Effect of an abiotic disturbance on a lotic predator-prey interaction.

A model derived from marine research, and recently applied to stream communities, suggests that community structure is more likely to be influenced by predators in benign versus harsh abiotic regimes. Experiments were conducted to determine if increasing the harshness of a particular regime would alter the impact of a stream invertebrate predator on prey densities in field enclosures. Density of a stonefly predator, Kogotus nonus, was varied in containers exposed to low (benign) and high (harsh) levels of fine sediment. As predicted by the model, the harsher regime eliminated predator effects in two of three experiments. In the third experiment, however, high levels of sediment actually enhanced the impact of the predator on the prey community. A consideration of the possible mechanisms underlying this model led to the conclusion that increasing the harshness of a regime can be expected to produce outcomes ranging from elimination to enhancement of predator effects, depending on how the regime is perceived by the predator versus the prey.