Density declines, richness increases, and composition shifts in stream macroinvertebrates

Abstract

Documenting trends of stream macroinvertebrate biodiversity is challenging because biomonitoring often has limited spatial, temporal, and taxonomic scopes. We analyzed biodiversity and composition of assemblages of >500 genera, spanning 27 years, and 6131 stream sites across forested, grassland, urban, and agricultural land uses throughout the United States. In this dataset, macroinvertebrate density declined by 11% and richness increased by 12.2%, and insect density and richness declined by 23.3 and 6.8%, respectively, over 27 years. In addition, differences in richness and composition between urban and agricultural versus forested and grassland streams have increased over time. Urban and agricultural streams lost the few disturbance-sensitive taxa they once had and gained disturbance-tolerant taxa. These results suggest that current efforts to protect and restore streams are not sufficient to mitigate anthropogenic effects.

Shifting taxonomic and functional community composition of rivers under land use change

“…Threshold responses of functional composition, such as those identified by our study, have the potential to introduce more nuance and rigor to prioritize biodiversity conservation strategies in light of substantial global land use changes (Gallagher et al, 2021;Rumschlag et al, 2023). Functional traits are powerful for their ability to highlight species that disproportionately enhance biodiversity and ecosystem functioning (e.g., McGill et al, 2006).…”

“…In accordance with our ecologically informed hypotheses, functional community composition consistently demonstrated abrupt shifts at lower levels of land use change when compared to taxonomic composition across taxonomic groups and geographic regions. Land use conversion has a cascading effect on freshwater habitats, altering species‐ and trait‐sorting processes (Burcher et al, 2007), which often causes widespread replacement of specialized species with narrow ecological requirements by more broadly tolerant generalists (Chen & Olden, 2020; Davison et al, 2021; Rumschlag et al, 2023). Communities with species exhibiting specialized traits could be sensitive to even low levels of urban and agricultural land use (e.g., Larsen & Ormerod, 2010; Leitão et al, 2018).…”

“…Emerging research shows that stark shifts in functional community composition can manifest at lower thresholds of environmental change than shifts in taxonomic composition (Clements & Ozgul, 2016; Rogers et al, 2018). This can occur because, although the taxonomic composition of a community may change (Rumschlag et al, 2023), whether or not concurrent changes in functional community composition also occur depends on trait constraints (phylogenetic and ecological) and redundancy among species, as well as the directional selection imposed by environmental pressures on particular trait(s). For example, Clements and Ozgul (2016) found that shifts in body size distributions signaled impending population decline well before changes in traditional demographic metrics.…”

finsyncR, an R package to synchronize 27 years of fish and invertebrate data across the United States

“…These data are used by the US government in assessment frameworks, but a wealth of additional knowledge can be gleaned from unique applications of these data. For instance, scientists have recently used data from federal biomonitoring programs to document long-term changes in stream biodiversity at a national scale 2 and to test ecological theory on the influence of environmental change on species coexistence 3 . While most data associated with these biomonitoring efforts are publicly available, barriers remain for new, outside users to apply these data without institutional guidance.…”

Towards a toolkit for global insect biodiversity monitoring

“…Other arthropod groups have only been monitored when and where academics or citizen scientists have had a personal interest and/or the required funding, leaving the majority of taxa and locations unstudied. Consequently, it has only recently been noticed that the abundance and, less frequently, the diversity of insects have significantly declined in many parts of the world [3][4][5], with formerly abundant species showing the strongest declines [6].…”