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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)