Overpopulation in animals facts for kids
Overpopulation or overabundance is a phenomenon in which a species' population becomes larger than the carrying capacity of its environment. This may be caused by increased birth rates, lowered mortality rates, reduced predation or large scale migration, leading to an overabundant species and other animals in the ecosystem competing for food, space, and resources. The animals in an overpopulated area may then be forced to migrate to areas not typically inhabited, or die off without access to necessary resources.
Contents
Population cycles
In the wild, rampant population growth of prey species often causes growth in the populations of predators. Such predator-prey relationships can form cycles.
In natural ecosystems, predator population growth lags just behind the prey populations. After the prey population crashes, the overpopulation of predators causes the entire population to be subjected to mass starvation. The population of the predator drops, as less young are able to survive into adulthood. This could be considered a perfect time for wildlife managers to allow hunters or trappers to harvest as much of these animals as necessary, for example lynx in Canada, although on the other hand this may impact the ability of the predator to rebound when the prey population begins to exponentially increase again. Such mathematical models are also crucial in determining the amount of fish which may be sustainably harvested in fisheries, this is known as the maximum sustainable yield.
Predator population growth has the effect of controlling the prey population, and can result in the evolution of prey species in favour 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 population cycles of rapid growth and subsequent decrease. Snowshoe hares populations similarly cycle dramatically, as did those of one of their predators, the lynx. Another example is the cycles among populations of grey wolves and moose in Isle Royale National Park. For some still unexplained reason, such patterns in mammal population dynamics are more prevalent in ecosystems found at more arctic latitudes.
Some species such as locusts experience large natural cyclic variations, experienced by farmers as plagues.
Determining population size/density
When determining whether a population is overpopulated a variety of factors must be looked at. Given the complexity of the issue, scientists and wildlife managers often differ in judging such claims. In many cases scientists will look to food sources and living space to gauge the abundance of a species in a particular area. National parks collect extensive data on the activities and quality of the environment they are established in. This data can be used to track whether a specific species is consuming larger amounts of their desired food source over time.
This is done typically in four ways, the first being "total counting". Researchers will use aerial photography to count large populations in a specific area such as deer, waterfowl, and other "flocking" or "herd" animals. Incomplete counts involve counting a small subsection of a population and extrapolating the data across the whole area. This method will take into account the behavior of the animals such as how much territory a herd may cover, the density of the population, and other potential factors that may come into question.
The third method is "indirect counts"; this is done by looking at the environment for signs of animal presence. Typically done by counting fecal matter or dens/nesting of a particular animal. This method is not as accurate as direct counting, but gives general counts of a population in a specific locale.
Lastly the method of mark-recapture is used extensively to determine general population sizes. This method involves the trapping of animals after which some form of tag is placed on the animal and it is released back into the wild. After which, other trappings will determine population size based on the number of marked versus unmarked animals.
Fish populations
Similar methods can be used to determine the population of fish however some key differences arise in the extrapolation of data. Unlike many land animals in-land fish populations are divided into smaller population sizes. Factors such as migration may not be relevant when determining population in a specific locales while more important for others such as the many species of salmon or trout. Monitoring of waterways and isolated bodies of water provide more frequently updated information on the populations in specific areas. This is done using similar methods to the mark-recapture methods of many land animals.
Introduced species
The introduction of a foreign species has often caused ecological disturbance, such as when deer and trout were introduced into Argentina, or when rabbits were introduced to Australia and predators were introduced in turn to attempt to control the rabbits.
When an introduced species is so successful that its population begins to increase exponentially and causes deleterious effects to farmers, fisheries, or the natural environment, these introduced species are called invasive species.
See also
