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Double jeopardy for ecologically rare birds and terrestrial mammals

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endangered species
Credit: Pixabay/CC0 Public Domain

Common assumptions notwithstanding, rare species can play unique and essential ecological roles. After studying two databases that together cover all known terrestrial mammals and birds worldwide, scientists from the CNRS, the Foundation for Biodiversity Research (FRB), Université Grenoble Alpes, and the University of Montpellier have demonstrated that, though these species are found on all continents, they are more threatened by human pressures than ecologically common species and will also be more impacted by future climate change. Thus, they are in double jeopardy. The researchers’ findings, published in Nature Communications (October 8, 2020), show that conservation programs must account for the ecological rarity of species.


It has long been thought that rare species contribute little to the functioning of ecosystems. Yet recent studies have discredited that idea: Rarity is a matter not only of the abundance or geographical range of a species, but also of the distinctiveness of its ecological functions. Because these functionally distinct species are irreplaceable, it is essential we understand their ecological characteristics, map their distributions, and evaluate how vulnerable they are to current and future threats.

Using two databases that collect information on the world’s terrestrial mammals (4,654 species) and birds (9,287 species), scientists from the FRB’s Center de Synthèse et d’Analyse de la Biodiversité (CESAB), CNRS research laboratories, Université Grenoble Alpes, the University of Montpellier, and partner institutes divided the earth’s surface into 50 × 50 km squares and determined the number of ecologically rare species within each. They showed that ecological rarity among mammals is concentrated in the tropics and the southern hemisphere, with peaks on Indonesian islands, in Madagascar, and in Costa Rica. Species concerned are mostly nocturnal frugivores, like bats and lemurs, and insectivores, such as small rodents. Ecologically rare bird species are mainly found in tropical and subtropical