Abstract
The multi-scalar complexity of social-ecological systems makes it challenging to quantify impacts from human activities on ecosystems, inspiring risk-based approaches to assessments of potential effects of human activities on valued ecosystem components. Risk assessments do not commonly include the risk from indirect effects as mediated via habitat and prey. In this case study from British Columbia, Canada, we illustrate how such “indirect risks” can be incorporated into risk assessments for seventeen ecosystem components. We ask whether (i) the addition of indirect risk changes the at-risk ranking of the seventeen ecosystem components and if (ii) risk scores correlate with trophic prey and habitat linkages in the food web. Even with conservative assumptions about the transfer of impacts or risks from prey species and habitats, the addition of indirect risks in the cumulative risk score changes the ranking of priorities for management. In particular, resident orca, Steller sea lion, and Pacific herring all increase in relative risk, more closely aligning these species with their “at-risk status” designations. Risk assessments are not a replacement for impact assessments, but—by considering the potential for indirect risks as we demonstrate here—they offer a crucial complementary perspective for the management of ecosystems and the organisms within.
Highlights
Most of the world’s ecosystems and the services they supply are threatened as a result of a wide-array of human activities [1,2]
The highest direct risk scores were that for Dungeness crab, salmon, and sponges
Our results demonstrate that incorporating food web and habitat relationships into estimates of cumulative risk to ecosystem components changes the risk scores and the relative ranking of ecosystem components
Summary
Most of the world’s ecosystems and the services they supply are threatened as a result of a wide-array of human activities [1,2]. Many overlapping human activities have diffuse impacts with time lags that vary over small temporal and spatial scales, such that quantitatively demonstrating an impact is time-consuming, expensive, and often impossible without more data than are practicable with available resources. Despite these challenges, decision makers still need methods to evaluate the distribution and intensity of land, coastal and ocean-based human activities, and the resulting impacts across species, habitats and ecosystems. Risk assessment is one approach decision-makers use for evaluating the risk to ecosystem components resulting
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