What term is given to the biological phenomenon where the size of animals isolated on an island increases dramatically over generations?
"Island gigantism Island gigantism or insular gigantism is a biological phenomenon in which the size of an animal isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general ""island effect"" or ""Foster's rule"", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies, and large species tend to evolve smaller bodies. With the arrival of humans and associated predators (dogs, cats, rats, pigs), many giant as well as other island endemics have become extinct. A similar size increase, as well as increased woodiness, has"
"Insular dwarfism Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf breeds, called dwarfing. This process has occurred many times throughout evolutionary history, with examples including dinosaurs, like ""Europasaurus"", and modern animals such as elephants and their relatives. This process, and other ""island genetics"" artifacts, can occur not only on islands, but also in other situations where an ecosystem is isolated from external resources"
"and breeding. This can include caves, desert oases, isolated valleys and isolated mountains (""sky islands""). Insular dwarfism is one aspect of the more general ""island effect"" or ""Foster's rule"", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies, and large species tend to evolve smaller bodies. There are several proposed explanations for the mechanism which produces such dwarfism. One is a selective process where only smaller animals trapped on the island survive, as food periodically declines to a borderline level. The smaller animals need fewer resources and smaller territories, and so are more likely"
"islands to their original states; New Zealand has used them to hold natural populations of species that would otherwise be unable to survive in the wild. The principal components of island restoration are the removal of introduced species and the reintroduction of native species. Isolated islands have been known to have greater levels of endemism since the 1970s when the theory of Island biogeography, formulated by Robert MacArthur and E.O. Wilson was developed. This higher occurrence of endemism is because isolation limits immigration of new species to the island, allowing new species to evolve separately from others on the mainland."
"initially described as a ""Velociraptor""-sized dromaeosaurid (and in consequence a dubious example of insular dwarfism), but has been since reclassified as a secondarily flightless stem bird, closer to modern birds than ""Jeholornis"" (thus actually an example of insular gigantism). Insular dwarfism Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf breeds, called dwarfing. This process has occurred many times throughout evolutionary history, with examples"
"Foster's rule Foster's rule, also known as the island rule or the island effect, is an ecogeographical rule in evolutionary biology stating that members of a species get smaller or bigger depending on the resources available in the environment. For example, it is known that pygmy mammoths evolved from normal mammoths on small islands. Similar evolutionary paths have been observed in elephants, hippopotamuses, boas, deer (such as Key deer) and humans. The rule was first stated by J. Bristol Foster in 1964. In it, he compared 116 island species to their mainland varieties. He proposed that certain island creatures evolved"
"are caused by inbreeding depression or genetic load. Island populations often also have small populations due to geographic isolation, limited habitat and high levels of endemism. Because their environments are so isolated gene flow is poor within island populations. Without the introduction of genetic diversity from gene flow, alleles are quickly fixed or lost. This reduces island populations' ability to adapt to any new circumstances and can result in higher levels of extinction. The majority of mammal, bird, and reptile extinctions since the 1600s have been from island populations. Moreover, 20% of bird species live on islands, but 90% of"
"study since the 1950s. The population makes an ideal model subject for scientists researching evolution, population dynamics and demography because the population is unmanaged, is closed (no emigration or immigration) and has no significant competitors or predators. The sheep exhibit a phenomenon known as overcompensatory density dependence, in which their population never reaches equilibrium. The population growth is so great as to exceed the carrying capacity of the island, which eventually causes a dramatic population crash, and then the cycle repeats. For example, in 1989, the population fell by two thirds within 12 weeks. The age and sex structure of"
"to survive and establish populations. As a result, islands have fewer species than mainland habitats. Island populations are small and exhibit low genetic variability (see founder effect), but are isolated from the predators and competitors that they initially evolved with. This can lead to a process called ecological release, where a species is released from its ancestral community interactions and then colonizes new niches. In response to these changing ecological pressures, island species can become much more docile than their mainland counterparts, and may grow larger (see island gigantism) or smaller (see island dwarfism). Some of these unique adaptations are"
"the distance of an island from a source of colonists (distance effect). Usually this source is the mainland, but it can also be other islands. Islands that are more isolated are less likely to receive immigrants than islands that are less isolated. The rate of extinction once a species manages to colonize an island is affected by island size; this is the species-area curve or effect. Larger islands contain larger habitat areas and opportunities for more different varieties of habitat. Larger habitat size reduces the probability of extinction due to chance events. Habitat heterogeneity increases the number of species that"
"record. Before the collapse, animal species distribution was very cosmopolitan – the same species existed everywhere across tropical Pangaea – but after the collapse, each surviving rainforest 'island' developed its own unique mix of species. Many amphibian species became extinct, while reptiles diversified into more species after the initial crisis. These patterns are explained by the theory of insular biogeography, a concept that explains how evolution progresses when populations are restricted into isolated pockets. This theory was originally developed for oceanic islands, but it can be applied equally well to any other ecosystem that is fragmented, only existing in small"
"be a founder effect operative when larger members of a mainland population are superior in their ability to colonize islands. Island size plays a role in determining the extent of gigantism. Smaller islands generally accelerate the rate of evolution of changes in organism size, and organisms there evolve greater extremes in size. Examples of island gigantism include: Many rodents grow larger on islands, whereas carnivores, proboscideans and artiodactyls usually become smaller. In addition to size increase, island grass plants may also exhibit ""insular woodiness"". The most notable examples are the megaherbs of New Zealand's subantarctic islands. Island gigantism Island gigantism"
"associated with the limited prey resources available on islands. As opposed to island dwarfism, island gigantism is found in most major vertebrate groups and in invertebrates. Territorialism may favor the evolution of island gigantism. A study on Anaho Island in Nevada determined that reptile species that were territorial tended to be larger on the island compared to the mainland, particularly in the smaller species. In territorial species, larger size makes individuals better able to compete to defend their territory. This gives additional impetus to evolution toward larger size in an insular population. A further means of establishing island gigantism may"
"reflected in charismatic island species such as the giant tortoise, Komodo dragon, or pygmy mammoths. Other adaptations to life on islands include increased poikilothermy, relaxed anti-predator behavior, and reduced sexual selection in animals, and loss of herbivore defenses and reduced dispersal in plants. The formation of new islands and their isolation from the mainland provides many unoccupied niches for species to adapt to. Since immigration of predators and competitors is limited, many organisms are able to persist in these new niches. This results in a high occurrence of endemism, where species are unique to a localized area. For example, 50%"
"of larger maximum body size is likely to be interrupted by the emergence of a series of constraints that must be overcome by evolutionary innovations before the process can continue. For both herbivores and carnivores, island size, the degree of island isolation and the size of the ancestral continental species appear not to be of major direct importance to the degree of dwarfing. However, when considering only the body masses of recent top herbivores and carnivores, and including data from both continental and island land masses, the body masses of the largest species in a land mass were found to"
"and one from Wrangel Island 4,300 years BP, indicates two major population crashes: one around 280,000 years ago from which the population recovered, and a second about 12,000 years ago, near the ice age's end, from which it did not. The Wrangel Island mammoths were isolated for 5000 years, and due to the small population present when the island was isolated by rising post-ice-age sea level, about 300 to 1000 individuals experienced a 20% to 30% loss of heterozygosity, and a 65% loss in mitochondrial DNA diversity. The population seems to have subsequently been stable, without suffering further significant loss"
"well-known example is the dodo, once found on the island of Mauritius. It evolved to become large, flightless and docile, and was subsequently driven to extinction by humans and introduced predators. The depletion of natural resources can have dramatic effects on island ecology. On Easter Island, the depletion of the forest by humans not only resulted in widespread loss of species, but also the collapse of the island civilization. Today there are over 500 million people on islands, all dependent on local resources either directly (traditional use) or indirectly (ecotourism revenue). Population growth and development result in heavy deforestation, pollution,"
"populations with larger amount of resources. These larger populations are called metapopulations and with the smaller separated sub-populations they create a mainland-island system. The ""Parnassius apollo"" can migrate from habitats and thus create a variation seen in each isolated population. New environmental pressures lead to the selection of a better suited colour variant within these isolated populations. With this variety there is a correlation with extinction. In high variation environments there is cause for extinction in greater numbers of individuals. For example, there is high variation in the Swiss Alps and presently there is a high rate of individuals becoming"
"important. In tiger snakes, insular dwarfism occurs on islands where available prey is restricted to smaller sizes than are normally taken by mainland snakes. Since prey size preference in snakes is generally proportional to body size, small snakes may be better adapted to take small prey. The inverse process, wherein small animals breeding on isolated islands lacking the predators of large land masses may become much larger than normal, is called island gigantism. An excellent example is the dodo, the ancestors of which were normal-sized pigeons. There are also several species of giant rats, one still extant, that coexisted with"
"species. Island tameness Island tameness is the tendency of many populations and species of animals living on isolated islands to lose their wariness of potential predators, particularly of large animals. The term is partly synonymous with ""ecological naïvete"", which also has a wider meaning referring to the loss of defensive behaviors and adaptations needed to deal with these ""new"" predators. Species retain such wariness of predators that exist in their environment, for example a Hawaiian goose retains its wariness of hawks, but lose such behaviors associated with mammals or other predators not found in their historical range. The most famous"
"pressures acting on island populations – including several species of the proboscidean genus ""Stegodon"", an elephant-like creature. (A dwarf stegodont species of Flores, ""Stegodon sondaari"", became extinct by about 850,000 years ago and was replaced by another species of normal size, ""Stegodon florensis"", which then also evolved into a dwarf form, ""Stegodon florensis insularis"", which disappeared about 12,000 years ago.) This theory posits that the tropical rainforests on the island are a calorically impoverished environment, causing a dietary strain on hominins, especially in the absence of agriculture. Because of reduced resources, smaller individuals have an advantage because of their lower"
"other. This brought about ""islands"" of individual populations that were disconnected for long periods of time. Over time the separate groups became different species because of the isolation. The rate at which each population speciated was different. The species that are more mobile have larger ranges and are less isolated. Since they are all still relatively close together, disturbances can make them highly susceptible to extinction. They require stable temperatures and often stay in remote corners or the ceiling of the cave that are the warmest. Since 1988 when these species were first listed as endangered, other caves containing these"
"the rapidly changing environment; this Carboniferous rainforest collapse event triggered an evolutionary burst among reptiles. The theory of island biogeography was experimentally tested by E. O. Wilson and his student Daniel Simberloff in the mangrove islands in the Florida Keys. Species richness on several small mangroves islands were surveyed. The islands were fumigated with methyl bromide to clear their arthropod communities. Following fumigation the immigration of species onto the islands was monitored. Within a year the islands had been recolonised. Islands closer to the mainland recovered faster as predicted by the Theory of Island Biogeography. The effect of island size"
"due to erosion and changing sea levels. When islands emerge, they undergo the process of ecological succession as species colonize the island (see theory of island biogeography). New species cannot immigrate via land, and instead must arrive via air, water, or wind. As a result, organisms with high dispersal capabilities, such as plants and birds, are much more common on islands than are poorly dispersing taxa like mammals. However, some mammals are present on islands, presumably from swimming or riding on natural “rafts” that are washed away from the mainland. Of the species that arrive, only some will be able"
"a period of time can lead to inbreeding within that population, resulting in increased genetic relatedness between breeding individuals. Inbreeding depression can also occur in a large population if individuals tend to mate with their relatives, instead of mating randomly. Many individuals in the first generation of inbreeding will never live to reproduce. Over time, with isolation, such as a population bottleneck caused by purposeful (assortative) breeding or natural environmental factors, the deleterious inherited traits are culled. Island species are often very inbred, as their isolation from the larger group on a mainland allows natural selection to work on their"
"Island restoration The ecological restoration of islands, or island restoration, is the application of the principles of ecological restoration to islands and island groups. Islands, due to their isolation, are home to many of the world's endemic species, as well as important breeding grounds for seabirds and some marine mammals. Their ecosystems are also very vulnerable to human disturbance and particularly to introduced species, due to their small size. Island groups such as New Zealand and Hawaii have undergone substantial extinctions and losses of habitat. Since the 1950s several organisations and government agencies around the world have worked to restore"
"tendency of small, isolated genetic pools to produce unusual traits. Examples include insular dwarfism and the radical changes among certain famous island chains, for example on Komodo. The Galápagos Islands are particularly famous for their influence on Charles Darwin. During his five weeks there he heard that Galápagos tortoises could be identified by island, and noticed that finches differed from one island to another, but it was only nine months later that he reflected that such facts could show that species were changeable. When he returned to England, his speculation on evolution deepened after experts informed him that these were"
"into larger versions of themselves (insular gigantism) while others became smaller versions of themselves (insular dwarfism). He proposed the simple explanation that smaller creatures get larger when predation pressure is relaxed because of the absence of some of the predators of the mainland, and larger creatures become smaller when food resources are limited because of land area constraints. The idea was expanded upon in ""The Theory of Island Biogeography"", by Robert MacArthur and Edward O. Wilson. In 1978, Ted J. Case published a longer paper on the topic in the journal ""Ecology"". Foster's rule Foster's rule, also known as the"
"Insular biogeography Insular biogeography or island biogeography is a field within biogeography that examines the factors that affect the species richness of isolated natural communities. The theory was originally developed to explain species richness of actual islands, principally oceanic. Under either name it is now used in reference to any ecosystem (present or past) that is isolated due to being surrounded by unlike ecosystems, and has been extended to mountain peaks, oases, fragmented forest, and even natural habitats isolated by human land development. The field was started in the 1960s by the ecologists Robert H. MacArthur and E. O. Wilson,"
"Island tameness Island tameness is the tendency of many populations and species of animals living on isolated islands to lose their wariness of potential predators, particularly of large animals. The term is partly synonymous with ""ecological naïvete"", which also has a wider meaning referring to the loss of defensive behaviors and adaptations needed to deal with these ""new"" predators. Species retain such wariness of predators that exist in their environment, for example a Hawaiian goose retains its wariness of hawks, but lose such behaviors associated with mammals or other predators not found in their historical range. The most famous example"
"""outsized"" and are not in the normal size range for the respective group. If considered singular entities, the largest organisms are clonal colonies which can spread over large areas. Pando, a clonal colony of the quaking aspen tree, is widely considered to be the largest such organism by mass. Even if such colonies are excluded, trees retain their dominance of this listing, with the giant sequoia being the most massive tree. In 2006 a huge clonal colony of ""Posidonia oceanica"" was discovered south of the island of Ibiza. At across, and estimated at around 100,000 years old, it may be"
"and color differences. During allopatric (from the ancient Greek ""allos"", ""other"" + ""patrā"", ""fatherland"") speciation, a population splits into two geographically isolated populations (for example, by habitat fragmentation due to geographical change such as mountain formation). The isolated populations then undergo genotypic or phenotypic divergence as: (a) they become subjected to dissimilar selective pressures; (b) they independently undergo genetic drift; (c) different mutations arise in the two populations. When the populations come back into contact, they have evolved such that they are reproductively isolated and are no longer capable of exchanging genes. Island genetics is the term associated with the"
"a result of tectonic activity. The most recent islands, called Isabela and Fernandina, are still in process of formation, the most recent volcanic eruption in 2009 has been recorded. The Galápagos Islands are famous for its numerous endemic species and Charles Darwin studies that led him to establish his Theory of Evolution by natural selection. Are called touristically, the «Enchanted Islands» as the flora and fauna found there is virtually unique and it can not be found anywhere else in the world. That is why many people visit them to know and enjoy the animals and unique plants. The Galápagos"