communities)

20. Examples of Human assisted dispersal of species
1. Dispersal of seeds on human clothes and
footwear
2. Seeds of weeds included in shipments of
imported crops
3. Domestic pet trade such as Janitor fish
4. Introduction of new species as raw materials
5. Domestic trade of ornamental plants

21. Though not all human-dispersed species can
create imbalance in any native ecosystem, those
that become invasive species do endanger the
species living in the native ecosystem.
The direct threats of invasive species are:
1.Preying on native species
2.Out-competing native species for food or other
resources
3.Causing or carrying disease
4.Preventing native species from reproducing or

22. The indirect threats of invasive species are:
1.Changing food webs
2.Decreasing biodiversity
3.Altering ecosystem conditions
Source: http://www.nwf.org

23. CHAPTER 9
POPULATION GROWTH

24. 1.What is the significance of
constructing a life table to an
ecologist?What information is
required to develop a life table and
what is this information used for?

25. What is a LifeTable?
* A more sophisticated method for
examining population abundance is to
construct a life table
*This table will have a schedule of all
births and deaths in all, or more likely
some portion, of a population

26. What information can you get
from a life table?
*Population age structure —Are there lots of:
young individuals? Old individuals?
Reproductive age individuals
* Population growth rate —How fast is the
population size growing (or shrinking)?
* Population survivorship patterns —Does most
mortality occur in the very young?The very old?
Or equally across all ages?
Source: http://iweb.tntech.edu

27. Source: http://iweb.tntech.edu

28. 2. Compare and contrast the two basic
types of life tables. Discuss the
advantages and disadvantages of each

29. Sources: www.life.illinois.edu
Elements of Ecology, 8th Ed.

30. 3. Illustrate the 3 types of
survivorship curves and give
examples of each.What factors
cause the three different types to
appear in nature?

31. Illustration of a survivorship curve
Source: www.uic.edu

32. Type 1:
Humans:
low mortality rate
(early on) and give
birth to few
young. Parental
care is high, rarely
preyed on, and
migration is low,
thus, more likely
to survive.
Type 2:
Squirrel:
Mortality rate is
common (linear),
birth rate is
medium to high,
and migrate an
average amount.
Parental care is
also not as long as
Type 1 andType
2s are more
preyed on.
Type 3:
Clam:
Birth rate is
extremely high
and mortality rate
is extremely high.
There is little to
usually no
parental care.
Source: www.uic.edu

33. 4. Explain how λ is used by
demographers to predict the future
size of a population.

34. Lambda (λ) is called the finite population
growth rate that gives the proportional
change in population size from one time
period to the next:
Where:
𝑵𝒕 + 𝟏 𝐢𝐬 𝐭𝐨𝐭𝐚𝐥 𝐧𝐮𝐦𝐛𝐞𝐫 𝐨𝐟 𝐢𝐧𝐝𝐢𝐯𝐢𝐝𝐮𝐚𝐥𝐬 𝐢𝐧 𝐲𝐞𝐚𝐫 𝒕 + 𝟏
Nt is the total number of individuals in the previous year
Source: Elements of Ecology, 8th Ed.

35. Source: http://www.uvm.edu

36. 5. Discuss 5 factors known to
cause extinction.Which of these
factors is considered the leading
cause of current extinctions and
why?

37. 5 Factors known to cause extinction:
1. Extreme environmental events
2. Overexploitation of resources
3. Invasive species in a native ecosystem
4. Loss of habitat due to human activities
5. Disease

38. Developmental activities such as urbanization, agriculture,
mining and deforestation had greatly affected the habitats of
many species. Many of which were forced to look for a more
suitable niche which could also mean that those said organisms
would have to adapt again to a new environment. Adaptation in
this case can be positive or can be detrimental to the organisms.
The latter could cause their extinction.

39. Source: Quantifying threats to imperiled species in the United States
According to a study conducted in 1998 by Wilcove,
Rothstein, Dubow, Phillips, and Losos (Quantifying threats
to imperiled species in the United States), the number one
cause of endangerment of species is extinction due to
human activities.

40. 6.What is the Allee effect? Give
several examples that illustrate
the potential catastrophic
impact of small size on
population persistence.

41. Allee Effect- The decline in either
reproduction or survival under
conditions of low population density
(Smith & Smith, 2012)

42. Examples illustrating Allee Effect:
1. Difficulty in finding mate for large cats
that are widely spread
2. Species using chemicals such as
pheromones to communicate and
attract mates
3. Likeliness of plants being pollinated
4. Predation on island fox (Urocyon
littoralis) by Golden Eagles
Sources: Elements of Ecology, 8th Ed.
http://www.ncbi.nlm.nih.gov

43. CHAPTER 10
LIFE HISTORY

44. 1. Contrast asexual and sexual
reproduction. What conditions
would favor the evolution of one
reproductive strategy over the
other.

45. Source: http://www.ck12.org

46. Sources: S. Otto, 2008- Sexual reproduction and the evolution of sex
http://www.ck12.org

47. 2. Explain the advantage of the
ability for an organism to possess
both male and female organs

48. An organism that possess both a female and a male
Sexual organ is called a hermaphrodite.
Hermaphroditism is quite common in invertebrates
& plants and exceedingly rare in vertebrates.
Most Perciforms (fish) are naturally hermaphrodite.

49. Earthworms
Examples of
Hermaphrodite organisms
Clownfish
Snail

50. Advantages:
1. Low density model
2. Size advantage model
3. Gene dispersal model
Source: M. Ghiselin –The Evolution of Hermaphroditism Among Animals (1969)

51. 3. Explain why most bird species
are monogamous while most
mammal species are polygamous.

52. “In all sexually reproducing species
there is a social framework involving
the selection of mates.The pattern of
mating between males and females in
a population is called mating
system”- Smith & Smith, 2012

53. Monogamy is common among birds because
most young birds are helpless at hatching
and need food, warmth and protection.
Male birds can increase his fitness more by
continuing his investment in the young.Also,
parental care of both parents is necessary to
raise the young successfully. Parents
alternate in giving protection and
nourishment to the young birds.

54. In mammals, polygamy is a common
practice. It can involve 1 male and several
female or vice versa.The individual having
multiple mates is generally not involved in
caring for the young. For some, since females
lactate, providing food for the young it is to
the advantage of the males to mate with as
many females as possible.
Source: Elements of Ecology, 8th. Ed.

55. 4. Explain sexual dimorphism
from a Darwinian perspective.

56. Darwin considered that most sexual dimorphism
was due to sexual selection, in which evolutionary
forces acted separately on the sexes.
Source: www.bbc.co.ukSource: www.bbc.co.uk
Source: http://www.cetus.ucsd.edu

57. 5. Contrast semelparous and
iteroparous reproductive
strategies and explain the
trade-offs of each.

58. Source: Elements of Ecology, 8th Ed.

59. 6. Explain why siblicide is common
among bird species when resources
are rare.Why is this an effective
strategy under these conditions?

60. Characteristics common to all siblicide:
1. Competition for food
2. Provision of food to the nestlings in small units
3. Weaponry
4. Competitive disparities between siblings
5. Spatial confinement Source: Avian Siblicide –R. Santana, D. Mock, H.
Drummond, H. Stinson

61. Parental Favoritism and Siblicide
Sometimes parents seem not only to tolerate
siblicide, but to actively encourage it.
For example, in Black Eagles incubation begins as
soon as the first egg is laid.
As a result the first egg hatches 3-7 days before the
second and so the older offspring has a huge size
advantage over its younger sibling and can easily
kill him.

62. Why parents play favorites and facilitate
siblicide?
There are two major reasons:
* Insurance against failure
* Environmental uncertainty

63. 7. Discuss the differences between
r-strategists and K- strategists.
Give an example of each.

64. Sources: Elements of Ecology, 8th Ed.

65. 8. Describe the different
strategies (S,C, and R) as
presented in Grime’s model of life
history variation in plants.

66. GRIME’S MODEL OF LIFE HISTORY

67. Ruderals (R)
• rapidly colonize disturbed sites
• small in stature and short lived
• allocation of resources is primarily to
reproduction with characteristics allowing for a
wide dispersal of seeds to newly disturbed
sites

68. Competitive (C)
• thrive in predictable habitats with abundant
resources
• Allocate resources to growth favoring resource
acquisition and competitive ability
Stress-Tolerant (S)
• Thrive in areas where resources are limited
• Allocate resource to maintenance

69. CHAPTER 11
INTRASPECIFIC POPULATION REGULATION

70. 1.What is the difference
between exponential growth
and logistic growth? Under
what ecological conditions does
each occur?

71. Exponential Population Growth-
characteristic of populations inhabiting
favorable environments at low densities such
as during the process of colonization &
establishment in new environments- Smith &
Smith (2012)
Associated with the name ofThomas Robert
Malthus (1766-1834) who first realized that
any species can potentially increase in
numbers according to a geometric series.
Source: A. Sharov, Quantitative Population Ecology

72. 3 possible model outcomes:
Source: A. Sharov, Quantitative Population Ecology

73. Assumptions of Exponential Model:
1. Continuous reproduction (e.g., no seasonality)
2. All organisms are identical (e.g., no age
structure)
3. Environment is constant in space and time
(e.g., resources are unlimited)
Source: A. Sharov, Quantitative Population Ecology

74. Logistic population growth- developed by
Belgian mathematician PierreVerhulst
(1838) who suggested that the rate of
population increase may be limited, i.e., it
may depend on population density

75. 3 possible model outcomes:
Logistic model combines two ecological processes: reproduction
and competition. Both processes depend on population numbers
(or density).The rate of both processes corresponds to the mass-
action law with coefficients: r0 for reproduction and ro/K for
competition.

76. 2. Discuss some of the
important issues involved when
trying to determine Earth’s
carrying capacity (K) for
humans.Why is it difficult to
calculate K for the human
population?

77. Scientists have been in the quest to find the
exact carrying capacity of Earth among human
beings. Aside from answering the question “how
many”, scientists have also quantified the
questions to – at what standard of living & at
what cost to the environment is the human
carrying capacity of the Earth has?

78. 2 scientist who presented their estimate of the
Earth’s carrying capacity (K) on humans:
1.C.T. DeWit- based solely on estimates of primary
production and the average annual per capita energy
requirement estimated that 1000 billion people could
live from Earth if photosynthesis is the limiting factor
2.H. R. Hulett- reached a conclusion that approximately
1 billion people represented the maximum world
population supportable at the then current agricultural
& industrial levels of production.
Source: Elements of Ecology, 8th Ed.

79. Issues about the conducted studies:
DeWit- uses assumptions in his calculation of
the Earth’s carrying capacity such as sufficient
water and nutrients for all human beings and an
assumption that the entire land area is
dedicated to the production of plants.
Hulett- used the standard of living and resource
consumption for the average U.S citizen as his
definition of optimal lifestyle.

80. 3. Contrast the density-dependent and
density-independent mechanism of
population regulation.

81. Sources: Elements of Ecology, 8th Ed.
www.tracy.k12.ca.us

82. 4.What is competition? Compare and
contrast scramble and contest
competition.

83. Competition- “competition is an interaction
between individuals, brought about by a shared
requirement for a resource [in limited supply],
and leading to a reduction in the survivorship,
growth and/or reproduction of at least some of
the competing individuals concerned”
(Begon et al., 2006)
Intraspecific competition- competition among
individuals of the same species

84. Source: Elements of Ecology, 8th Ed.

85. 5. Explain why high population density
might stress an organism. Provide
several examples of some of the
negative impacts of stress on an
organism.

86. High density population is stressful to individuals
since restricted space can often lead to aggressive
contacts among individuals. Increased crowding
and social contact can cause stress.
Stress triggers:
1. Hormonal changes
2. Suppress immune system
3. Increase mortality of the young in the fetal
stage (decreased birth & increased mortality)

87. 6.Why are social organization and
territoriality adaptive? How do
human populations exhibit these
two behaviors?

88. Social behavior appears to be a mechanism that
limits the number of animals living in a particular
habitat, having access to a common food supply,
and engaging in reproductive activities.
Social dominance plays a role in population
regulation when it affects reproduction &
survival in a density-dependent manner.
Territoriality secures the individual sole access
to an area of habitat and the resources it
contains.

89. 7.Why do some species have a
larger home range than others?
Explain why a carnivorous
mammal requires a larger range
than an herbivorous mammal of
similar body size?

90. Home range- the area that an animal normally
uses during a year.
Overall size of the home range varies with the
available food resources, mode of food
gathering, body size, and metabolic needs.

91. For a given body mass, the home range of
carnivores is larger than that of herbivores
because the home range of a carnivore must be
large enough to support a population of the
prey that it feeds upon- Harastad & Bunnell, 1979