Movement behaviour and dynamics of an aquatic insect in a stream benthic landscape

Understanding not just where organisms move but how they move is an important step towards integrating animal behaviour into landscape ecology. The three-dimensional landscape of a streambed provides an ideal setting for forging this integration because of the persuasive effects of flowing water. In this study, we experimentally examine the larval movement of the case-building caddisfly Agapetus boulderensis Milne, 1936 in response to two current velocities in each of five levels of contrasting habitat types (i.e., smooth patches that facilitate movement and thick algal patches that constrain movement). Detailed behavioural observations showed that larvae employed two distinctly different strategies of movement in different current velocities: faster crawling and slower pivoting. Our results suggest that individual decision-making between crawling and pivoting is related to the magnitude of current velocity across the streambed, and the frequency at which larvae employ these behaviours translates into differential movement rates and directions. Strong concordance between a conceptual model and our results supports the notion that the presence of structural "nonhabitat" patches at high current velocities may create areas of local flow interruption and refugia. This, in turn, plays an important role in eliciting either crawling or pivoting and in shaping patterns and directions of larval movement, and by extension resource acquisition.