Insular biogeography
The theory was originally developed to explain the pattern of the species–area relationship occurring in oceanic islands.
Under either name it is now used in reference to any ecosystem (present or past[2]) that is isolated due to being surrounded by unlike ecosystems, and has been extended to mountain peaks, seamounts, oases, fragmented forests, 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,[3] who coined the term island biogeography in their inaugural contribution to Princeton's Monograph in Population Biology series, which attempted to predict the number of species that would exist on a newly created island.
[citation needed] While this may be a traditional island—a mass of land surrounded by water—the term may also be applied to many nontraditional "islands", such as the peaks of mountains,[1] isolated springs or lakes,[4] and non-contiguous woodlands.
And further, that the isolated populations may follow different evolutionary routes, as shown by Darwin's observation of finches in the Galapagos Islands.
Larger habitat size reduces the probability of extinction due to chance events.
Over time, the countervailing forces of extinction and immigration result in an equilibrium level of species richness.
In addition to having an effect on extinction, island size can also affect immigration rates.
300 million years ago, Europe and North America lay on the equator and were covered by steamy tropical rainforests.
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.
However, Simberloff and Wilson contended this final species richness was oscillating in quasi-equilibrium.
Research conducted at the rainforest research station on Barro Colorado Island 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.
Similarly, in an ILS the “mainland” is the source of immigrating species, however the matrix is far more varied.
It is typically observed that as the area of an ecosystem increases, the species richness is directly proportional.
[14] Within a few years of the publishing of the theory, its potential application to the field of conservation biology had been realised and was being vigorously debated in ecological circles.
[16] The idea that reserves and national parks formed islands inside human-altered landscapes (habitat fragmentation), and that these reserves could lose species as they 'relaxed towards equilibrium' (that is they would lose species as they achieved their new equilibrium number, known as ecosystem decay) caused a great deal of concern.
A study by William Newmark, published in the journal Nature and reported in The New York Times, showed a strong correlation between the size of a protected U.S. National Park and the number of species of mammals.
This led to the debate known as single large or several small (SLOSS), described by writer David Quammen in The Song of the Dodo as "ecology's own genteel version of trench warfare".
This led to concern by other ecologists, including Dan Simberloff, who considered this to be an unproven over-simplification that would damage conservation efforts.
Wildlife corridors can increase the movement of species between parks and reserves and therefore increase the number of species that can be supported, but they can also allow for the spread of disease and pathogens between populations, complicating the simple proscription of connectivity being good for biodiversity.
