Many prey have plastic defenses that they use only when at risk of predation, otherwise saving the costs of defense. In some contexts, these plastic responses and their costs can have surprisingly large consequences both for individuals later in life and for population dynamics. In other contexts the lethal effects of predation matter much more. This collaborative project focuses on predator-induced plasticity in hatching and metamorphosis, two ecologically pivotal events that exemplify the life-stage transitions common among animals. The focal species, red-eyed treefrogs, hatch early to escape egg predators, metamorphose early in response to tadpole predators, and delay metamorphosis in response to predators of froglets. The project uses mathematical models and field experiments integrated across these three life stages to assess how environmental context shapes the relative importance of plastic responses to risk and direct predation for both population dynamics and individual fitness.
This will advance understanding of population ecology, life history, and development, and strengthen links among these fields. It will directly support a postdoctoral researcher, 2-3 graduate students, and 6 undergraduate interns, and provide research opportunities for 15-20 more undergraduates. Students will gain cross-cultural experience and training in tropical field biology and ecology. Results will be broadly disseminated - the Principal Investigator's prior research has been widely reported in the popular media and in textbooks.
Predator-prey relationships are a fundamental part of ecology. Predators directly kill prey, but prey also change their behavior and development in response to predators. This project addressed the relative importance and context-dependence of direct predation and the responses of prey to predators for population processes and natural selection. Most species have complex life cycles, with distinct life stages. The timing of transitions between stages is critically important for survival and often altered in response to stage-specific risks and opportunities. This project focused on red-eyed treefrogs, a species that lays eggs in trees and has aquatic tadpoles. This frog can accelerate hatching to escape from egg predators, accelerate metamorphosis in response to aquatic predators of tadpoles, and delay metamorphosis in response to semiterrestrial predators of froglets. The investigators experimentally manipulated both the direct effects of predators (prey density and mortality) and their indirect effects (cues that elicit prey responses) across egg, tadpole, and froglet stages to assess their individual and interacting, cumulative effects in combination with other ecologically relevant variables. They developed mathematical models based on the results of short-term experiments that measured simple combinations of size- and density-dependent processes, then used these models in simulations that were able to accurately predict the outcomes of longer, more complex experiments across multiple life stages. The modeling framework provides innovative and broadly applicable quantitative methods for predicting predator effects on growing prey. Their work shows the importance of understanding how effects in early life stages alter fundamental ecological processes in later stages that occur in completely different habitats. The simulations and longer-term experimental results show that egg stage effects – both direct effects of egg predators and embryo responses to egg predators – can alter growth and survival in the aquatic larval stage and can continue to affect animals at metamorphosis. The experimentally validated modeling framework the investigators developed has broad relevance for understanding the relative importance of predator effects on prey abundance and on prey development and behavior for population-level processes by assessing their magnitude across key axes of environmental variation (e.g., resource availability and risk in particular stages). Furthermore, this work enhances our understanding of development by quantifying how the effects of early environments can persist to affect the characteristics of animals and their responses in later life stages, and to what extent this varies across ecological contexts. This project directly supported international collaborative research and training of 60 people from 12 different countries (USA, Canada, Denmark, the UK, Belize, Panama, Venezuela, Costa Rica, Columbia, Guatemala, Mexico and Argentina). Participants included the 2 PIs, 3 ROA collaborators, 4 postdoctoral associates, 10 graduate students, and 41 interns (8 Latin Americans, 31 US undergraduates, 5 US minorities). The project produced 9 undergraduate theses, 6 Masters theses and contributed to 2 completed PhD dissertations plus 2 more in progress. It generated 64 research presentations and a large and growing number of peer reviewed research publications (see below). Project related outreach activities in Panama and the United States engaged hundreds of students from K-12 through graduate programs and the work has been featured broadly in the popular media in the USA and internationally.
