The relative role of intrinsic and extrinsic drivers in regulating population change and survival of African wild dogs (Lycaon pictus)

DATA AVAILABILITY : The datasets generated during and/or analysed during the current study are available in the figshare repository https://doi.org/10.6084/m9.figshare.14368043.v1.CODE AVAILABILITY : The code generated during and/or analysed during the current study are available in the figshare repository https://doi.org/10.6084/m9.figshare.14368043.v1.Evaluating how intrinsic (intraspecific density), extrinsic (interspecific density and prey density) and anthropogenic (management intervention) factors affect African wild dog (Lycaon pictus) population performance is key to implementing effective conservation strategies. Lions (Panthera leo) can affect wild dog populations, and in small and highly managed protected areas, populations of wild dogs and lions often co-occur at high densities. It is unknown what mediates these co-occurring high densities and how trophic interactions facilitate the persistence of wild dogs in areas with high lion densities. In this study, we modelled how intrinsic and extrinsic factors affected population change and survival of 590 individually identifiable wild dogs in Hluhluwe–iMfolozi Park (HiP), South Africa, an area with high lion density. The wild dog population in HiP grew significantly and comprised one of the highest population densities and the largest pack sizes in Africa. Pup survival rate was also the highest known in Africa, and the median individual survival was 29 months. During low lion density periods, the rate of wild dog population change increased despite low prey density, while at higher lion density, the rate of population change decreased only when prey density decreased. Survival for all age classes increased as population density increased, suggesting there is an important density-dependent effect on survival for all age classes that manifests at the population level. While increasing lion density had negative effects on adult and yearling survival, it did not affect pup survival. Our results suggest that both intrinsic and extrinsic drivers regulated the HiP wild dog population. Importantly, populations of wild dogs in small (~ 900 km2), fenced protected areas are highly adaptable and can co-exist at high levels of interspecific competition over many generations as long as there is an intact and abundant prey base.The National Research Foundation of South Africa Scarce Skills Development Fund; the Rufford Small Grants Foundation; the Endangered Wildlife Trust (South Africa); the Wildlife ACT Fund (South Africa) and the Claude Leon Foundation.https://link.springer.com/journal/429912023-09-06hj2023Mammal Research InstituteZoology and Entomolog

Fence management and time since pack formation influence African wild dog escapes from protected areas in South Africa

In human-dominated and highly fragmented landscapes, keeping wildlife within reserve boundaries is vital for conservation success. In South Africa, fences are a widely employed conservation management tool for protected areas and are successful in mitigating human-wildlife conflict. However, fences are permeable, and predators are able to cross through reserve fences. African wild dogs (Lycaon pictus) often leave fenced boundaries, resulting in high capture and translocation costs. Moreover, when wild dog packs (up to 30 individuals) leave fenced reserves they enter human-dominated landscapes where they face strong persecution and livestock predation incurs high costs. The factors driving packs to leave managed reserves are poorly understood, thus, to effectively manage wild dogs in fenced systems, it is important to understand why they leave reserve boundaries. There are several hypotheses as to why wild dogs cross through reserve fences, including inter- and intra-specific competition, social behaviour, management, prey density and environmental variability. Using a long-term dataset comprising 32 resident packs across five reserves, we investigated the relative strength of these hypotheses on the probability of wild dogs exiting a fenced reserve. During the 14-year study period, we recorded 154 exit events. We found that the interaction of fence integrity and time since pack formation were the primary factors affecting the probability of a pack leaving a reserve. When fence integrity was poor, escape probability decreased with pack age likely due to the exploratory behaviour of new packs. When fence integrity was average, escape probability increased with pack age likely due to the fitness benefits of holding larger and more exclusive territories as packs age. When fence integrity was good, the probability of a pack escaping was very low (only 1% occurrence). The implications of this research suggest that the primary management consideration for reducing wild dog escapes from fenced reserves should be maintaining adequate reserve-wide fence integrity, rather than focusing on social structure or drivers of inter- and intra-specific competition

Top–down limits on prey populations may be more severe in larger prey species, despite having fewer predators

Variation in the vulnerability of herbivore prey to predation is linked to body size, yet whether this relationship is size‐nested or size‐partitioned remains debated. If size‐partitioned, predators would be focused on prey within their preferred prey size range. If size‐nested, smaller prey species should become increasingly more vulnerable because increasingly more predators are capable of catching them. Yet, whether either of these strategies manifests in top–down prey population limitation would depend both on the number of potential predator species as well as the total mortality imposed. Here we use a rare ecosystem scale ‘natural experiment’ comparing prey population dynamics between a period of intense predator persecution and hence low predator densities and a period of active predator protection and population recovery. We use three decades of data on herbivore abundance and distribution to test the role of predation as a mechanism of population limitation among prey species that vary widely in body size. Notably, we test this within one of the few remaining systems where a near‐full suite of megaherbivores occur in high density and are thus able to include a thirtyfold range in herbivore body size gradient. We test whether top–down limitation on prey species of particular body size leads to compositional shifts in the mammalian herbivore community. Our results support both size‐nested and size‐partitioning predation but suggest that the relative top–down limiting impact on prey populations may be more severe for intermediate sized species, despite having fewer predators than small species. In addition we show that the gradual recovery of predator populations shifted the herbivore community assemblage towards large‐bodied species and has led to a community that is strongly dominated by large herbivore biomass.The Earthwatch Institute, Ezemvelo KwaZulu-Natal Wildlife and a Marie Curie Grant held by JC (grant # PCIG10-GA-2011-304128). ElR was supported by the South African National Research Foundation, Nelson Mandela Univ. and the Claude Leon Foundation.http://www.ecography.org2020-06-01hj2019Centre for Wildlife Managemen

Environmental controls on African herbivore responses to landscapes of fear

Herbivores balance forage acquisition with the need to avoid predation, often leading to tradeoffs between forgoing resources to avoid areas of high predation risk, or tolerating increased risk in exchange for improved forage. The outcome of these decisions is likely to change with varying resource levels, with herbivores altering their response to predation risk across heterogeneous landscapes. Such contrasting responses will alter the strength of non-consumptive predation effects, but are poorly understood in multiple-predator/multiple-prey systems. We combined fine-scaled spatial information on two predator and 11 herbivore species with remotely-sensed measurements of forage quantity and vegetation structure to assess variation in herbivore response to predation risk with changing environmental context, herbivore body size, herbivore foraging strategy (browsers versus grazers), predator type (ambush versus coursing hunters) and group size across a South African savanna landscape. Medium-sized herbivore species were more likely to adjust their response to risk with a changing resource landscape: warthog, nyala and wildebeest tolerated increased long-term predator encounter risk in exchange for abundant (warthog and nyala) or preferred (wildebeest) forage, and nyala selected areas with higher visibility only in landscapes where food was abundant. Impala were more likely to be observed in areas of high visibility where wild dog risk was high. In addition, although buffalo did not avoid areas of high lion encounter risk, large buffalo groups were more frequently observed in open areas where lion encounter risk was high, whereas small groups did not alter their space use across varying levels of risk. Our findings suggest that risk effects are not uniform across landscapes for medium-sized herbivores and large buffalo groups, instead varying with environmental context and leading to a dynamic landscape of fear. However, responses among these and other prey species were variable and not consistent, highlighting the complexities inherent to multi-predator/multi-prey systems.Data availability statement: Data available from the Dryad Digital Repository: (Davies et al. 2020).http://www.oikosjournal.orghj2022Mammal Research InstituteZoology and Entomolog

Structural diversity and tree density drives variation in the biodiversity-ecosystem function relationship of woodlands and savannas

Positive biodiversity-ecosystem function relationships (BEFRs) have been widely documented, but it is unclear if BEFRs should be expected in disturbance-driven systems. Disturbance may limit competition and niche differentiation, which are frequently posited to underlie BEFRs. We provide the first exploration of the relationship between tree species diversity and biomass, one measure of ecosystem function, across southern African woodlands and savannas, an ecological system rife with disturbance from fire, herbivores and humans. We used >1000 vegetation plots distributed across 10 southern African countries, and structural equation modelling, to determine the relationship between tree species diversity and aboveground woody biomass, accounting for interacting effects of resource availability, disturbance by fire, tree stem density and vegetation type. We found positive effects of tree species diversity on aboveground biomass, operating via increased structural diversity. The observed BEFR was highly dependent on organismal density, with a minimum threshold of c. 180 mature stems ha-1. We found that water availability mainly affects biomass indirectly, via increasing species diversity. The study underlines the close association between tree diversity, ecosystem structure, environment and function in highly disturbed savannas and woodlands. We suggest that tree diversity is an under-appreciated determinant of wooded ecosystem structure and function

Ecological Thresholds in the Savanna Landscape: Developing a Protocol for Monitoring the Change in Composition and Utilisation of Large Trees

BACKGROUND: Acquiring greater understanding of the factors causing changes in vegetation structure -- particularly with the potential to cause regime shifts -- is important in adaptively managed conservation areas. Large trees (> or =5 m in height) play an important ecosystem function, and are associated with a stable ecological state in the African savanna. There is concern that large tree densities are declining in a number of protected areas, including the Kruger National Park, South Africa. In this paper the results of a field study designed to monitor change in a savanna system are presented and discussed. METHODOLOGY/PRINCIPAL FINDINGS: Developing the first phase of a monitoring protocol to measure the change in tree species composition, density and size distribution, whilst also identifying factors driving change. A central issue is the discrete spatial distribution of large trees in the landscape, making point sampling approaches relatively ineffective. Accordingly, fourteen 10 m wide transects were aligned perpendicular to large rivers (3.0-6.6 km in length) and eight transects were located at fixed-point photographic locations (1.0-1.6 km in length). Using accumulation curves, we established that the majority of tree species were sampled within 3 km. Furthermore, the key ecological drivers (e.g. fire, herbivory, drought and disease) which influence large tree use and impact were also recorded within 3 km. CONCLUSIONS/SIGNIFICANCE: The technique presented provides an effective method for monitoring changes in large tree abundance, size distribution and use by the main ecological drivers across the savanna landscape. However, the monitoring of rare tree species would require individual marking approaches due to their low densities and specific habitat requirements. Repeat sampling intervals would vary depending on the factor of concern and proposed management mitigation. Once a monitoring protocol has been identified and evaluated, the next stage is to integrate that protocol into a decision-making system, which highlights potential leading indicators of change. Frequent monitoring would be required to establish the rate and direction of change. This approach may be useful in generating monitoring protocols for other dynamic systems

Data from: Demography and social dynamics of an African elephant population 35 years after reintroduction as juveniles

1. Given their vulnerability to local extinction, the reintroduction of megafauna species (often long-lived, ecologically-influential and highly-social) is an increasingly relevant conservation intervention. Studies that evaluate past megafauna reintroductions are both critical and rare. 2. Between 1981 and 1996, 12 cohorts of a total of 200 juvenile (10 years old) composed 30% of the population in 2016. The population remains relatively young and forecasts suggest high potential for sustained growth over the next decade. 4. The first calf was born to a reintroduced female in 1990 and since then mother-calf units have gradually developed into semi-independent multi-generation families (7-15 individuals in size in 2016). The size of observed cow-calf groups was highly variable (mean=21.4 individuals, range: 7-109), with repeat observation of individual collared females revealing fusion and fission among different family groups through time, as is typical of more natural elephant populations. 5. Synthesis and applications: The development of normal elephant demography and sociality from an irregular founder population may be an encouragement for the reintroduction of other megaherbivores. The potential for rapid population growth must however be carefully considered, especially when ecologically-influential species are introduced to closed systems. The observed age class distribution and the estimated potential for future growth over the next decade have implications for the park’s contraception strategy. Finally, our study provides key long-term insights for elephant translocations, which are becoming an increasingly common and necessary management intervention (due to overpopulation in some areas and local extinction in others).04-Jun-201

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

Understanding factors that affect the reproductive output and growth of a population of endangered carnivores is key to providing information for their effective conservation. Here, we assessed patterns in reproduction for a small population of endangered African wild dogs (Lycaon pictus) over 90 pack years. We tested how availability of prey, pack size, pack density, rainfall, temperature and female age affected the age of first litter, litter size and pup survival. We found that females bred younger when pack density, availability of prey and pack size were large. We also found that fecundity increased significantly with age while the population was male biased only for 1-, 2- and 4-year olds. Larger litters were produced by larger packs, suggesting strong reproductive benefits of grouping related to cooperative hunting and food provisioning for helpers and alpha females. We also found an interaction between breeding female age and pack size where older females in large packs raised a high proportion of pups. Additionally, large litters and large packs were important for raising a greater number of pups to 6 and 12 months, respectively, suggesting that while litter size is important for pup survival, the benefits of a large pack are only realised when pups are older and mobile with the pack. Collectively, these results illustrate the novel finding that prey availability is critically important in initiating reproduction in wild dogs and that the number of non-breeding helpers, female age and litter size is essential to pup survival.The National Research Foundation of South Africa Scarce Skills Development Fund (grant number SFH13072423287) and The Rufford Small Grants Foundation (grant number: 14409-1).http://link.springer.com/journal/2652020-05-01hj2019Mammal Research InstituteZoology and Entomolog