Key Concepts in Population Ecology

Population

a group of organisms that belong to the same species and live in a particular place at the same time

Demography

statistical study of populations predicts how the size of a population will change

Population size

the # of individuals that the population contains.

Population rate

rate = amt.of change/amt. of time

Population Density

measures how crowded a population is & D = # of individuals/unit of area

Dispersion

the spatial distribution of individuals within the population

Uniform Distribution

individuals are separated by a fairly consistent distance. Ex: Trees in a nursery (planted in rows), some territorial animals such as damselfish which have territories of space 10 ft from each other, penguins

Clumped Distribution

when individuals are clustered together. Ex: school of fish, herd animals (bison, cattle) or social animals (chimps, dolphins, wolves)

Random Distribution

Each individual's location is independent of the locations of other individuals in the population. Ex: Solitary animals with large territories (bears, tigers, racoons), dandelion seeds dispersed by wind

Birth rate (or natality rate)

the number of births occurring in a period of time

Death rate (or mortality rate)

the number of deaths in a period of time

Life expectancy

how long on average an individual is expected to live

Age structure

the distribution of individuals among different ages in a population

survivorship curves

it show the probability that members of a population will survive to a certain age

Type I Survivorship Curve

High death rate in post-reproductive years. Ex: Humans and elephants

Type II Survivorship Curve

Constant mortality rate throughout life span. Ex: Birds and squirrels

Type III Survivorship Curve

Very high early mortality but the few survivors then live long (stay reproductive) Ex: Turtles and frogs