DN dN N 111

where the change in the population over time is a function of a birth rate minus death rate (which is equal to the intrinsic rate of increase r) times the current population size times one minus the current population size divided by the carrying capacity K (the maximum population size that can be supported by the environment). As the population becomes larger, there are fewer resources available, thereby increasing density-dependent mortality and decreasing fecundity (Figure 3). When a population's mortality rate equals its birth rate, a population will no longer grow and it will have reached its carrying capacity (Figure 3).

Many species' populations will fluctuate around their carrying capacity. For species living in temperate or polar climates that exhibit birth pulses during the spring and summer months, their populations have the potential to

Figure 3 (a) The logistic growth curve where a population's growth is dampened as it approaches its carrying capacity. (b) As a population approaches its carrying capacity and resources decline, density-dependent mortality increases while density-dependent natality increases.

Population size (N )

Figure 3 (a) The logistic growth curve where a population's growth is dampened as it approaches its carrying capacity. (b) As a population approaches its carrying capacity and resources decline, density-dependent mortality increases while density-dependent natality increases.

exceed the habitat's carrying capacity during the fall and winter months when resource availability declines. Consequently, density-dependent mortality is strong during this time reducing the population below its carrying capacity.

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