Population sizes change depending on birth rate, death rate and migration in and out of the population.
These factors are affected by food supply, predation, reproductive abilities and disease. In a stable ecosystem, where these factors stay fairly balanced, the population size remains fairly constant.
Limiting factors = factors that keep a population at a maximum size that can be sustained by the ecosystem (eg. food supply).
Carrying capacity = the population size that can be sustained by an ecosystem.
Environmental resistance = collective term for the limiting factors that keep a population at carrying capacity.
Limiting factors keep the population at the carrying capacity, and the limiting factors which determine it's size are collectively called environmental resistance.
On a population growth curve (graph showing the growth of a population over time) there are usually three clear stages:
- Lag phase - growth is slow because the population is so small that even doubling…