Changes in feeding behavior and patch use by herbivores in response to the introduction of a new predator

Top-order carnivores are naturally returning, or are being reintroduced, in a number of places where they have previously been extirpated. To explore how prey species adjust their antipredator behavior in response to these predators, we measured giving-up densities (GUDs) in experimental feeding patches and time spent vigilant for greater kudu (Tragelaphus strepsiceros), sable antelope (Hippotragus niger), and warthogs (Phacochoerus africanus) before and after an introduction of wild dogs (Lycaon pictus). Before the introduction, the only predators in the system were cheetahs (Acinonyx jubatus). After the release, none of the prey species changed their microhabitat preference, in that they all preferred open grasslands to mixed tree and bush-clumps and bush-clumps. However, kudu and sable fed more intensively (i.e., achieved lower GUDs) and had lower vigilance in open grasslands, while reducing their feeding effort (i.e., higher GUDs) and increasing their vigilance near denser vegetation. When the wild dogs denned in the study site, potentially increasing contact with the prey species, the time kudu spent vigilant and their GUDs increased significantly across all patches, and continued to increase over time. In contrast, sable and warthogs stopped feeding from the experimental patches altogether during this period. The change in feeding intensity and vigilance levels by kudu likely reflected an additive antipredator response to both cheetahs and wild dogs, whereas sable and warthogs only responded to the increased risk from the wild dogs. Our results indicate that the addition of wild dogs influenced the foraging-safety trade-off for the 3 prey species, but that the antipredator behaviors utilized by these species to mitigate predation risk varied within the newly established 2-predator system.The National Research Foundation (grant number 77582 to AMS), UKZN, GreenMatter, and the Tswalu Foundation.http://jmammal.oxfordjournals.org2019-04-03hj2018Mammal Research InstituteZoology and Entomolog

Do Changes in the Pace of Events Affect One-Off Judgments of Duration?

Five experiments examined whether changes in the pace of external events influence people’s judgments of duration. In Experiments 1a–1c, participants heard pieces of music whose tempo accelerated, decelerated, or remained constant. In Experiment 2, participants completed a visuo-motor task in which the rate of stimulus presentation accelerated, decelerated, or remained constant. In Experiment 3, participants completed a reading task in which facts appeared on-screen at accelerating, decelerating, or constant rates. In all experiments, the physical duration of the to-be-judged interval was the same across conditions. We found no significant effects of temporal structure on duration judgments in any of the experiments, either when participants knew that a time estimate would be required (prospective judgments) or when they did not (retrospective judgments). These results provide a starting point for the investigation of how temporal structure affects one-off judgments of duration like those typically made in natural settings

Selective predation and prey class behaviour as possible mechanisms explaining cheetah impacts on kudu demographics

A number of predator–prey studies show that certain prey demographic classes are targeted over others. The possible mechanisms driving these effects can be two-fold. Firstly, a preference for a certain demographic class results in selective predation by a predator. Secondly, different demographic classes exhibit varied behaviour and thus susceptibility to predation risk. To test these mechanisms, a study was conducted on Samara Private Game Reserve to investigate the potential impact cheetah (Acinonyx jubatus) predation has had on the kudu (Tragelaphus strepciseros) population. Kudu age and sex data were collected across both predator-present and predator-absent sections using a spotlight-count method. Results suggest that juvenile kudu and subadult male kudu are selectively hunted by cheetah. This was reflected in significantly lower proportions of these two demographic classes within the predator-present section (both 6.0%, respectively) compared with the predator-absent section (16.8% and 17.4%, respectively). These findings indicate that the shift in the demographics of the kudu population within Samara could be explained by a combination of these two mechanisms.Keywords: kudu demographics, population, prey preference, selective predatio

Alarm calls or predator calls : which elicit stronger responses in ungulate communities living with and without lions?

Alarm calls and predator vocalizations convey information on predator presence and potential risk. Generally, prey employ anti-predator behaviours more in response to alarm calls. However, occasionally prey respond more to the vocalizations of specific predators. A key question is do prey still respond to alarm calls and predator vocalizations when a dangerous predator is absent? Additionally, would the prey species’ response (e.g. vigilance) differ from prey already living with these predators? Using auditory playbacks, we tested whether four herbivore species living with lions responded more to alarm calls than lion vocalizations compared to a black cuckoo control call. Overall, red hartebeest, wildebeest and zebra had greater vigilance in response to the lion roars compared to the alarm calls. The differences in vigilance suggest that, despite the lion roars not being related to hunting, these herbivores perceived the predator vocalizations as a more immediate indicator of risk than the alarm calls. We then tested whether herbivores living with lions increased their vigilance more in response to the calls than conspecifics in a lion-free section. Despite greater overall vigilance in the lion section, gemsbok and zebra in the lion-free section significantly increased their vigilance in response to the lion roars. This indicates that species under the greatest threat from a predator (e.g. preferred prey) may maintain innate anti-predator responses to an absent but dangerous predator longer than less preferred prey. Ultimately, our results indicate that cues from dangerous predators can have greater effects on anti-predator behaviours than alarm calls for some prey species.Aresearch grant from the College of Agriculture, Engineering, and Science at UKZN awarded to DF Makin, an NRF Research Grant (77582) through AM Shrader, and funding through the Tswalu Foundation. DFM was also supported during this research through a personal grant awarded by GreenMatter.http://link.springer.com/journal/4422020-05-01hj2019Mammal Research InstituteZoology and Entomolog