Population Ecology Chapter 36

Population Group of individuals of a single species that occupy the same general area. Population density = number of individuals unit area – The number of oak trees per square kilometer in a forest. – The number of earthworms per cubic meter in forest soil.

Dispersion patterns Way individuals in a population are spaced within an area.  Clumped  Uniform  Random

Clumped dispersion individuals are grouped in patches.  Most common dispersion pattern.  Result of need for resources.

Uniform dispersion individuals are equally spaced in the environment  Result of territorial behavior.

Random dispersion individuals in a population are spaced in an unpredictable way  Least common dispersion pattern.

Survivorship curve A plot of the proportion of individuals alive at each age. – Type I – Type II – Type III

Type I Survive to old age.  Humans, large mammals  Produce few offspring & provides good care.

Type II Likelihood of death constant throughout life.  Lizards, rodents, birds.

Type III Low survival rate for the very young.  Oysters, invertebrates, seed plants  Produce large numbers of offspring, & little care.

Exponential Growth Model Gives an idealized picture of unregulated population growth. Occurs when there are NO limiting factors Population doubles every generation  Ex. Population grows from 2 to 4 to 8 to 16 to 32  Bacteria, humans

Logistic Growth Model Growth that occurs when there are limiting factors Limiting factors - Environmental factors that restrict population growth.  Food, competition, space, predation Population will grow quickly (more births than deaths) at the beginning then will level off (equal number of deaths and births) when the population reaches the environment’s carrying capacity  Carrying capacity – Maximum number of individuals that an environment can support based off the resources available (based off of the limiting factors)