Predator search pattern and the strength of interference through prey depression

We develop a model of predators foraging within a single patch, on prey tha t become temporarily immune to predation (depressed) after detecting a pred ator. Interference through prey depression occurs because the proportion of vulnerable prey land hence intake rate) decreases as predator density incr eases. Predators in our model are not forced to move randomly within the pa tch, as is the case in other similar models, but can avoid areas of depress ed prey and so preferentially forage over vulnerable prey. We compare the e xtent to which different avoidance rules (e.g., move more quickly over depr essed prey or turn if approaching depressed prey) influence the amount of t ime spent foraging over depressed and vulnerable prey, and how this influen ces the strength of interference. Although based on a different mechanism, our model produces two similar general predictions to interference models b ased on direct interactions between predators: the strength of interference increases with (1) increased competitor density and (2) decreased prey enc ounter rate. This suggests that there are underlying similarities in the na ture of interference even when it arises through different processes. Not s urprisingly, avoidance of depressed prey can substantially reduce the stren gth of interference compared with random foraging. However, we identify the region of the model's parameter space in which this reduction is particula rly large and show that the only system for which suitable data are availab le, redshank Tringa totanus feeding on Corophium volutator; falls within th is region. The model shows that, by adjusting its search path to avoid area s of depressed prey, a predator can substantially reduce the amount of the interference it experiences and that this applies over a wide range of para meter space, including the region occupied by a real system. This suggests that behavior-based interference models should consider predator search pat tern if they are to accurately predict the strength of the interference.