Predation risk and habitat complexity modify intermediate predator feeding rates and energetic efficiencies in a tri‐trophic system

Abstract

To understand the effects of environmental changes on ecosystems, it is important to determine the factors and mechanisms influencing the strength of species interactions in food webs. However, joint effects of predation risk and additional environmental factors on species interaction strengths in multitrophic systems remain largely unexplored, leaving a substantial gap in our understanding of the links between local environmental characteristics and food web properties. To fill this gap, we investigated the effects of habitat complexity and predation risk by top predatory dragonfly larvae (Aeshna cyanea) on feeding rates and energetic efficiency (i.e. the ratio of acquired and expended energy) of the larvae of three intermediate predatory odonate species (Libellula quadrimaculata, Sympetrum sanguineum, and Ischnura elegans) preying on cladocerans. We hypothesised that predation risk would decrease the feeding rate, especially in the structurally simple habitat, and increase the metabolic rate of all intermediate predators. We also expected higher feeding rates of intermediate predators using aquatic vegetation as a perching site (i.e. Sympetrum and Ischnura) in the structurally complex habitat. Finally, we expected to observe habitat‐ and predation risk‐dependent energetic efficiencies of the intermediate predators driven by changes in feeding and metabolic rates. The effect of predation risk on feeding rates was species specific and differed between the structurally simple and complex habitat. Habitat complexity increased feeding rates but only in the absence of predation risk. Moreover, predation risk signalled by chemical cues significantly increased Sympetrum vulgatum feeding rates but did not influence the feeding rates of the two other intermediate predators. Metabolic rates varied among the three intermediate predators but were not affected by predation risk. Estimated energetic efficiency decreased with intermediate predator body mass and depended, to a lesser extent, on the interactive effect of habitat complexity and predation risk. Our results imply that the effects of habitat complexity and predation risk on trophic interactions are likely to be determined by traits related to foraging and defence of the intermediate predators and their habitat domains, and that energetic efficiency is mainly determined by predator mass. Given that habitat complexity and predation risk can vary substantially across habitats, we conclude that it is important to consider habitat complexity and predation risk to better understand and predict the effects of environmentally driven variations on trophic interaction strength and metabolic rates that underlie the energetic efficiency of individual consumers. This has important implications for population and community dynamics as well as ecosystem functioning.

From individuals to communities: Habitat complexity affects all levels of organization in aquatic environments

“…However, these expectations depend on predator and prey microhabitat use and predator foraging tactics (Klecka & Boukal, 2014) and may be further modified by case‐specific variables such as the physical characteristics of the submerged plants providing the HC (Grutters et al, 2015). Other factors, such as temperature (Wasserman et al, 2016) or predation risk posed by a higher‐level predator (Kolar et al, 2019) can modify the baseline effect so that it only manifests in high temperatures or depends on intermediate predator identity. Finally, HC may not alter trophic relationships at all, as found in an intraguild predation system with dragonfly and beetle predators (Carter et al, 2018).…”

Chemical cannibalistic cues make damselfly larvae hide rather than hunt

“…6 A). Also Kolar found no increased respiration rate under predator pressure in Ischnura larvae 69 . The lack of impact may be due to a change in respiratory-related behavior serving as compensatory behavior and resulting from the anti-predation strategy.…”

Habitat preferences of the endangered diving beetleGraphoderus bilineatus: implications for conservation management

“…Submerged macrophyte stands often harbour more diverse fauna than open waters (Nilsson & Svensson, 1995; Tolonen et al ., 2003; Declerck et al ., 2011) because they serve as a refuge for aquatic invertebrates, amphibians and small fish (e.g., Eklöv & van Kooten, 2001; Klecka & Boukal, 2014). Submerged macrophytes may also enhance predation success of some insect predators (Klecka & Boukal, 2014; Kolar et al ., 2019) including diving beetle larvae (Yee, 2010). Moreover, submerged plants increase available habitat surface and thus increase the diversity and abundance of prey base communities (Canion & Heck, 2009).…”