Food, family and female age affect reproduction and pup survival of African wild dogs

It has long been recognized that superior carnivores can impact on the demography and ecology of smaller members of the guild, although exact mechanisms remain unclear. Here we use original data from a unique natural experiment to study some of the mechanisms by which African lions Panthera leo impact on African wild dogs Lycaon pictus. Using a study site where wild dogs outnumbered lions for several years prior to lion population recovery, we aimed to investigate whether or not, and by which means, wild dog populations are regulated and influenced by lions. We used 38 pack‐years of demographic and behavioural data across two 4‐year periods where lion density differed 20‐fold (pre‐lion era: 1996–1999 and lion era: 2010–2013) to assess how lions may affect wild dog pack size and age structure, litter size and pup survival (n = 329 pups), as well as den site selection (n = 46 dens). Pack size was significantly greater during the pre‐lion era. The pup to adult ratio was lower during the lion era and the change in pack composition was directly attributable to significantly greater lion‐induced pup mortality. We also demonstrate a behavioural shift, with locations selected for the vulnerable denning period being in more rugged terrain and in areas with lower prey densities during the lion era, as compared with the pre‐lion era. Lower adult recruitment into a population of an obligate cooperative breeder like the African wild dog can have complex consequences, including on feeding and defence of young, and mate finding.

Abstract: The conservation of wild dogs depends on the persistence of small populations because African wild dog ( Lycaon pictus ) populations are low in density, are limited by range loss, and are often restricted to parks containing fewer than 100 adults. Although major limiting factors for wild dog populations have been identified, including interspecific competition and diseases, such factors have not been translated into extinction risk. To assess wild dog extinction risks, we used individual‐based simulations constructed from data from a 6‐year field study in the Selous Game Reserve, Tanzania. Our simulations predicted that extinction risk for wild dogs was extremely sensitive to competition with lions. Extinction rates ( for periods as short as 20 years) rose sharply to near 1.0 when lion populations exceeded moderate densities (approximately 110–140 lions/1000 km 2 ). This prediction is remarkably consistent with, and highlights, ecological processes that may be responsible for recent patterns of extinction among wild dog populations. Infectious diseases that kill adults, such as rabies, also reduced population persistence if they increased mortality by ≥0.3 and occurred at average intervals of ≤10 years. In contrast, diseases killing only pups, such as canine parvovirus, had weaker effects on persistence. Although persistence declined sharply for mean litter sizes ≤6, persistence was unaffected by increasing mean litter size above its normal range (i.e., 8–12 in Selous). Increasing mean pack size from typical levels reduced extinction risk, but reproductive suppression may set an upper limit on pack size. Although the risk of extinction for 20‐ to 100‐year time frames was appreciable for many realistic ecological and demographic conditions, even low immigration rates substantially increased persistence probabilities. Active management to mitigate the effects of interspecific competition, facilitate dispersal among populations, or augment population size appears essential for wild dog conservation.

The reasons African wild dog (Lycaon pictus) populations declined to endangered status continent-wide have been difficult to document. However, demographic research to date indicates the following. Annual pack range size (150–3800 km2), density (2–35 dogs/1,000 km2), and territorial propensity of wild dogs appear related to prey density and temporal distribution, and habitat structure. Wild dogs usually live in packs of 10–14 composed of 1 or more adult females unrelated to 1 or more adult males, and their current or older offspring. Sex ratios of adults, yearlings, and pups usually are skewed toward males. Annually, usually 1 but sometimes 2 pack females breed and produce 8–12 pups each (up to 23 total); timing and frequency of parturition appears to coincide with prey abundance. Annual adult survival usually ranges from 0.65–0.85 and likely is most influenced by human-related mortality factors and disease (e.g., rabies and anthrax). Pup survival (0.1473x2013;0.73) appears to be influenced by number of adults in the pack and food availability. Dispersing wild dogs usually do so with same-sex siblings when 1.0–2.0 years old. Nutritional factors and perhaps natal pack composition likely affect the rates at which male or female wild dogs disperse. Dispersing groups join established packs or meet up with opposite sex groups and settle to establish new packs; dispersal distances may exceed 200 km. Observed annual finite rates of increase (k) for African wild dogs have ranged from 0.83–1.77, but potential rates may exceed 2.0. Reduced adult mortality, coupled with high pup survival and their subsequent dispersal as yearlings, can provide a mechanism by which populations decimated by catastrophic disease or human destruction can quickly rebuild if sufficient habitat is available. Collaborative ongoing research throughout a variety of habitats in Africa will facilitate examination of wild dog population dynamics, and provide information critical to conservation efforts.

South Africa is one of only seven countries with a viable population of African wild dogs (Lycaon pictus). The national population in 2017 was 372 adults and yearlings and comprised three subpopulations: 1) Kruger National Park (Kruger), 2) an intensively managed metapopulation established through reintroductions into isolated, fenced reserves, and 3) a free-roaming population that occurs naturally outside protected areas. We assessed the long-term (four wild dog generations, ∼20 years) trends in population size and growth rate within each of these three subpopulations. We found that Kruger supports a substantial population, which has declined over time. The metapopulation is the only subpopulation that has increased significantly over time (both in population size and number of packs), likely due to intensive conservation efforts and the reintroduction of wild dogs into 15 additional reserves since 1998. The free-roaming subpopulation has remained small but stable, even though the number of packs has declined due to anthropogenic threats. The overall national population has remained stable even though the number of packs has increased. Kruger has consistently supported the highest proportion of the national population over the last two decades. However, the contribution of the metapopulation has increased significantly over time. It is clear that despite differences in survey effort among the three subpopulations, South Africa has a small (∼500) but stable population of wild dogs, with the metapopulation contribution becoming increasingly important. The circumstances in the country necessitate, and demonstrate the benefit of, intensive, adaptive management for the national population of wild dogs. While this assessment provides baseline information for the three subpopulations, wild dog conservation in South Africa would benefit greatly from equal survey effort and standardized methods to accurately assess long-term population trends.

The local resource enhancement (LRE) model predicts that in cooperatively breeding species, sex ratios will be biased in favor of the more helpful sex. In this study, we assess the assumptions underlying the LRE model in a population of cooperatively breeding wild dogs (Lycaon pictus) in Northern Botswana monitored over a 15-year period. In this population, litter size and pup survival to 1 year are strongly affected by pack size and the breeding female’s age, but adult males have a stronger and more linear effect on females’ reproductive performance than do adult females. This asymmetry in the benefits derived from male and female helpers is reflected in male-biased sex ratios in litters at the time pups emerge from the den. Sex ratio biases are most pronounced in the litters of the youngest mothers who live in significantly smaller packs than older females. The presence of potential rivals for the dominant female’s position depresses pup production at the time of emergence, suggesting that competition among females for breeding positions may also contribute to the selective forces affecting birth sex ratios.

Although the massive organized slaughter of African wild dogs, Lycaon pictus, largely ended several decades ago, this endangered canid continues to decline and faces extinction. Several lines of evidence suggest that this arises from obligate cooperative breeding, which makes Lycaon more sensitive to anthropogenic mortality. A number of behaviours in this species are characterized by a reliance on helpers. These include cooperative hunting, defence from kleptoparasitism, pup feeding and baby‐sitting. As a result, there are strong, positive relationships between pack size and the production and survival of pups, and pairs of wild dogs are often unsuccessful at raising offspring without the assistance of helpers. Consequently, a pack in which membership drops below a critical size may be caught in a positive feedback loop: poor reproduction and low survival further reduce pack size, culminating in failure of the whole pack. Here, we review the literature to reveal the importance of pack size in the African wild dog. Most importantly, we argue that there is a critical minimum threshold, below which packs face an increasing probability of extinction ‐ an Allee effect with consequences for the conservation of this species, and of other obligate cooperators.

For cooperative breeders, we hypothesize that the effects of group size on reproduction and survival might run in opposition if the benefits of grouping cannot be shared without cost. We tested this hypothesis by examining relationships between group size, survival, and reproduction in African wild dogs (Lycaon pictus), cooperative hunters with highly cohesive packs within which reproduction is monopolized by the dominant male and female. The production and survival of pups are known to increase with increasing pack size, but the effect of pack size on adult survival has not been examined previously. Data from 366 individuals over a period of 6 years showed that the survival of adults decreased with increasing pack size, with a 25% difference between the largest and smallest packs after controlling for the effects of age, sex, social status, year of study, and pack identity. Several tests confirmed that undetected dispersal is unlikely to have produced this pattern. These results suggest that cooperative breeding in wild dogs cannot be fully explained by mutual direct benefit, thus reinforcing the prior inference that kin selection plays an important role in the evolution of their cooperation. The results also weaken support for the hypothesis that wild dogs are extinction prone due to group-level Allee effects. More broadly, the relationship of effects of group size on survival and reproduction might be predicted by considering whether cooperation yields benefits that accrue to all group members (e.g., through cooperative vigilance) or benefits that must be apportioned to individuals (e.g., through cooperative hunting).

Summary1. Infectious diseases seriously threaten the populations of many endangered mammals, including African wild dogsLycaon pictus. Extinction risks may be particularly high where the endangered host lives alongside a more abundant host species which can maintain infection with virulent pathogens. Domestic dogsCanis familiarisare often assumed to act as such ‘reservoir hosts’ for pathogens threatening wild dogs.2. We present the first empirical study of contact within and between populations of sympatric wild dogs and domestic dogs. We studied the densities and movement patterns of both species in a Kenyan rangeland, using Global Positioning System‐collars and conventional radiotelemetry.3. Wild dogs lived at low population densities, and direct encounters between packs were rare. In contrast, domestic dogs lived at higher densities and encountered one another more frequently. These differences suggest that directly transmitted virulent pathogens would be more likely to persist within populations of domestic dogs than within wild dog populations. However, wild dog populations alone might maintain pathogens that are indirectly transmitted through vectors or environmental persistence.4. The risk of contact between the two host species was limited by their behaviour: domestic dogs were associated with human settlements, which wild dogs avoided. Clustering of settlements, reflecting grazing traditions of local pastoralists, accentuated these patterns.5. We predict that, in this landscape, spillover of directly transmitted pathogens from domestic dogs to wild dogs might be infrequent and rarely followed by onward transmission to other wild dog packs. This may explain the recent growth of the local wild dog population despite sporadic cases of rabies.6. Synthesis and applications. In this study area, the behaviour of wild and domestic dogs, combined with local land use practices, appeared to limit interspecific disease transmission and hence promote the recovery of the African wild dog population. However, different patterns may occur elsewhere. Moreover, land use changes like those occurring in other African rangelands would undermine such conservation benefits.

African wild dogs (Lycaon pictus) are obligate cooperative breeders and are generally considered mono-oestrus. As such, the birth of two litters within the same year rarely occurs, except for when pups from the initial litter are lost soon after birth. We report on a rare occurrence where a wild dog female (Vee) produced three litters of pups within a 13-month, 2-week period from March 2015 to June 2016, with surviving pups from each litter. Data on breeding females from wild dog packs in the study area (Savé Valley Conservancy, Zimbabwe) were used to identify whether any predictor variables (e.g. environmental or pack dynamics) could have influenced this unusual occurrence. The period over which the high number of litters were born had high prey densities and there was some evidence that it was associated with lower temperatures. High impala (Aepyceros melampus) densities during 2015 was likely to have been advantageous for the packs' hunting behaviours, while lower temperatures have been shown to increase the percentage of the day that is cool enough for wild dogs to hunt. Pack size during this period was higher in the pack that produced multiple litters (by the same female) than for other packs in the study site, which supports existing evidence that larger packs are able to produce more pups. Our results suggest that either 1) under ideal environmental and social conditions African wild dog females are capable of producing multiple litters throughout the year or that 2) this occurrence was an anomaly unique to Vee and her physiology.

Compared to their main competitors, African wild dogs (Lycaon pictus) have inferior competitive abilities and interspecific competition is a serious fitness-limiting factor. Lions (Panthera leo) are the dominant large carnivore in African savannah ecosystems and wild dogs avoid them both spatially and temporally. Wild dog young are particularly vulnerable and suffer high rates of mortality from lions. Since lions do not utilize all parts of the landscape with an equal intensity, spatial variation in lion densities can be exploited by wild dogs both during their general ranging behaviour, but more specifically when they are confined to a den with vulnerable young. Since patches of rugged terrain are associated with lower lion densities, we hypothesized that these comparatively safe habitats should be selected by wild dogs for denning. We investigated the relationship between the distribution of 100 wild dog den sites and the occurrence of rugged terrain in four wild dog populations located in Tanzania, Zimbabwe and South Africa. A terrain ruggedness index was derived from a 90 m digital elevation model and used to map terrain ruggedness at each site. We compared characteristics of actual and potential (random) den sites to determine how wild dogs select den sites. The distributions of wild dog dens were strongly associated with rugged terrain and wild dogs actively selected terrain that was more rugged than that available on average. The likelihood of encountering lions is reduced in these habitats, minimizing the risk to both adults and pups. Our findings have important implications for the conservation management of the species, especially when assessing habitat suitability for potential reintroductions. The simple technique used to assess terrain ruggedness may be useful to investigate habitat suitability, and even predict highly suitable denning areas, across large landscapes.

Division of labour, in terms of providing for offspring, in obligate cooperatively breeding mammalian species is poorly understood. To understand offspring provisioning in a cooperatively breeding canid, we analysed a long-term dataset comprising 22 African wild dog, Lycaon pictus, denning events (nine packs over nine consecutive years). We investigated the effects of sex, age class, social status, and pack size on the likelihood and frequency of regurgitating food to pups at the den. We found that the interaction of social status and pack size affected the likelihood of regurgitation. Specifically, when in a large (≤15) pack, dominant individuals were less likely to regurgitate than subordinate individuals. However, in smaller (≤ 15) packs, dominant individuals were more likely to regurgitate than subordinate individuals. We also found that the interaction of age and pack size affected the frequency of regurgitation. Specifically, in large packs, yearlings regurgitated more frequently per observation period than adults. Contrastingly, in smaller packs, adults regurgitated more frequently. Sex did not affect pup provisioning. We suggest that these contrasting patterns of helping are best explained by a strong selection pressure for individual behaviour that results in larger pack sizes in this species. When in larger packs, costs are shared as the division of labour spreads amongst individuals. In smaller packs, a division of labour requires individuals that already experience costs (such as reproduction) to be further burdened by provisioning. Overall, our results support that the need for more helpers to care for offspring contributes to the evolutionary consequence of an inverse density dependence.

The relationship between pack size and two parameters of reproductive success (litter size at 7–8 months and pup weights at 5–6 months) were determined for two wolf (Canis lupus) populations in northern Minnesota. Pup weights were not correlated with pack size for either population. Litter size, however, was correlated with pack size, but the direction of the relationship varied between the two study populations. In the superior National Forest, where prey were scarce and the wolf population was declining from high densities, litter size and pack size were inversely related. Pairs produced more surviving pups than did larger packs with one or more potential helpers. In the Beltrami Island State Forest, where prey were relatively abundant and the wolf population was increasing, pack size and litter size were positively correlated. The results suggest that ecological factors, such as prey availability, affected the ability or willingness of various pack members to provide food or other care for the pups. The lack of correlation between number of auxiliaries and number of pups in canid populations with low and declining prey densities may be explained on the basis of heterogeneous prey density resulting in drastic annual variation in litter production. No study to date has measured the actual benefit that pups derive from helping by auxiliaries, and the costs and benefits of it. The relationships discussed herein can be considered valid only after such research is completed.

Cooperative breeding, a rare trait in <1% of mammals, is explored within African wild dog packs ( Lycaon pictus ), where alpha females typically produce the first litters, but subordinate females may also breed, resulting in second litters within the same pack. We investigated the reproductive dynamics of wild dog packs in Zimbabwe's Savé Valley Conservancy (SVC) using 14 years of data from 49 packs and 131 den sites, obtained through spoor tracking, radio telemetry, sighting reports and camera traps during denning periods. Among packs capable of multiple litters, 41.15% of breeding events produced multiple litters annually, with 24.86% of all litters from subordinate females, primarily litter sisters of the alpha. Generalized linear mixed models revealed that younger packs and those with more subordinate females were significantly more likely to produce multiple litters, indicating weaker dominance hierarchies. Within multiple litter packs, pup survival to 1 year was significantly higher for second‐born than first‐born litters. However, 2‐year survival significantly increased with higher pre‐emergence rainfall, older alpha females and higher maximum temperatures. Across both litter types, 1‐year and 2‐year pup survival significantly improved with larger packs, while 2‐year survival also significantly increased with pre‐emergence rainfall. Pups from single litters had significantly lower survival to 2 years compared to multiple litters. Despite the potential for reproductive conflict, we found low infanticide (2%) and moderate pup stealing or adoption (14%), suggesting that kin selection promotes reproductive tolerance. These findings highlight the social and ecological complexity of cooperative breeding and its conservation relevance.

African wild dogs (Lycaon pictus) are endangered, having disappeared from many areas where other large carnivore species have persisted. The relative vulnerability of this species has been attributed variously to its disproportionate exposure to anthropogenic threats, limitation by larger competing predators, and Allee effects caused by obligate cooperative breeding. The natural recovery of a wild dog population living on private and community land in northern Kenya provided an opportunity to investigate these potential constraints on population growth. Within a decade the population increased from near-extinction to become the 6th largest in the world. Rates and causes of mortality, and reproductive rates, were similar on community lands, where people and livestock were abundant but competing predators suppressed, and on commercial ranches, where human and livestock densities were lower but competitors more abundant. Larger packs produced larger litters, indicating a component Allee effect. However, because pack size was unrelated to population size, growth of the population was not impeded at low densities; that is, no demographic Allee effect was detectable. These results show that, despite earlier concerns, wild dogs can achieve rapid population recovery, even in a human-dominated landscape. This recovery was probably facilitated by local pastoralist traditions, which combine vigilant herding of livestock with little or no hunting of wild prey. This success might be replicated in other areas where traditional pastoralism is still practiced.

Communal hunting and pack size in African wild dogs, Lycaon pictus