N = Natality
I = Immigration
M = Mortality
E = Emigration
(N + I) - (M + E)
Natality and immigration increase size.
Mortality and emigration decrease size.
Sigmoid (S-Shaped) population growth curve
Phases of population growth curve
Exponential growth phase: population increases exponentially, adequate nutrients available and little accumulation of waste. High natality.
Linear growth: Natality rate decreases, but still exceeds rising mortality rate. Developing shortage of nutrients and accumulating waste products.
Plateau: Natality and immortality equals population. Nutrient supply and level of waste do not support growth in numbers.
Limits to population increase
Predation
Disease
Natural disasters
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