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

Abstract

Global change is increasing biotic homogenization globally, which modifies the functioning of ecosystems. While tendencies towards taxonomic homogenization in biological communities have been extensively studied, functional homogenization remains an understudied facet of biodiversity. Here, we tested four hypotheses related to long-term changes (1991-2016) in the taxonomic and functional arrangement of freshwater macroinvertebrate assemblages across space and possible drivers of these changes. Using data collected annually at 64 river sites in mainland New Zealand, we related temporal changes in taxonomic and functional spatial β-diversity, and the contribution of individual sites to β-diversity, to a set of global, regional, catchment and reach-scale environmental descriptors. We observed long-term, mostly climate-induced, temporal trends towards taxonomic homogenization but functional differentiation among macroinvertebrate assemblages. These changes were mainly driven by replacements of species and functional traits among assemblages, rather than nested species loss. In addition, there was no difference between the mean rate of change in the taxonomic and functional facets of β-diversity. Climatic processes governed overall population and community changes in these freshwater ecosystems, but were amplified by multiple anthropogenic, topographic and biotic drivers of environmental change, acting widely across the landscape. The functional diversification of communities could potentially provide communities with greater stability, resistance and resilience capacity to environmental change, despite ongoing taxonomic homogenization. Therefore, our study highlights a need to further understand temporal trajectories in both taxonomic and functional components of species communities, which could enable a clearer picture of how biodiversity and ecosystems will respond to future global changes. K E Y W O R D S β-diversity, biotic homogenization, climate change, freshwater macroinvertebrates, functional diversity, human disturbance | 6905 MOUTON eT al.

Climate and land‐use driven reorganisation of structure and function in river macroinvertebrate communities

“…Here, we complement recent findings from Mouton et al (2020), who reported decreasing spatial taxonomic β diversity (taxonomic homogenisation) but increasing spatial functional β diversity (functional differentiation) among river macroinvertebrate assemblages. We capitalise on the same high-resolution time-series datasets, comprising macroinvertebrate communities collected annually from 1991 to 2016, at 64 mainstem river sites across New Zealand's two mainland islands.…”

“…We capitalise on the same high-resolution time-series datasets, comprising macroinvertebrate communities collected annually from 1991 to 2016, at 64 mainstem river sites across New Zealand's two mainland islands. The two studies are complementary in the sense that Mouton et al (2020) explored how climate change affects the spatial organization of assemblages while the present study aims at evaluating how both climate and land-use changes influence temporal differences in community composition within sites.…”

“…Given widespread evidence of freshwater macroinvertebrates response to ongoing climate change (Pyne and Poff 2017, Floury et al 2018, Mouton et al 2020, we first expected a latitudinal pattern in temporal β diversity (E 1 ), owing to climate-driven species range shifts. Specifically, we expected (E 1a ) increasing species colonisations at the leading edges (southern margins of New Zealand) but (E 1b ) increasing extirpations at the rear edges (northern margin of New Zealand).…”

Hydrological Season Can Have Unexpectedly Insignificant Influences on the Elevational Patterns of Functional Diversity of Riverine Macroinvertebrates

“…The species characteristics resulted in a large increase in Ephemeroptera numbers during this period compared to other populations. Thus, changes in the community structure over time affect functional uniformity [ 70 , 71 ].…”

Distance decay 2.0 – a global synthesis of taxonomic and functional turnover in ecological communities

“…1a), and the gain or loss of species does not inform about variations in functional β-diversity whenever trait redundancy is high 36 . For example, taxonomic homogenization does not lead to functional homogenization if the newly introduced species in the assemblages are functionally similar to each other 30,37,38 . The most pressing question is whether functional features explain more of the distance decay along environmental gradients than species identities, as suggested by some earlier studies [39][40][41][42][43] .…”