Predation decreases cohort foraging activity and growth, yet increases individual size variation in prey
There is increasing evidence that size variability within a cohort can have important consequences on community ecology and evolution. It is commonly assumed that the threat of predation can influence cohort size variability by homogenizing foraging behavior among members. We combined predictions of growth–defense models with those from models of genesis of size variation to test the non-lethal effects of size-selective newt and gape-unconstrained aeshnid dragonfly larva predators on the size structure of Rhacophorus arboreus tadpoles in a controlled laboratory experiment. We hypothesized that the predators would induce differential growth and behavioral responses in the tadpoles, and would decrease cohort size variation. The tadpoles reduced activity levels in the presence of the predators, but the responses were generally stronger in the presence of dragonfly larvae. Growth costs were commensurate with the levels of behavioral defense investments in the tadpoles. Despite strong reductions in activity levels and growth, cohort size variation increased in the presence of predators, contrasting current models on relationship between foraging rates, growth, and cohort size variation in prey. The underlying mechanisms are unclear, but it is possible that reduced rates of movement limited access to food for some cohort members or that predation risk enhanced the expression of behavioral variation among individuals.
KeywordsInducible defense Inter-individual size difference Gape-constrained predators Non-lethal predator effects Tadpole
We thank Yoshihiro Natsuhara and the Ecology Group of Nagoya University for hosting the experiment. We thank Harisoa Rakotonoely for the laboratory assistance, Kosuke Nakanishi and Daiki Murakami for their help in collecting the subjects used in the study. We would like to thank the Associate Editor and the two referees for their constructive comments from which our paper has benefited greatly. The work was carried out under current laws and guidelines of Japan and Nagoya University, however no specific permit was required for the conducting the experiment.
The experiment was partly supported by the Ecological Society of Japan, Chubu division.
Conflict of interest
The authors declare that they have no conflict of interest.
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