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 = rNWhere:

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)/KWhere:

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 Out-Compete Native Species

perch: nativesmelt: introduced