Quantifying perceived risk in a small mesocarnivore, the bat-eared fox
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Date
2018-01
Authors
Welch, Rebecca Jane
Journal Title
Journal ISSN
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Publisher
University of the Free State (Qwaqwa Campus)
Abstract
The perceived risk of predation can induce anti-predator responses such as the spatial and
temporal avoidance of predators. However, such responses come with a level of cost that
can potentially have implications for fitness – described as ‘non-lethal effects’. While the
non-lethal effects of predators on herbivore prey are well investigated, the non-lethal impacts
of predators on mesopredators/mesocarnivores are less understood. Importantly, there is
reason to expect mesopredators’ anti-predator responses to be greater than those of
herbivores, considering that apex predators represent both predation risk and competition. In
this thesis, the effects of temporal, spatial, social and anthropogenic factors on the perceived
risk of a small mesopredator, the bat-eared fox (Otocyon megalotis), were explored using
both experimental and observational approaches. The anti-predator behaviours of this
species are virtually undescribed and as large predators, e.g. lions (Panthera leo) and
spotted hyaenas (Crocuta crocuta), were historically extirpated from the area, it was unclear
if anti-predator responses would have disappeared, or still remain. Using giving-up-density
(GUD) experiments, I demonstrated that bat-eared foxes experience greater perceived risk
in dark conditions and lower perceived risk in the presence of humans. Vigilance, however,
did not appear to vary with these same factors, suggesting that GUDs are capable of
detecting more subtle differences in perceived risk. Furthermore, by evaluating how bateared
foxes use high-cost vigilance (which interrupts other activities) and low-cost vigilance
(which occurs simultaneously with other activities), I demonstrated that fox vigilance
behaviour is dynamic. Vigilance was generally focused towards that of low-cost, with the
occasional use of high-cost vigilance under certain conditions. High-cost vigilance increased
with vegetation height, in the presence of adult conspecifics, and in winter. These effects
were most likely due to impeded lines of sight, higher levels of competition, and increased
social interactions respectively. My results suggest that in areas of low predation risk, mesopredators retain responses to certain cues of risk, but adapt behaviours to reduce the
associated costs, allowing more time to be allocated to other activities. Finally, I determine
that personality and plasticity was evident in this population of bat-eared foxes, varying
across lunar illumination, wind speed, and temperature. Interestingly, these patterns were
only distinct when vigilance was classified as high- and low-cost, and patterns were masked
when vigilance types were combined. Individual foxes demonstrated distinct strategies when
engaged in high-cost vigilance, where duration of vigilance did not fluctuate among
individuals but rate varied significantly. Comparatively, individuals consistently differed in
both bout duration and frequency of low-cost vigilance. I propose that the area’s low
predation pressure is unlikely to constrain individual variation in behaviours. Thus, individual
differences in high-cost vigilance may also be adaptive – in contrast to the ecological
hypothesis of Favreau et al. (2014), whereby individuals that experience similar ecological
conditions behave in a similar manner. Until this study, personality and plasticity in different
types of vigilance behaviours has never been demonstrated in mesopredators. Ultimately,
my research highlights that when predation pressure is extremely low, it is premature to
assume that anti-predator behaviours have been lost. Anti-predator behaviours may still
persist, and vary with spatiotemporal changes, in the presence of conspecifics, and amongst
individuals. Future research on mesopredator responses to perceived risk should consider
investigating different types of vigilance behaviour, as well as the inclusion of individual
differences. Combining vigilance types may mask biologically salient differences in
personality and plasticity, and distinct behavioural patterns may be undetectable without the
consideration of individual variation. Importantly, these differences may be crucial in
revealing information on the ecological constraints placed on populations.
Key terms: Giving up densities, Habituated foxes, High-cost vigilance, Individual variation,
Low-cost vigilance, Observer effects, Otocyon megalotis, Spatiotemporal effects.
Description
Keywords
Giving up densities, Habituated foxes, High-cost vigilance, Individual variation, Low-cost vigilance, Observer effects, Otocyon megalotis, Spatiotemporal effects, Thesis (D.Phil. (Zoology and Entomology))--University of the Free State, 2018