Pattern and process of biotic homogenization in the New Pangaea

Abstract

Human activities have reorganized the earth's biota resulting in spatially disparate locales becoming more or less similar in species composition over time through the processes of biotic homogenization and biotic differentiation, respectively. Despite mounting evidence suggesting that this process may be widespread in both aquatic and terrestrial systems, past studies have predominantly focused on single taxonomic groups at a single spatial scale. Furthermore, change in pairwise similarity is itself dependent on two distinct processes, spatial turnover in species composition and changes in gradients of species richness. Most past research has failed to disentangle the effect of these two mechanisms on homogenization patterns. Here, we use recent statistical advances and collate a global database of homogenization studies (20 studies, 50 datasets) to provide the first global investigation of the homogenization process across major faunal and floral groups and elucidate the relative role of changes in species richness and turnover. We found evidence of homogenization (change in similarity ranging from 20.02 to 0.09) across nearly all taxonomic groups, spatial extent and grain sizes. Partitioning of change in pairwise similarity shows that overall change in community similarity is driven by changes in species richness. Our results show that biotic homogenization is truly a global phenomenon and put into question many of the ecological mechanisms invoked in previous studies to explain patterns of homogenization.

Land-use effects on local biodiversity in tropical forests vary between continents

“…Many previous studies of biotic homogenisation have analysed changes over time (e.g. Olden and Rooney 2006;Lôbo et al 2011); however, data on spatially distinct communities are much more widely available than temporal data (McKinney 2006) and have increasingly been used to quantify homogenization (Baiser et al 2012;de Solar et al 2015). If anything, spatial comparisons are likely to underestimate the effects of land conversion on biodiversity (França et al 2016).…”

Evaluating taxonomic homogenization of freshwater fish assemblages in Chile

“…Conversely, TD has been the dominant process within biotic units, and many non-native taxa with narrow geographic distributions might be the cause for this process. Parallel assessments in regions with similar climates have been crucial to improve our understanding of drivers of biological invasions (e.g., plants: Pauchard et al 2004;fishes: Marr et al 2010fishes: Marr et al , 2013; but see Baiser et al 2012 world, including central Chile (32°S-40°S); they found that TH was prevalent with a ΔCS av = 8.4 %, and this is higher than our estimate for comparisons involving watersheds in Central (U3) and South-Central (U4) (ΔCS av = 2.9 %). Clearly, scale (level of resolution or grain and geographic coverage) has an impact on assessments of TH as well as differential species richness and turnover (see McKinney 2004;Olden, 2006;Baiser et al 2012).…”

“…Parallel assessments in regions with similar climates have been crucial to improve our understanding of drivers of biological invasions (e.g., plants: Pauchard et al 2004;fishes: Marr et al 2010fishes: Marr et al , 2013; but see Baiser et al 2012 world, including central Chile (32°S-40°S); they found that TH was prevalent with a ΔCS av = 8.4 %, and this is higher than our estimate for comparisons involving watersheds in Central (U3) and South-Central (U4) (ΔCS av = 2.9 %). Clearly, scale (level of resolution or grain and geographic coverage) has an impact on assessments of TH as well as differential species richness and turnover (see McKinney 2004;Olden, 2006;Baiser et al 2012). Because we document no local extinctions, species turnover seems less likely to have a significant impact, suggesting a difference in the level of resolution might be the best explanation for differences between Marr et al (2010) and this study.…”

“…This phenomenon might include loss of taxonomic, functional, or genetic differentiation (Olden 2006). Our focus was the magnitude of taxonomic homogenization (TH), which depends on the resolution and extent of the spatial scale, in addition to species richness and turnover (Baiser et al 2012). On the contrary, if communities become more different as a result of introductions of non-native species, taxonomic differentiation (TD) might occur (McKinney, 2004;Olden 2006).…”

17 years of grassland management leads to parallel local and regional biodiversity shifts among a wide range of taxonomic groups

“…The resulting genetic, taxonomic and functional impoverishment is viewed as a major threat to biodiversity (Olden et al 2004;Mouillot et al 2013). Biotic homogenization has been demonstrated to occur across nearly all taxonomic groups, spatial scales and grain sizes (Baiser et al 2012). This makes it paramount to understand how biotic homogenization can be counteracted at each of these scales.…”