Editing Island (section)

== Life on islands ==
The field of [[insular biogeography]] studies the ecological processes that take place on islands, with a focus on what factors effect the [[evolution]], [[extinction]], and [[Species richness|richness]] of species. Scientists often study islands as an isolated [[model]] of how the process of [[natural selection]] takes place.<ref>{{Cite journal |last1=Whittaker |first1=Robert J. |last2=Fernández-Palacios |first2=José María |last3=Matthews |first3=Thomas J. |last4=Borregaard |first4=Michael K. |last5=Triantis |first5=Kostas A. |date=September 2017 |title=Island biogeography: Taking the long view of nature's laboratories |url=https://www.science.org/doi/10.1126/science.aam8326 |journal=Science |language=en |volume=357 |issue=6354 |doi=10.1126/science.aam8326 |pmid=28860356 |issn=0036-8075}}</ref><ref name=":27">{{Cite journal |last1=Graham |first1=Natalie R. |last2=Gruner |first2=Daniel S. |last3=Lim |first3=Jun Y. |last4=Gillespie |first4=Rosemary G. |date=June 27, 2017 |title=Island ecology and evolution: challenges in the Anthropocene |url=https://www.cambridge.org/core/journals/environmental-conservation/article/island-ecology-and-evolution-challenges-in-the-anthropocene/ED544F1DC261A1F7B9DD9DCF1C51C9F5 |journal=Environmental Conservation |language=en |volume=44 |issue=4 |pages=323–335 |doi=10.1017/S0376892917000315 |bibcode=2017EnvCo..44..323G |issn=0376-8929}}</ref> [[Island ecology]] studies organisms on islands and their environment. It has yielded important insights for its parent field of [[ecology]] since the time of [[Charles Darwin]].<ref name=":27" />

=== Endemism ===
{{Main article|Endemism}}
[[File:Galápagos penguin (Spheniscus mendiculus) male.jpg|thumb|The [[Galapagos penguin]] is endemic to the Galápagos Islands.]]
In biology, endemism is defined as the phenomenon where species or genus is only found in a certain geographical area. Islands isolate land organisms from others with water, and isolate aquatic organisms living on them with land.<ref name=":27" /> Island ecosystems have the highest rates of endemism globally. This means that islands contribute heavily to global [[biodiversity]].<ref>{{Cite journal |last1=Veron |first1=Simon |last2=Haevermans |first2=Thomas |last3=Govaerts |first3=Rafaël |last4=Mouchet |first4=Maud |last5=Pellens |first5=Roseli |date=August 12, 2019 |title=Distribution and relative age of endemism across islands worldwide |journal=Scientific Reports |language=en |volume=9 |issue=1 |pages=11693 |doi=10.1038/s41598-019-47951-6 |pmid=31406123 |issn=2045-2322|pmc=6690940 |bibcode=2019NatSR...911693V }}</ref> Areas with high lives of biodiversity are a priority target of [[Conservation movement|conservation]] efforts, to prevent the extinction of these species.<ref>{{Cite journal |last1=Harrison |first1=Susan |last2=Noss |first2=Reed |date=January 7, 2017 |title=Endemism hotspots are linked to stable climatic refugia |journal=Annals of Botany |volume=119 |issue=2 |pages=207–214 |doi=10.1093/aob/mcw248 |issn=0305-7364 |pmc=5321063 |pmid=28064195}}</ref> Despite high levels of endemism, the total [[species richness]], the total number of unique species in a region, is lower on islands than on mainlands.<ref>{{Cite journal |last1=Kier |first1=Gerold |last2=Kreft |first2=Holger |last3=Lee |first3=Tien Ming |last4=Jetz |first4=Walter |last5=Ibisch |first5=Pierre L. |last6=Nowicki |first6=Christoph |last7=Mutke |first7=Jens |last8=Barthlott |first8=Wilhelm |date=June 9, 2009 |title=A global assessment of endemism and species richness across island and mainland regions |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=106 |issue=23 |pages=9322–9327 |doi=10.1073/pnas.0810306106 |doi-access=free |issn=0027-8424 |pmc=2685248 |pmid=19470638|bibcode=2009PNAS..106.9322K }}</ref> The level of species richness on islands is proportional to the area of that island, a phenomenon known as the [[species-area relationship]]. This is because larger areas have more resources and thus can support more organisms. Populations with a higher [[carrying capacity]] also have more [[genetic diversity]], which promotes [[speciation]].<ref name=":27" />

=== Dispersal ===
[[File:Pteropus seychellensis.jpg|alt=An orange bat hanging upside down from a tree.|thumb|The [[Seychelles fruit bat]] has a major role in distributing the seeds of trees between islands, a form of oceanic dispersal.<ref>{{Cite journal |last=Gerlach |first=Justin |date=2004 |title=The bats of Silhouette Island, Seychelles |url=https://islandbiodiversity.com/Phelsuma%2012-4.pdf |journal=Phelsuma |volume=12 |pages=78–90 |via=Nature Protection Trust of Seychelles}}</ref>]]
Oceanic islands, ones that have never been connected to shore, are only populated by life that can cross the sea. This means that any animals present on the island had to have flown there, in the case of [[birds]] or [[bats]], were carried by such animals, or were carried in a sea current in what is known as a "rafting event". This phenomenon is known as [[oceanic dispersal]].<ref name=":28">{{Cite journal |last=de Queiroz |first=Alan |date=February 2005 |title=The resurrection of oceanic dispersal in historical biogeography |url=https://www.zoology.ubc.ca/~jankowsk/deQueiroz2005.pdf |journal=[[Elsevier]] |volume=20 |issue=2 |via=Elesevier Science Direct}}</ref> [[Tropical cyclone]]s have the capacity to transport species over great distances.<ref name=":23">{{Cite web |date=October 27, 2020 |title=Intensifying hurricanes are helping invasive species spread across the U.S. |url=https://www.nationalgeographic.com/animals/article/intensifying-hurricanes-spreading-invasive-species-across-the-us |access-date=July 11, 2024 |website=Animals |language=en}}</ref> Animals like tortoises can live for weeks without food or water, and are able to survive floating on debris in the sea.<ref>{{Cite web |date=May 18, 2021 |title=How rafts helped primates rule the world |url=https://www.bbc.com/future/article/20210511-how-rafts-helped-primates-rule-the-world |access-date=July 13, 2024 |website=www.bbc.com |language=en-GB}}</ref> One case study showed that in 1995, fifteen [[iguanas]] survived a 300 km journey to [[Anguilla]] in the [[Caribbean]], an island which no iguana had lived on previously. They survived floating on a mass of uprooted trees from a storm.<ref>{{Cite journal |last1=Censky |first1=Ellen J. |last2=Hodge |first2=Karim |last3=Dudley |first3=Judy |date=1998 |title=Over-water dispersal of lizards due to hurricanes |url=https://www.nature.com/articles/26886 |journal=Nature |language=en |volume=395 |issue=6702 |pages=556 |doi=10.1038/26886 |bibcode=1998Natur.395..556C |issn=1476-4687}}</ref>  Plant species are thought to be able to travel great distances of ocean. New Zealand and Australia share 200 native plant species, despite being separated by 1500 km.<ref name=":28" />

Continental islands, islands that were at one point connected to a continent, are expected to share a common history of plant and animal life up until the point that the island broke away from the continent.<ref name=":28" /> For example, the presence of [[freshwater fish]] on an island surrounded by ocean would indicate that it once was attached to a continent, since these fish cannot traverse the ocean on their own.<ref name=":27" /> Over the course of time, evolution and extinction changes the nature of animal life on a continental island, but only once it splits from the mainland. An example is that of the [[southern beech]], a tree that is present in Australia, New Zealand, parts of South American, and New Guinea, places that today are geographically distant. A possible explanation for this phenomenon is that these landmasses were once all part of the continent [[Gondwana]] and separated by tectonic drift. However, there are competing theories that suggest this species may have reached faraway places by way of oceanic dispersal.<ref name=":28" />

=== Evolution on island groups ===
[[File:Finchadaptiveradiation.png|thumb|[[Adaptive radiation]] of finch A (''[[Geospiza magnirostris]]'') into three other species of finches on the [[Galapagos Islands]]. Due to the absence of other birds, [[Darwin's finches]] adapted to new niches. Their seed-eating beaks evolved to handle foods such as nuts, fruits, and insects.]]
Species that colonize island archipelagos exhibit a specific property known as [[adaptive radiation]]. In this process, a species that arrives on a group of islands rapidly becomes more diverse over time, splitting off into new species or subspecies. A species that reaches an island ecosystem may face little competition for resources, or may find that the resources that they found in their previous habitat are not available. These factors together result in individual evolutionary branches with different means of survival.<ref name=":29">{{Cite web |last=Lovette |first=Irby |date=December 20, 2018 |title=Why Evolution Goes Wild on Islands: The Science of Adaptive Radiation |url=https://www.allaboutbirds.org/news/why-evolution-goes-wild-on-islands-the-science-of-adaptive-radiation/ |access-date=July 13, 2024 |website=All About Birds |language=en-US}}</ref>

The classical example of this is [[Darwin's finches]], a group of up to fifteen [[tanager]] species that are endemic to the Galápagos Islands.<ref>{{Cite journal |last=Sato |first=Akie |date=March 1, 2001 |title=On the Origin of Darwin's Finches |url=https://academic.oup.com/mbe/article/18/3/299/1073209 |access-date=July 13, 2024 |journal=Molecular Biology and Evolution |volume=18 |issue=3 |pages=299–311 |doi=10.1093/oxfordjournals.molbev.a003806|pmid=11230531 }}</ref> These birds evolved different [[beaks]] in order to eat different kinds of food available on the islands. The [[large ground finch]] has a large bill used to crack seeds and eat fruit. The [[Genovesa cactus finch]] prefers [[cacti]] as a food source, and has a beak adapted for removing pulp and flowers from cacti. The [[green warbler-finch]] (in the habit of true [[warbler]] species) consumes spiders and insects that live on plants.<ref name=":29" /> Other examples of this phenomenon exist worldwide, including in Hawaii and Madagascar, and are not limited to island ecosystems.<ref name=":29" />

==== The island rule ====

[[File:Dronte dodo Raphus cucullatus.jpg|alt=A plaster and wax model of a large bird with a beak.|thumb|The extinct [[Dodo]] is an example of island gigantism.]]

Species endemic to islands show a common evolutionary trajectory. [[Foster's rule]] (also known as the island rule), states that small mammals such as [[rodents]] evolve to become larger, known as [[island gigantism]]. One such example is the [[giant tortoise]] of the [[Seychelles]], though it is unknown if it grew in size before or after reaching the island. Larger animals such as the [[hippopotamus]] tend to become smaller, such as in the case of the [[pygmy hippopotamus]]. This is known as [[insular dwarfism]].<ref name=":30">{{Cite web |last=Tyson |first=Peter |date=November 1, 2000 |title=Gigantism & Dwarfism on Islands |url=https://www.pbs.org/wgbh/nova/article/gigantism-and-dwarfism-islands/ |access-date=July 13, 2024 |website=www.pbs.org |language=en-US}}</ref> In the case of smaller animals, it has been hypothesized that animals on islands may have fewer [[predators]] and competitors, resulting in selection pressure towards larger animals. Larger animals may exhaust food resources quickly due to their size, causing [[malnutrition]] in their young, resulting in a selection pressure for smaller animals that require less food. Having fewer predators would mean these animals did not need not be large to survive.<ref name=":30" />

=== Darwin, the Galápagos, and natural selection ===
[[Charles Darwin]] formulated the theory of [[natural selection]] through the study of island ecology.<ref name=":27" /> The species he observed on the [[Galápagos Islands]], including tanager birds, contributed to his understanding of how evolution works.<ref>{{Cite web |last=MacPherson |first=Rick |date=February 6, 2017 |title=Darwin's Islands |url=https://www.americanscientist.org/article/darwins-islands |access-date=July 11, 2024 |website=American Scientist |language=en}}</ref> He first traveled to the islands as a [[naturalist]] on [[HMS Beagle]] in 1835, as part of a five-year [[circumnavigation]] of Earth. He wrote that "the different islands to a considerable extent are inhabited by a different set of beings".<ref name=":22">{{Cite web |last1=Magazine |first1=Smithsonian |last2=Helmuth |first2=Laura |title=Evolution World Tour: Galápagos Islands, Ecuador |url=https://www.smithsonianmag.com/arts-culture/evolution-world-tour-galapagos-islands-ecuador-5974755/ |access-date=July 14, 2024 |website=Smithsonian Magazine |language=en}}</ref> Through the study of the finches and other animals he realized that organisms survive by changing to adapt to their habitat.<ref name=":22" /> It would be over twenty years before he published his theories in ''[[On the Origin of Species]]''.<ref name=":31">{{Cite web |last=Stix |first=Gary |date=January 1, 2009 |title=Darwin's Living Legacy--Evolutionary Theory 150 Years Later |url=https://www.scientificamerican.com/article/darwins-living-legacy/ |access-date=July 14, 2024 |website=Scientific American |language=en}}</ref>