Simon Thirgood’s research while affiliated with James Hutton Institute and other places

Wildebeest are abundant in Serengeti. Comparisons of specific attributes of wildebeest with other sympatric herbivores are necessary. Each section builds on the results of the previous sections to form a complete story that combines biology, behavior, and the geomorphology of the Serengeti ecosystem; it explains how a single species can outnumber all other species. Specific aspects of wildebeest diet and reproduction, combined with their capacity to move long distances in an ecosystem with a predictable nutrient gradient enables migrant wildebeest to escape regulation by predation or food quality, and this combination enables wildebeest to dominate the ecosystem beyond the capacity of any other competitor species. Wildebeest are super-abundant in Serengeti because the ecosystem closely matches their requirements.

Feedback between population density and demographic parameters often plays a determining role in population dynamics, and it is particularly important in managing exploited or harvested populations. The mountain hare Lepus timidus is a traditional game species, which is hunted in Scotland for sport and population control. However, information about how population parameters respond to changes in population density is lacking. To assess how reproduction and juvenile recruitment change in response to population density, we sampled 189 hares (88 females and 101 males) from 10 independent private hunting estates. We found a significant negative correlation between population density and the proportion of juveniles recruited into the breeding population, along with a significant interaction between population density and sex, which revealed that the proportion of juvenile females recruited decreases more rapidly with population density compared to the proportion of male juveniles. However, we found no evidence of density-dependent fecundity. Our results suggest density-dependent compensation in this species, acting on recruitment, not fecundity, with rates of juvenile recruitment differing between the sexes. We conclude that the significant correlation between population density and juvenile recruitment may provide harvested populations with the potential for compensatory juvenile recruitment, although harvesting rates need to be accurately estimated to avoid the risk of overharvesting.

Estimating density, age and sex structure of wild populations is a key objective in wildlife management. Live trapping is frequently used to collect data on populations of small and medium-sized mammals. Ideally, sampling mammal populations by live capturing of individuals provides a random and representative sample of the target population. Trapping data may, however, be biased. We used live-capture data from mountain hares Lepus timidus in Scotland to assess sampling bias between two different capture methods. We captured hares using baited cage traps and long nets on five study areas in the Scottish Highlands. After controlling for the effects of body size, individuals caught in traps were lighter than individuals caught using long nets, suggesting that the body condition of hares differed between the capture methods. This tendency may reflect an increased risk-taking of individuals in poorer body condition and less aversion to entering traps in order to benefit from eating bait. Overall, we caught more adult hares than juveniles and more female hares than males. Our results show that estimates of density and population structure of mountain hares using live-capture data could be affected by the capture method used. We suggest that live-capture studies employ more than one capture method and test for heterogeneity in capture probability to minimise potential bias and achieve reliable estimates of population parameters.

Context. The risk-disturbance hypothesis predicts that animals exhibit risk-avoidance behaviours when exposed to human disturbance because they perceive the disturbance as a predatory threat. Aims. This study aimed to examine whether Tibetan antelopes (Pantholops hodgsoni) exhibit risk-avoidance behaviour with proximity to a major highway and with increasing traffic flow consistent with the risk-disturbance hypothesis. Methods. Focal-animal sampling was used to observe the behaviour of Tibetan antelopes. The behaviours were categorised as foraging, vigilance, resting, moving, or other. The time, frequency, and duration of foraging and vigilance were calculated. Key results. As distance from the road increased, time spent foraging and foraging duration increased while foraging frequency, time spent being vigilant and vigilance frequency decreased, indicating that there is a risk perception associated with roads. Tibetan antelopes presented more risk-avoidance behaviours during high-traffic periods compared with low-traffic periods. Conclusions. Tibetan antelopes exhibited risk-avoidance behaviour towards roads that varied with proximity and traffic levels, which is consistent with the risk-disturbance hypothesis. Implications. The consequences of risk-avoidance behaviour should be reflected in wildlife management by considering human disturbance and road design.

Livestock grazing, which has a large influence on habitat structure, is associated with the widespread decline of various bird species across the world, yet there are few experimental studies that investigate how grazing pressure influences avian reproduction. We manipulated grazing pressure using a replicated field experiment, and found that the offspring sex ratio of a common upland passerine, the meadow pipit Anthus pratensis, varied significantly between grazing treatments. The proportion of sons was lowest in the ungrazed and intensively grazed treatments and highest in treatments grazed at low intensity (by sheep, or a mixture of sheep and cattle). This response was not related to maternal body condition. These results demonstrate the sensitivity of avian reproductive biology to variation in local conditions, and support growing evidence that too much grazing, or the complete removal of livestock from upland areas, is detrimental for common breeding birds.

There is a growing awareness that cyclic population dynamics in vertebrate species are driven by a complex set of interactions rather than a single causal factor. While theory suggests that direct host–parasite interactions may destabilise population dynamics, the interaction between host and parasite may also influence population dynamics through indirect effects that result in delayed responses to either density or to life-history traits. Using empirical data on mountain hares (Lepus timidus) infected with a nematode parasite (Trichostrongylus retortaeformis), we developed an individual-based model (IBM) that incorporated direct effects and delayed life-history effects (DLHEs) of a macroparasite, alternative transmission mechanisms and seasonality in host population dynamics. The full model describes mean characteristics of observed mountain hare time series and parasite abundance, but by systematically removing model structure we dissect out dynamic influences of DLHEs. The DLHEs were weakly destabilising, increasing the propensity for cyclic dynamics and suggesting DLHEs could be important processes in host–parasite systems. Further, by modifying model structure we identify a strong influence of parasite transmission mechanism on host population stability, and discuss the implications for parasite aggregation mechanisms, host movement and natural geographical variation in host population dynamics. The effect of T. retortaeformis on mountain hares likely forms part of a complex set of interactions that lead to population cycles.

In the Web Valley of the Bale Mountains National Park, the pastoral people suffer from livestock predation by wild carnivores. A total of 704 livestock were reported to be killed by wild carnivores over a 3-year period, causing a loss of potential revenue of 12 USD per year per household. Reported annual predation rates equated to 1.4% of the livestock population of the study area. Spotted hyaenas were responsible for most livestock predation (57%), followed by leopards (18%), common jackals (16%) and servals (9%). Hyaenas killed all livestock types (horses, donkeys, mules, cattle, goats and sheep) whilst leopards, common jackals and servals killed mostly goats and sheep. A survey of 362 households revealed that the pastoral people keep dogs to protect livestock from carnivores. During 250 nights of observation in the ten settlements, pastoralists were alerted to the presence of hyaenas on 80 occasions by the barking of their dogs. Such tradition of keeping dogs presents a threat to the persistence of the endangered Ethiopian wolf through diseases transmission. Given the frequency of carnivore attacks on livestock, it is desirable to develop alternative livestock protection methods that both minimize livestock losses and reduce the risk of disease transmission to Ethiopian wolves.