2. AP Biology
Why Population Ecology?
Scientific goal
understanding the factors that influence the
size of populations
general principles
specific cases
Practical goal
management of populations
increase population size
endangered species
decrease population size
pests
maintain population size
fisheries management
maintain & maximize sustained yield
3. AP Biology
Life takes place in populations
Population
group of individuals of same species in
same area at same time
rely on same
resources
interact
interbreed
rely on same
resources
interact
interbreed
Population Ecology: What factors affect a population?Population Ecology: What factors affect a population?
4. AP Biology
Abiotic factors
sunlight & temperature
precipitation / water
soil / nutrients
Biotic factors
other living organisms
prey (food)
competitors
predators, parasites,
disease
Intrinsic factors
adaptations
Factors that affect Population Size
5. AP Biology
Characterizing a Population
Describing a population
population range
pattern of Dispersion
Density of population
#individuals per unit area
1937
1943
1951
1958
1961
1960
19651964
1966 1970
1970
1956
Immigration
from Africa
~1900
Equator
range
6. AP Biology
Population Range
Geographical limitations
abiotic & biotic factors
temperature, rainfall, food, predators, etc.
habitat
adaptations to
polar biome
adaptations to
polar biome
adaptations to
rainforest biome
adaptations to
rainforest biome
7. AP Biology
Population Dispersion
Spacing patterns within a population
uniform
random
clumped
Provides insight into the
environmental associations
& social interactions of
individuals in population
Provides insight into the
environmental associations
& social interactions of
individuals in population
Why uniform?
Why clump?
Why random?
9. AP Biology
Population Growth Rates
Factors affecting population growth rate
sex ratio
how many females vs. males?
generation time
at what age do females reproduce?
age structure
#females at reproductive age in cohort?
10. AP Biology
Life tableLife table
Demography
Study of a populations vital statistics and
how they change over time
Life tables, Age Structure Diagrams and Survivorship
Graphs
Why do teenage boys pay high car insurance rates?Why do teenage boys pay high car insurance rates?
females males
What adaptations have
led to this difference
in male vs. female
mortality?
11. AP Biology
Age structure
Relative number of individuals of each age
What do these data imply about population growth
in these countries?
12. AP Biology
Survivorship curves
Graphic representation of life table
Belding ground squirrel
The relatively straight lines of the plots indicate relatively constant
rates of death; however, males have a lower survival rate overall
than females.
The relatively straight lines of the plots indicate relatively constant
rates of death; however, males have a lower survival rate overall
than females.
13. AP Biology
Survivorship curves
Generalized strategies
What do these graphs
tell about survival &
strategy of a species?
What do these graphs
tell about survival &
strategy of a species?
0 25
1000
100
Human
(type I)
Hydra
(type II)
Oyster
(type III)
10
1
50
Percent of maximum life span
10075
Survivalperthousand
I. High death rate in
post-reproductive
years
I. High death rate in
post-reproductive
years
II. Constant mortality
rate throughout life
span
II. Constant mortality
rate throughout life
span
III. Very high early
mortality but the
few survivors then
live long (stay
reproductive)
III. Very high early
mortality but the
few survivors then
live long (stay
reproductive)
14. AP Biology
Trade-offs: survival vs. reproduction
The cost of reproduction
To increase reproduction may decrease
survival: (think about…)
age at first reproduction
investment per offspring
number of reproductive cycles per lifetime
parents not equally invested
offspring mutations
Life History determined by costs
and benefits of all adaptations.
Natural selection
favors a life history
that maximizes
lifetime
reproductive
success
Natural selection
favors a life history
that maximizes
lifetime
reproductive
success
15. AP Biology
Reproductive strategies
K-selected
late reproduction
few offspring
invest a lot in raising offspring
primates
coconut
r-selected
early reproduction
many offspring
little parental care
insects
many plants
K-selected
r-selected
16. AP Biology
Trade offs
Number & size of offspring
vs.
Survival of offspring or parent
Number & size of offspring
vs.
Survival of offspring or parent
r-selected
K-selected
“Of course, long before you mature,
most of you will be eaten.”
17. AP Biology
Survivorship Curves with Reproductive Strategy
0 25
1000
100
Human
(type I)
Hydra
(type II)
Oyster
(type III)
10
1
50
Percent of maximum life span
10075
Survivalperthousand
K-selection
r-selection
18. AP Biology
Population Growth Rate Models
Exponential growth
Rapid growth
No constraints
Logistic growth
Environmental constraints
Limited growth
19. AP Biology
Population Growth Math
Change in population = Births – Deaths
Per capita birth rate = b
Per capita death rate = d
# of individuals = N
Rate of population growth (r) = b – d
Survivorship = % surviving
Ex: If there are 50 deer in a population, 13 die and 27 are born the next
month. What is the population size the following month?
(Answer: 27-13 = 14, so new population is 64)
Ex: What is the birth rate for the deer? #Births/N = b
Answer: 27/50 = .54
Death rate (d) = 13/50 = .26
Ex: What is the rate of growth for the deer? r = .54 -.26 = .28
20. AP Biology
Exponential Growth (ideal conditions)
No environmental barriers
Growth is at maximum rate
dN/dt = rmaxN
N = # individuals
Rmax = growth rate
21. AP Biology
African elephant
protected from hunting
Whooping crane
coming back from near extinction
Exponential Growth
Characteristic of populations without
limiting factors
introduced to a new environment or rebounding
from a catastrophe
22. AP Biology
K =
carrying
capacity
K =
carrying
capacity
Logistic rate of growth
Can populations continue to grow
exponentially? Of course not!Of course not!
effect of
natural controls
effect of
natural controls
no natural controlsno natural controls
What happens as
N approaches K?
23. AP Biology
Logistic Growth Equation
dN/dt = rmaxN(K-N)/K
K = carrying capacity of population
Ex: If a population has a carrying capacity of 900 and the rmax is
1, what is the population growth when the population is 435?
1 x 435 (900-435)/900 = 224
What if the population is at 850?
What if it is at 1010?
Explain the results of each problem.
24. AP Biology
500
400
300
200
100
0
200 10 30 5040 60
Time (days)
Numberofcladocerans
(per200ml)
Maximum
population size
that environment
can support with
no degradation
of habitat
varies with
changes in
resources
Time (years)
1915 1925 1935 1945
10
8
6
4
2
0
Numberofbreedingmale
furseals(thousands)
Carrying capacity
What’s going
on with the
plankton?
25. AP Biology
Changes in Carrying Capacity
Population cycles
predator – prey
interactions
KK
KK
26. AP Biology
Regulation of population size
Limiting factors
density dependent
competition: food, mates,
nesting sites
predators, parasites,
pathogens
density independent
abiotic factors
sunlight (energy)
temperature
rainfall
swarming locusts
marking territory
= competition
competition for nesting sites
27. AP Biology
Introduced species
Non-native species (INVASIVE)
transplanted populations grow
exponentially in new area
out-compete native species
reduce diversity
examples
African honeybee
gypsy moth
kudzu
gypsy moth
28. AP Biology
Zebra musselssel
ecological & economic damage
~2 months
reduces diversity
loss of food & nesting sites
for animals
economic damage
reduces diversity
loss of food & nesting sites
for animals
economic damage
29. AP Biology
Purple loosestrife
19681968 19781978
reduces diversity
loss of food & nesting sites
for animals
reduces diversity
loss of food & nesting sites
for animals
Within a population’s geographic range, local densities may vary substantially. Variations in local density are among the most important characteristics that a population ecologist might study, since they provide insight into the environmental associations and social interactions of individuals in the population. Environmental differences—even at a local level—contribute to variation in population density; some habitat patches are simply more suitable for a species than are others. Social interactions between members of the population, which may maintain patterns of spacing between individuals, can also contribute to variation in population density.
A Type I curve is flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups. Humans and many other large mammals that produce few offspring but provide them with good care often exhibit this kind of curve. In contrast, a Type III curve drops sharply at the start, reflecting very high death rates for the young, but then flattens out as death rates decline for those few individuals that have survived to a certain critical age. This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as long–lived plants, many fishes, and marine invertebrates. An oyster, for example, may release millions of eggs, but most offspring die as larvae from predation or other causes. Those few that survive long enough to attach to a suitable substrate and begin growing a hard shell will probably survive for a relatively long time. Type II curves are intermediate, with a constant death rate over the organism’s life span. This kind of survivorship occurs in Belding’s ground squirrels and some other rodents, various invertebrates, some lizards, and some annual plants.
A Type I curve is flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups. Humans and many other large mammals that produce few offspring but provide them with good care often exhibit this kind of curve. In contrast, a Type III curve drops sharply at the start, reflecting very high death rates for the young, but then flattens out as death rates decline for those few individuals that have survived to a certain critical age. This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as long–lived plants, many fishes, and marine invertebrates. An oyster, for example, may release millions of eggs, but most offspring die as larvae from predation or other causes. Those few that survive long enough to attach to a suitable substrate and begin growing a hard shell will probably survive for a relatively long time. Type II curves are intermediate, with a constant death rate over the organism’s life span. This kind of survivorship occurs in Belding’s ground squirrels and some other rodents, various invertebrates, some lizards, and some annual plants.
The J–shaped curve of exponential growth is characteristic of some populations that are introduced into a new or unfilled environment or whose numbers have been drastically reduced by a catastrophic event and are rebounding. The graph illustrates the exponential population growth that occurred in the population of elephants in Kruger National Park, South Africa, after they were protected from hunting. After approximately 60 years of exponential growth, the large number of elephants had caused enough damage to the park vegetation that a collapse in the elephant food supply was likely, leading to an end to population growth through starvation. To protect other species and the park ecosystem before that happened, park managers began limiting the elephant population by using birth control and exporting elephants to other countries.
