Predator stimulus and habitat structure jointly shape antipredator behavior in frog species

When encountering a predator, prey must choose between immobility and flight, a decision shaped by predator proximity, habitat structure, body size, and evolutionary history. Despite extensive work on optimal escape theory, few studies jointly model the decision to flee and the intensity of flight in a phylogenetic comparative framework. Here, we used a Bayesian phylogenetic hurdle log-normal model to analyze immobility probability and conditional jump distance in 534 trials from 89 males of 17 Neotropical frog species (seven families), exposed to a simulated snake in three arenas of varying structural complexity. Physical contact (touch) was the strongest predictor, reducing immobility probability from 94% to 15% and increasing jump distance by 26%. Habitat complexity increased immobility (bush > leaf litter > empty), and frogs in open arenas jumped 31% farther. Larger species were much more likely to remain immobile but did not jump farther, indicating that body size determines strategy choice rather than locomotor magnitude. Phylogenetic signal was strong for both components (Pagel's λ = 0.80 for jump distance; λ = 0.71 for immobility), with phylogeny accounting for 69–71% of variance. Species’ random effects formed a phylomorphospace in which fossorial species showed highest immobility and arboreal and torrent species favored active escape. Substantial individual variation in immobility tendency (30% of variance) provides a heritable substrate for selection. In this Atlantic Forest assemblage, frog antipredator strategies were jointly shaped by ecological context and evolutionary history, and hurdle models offer a powerful framework for decomposing behavioral decisions into their strategic and kinematic components.