Populations Populations Populations are groups of individuals that

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?