Disentangling effects of predators and landscape factors as drivers of stream fish community structure

Experimental and fine-scale studies indicate predators can have strong effects on stream fishes. It is unclear, however, how predators interact with landscape factors to influence stream fish communities at scales relevant to management and conservation. Because predators and prey respond to environmental variability, measuring community responses to predators requires resolving the effects of abiotic factors on both predators and prey. We collected stream fish community data in the summers of 2017 and 2018 and paired structural equation modelling with multivariate methods to identify abiotic factors that influenced the distribution of a predatory fish, largemouth bass (Micropterus salmoides) and community structure of stream fish. We then compared how fish species richness and community composition responded to the presence of bass mediated by environmental factors. Probability of occurrence of bass increased with catchment area, while richness responded to both natural and anthropogenic characteristics of streams and their catchments. Contrary to our prediction, richness was higher at sites with bass and several species exhibited positive co-occurrence and abundance patterns with bass, while only one species had a negative relationship. Higher diversity of stream fishes in the presence of bass highlights the difficulties in understanding the combined effects of predators and environmental variation, both natural and human induced, as drivers of community structure. We discuss several challenges to understanding the effects of predators in natural systems, including unmeasured environmental variability, mismatch of spatial and temporal scales, and context dependency of ecological responses.

Automated summary

Experimental studies show predators can affect stream fishes, but their interaction with landscape factors remains unclear. Research indicates higher species richness and positive co-occurrence with bass at sites where bass are present, highlighting the challenges of understanding combined effects of predators and environmental variation in driving community structure.