Risk Assessment and Behavioral Choices of Larval Anurans (Lithobates Sphenocephalus)

Larval anurans assess risk and make behavioral choices to avoid predation. Since antipredator behaviors may reduce foraging opportunities, prey behavioral decisions can be constrained by a tradeoff between survival and growth. To improve our understanding of prey risk assessment, I asked whether L. sphenocephalus tadpoles make antipredator behavioral choices based on characteristics of predators such as their lethality, microhabitat use, or taxonomic group. To test this question, I ran an experiment in aquaria that included 13 treatments (6 predators x lethal/nonlethal plus a no-predator control), replicated eight times in a temporal block design. Three predators occupy benthic microhabitats (white crayfish, Pachydiplax dragonfly larvae, and pirate perch), and three occupy pelagic microhabitats (bluegill sunfish, broken-striped newt, and fishing spider). I made behavioral observations of each aquarium twice during each trial, and recorded the prey remaining at the end of each 20-hour trial. Prey antipredator behaviors differed when in the presence of predators from different microhabitats or different taxonomic groupings. When confronted with vertebrate predators (e.g., the fish and the newt) fewer proportions of tadpoles were outside of refuges. The predator microhabitat usage impacted activity levels of tadpoles, as significantly fewer tadpoles were active when presented with a pelagic predator. Species-specific reactions appeared to play a role as large numbers of tadpoles avoided the benthos when sharing habitat with the crayfish. The proportions of visible and moving tadpoles were different between observation periods, which indicates that tadpoles are able to progressively gauge whether the presence of a predator is a threat, since tadpoles increased their visibility and movement levels during the second observation period in nonlethal treatments. Predator lethality did not impact which antipredator behavior was chosen by the tadpole, but it did appear to affect the strength of the response. Predator characteristics such as microhabitat use, taxonomic affiliation, and lethality influence tadpoles as they determine the potential threat of predation and the appropriate behavioral response.M.S