Fluctuations In Population Sizes

Fluctuations In Population Sizes How do ecologists study populations?

Vocabulary • • • • • •

Population density Immigration Emigration Exponential growth Logistic growth Carrying capacity

Characteristics of a population 1. Geographic Distribution 2. Density 3. Growth Rate 4. Age Structure

Geographic distribution • Organisms need space. • They move through seasonal cycles. • Range of animal’s habitat can be very large or very small.

Density • Number of individuals per unit area. • Varies depending upon the species and it’s habitat. Population Density= number of individuals ÷ unit area • What is the population density of our classroom?

Population growth Affected by: 2. # of births: birth rate 3. # of deaths: mortality rate 4. # of individuals that leave or enter the population: immigration and emigration

Movement of individuals • Immigration: when individuals move into an area. • Emigration: when individuals move out of an area. • Both affect the size of the population.

Exponential growth • When a population has abundant space and food. • Disease and predator free. • Population size increases.

Logistic Population growth • Most populations do not grow exponentially for a long time. • After a period of such growth, environmental resistance limits further growth- carrying capacity is reached. • Most populations show an S-shaped curve.

Limits to growth • Limiting factors- factors that causes population size to decrease. • See figure 5-5 (p. 124) • What is the difference between density-dependent and density-independent limiting factors? Use your textbook to list 3 examples of each.

Density-Dependent Factors • Factors that limit population growth. • Factors whose effect depends upon numbers. • Space- limited to a certain number. • Predation- predators hunt abundant species. • Disease- rabies

Density- Independent Factors • • • •

Freezing temperatures Sensitivity to cold or hot Natural disasters Human activity