Reefscapes of fear: predation risk and reef hetero‐geneity interact to shape herbivore foraging behaviour

Abstract

Predators can exert strong direct and indirect effects on ecological communities by intimidating their prey. The nature of predation risk effects is often context dependent, but in some ecosystems these contingencies are often overlooked. Risk effects are often not uniform across landscapes or among species. Indeed, they can vary widely across gradients of habitat complexity and with different prey escape tactics. These context dependencies may be especially important for ecosystems such as coral reefs that vary widely in habitat complexity and have species-rich predator and prey communities. With field experiments using predator decoys of the black grouper (Mycteroperca bonaci), we investigated how reef complexity interacts with predation risk to affect the foraging behaviour and herbivory rates of large herbivorous fishes (e.g. parrotfishes and surgeonfishes) across four coral reefs in the Florida Keys (USA). In both high and low complexity areas of the reef, we measured how herbivory changed with increasing distance from the predator decoy to examine how herbivorous fishes reconcile the conflicting demands of avoiding predation vs. foraging within a reefscape context. We show that with increasing risk, herbivorous fishes consumed dramatically less food (ca. 90%) but fed at a faster rate when they did feed (ca. 26%). Furthermore, we show that fishes foraging closest to the predator decoy were 40% smaller than those that foraged at further distances. Thus, smaller individuals showed muted response to predation risk compared to their larger counterparts, potentially due to their decreased risk to predation or lower reproductive value (i.e. the asset protection principle). Habitat heterogeneity mediated risk effects differently for different species of herbivores, with predation risk more strongly suppressing herbivore feeding in more complex areas and for individuals at higher risk of predation. Predators appear to create a reefscape of fear that changes the size structure of herbivores towards smaller individuals, increases individual feeding rates, but suppresses overall amounts of primary producers consumed, potentially altering patterns of herbivory, an ecosystem process critical for healthy coral reefs.

Context‐dependent landscape of fear: algal density elicits risky herbivory in a coral reef

“…These observations indicate that our resource patches offered diminishing returns to herbivores, and, thus, quitting harvest rates scaled linearly with our recorded metric of individual average bite rate (Appendix S4: Fig. Our findings both reinforce and contrast recent work in the Florida Keys: Catano et al (2016) observed depressed herbivory and higher individual bite rates by herbivores in riskier habitat, but also showed that risk increased with structural complexity of the habitat. Consequently, the more than two-fold (1.22 bites/s) increase in individual average bite rate we observed between our within-reef (2 m in from reef edge) patch and our furthest patch from the refuge habitat of the reef (30 m away) largely reflects higher costs of predation (i.e., higher perceived predation risk by herbivores).…”

“…S5). This latter distinction likely reflects predominant predator hunting modes, with ambush predators (grouper) in the Keys (Catano et al 2016) but chase predators (reef sharks) in Mo'orea (Mourier et al 2012, 2013, Brooks 2016, and suggests that the features that drive landscapes of fear in reef fishes depend on the composition of the predator assemblage. In addition, we observed a significant, albeit weak, trend toward larger fish total length with increased distance from refuge; this could reflect diminishing predation risk, as prey movement speed (and, thus, escape potential) can increase with body size (Bejan and Marden 2006).…”

Diel predator activity drives a dynamic landscape of fear

“…, Catano et al. ). It has also been argued that effective ecological restoration may depend on reestablishing landscapes of fear because fear may be as or more important than direct killing in structuring food webs and modifying ecosystem function (Manning et al.…”

Prozac in the water: Chronic fluoxetine exposure and predation risk interact to shape behaviors in an estuarine crab

“…In the presence of predators, prey will often modify their behaviors to balance the risk of mortality with the reward of accessing food, mates, or other resources (Catano et al., 2016; Sih, Cote, Evans, Fogarty, & Pruitt, 2012; Snell‐Rood, 2013). Prey may reduce their activity levels, utilize defenses, or seek refuge when they perceive the risk to be high (Lima & Dill, 1990; Lindberg, 1980).…”