M. G. L. Mills

University of Oxford, Oxford, England, United Kingdom

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Publications (35)80.66 Total impact

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    ABSTRACT: Population viability is driven by individual survival, which in turn depends on individuals balancing energy budgets. As carnivores may function close to maximum sustained power outputs, decreased food availability or increased activity may render some populations energetically vulnerable. Prey theft may compromise energetic budgets of mesopredators, such as cheetahs and wild dogs, which are susceptible to competition from larger carnivores. We show that daily energy expenditure (DEE) of cheetahs was similar to size-based predictions and positively related to distance traveled. Theft at 25% only requires cheetahs to hunt for an extra 1.1 hour per day, increasing DEE by just 12%. Therefore, not all mesopredators are energetically constrained by direct competition. Other factors that increase DEE, such as those that increase travel, may be more important for population viability.
    Science (New York, N.Y.). 10/2014; 346(6205):79-81.
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    ABSTRACT: Top predators can dramatically suppress populations of smaller predators, with cascading effects throughout communities, and this pressure is often unquestioningy accepted as a constraint on mesopredator populations.In this study, we reassess whether African lions suppress populations of cheetahs and African wild dogs, and examine possible mechanisms for coexistence between these species.Using long-term records from Serengeti National Park, we tested 30 years of population data for evidence of mesopredator suppression and we examined six years of concurrent radio-telemetry data for evidence of large-scale spatial displacement.The Serengeti lion population nearly tripled between 1966 and 1998; during this time, wild dogs declined but cheetah numbers remained largely unchanged. Prior to their local extinction, wild dogs primarily occupied low-lion density areas, and apparently abandoned the long-term study area as the lion population “saturated” the region. In contrast, cheetahs mostly utilized areas of high lion density, and the stability of the cheetah population indicates that neither high levels of lion-inflicted mortality nor behavioral avoidance inflict sufficient demographic consequences to translate into population-level effects.Population data from fenced reserves in southern Africa revealed a similar contrast between wild dogs and cheetahs in their ability to coexist with lions.These findings demonstrate differential responses of subordinate species within the same guild and challenge a widespread perception that lions undermine cheetah conservation efforts. Paired with several recent studies that document fine-scale lion-avoidance by cheetahs, this study further highlights fine-scale spatial avoidance as a possible mechanism for mitigating mesopredator suppression.This article is protected by copyright. All rights reserved.
    Journal of Animal Ecology 04/2014; · 4.84 Impact Factor
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    ABSTRACT: Human-mediated changes in habitat structure may disturb predator–prey relationships.We investigated the influence of perimeter fences on the diet of a reintroduced population of African wild dogs Lycaon pictus Temminck 1820 in a 316 km2, fenced reserve in South Africa, by tracking radio-collared individuals during hunting periods to determine dietary composition from observed kills.Nutritional status of impala Aepyceros melampus and kudu Tragelaphus strepsiceros prey, as measured by the percentage of femur marrow fat, was significantly lower than that of unselectively culled individuals. This supports the hypothesis that wild dog predation is at least partially compensatory.Fence-impeded kills (those for which escape was deemed to be compromised by the fence) comprised 40·5% of kills (n = 316), and 54·1% of all edible biomass consumed. Compared with fence-unimpeded kills, fence-impeded kills comprised larger species (32·9 vs. 25·0 kg, W = 25667·0, P ≪ 0·001), older age classes for one prey category (female kudu: Fisher's exact test, P = 0·02, n = 65) and animals in better condition for adult impala males (Mann–Whitney, W = 111·0, P = 0·012, n = 28).Fence-impeded kills also provided greater catch per unit hunting effort (27·3 vs. 12·2 kg km−1; χ2 = 7·89, P = 0·005), resulting in longer interkill intervals. Movement of the pack towards the fence at the start of each hunting period suggested a decision to exploit the advantage that fences conferred for capturing prey.Synthesis and applications. By enabling coursing predators to capture prey that would otherwise have escaped, fences may reduce the compensatory nature of predation, causing shifts in predator–prey dynamics that could influence the ability of small reserves to support such predators. The establishment of larger conservation areas to reduce perimeter-to-area ratios should be encouraged to limit the undesired effects of fences on predator–prey dynamics.
    Journal of Applied Ecology 12/2013; 50(6). · 4.74 Impact Factor
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    ABSTRACT: Predator-prey interactions are fundamental in the evolution and structure of ecological communities. Our understanding, however, of the strategies used in pursuit and evasion remains limited. Here, we report on the hunting dynamics of the world's fastest land animal, the cheetah, Acinonyx jubatus. Using miniaturized data loggers, we recorded fine-scale movement, speed and acceleration of free-ranging cheetahs to measure how hunting dynamics relate to chasing different sized prey. Cheetahs attained hunting speeds of up to 18.94 m s(-1) and accelerated up to 7.5 m s(-2) with greatest angular velocities achieved during the terminal phase of the hunt. The interplay between forward and lateral acceleration during chases showed that the total forces involved in speed changes and turning were approximately constant over time but varied with prey type. Thus, rather than a simple maximum speed chase, cheetahs first accelerate to decrease the distance to their prey, before reducing speed 5-8 s from the end of the hunt, so as to facilitate rapid turns to match prey escape tactics, varying the precise strategy according to prey species. Predator and prey thus pit a fine balance of speed against manoeuvring capability in a race for survival.
    Biology letters 01/2013; 9(5):20130620. · 3.35 Impact Factor
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    African Journal of Ecology 12/2012; · 0.63 Impact Factor
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    ABSTRACT: Deciphering patterns of genetic variation within a species is essential for understanding population structure, local adaptation and differences in diversity between populations. Whilst neutrally evolving genetic markers can be used to elucidate demographic processes and genetic structure, they are not subject to selection and therefore are not informative about patterns of adaptive variation. As such, assessments of pertinent adaptive loci, such as the immunity genes of the major histocompatibility complex (MHC), are increasingly being incorporated into genetic studies. In this study, we combined neutral (microsatellite, mtDNA) and adaptive (MHC class II DLA-DRB1 locus) markers to elucidate the factors influencing patterns of genetic variation in the African wild dog (Lycaon pictus); an endangered canid that has suffered extensive declines in distribution and abundance. Our genetic analyses found all extant wild dog populations to be relatively small (N(e)  < 30). Furthermore, through coalescent modelling, we detected a genetic signature of a recent and substantial demographic decline, which correlates with human expansion, but contrasts with findings in some other African mammals. We found strong structuring of wild dog populations, indicating the negative influence of extensive habitat fragmentation and loss of gene flow between habitat patches. Across populations, we found that the spatial and temporal structure of microsatellite diversity and MHC diversity were correlated and strongly influenced by demographic stability and population size, indicating the effects of genetic drift in these small populations. Despite this correlation, we detected signatures of selection at the MHC, implying that selection has not been completely overwhelmed by genetic drift.
    Molecular Ecology 03/2012; 21(6):1379-93. · 6.28 Impact Factor
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    ABSTRACT: To develop guidelines for the collection of independent field samples of scats for the quantification of wild dog (Lycaon pictus) diet we determined the passage rates of different wild dog prey items from feeding trials on a captive pack held at Marakele National Park, Limpopo Province. The minimum time to first detection was 5.5 hours after feeding (S.E. +/- 1.52, n = 5) and prey items remained in the gut for an average of 79.4 hours (S.E. +/- 6.00, n = 3). Differential passage rates of prey species were not pronounced. Observed passage rates were used to devise a sampling protocol for scats collected during a field study where scats were separated by a minimum period of 120 hours to ensure independence of samples. Comparison of the percentage occurrence of prey species in field-collected scats with the percentage occurrence from direct observations of kills illustrated the tendency for small prey to be underrepresented in the latter. However, the strong correlation between percentage occurrences in diet as determined by the two methods (r(s) = 0.85, P < 0.01, 13 d.f.) suggests that both methods can reliably determine the relative importance of prey in the diets of obligate carnivores such as wild dogs. The determination of maximum passage rates and subsequent guidelines for collection of independent faecal samples in the field could be a valuable tool for reducing inherent biases in carnivore diet studies.
    South African Journal of Wildlife Research 10/2010; 40(2):105-113. · 0.29 Impact Factor
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    01/2009; Endangered Wildlife Trust / Conservation Breeding Specialist Group Southern Africa / SSC/ IUCN CBSG.
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    ABSTRACT: The only viable population of African wild dogs, Lycaon pictus (Temminck 1820), in South Africa occurs in the Kruger National Park. In 1997, a panel of experts identified the establishment of a second viable population as a conservation priority. However, the absence of suitable large conservation areas required that this population be established as what we call a managed metapopulation: namely a series of small, isolated subpopulations that would be managed as a single population by moving wild dogs between areas. Between 1998 and 2006, 66 founder animals were used to establish nine such subpopulations, and the metapopulation reached a peak of 264 animals in 17 packs in June 2005. Pup survival was 64% and yearling survival 71%. Mean annual wild dog densities were 3.3 animals•100 km−2 and approached the upper limit of wild dog densities reported from larger conservation areas. Although the metapopulation strategy was successful in terms of enriching species assemblages and stimulating ecotourism, the process of establishing subpopulations was management intensive. A number of management challenges were revealed, including managing conflict with neighbours following breakouts, addressing concerns over the ability of prey populations to sustain wild dog predation, and the necessity of overcoming stochastic processes that affect small populations, and which curtail natural population dynamics. Experiences gained over the past 10 years have improved technical capacity to capture and translocate wild dogs, and this is likely to inform wild dog conservation management elsewhere in Africa. The managed metapopulation approach might be successfully applied to other large mammal species occupying fragmented habitats and, in some cases, this may be a necessary last resort to stave off extinction. However, such an approach requires considerable inputs of time and money and, where they are an option, priority should be given to conservation strategies that will promote natural dispersal and population self-regulation.
    Reintroduction of Top Order Predators, Edited by Matthew Hayward, Michael J. Somers, 01/2009; Blackwell Publishing.
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    Norman Owen-Smith, M G L Mills
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    ABSTRACT: Shifting prey selection has been identified as a mechanism potentially regulating predator-prey interactions, but it may also lead to different outcomes, especially in more complex systems with multiple prey species available. We assessed changing prey selection by lions, the major predator for 12 large herbivore species in South Africa's Kruger National Park. The database was provided by records of found carcasses ascribed to kills by lions assembled over 70 years, coupled with counts of changing prey abundance extending over 30 years. Wildebeest and zebra constituted the most favored prey species during the early portion of the study period, while selection for buffalo rose in the south of the park after a severe drought increased their vulnerability. Rainfall had a negative influence on the proportional representation of buffalo in lion kills, but wildebeest and zebra appeared less susceptible to being killed under conditions of low rainfall. Selection by lions for alternative prey species, including giraffe, kudu, waterbuck, and warthog, was influenced by the changing relative abundance and vulnerability of the three principal prey species. Simultaneous declines in the abundance of rarer antelope species were associated with a sharp increase in selection for these species at a time when all three principal prey species were less available. Hence shifting prey selection by lions affected the dynamics of herbivore populations in different ways: promoting contrasting responses by principal prey species to rainfall variation, while apparently being the main cause of sharp declines by alternative prey species under certain conditions. Accordingly, adaptive responses by predators, to both the changing relative abundance of the principal prey species, and other conditions affecting the relative vulnerability of various species, should be taken into account to understand the interactive dynamics of multispecies predator-prey webs.
    Ecology 05/2008; 89(4):1120-33. · 5.18 Impact Factor
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    ABSTRACT: Knowledge of a species' ranging behaviour is both fundamental to understanding its behavioural ecology and a prerequisite to planning its management. Few data exist on the spatial ecology of cheetahs Acinonyx jubatus outside protected areas, but such areas are particularly important to their conservation. Cheetahs on Namibian farmlands occupied exceptionally large home ranges, averaging 1651 km2 (±1594 km2), with no detectable effect of sex, social grouping or seasonality. Despite such large ranges, cheetahs tended to utilize intensively only a small fraction of that area: 50% of the fixes were located within an average of 13.9±5.3% of the home range. Ranges were not exclusive, overlapping on average by 15.8±17.0%, with male cheetahs showing more intra-sexual range overlap than did females. Coalitions of males appeared to select for a dense, prey-rich habitat, but this preference was not apparent for other social groupings. Conflict with humans is an important contributor to the species' decline, and these large, overlapping cheetah home ranges result in the movements of each individual cheetah encompassing many farms (21 based on the average home-range size). Consequently, many cheetahs may be exposed to a minority of farmers attempting to kill them, and also that many farmers may see the same cheetahs, thereby gaining an exaggerated impression of their abundance. Conservation priorities for cheetahs outside protected areas are the development of techniques for conflict resolution, as well as the maintenance and restoration of suitable habitat and promotion of land-management practices compatible with the continued existence of large carnivores.
    Journal of Zoology 02/2008; 274(3):226 - 238. · 2.04 Impact Factor
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    Norman Owen-Smith, M G L Mills
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    ABSTRACT: 1. Size relationships are central in structuring trophic linkages within food webs, leading to suggestions that the dietary niche of smaller carnivores is nested within that of larger species. However, past analyses have not taken into account the differing selection shown by carnivores for specific size ranges of prey, nor the extent to which the greater carcass mass of larger prey outweighs the greater numerical representation of smaller prey species in the predator diet. Furthermore, the top-down impact that predation has on prey abundance cannot be assessed simply in terms of the number of predator species involved. 2. Records of found carcasses and cause of death assembled over 46 years in the Kruger National Park, South Africa, corrected for under-recording of smaller species, enabled a definitive assessment of size relationships between large mammalian carnivores and their ungulate prey. Five carnivore species were considered, including lion (Panthera leo), leopard (Panthera pardus), cheetah (Acinonyx jubatus), African wild dog (Lycaon pictus) and spotted hyena (Crocuta crocuta), and 22 herbivore prey species larger than 10 kg in adult body mass. 3. These carnivores selectively favoured prey species approximately half to twice their mass, within a total prey size range from an order of magnitude below to an order of magnitude above the body mass of the predator. The three smallest carnivores, i.e. leopard, cheetah and wild dog, showed high similarity in prey species favoured. Despite overlap in prey size range, each carnivore showed a distinct dietary preference. 4. Almost all mortality was through the agency of a predator for ungulate species up to the size of a giraffe (800-1200 kg). Ungulates larger than twice the mass of the predator contributed substantially to the dietary intake of lions, despite the low proportional mortality inflicted by predation on these species. Only for megaherbivores substantially exceeding 1000 kg in adult body mass did predation become a negligible cause of mortality. 5. Hence, the relative size of predators and prey had a pervasive structuring influence on biomass fluxes within this large-mammal food web. Nevertheless, the large carnivore assemblage was dominated overwhelmingly by the largest predator, which contributed the major share of animals killed across a wide size range.
    Journal of Animal Ecology 02/2008; 77(1):173-83. · 4.84 Impact Factor
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    ABSTRACT: Ecotourism has a potentially vital role to play in conservation by generating economic incentives for nature conservation. However, some authors contend that this potential may be limited by narrow viewing preferences among visitors to protected areas, suggesting that most tourists are primarily interested in seeing charismatic mega-fauna largely confined to government or privately-owned parks. We assessed viewing preferences among tourists at four protected areas in South Africa to test the validity of this contention. Mega-herbivores and large carnivores were the most popular species, particularly among first-time and overseas visitors, but African visitors and experienced wildlife viewers were more interested in bird and plant diversity, scenery, and rarer, less easily-observed and/or less high-profile mammals. Several of these favored species are extinction prone and often absent from wildlife areas due to sensitivity to human encroachment and competition with more abundant species. Hence, ecotourism may provide incentives for the conservation of intact guilds, and management for ecotourism may align more closely with biodiversity conservation objectives than suggested by critics. This potential could be enhanced by diversification of tour operator advertising to feature aspects of biodiversity other than the ‘big five’. Nonetheless, charismatic mega-fauna have a vital flagship role by attracting most overseas and first-time visitors to protected areas.
    Journal of Ecotourism 01/2007; 6(1):19-33.
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    ABSTRACT: African wild dog Lycaon pictus populations are declining due to persecution as well as habitat destruction and fragmentation. Understanding the natural mechanisms driving population dynamics is important for conservation management as it clarifies natural from human-induced factors. Therefore, this understanding is essential to compensate for disadvantaging ecological factors and successfully apply conservation actions. Juvenile survival is important in driving wild dog population dynamics, and therefore this study investigated the influence of rainfall and pack size on the survival of juveniles up to the age of 12 months. We found that past rainfall significantly influenced pup survival up to 9 months of age, such that pups benefited from preceding dry periods. The positive effects of pack size on juvenile survival only became evident for pups older than 9 months and, despite this delayed Allee effect, we found no evidence of reproductive failure in small packs as compared with larger ones.
    Journal of Zoology 09/2006; 272(1):10 - 19. · 2.04 Impact Factor
  • M. G. L. Mills, J. M. Juritz, W. Zucchini
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    ABSTRACT: Conventional census techniques are inappropriate for estimating numbers of nocturnal animals such as the spotted hyaena (Crocuta crocuta). A technique based on attracting animals by taped sounds to calling stations is described. A simple independent experiment to estimate the probability of response to the sounds, as well as a probability model for estimating the population size in a given habitat based on the response counts, is proposed. The model allows for the possibility that some animals may not respond to sounds. The estimate of the population size has a simple form and the sensitivity of the estimate to changes in the response probability can be assessed. The model allows statistical comparisons to be made between different habitats or different times. Likelihood-based confidence intervals can be found for all estimates. The results of surveys in the Kruger National Park illustrate the technique which can be applied in different areas and possibly to other species.
    Animal Conservation 02/2006; 4(4):335 - 343. · 2.69 Impact Factor
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    M. G. L. Mills
    Animal Conservation 02/2006; 9(2):123 - 124. · 2.69 Impact Factor
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    ABSTRACT: African wild dogs are endangered, and in South Africa as elsewhere, they inhabit a fraction of their former range. In this study, we assessed the potential for economic benefits derived from ecotourism to offset the costs of three wild dog conservation options using a contingent valuation study of the willingness of visitors to four protected areas to pay to see wild dogs at the den – within a viable population in a large protected area (Kruger National Park), through reintroduction into nature reserves, and through the conservation of wild dogs occurring on ranchland in situ. Results indicated that tourism revenue from wild dogs in large protected areas is more than sufficient to offset the costs and could potentially be used to subsidise wild dog reintroductions or the conservation of wild dogs in situ on ranchland. On ranchland and for reintroductions, tourism revenue was generally predicted to offset most of the costs of conserving wild dogs where predation costs are low, and to exceed the costs where willingness to pay is high, and/or where the costs of predation by wild dogs are zero. Conservation efforts should facilitate the derivation of eco-tourism-related benefits from wild dogs on ranchland and in private reserves to create incentives for wild dog conservation. Ecotourism should be part of a multifaceted approach to wild dog conservation which also includes education and awareness campaigns, and efforts to encourage landowners to cooperate to form conservancies.
    Biological Conservation. 01/2005;
  • C. M. Begg, K. S. Begg, J. T. Du Toit, M. G. L. Mills
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    ABSTRACT: Radio-tracking locations of 25 individuals (13 females; 12 males) and visual observations of nine habituated individuals were used to investigate the spatial organization and movement patterns of the honey badger Mellivora capensis in the southern Kalahari. The home ranges of adult male honey badgers (541 ± 93 km2) were significantly larger than the home ranges of adult females (126 ± 13 km2). Female home-range size was five times larger than predicted from body mass. The extensive home ranges of females were likely to be a function of relatively low prey availability in the semi-arid Kalahari and the long period of cub dependence (12–16 months). While mean home-range overlap in females was moderate (13%) and home-range centres were regularly spaced, females did not appear to actively defend a territory and no direct interactions between females were observed. Scent marking appears to mediate spatio-temporal separation and females show a loosely territorial spacing pattern. In contrast, males did not support the typical mustelid pattern of intra-sexual territoriality but instead encompassed the overlapping home ranges of up to 13 females. Males and females differed significantly in their rate of travel (3.8 ± 0.3 km/h vs 2.7 ± 0.2km/h), straight line (6.2 ± 0.5 km vs 2.4 ± 0.2 km) and actual distance (13.8 ± 0.9 km vs 7.7 ± 0.7 km) moved during an active period but do not differ in the percentage of their home-range area traversed in a single day (3%). Young males tended to have smaller home ranges (151 ± 45 km2) than adult males and showed a spacing pattern more similar to adult females than adult males. In common with other solitary mustelids, the spatial organization suggests a polygynous or promiscuous mating system.
    Journal of Zoology 01/2005; 265(1):23-35. · 2.04 Impact Factor
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    ABSTRACT: In South Africa, wild dogs are limited to a single viable population in Kruger National Park. Current conservation efforts aim to develop a meta-population through the reintroduction of wild dogs into fenced reserves. However, significant potential also exists for conserving naturally occurring wild dogs in situ on ranchland. This study represents an assessment of the attitudes of southern African landowners towards wild dogs to determine the scope for conserving them on private land, and to identify the conditions under which conservation efforts might succeed. Over half of ranchers interviewed indicated that they would like to have wild dogs on their property. Younger ranchers were more positive than older ranchers, suggesting that traditional prejudices against wild dogs are fading. Attitudes were generally negative where ranches are game-fenced, and where cattle or consumptive wildlife utilisation dominate land use. Negative attitudes were typically related to economic costs associated with wild dogs, and conservation initiatives aimed at reducing costs or creating benefits from the species represent the most direct way to improve attitudes. Many ranchers recognised the potential ecotourism value of wild dogs, and attitudes were most positive where ranches belong to conservancies, and where ecotourism-based land uses predominate. Similar relationships were found between ranch/rancher characteristics and attitudes towards most large carnivores. Thus, our findings have general relevance for large carnivore conservation on private land in southern Africa. Encouraging the formation of conservancies should be a priority for carnivore conservation efforts on ranchland, to reduce conflict and promote coexistence between people and predators.
    Biological Conservation. 01/2005;

Publication Stats

781 Citations
80.66 Total Impact Points

Institutions

  • 2013–2014
    • University of Oxford
      Oxford, England, United Kingdom
  • 2008
    • University of the Witwatersrand
      • School of Animal, Plant and Environmental Sciences
      Johannesburg, Gauteng, South Africa
  • 2003–2008
    • University of Pretoria
      • • Mammal Research Institute
      • • Department of Zoology and Entomology
      Πρετόρια/Πόλη του Ακρωτηρίου, Gauteng, South Africa
  • 2006
    • Utah State University
      Logan, Ohio, United States
  • 2001
    • Sonoma State University
      • Department of Biology
      Rohnert Park, CA, United States