Populations

Populations Populations are groups of individuals that belong to the same species and live in the same area There are three important characteristics of populations…

Population Characteristics Geographic Distribution – what area does the population inhabit? Density – # of individuals concentrated in the area Growth Rate – how slowly or quickly a population grows

Population Characteristics Three factors affect population size: The number of births The number of deaths The number of individuals that enter or leave

Immigration versus Emigration

Population Growth Exponential Growth – when individuals of a population reproduce at a constant rate. Occurs only under IDEAL conditions J-curve plot

Population Growth Logistic Growth – when growth slows or stops following exponential growth Occurs when resources become less available Looks like an “S”- shaped curve

Carrying Capacity… the maximum amount of individuals of a population that an environment can support. Generally when birthrate = deathrate

Limiting Factor (LF) Affects an organism’s ability to survive and causes population growth to decrease What are some examples?

Limiting Factor (LF) Density DEPENDENT – factors that depend on population size Competition (resources can become scarce) Disease: some examples include Pfisteria, Dutch elm disease, AIDS Predation Parasitism

Limiting Factor (LF) Density INDEPENDENT – factors that affect all populations regardless of size Ex. Natural disasters, weather, human actions, forest fires, etc.

Limiting Factor (LF) Most populations can adapt to a certain amount of change, but major upsets can lead to long-term declines in population sizes… What might be the outcome of this?