Trait flexibility of generalist invertebrates exposed to contrasting predation and drying stressors

Abstract

Summary How different generalist species are able to exploit heterogeneous landscapes likely depends on whether their life‐history strategies confer resilience to multiple environmental selection pressures. We investigated the life‐history strategies of two generalist invertebrates, Xanthocnemis zealandica damselflies and Sigara arguta waterboatmen, which inhabit ponds varying in drying and predator presence. Using mesocosm experiments with temporary‐ and permanent‐pond nymphs, we determined the flexibility of their predator avoidance and drying resistance. Xanthocnemis zealandica was most susceptible to predatory fish regardless of natal habitat, with permanent‐pond nymphs more likely to have reduced movement, higher refuge use and slower growth than temporary‐pond nymphs; growth was, however, not influenced by predator presence. Xanthocnemis zealandica had a fixed response to drying stress, with high survival rates (80–90%) during short drying periods (2–8 days), regardless of natal habitat. In contrast to X. zealandica, S. arguta had a completely inflexible life‐history with no differences in predator avoidance between permanent‐ and temporary‐pond nymphs, and a complete inability to survive drying. Without flexible traits S. arguta may counter potentially high costs of predation in permanent ponds and drying mortality in temporary ponds through rapid development and terrestrial dispersal. Xanthocnemis zealandica's flexible life‐history is likely driven by longer nymphal development which requires adaptation to both predator and drying stressors to complete their life‐cycle over the range of habitats they occupy. Overall, these two species exemplify how generalists can strongly differ in their life‐history strategies but still persist across a similar range of habitats.