POPULATION DENSITY, DISTRIBUTION &

GROWTH

Density is a measure of how closely packed organisms are in a population Calculated by …

DENSITY

# of individualsarea (units2)

= population density

Distribution refers to how organisms are spaced out in their habitat

DISTRIBUTION

A population’s size changes are the result of 4 factors Births, deaths, immigration, emigration

Births and immigration increase size Deaths and emigration decrease size

GROWTH

Population growth is first influenced by available resources Food, water, territory

Populations grow exponentially if resources are unlimited

GROWTH

Resource limitations eventually slow a population’s growth Logistic growth has a “leveling off” period of time

Population reaches itscarrying capacity

Carrying capacity = maximum # of individualshabitat can support

GROWTH

Limits to growth fall into two categories Density dependent limiting factors

Increase their pressure as population size grows Examples: predation, competition, disease

Density independent limiting factors Pressure remains constant regardless of population size Examples: weather, natural disasters, seasonal changes

LIMITS TO GROWTH