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Populations
Populations
• A group of individuals that belong
to the same species and live in
the same area, at the same time.
• A population is an interbreeding
(and evolving) group.
• Population dynamics include
growth, decline, or stability
depending on the birth rate, death
rate, immigration rate, and
emigration rate in the population
BIDE rule:
(B+I) – (D+E) = change in pop. size
Population Growth
• Populations tend to grow
exponentially (J-curve)
given unlimited resources
(food, space, etc)
• Limiting factors (competition
for food/nutrients, predation,
parasitism etc.) tend to limit
growth
• Limiting factors force
populations into logistic
growth (S-curve) where
population levels off at
carrying capacity of the
environment
Exponential Growth
G = rN
Where:
G = number of individuals
added per unit of time
r = rate of increase
(B + I) – (D + E )
N = population size
If an aphid population of 10 individuals increases by a rate of 0.4
individuals per week. How many aphids will there be by the end of
the first week? second? third? (assume living individuals survive)
Logistic Growth
G = rN(K-N)/K
Where:
K = carrying capacity of
the environment
You are an ecologist attempting to manage the catch of a salmon
population so that replacement of caught fish will happen at the fastest
rate. The salmon population size is estimated to be about 80,000 fish and
the carrying capacity of this environment is estimated to be about 100,000
fish. Given this information, how many fish should you allow to be caught?
Introduced (Invasive) Species May OutCompete Native Species
perch: native
smelt: introduced