Egg predation and predator‐induced hatching plasticity in the African reed frog,Hyperolius spinigularis

Abstract

Predators can reduce prey density through consumption and induce changes in the phenotypes of surviving prey (e.g. their behavior, morphology, life history). Recent reviews have highlighted the importance of both types of effects for understanding species interactions in food webs. However, most studies focus on only density or trait effects‐few have examined both within a single predator–prey system. Here I examine both the density and trait effects of egg‐stage predators of the East African reed frog,Hyperolius spinigularis,a species with arboreal clutches and aquatic larvae. To quantify the density effects of egg predators, I monitored seasonal clutch production and survivorship over two breeding seasons and thus estimated the effects of different predators on larval input into the aquatic habitat. I also quantified the effects of egg predators on the timing of hatching and hatchling phenotype. The reed frog,Afrixalus fornasini, and the ephydrid fly,Typopsilopasp., caused most of the mortality ofH. spinigulariseggs, so I focused on these two predators. Egg predation reduced larval densities from 18 to 82% depending upon the time of the season. Predation byAfrixalusandTypopsilopacaused surviving embryos to hatch 3–4 days earlier, at an earlier developmental stage, and at sizes that were 20–30% smaller compared to hatchlings from undisturbed clutches. Recent experimental studies in this system have demonstrated that reductions in larval density and size due to egg‐stage predators facilitate larval survival in the presence of aquatic predators. Reductions in larval density increase larval survival by reducing larval competition and increasing growth through vulnerable size classes. Predator‐induced early‐hatched tadpoles exhibited higher larval growth rates than tadpoles from undisturbed clutches, and thus realized higher survival by growing more rapidly though vulnerable size classes. Thus both the density and trait effects of egg‐stage predators have important, sometimes unexpected, consequences for survival in subsequent life‐stages.