Population Ecology

How do populations change over time?

Properties of populations

1) pop. Size – is the # of individuals in the pop.

2) Pop. Density – how crowded a pop. is.

3) Dispersion – the distribution of the members of a pop.

a) Can be clumped

b) Evenly distributed

c) Randomly distributed

Population dynamics & growth

Populations change over time:

1) increase or decrease in size

2) age & mortality

Demography – the study of human population dynamics.

Measuring pop. Growth rates

1) Exponential growth model – rapidly increasing or doubling in size.

Shown with a J- shaped curve

EX: mosquitoes, bacteria, some rodents, etc…

Exponential Growth

2) Logistical model – growth increase then stabilizes when the carrying capacity is reached.

Shown with an S-Shaped curve

EX: most larger organisms, lions, elephants, etc…

Logistical Model – carrying capacity

What limits a population?

1) RESOURCES!!!!!

Any single resource that limits a population is called the limiting resource!

Some factors that control population…

1) Density Dependant Factors – any factor that limits a population because of the size of the population.

EX: Food, space, water, disease, etc..

2) Density – Independent Factors – a factor that can affect a population of any size.

EX: natural disasters, weather, etc…

SUCCESSION

How do habitats change over time?

Primary Succession

Succession is the gradual, sequential changing of an area.

The habitat changes until the “climax community” is formed.

Primary succession

1) Occurs in areas that have no soil

2) No plants or animals in the area

3) 1st inhabitant is called a “pioneer species” – it usually lichen.

4) Soil is slowly formed and new plants/ animals gradually move into the area

5) Can occur because of a volcano or a new island forms or an icecap recedes

Primary Succession

Secondary succession

1) Occurs in an area that has soil

2) Is usually the result of some disruption to a previous community. (fire, flood, etc…)

3) Happens quicker than primary succession.

Secondary Succession