The carrying capacity is the maximum population size of a species that an ecosystem can support. It is set by the supply of resources, such as food, water, space and light, and by other limiting factors in the environment.When a species colonises a new area, its population usually grows in a pattern called a sigmoid (S-shaped) growth curve.
• Log (exponential) phase: resources are plentiful and few factors are limiting, so the birth rate is much higher than the death rate and numbers rise rapidly.
• Stationary phase: resources become limiting and competition increases, so the birth rate falls and the death rate rises until they are roughly equal. The population then fluctuates around the carrying capacity.The carrying capacity is not fixed. If the environment changes, for example a drought reduces the food supply or a new predator arrives, the carrying capacity can fall. An increase in resources can raise it.Worked example
A population of beetles grows from 150 to 1350 during a 12 week log phase. Calculate the mean rate of population growth.rate = (1350 − 150) ÷ 12 = 100 beetles per week
• Log (exponential) phase: resources are plentiful and few factors are limiting, so the birth rate is much higher than the death rate and numbers rise rapidly.
• Stationary phase: resources become limiting and competition increases, so the birth rate falls and the death rate rises until they are roughly equal. The population then fluctuates around the carrying capacity.The carrying capacity is not fixed. If the environment changes, for example a drought reduces the food supply or a new predator arrives, the carrying capacity can fall. An increase in resources can raise it.Worked example
A population of beetles grows from 150 to 1350 during a 12 week log phase. Calculate the mean rate of population growth.