Overpopulation

Overpopulation occurs when a species' population exceeds the carrying capacity of its ecological niche. It can result from an increase in births (fertility rate), a decline in the mortality rate, an increase in immigration, or an unsustainable biome and depletion of resources. When overpopulation occurs, individuals limit available resources to survive. The change in number of individuals per unit area in a given locality is an important variable that has a significant impact on the entire ecosystem. In the wild, overpopulation often causes growth in the populations of predators. This has the effect of controlling the prey population and ensuring its evolution in favor of genetic characteristics that render it less vulnerable to predation (and the predator may co-evolve, in response). In the absence of predators, species are bound by the resources they can find in their environment, but this does not necessarily control overpopulation, at least in the short term. An abundant supply of resources can produce a population boom followed by a population crash. Rodents such as lemmings and voles have such cycles of rapid population growth and subsequent decrease. Snowshoe hares populations similarly cycled dramatically, as did those of one of their predators, the lynx. The introduction of a foreign species has often caused ecological disturbance, as when deer and trout were introduced into Argentina when rabbits were introduced to Australia, and indeed when predators such as cats were introduced in turn to attempt to control the rabbits. Some species such as locusts experience large natural cyclic variations, experienced by farmers as plagues. Human overpopulation occurs when the ecological footprint of a human population in a specific geographical location exceeds the carrying capacity of the place occupied by that group. Overpopulation can further be viewed, in a long term perspective, as existing when a population cannot be maintained given the rapid depletion of non-renewable resources or given the degradation of the capacity of the environment to give support to the population.