The number of organisms per unit areaDispersion: The pattern of spacing a population within an area3 main types of dispersion

Clumped Uniform Random

The primary cause of dispersion is resource availability

How fast a population grows Factors that influence this are:

Birth rate Mortality Emigration Immigration

A limiting factor places an upper limit on the size of a population. Limiting

factors can be biotic (for example, lack of food) or abiotic

(for example, access to water).

Every species is able to survive within a range of abiotic

factors such as temperature, light, and soil. This range is

called the species’ tolerance range.

Abiotic Limiting factors include:

Temperature

Rain fall

Nutrients

the maximum, equilibrium number of organisms of a particular species that can be supported indefinitely in a given environment. 

Abbreviation:  K

Density Independent Factors

Affect population regardless of size or distribution

Usually abiotic

Examples: drought, fire, flood…

Density Dependent Factors

Usually biotic

Examples: Predation, parasites, disease

Which would you choose? An employer offers you two equal jobs for one

hour each day for fourteen days. The first pays $10 an hour. The second pays only 1 cent a day, but the rate

doubles each day. Which job will you accept?

Population Ecology: Population Growth Rate

Ten dollar flat rate

Lag

Final payment

Population growth modelsExponential growth model

J-curve Grows slowly at first “lags” After lag grows very fast! (exponentially) Example: Bacterial growth

Population Ecology: Population Growth Rate

We will probably reach our carrying capacity.

Our growth rate will start to look like most organisms, which is the Logistic Growth Model

Carrying Capacity (k)

What letter does this curve kind of look like?

Logistic Growth Model Often called the S-shaped growth curve Occurs when a population’s growth slows or stops

following exponential growth. Growth stops at the population’s carrying capacity

Population Ecology: Population Growth Models