User:Sarah Rackowski/Insular biogeography

Examples edit

While physical Islands are the most commonly cited settings insular biology, other environments can act as "islands" including, but not limited to:

Cave dwelling species like this eyeless Amblyopsidae cave fish are effected by insular pressures much like island-dwelling species.

Mountain and ridge-tops (often called sky islands).

Patches of coral reef

Protected nature parks

Urban parks

Glacial refugia

Caves

Lakes and ponds ^[1]^[2]^[3]^[4]^[5]^[6]^[7]

insular effects:

effects known to precipitate from a species living and evolving in insular circumstances include:

insular dwarfism (islands)- dwelling species may be smaller than their mainland counterparts. The effect is most commonly seen in "large" animals such as Cervids, Proboscideans, and Bovids, and is believed to be linked to the lack of resources available to these species on islands needed to maintain a large body size. Dwarf mammoths (Mammuthus exilis) are commonly cited as as extreme examples of this phenomenon.^[8]

A "dwarf mammoth" commonly used as an example of insular dwarfism

Insular gigantism (islands)- In many "small" animals (often reptiles), island dwelling species or populations are known to have a larger body size than those on the mainland. Much like insular dwarfism, insular gigantism is believed to be tied with resource availability. Islands often have less competition for resources that small species can exploit than mainlands, and therefore island-dwellers have the resources present to become larger. Giant tortoises (Chelonoidis niger) are often cited an an example of this phenomenon.^[9]

genetic bottleneck- When populations are forced into insular conditions, a genetic bottleneck often forms as founding populations are often small. See /founder effect/^[10]

Research experiments[edit]

Insular biogeography can be studied through experimental modification of an existing system, creation of a new experimental system, or observation of an existing system.

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 recolonized to pre-fumigation levels. However, Simberloff and Wilson contended this final species richness was oscillating in quasi-equilibrium. Islands closer to the mainland recovered faster as predicted by the Theory of Island Biogeography. The effect of island size was not tested, since all islands were of approximately equal size.

Research conducted at the rainforest research station on Barro Colorado Island in Panama has yielded a large number of publications concerning the ecological changes following the formation of islands, such as the local extinction of large predators and the subsequent changes in prey populations. Research on Barrow Colorado, a man-made island in a lake, began in 1923. Since its construction, the island has been host to studies of secession from a bare soil to a mature forest as of 1984. Species trends such as such as antbirds becoming locally extinct, and late-stage succession plants such as lianas colonizing and changing the landscape formed the backbone of such studies ^[11]^[12]^[13]

A 1978 study of flies and beetles (Diptera and Coleoptera) in urban parks and green spaces in Cincinnati, Ohio, USA found species richness values in parks where nearly the same as would be expected, not quite from oceanic islands, but like other insular environments like sky islands. From this, the authors presume that these "urban islands" presumably have similar patterns of extinction and repopulation as natural habitat patches. A similar study published in 1979 on plant communities in vacant lots in Chicago, Illinois, USA further supported the position of urban habitat as acting like islands.^[14]

Studies of exotic species introduced by humans, such as anoles (Anolis) on Caribbean islands have also been important in the history of these studies. Caribbean anoles after human introduction my ships redistributed them in a case where where natural water based dispersal is nearly impossible such small, fragile, terrestrial lizards. Studies on these anoles have investigated species richness and genetic composition.^[15] Studies on introduced plant species on islands have also occurred, however, like bird studies, plants are considered to be more likely to be able to travel over water than terrestrial animals.^[16]

Other important sites for research on insular biogeography have included the Madrean Sky islands of southeastern North America, coral reef and island systems in the South Pacific, and the caves of the Greenbriar valley, West Virginia.^[17]^[18]

historical record:

The theory can be studied through the fossils, which provide a record of life on Earth. 300 million years ago, Europe and North America lay on the equator and were covered by steamy tropical rainforests. Climate change devastated these tropical rainforests during the Carboniferous Period and as the climate grew drier, rainforests fragmented. Shrunken islands of forest were uninhabitable for amphibians but were well suited to reptiles, which became more diverse and even varied their diet in the rapidly changing environment; this Carboniferous rainforest collapse event triggered an evolutionary burst among reptiles.

Many inland habitat patches where insular biology take place in historical isolated habitat patches such as glacial refugia, which may not be apparent on a preliminary review of the landscape.