Seasonal variation in the strength of interference competition among headwater stream predators

1. Vertebrate communities in headwater streams are assumed to be regulated through competitive and predatory interactions. Although documented predation is rare, studies regularly report competitive dominance by fish that, as larger competitors reliant on aquatic habitat, exclude semi-aquatic salamanders to marginal stream habitat. However, it is unclear whether fish interact with stream-breeding salamanders through indirect effects such as, competition for resources (e.g., food or cover) or fear (i.e., threat of predation) nor is it known whether these interactions are consistent through time. 2. This study used a novel caging approach to determine if competitive outcomes between a headwater fish and salamanders were regulated primarily through resource depletion (exploitative competition) or behavioural avoidance (interference competition). 3. We paired banded sculpin (Cottus carolinae) and larval red salamanders (Pseudotriton ruber) of similar body size in independent flow thro...