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87 result(s) for "Kerley, Graham I. H."
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Effects of Vegetation Structure on the Location of Lion Kill Sites in African Thicket
Predator-prey relationships are integral to ecosystem stability and functioning. These relationships are, however, difficult to maintain in protected areas where large predators are increasingly being reintroduced and confined. Where predators make kills has a profound influence on their role in ecosystems, but the relative importance of environmental variables in determining kill sites, and how these might vary across ecosystems is poorly known. We investigated kill sites for lions in South Africa's thicket biome, testing the importance of vegetation structure for kill site locations compared to other environmental variables. Kill sites were located over four years using GPS telemetry and compared to non-kill sites that had been occupied by lions, as well as to random sites within lion ranges. Measurements of 3D vegetation structure obtained from Light Detection and Ranging (LiDAR) were used to calculate the visible area (viewshed) around each site and, along with wind and moonlight data, used to compare kill sites between lion sexes, prey species and prey sexes. Viewshed area was the most important predictor of kill sites (sites in dense vegetation were twice as likely to be kill sites compared to open areas), followed by wind speed and, less so, moonlight. Kill sites for different prey species varied with vegetation structure, and male prey were killed when wind speeds were higher compared to female prey of the same species. Our results demonstrate that vegetation structure is an important component of predator-prey interactions, with varying effects across ecosystems. Such differences require consideration in terms of the ecological roles performed by predators, and in predator and prey conservation.
Temporal shifts in activity of prey following large predator reintroductions
The response of prey to prédation risk varies through time and space. These responses relate to trade-offs between foraging and predator avoidance. Following the extirpation of predators from many landscapes, the responses related to predator avoidance may have been lost or diluted. Investigating the activity pattern of prey species on comparable landscapes with and without large predators provides an opportunity to understand how predators may shape prey activity and behaviour. Using camera trap data from neighbouring fenced sections of the Addo Elephant National Park (Eastern Cape, South Africa), we investigated the activity patterns of species exposed to large predators, where the predators were only present in one of the sections. Our results suggest that prey species at risk of prédation (e.g., buffalo, kudu and warthog) are more likely to be active diurnally when co-existing with nocturnally active predators, thereby reducing the activity overlap with these predators. In the absence of predators, kudu and buffalo were more active at night resulting in a low overlap in activity between sections. Warthog activity was predominantly diurnal in both sections, resulting in a high overlap in activity between sections. The presence of predators reduced the nocturnal activity of warthogs from 6 to 0.6 % of all warthog captures in each section. Elephants, which are above the preferred prey weight range of the predators and therefore have a low risk of predation, showed higher overlap in activity periodicity between predator-present and predator-absent areas. Our findings suggest that maintaining prey with their predators has the added benefit of conserving the full spectrum of prey adaptive behaviours.
The inappropriate use of time‐to‐independence biases estimates of activity patterns of free‐ranging mammals derived from camera traps
Measuring and comparing activity patterns provide key insights into the behavioral trade‐offs that result in animal activity and their extrinsic and intrinsic drivers. Camera traps are a recently emerged source of data for sampling animal activity used to estimate activity patterns. However, nearly 70% of studies using such data to estimate activity patterns apply a time‐to‐independence data filter to discard appreciable periods of sampling effort. This treatment of activity as a discrete event emerged from the use of camera trap data to estimate animal abundances, but does not reflect the continuous nature of behavior, and may bias resulting estimates of activity patterns. We used a large, freely available camera trap dataset to test the effects of time to independence on the estimated activity of eight medium‐ to large‐sized African mammals. We show that discarding data through the use of time‐to‐independence filters causes substantial losses in sample sizes and differences in the estimated activity of species. Activity patterns estimated for herbivore species were more affected by the application of time‐to‐independence data filters than carnivores, this extending to estimates of potential interactions (activity overlap) between herbivore species. We hypothesize that this pattern could reflect the typically more abundant, social, and patch‐specific foraging patterns of herbivores and suggest that this effect may bias estimates of predator–prey interactions. Activity estimates of rare species, with less data available, may be particularly vulnerable to loss of data through the application of time‐to‐independence data filters. We conclude that the application of time‐to‐independence data filters in camera trap‐based estimates of activity patterns is not valid and should not be used. A rapidly growing body of literature is using data from camera traps to describe and compare activity patterns in animals, but most such studies arbitrarily apply an inappropriate data filter of removing activity records for a time after each sample used, the so‐called time to independence. Using data for eight African large mammals, we show that this approach is not conceptually valid and leads to biases in the estimated activity patterns and that tests for interactions (overlap) using such estimates may not be useful.
Understanding Tourists’ Preference for Mammal Species in Private Protected Areas: Is There a Case for Extralimital Species for Ecotourism?
Private Protected Areas (PPAs) often use wildlife-based ecotourism as their primary means of generating business. Achieving tourist satisfaction has become a strong driving goal in the management of many PPAs, often at the expense of biodiversity. Many extralimitral species, those which historically did not occur in an area, are stocked in PPAs with the intention of increasing ecotourism attractions. Even though the ecological and economic costs of stocking these species are high, the social benefits are not understood and little information exists globally on the ecotourism role of extralimital species. This study assessed the value of stocking extralimital species using questionnaire-based surveys and observing tourists in Shamwari Private Game Reserve in the Eastern Cape Province of South Africa. No difference was found between indigenous and extralimital species with regards to the tourists' weighted scoring system, average amount tourists were willing to pay, total viewing time, average viewing time or the likelihood of stopping to view species when encountered on game drives. During game drives a strong preference was found for the elephant (Loxodonta africana), lion (Panthera leo), leopard (Panthera pardus) and cheetah (Acynonix jubatus). With the exception of the cheetah, these species are all members of the \"big five\" and are indigenous. Species availability and visibility, however, may influence the amount of time tourists spend at an animal sighting. Our analysis suggests that certain extralimital species (typically larger and charismatic species) contribute to tourist satisfaction, while particularly the smaller extralimital species add little to the game viewing experience, but add to the costs and risks of the PPAs. We recommend that extralimital species introductions for ecotourism purposes should be approached with caution with regards to the risks to the sustainability of PPAs.
Compensatory life‐history responses of a mesopredator may undermine carnivore management efforts
Lethal carnivore management, aimed at reducing carnivore impacts, is a global phenomenon threatening the persistence of many carnivores. Black‐backed jackals Canis mesomelas, the dominant cause of livestock predation in southern Africa, are widely hunted to reduce livestock predation. Despite centuries of lethal management, jackals persist. Smaller canids, like jackals, are highly adaptable and display variable responses to mortality sources, which may affect management outcomes. The effects of killing carnivores will depend on their behaviour, social organization, reproduction and dispersal patterns. We predicted that hunted jackals will alter demographic and reproductive patterns to compensate for increased mortality. Here, we collected demographic and reproductive information from harvested jackals and compared it between continually hunted (farms) and unmanaged populations (reserves). The removal of jackals from farms results in a decrease in median age from 5–6 years (reserves) to 2–3 years (farms). Hunting also changed the age structure of jackal populations from a stable population to an expanding population. This may be ascribed to the compensatory immigration of individuals from neighbouring unmanaged areas, suggesting the formation of a source–sink system. Unmanaged areas may act as source populations exporting young, dispersing individuals to hunted areas which may act as sinks. This is likely driven by disruptions in the normal, mutually exclusive territorial system resulting in low densities of conspecifics on farms. The low density of conspecifics allows younger individuals that would be socially precluded from reproducing to reproduce. Jackals on farms compensated for increased mortality by increasing the pregnancy rate of young individuals and increasing the litter size at younger ages, thereby increasing reproductive output. Synthesis and applications. The lethal management of predators is the prevailing strategy to reduce livestock predation. However, the highly adaptable nature of jackals and the combination of compensatory mechanisms such as increased reproduction and potential for immigration allow these predators to persist in the face of severe anthropogenic mortality, possibly through the formation of a source–sink system. These compensatory processes will continue to counter population management actions as long as recruitment from unmanaged areas persists.
An Objective Approach to Determining the Weight Ranges of Prey Preferred by and Accessible to the Five Large African Carnivores
Broad-scale models describing predator prey preferences serve as useful departure points for understanding predator-prey interactions at finer scales. Previous analyses used a subjective approach to identify prey weight preferences of the five large African carnivores, hence their accuracy is questionable. This study uses a segmented model of prey weight versus prey preference to objectively quantify the prey weight preferences of the five large African carnivores. Based on simulations of known predator prey preference, for prey species sample sizes above 32 the segmented model approach detects up to four known changes in prey weight preference (represented by model break-points) with high rates of detection (75% to 100% of simulations, depending on number of break-points) and accuracy (within 1.3±4.0 to 2.7±4.4 of known break-point). When applied to the five large African carnivores, using carnivore diet information from across Africa, the model detected weight ranges of prey that are preferred, killed relative to their abundance, and avoided by each carnivore. Prey in the weight ranges preferred and killed relative to their abundance are together termed \"accessible prey\". Accessible prey weight ranges were found to be 14-135 kg for cheetah Acinonyx jubatus, 1-45 kg for leopard Panthera pardus, 32-632 kg for lion Panthera leo, 15-1600 kg for spotted hyaena Crocuta crocuta and 10-289 kg for wild dog Lycaon pictus. An assessment of carnivore diets throughout Africa found these accessible prey weight ranges include 88±2% (cheetah), 82±3% (leopard), 81±2% (lion), 97±2% (spotted hyaena) and 96±2% (wild dog) of kills. These descriptions of prey weight preferences therefore contribute to our understanding of the diet spectrum of the five large African carnivores. Where datasets meet the minimum sample size requirements, the segmented model approach provides a means of determining, and comparing, the prey weight range preferences of any carnivore species.
When Should ‘Clever’ Cheetah Breed? Seasonal Variability in Prey Availability and Its Effect on Cheetah Reproductive Patterns
Breeding is energetically demanding for female mammals, with maternal and cub nutrition playing a major role in reproductive phases like conception, gestation, lactation and weaning. To meet these demands, adaptations to seasonal shifts in food availability are expected. Some predators may shift prey selection seasonally, optimizing foraging during energetically costly periods. Cheetah, Acinonyx jubatus, prefer adult prey in the dry season when younger prey are scarce but switch to neonate and juvenile prey during the wet season, presumably to optimize foraging during gestation and lactation. Given the wide distribution of cheetah across seasonal (i.e., distinct wet and dry seasons) and aseasonal environments (rainfall throughout the year) and the associated shifts in availability of prey demographic classes, we hypothesized that seasonal prey availability in seasonal systems, but not aseasonal systems, influences the timing of cheetah reproductive phases. Based on the birth dates of cheetahs in seasonal (n = 142) and aseasonal (n = 106) rainfall areas, 58.5% of litters were conceived during the wet season, with 60.6% born in the dry season. In contrast, aseasonal areas showed no seasonality in birth dates. Cheetah reproduction in seasonal environments is driven by the availability of neonate and juvenile prey, with conception and cub independence aligning with peaks in easy‐to‐catch neonates, while lactation coincides with the availability of larger juveniles. Although cheetahs are often viewed as specialized predators with limited ability to adapt to local environmental conditions, our findings suggest they can adjust reproductive patterns in response to prey availability. This adaptability is important as it will allow cheetahs to successfully raise cubs in the face of changing prey reproductive patterns in response to climate change. We develop and test the hypothesis that the seasonal availability of preferred prey demographic classes, like neonates and juveniles, drives cheetah reproductive patterns in seasonal systems. Cheetah reproductive cycles are synchronized with prey reproductive cycles in seasonal systems, allowing for key cheetah reproductive phases with high energy requirements to coincide with high availability of preferred easy‐to‐catch prey. Highlighting that cheetahs are able to adapt to local environmental conditions, and adjust their reproductive patterns to exploit that of their prey species.
Shift in Black Rhinoceros Diet in the Presence of Elephant: Evidence for Competition?
In African large herbivore assemblages, megaherbivores dominate the biomass and utilise the greatest share of available resources. Consequently, they are considered a separate trophic guild that structures the food niches of coexisting large herbivores. However, there exists little empirical evidence on how food resources are shared within this guild, and none for direct competition for food between megaherbivores. Using the histological analysis of faeces, we explore this phenomenon for African elephant Loxodonta africana and black rhinoceros Diceros bicornis in the Addo Elephant National Park, South Africa, where the accumulated impacts of elephant have reduced browse availability. Despite being unable to generalise beyond our study sites, our observations support the predictions of competition theory (as opposed to optimality theory) by showing (1) a clear seasonal separation in resource use between these megaherbivores that increased as resource availability declined, and (2) rhinoceros changed their selectivity in the absence of elephant (using an adjacent site) by expanding and shifting their diet along the grass-browse continuum, and in relation to availability. Although black rhinoceros are generally considered strict browsers, the most significant shift in diet occurred as rhinoceros increased their preferences for grasses in the presence of elephant. We speculate that the lack of specialised grazing adaptations may increase foraging costs in rhinoceros, through reduced harvest- and handling-efficiencies of grasses. In the short-term, this may be off-set by an enhanced tolerance for low quality food and by seasonally mobilising fat reserves; however, the long-term fitness consequences require further study. Our data suggest that managing elephant at high densities may compromise the foraging opportunities of coexisting browsers. This may be particularly important in small, fenced areas and overlapping preferred habitats where impacts intensify.
Skull morphology analysis suggests the extinct Cape lion, Panthera leo melanochaita (Smith, 1842), is not distinctive
The lion ( Panthera leo ) was extirpated from the Cape region of South Africa during the mid-nineteenth century. Whilst historically classified as a distinct subspecies known as the Cape lion ( P. l. melanochaita ), recent molecular studies challenge the distinctiveness of this population, suggesting that it represents the southernmost population of the species' Southern Clade. The Cape lion is often cited as having a distinctive skull morphology, which has justified its subspecific classification, but only a limited number of specimens have been available for examination, so that the Cape lion’s skull morphology has not been satisfactorily understood. In this study we collected morphometric data from a greatly enlarged sample of 22 Cape lion skulls, including 12 adults, constituting the largest sample size analysed for this possible subspecies. The results suggest that (1) morphological characteristics of the skull previously thought to distinguish the Cape lion are not diagnostic, and (2) nor is the skull morphology of male and female Cape lions distinct from that of males and females of other southern African lions. Our results independently support those based on molecular investigations, which suggest that the Cape lion was not distinct from other lions within the Southern Clade.
Standardising Home Range Studies for Improved Management of the Critically Endangered Black Rhinoceros
Comparisons of recent estimations of home range sizes for the critically endangered black rhinoceros in Hluhluwe-iMfolozi Park (HiP), South Africa, with historical estimates led reports of a substantial (54%) increase, attributed to over-stocking and habitat deterioration that has far-reaching implications for rhino conservation. Other reports, however, suggest the increase is more likely an artefact caused by applying various home range estimators to non-standardised datasets. We collected 1939 locations of 25 black rhino over six years (2004-2009) to estimate annual home ranges and evaluate the hypothesis that they have increased in size. A minimum of 30 and 25 locations were required for accurate 95% MCP estimation of home range of adult rhinos, during the dry and wet seasons respectively. Forty and 55 locations were required for adult female and male annual MCP home ranges, respectively, and 30 locations were necessary for estimating 90% bivariate kernel home ranges accurately. Average annual 95% bivariate kernel home ranges were 20.4 ± 1.2 km(2), 53 ± 1.9% larger than 95% MCP ranges (9.8 km(2) ± 0.9). When home range techniques used during the late-1960s in HiP were applied to our dataset, estimates were similar, indicating that ranges have not changed substantially in 50 years. Inaccurate, non-standardised, home range estimates and their comparison have the potential to mislead black rhino population management. We recommend that more care be taken to collect adequate numbers of rhino locations within standardized time periods (i.e., season or year) and that the comparison of home ranges estimated using dissimilar procedures be avoided. Home range studies of black rhino have been data deficient and procedurally inconsistent. Standardisation of methods is required.