Trading off mortality risk against foraging effort in damselflies that differ in life cycle length

Life history theory predicts that size and age at emergence depend on the slope and shape of the relationship between mortality rate and foraging effort. Given the high expected foraging effort in obligate univoltine species compared with semivoltine species we expected a low slope and an increase in foraging effort in the presence of a predator for the former and the opposite: pattern for the latter. We tested these predictions in two damselfly species of the univoltine genus Lestes, and the semivoltine genus Coenagrion when confronted with perch. We determined for each of the four study species the relationships between mortality rate and foraging effort at an individual level. As expected by the different growth demands associated with differences in life cycle length, both Lestes species had a higher foraging effort than the two Coenagrion species in the absence as well as in the presence of perch. As a result, lestids also suffered a higher mortality rate. The slope of the regression between mortality rate and foraging effort was, as predicted, lower for lestids than for coenagrionids, for one species pair. Despite this, and opposite to our prediction, the lestids decreased foraging effort even more than coenagrionids in the presence of perch. We discuss these findings in the light of life history responses in species that differ in life cycle length.