1. Compare and contrast the assumptions of exponential and
logistic growth models
In both equations r is the intrinsic rate of increase and is the same.
- Exponential growth model has density INDEPENDENT growth rate (r is constant!)
- Exponential growth model assumptions:
- dN/dt = r x N
- Ideal conditions
- Continuous birth and death
- Intrinsic rate of increase r
- Logistic Model: The observed growth rate, robserved, declines with increasing
population size (DENSITY DEPENDENT)
- r(observed) = dN/dt = rN[(K-N)/K]
- K is carrying capacity where r(observed) = 0
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- Maximum population size that an area can support!
- r(observed) = r[(K-N)/K]
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- K/2 is the inflection point, fastest dN/dt
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- Graphs of dN/dt
- Logistic Graph Assumptions:
- Logistic models assume that population birth and death rates respond
immediately to their current population size.
- But there can be a time lag before the population’s birth and death rates
change
