Local changes dominate variation in biotic homogenization and differentiation

Abstract

Earth’s biodiversity continues to change rapidly through the Anthropocene1, including widespread reordering of species in space2,3 and time4,5. A common expectation of this reordering is that the species composition of sites is becoming increasingly similar across space, known as biotic homogenization, due to anthropogenic pressures and invasive species6,7. While many have argued that homogenisationis a common phenomenon (e.g., 6–10), it is equally plausible that communities can become more different through time, known as differentiation, including through human impacts11,12. Here, we used a novel adaptation of Whittaker’s (1960)13 spatial-scale explicit diversity partition to assess the prevalence of biotic homogenisation and differentiation, and associated changes in species richness at smaller and larger spatial scales. We applied this approach to a compilation of species assemblages from 205 metacommunities that were surveyed for 10-64 years, and 54 ‘checklists’ that spanned 50-500+ years. Scale-dependent changes of species richness were highly heterogeneous, with approximately equal evidence for homogenisation(i.e., lower β-diversity) and differentiation (i.e., higher β-diversity) through time across all regions, taxa and data types. Homogenisation was most often due to increased numbers of widespread species, which tended to increase both local and regional richness through time. These results emphasise that an explicit consideration of spatial scale is needed to fully understand biodiversity change in the Anthropocene.

Regional occupancy increases for widespread species but decreases for narrowly distributed species in metacommunity time series

“…Globally, the turnover of species composition in communities through time tends to be occurring more rapidly than expected due to random chance 25,50 . What has been less clear is whether there are species characteristics that lend advantages or disadvantages in response to environmental change through time, which might ultimately lead to scale-dependent biodiversity changes 51 and/or biotic homogenization 3,52 . Our results show a general trend that smallerranged species are decreasing in occupancy through time, and that these tend to be replaced by larger-ranged species that are increasing in occupancy through time.…”

Local nutrient addition drives plant biodiversity losses but not biotic homogenization in global grasslands

“…A recently developed conceptual framework enables us to investigate this important question by explicitly considering change in alpha (∆α), gamma (∆γ), and beta (∆β) diversity simultaneously through changing localized and/or widespread species (Fig. 1E) (34). This framework extends Whittaker's multiplicative β diversity and quantifies ∆β as ∆γ/∆α.…”

Looking back on biodiversity change: lessons for the road ahead

“…Sea have seen increasing taxonomic differentiation [64]. In fact, the largest meta-analysis of trends in spatial beta-diversity to date reveals a mix of both patterns, but a central tendency leaning slightly more towards homogenization than differentiation that was nevertheless not statistically distinguishable from no change [149]. At the regional scale, there are empirical examples across the whole range from differentiation to homogenization.…”