Geomorphological effects of animals in mountain streams: Impact and role.

Elucidating the impact of faunal activity on stream channels is an emerging field wherein ecologists, fluvial geomorphologists, and engineers collaborate to research and manage fluvial ecosystems. Here, we focused on the geomorphological effects of animals in mountain streams. This ecosystem merits conservation measures as it furnishes cold-water refugia. We searched literature addressing the impact of various animal taxa on the river/stream bed structure. The citation sources were the Web of Science, Scopus, and ScienceDirect databases covering 1975-early 2020. We examined all animal taxa with documented or potential zoogeomorphological effects upon streams and assigned spatiotemporal scales to their impacts. Interpreting the literature was challenging due to a lack of uniformity in data treatment between species groups and over time. Though human interactions prevail in stream channels, animals also have a substantial effect on a spatial scale and their modifications are more durable. In general, animals markedly influence aquatic habitats. This literature compilation revealed much information about the geomorphological effects of beavers, redd-building fish, and large bottom-dwelling fish. The scale of impact of invertebrates such as crayfish or case-building caddisfly larvae on stony-gravel bottoms has previously been demonstrated. However, previous research has concentrated on only one taxon and has not demonstrated the bioaccumulation effect of multiple taxa. Quantitative data have been presented only for large terrestrial mammals crossing streams. There was comparatively little information on the impact of other terrestrial taxa on stream geomorphology. There were also few or no quantitative data on the impacts of aquatic fauna on mountain stream channels. Much has been reported about the effects of burying invertebrates but relatively little is known about the impacts of burying fish such as lamprey larvae. The present review highlights numerous outstanding information gaps. It is hoped that this review will facilitate ongoing zoogeomorphological research.