Friends because of foes: the interplay between space use and sociality in mediating predation risk

From the perspective of prey, movement synchrony can represent either a potent anti-predator strategy or a dangerous liability. Prey must balance the costs and benefits of using conspecifics to mediate risk and the emergent patterns of risk-driven sociality depends on the spatial variation and trait composition of the system. Our literature review outlined the prevailing, but not universal, trend of animals using sociality as an antipredator strategy. Empirically, we then used movement synchrony as a measure of social antipredator response of two ungulates to spatial variation in predator and prey habitat domains. We demonstrated that these responses vary based on prey vulnerability and predator hunting modes. Prey favored asynchrony when calves were present and within habitat domains of ambush predators but not pursuit predators. By unifying community ecology concepts such as habitat domains with movement ecology we provided a comprehensive evaluation of factors mediating prey social response to predation risk.

Behavioral adjustments to prior predation experience and food deprivation of a common cyprinid fish species vary between singletons and a group

Fish often undergo predation stress and food shortages in nature, and living in groups may provide the ecological benefits of decreased predator risk but the costs of increased food competition. The main aim of the present study was to test whether the behavioral response of qingbo (Spinibarbus sinensis) to predators and/or starvation differed between a singleton and a group. We measured the locomotor activity and distance to a predator and/or food item of prior predator-experienced, starved, double-treated and control qingbo; the qingbo were tested both as singletons and in a group (five individuals). Fish from all groups showed increased activity when tested collectively compared to individually. The predator-experienced fish showed decreased locomotor activity to predators as an antipredator strategy when tested as singletons; however, increased locomotor activity occurred when tested in a group, which might be partially due to the decreased predator risk when living in a group and thus higher levels of boldness. As expected, starvation elicited increased activity indicating increased foraging willingness when tested in a group; however, the difference between starved and normal-fed fish was no longer significant when they were tested as singletons, possibly due to the increased predation risk and decreased food competition when living individually and higher behavioral variation among individual fish than among those in a shoal. Compared with the control fish, the double-treated fish showed no difference in activity when tested both individually and collectively (except a slower speed when tested in a group). The reason for the results from the singletons might be an offset of the effect of predator exposure and starvation. The reason for this difference in the group might be due to the impaired body condition indicated by a slower swimming speed as a consequence of severe stress. The present study demonstrated that behavioral adjustment was closely related to the size of the group, which might be due to differences in the predation risk and food competition.

Behavioural Plasticity by Eastern Grey Kangaroos in Response to Human Behaviour

Sharing landscapes with humans is an increasingly fraught challenge for wildlife across the globe. While some species benefit from humans by exploiting novel opportunities (e.g., provision of resources or removal of competitors or predators), many wildlife experience harmful effects, either directly through persecution or indirectly through loss of habitat. Consequently, some species have been shown to be attracted to human presence while others avoid us. For any given population of a single species, though, the question of whether they can recognise and change their response to human presence depending on the type of human actions (i.e., either positive or negative) has received little attention to date. In this study, we chose to examine the behavioural plasticity within a single population of eastern grey kangaroos (Macropus giganteus) to both positive and negative human activity. Within a relatively small and contiguous landscape, we identified areas where kangaroos experience a combination of either low and high frequencies of benign and harmful human disturbances. From six sampling sessions over five months, we found that density and group sizes were higher where humans acted benignly towards them, and that these groups had higher representations of sub-adults and juveniles than where humans had harmful intentions. Importantly, we found that the vital antipredator strategy of increasing group size with distance from cover was not detectable at sites with low and high levels of harm. Our findings suggest that these kangaroos are recognising and adjusting their behavioural response to humans at fine spatial scales, a plasticity trait that may be key to the survival of these species in human dominated landscapes.

Antipredator behaviour of old-world tropical lizard, common agama Agama agama, in an urban environment

Escape behaviour is a common antipredator strategy of lizards. Here, we studied the effect of several variables predicted to have a potential effect on escape behaviour of lizards. Specifically, we measured the effects of starting distance (SD), distance to cover, sex–age and the observer’s head orientation on flight initiation distance (FID) in the common agama Agama agama. Agamas were approached in urban localities in Limbe city, Cameroon, where they were habituated to the presence of humans. We found no association between FID and SD, but individuals closer to potential cover had shorter FID than individuals farther from a refuge. Juveniles escaped later than adults, but no significant differences were found in the FID between adult males and females. Head direction of the approaching observer had no effect on FID. This is, to the best of our knowledge, the first study investigating factors affecting FID in common agamas, extending our knowledge of risk-related behaviour in lizards of the Old World tropics.

Transparency reduces predator detection in chemically protected clearwing butterflies

Abstract1. Predation is an important selective pressure and some prey have evolved warning colour signals advertising unpalatability (i.e. aposematism) as an antipredator strategy. Unexpectedly, some butterfly species from the unpalatable tribe Ithomiini possess transparent wings, an adaptation rare on land but common in water where it helps avoiding predator detection.2. We tested if transparency of butterfly wings was associated with decreased detectability by predators, by comparing four butterfly species exhibiting different degrees of transparency, ranging from fully opaque to largely transparent. We tested our prediction using using both wild birds and humans in behavioural experiments. Vision modelling predicted detectability to be similar for these two predator types.3. In concordance with predictions, more transparent species were almost never the first detected items and were detected less often than the opaque species by both birds and humans, suggesting that transparency enhances crypsis. However, humans could learn to better detect the most transparent species over time. Our study demonstrates for the first time that transparency on land likely decreases detectability by visual predators.