A global assessment of nested patterns in insular mammal assemblages

Aim

A nested pattern (nestedness) in species composition is a frequent signature of insular communities. However, it remains unclear whether the drivers of nestedness are consistent across multiple island systems. Here, we investigated the pattern and drivers of taxonomic, functional and phylogenetic nestedness in terrestrial mammal assemblages from 10 distinct island systems (archipelagos).

Location

Global.

Time period

Contemporary.

Major taxa studied

Terrestrial mammals.

Methods

We compiled occurrence data and species traits of terrestrial mammals from 228 islands in 10 distinct island assemblages. We assembled a dataset of island biogeographic characteristics for each of these islands, including island area, isolation index and maximum elevation. For all 10 assemblages, we first tested for significant patterns of taxonomic, functional and phylogenetic nestedness. We then examined the associations between nestedness, island biogeographic characteristics and species traits.

Results

We detected significant patterns of taxonomic, functional or phylogenetic nestedness in mammal assemblages from all 10 archipelagos. Biogeographic characteristics of islands affecting the rate of extinction in island species, namely, island area and elevation, were significantly associated with the degree of nestedness in these assemblages. Traits associated with the extinction probability of a species, such as litter size, further drove the nested pattern in some assemblages.

Main conclusions

All analyses pointed to selective extinction as a main mechanism shaping the observed nested patterns in island mammal assemblages. From a conservation point of view, different management strategies should be implemented for mammal assemblages in these island systems by identifying the drivers of species extinction rates specific to each island system and species occurring on these islands.