I. Population Ecology

A. Density and Dispersion2. Dispersion

• Spatial distribution of organisms

a. Clumped/Aggregated/Patchy• Patches may occur on variety of scales• Most common type of distribution• May result from

1) Patchy distribution of resources (food, water, shelter, soil type)

2) Social behavior in animals (pairing, schooling, pack formation, family groups)

3) Limited dispersal of propagules (seeds, larvae, fragments)

I. Population Ecology

A. Density and Dispersion2. Dispersion

b. Uniform• Individuals evenly spaced• May result from1) Territoriality (seabird nests, wolf territories)2) Competition (plants with allelopathic defenses)

c. Random• No distinct distribution pattern• Relatively rare (environment usually imposes

pattern on distribution)

• May change over time• Ex: Trees may be patchy when young and

become more uniform as they grow larger

I. Population Ecology

B. Demography• Study of vital statistics that affect populations• Changes in population size caused by four

processes1) Natality (birth rate)

2) Mortality (death rate)

3) Immigration rate

4) Emigration rate

Fig. 53.3

I. Population Ecology

B. Demography• Patterns can be studied with life table• Used to track cohorts

I. Population Ecology

B. Demography• Data in life table may be easier to visualize

graphically – survivorship curve

Fig. 53.5

Fig. 53.6

Fig. 53.14

I. Population Ecology

C. Life History• Includes strategic tradeoffs among traits

1) Age at first reproduction (age at maturity)2) Frequency of reproduction3) Number of offspring per reproductive event4) Parental care

1. Semelparity – “Big Bang” Reproduction• Ex: Salmon, Agave (century plant)• Favored in unpredictable environments with high

offspring mortality

2. Iteroparity – Repeated Reproduction• Ex: Humans, most mammals• Favored in predictable environments with intense

competition for resources

• How does parental care affect parent survival?

Fig.53.13

3-4 5-6 7-8

European kestrel

I. Population Ecology

D. Population Dynamics• In a closed system (no I or E), change in

population caused only by birth & death

ΔN/Δt = B - D

• N – Population size• t - Time• B – Birth rate• D – Death rate

I. Population Ecology

D. Population Dynamics• b – Per capita birth rate• m – Per capita death rate• B = bN• D = mN• r = b - m• r = Per capita growth rate

ΔN/Δt = bN - mN = rN

dN/dt = rN

• r > 0 population growing• r < 0 population shrinking• r = 0 ZPG

I. Population Ecology

D. Population Dynamics1. Exponential population growth• Under ideal conditions, r is as high as possible

for a species• rmax – Intrinsic rate of increase

• Inversely related to generation time

dN/dt = rmaxN

Fig. 53.7

Fig. 53.8Kruger National Park, South Africa

I. Population Ecology

D. Population Dynamics2. Logistic population growth• Exponential growth not sustainable indefinitely

in the real world• Assumes/Requires unlimited resources

• Increasing population density limits ability of individuals to acquire resources

• Density affects/limits population growth rate

• Given environment only can support limited number of individuals

• Carrying capacity (K)

dN/dt = rmaxN (K-N)/K

Fig. 53.9