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Data from: Environmental controls on African herbivore responses to landscapes of fear

Citation

Davies, Andrew et al. (2022), Data from: Environmental controls on African herbivore responses to landscapes of fear, Dryad, Dataset, https://doi.org/10.5061/dryad.kprr4xh3g

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.

Methods

From 12 July to 18 September 2014, which is the late dry season in HiP, groups of two trained observers (one field ranger paired with a volunteer) walked 30 line transects ranging in length from 2 to 11 km, for a total of 232 km, and recorded the locations and group sizes of all herbivores encountered with the use of binoculars, a GPS unit, compass and Bushnell Yardage Pro 1000 range finder. The field ranger was largely responsible for the observations, while the volunteer recorded them into the database. This census is performed biennially in HiP and is highly standardized across years and between transects, making consistent observer bias highly unlikely. The bearing of, and distance to, each sighting (using herd centres when groups were encountered) were recorded to calculate the location of each observation relative to the transect line. In cases where animals moved after they had been sighted, observations were recorded where the animal (or herd) was first seen. If an animal (or herd) was not initially observed, but rather disturbed by the observers and then seen running off, it was not recorded. Effects of detectability and distance on group counts were accounted for using Distance software. Each transect was walked between five and thirteen times over the course of the survey, yielding a total survey distance of 2715 km. To avoid potential detection bias across different habitat types and vegetation densities, the datasets only include the observations recorded within 100 m of the observer (number of observations per species: red duiker = 52, grey duiker = 105, impala = 266, nyala = 287, kudu = 41, giraffe = 59, warthog = 101, wildebeest = 37, zebra = 82, buffalo = 145 and white rhinoceros = 326). Transects were evenly distributed throughout the park, apart from the access-limited, south-western wilderness area that excluded from the study due to no available lion spatial data, encompassing all main vegetation types and variability in rainfall and elevation. An equal number of random points, matching the maximum number of observations for any one herbivore species (i.e. 326), were generated within 100 m buffers around the surveyed transects to represent available habitat.

Usage Notes

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Funding

Andrew W. Mellon Foundation, Award: 41300627-GA

Avatar Alliance Foundation