General Principles • The potential size of a population is limited in an ecosystem is limited. Limiting factors include food, nesting sites, and similar factors. • (births - deaths) + (immigrants - emigrants) = change in population size. • Biotic potential can lead to exponential growth, but there is always an upper limit.
Exponential Growth Exponential growth produces a J-shaped population graph.
Growth Rates Age of first reproduction affects the rate of population growth.
Death Rates Average lifespan also affects growth rate.
Carrying Capacity # births = # deaths The upper limit for population growth is determined by the carrying capacity of the environment.
Overshooting Capacity If a population overshoots the carrying capacity of the environment, the result is a population crash.
Logistic Growth Available space limits barnacle populations. Where there are many natural controls, populations tend to demonstrate logistic growth.
Population Crash Where there are few natural controls, a population may rise rapidly, exceed carrying capacity, then crash as most of the population starves.
Human Growth Curve What is carrying capacity for humans? What happens if we have overshot it?
Age Structures Why are these so different? What may be the consequences?
Worldwide Populations Why are these so different? What may be the consequences?
U.S. Population Where are we on the S-shaped curve? What factors could cause our population to stabilize?
Easter Island • The culture that built these statues on Easter Island overshot the island’s carrying capacity, severely damaging the ecosystem, and crashed. • What lessons can today’s world population learn from this?