Abstract
ABSTRACT In ectotherms, defensive responses to predators usually depend on cost-benefit relationships between death risk and the energy required to flee. In this study we investigate Amazonian lizards to test the hypothesis that the minimum predator approach distance (PAD) is influenced by temperature and camouflage. We test the hypothesis that PAD estimated for species with different thermoregulation modes respond differently to temperature and camouflage. We sampled 35 lizards of a heliotherm and a non-heliotherm species, for which we simulated a terrestrial visually oriented predator. Using a fixed-effects linear model, temperature positively affected PAD estimates, but the camouflage did not contribute to the model. Using a mixed linear model assuming thermoregulation mode as a random factor, camouflage negatively affected PAD estimates, independently of temperature. Our findings suggest that high exposure to predators in open habitats may be compensated by rapid fleeing optimized by high temperatures, and low fleeing performance, usually caused by relatively low temperatures in shaded habitats, may be compensated by camouflage. However, identifying the best PAD predictor greatly depended on accounting for thermoregulation mode in hypothesis testing, although the results obtained by both fixed and mixed-effects models may be relevant for conservation.
Highlights
Mortality rates are widely influenced by the distance to which prey allows the predator to approach, which in turn can be determined by cost-benefit relationships between death risk and the energy cost to flee (Ydenberg and Dill 1986)
The predator approach distance (PAD) estimates were significantly higher in C. lemniscatus (Figure 2a) compared to G. humeralis (KruskalWallis, X2 = 20.75, P < 0.0001), which was consistently captured by the fixed-effects multiple linear model (Figure 2b), showing that PAD is not random (r2 = 0.52, p < 0.001, standard error = 0.81), but positively related to substrate temperature (t = 5.84, p < 0.001)
The mixed linear model captured 80% of the variance in PAD conditioned by the thermoregulation mode, and showed a negative effect of camouflage on PAD
Summary
Mortality rates are widely influenced by the distance to which prey allows the predator to approach, which in turn can be determined by cost-benefit relationships between death risk and the energy cost to flee (Ydenberg and Dill 1986). The effects of temperature on ectotherms (e.g. metabolic activity, fitness) have been described as a continuous gradient from passive thermoconformity to metabolic regulation at approximate homeostasis (Fitzgerald et al 2003; Seebacher and Shine 2004) Proportions of this gradient that are occupied by a species depend on a combination of habitat thermal quality, cost-benefit of thermoregulation, and behavioral repertoires related to the optimization of heatsource use (Huey and Slatkin 1976; De Lanuza et al 2016). Non-heliotherms are nocturnal or occupy shaded habitats where direct sunlight rarely penetrates For these animals, the benefits of thermoregulation hardly compensate the energy cost of searching for heat sources, so they tend to select habitats regardless of thermal quality (Fitzgerald et al 2003)
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