Ecology & Evolution

7 billion people and growing

Logistic growth Q 6, 7, 8 Population growth Add this question at the end: List three abiotic or biotic factors which set limits to population increase

What sets a limit to population increase? Density-dependent, biotic factors – mortality due to disease – mortality due to predation – intraspecific competition Density-independent, abiotic factors – mortality due to weather – mortality due to natural disasters: fire, hurricane, floods, earthquakes

Logistic growth curve Exponential growth phase – Species doubles per unit time – No limiting factors: nutrients, oxygen, space in ample supply Transitional phase – Population growth continues but at a slower rate – Limiting factors slow growth rate: nutrients, oxygen, space in short supply Plateau phase – Population growth slows to zero – Limiting factors inhibit population growth: nutrients, oxygen, space in short supply Carrying capacity (K) = maximum number of individuals in a species that can sustainably be supported in an environment

Factors affecting population size Natality: birth rate Immigration: rate at which individuals move into a population Mortality: death rate Emigration: rate at which individuals move out of the population P = (N + I) – (M + E)

Logistic growth curve Exponential growth phase – N + I > M + E Transitional phase – N + I > M + E Plateau phase – N + I = M + E