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 have jointly modelled both 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 the probability of immobility and the conditional jump distance in 534 trials from 89 males across 17 Neotropical frog species (seven families), exposed to a simulated snake predator in three arenas of varying structural complexity. Physical contact with the predator (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-bodied species were substantially 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 lambda = 0.80 for jump distance; lambda = 0.71 for immobility), with phylogeny accounting for 69 to 75% of variance. Species' random effects formed a phylomorphospace in which fossorial species showed highest immobility and arboreal/torrent species favored active escape. Substantial individual-level variation in immobility tendency (25% of variance) provides a heritable substrate for ongoing selection. Frog antipredator strategies are jointly shaped by ecological context and evolutionary history; hurdle models offer a powerful framework for decomposing behavioral decisions.