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 cycles is one of the major unsolved ecological problems. There are a number of factors which influence population change such as availability of food, predators, diseases and climate.
Olaus Magnus, the Archbishop of Uppsala in central Sweden, identified that species of northern rodents had periodic peaks in population and published two reports on the subject in the middle of the 16th century.
In North America, the phenomenon was identified in populations of the snowshoe hare. [1] [2] In 1865, trappers with the Hudson's Bay Company were catching plenty of animals. By 1870, they were catching very few. It was finally identified that the cycle of high and low catches ran over approximately a ten-year period.
The most well known example of creatures which have a population cycle is the lemming. [3] The biologist Charles Sutherland Elton first identified in 1924 that the lemming had regular cycles of population growth and decline. When their population outgrows the resources of their habitat, lemmings migrate, although contrary to popular myth, they do not jump into the sea.
Mouse plagues in Australia happen at intervals of about four years.
While the phenomenon is often associated with rodents, it does occur in other species such as the ruffed grouse. There are other species which have irregular population explosions such as grasshoppers where overpopulation results in locust swarms in Africa and Australia.
There is also an interaction between prey with periodic cycles and predators. As the population expands, there is more food available for predators. As it contracts, there is less food available for predators, putting pressure on their population numbers.
Each population cycle tends to last as long as a species' life expectancy (i.e. lemmings, rabbits and locusts)
There is strong evidence that humans also display population cycles. Societies as diverse as those of England and France during the Roman, medieval, and early modern eras, of Egypt during Greco-Roman and Ottoman rule, and of various dynasties in China all showed similar patterns of political instability and violence becoming considerably more common after times of relative peace, prosperity, and sustained population growth. Quantitatively, periods of unrest included many times more events of instability per decade and occurred when the population was declining, rather than increasing. [4]
The snowshoe hare, also called the varying hare or snowshoe rabbit, is a species of hare found in North America. It has the name "snowshoe" because of the large size of its hind feet. The animal's feet prevent it from sinking into the snow when it hops and walks. Its feet also have fur on the soles to protect it from freezing temperatures.
The snowy owl, also known as the polar owl, the white owl and the Arctic owl, is a large, white owl of the true owl family. Snowy owls are native to the Arctic regions of both North America and the Palearctic, breeding mostly on the tundra. It has a number of unique adaptations to its habitat and lifestyle, which are quite distinct from other extant owls. One of the largest species of owl, it is the only owl with mainly white plumage. Males tend to be a purer white overall while females tend to more have more extensive flecks of dark brown. Juvenile male snowy owls have dark markings that may appear similar to females until maturity, at which point they typically turn whiter. The composition of brown markings about the wing, although not foolproof, is the most reliable technique to age and sex individual snowy owls.
The Canada lynx or Canadian lynx is one of the four living species in the genus Lynx. It is a medium-sized wild cat characterized by long, dense fur, triangular ears with black tufts at the tips, and broad, snowshoe-like paws. Its hindlimbs are longer than the forelimbs, so its back slopes downward to the front. The Canada lynx stands 48–56 cm (19–22 in) tall at the shoulder and weighs between 5 and 17 kg. It is a good swimmer and an agile climber.
The northern hawk-owl or northern hawk owl is a medium-sized true owl of the northern latitudes. It is non-migratory and usually stays within its breeding range, though it sometimes irrupts southward. It is one of the few owls that is neither nocturnal nor crepuscular, being active only during the day. This is the only living species in the genus Surnia of the family Strigidae, the "typical" owls. The species is sometimes called simply the hawk owl; however, many species of owls in the genus Ninox are also called "hawk owls".
The Lotka–Volterra equations, also known as the Lotka–Volterra predator–prey model, are a pair of first-order nonlinear differential equations, frequently used to describe the dynamics of biological systems in which two species interact, one as a predator and the other as prey. The populations change through time according to the pair of equations:
The Arctic wolf, also known as the white wolf, polar wolf, and the Arctic grey wolf, is a subspecies of grey wolf native to the High Arctic tundra of Canada's Queen Elizabeth Islands, from Melville Island to Ellesmere Island. Unlike some populations that move between tundra and forest regions, Arctic wolves spend their entire lives north of the northern treeline. Their distribution to south is limited to the northern fringes of the Middle Arctic tundra on the southern half of Prince of Wales and Somerset Islands. It is a medium-sized subspecies, distinguished from the northwestern wolf by its smaller size, its whiter colouration, its narrower braincase, and larger carnassials. Since 1930, there has been a progressive reduction in size in Arctic wolf skulls, which is likely the result of wolf-dog hybridization.
The Norway lemming, also known as the Norwegian lemming is a common species of lemming found in northern Fennoscandia, where it is the only vertebrate species endemic to the region. The Norway lemming dwells in tundra and fells, and prefers to live near water. Adults feed primarily on sedges, grasses and moss. They are active at both day and night, alternating naps with periods of activity.
Competition is an interaction between organisms or species in which both require a resource that is in limited supply. Competition lowers the fitness of both organisms involved since the presence of one of the organisms always reduces the amount of the resource available to the other.
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 subsequent decline. It is a phenomenon typically associated with r-strategists.
Bamboo blossoming is a natural phenomenon in which the bamboos in a location blossom and become hung with bamboo seeds.
The Arctic lemming is a species of rodent in the family Cricetidae.
The Forrest's mouse, or desert short-tailed mouse, is a small species of rodent in the family Muridae. It is a widespread but sparsely distributed species found across arid and semi-arid inland Australia, commonly found in tussock grassland, chenopod shrubland, and mulga or savannah woodlands.
The wood lemming is a species of rodent in the family Cricetidae. It belongs to the rodent subfamily Arvicolinae, so is a relative of the voles, lemmings, and muskrats. It is found in the taiga biome of China, Estonia, Finland, Mongolia, Norway, Russia, and Sweden.
Bolam's mouse is a species of nocturnal, burrowing rodent in the family Muridae that inhabits the semi arid and southern arid regions of Australia. It has a number of physiological and behavioural adaptations developed to cope with an extremely varied climate. Including the ability survive by extracting water from seeds alone, the production of highly concentrated urine, low water content faeces and nocturnal activity.
The Newfoundland pine marten is a genetically distinct subspecies of the American marten found only on the island of Newfoundland in the province of Newfoundland and Labrador, Canada; it is one of only 14 species of land mammals native to the island. The marten was listed as endangered by the COSEWIC in 2001 and has been protected since 1934, however the population still declines. The Newfoundland marten has been geographically and reproductively isolated from the mainland marten population for 7000 years. The Newfoundland pine marten is similar in appearance to its continental cousin, but is slightly larger, with dark brown fur with an orange/yellow patch on the throat. Females are an average weight of 772 grams and males have an average weight of 1275 grams. The Newfoundland subspecies is also observed to inhabit a wider range of forest types than its mainland counterparts. The population characteristics suggest that the Newfoundland marten is a product of unique ecological setting and evolutionary selective factors acting on the isolated island population. The Newfoundland pine marten is omnivorous, feeding on mainly small mammals, along with birds, old carcasses, insects and fruits; it is currently found in suitable pockets of mature forest habitat, on the west coast of Newfoundland and in and around Terra Nova National Park. The Pine Marten Study Area (PMSA) is located in southwestern Newfoundland and is a 2078 km2 wildlife reserve that was created in 1973 to protect the Newfoundland Marten.
Predator satiation is an anti-predator adaptation in which prey briefly occur at high population densities, reducing the probability of an individual organism being eaten. When predators are flooded with potential prey, they can consume only a certain amount, so by occurring at high densities prey benefit from a safety in numbers effect. This strategy has evolved in a diverse range of prey, including notably many species of plants, insects, and fish. Predator satiation can be considered a type of refuge from predators.
A lemming is a small rodent, usually found in or near the Arctic in tundra biomes. Lemmings form the subfamily Arvicolinae together with voles and muskrats, which form part of the superfamily Muroidea, which also includes rats, mice, hamsters, and gerbils. In popular culture, a longstanding myth holds that they exhibit herd mentality and jump off cliffs, committing mass suicide.
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.
Grands-Jardins National Park is a provincial park, located in the Unorganized Territory of Lac-Pikauba, in the Charlevoix Regional County Municipality, an administrative region of Capitale-Nationale, in Quebec, Canada.
Population control is the practice of artificially maintaining the size of any population. It simply refers to the act of limiting the size of an animal population so that it remains manageable, as opposed to the act of protecting a species from excessive rates of extinction, which is referred to as conservation biology.