Physiological and Behavioral Responses to Predators Shape the Growth/Predation Risk Trade-Off in Damselflies

Abstract

Most organisms must simultaneously find enough food for themselves while trying not to become food for some other organism. Previous field experiments have shown that larvae of Enallagma and Ischnura species are able to coexist in the littoral zones of lakes because they resolve this growth/predation risk trade-off differently: Ischnura species grow more quickly than Enallagma species, but Ischnura species suffer higher mortality rates than Enallagma. We performed a series of laboratory studies to explore the mechanistic basis for the difference in growth between the genera. When held in complete isolation and with unlimited food, larvae of a number of Enallagma species that coexist with fish accumulated mass at much faster rates than Ischnura species. This difference in isolation was due to the fish-lake Enallagma simply ingesting more food. In contrast, when held in the presence of other damselflies or a fish predator, Ischnura had significantly higher growth rates than Enallagma species from fish lakes. All species decreased the amount of food they ingested in the presence of the fish predator as compared to when fish were absent, which resulted in decreased growth in the presence of the predator for all species. However, the interspecific differences in growth rate were due primarily to differences in the abilities of the species to convert ingested food into their own biomass; in the presence of fish, comparably sized larvae ingested nearly identical amounts of food, but Ischnura larvae grew faster because they converted significantly more ingested food into their own biomass than did larvae of Enallagma species from fish lakes. This difference in conversion efficiency between the genera was not apparent when larvae were raised in complete isolation. These results indicate that Enallagma and Ischnura species differ in physiological stress responses to the presence of predators, and this difference may facilitate the coexistence of Enallagma and Ischnura species in the field.

Optimizing Time and Resource Allocation Trade‐Offs for Investment into Morphological and Behavioral Defense

“…UP 1 ϩ Ra Our assumption that larger individuals ingest more food than small individuals is supported by a linear increase between body size and food ingested shown in damselflies (McPeek et al 2001). The absolute amount of resources that can potentially be harvested increases linearly with increasing foraging activity and abundance of resources in the environment.…”

Microhabitat-scale influences of resources and refuge on habitat selection by an estuarine opportunist fish

“…energy allocated to other predation-avoidance behaviors) might interact with resource productivity. The presence of a predator has been shown to reduce the growth rate of damselflies through stress effects, without reducing food uptake, which may lower assimilation efficiency and/or increase metabolic rate (Stoks 2001) and differences among 2 damselfly genera in this stress response might facilitate coexistence (McPeek et al 2001).…”

The Temperature Dependence of Predation Stress and Prey Nutritional Stoichiometry

“…Elevated metabolic rate helps keep prey in a heightened state of alertness to increase their escape performance, thereby lowering the likelihood that predators will capture them (Hawlena et al, 2011;Zanette et al, 2011;Clinchy et al, 2013). But elevated metabolism arising from perceived predation risk may change organismal nutrient demand and hence the kinds of resources consumed by prey (McPeek et al, 2001;Hawlena and Schmitz, 2010b;Thaler et al, 2012). This also has implications for organismal fitness, but through a physiological trade-off in nutrient allocation between maintenance, growth, and reproduction.…”

“…These shifts in nutrient intake should also be reflected in body element stoichiometry, with stressed prey having higher carbon [C]:nitrogen [N] ratios than non-stressed prey (Hawlena and Schmitz, 2010a). Some experiments have shown that such shifts in nutrient intake and body stoichiometry can indeed occur between conditions with and without perceived predation risk (McPeek et al, 2001;Hawlena and Schmitz, 2010b;Jansens et al, 2015). Other experiments have, however, shown that the predicted responses do not occur (Costello and Michel, 2013;Dalton and Flecker, 2014;Kaplan et al, 2014;Guariento et al, 2015;Kirschman et al, 2016;Van Dievel et al, 2016;Zhang et al, 2016), thereby calling into question the generality of the predicted stress response.…”