African wild dog movements show contrasting responses to long and short term risk of encountering lions: analysis using dynamic Brownian bridge movement models

Background Prey depletion is a threat to the world's large carnivores, and is likely to affect subordinate competitors within the large carnivore guild disproportionately. African lions limit African wild dog populations through interference competition and intraguild predation. When lion density is reduced as a result of prey depletion, wild dogs are not competitively released, and their population density remains low. Research examining distributions has demonstrated spatial avoidance of lions by wild dogs, but the effects of lions on patterns of movement have not been tested. Movement is one of the most energetically costly activities for many species and is particularly costly for cursorial hunters like wild dogs. Therefore, testing how top-down, bottom-up, and anthropogenic variables affect movement patterns can provide insight into mechanisms that limit wild dogs (and other subordinate competitors) in resource-depleted ecosystems. Methods We measured movement rates using the motion variance from dynamic Brownian Bridge Movement Models (dBBMMs) fit to data from GPS-collared wild dogs, then used a generalized linear model to test for effects on movement of predation risk from lions, predictors of prey density, and anthropogenic and seasonal variables. Results Wild dogs proactively reduced movement in areas with high lion density, but reactively increased movement when lions were immediately nearby. Predictors of prey density had consistently weaker effects on movement than lions did, but movements were reduced in the wet season and when dependent offspring were present. Conclusion Wild dogs alter their patterns of movement in response to lions in ways that are likely to have important energetic consequences. Our results support the recent suggestion that competitive limitation of wild dogs by lions remains strong in ecosystems where lion and wild dog densities are both low as a result of anthropogenic prey depletion. Our results reinforce an emerging pattern that movements often show contrasting responses to long-term and short-term variation in predation risk

Leopard Panthera pardus density and survival in an ecosystem with depressed abundance of prey and dominant competitors

The leopard Panthera pardus is in range-wide decline, and many populations are highly threatened. Prey depletion is a major cause of global carnivore declines, but the response of leopard survival and density to this threat is unclear: by reducing the density of a dominant competitor (the lion Panthera leo) prey depletion could create both costs and benefits for subordinate competitors. We used capture-recapture models fitted to data from a 7-year camera-trap study in Kafue National Park, Zambia, to obtain baseline estimates of leopard population density and sex-specific apparent survival rates. Kafue is affected by prey depletion, and densities of large herbivores preferred by lions have declined more than the densities of smaller herbivores preferred by leopards. Lion density is consequently low. Estimates of leopard density were comparable to ecosystems with more intensive protection and favourable prey densities. However, our study site is located in an area with good ecological conditions and high levels of protection relative to other portions of the ecosystem, so extrapolating our estimates across the Park or into adjacent Game Management Areas would not be valid. Our results show that leopard density and survival within north-central Kafue remain good despite prey depletion, perhaps because (1) prey depletion has had weaker effects on preferred leopard prey compared to larger prey preferred by lions, and (2) the density of dominant competitors is consequently low. Our results show that the effects of prey depletion can be more complex than uniform decline of all large carnivore species, and warrant further investigation

Testing the effects of anthropogenic pressures on a diverse African herbivore community

Large herbivore communities around the world have declined steeply in recent decades. Although excessive bushmeat harvesting is thought to be the primary cause of herbivore declines in many ecosystems, the direct effects of anthropogenic pressures on large herbivore populations remain poorly described in most of the systems experiencing decline. To test the extent to which large herbivores are impacted by ecological and anthropogenic factors in a protected area (PA) thought to be experiencing human-caused decline, we fit distance sampling models to seven years of data from systematic ground-based surveys in Kafue National Park (KNP) to estimate the population densities and distributions of 10 species of large herbivores, and to test what factors affect these parameters. Population densities of the ten most abundant large herbivores in KNP were substantially lower than those reported for an ecologically similar PA with less poaching pressure. Low densities were consistent across species and areas, though there was ecologically important variation among species and size classes. Densities of larger-bodied herbivores were greatly depressed relative to smaller species. This pattern has direct and indirect effects on large carnivore populations, with broad implications for the ecotourism and trophy hunting industries. Statistically and methodologically rigorous methods to test the effects of anthropogenic and environmental variables on density and distribution exist, but are rarely applied to large herbivores. To quantify trends in herbivore populations and evaluate the effectiveness of conservation actions, our results show that distance sampling with stratified ground-based monitoring is an efficient and effective method. In the Greater Kafue Ecosystem (GKE), continued increases in resource protection are needed to facilitate the recovery of an economically and ecologically important large herbivore guild. More broadly, our results confirm that anthropogenic effects on large herbivore distribution and abundance can be strong over wide areas for all species (particularly the larger members of the guild), even in very large PAs

Data from: Changes in African large carnivore diets over the past half-century reveal the loss of large prey

1. Globally, large carnivores are declining due to direct persecution, habitat loss and prey depletion. The effects of prey depletion could be amplified by changes in the composition of the herbivore (prey) community that provoke changes in carnivore diets, but this possibility has received little attention. 2. Here, we tested for changes over the past half century in prey selection by the large carnivore guild in Zambia’s Kafue National Park. 3. Across 52 predator-prey dyads, 71% of the changes we observed were consistent with the hypothesis that large prey have become less important and small prey have become more important. Dietary niche breadth has decreased for KNP carnivores, and niche overlap has consequently increased. 4. We tested whether changes in the importance of prey species are related to their current abundance, and uniformly found that prey that have increased in importance are now relatively common, while those that have decreased in importance are now relatively rare. 5. We identify four potential effects of these changes for conservation (through potential effects on intra-guild competition, group size, the energetics of hunting and vulnerability to snaring) that warrant investigation. Synthesis and applications: Patterns of prey selection by the large carnivores in Kafue National Park have changed appreciably over the past half century. Decreased predation on large prey, which are now relatively rare, has caused niche compression and increased the overlap in carnivore diets. Predation by all of the large carnivores in the ecosystem now concentrates on four small prey species that remain relatively abundant (impala, puku, lechwe and warthog). Methods to detect the changes in predator-prey relationships we observed are well-established, but are rarely applied to large carnivore-ungulate systems. To guide conservation of ecosystem function, monitoring programs should be designed to consider whether prey depletion alters patterns of predation or competition within the predator guild, because these interactions have well-established effects on the distribution and abundance of both predators and prey. If the patterns seen in Kafue prove to be general, then where carnivores are limited by prey depletion, conservation efforts will be most effective if they focus particularly on mitigating the loss of large prey. In Kafue, targeted efforts to protect prey larger than 200 kilograms, particularly buffalo, should be a priority.13-Jun-201