HOME

TheInfoList



OR:

Overpopulation or overabundance is a phenomenon in which a
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
' population becomes larger than the
carrying capacity The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as ...
of its
environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...
. This may be caused by increased birth rates, lowered
mortality rate Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of de ...
s, reduced predation or large scale
migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
, leading to an overabundant species and other animals in the ecosystem
competing Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indivi ...
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. Judgements regarding overpopulation always involve both facts and values. Animals often are judged overpopulated when their numbers cause impacts that people find dangerous, damaging, expensive, or otherwise harmful. Societies may be judged overpopulated when their human numbers cause impacts that degrade ecosystem services, decrease human health and well-being, or crowed other species out of existence.


Background

In ecology, overpopulation is a concept used primarily in
wildlife management Wildlife management is the management process influencing interactions among and between wildlife, its habitats and people to achieve predefined impacts. It attempts to balance the needs of wildlife with the needs of people using the best availabl ...
.K. G. Poole. (1994). Characteristics of an Unharvested Lynx Population during a Snowshoe Hare Decline The Journal of Wildlife Management, 58(4), 608-61

/ref> Typically, an overpopulation causes the entire population of the species in question to become weaker, as no single individual is able to find enough food or shelter. As such, overpopulation is thus characterized by an increase in the diseases and parasite-load which live upon the species in question, as the entire population is weaker. Other characteristics of overpopulation are lower fecundity, adverse effects on the environment (soil, vegetation or fauna) and lower average body weights. Especially the worldwide increase of deer populations, which usually show
irruptive growth Irruptive growth is a growth pattern over time, defined by a sudden rapid growth in the population of an organism. Irruptive growth is studied in population ecology. Population cycles often display irruptive growth, but with a predictable pattern ...
, is proving to be of ecological concern. Ironically, where ecologists were preoccupied with conserving or augmenting deer populations only a century ago, the focus has now shifted in the direct opposite, and ecologists are now more concerned with limiting the populations of such animals. Supplemental feeding of charismatic species or interesting game species is a major problem in causing overpopulation, as is too little hunting or trapping of such species. Management solutions are increasing hunting by making it easier or cheaper for (foreign) hunters to hunt, banning supplemental feeding, awarding bounties, forcing landowners to hunt or contract professional hunters, using
immunocontraception Immunocontraception is the use of an animal's immune system to prevent it from fertilizing offspring. Contraceptives of this type are not currently approved for human use. Typically immunocontraception involves the administration of a vaccine that ...
, promoting the harvest of venison or other wild meats, introducing large predators (
rewilding Rewilding may refer to: *Rewilding (conservation biology), the return of habitats to a natural state ** Rewilding Europe, a programme to do so in Europe *** Pleistocene rewilding, a form of species reintroduction ** Rewilding Institute, an organ ...
), poisonings or introducing diseases. A useful tool in wildlife culling is the use of mobile freezer trailers in which to store carcasses. The harvest of meat from wild animals is a sustainable method of creating a
circular economy A circular economy (also referred to as circularity and CE) is a model of production and consumption, which involves sharing, leasing, reusing, repairing, refurbishing and recycling existing materials and products as long as possible. CE aims ...
.
Immunocontraception Immunocontraception is the use of an animal's immune system to prevent it from fertilizing offspring. Contraceptives of this type are not currently approved for human use. Typically immunocontraception involves the administration of a vaccine that ...
is a non-lethal method of regulating wild-animal population growth. Immunocontraception has been successfully used or tested in a variety of wild-animal populations including those of
bison Bison are large bovines in the genus ''Bison'' (Greek: "wild ox" (bison)) within the tribe Bovini. Two extant taxon, extant and numerous extinction, extinct species are recognised. Of the two surviving species, the American bison, ''B. bison'' ...
, deer,
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae a ...
s,
gray squirrel Gray squirrel or grey squirrel may refer to several species of squirrel indigenous to North America: *The eastern gray squirrel (''Sciurus carolinensis''), from the eastern United States and southeastern Canada; introduced into the United Kingdom, I ...
s,
pigeons Columbidae () is a bird family consisting of doves and pigeons. It is the only family in the order Columbiformes. These are stout-bodied birds with short necks and short slender bills that in some species feature fleshy ceres. They primarily ...
, rats and wild horses. Among the limitations of injectable immunocontraceptives are a relatively long time between vaccine administration and a reduction in population size (although stabilization of population size occurs faster) and the need to be in close proximity with animals for injection. Oral vaccines do not have the latter limitation, but they are still not as well developed as injectable vaccines. Judgements about overpopulation of wildlife or domestic animals typically are made in terms of human purposes and interests; since these vary, such judgements may vary, too. Judgements about human overpopulation are even more contentious, since the purposes and interests involved may be very important, even rising to the level of existence itself. Nevertheless, all people and every society have an interest in preserving a habitable biosphere, which may be compromised or degraded by too may people. In the context of rapid climate change, mass species extinction and other global environmental problems, discussions regarding human overpopulation are inevitable. Recent scientific evidence from many sources suggests Earth may be overpopulated currently. Evidence of rapidly declining ecosystem services was presented in detail in the Millennium Ecosystem Assessment of 2005, a collaborative effort involving more than 1,360 experts worldwide. More recent scientific accounts are provided by ecological footprint accounting and interdisciplinary research on
planetary boundaries Planetary boundaries is a concept highlighting human-caused perturbations of Earth systems making them relevant in a way not accommodated by the environmental boundaries separating the three ages within the Holocene epoch. Crossing a planetar ...
for safe human use of biosphere. The Sixth Assessment Report on Climate Change from the IPCC and the First Assessment Report on Biodiversity and Ecosystem Services by the IPBES, large international summaries of the state of scientific knowledge regarding climate disruption and biodiversity loss, also support the view that unprecedented human numbers are contributing to global ecological decline.IPBES. (2019). ''Summary for policymakers. Global assessment report on biodiversity and ecosystem services''. Intergovernmental Panel on Biodiversity and Ecosystem Services Secretariat. Recent estimates of a sustainable global human population run between two to four billion people. Judgements about human or animal overpopulation hinge partly on whether people feel a moral obligation to leave sufficient habitat and resources to preserve viable populations of other species. Recent biodiversity losses show that humanity's success in supporting larger human populations over the past century has depended on reducing the populations of many of Earth's other species.Foreman, D., & Carroll, L. (2014). ''Man swarm: How overpopulation is killing the wild world''. Live True Books. This is a special example of the
competitive exclusion principle In ecology, the competitive exclusion principle, sometimes referred to as Gause's law, is a proposition that two species which compete for the same limited resource cannot coexist at constant population values. When one species has even the sligh ...
in ecology, which states that two species which compete for the same limited resource cannot coexist at constant population values. Today humanity essentially competes with other species everywhere on Earth. We thus face choices regarding whether to preserve populations of other species and limit our own, or not. These essentially ethical choices  will make a difference in future judgements about overpopulation.


Well studied species


Deer

In Scotland the program of having landowners privately cull the overpopulation of red deer in the highlands has proved an abject failure. Scotland's deer are stunted, emaciated, and frequently starve in the Spring. As of 2016 the population is now so high, that 100,000 deer would need to be culled each year only to maintain the current population. A number of landowners have proven unwilling to accede to the law, requiring government intervention anyway. It has been necessary to contract professional hunters in order to satisfy landowner legislation regarding the annual cull. Millions of pounds of taxpayers' cash is spent on the annual cull. As of 2020, 100,000 deer are shot each year. Compounding the problem, some landowners have used supplemental feeding at certain shooting blinds in order to ease sport hunting. Overpopulation can have effects on
forage Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used m ...
plants, eventually causing a species to thus alter the greater environment. Natural ecosystems are extremely complex. The overpopulation of deer in Britain has been caused by legislation making hunting more difficult, but another reason may be the proliferation of forests, used by different deer species to breed and shelter. Forests and parks have caused Britain to be much more forested than it was in recent history, and may thus perversely be causing
biodiversity loss Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...
, conversion of heath habitat to grassland, extirpation of grassland and woodland plants due to
overgrazing Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature res ...
and the changing of the habitat structure. Examples are bluebells and primroses. Deer open up the forest and reduce the amount of brambles, which then has knock-on effects on
dormice A dormouse is a rodent of the family Gliridae (this family is also variously called Myoxidae or Muscardinidae by different taxonomists). Dormice are nocturnal animals found in Africa, Asia, and Europe. They are named for their long, dormant hibe ...
and certain birds which nest near the ground, such as the
capercaillie ''Tetrao'' is a genus of birds in the grouse subfamily known as capercaillies. They are some of the largest living grouse. Taxonomy The genus ''Tetrao'' was introduced in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of hi ...
, dunnock, nightingale, song thrush,
willow warbler The willow warbler (''Phylloscopus trochilus'') is a very common and widespread leaf warbler which breeds throughout northern and temperate Europe and the Palearctic, from Ireland east to the Anadyr River basin in eastern Siberia. It is strongly ...
, marsh tit,
willow tit The willow tit (''Poecile montanus'') is a passerine bird in the tit family, Paridae. It is a widespread and common resident breeder throughout temperate and subarctic Europe and across the Palearctic. The plumage is grey-brown and off-white w ...
and
bullfinch Bullfinch is a name given to two groups of passerine birds. True bullfinches The true bullfinches are thick-billed finches in the passerine family Fringillidae. They comprise the genus ''Pyrrhula''. These birds are restricted to the Old World, an ...
. Populations of the nightingale and the European turtle dove are believed to be primarily impacted by muntjac. Grouse populations suffer due to smashing into the fencing needed to protect against deer. A significant amount of the environmental destruction in Britain is caused by an overabundance of deer. Besides ecological effects, overpopulation of deer causes economic effects due to browsing on crops, expensive fencing needed to combat this and protect new
afforestation Afforestation is the establishment of a forest or stand of trees (forestation) in an area where there was no previous tree cover. Many government and non-governmental organizations directly engage in afforestation programs to create forests a ...
planting and
coppice Coppicing is a traditional method of woodland management which exploits the capacity of many species of trees to put out new shoots from their stump or roots if cut down. In a coppiced wood, which is called a copse, young tree stems are repeate ...
growth, and increasing numbers of road traffic incidents. Deer are in fact the most lethal animals of Britain, killing approximately 20 people a year from road accidents. In Scotland, the cost of road accidents due to these animals is estimated to be £7 million, and such collisions cause injuries to 50 to 100 people a year. High populations cause stripping of the bark of trees, eventually destroying forests. Protecting forests from deer costs on average three times as much as planting the forest in the first place. The NGO Trees for Life spent weeks planting native trees in Scotland, aiming to rebuild the ancient Caledonian Forest. After winter snowdrifts in 2014/2015 flattened the deer fences, more than a decade's growth was lost in a matter of weeks. In 2009 – 2010 the cost of
forest protection Forest protection is a branch of forestry which is concerned with the preservation or improvement of a forest and prevention and control of damage to forest by natural or man made causes like forest fires, plant pests, and adverse climatic cond ...
in Scotland ran to £10.5m. Some animals, such as muntjac, are too small and boring for most hunters to shoot, which poses additional management problems. In the United States the exact same problem is seen with
white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
, where populations have exploded and become invasive species in some areas. The state of Wisconsin has an estimated population of 1.9 million White tail deer, measured in 2020. In continental Europe roe deer pose a similar problem, although the populations were formerly much less, they have swelled in the 20th century so that although two and a half million are shot each year by hunters in Western Europe alone, as of 1998, the population still appears to be increasing, causing problems for forestry and traffic. In an experiment where roe deer on a Norwegian island was freed from human harvest and predators, the deer showed a doubling of the population each year or two. In the Netherlands and southern England roe deer were extirpated from the entirety of the country except for a few small areas around 1875. In the 1970s the species was still completely absent from Wales, but as of 2013, it has colonized the entire country.Algemeen Dagblad; Hoera, daar ligt weer een dode otter
/ref> As new forests were planted in the Netherlands in the 20th century, the population began to expand rapidly. As of 2016 there are some 110,000 deer in the country.


Birds

Aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
operations, recreation angling and populations of endangered fish such as the
schelly The schelly (''Coregonus stigmaticus'') is a living fresh water fish of the salmon family, endemic to four lakes in the Lake District, England. Its taxonomy is disputed with some recognizing it as a distinct species and others as a variant of ...
are impacted by
cormorant Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven gen ...
populations. Open aquaculture ponds provide winter or year-round homes and food for cormorants. Cormorants' effect on the aquaculture industry is significant, with a dense flock capable of consuming an entire harvest. Cormorants are estimated to cost the catfish industry in Mississippi alone between $10 million and $25 million annually.
Cormorant culling Cormorant culling is the intentional killing of cormorants by humans for the purposes of wildlife management. It has been practiced for centuries, with supporters of culling generally arising from the angling community. Culling techniques may in ...
is commonly achieved by sharp-shooting, nest destruction, roost dispersal and oiling the eggs. Geese numbers have also been called overpopulated. In the Canadian Arctic region, snow geese, Ross's geese, greater white-fronted geese and some populations of
Canada geese The Canada goose (''Branta canadensis''), or Canadian goose, is a large wild goose with a black head and neck, white cheeks, white under its chin, and a brown body. It is native to the arctic and temperate regions of North America, and it is o ...
have been increasing significantly over the past decades. Lesser snow geese populations have increased to over three million, and continue to increase by some 5% per year. Giant Canada geese have grown from near extinction to nuisance levels. Average body sizes have decreased and parasite loads are higher. Before the 1980s, Arctic geese populations had boom and bust cycles (see above) thought to be based on food availability, although there are still some bust years, this no longer seems the case. It is difficult to know what the numbers of geese were before the 20th century, before human impact presumably altered them. There are a few anecdotal claims from that time of two or three million, but these are likely exaggerations, as that would imply a massive die-off or vast amounts harvested, for which there is no evidence. More likely estimates from the period of 1500 to 1900 are a few hundred thousand animals, which implies that with the exception of Ross's geese, modern populations of geese are many millions more than in pre-industrial levels. Humans are blamed as the ultimate cause for the increase, directly and indirectly, due to management legislation limiting hunting introduced specifically in order to protect bird populations, but most importantly due to the increase in agriculture and large parks, which has had the effect of creating vast amounts of unintentional sanctuaries filled with food. Urban geese flocks have increased enormously. City ordinances generally prohibit discharging firearms, keeping such flocks safe, and there is abundant food. Geese profit from agricultural grain crops, and seem to be shifting their habitat preferences to such farmlands. Ironically, the creation of wildlife refuges may have exacerbated this: as geese overpopulations destroyed the ''
Scirpus ''Scirpus'' is a genus of grass-like species in the sedge family Cyperaceae many with the common names club-rush, wood club-rush or bulrush (see also bulrush for other plant genera so-named). They mostly inhabit wetlands and damp locations. Taxo ...
''
salt marsh A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominate ...
habitats that they were originally restricted to, this has speeded their conversion to adopt new feeding habitats, while maintaining roosting sites in refuges. The creation of wildlife refuges to protect wetland habitats in the continental United States from the 1930s to 1950s seems to have had the effect of disrupting the migration routes, as geese no longer fly as far south to Texas and Louisiana as they once did. Reduction of goose hunting in the US since the 1970s seems to have further had the effect of protecting populations. In Canada hunting has also decreased dramatically, from 43.384% harvest rates in the 1960s to 8% in the 1990s. Nonetheless, when kill rates were compared to populations, hunting alone does not seems to be solely responsible for the increase -weather or a not yet completed shift in habitat preference to agricultural land may also be factors. Although hunting may have formerly been the main factor in maintaining stable populations, ecologists no longer consider it a practical management solution, as public interest in the practice has continued to wane, and the population is now so large that the massive culls needed are unrealistic to ask from the public. Climate change in the Arctic would appear to be an obvious cause for the increase, but when subpopulations are correlated with local climatic increases, this does not seem to hold true, and furthermore, breeding regions seem to be shifting southwards anyway, irrespective of climate change. The nutrient subsidy provided by foraging in agricultural land has made the overall landscape use by geese unsustainable. Where such geese congregate local plant communities have been substantially altered; these chronic effects are cumulative, and have been considered a threat to the Arctic ecosystems, due to knock-on effects on native ducks, shorebirds and passerines. Grubbing and
overgrazing Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature res ...
by geese completely denudes the tundra and marshland, in combination with abiotic processes, this creates large desert expanses of hypersaline, anoxic mud which continue to increase each year -eventually these habitat changes become irreversible remaining in this state for decades.
Biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') le ...
drops to only one or two species which are inedible for geese, such as '' Senecio congestus'', '' Salicornia borealis'' and '' Atriplex hastata''. Because grazing occurs in serial stages, with biodiversity decreasing at each stage, floral composition may be used as an indicator of the degree of goose foraging at a site. Other effects are destruction of the vegetation holding dunes in place, the shift from sedge
meadow A meadow ( ) is an open habitat, or field, vegetated by grasses, herbs, and other non-woody plants. Trees or shrubs may sparsely populate meadows, as long as these areas maintain an open character. Meadows may be naturally occurring or artifici ...
s and grassy swards with herbaceous plants to moss fields, which can eventually give way to bare ground called 'peat barrens', and the erosion of this bare peat until glacial gravel and till is bared. In the High Arctic research is less developed: '' Eriophorum scheuchzeri'' and ''E. angustifolium'' fens appear to be affected, and are being replaced by carpets of moss, whereas meadows covered in '' Dupontia fisheri'' appear to be escaping destruction. There does not appear to be the damage found at lower latitudes in the Arctic. There is little proper research in effects on other birds. The yellow rail ('' Coturnicops noveboracensis'') appears to be extirpated from areas of Manitoba due habitat loss caused by the geese, whereas on the other hand the semipalmated plover ('' Charadrius semipalmatus'') appears to be taking advantage of the large areas of dead willows as a breeding ground. In the wintering grounds in continental USA, effects are much less pronounced. Experimentally excluding geese by means of fencing in North Carolina has found heavily affected areas can regenerate after only two years. Bulrush stands ('' Schoenoplectus americanus'') are still an important component of the diet, but there are indications the bulrush is being impacted, with soft mudflats gradually replacing areas where it grows. Damage to agriculture is primarily to seedlings, winter wheat and hay production. Changing the species composition to species less palatable to geese, such as ''Lotus'' may alleviate losses in hay operations. Geese also feed on agricultural land without causing economic loss, gleaning seeds from corn, soya or other grains and feeding on wheat, potato and corn stubble. In Québec crop damage insurance for the hay industry began in 1992 and claims increased yearly; actual compensation paid by the government, including administrative costs, amount to some half a million dollars a year. The fact that Arctic regions are remote, there is little public understanding for combatting the problem, and ecologists as yet do not have any effective solutions for combatting the problem anyway. In Canada, the most important hunters of geese are the
Cree people The Cree ( cr, néhinaw, script=Latn, , etc.; french: link=no, Cri) are a North American Indigenous people. They live primarily in Canada, where they form one of the country's largest First Nations. In Canada, over 350,000 people are Cree o ...
around Hudson Bay, members of the Mushkegowuk Harvesters Association, with an average kill rate of up to 60.75 birds per species per hunter in the 1970s. Kill rates have dropped, with hunters taking only half as much in the 1990s. However, total numbers of kills have increased, i.e. there are more hunters, but they are killing less per person. Nonetheless, per household the kills are approximately the same, at 100 birds. This indicates that stimulating an increase in native hunting might be difficult to achieve. The Cree population has increased. Elders say the taste of the birds has gotten worse, and they are thinner, both possibly effects due to the overpopulation. Elders also say that hunting has gotten more difficult, because there are less young and goslings, which are more likely to fall for
decoys A decoy (derived from the Dutch ''de'' ''kooi'', literally "the cage" or possibly ''ende kooi'', " duck cage") is usually a person, device, or event which resembles what an individual or a group might be looking for, but it is only meant to lu ...
. Inuit and other people in the north do much less hunting of geese, with kill rates of 1 to 24 per species per hunter. Per kilogram, hunters save some $8.14 to $11.40 from buying poultry at stores. Total kill numbers from hunters elsewhere in the US and southern Canada has been falling steadily. This is blamed on a decline in people interested in hunting, more feeding areas for the birds, and larger flocks with more experienced adult birds which makes decoying difficult. Individual hunters are bagging higher numbers, compensating lower hunter numbers. Management strategies in the USA include increasing the bag limit and the number of open hunting days, goose egg addling, trapping and relocation, and egg and nest destruction, managing habitat to make it less attractive to geese, harassment and direct culling. In Denver, Colorado, during moulting season biologists rounded up 300Canada geese (of 5,000 in the city), ironically on
Canada Day Canada Day (french: Fête du Canada), formerly known as Dominion Day (french: Fête du Dominion), is the national day of Canada. A federal statutory holiday, it celebrates the anniversary of Canadian Confederation which occurred on July 1, 1 ...
, killing them and distributing the meat to needy families (as opposed to sending it to a landfill), to try to curb the number of geese, following such programs in New York, Pennsylvania, Oregon and Maryland. Complaints about the birds were that they had taken over the golf courses, pooped all over the place, devoured native plants and scared citizens. Such culls have proven socially controversial, with intense backlash by some citizens. Park officials had tried dipping eggs in oil, using noise-makers and planting tall plants, but this was not sufficient. In Russia, the problem does not seem to exist, likely due to human harvest and local long-term cooling climate trends in the Russian Far East and
Wrangel Island Wrangel Island ( rus, О́стров Вра́нгеля, r=Ostrov Vrangelya, p=ˈostrəf ˈvrangʲɪlʲə; ckt, Умӄиԓир, translit=Umqiḷir) is an island of the Chukotka Autonomous Okrug, Russia. It is the 91st largest island in the ...
. It is also possible that the population growth is completely natural, and that when the carrying capacity of the environment is reached the population will stop growing. For organisations such as
Ducks Unlimited Ducks Unlimited (DU) is an American nonprofit organization 501(c) dedicated to the conservation of wetlands and associated upland habitats for waterfowl, other wildlife, and people. It has had a membership of around 700,000 since January 2013 ...
, the resurgence of goose populations in North America can be called one of the greatest success story in wildlife management. By 2003 the US goose harvest was approaching 4 million, three times the numbers 30 years ago.


Pets

In the United States, over half of the households own a dog or a cat. Even with so much pet ownership there is still an issue with pet overpopulation, especially seen in shelters. Because of this problem it is estimated that between 10 and 25 percent of dogs and cats are killed yearly. The animals are killed humanely, but the goal is to greatly lower and eventually completely avoid this. Estimating the overpopulation of pets, especially cats and dogs, is a difficult task, but it has been a continuous problem. It has been hard to determine the number of shelters and animals in each shelter around even just the US. Animals are constantly being moved around or euthanized, so it is difficult to keep track of those numbers across the country. It is becoming universally agreed upon that sterilization is a tool that can help reduce population size so that less offspring are produced in the future With less offspring, pet populations can start to decrease which reduces the amount that get killed each year.


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, which are usually mathematically modelled as Lotka–Volterra equations. 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 A lynx is a type of wild cat. Lynx may also refer to: Astronomy * Lynx (constellation) * Lynx (Chinese astronomy) * Lynx X-ray Observatory, a NASA-funded mission concept for a next-generation X-ray space observatory Places Canada * Lynx, O ...
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 Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, bot ...
, 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
lemming A lemming is a small rodent, usually found in or near the Arctic in tundra biomes. Lemmings form the subfamily Arvicolinae (also known as Microtinae) together with voles and muskrats, which form part of the superfamily Muroidea, which also includ ...
s and voles have such
population cycle A population cycle in zoology is a phenomenon where populations rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population ...
s of rapid growth and subsequent decrease. Snowshoe hares populations similarly cycle dramatically, as did those of one of their predators, the
lynx A lynx is a type of wild cat. Lynx may also refer to: Astronomy * Lynx (constellation) * Lynx (Chinese astronomy) * Lynx X-ray Observatory, a NASA-funded mission concept for a next-generation X-ray space observatory Places Canada * Lynx, O ...
. Another example is the cycles among populations of grey wolves and moose in
Isle Royale National Park Isle Royale National Park is an American national park consisting of Isle Royale – known as Minong to the native Ojibwe – along with more than 400 small adjacent islands and the surrounding waters of Lake Superior, in the state of Michigan. ...
. 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.Simpson, Stephen J.; Sword, Gregory A. (2008). "Locusts". ''
Current Biology ''Current Biology'' is a biweekly peer-reviewed scientific journal that covers all areas of biology, especially molecular biology, cell biology, genetics, neurobiology, ecology, and evolutionary biology. The journal includes research articles, var ...
'' 18:r364-366.


Determining population size/density

When determining whether a population is overpopulated a variety of factors must be looked at. Given complexity of the issue, often it is determined by scientist and wildlife management as to what constitutes such a claim. 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 an accurate method, 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 when 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. In the case of the Mute swan, ''Cygnus olor'', their population has rapidly spread across much of North America as well as parts of Canada and western Europe. This species of swan has caused much concern for wildlife management as they damage aquatic vegetation, and harass other waterfowl, dislocating them. The population of the Mute swan has seen an average increase of around 10-18% per year which further threatens to impact the areas they inhabit. Management of the species comes in a variety of ways. Similar to overpopulated or invasive species, hunting is one of the most effective methods of population control. Other methods may involve trapping, relocation, or euthanasia.


Criticism

In natural ecosystems, populations naturally expand until they reach the
carrying capacity The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as ...
of the environment; if the resources on which they depend are exhausted, they naturally collapse. According to the
animal rights Animal rights is the philosophy according to which many or all sentient animals have moral worth that is independent of their utility for humans, and that their most basic interests—such as avoiding suffering—should be afforded the sam ...
movement, calling this an 'overpopulation' is more an ethics question than a scientific fact. Animal rights organisations are commonly critics of ecological systems and wildlife management. Animal rights activists and locals earning income from commercial hunts counter that scientists are outsiders who do not know wildlife issues, and that any slaughter of animals is evil. Various case studies indicate that use of cattle as ' natural grazers' in many European nature parks due to absence of hunting, culling or natural predators (such as wolves),may cause an overpopulation because the cattle do not migrate. This has the effect of reducing plant
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') le ...
, as the cattle consume native plants. Because such cattle populations begin to starve and die in the winter as available
forage Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used m ...
drops, this has caused animal rights activists to advocate supplemental feeding, which has the effect of exacerbating the ecological effects, causing nitrification and eutrophication due to excess faeces, deforestation as trees are destroyed, and
biodiversity loss Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...
. Despite the ecological effects of overpopulation, wildlife managers may want such high populations in order to satisfy public enjoyment of seeing wild animals. Others contend that introducing large predators such as lynx and wolves may have similar economic benefits, even if tourists rarely actually catch glimpses of such creatures. In regards to population size, most of the methods used give estimates that vary in accuracy to the actual size and density of the population. Criticisms of theses methods generally fall onto the efficacy of methods used.


Human overpopulation

Overpopulation can result from an increase in births, a decline in
mortality rate Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of de ...
s against the background of high fertility rates. It is possible for very sparsely populated areas to be overpopulated if the area has a meagre or non-existent capability to sustain life (e.g. a desert). Advocates of population moderation cite issues like quality of life and risk of starvation and disease and human pressures on the environment as a basis to argue against continuing high human population growth and for
population decline A population decline (also sometimes called underpopulation, depopulation, or population collapse) in humans is a reduction in a human population size. Over the long term, stretching from prehistory to the present, Earth's total human population ...
.


See also

*
Overshoot (population) In environmental science, the concept of overshoot means demand in excess of regeneration. It can apply to animal populations and people. Environmental science studies to what extent human populations through their resource consumption have risen ...


References

{{Global catastrophic risks Population density Population ecology Zoology