Citation:

Crabot, J., C. Mondy, P. Usseglio-Polatera, K. Fritz, P. Wood, M. Greenwood, M. Bogan, E. Meyer, AND T. Datry. A global perspective on the functional responses of stream communities to flow intermittence. ECOGRAPHY. Blackwell Publishing, Malden, MA, 44(10):1511-1523, (2021). https://doi.org/10.1111/ecog.05697

Impact/Purpose:

Biodiversity loss has been disproportionately high in freshwater environments, and biodiversity is a major factor governing the ecological integrity and ecosystem services provisioned from these environments. An increasing proportion of river networks are drying due to climate change and increased water abstraction. Streams that dry for a portion of the year (= temporary or non-perennial) represent the world's most widespread type of flowing waterbody. Streams shifting from perennial to non-perennial represents a substantial threshold for stream biota and processes because many aquatic biota have limited capacity to withstand drying. Biodiversity can be characterized in terms of the number and variation of taxonomic species as well as the functional diversity or the groups of species that harbor the same traits (e.g., body size, life span, dispersal ability). In this study we compare how taxonomic and functional diversity of aquatic invertebrate assemblages vary along gradients of flow duration across multiple river systems from three continents to test hypotheses about the impact of drying to stream biodiversity. With increased drying, invertebrates tended to have shorter life spans, smaller body sizes, and higher fecundity. Unexpectedly, functional diversity declined sharply with longer periods of stream drying and its decline was not different than that of taxonomic diversity. This indicates stream drying is likely a global threat to river biodiversity as functional redundancy was consistently lacking in invertebrate communities across naturally intermittent rivers from different continents and climate zones. These results highlight the pressing need to consider drying as a major threat to freshwater biodiversity, ecosystem functions and services in rivers networks.

Description:

  The current erosion of biodiversity is a major concern that threatens the ecological integrity of ecosystems and the ecosystem services they provide. Due to global change, an increasing proportion of river networks are drying and changes from perennial to non-perennial flow regimes represent dramatic ecological shifts with potentially irreversible alterations of community and ecosystem dynamics. However, there is minimal understanding of how biological communities respond functionally to drying. Here, we highlight the taxonomic and functional responses of aquatic macroinvertebrate communities to flow intermittence across river networks from three continents, to test predictions from underlying trait-based conceptual theory. We found a significant breakpoint in the relationship between taxonomic and functional richness, indicating higher functional redundancy at sites with flow intermittence higher than 28%. Multiple strands of evidence, including patterns of alpha and beta diversity and functional group membership, indicated that functional redundancy did not compensate for biodiversity loss associated with increasing intermittence, contrary to received wisdom. A specific set of functional trait modalities, including small body size, short life span and high fecundity, were selected with increasing flow intermittence. These results demonstrate the functional responses of river communities to drying and suggest that on-going biodiversity reduction due to global change in drying river networks is threatening their functional integrity. These results indicate that such patterns might be common in these ecosystems, even where drying is considered a predictable disturbance. This highlights the need for the conservation of natural drying regimes of intermittent rivers to secure their ecological integrity.

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