Effects of temperature and resource level on interspecific interactions in two species of Odonata larvae

Identifying how temperature and food resources affect interactions between species is important for understanding how climate change will shape community structure in the future. Here, we tested how temperature and resource density affect survival and growth in the larval stage of two coexisting odonates: the damselfly Lestes sponsa and the dragonfly Sympetrum vulgatum. We performed a laboratory experiment at two temperatures (21 and 24°C) with two resource densities. We estimated the timing of egg hatching of individual egg clutches and thereafter the larval growth rate-, survival- and size-mediated priority effects under interspecific conditions. Eggs of both species hatched slightly faster at 24°C, and S. vulgatum eggs started hatching approximately 1 day earlier than L. sponsa eggs. However, this earlier hatching did not result in a size-mediated priority effect, that is, a higher predation on the later hatching L. sponsa. Nevertheless, L. sponsa larvae were significantly larger than S. vulgatum at hatching. Growth rate and survival were significantly higher: (1) at 24°C compared with 21°C, (2) at high compared with low-resource density and (3) in L. sponsa compared with S. vulgatum. Several significant interaction effects between resource density and temperature and between temperature and species were found. At high temperature, L. sponsa had a higher growth rate than S. vulgatum, but no difference in growth rate between species was found at low temperature. Additionally, a high-resource density resulted in a higher growth rate in both species, but only under high temperature. There was a negative relationship between growth rate and survival in both species, suggesting that the higher growth rate of larvae was to some degree driven by intraguild predation and/or cannibalism. Our results imply that resource levels interact with temperature to affect interactions between the species.