Delayed density dependence
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In population ecology delayed density dependence describes a situation where population growth is controlled by negative feedback operating with a time lag.[1]
Delayed density dependence has been used by ecologists to explain population cycles.[2] Ecologists have been unable to successfully explain regular population cycles for many decades; delayed density dependence may hold the answer.[2] Here populations are allowed to increase above their normal capacity because there is a time lag until negative feedback mechanisms bring the population back down. This effect has been used to explain the widely fluctuating population cycles of lemmings,[3] forest insects as well as the population cycles of larger mammals such as moose and wolves.[4] Other causes of population cycles include cycling abiotic factors.[5]
Causes
The causes of delayed density dependence vary in each situation. In lemmings, food supply and predation are the most important factors that lead to delayed density dependence.[3] Competition between life stages is another cause. In some species of moth the practice of egg cannibalism takes place where older moths eat eggs of their own species.[6] This produces imbalances in the population levels of different generations leading to delayed density dependence.[6] Disease is another causative factor. The delay is introduced because of the time it takes for enough susceptible individuals to be present for the disease to spread again.[7] The delay to sexual maturity introduces delayed density dependence in many instances. In this case there is density dependent inhibition applied to organisms when they are sexually immature.[8] When this generation reaches sexual maturity there are fewer offspring, continuing the pattern.