Considerable progress has been made in the development of statistical tools to quantify trophic relationships using stable isotope ratios, including tools that address size and overlap of isotopic niches. We build upon recent progress and propose a new probabilistic method for determining niche region and pairwise niche overlap that can be extended beyond two dimensions, provides directional estimates of niche overlap, accounts for species-specific distributions in niche space, and, unlike geometric methods, produces consistent and unique bivariate projections of multivariate data. We define the niche region (NR) as a given 95% (or user-defined a) probability region in multivariate space. Overlap is calculated as the probability that an individual from species A is found in the N(R) of species B. Uncertainty is accounted for in a Bayesian framework, and is the only aspect of the methodology that depends on sample size. Application is illustrated with three-dimensional stable isotope data, but practitioners could use any continuous indicator of ecological niche in any number of dimensions. We suggest that this represents an advance in our ability to quantify and compare ecological niches in a way that is more consistent with Hutchinson's concept of an "n-dimensional hypervolume".

Summary Water clarity can have a profound influence on aquatic ecosystem structure and processes via its effects on physical habitat (e.g., thermal regime, macrophyte density) and behavioural responses of biota (e.g., predator avoidance, reaction distances, foraging efficiency). Changes in foraging efficiencies under varying water clarity conditions are well documented for many freshwater piscivores in laboratory studies, but the influence of visual foraging conditions on interspecific trophic dynamics is poorly understood in wild populations, especially within water clarity ranges that are realistic for north‐temperate boreal lakes. Here, we used stable isotopes of nitrogen (15N/14N) and carbon (13C/12C) in fish muscle tissue to investigate how resource partitioning between two sympatric visual piscivores is related to water clarity and other habitat variables in 28 small (100–200 ha) Boreal Shield lakes. One of the species is adapted for foraging in low subsurface illumination (walleye, Sander vitreus) and the other in high subsurface illumination (smallmouth bass, Micropterus dolomieu). Trophic niche dimensions of the dark‐adapted predator did not respond significantly to differences in water clarity. In contrast, total isotopic niche space of the light‐adapted predator decreased significantly with increasing water clarity through greater use of pelagic resources and a narrower range of trophic levels, although these relationships were weak. Niche overlap ranged from 0 to 65%, but was not significantly related to water clarity. Rather, indices of prey availability appeared to be much stronger predictors of trophic interactions. Both species occupied more similar food‐web positions when yellow perch (Perca flavescens) abundance was higher, and had more similar niche size and trophic evenness with decreasing prey fish species richness. Results indicate that the trophic ecology of predators adapted to foraging in low light conditions is less influenced by water clarity than that of predators adapted to foraging in high light conditions. However, prey availability, rather than the environmental conditions in which foraging occurs, may be a more important driver of resource partitioning among generalists even when light conditions favour one species’ foraging strategy over another.

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Restoration of streams impacted by acid mine drainage (AMD) often require extensive and expensive engineering solutions, but the long-term effectiveness of these treatments in terms of improving downstream biological communities, is rarely tested. A rather novel treatment for the elimination of AMD at a site on Junction Creek in Sudbury Canada, involved damming and diversion of AMD deep underground, with subsequent limestone treatment of the waters outside the watershed. We used a rapid bioassessment technique to assess the recovery of benthic macroinvertebrate communities in response to this diversion. Biological summary metrics including taxa richness, EPT (sum of Ephemeroptera, Plecoptera, Tricoptera) richness, Simpson diversity, as well as multivariate descriptors of relative taxa abundance were used to compare the test site to nine reference sites. There was rapid recolonization of many families of benthic invertebrates but the site remained significantly impaired 8 years after the diversion, with a particular scarcity of large sensitive organisms. Multiple factors, including drought events, delayed or set back recovery. This study indicated that ecological risk managers need to consider both shortterm and long term (e.g., watershed revegetation) strategies to promote ecosystem recovery in such situations.

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