Functional redundancy of non-volant small mammals increases in human-modified habitats

Abstract

Aim: Humans are rapidly altering natural habitats across much of the globe. Here we compared 264 globally distributed communities in natural and human-modified habitats to detect changes in community richness and functional diversity with human influence. Location: Global. Taxon: Non-volant small mammals. Methods: We calculated differences in observed to potential species richness (ΔSR) and observed to potential functional diversity (ΔFD) to account for regional pool differences. Then we determined the prevalence of four distinct scenarios of richness and functional diversity differences between human-modified and natural habitats, and evaluated local and geographical variation in these differences. We obtained potential richness by calculating a probabilistic species pool and obtained potential functional diversity through the n-dimensional hypervolume based on pool composition. We tested for differences in average ΔSR and ΔFD between habitats, and determined the most common scenario of ΔSR and ΔFD in human-modified and natural habitats. Results: We found lower ΔSR in human-modified than natural habitats, but no difference in ΔFD. Low ΔSR and high ΔFD predominated in human-modified habitats, and high ΔSR and ΔFD in natural habitats. Low ΔSR and high ΔFD predominated in temperate forests, whereas high ΔSR and ΔFD in tropical forests and grasslands. Scenarios of low ΔSR and high ΔFD, and high ΔSR and low ΔFD, were most common in human-modified and natural habitats of temperate grasslands. Main conclusions: A larger richness in human-modified habitats does not result in larger functional diversity. Rather there seems to be an increase in functional redundancy because species which profit from human modification do not bring new functions into human-modified habitats. While greater richness is found in humanmodified habitats from temperate biomes, this is not the case in extremely biodiverse tropical biomes. Assuming a positive relationship between richness, functional traits and ecosystem function, greater richness in modified habitats may not yield greater function.