The global loss of floristic uniqueness

Abstract

Regional species assemblages have been shaped by colonization, speciation and extinction over millions of years. Humans have altered biogeography by introducing species to new ranges. However, an analysis of how strongly naturalized plant species (i.e. alien plants that have established self-sustaining populations) affect the taxonomic and phylogenetic uniqueness of regional floras globally is still missing. Here, we present such an analysis with data from native and naturalized alien floras in 658 regions around the world. We find strong taxonomic and phylogenetic floristic homogenization overall, and that the natural decline in floristic similarity with increasing geographic distance is weakened by naturalized species. Floristic homogenization increases with climatic similarity, which emphasizes the importance of climate matching in plant naturalization. Moreover, floristic homogenization is greater between regions with current or past administrative relationships, indicating that being part of the same country as well as historical colonial ties facilitate floristic exchange, most likely due to more intensive trade and transport between such regions. Our findings show that naturalization of alien plants threatens taxonomic and phylogenetic uniqueness of regional floras globally. Unless more effective biosecurity measures are implemented, it is likely that with ongoing globalization, even the most distant regions will lose their floristic uniqueness.

Soil heterogeneity tends to promote the growth of naturalized aliens when competing with native plant communities

“…Currently, more than 13,000 plant species have established outside their native ranges (i.e. have become naturalized; van Kleunen et al, 2015), resulting in floristic homogenization (Yang et al, 2021). Therefore, one of the key questions in ecology is how alien species can invade native communities and can coexist with the natives or even replace them (Valladares et al, 2015).…”

Species range size shapes distance‐decay in community similarity

“…Understanding the link between species range size and how community similarity decreases with spatial distance is relevant for conservation biogeography. Biotic homogenization, that is, “the replacement of local biotas with non‐indigenous species, usually introduced by humans” (McKinney & Lockwood, 1999), is one of the major threats for biodiversity (Baiser et al, 2012; Olden et al, 2004; Yang et al, 2021). Biotic homogenization is usually linked to human activities that lead to range expansions of invasive species and range contraction of specialist and endemic species (Clavel et al, 2011; Olden & Poff, 2003).…”

Population demography maintains biogeographic boundaries

“…Urbanization alters the demography, distribution, and genetics of wildlife populations across species in ways that might reshape and reorganize biogeographic regions (Johnson and Munshi-South 2017; Miles et al 2019; Schmidt et al 2020b; Schmidt and Garroway 2021). Finally, translocations and invasive species are a major threat to endemics and homogenize biological communities (Capinha et al 2015; Daru et al 2021; Yang et al 2021). Biogeographic region delimitations set our reference points for understanding the distribution and origins of biodiversity and its conservation, thus we need a better understanding of how humans alter their shape and composition.…”