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

Abstract

Foraging theory posits that isolation from refuge habitat within a landscape increases perceived predation risk and, thus, suppresses the foraging behavior of prey species. However, these effects may depend fundamentally on resource availability, which could affect prey boldness and can change considerably through bottom-up processes. We conducted a field survey and experiment in a coral reef to test the effects of isolation from refuge habitat (i.e., reef structure) on herbivory by reef fishes and whether these effects depend on resource density. By fitting continuous-time, pure death Markov processes to our data, we found that at both the local and landscape scale distance from refuge habitat reduced herbivory in attractive resource patches of palatable benthic algae. However, our field experiment revealed that higher initial resource densities weakened negative effects of distance from refuge habitat on herbivory. Furthermore, we observed higher bite rates and greater total lengths of herbivorous fishes with greater distance from refuge habitat-responses consistent with higher perceived predation risk. Our results suggest that while the loss or fragmentation of refuge habitat reduces consumer control of resources, greater resource densities can partially counteract this effect by altering landscapes of fear of consumer species. Our findings emphasize the importance of considering the spatial context of species interactions that structure communities.

Predators Shape Sedimentary Organic Carbon Storage in a Coral Reef Ecosystem

“…However, Ogden et al (1973) found that when the herbivore Diadema antillarum was removed from heavily fished patch reefs in the West Indies, seagrass grew right to the reef edge and previously well-developed halos disappeared. These results have led many to argue that although physical processes may aid in the formation and maintenance of halos around patch reefs, the main mechanism driving halo formation is grazing patterns of herbivores (Randall, 1965;Sweatman and Robertson, 1994;Price et al, 2010;Madin et al, 2011;Gil et al, 2017). This has led to halos surrounding patch reefs being called "grazing halos.…”

“…Trophic cascades can be initiated as a result of predators consuming prey, which in turn reduces the preys' effects on their food source (densitymediated trophic cascade), or non-consumptive effects where the prey alters its foraging behavior in an attempt to avoid predation (behaviorally-mediated trophic cascade; Ripple et al, 2016). Although not well tested, it is thought that anti-predator shifts in herbivore foraging behavior are one of the underlying mechanisms behind the concentration of grazing close to patch reefs, which ultimately leads to halo formation (Madin et al, 2016;Gil et al, 2017). This risk of predation can create a "seascape of fear, " whereby spatial variation in prey and primary producer biomass are inversely related as a function of predation risk levels across space (Brown and Kotler, 2004;Madin et al, 2010Madin et al, , 2011.…”

Deconstructing the landscape of fear in stable multi‐species societies

“…Assessments of predation risk can affect movement decisions (Turcotte and Desrochers ), foraging decisions (Gil et al. ) the tendency for animals to remain in groups (Rodríguez et al. ), and can ultimately influence reproductive success and overall fitness (McNamara and Dall , Zanette et al.…”

“…For example, migrating birds have been shown to use resident species to gather information about the environment for decisions on where to nest (Thomson et al 2003). Assessments of predation risk can affect movement decisions (Turcotte and Desrochers 2003), foraging decisions (Gil et al 2017) the tendency for animals to remain in groups (Rodr ıguez et al 2001), and can ultimately influence reproductive success and overall fitness (McNamara andDall 2010, Zanette et al 2011). Eavesdropping species change foraging habitat to riskier areas when a sentinel species is detected, presumably affecting overall foraging strategy and fitness of the eavesdropping species (Ridley et al 2014).…”

Spatially explicit modelling of kelp-grazer interactions: a seascape approach for effective habitat enhancement using artificial reefs

“…For example, predation risk for Mediterranean sea urchin Paracentrotus lividus and predator identity emerged as a function of the arrangement of seagrass patches (Farina et al, 2016). Aerial imagery in clear tropical water systems allowed to show that grazing pressure on macroalgae decreases with the distance from the nearest coral reef providing shelter to fish (Gil, Zill, & Ponciano, 2017; Madin, Madin, & Booth, 2011).…”