Resource abundance influences the fitness cost of antipredator responses.

Predation risk induces antipredator responses in prey which, if prolonged, can negatively affect their fitness. However, risk effects on prey traits and fitness are often modulated by other ecological factors, such as food resources. While few studies explicitly link antipredator responses with prey fitness, even fewer examine the influence of food resources on the strength and direction of nonconsumptive effects (NCEs). To understand the mechanistic underpinnings of NCEs and how resource abundance modulates them, we measured multiple antipredator responses and fitness in wild Indian spiny-tailed lizards Saara hardwickii in natural environments that varied in both predation risk and resource abundance. Specifically, we measured behavioral (flight initiation distance (FID), total hiding duration, and foraging range) and physiological (stress-induced glucocorticoid levels) responses of lizards in four patch types-(1) high risk-high resource, (2) high risk-low resource, (3) low risk-high resource, and (4) low risk-low resource. We also measured body condition (scaled mass index) and number of offspring for lizards inhabiting all four patch types. Using a structural equation modeling approach, we examined the mechanistic links between specific antipredator responses and prey fitness and tested whether these links were amenable to changes in resource levels. We found that predation risk affected behavioral, but not physiological, responses such that lizards in high-risk habitats had shorter FIDs and foraging ranges, and longer hiding durations. In resource-poor habitats, risk-induced changes in prey behavior adversely affected food intake, resulting in lower body condition and fewer offspring. By contrast, where resources were abundant, individuals in high-risk habitats maintained their food intake, with no negative effects on body condition and fitness. To maintain similar food intakes, individuals in low-risk-low-resource areas foraged for longer durations and distances compared to those in low-risk-high-resource areas. Overall, we show that while predation risk significantly influences prey traits, resource availability can determine the cost of these NCEs. By measuring multiple responses, our findings provide mechanistic insights into how habitat conditions can interact with the landscape of fear and give rise to variable fitness outcomes in heterogeneous environments.