Which continent has the most bird species

What factors explain the number of bird species on islands

Press release, 02/19/2020

A team of researchers led by Luis Valente (Museum für Naturkunde Berlin / Naturalis Biodiversity Center) shows in the journal Nature how the population rate of islands, speciation and the natural extinction of species on them with the size of the islands and the distance from Continent vary. This study is based on molecular data from hundreds of bird species from 41 oceanic archipelagos worldwide and reveals fundamental processes that led to their biodiversity.

Biodiversity is unevenly distributed across the planet. But why are some islands like the Galápagos Islands and Hawaii home to so many unique bird species? In the 1960s, one of the most influential theories in biology - the theory of island biogeography - proposed a simple model that describes island biodiversity as the balance between settlement and extinction in relation to the island's area and its isolation from the continent. So far, however, no study on a global level has shown how island area and isolation determine the speed with which species colonize new islands, develop new species or become extinct.

A team of ornithologists, evolutionary biologists and mathematical modelers led by Dr. Luis Valente (Museum für Naturkunde Berlin / Naturalis Biodiversity Center) is now publishing for the first time in the journal Nature how the population rate of islands, the speed of speciation and natural extinction of species vary with the size of the islands and the distance from the continent. The study is based on a new global data set of island birds in oceanic islands. The researchers found that settlement decreases with isolation of the island, that extinction continues to decrease with area, but speciation increases with area and isolation. These results may seem intuitive, but to date researchers have lacked the data and statistical methods to test this theory globally.

Using molecular data from hundreds of island birds collected over the years on field expeditions, the authors developed a new model that can predict biodiversity on many islands around the world. The number of bird species can be predicted well in some archipelagos - such as the Canary Islands or Hawaii. However, some archipelagos, deviating from the model, had an extraordinarily high diversity of birds, e.g. the Comoros and São Tomé & Príncipe.

Another fascinating finding from this study was that, while islands are best known for their spectacular bird speciation - like Darwin's finches in the Galápagos - the vast majority of island bird species are unique evolutionary branches that are not closely related on the islands have on which they live.

Publication: Luis Valente, Albert B. Phillimore, Martim Melo, Ben H. Warren, Sonya M. Clegg, Katja Havenstein, Ralph Tiedemann, Juan Carlos Illera, Christophe Thébaud, Tina Aschenbach, Rampal S. Etienne. A simple dynamic model explains island bird diversity worldwide. Nature.

The publication is available here: https://www.nature.com/articles/s41586-020-2022-5.

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