Ecosystem-consequences of community disassembly in freshwater ecosystems

Background/Question/Methods

Anthropogenic environmental change is driving biodiversity shifts through simultaneous declines of native species coupled with increases in non-native species with unknown consequences for ecosystems. In other words, humans are shuffling the deck by taking communities apart and putting them back together in novel ways. Past studies suggest that this community disassembly appears somewhat predictable, traits influence whether a species is a particularly successful invasive or sensitive to anthropogenic change. In the biodiversity-ecosystem functioning literature, there is growing appreciation that the ecosystem consequences of community change will be influenced by the traits of species that compose the novel community. However, there remains a need to integrate understanding of community change with the ultimate ecosystem-consequences. We asked two linked questions: First, how have communities fallen apart and how are they being put back together? Second, given the pattern of community disassembly, what are the predicted changes to ecosystem processes? We used large existing data-sets of stream fish and invertebrates (>5000 sites) across the United States to quantify spatial patterns of community disassembly across gradients of urban and agricultural land use. Specifically, we quantified taxa-specific vulnerability to habitat alteration using threshold analyses, and link these vulnerabilities to existing data-sets on species-traits that are direct correlates of ecosystem function.

Results/Conclusions

Stream invertebrates and fishes exhibited strong patterns of community disassembly across the United States, and species varied dramatically in their inferred-vulnerabilities to human habitat alteration. Different biological and ecological traits correlated to different degrees with these inferred-vulnerabilities; many of which corresponded to traits that can govern ecosystem processes. For example, some ecosystem processes controlled by rates of consumption (i.e., leaf litter break-down) are governed by allometric rules. Thus, different vulnerabilities of differently sized taxa will drive non-linear ecosystem consequences. Alternatively, other ecosystem processes are controlled more by phylogenic constraints. Together, these results were used to parameterize realistic extinction scenarios. These simulations revealed strong nonlinear relationships between habitat alteration and ecosystem processes. Thus, insights into community disassembly rules can shed light on the ecosystem-consequences of human-induced environmental change.