populations

Geographic range

• area inhabited by population
• depending on species, could be large or small range

Density

• number of individuals per unit area
• different species have very different densities, even in same environment

Distribution

• how individuals spread out across range
• randomly, uniformly, clumps

Population growth

(birth rate + immigration rate) - (death rate + emigration rate)

Logistic growth

population growth that starts off exponential but shows down and stops as time goes on

Carrying capacity

max number of individuals of a species that an environment can support

• population stabilizes
• if carrying capacity too low, populations can die, leading to extinction

Limits to growth

• limiting factors prevent populations from getting too big
• two types: density dependent and independent

Density dependent factors

disease, predation, herbivory, stress from overcrowding, competition

• mostly in large populations

Density independent factors

• effect regardless of population size and density
• natural disasters, drought, etc.
• can sometimes strengthen density-dependent factors

Predator prey cycle

• predator population goes up, prey population goes down, leading to predator population going down, increasing prey population, leading to predator population going up
• cycle repeats
• same thing for herbivory (herbivores and plants)