Equilibrium A Distant Dream for Island Bats


Island Conservation posted this fascinating (and very sad) article by Sara Kaiser, who reports on a study that shows that bat biodiversity in the Caribbean will take 8 million years to recover. Here are excerpts; please access the full article at Island Conservation:

Once biodiversity is lost, can it be recovered? A paper published in the journal Nature Ecology and Evolution, “Recent Extinctions Disturb Path to Equilibrium Diversity in Caribbean Bats,” by Luis ValenteRampal S. Etienne, and Liliana M. Dávalos offers helpful new insight into this complex question. The researchers turned to islands to better understand the consequences of biodiversity loss.

Biodiversity and the Island Equilibrium Theory of Biogeography

The study is based on the Island Equilibrium Theory of Biogeography, first introduced by Robert MacArthur of Princeton University and E.O. Wilson of Harvard. According to this theory, there is a relationship between the number of species that travel to an island and species on the island going extinct. The rate at which species populate and go extinct from an island depends on the type, size, and location of the island.

Most islands start out with no species present but may be colonized over time. Species swim or fly to the island, and over time some of these species can undergo adaptive radiation–that is, branching out into more species (such as the Darwin’s finches did in the Galápagos). The theory states that the number of species on oceanic islands gradually increases until it reaches a diversity steady state, with no significant additions or losses. Scientists call this the dynamic equilibrium value.

The Greater Antilles, (including Cuba, Jamaica, Puerto Rico and Hispaniola) from which the researchers took samples from, are hotspots of island species diversity (home to many adaptive radiations – including the famous Anolis lizards). However, until now, scientists did not know whether these ecologically important islands were at equilibrium or not.

Usually, the larger the island and the nearer the mainland, the higher the number of species present once equilibrium is reached. Biodiversity is the key to ecosystem resilience. Ecosystems with a wide variety of species have higher resistance to stressors, such as disease or climate change, than ecosystems with low biodiversity.

Fossilized bats help scientists understand biodiversity

The scientists examined samples from a fossil record of bats native to the Greater Antilles Islands of the Caribbean. The specimens included existing and extinct species. By examining the fossil record, the scientists were able to confirm that the bats had reached equilibrium diversity. This stable point was disturbed however, after humans colonized the Greater Antilles. Almost a third of island lineages disappeared, constituting a sharp downturn for bat diversity.

These losses brought the number of bat species below their once-stable equilibrium value. The scientists performed calculations to answer a nerve-wracking question: How long would it take for nature to undo the damage humans had brought on? [. . .]

[Photo above: Jamaican Fruit Bat on Grand Cayman Island. Extinctions have disturbed the bats’ Equilibrium Diversity in the Caribbean. Credit: Mark Yokoyama]

For full article, see https://www.islandconservation.org/8-million-years-equilibrium-diversity/

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