The influence of predator species and prey age on the immediate survival value of antipredator behaviours in a damselfly

The efficacy of antipredator behaviours may depend on both intrinsic and ex trinsic factors. We experimentally studied the effects of predator species and prey age on the immediate survival value of swimming and lamellae loss in larval damselflies. Four predators: two invertebrates (the notonectid, N otonecta viridis and the dragonfly larva Aeshna cyanea), and two vertebrate s (the three-spined stickleback Gasterosteus aculeatus and the sunfish Lepo mis gibbosus) were tested with all combinations of two instars of the damse lfly Lestes sponsa (F-0 and F-2). The number of escapes by swimming away we re much lower when larvae were attacked by the two fishes than by the two i nvertebrates. Moreover Lepomis never removed lamellae and killed all larvae . The instars did not differ in the number of escapes by swimming, but F-0 instars were caught more at the lamellae than F-2 instars. All larvae that survived a capture were caught at the lamellae and the majority (90 %) did so by autotomy. The ontogenetic increase in the immediate survival value of this antipredator behaviour was dependent upon the predator species. It wa s highest in captures by the Notonecta (40 %), and lower when larvae were c aught by the Aeshna or Gasterosteus (ca. 17 %). This was probably because t he biological relevance of the magnitude of the speed difference between da mselfly instars depends upon the predator's attack performance. We discuss the consequences of these findings for the macrohabitat distribution of the larvae and for the multicomponent antipredator behaviours prey may use.