Does functional homogenization accompany taxonomic homogenization of British birds and how do biotic factors and climate affect these processes?

Abstract

Environmental change has reshuffled communities often causing taxonomic homogenization rather than differentiation. Some studies suggest that this increasing similarity of species composition between communities is accompanied by an increase in similarity of trait composition—functional homogenization—although different methodologies have failed to come to any consistent conclusions. Functional homogenization could have a large effect on ecosystem functioning and stability. Here, we use the general definition of homogenization as “reduced spatial turnover over time” to compare changes in Simpson's beta diversity (taxonomic turnover) with changes in Rao's quadratic entropy beta diversity (functional turnover) in British breeding birds at three spatial scales. Using biotic and climatic variables, we identify which factors may predispose a site to homogenization. The change in turnover measures between two time periods, 20 years apart, was calculated. A null model approach was taken to identify occurrences of functional homogenization and differentiation independent of changes in taxonomic turnover. We used conditional autoregressive models fitted using integrated nested Laplace approximations to determine how environmental drivers and factors relating to species distributions affect changes in spatial turnover of species and functional diversity. The measurement of functional homogenization affects the chance of rejection of the null models, with many sites showing taxonomic homogenization unaccompanied by functional homogenization, although occurrence varies with spatial scale. At the smallest scale, while temperature‐related variables drive changes in taxonomic turnover, changes in functional turnover are associated with variation in growing degree days; however, changes in functional turnover become more difficult to predict at larger spatial scales. Our results highlight the multifactorial processes underlying taxonomic and functional homogenization and that redundancy in species traits may allow ecosystem functioning to be maintained in some areas despite changes in species composition.

Increasing climate‐driven taxonomic homogenization but functional differentiation among river macroinvertebrate assemblages

“…Although a relationship between temporal changes in taxonomic and functional LCBD was observed on the South Island, the pattern did not hold on the North Island. This discrepancy highlights the need to consider explicitly both the taxonomic and functional facets of biodiversity, as changes in functional β-diversity cannot necessarily be predicted by changes in taxonomic β-diversity (Baiser & Lockwood, 2011;Villéger et al, 2014;White et al, 2018).…”

“…Increases in the similarity of functional trait composition among species assemblages over time, leading to functional homogenization, are likely to decrease the resistance and resilience capacity of communities facing disturbances (Clavel et al., 2011; de Juan et al., 2013; Olden, 2006). However, in some cases, there may be no direct relationship between changes in taxonomic and functional β‐diversity among species assemblages (Sonnier et al., 2014; Villéger et al., 2014; White et al., 2018). For instance, assemblages that exhibit taxonomic homogenization can be functionally differentiated if the newly introduced species in each assemblage are functionally dissimilar to each other (Villéger et al., 2014).…”

Fish communities diverge in species but converge in traits over three decades of warming

“…Yet, examining changes in taxonomic and trait diversity simultaneously may best describe community dynamics (Dencker et al, ; Monnet et al, ; Villéger, Miranda, Hernández, & Mouillot, ). For instance, changes in species composition may not lead to changes in trait diversity if loser species are replaced by species with similar traits (Clare, Robinson, & Frid, ; Villéger et al, ; White, Montgomery, Storchová, Hořák, & Lennon, ). Conversely, declines of a few rare species with unique trait values may have major impacts on trait diversity without notable changes in species composition (Mouillot, Bellwood, et al, ; Mouillot et al, ; Violle et al, ).…”

“…However, most studies have examined biotic homogenization through species‐based approaches, which offer less insight for understanding the mechanisms driving homogenization and the consequences for ecosystem functioning. Yet, trait homogenization often results from taxonomic homogenization, and the relationship between trait homogenization and taxonomic homogenization is not entirely understood (Baiser & Lockwood, ; White et al, ).…”

“…Yet, trait homogenization often results from taxonomic homogenization, and the relationship between trait homogenization and taxonomic homogenization is not entirely understood (Baiser & Lockwood, 2011;White et al, 2018).…”