Lion Density Research Articles

Spatial Risk Effects From Lions Compound Impacts of Prey Depletion on African Wild Dogs.

Prey depletion threatens many carnivore species across the world and can especially threaten low-density subordinate competitors, particularly if subordinates are limited to low densities by their dominant competitors. Understanding the mechanisms that drive responses of carnivore density to prey depletion is not only crucial for conservation but also elucidates the balance between top-down and bottom-up limitations within the large carnivore guild. To avoid predation, competitively subordinate African wild dogs typically avoid their dominant competitors (lions) and the prey rich areas they are associated with, but no prior research has tested whether this pattern persists in ecosystems with anthropogenically-reduced prey density, and reduced lion density as a result. We used spatial data from wild dogs and lions in the prey-depleted Greater Kafue Ecosystem to test if wild dogs continue to avoid lions (despite their low density), and consequently avoid habitats with higher densities of their dominant prey species. We found that although lion density is 3X lower than comparable ecosystems, wild dogs continue to strongly avoid lions, and consequently avoid habitats associated with their two most important prey species. Although the density of lions in the GKE is low due to prey depletion, their competitive effects on wild dogs remain strong. These effects are likely compounded by prey-base homogenization, as lions in the GKE now rely heavily on the same prey preferred by wild dogs. These results suggest that a reduction in lion density does not necessarily reduce competition, and helps explain why wild dogs decline in parallel with their dominant competitors in ecosystems suffering from anthropogenic prey depletion. Protecting prey populations within the few remaining strongholds for wild dogs is vitally important to avoid substantial population declines. Globally, understanding the impacts of prey depletion on carnivore guild dynamics should be an increasingly important area of focus for conservation.

Long-term data reveal fitness costs of anthropogenic prey depletion for a subordinate competitor, the African wild dog (Lycaon pictus).

Within carnivore guilds, dominant competitors (e.g., lions, Panthera leo) are limited primarily by the density of prey, while subordinate competitors (e.g., African wild dogs, Lycaon pictus) have been limited by the density of dominant competitors. Historically, the fitness and population density of subordinate competitors have not been tightly linked to prey density. However, populations of large herbivores have declined substantially across sub-Saharan Africa due to human impacts, and where prey depletion is severe, fitness costs for competitive subordinates may begin to outweigh the benefits of competitive release. Using long-term intensive monitoring of African wild dogs in Zambia's Luangwa Valley Ecosystem (LVE), we tested the effects of prey depletion on survival and reproduction. We hypothesized that African wild dog fitness would be lower in prey-depleted areas, despite lower lion densities. Our study area included four contiguous regions that varied in protection level, prey density, and lion density. We fit Bayesian Cormack-Jolly-Seber and closed-capture models to estimate effects on survival and population density, and generalized linear models to estimate effects on reproductive success. We found that the LVE is a stronghold for African wild dogs, with an estimated median density of 4.0 individuals/100 km2. Despite this high density, survival and reproduction differed among regions, and both components of fitness were substantially reduced in the region with the lowest prey density. Anthropogenic prey depletion is becoming an important limiting factor for African wild dogs. If prey depletion (or any other form of habitat degradation) becomes severe enough that its fitness costs outweigh the benefits of competitive release, such changes can fundamentally alter the balance between limiting factors for competitively subordinate species.

Population size and social structure of lions in a west African protected area

AbstractTo inform the conservation of the Regionally Critically Endangered West African lion, we studied lion population size and social structure in Niokolo Koba National Park (NKNP), Senegal. Calling station and camera trap surveys were conducted and opportunistic lion observations were documented from 2015 to 2020. The average lion density was calculated as 0.50 lion/100 km2 and the population size was estimated as 28–56 individuals. Average lion group size was 2.1 ± 1.45 lions (range 1–8 lions). There were no significant differences between observations of single individuals (43%), groups of two (22%), three (19%), four (4%) and more than four (5%) individual lions (X2 = 30.021, p‐value = 0.06452). Sex ratio showed a ratio of male:female of 1:1.1 to 1:2.8. About 13.59% of the lion population was composed of cubs while, respectively, 81.22% and 5.17% were adults and subadults. Based on the analysis of activity patterns, lions in NKNP are mainly nocturno‐crepuscular (18:00–01:00) and matutinal (06:00–08:00). Lion population size and density are still low in NKNP compared to earlier estimates from the same area, in the late 1990s. We therefore conclude that the conservation of lions in NKNP must be further improved to safeguard this population in the long term.

Spotted hyaena population density across habitat and land use types in southern Tanzania

AbstractAlthough the spotted hyaena (Crocuta crocuta) has been widely considered to be resilient to human disturbance, the species is now thought to be undergoing widespread population declines. Nevertheless, only a handful of population density estimates are available for the species, despite the importance of this information for informing conservation management. This is a consequence of both a lack of surveys and logistical challenges associated with processing spotted hyaena data. In this study, we collaborated with a cohort of students to process camera trap data from the Ruaha‐Rungwa landscape initially collected to estimate lion (Panthera leo) and leopard (Panthera pardus) population density. By doing so, we provide the first spatially explicit population density estimates for spotted hyaena in Tanzania, via spatially explicit capture‐recapture (SECR) modelling. We also examine the relationship between population densities of spotted hyaena, lion and leopard at each site. Spotted hyaena densities varied from 3.55 ± 0.72 adults and sub‐adults per 100 km2 in a miombo (Brachystegia‐Julbernardia) woodland area of Ruaha National Park, to 10.80 ± 1.08 per 100 km2 in a prey‐rich open woodland savannah habitat in Ruaha National Park, with intermediate densities recorded in Rungwa Game Reserve and MBOMIPA Wildlife Management Area. Our results suggest that spotted hyaena density is influenced by prey availability and protection, and the species may be less resilient to human pressures than widely thought. Spotted hyaena densities were generally positively correlated with densities of lion and leopard, suggesting that prey availability and anthropogenic disturbance had a greater impact than interspecific effects in shaping large carnivore densities in this system. Overall, our study provides some of the first insights into an under‐studied species in an under‐researched part of its range, while shedding light into the impact of anthropogenic versus interspecific effects in shaping population status of spotted hyaena in human‐impacted African systems.

Considerations on effort, precision and accuracy for long-term monitoring of African lions (Panthera leo), when using Bayesian spatial explicit capture-recapture models, in fenced protected areas.

Intensive management is frequently required in fenced wildlife areas to reduce deleterious effects of isolation. Decisions on how best to manage such wildlife are ideally informed by regular and reliable estimates of spatiotemporal fluctuations in population size and structure. However, even in small, fenced areas, it is difficult and costly to regularly monitor key species using advanced methods. This is particularly the case for large carnivores, which typically occur at low density and are elusive yet are central to management decision-making due to their top-down effects in ecosystems and attracting tourism. In this study, we aimed to provide robust estimates of population parameters for African lions (Panthera leo) and use the data to inform a resource-efficient long-term monitoring programme. To achieve this, we used unstructured spatial sampling to collect data on lions in Pilanesberg National Park, a small (~550 km2) fenced protected area in South Africa. We used Bayesian spatial capture-recapture models to estimate density, abundance, sex ratio and home range size of lions over the age of 1 year. Finally, to provide guidance on resource requirements for regular monitoring, we rarefied our empirical data set incrementally and analysed the subsets. Lion density was estimated to be 8.8 per 100 km2 (posterior SD = 0.6), which was lower than anticipated by park management. Sex ratio was estimated close to parity (0.9♀:1♂), consistent with emerging evidence in fenced lion populations, yet discordant with unfenced populations, which are usually ~2♀:1♂ in healthy, source populations. Our rarefied data suggest that a minimum of 4000 km search effort needs to be invested in future monitoring to obtain accurate and precise estimates, while assuming similar detection rates. This study demonstrates an important utility of Bayesian spatial explicit capture-recapture methods for obtaining robust estimates of lion densities and other important parameters in fence-protected areas to inform decision-making.

Effects of Community Participation in the Restoration of Rumuruti Forest in Laikipia County, Kenya

Reforestation is a concerted effort to discover forest formation, biodiversity, and ecosystem practices through tree planting. There is a drive by international organizations to reclaim about 150 million ha of degraded forests by 2030. The Rumuruti Forest is located in the Laikipia County of Kenya. It is a unique and biodiverse forest renowned for its high density of large mammals, including elephants, lions, leopards, and rhinoceroses. The forest is home to several rare species, such as the upright-horned antelope, the black-faced vervet monkey, and the yellow-necked spurfowl. Rumuruti Forest is an expansive 15,378-acre forest located in Laikipia County, Kenya. These benefits had been offset by rapid habitat loss and degradation despite concerted efforts by the Kenyan government to restore as well as maintain this resource. Besides, previous restoration attempts of Rumuruti forest had been ineffective, as indicated by the widespread withering of recently planted seedlings, resulting in a doubling of replanting operations. A descriptive research design was applied to describe the current state of variables that could be identified. The study's specific objective was to investigate the potential socio-economic benefits of Rumuruti forest restoration to community members. A descriptive research design was applied to describe the current state of variables that could be identified. Research took place in Rumuruti town, Laikipia County, Kenya. It is located 40 km due North of Nyahururu. The geographical coordinates of Rumuruti town are 0.25996°N, 36.53633°E, with a population of 31649 people. The target population for this study was 4,800 people. The sample size was 139 households. The study concluded that the community was considerably more eager to work with the government and NGOs to contribute to the restoration of the Rumuruti forest. The community desired to be more involved in the restoration operations, including tree planting, tendering, and protection. As a result, effective processes were put in place to maximize the potential to achieve optimal regeneration of the Rumuruti forest.

Environmental and anthropogenic drivers of African leopard Panthera pardus population density

Globally three quarters of large terrestrial mammalian predators are in decline and many populations are data deficient, including those of African leopards across much of their range. Here we assess the drivers of decline African leopard populations in 16 camera trap surveys covering a total area of 15,120 km2, across a gradient of anthropogenic impact, management and geography, in protected areas across the Zimbabwean component of the Kavango-Zambezi (KAZA) Transfrontier Conservation Area. Population density was calculated using spatially explicit mark-recapture estimators and Generalised Additive Models (GAM) were used to assess factors affecting population density. Density estimates ranged from 0.7 to 12.2 (mean 2.9 ± 2.7) leopards/100km2. Leopard density was higher in wooded sites and rugged terrain but negatively affected by human factors including human appropriation of net primary productivity (HANPP), trophy hunting risk and bush-meat poaching. High lion densities (>6.0 lions/ 100km2) negatively affected leopard density. Annual rainfall over a gradient of ~300 mm across survey sites was not influential in predicting population density.Previous assessments of the drivers of declining leopard population density (CITES 1988), asserting that leopard densities can be predicted by annual rainfall and are unaffected by human disturbance in unmodified habitat are not supported by our findings. We recommend that the 1988 assessment, used to manage CITES leopard trophy hunting export quotas since the late 1980s, should be reviewed.

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

BackgroundPrey 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.MethodsWe 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.ResultsWild 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.ConclusionWild 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.

Lions in a coexistence landscape: Repurposing a traditional field technique to monitor an elusive carnivore.

Throughout Africa, lions are thought to have experienced dramatic population decline and range contraction. The greatest declines are likely occurring in human‐dominated landscapes where reliably estimating lion populations is particularly challenging. By adapting a method that has thus far only been applied to animals that are habituated to vehicles, we estimate lion density in two community areas in Kenya's South Rift, located more than 100 km from the nearest protected area (PA). More specifically, we conducted an 89‐day survey using unstructured spatial sampling coupled with playbacks, a commonly used field technique, and estimated lion density using spatial capture‐recapture (SCR) models. Our estimated density of 5.9 lions over the age of 1 year per 100 km2 compares favorably with many PAs and suggests that this is a key lion population that could be crucial for connectivity across the wider landscape. We discuss the possible mechanisms supporting this density and demonstrate how rigorous field methods combined with robust analyses can produce reliable population estimates within human‐dominated landscapes.

African Lion Population Estimates in Tanzania’s Ruaha National Park

Tanzania is considered a country with the largest number of African lions (Panthera leo). However, the continued absence of ecological population estimates and understanding of the associated factors influencing lion distribution hinders the development of conservation planning. This is particularly true in the Ruaha-Rungwa landscape, where it was estimated that more than 10% of the global lion population currently resides. By using a call-back survey method, we aimed to provide population estimates (population size and density) of African lions in the Ruaha National Park, between wet (March 2019) and dry (October 2019) seasons. We also assessed the key factors that influenced the distribution of the observed lions towards call-back stations. Ferreira & Funston’s (2010) formula was used to calculate population size and in turn used to estimate density in the sampled area, while the Generalized Linear Model (GLMM) with zero-inflated Poisson error distribution was used to determine factors that influence the distribution of the observed lions to call-back stations. The population size we calculated for the sampled area of 3137.2 km2 revealed 286 lions (95% CI, 236 - 335) during the wet season, and 196 lions (95% CI, 192 - 200) during the dry season. The density of lions was 9.1/100 km2 during the wet season, and 6.3/100 km2 during the dry season. Distance to water source had a significant negative effect on the distribution of the observed lions to the call-back stations, while habitat had a marginal effect. Our findings show that, although lion population estimates were larger during the wet season than the dry season, the season had no effect on the distribution of the observed lions to call-back stations. We suggest that the proximity to water sources is important in study design. Further, we suggest that density and population size are useful indices in identifying conservation area priorities and lion coexistence strategies.

Estimates of Density and Population Size of African Lions in the Katavi National Park, Tanzania

Lion populations are declining globally, including in Tanzania, and Africa. However, Katavi National Park is a landscape with potential for a sustainable and healthy population of African lions (Panthera leo), but there is currently limited reliable data indicating density and population size. This hinders the development of conservation action plans, including population monitoring, for this species. To address this data gap, we assessed lions’ demography and population estimates (population size and density) in the Katavi National Park using a call-back survey method. In addition, we assessed ecological factors that influenced distribution of lions to the call-back stations. Our estimated population size revealed 84 lions (95% CI 53 - 116), with a density of 5/100 km2 (95% CI 3.14 - 6.86) in the sampled area, representing 38% of the total park. This resulted in an estimated 214 individuals when extrapolated to the whole park. Sixty-seven percent of lions that responded to the stations were female, and ecological factors that significantly influenced their distribution included elevation, land cover, precipitation, temperature, wind speed, and prey abundance. Our results suggest that female lions are more abundant than males in Katavi National Park and that population size and density estimates, as well as understanding prey-lion relations, are important indices for lion monitoring and identifying conservation priorities. Further, our study suggests that the call-back survey method is an effective, rapid, and less costly population assessment method for lions, may be useful for assessing other social species in the Katavi ecosystem and can be a useful tool for community engagement and contributing to scientific monitoring.

Camera trapping and spatially explicit capture–recapture for the monitoring and conservation management of lions: Insights from a globally important population in Tanzania

Abstract Accurate and precise estimates of population status are required to inform and evaluate conservation management and policy interventions. Although the lion (Panthera leo) is a charismatic species receiving increased conservation attention, robust status estimates are lacking for most populations. While for many large carnivores population density is often estimated through spatially explicit capture–recapture (SECR) applied to camera trap data, the lack of pelage patterns in lions has limited the application of this technique to the species. Here, we present one of the first applications of this methodology to lion, in Tanzania's Ruaha‐Rungwa landscape, a stronghold for the species for which no empirical estimates of status are available. We deployed four camera trap grids across habitat and land management types, and we identified individual lions through whisker spots, scars and marks, and multiple additional features. Double‐blind identification revealed low inter‐observer variation in photo identification (92% agreement), due to the use of xenon‐flash cameras and consistent framing and angles of photographs. Lion occurred at highest densities in a prey‐rich area of Ruaha National Park (6.12 ± SE 0.94 per 100 km2), and at relatively high densities (4.06 ± SE 1.03 per 100 km2) in a community‐managed area of similar riparian‐grassland habitat. Miombo woodland in both photographic and trophy hunting areas sustained intermediate lion densities (1.75 ± SE 0.62 and 2.25 ± SE 0.52 per 100 km2, respectively). These are the first spatially explicit density estimates for lion in Tanzania, including the first for a trophy hunting and a community‐managed area, and also provide some of the first insights into lion status in understudied miombo habitats. We discuss in detail the methodology employed, the potential for scaling‐up over larger areas, and its limitations. We suggest that the method can be an important tool for lion monitoring and explore the implications of our findings for lion management.

Lion (Panthera leo) ecology and survival in protected areas of Ethiopia

Ethiopia is renowned for its cultural and biological diversity and covers an important share of lion habitat in Africa, providing connectivity between East and Central Africa. The aim of this study was to investigate the status of lions and human–lion conflict in several protected areas of Ethiopia and to present an overview on lion distribution nationally. We used call-ups and semi-structured interviews with 809 randomly selected pastoralists to investigate human–lion conflict and pastoralist perceptions towards lions in five priority sites and collected further anecdotal information for all other known or possible lion range. We had chance encounters with six lions, but we observed no lion responses to the call-ups. We recorded 145 spotted hyaena and 23 jackal responses at, respectively, 25 and 13 of the 46 call-up stations. Overall, respondents viewed lions as dangerous carnivores, but nonetheless responded that lions should be present regionally, preferably in restricted areas. Most respondents disagreed that the killing of lions should be allowed, but we note that a small minority strongly agreed to killing. A large majority of respondents agreed that more people need to be given information about lions. Respondents mentioned spotted hyaena and leopard as the main predators on all livestock followed by jackal (shoats) and lion (mainly cattle). The impact of depredation on livestock mortality was nearly twice that of disease. Our results strongly suggest that lion densities are low and may have substantially decreased in Awash, Nechisar, Chebera-Churchura, and Mago National Parks and in Kaffa Biosphere Reserve due to conflict, habitat loss and especially ineffective protection. Anecdotal information suggests that lions are widespread but rare and that there is no stronghold in Ethiopia. Considering the unique evolutionary background of Ethiopia as the bridge between Central and East African lion populations, and the significant role of the lion in Ethiopian history and culture, we argue that more emphasis should be given to the protection of prioritized lion populations.

LeopardPanthera pardusdensity and survival in an ecosystem with depressed abundance of prey and dominant competitors

AbstractThe leopardPanthera pardusis 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 lionPanthera 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.

Low apex carnivore density does not release a subordinate competitor when driven by prey depletion

Conservation of competitively subordinate carnivores presents a difficult challenge because they are limited by dominant competitors. Prey depletion is one of the leading causes of large carnivore decline worldwide, but little is known about the net effect of prey depletion on subordinate carnivores when their dominant competitors are also reduced. African wild dogs are often limited by high densities of dominant competitors, particularly lions. We measured African wild dog density and survival, using mark-recapture models fit to 8 years of data from 425 known individuals in the Greater Kafue Ecosystem, Zambia. The GKE is affected by prey depletion, particularly of large herbivores, and thus the density of lions is significantly lower than ecologically comparable ecosystems. Counter to expectations from mesopredator release theory, wild dog density in GKE was far lower than comparable ecosystems with higher lion and prey density, though annual survival rates were comparable to large and stable populations. Average pack size was small and home range size was among the largest recorded. Our results show that low lion density did not competitively release the GKE wild dog population and we infer that the low density of wild dogs was a product of low prey density. Our results suggest that there is an optimal ratio of prey and competitors at which wild dogs achieve their highest densities. This finding has immediate implications for the conservation of the endangered African wild dog, and broad implications for the conservation of subordinate species affected by resource depletion and intraguild competition.

Reproductive state influences the degree of risk tolerance for a seasonally breeding mesopredator

AbstractThe risk of predation can alter the way animals perceive costs and benefits in their environment, on which foraging decisions are made. To maximize fitness, animals with offspring show the most pronounced alteration in behavior because mothers experience increased nutritional requirements and increased vulnerability to predation. Therefore, the tolerance of risk is shaped, in part, by reproductive state. Like prey species, mesopredators balance a trade-off between food and predation to maximize fitness. However, few studies have acknowledged its importance. We investigated how mesopredators may alter their space use between periods when young are and are not vulnerable. Investigating the fine-scale space use of 19 packs of African wild dogs Lycaon pictus in the Kruger National Park, we found lower risk tolerance of denning packs; they re-visited area less frequently as lion and impala density increased and thus reduced the likelihood of risky encounters by avoiding areas where both risk and reward were high. By contrast, non-denning packs re-visited area less frequently as lion density increased and impala density decreased and thus avoided areas where reward was low, especially if risk was high. These results suggest that wild dogs shift their patterns of space use when the pack is most vulnerable. Ultimately, we found evidence of decreased risk tolerance by denning packs, likely because of increased vulnerability of lactating mothers and immobile pups. More broadly, our findings suggest that risk tolerance is dependent on reproductive state for mesopredators and should be considered as a possible mechanism for other mesopredators as well.

Response of lion demography and dynamics to the loss of preferred larger prey.

Large carnivores are experiencing range contraction and population declines globally. Prey depletion due to illegal offtake is considered a major contributor, but the effects of prey depletion on large carnivore demography are rarely tested. We measured African lion density and tested the factors that affect survival using mark-recapture models fit to six years of data from known individuals in Kafue National Park (KNP), Zambia. KNP is affected by prey depletion, particularly for large herbivores that were preferred prey for KNP lions a half-century ago. This provides a unique opportunity to test whether variables that explain local prey density also affect lion survival. Average lion density within our study area was 3.43 individuals/100 km2 (95% CI, 2.79-4.23), which was much lower than lion density reported for another miombo ecosystem with similar vegetation structure and rainfall that was less affected by prey depletion. Despite this, comparison to other lion populations showed that age- and sex-specific survival rates for KNP lions were generally good, and factors known to correlate with local prey density had small effects on lion survival. In contrast, recruitment of cubs was poor and average pride size was small. In particular, the proportion of the population comprised of second-year cubs was low, indicating that few cubs are recruited into the subadult age class. Our findings suggest that low recruitment might be a better signal of low prey density than survival. Thus, describing a lion population's age structure in addition to average pride size may be a simple and effective method of initially evaluating whether a lion population is affected by prey depletion. These dynamics should be evaluated for other lion populations and other large carnivore species. Increased resource protection and reducing the underlying drivers of prey depletion are urgent conservation needs for lions and other large carnivores as their conservation is increasingly threatened by range contraction and population declines.

Plains zebras bring evidence that dilution and detection effects may not always matter behaviorally and demographically

AbstractGroup living is assumed to benefit prey by reducing predation risk due to dilution and detection effects. This increased safety could be exchanged against a reduced individual vigilance leading to increased foraging and fitness until costs of intra‐group competition offset this benefit. However, very few studies have been able to directly test the relationship between individual fitness and group size in non‐cooperative breeding species. Therefore, evidence that dilution and detection effects do indeed translate into increased fitness under predation risk remains mostly theoretical. Here, we aimed at empirically testing whether group size influences beneficial and costly behaviors, and ultimately the survival of individuals, in a prey species facing heavy predation pressure. We focused on plains zebra Equus quagga of Hwange National Park in Zimbabwe, a high lion density area. We collected behavioral data (i.e., individual vigilance and foraging, collective vigilance, and agonistic interactions) that we used as proxies to investigate the costs and benefits of grouping in this species. We then fitted multistate capture‐mark‐recapture and Cox proportional‐hazards models to estimate apparent survival of adults and young zebras, respectively, and assess whether a demographic signal of group size could be found. Our results show that collective vigilance increases with group size, a prerequisite of the detection effect, but individual vigilance does not consistently decrease with group size, which suggests that there is no group size effect on individual vigilance. Agonistic interactions were rare. These results suggest that there are no foraging costs of grouping here, and even some benefits such as a better collective vigilance. However, any benefits of being in larger groups did not translate into increased survival, as we found no effect of group size on the apparent survival of individuals. Since dilution and detection effects do not matter behaviorally and demographically in these plains zebras living under high predation risk, these results challenge our understanding of how predation shapes animal sociality: fitness benefits of dilution or detection should not be assumed.

Integrating distance sampling and presence-only data to estimate species abundance.

Integrated models combine multiple data types within a unified analysis to estimate species abundance and covariate effects. By sharing biological parameters, integrated models improve the accuracy and precision of estimates compared to separate analyses of individual data sets. We developed an integrated point process model to combine presence-only and distance sampling data for estimation of spatially explicit abundance patterns. Simulations across a range of parameter values demonstrate that our model can recover estimates of biological covariates, but parameter accuracy and precision varied with the quantity of each data type. We applied our model to a case study of black-backed jackals in the Masai Mara National Reserve, Kenya, to examine effects of spatially varying covariates on jackal abundance patterns. The model revealed that jackals were positively affected by anthropogenic disturbance on the landscape, with highest abundance estimated along the Reserve border near human activity. We found minimal effects of landscape cover, lion density, and distance to water source, suggesting that human use of the Reserve may be the biggest driver of jackal abundance patterns. Our integrated model expands the scope of ecological inference by taking advantage of widely available presence-only data, while simultaneously leveraging richer, but typically limited, distance sampling data.

Detecting early warnings of pressure on an African lion (Panthera leo) population in the Queen Elizabeth Conservation Area, Uganda

Abstract African lions are declining across much of their range, yet robust measures of population densities remain rare. The Queen Elizabeth Conservation Area (QECA; 2,400 km2) in East Africa's Albertine Rift has potential to support a significant lion population. However, QECA lions are threatened, and information on the status of lions in the region is lacking. Here, we use a spatially explicit search encounter approach to estimate key population parameters of lions in the QECA. We then compare home range sizes estimated from our models to those from a radio‐collaring study implemented a decade earlier. We recorded 8,243.5 km of search effort over 93 days, detecting 30 individual lions (16 female and 14 male) on 165 occasions at a rate of 2 lion detections/100 km2. Lion density in the QECA was 2.70 adult lions/100 km2 (SD = 0.47), while mean abundance was 71 individuals (SD = 11.05). Worryingly, the movement parameter for male lions was 3.27 km and 2.22 km for females, suggesting > 400%, and > 100% increases in home range size, respectively, compared to a decade earlier. Sex ratio of lions in the QECA was lower (1 male: 0.75 females), when compared to a previously published review (mean = 1:2.33). The large movements and skewed sex ratios we report on in this paper are likely a result of human‐driven prey depletion. Our results suggest lions in the QECA are in a precarious state, and the lion densities are significantly lower than what they could be. As lions are under pressure throughout much of Africa, our study presents the utility of a census technique that could be used elsewhere as an early warning of lion declines.