I Population Ecology A Density and Dispersion 2

I. Population Ecology A. Density and Dispersion 2. Dispersion • a. Spatial distribution of organisms 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 Dispersion 2. Dispersion b. Uniform • Individuals evenly spaced • May result from 1) 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 processes 1) 2) 3) 4) Natality (birth rate) Mortality (death rate) Immigration rate Emigration rate

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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

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I. Population Ecology C. Life History • Includes strategic tradeoffs among traits 1) 2) 3) 4) 1. Semelparity – “Big Bang” Reproduction • • 2. Ex: Salmon, Agave (century plant) Favored in unpredictable environments with high offspring mortality Iteroparity – Repeated Reproduction • • • Age at first reproduction (age at maturity) Frequency of reproduction Number of offspring per reproductive event Parental care Ex: Humans, most mammals Favored in predictable environments with intense competition for resources How does parental care affect parent survival?

European kestrel Fig. 53. 13 3 -4 5 -6 7 -8

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 = b. N D = m. N r=b-m r = Per capita growth rate ΔN/Δt = b. N - m. N = r. N d. N/dt = r. N • • • r>0 r<0 r=0 population growing population shrinking ZPG

I. Population Ecology D. Population Dynamics 1. • 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 d. N/dt = rmax. N

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Kruger National Park, South Africa Fig. 53. 8

I. Population Ecology D. Population Dynamics 2. • 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) d. N/dt = rmax. N (K-N)/K

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