Area, isolation, and climate explain the diversity of mammals on island worldwide

Elisa Barreto Sr. and Thiago F. Rangel Sr., Ecology, Universidade Federal de Goiás (UFG), Goiânia, Brazil, Elisa Barreto Sr., Catherine H. Graham and Loïc Pellissier, Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf, Switzerland

Background/Question/Methods
To identify the determinants of insular biodiversity at large spatial scales remains a fundamental question in island biogeography. We conducted a global test of island biogeography theory by evaluating the relative importance of island physical, environmental, and historical characteristics on the species richness and endemism of terrestrial mammals. We derived a global database of insular mammals from IUCN range maps and calculated species richness, number of single island endemics (SIE) and proportion of SIE. For each island, we summarized current and historical climatic (temperature, precipitation, velocity of climate change since the last glacial maximum) and physical (area, current and past isolation, elevation) characteristics. We quantified the effects of island characteristics on the three diversity measures, while accommodating variation among biogeographic realms, by fitting generalized linear and mixed models. Analyzes were also performed separately for bats and non-volant mammals.
Results/Conclusions
Physical characteristics most consistently influenced patterns of diversity on islands, with area positively effecting all measures of mammal diversity, but SIE of non-volant species in particular. Island isolation, both current and past, was associated with lower richness but greater endemism. Flight capacity modified the relative importance of past versus current isolation, with bats responding more strongly to current and non-volants to past isolation. Environmental effects on biodiversity were more variable depending on taxonomic group (bats vs non-volants), biogeographic realm, and the measure of diversity, with a tendency for greater effects on endemism than on richness. Unexpectedly, climate change velocity was positively associated with endemism. In conclusion, in line with island biogeography theory, we found that area and isolation are among the strongest drivers of overall mammalian biodiversity. Moreover, our results support the growing evidence on the importance of past conditions (i.e., isolation and velocity of climate change) on current patterns, particularly on non-volant species, and highlight that connections between landmasses are vital to the origin and maintenance of biodiversity.