Population Ecology

PopulationPopulation-a group of organisms of one species living in the same place at the same time that interbreed and compete with each other for resources (ex. food, mates, shelter)

What characteristics are used to describe a population? Copyright Pearson Prentice Hall

 Geographical distribution – Describes how a population is spaced  Population Density – The # of individuals divided by the area  Growth Rate – The change in # within a population due to births, deaths, immigration, & emigration

What factors affect population size? Copyright Pearson Prentice Hall

Population Growth Three factors can affect population size:  the number of births  the number of deaths  the number of individuals that enter or leave the population A population can grow when its birthrate is greater than its death rate.

Immigration: the movement of individuals into an area, is another factor that can cause a population to grow. Emigration: the movement of individuals out of an area, can cause a population to decrease in size. Copyright Pearson Prentice Hall

What are exponential growth and logistic growth? Copyright Pearson Prentice Hall

Exponential Growth Under ideal conditions with unlimited resources, a population will continue to grow Exponential growth occurs when the individuals in a population reproduce at a constant rate.

Copyright Pearson Prentice Hall Exponential Growth

Kruger National Park, South Africa

Copyright Pearson Prentice Hall Logistic Growth As resources become less available, the growth of a population slows or stops. Logistic growth occurs when a population's growth slows or stops following a period of exponential growth.

Logistic growth is characterized by an S- shaped curve. Copyright Pearson Prentice Hall

Occurs when resources become less available (Slows population growth rate) Slow population growth rate due to 1. Decrease in birthrate 2. Increase in deathrate 3. Immigration decreases 4. Emigration increases

The largest # of individuals an environment can support

Copyright Pearson Prentice Hall  Limiting Factor: is a factor that causes population growth to decrease.

Limited resources  Food  Water  Space  Shelter  Mates  Sunlight

Copyright Pearson Prentice Hall  Density-Dependent Factors  A limiting factor that depends on population size is called a density- dependent limiting factor.

Copyright Pearson Prentice Hall Density-dependent limiting factors include:  competition  predation  parasitism  disease

Copyright Pearson Prentice Hall Wolf and Moose Populations on Isle Royale Moose Wolves

Copyright Pearson Prentice Hall  Density-Independent Factors  Density-independent limiting factors affect all populations in similar ways, regardless of the population size.

Copyright Pearson Prentice Hall  unusual weather  natural disasters  seasonal cycles  certain human activities—such as damming rivers and clear-cutting forests