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Large herbivores are in decline in much of the world, including sub-Saharan Africa, and true apex carnivores like the lion (Panthera leo) decline in parallel with their prey. As a consequence, competitively subordinate carnivores like the African wild dog (Lycaon pictus) are simultaneously experiencing a costly reduction in resources and a beneficial reduction in dominant competitors. The net effect is not intuitively obvious, but wild dogs’ density, survival, and reproduction are all low in areas that are strongly affected by prey depletion. To assess whether these correlations are causal, we tested the hypothesized mechanism, using data from 13 wild dog packs in two ecosystems to relate the energetic costs and benefits of hunting to variation in prey density, while controlling for the effects of local lion density, pack size, the number of dependent pups, and the level of protection. All of these variables affected the energetic costs and benefits of hunting. In areas with low prey density, the magnitude of movements and vectorial dynamic body acceleration (a measure of energy expenditure) both increased, the mass of killed prey decreased, and the number of kills per day did not change detectably. Programs to reduce or reverse the decline of large herbivore populations should be an effective means of improving the status of endangered subordinate competitors like the wild dog, and should be a high priority. Our results demonstrate the utility of research that integrates data from biomonitoring with direct, long-term observation of endangered species, their competitors, and their resources. 

Introduction: Predators can affect prey not only by killing them, but also by causing them to alter their behavior, including patterns of habitat selection. Prey can reduce the risk of predation by moving to habitats where predators are less likely to detect them, less likely to attack, or less likely to succeed. The interaction of such responses to risk with other ecological processes remains relatively unstudied, but in some cases, changes in habitat use to avoid predation may be constrained by competition: larger, dominant competitors should respond freely to predation risk, but the responses of smaller, subordinate competitors may be constrained by the responses of dominant competitors. For large grazing herbivores, an alternative hypothesis proposes that smaller prey species are vulnerable to more predators, and thus should respond more strongly to predation risk. Methods: Here, we tested these two hypotheses with 775 observations of habitat selection by four species of obligate grazers (zebra, wildebeest, puku and oribi) in the immediate presence or absence of four large carnivores (lion, spotted hyena, African wild dog and cheetah) in three ecosystems (Greater Liuwa, Greater Kafue and Luangwa Valley). Patterns of predation within this set were described by observation of 1,105 kills. Results:Our results support the hypothesis that responses to predation risk are strongest for larger, dominant competitors. Even though zebras were killed least often, they showed the strongest shift into cover when carnivores were present. Wildebeest, puku and oribi showed weaker habitat shifts, even though they were more frequently killed. These patterns remained consistent in models that controlled for differences in the hunting mode of the predator (stalking, coursing, or intermediate) and for differences among ecosystems. There was no evidence that smaller species were subject to predation by a broader set of predators. Instead, smaller prey were killed often by smaller predators, and larger prey were killed often by larger predators. Discussion: Broadly, our results show that responses to predation risk interact with interspecific competition. Accounting for such interactions should help to explain the considerable variation in the strength of responses to predation risk that has been observed. 

Abstract 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. 

Abstract Large carnivores such as the lion are declining across Africa, in part because their large herbivore prey is declining. There is consensus that increased protection from prey depletion will be necessary to reverse the decline of lion populations, but few studies have tested whether increased protection is sufficient to reverse the decline, particularly in the large, open ecosystems where most lions remain. Here, we used an integrated population model to test whether lion demography and population dynamics were measurably improved by increased protection. We used data from monitoring of 358 individuals from 2013 to 2021 in the Greater Kafue Ecosystem, where prior research showed that lions were strongly limited by prey depletion, but protection increased in several well‐defined areas beginning in 2018. In some other areas, protection decreased. In areas with high protection, lion fecundity was 29% higher, and mean annual apparent survival (φ) was 8.3% higher (with a minimum difference of 6.0% for prime‐aged adult females and a maximum difference of 11.9% for sub‐adult males). These demographic benefits combined to produce likely population growth in areas with high protection ( = 1.085, 90% CI = 0.97, 1.21), despite likely population decline in areas with low protection ( = 0.970, 90% CI = 0.88, 1.07). For the ecosystem as a whole, population size remained relatively constant at a moderate density of 3.74 (±0.49 SD) to 4.13 (±0.52 SD) lions/100 km². With the growth observed in areas with high protection, the expected doubling time was 10 years. Despite this, recovery at the scale of the entire ecosystem is likely to be slow without increased protection; the current growth rate would require 50 years to double. Our results demonstrate that increased protection is likely to improve the reproduction and population growth rate of lions at a large scale within an unfenced ecosystem that has been greatly affected by poaching.