Environmental controls on African herbivore responses to landscapes of fear

Abstract

Herbivores balance forage acquisition with the need to avoid predation, often leading to tradeoffs between forgoing resources to avoid areas of high predation risk, or tolerating increased risk in exchange for improved forage. The outcome of these decisions is likely to change with varying resource levels, with herbivores altering their response to predation risk across heterogeneous landscapes. Such contrasting responses will alter the strength of non‐consumptive predation effects, but are poorly understood in multiple‐predator/multiple‐prey systems. We combined fine‐scaled spatial information on two predator and 11 herbivore species with remotely‐sensed measurements of forage quantity and vegetation structure to assess variation in herbivore response to predation risk with changing environmental context, herbivore body size, herbivore foraging strategy (browsers versus grazers), predator type (ambush versus coursing hunters) and group size across a South African savanna landscape. Medium‐sized herbivore species were more likely to adjust their response to risk with a changing resource landscape: warthog, nyala and wildebeest tolerated increased long‐term predator encounter risk in exchange for abundant (warthog and nyala) or preferred (wildebeest) forage, and nyala selected areas with higher visibility only in landscapes where food was abundant. Impala were more likely to be observed in areas of high visibility where wild dog risk was high. In addition, although buffalo did not avoid areas of high lion encounter risk, large buffalo groups were more frequently observed in open areas where lion encounter risk was high, whereas small groups did not alter their space use across varying levels of risk. Our findings suggest that risk effects are not uniform across landscapes for medium‐sized herbivores and large buffalo groups, instead varying with environmental context and leading to a dynamic landscape of fear. However, responses among these and other prey species were variable and not consistent, highlighting the complexities inherent to multi‐predator/multi‐prey systems.

Integrating herbivore assemblages and woody plant cover in an African savanna to reveal how herbivores respond to ecosystem management

“…Furthermore, within habitats that span an intermediate woody plant cover range, we found multiple configurations within similar levels of woody plant cover (e.g., D2 and D3, D4 and D5). This likely results from somewhat different use of habitats by the species [ 32 , 46 , 51 ], implying that relatively small changes in woody plant cover may lead to a restructuring of the herbivore community [see 10 ].…”

“…To assess the abundance and habitat associations of the herbivores, we conducted standardized daily driving transects (20 or 40 km per day) during the wet (January–March, n = 33 days) and dry (July–September, n = 47 days) seasons of 2018, following the guidelines of Caro [ 30 ]. Such transects are a common approach to quantifying herbivore habitat use associations [ 8 , 30 – 32 ]. These transects were conducted from established dirt roads, which run through representative habitats within the study area, as per Caro [ 30 ].…”

Prey defence phenotype mediates multiple‐predator effects in tri‐trophic food webs

“…Thus, the ‘landscape of fear’ (Laundré et al, 2001) can become a useful framework for understanding multiple‐predator effects across space. However, Davies et al (2021) showed that prey response to predators in the landscape can be highly variable, highlighting the complexities of multi‐predator effects at broader scales. These authors showed that even though prey species tended to adjust their response to predation risk, risk effects were not uniform across landscapes, varying in response to changing resource availability.…”

“…Due to taxon‐specific differences in biomechanics, habitat use and foraging traits, appropriate functional responses should be chosen according to the organisms of interest (Dunn & Hovel, 2020), or different functional responses can be evaluated to determine the reliance of the model results on this particular feature (Vos et al, 2004). In addition, responses to predators can be strongly contingent on prey density, due to prey risk assessment (Guariento et al, 2015), or resource availability (Davies et al, 2021), which ultimately determines risk costs. Therefore, as an avenue for future research, we suggest treating costs as a function of prey density, or other environmental variables, and using more realistic functional responses that can better predict phenotype prevalence under specific scenarios, especially when the interaction among prey individuals is of interest.…”

Feedback loops between 3D vegetation structure and ecological functions of animals

“…Whether vegetation cover lends an advantage to predator or prey may therefore depend on the hunting mode of the predator and defense mechanisms of the prey. Animal behavioral traits, such as ambush versus cursorial predation and running escape versus hiding, influence how risk and reward are perceived in the context of a habitat's vegetation structure (Davies et al 2021).…”