Download Logistic growth curve

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