Shifting prey selection generates contrasting herbivore dynamics within a large-mammal predator-prey web.

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.

Predator-prey size relationships in an African large-mammal food web.

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.

Handling-induced stress and mortalities in African wild dogs (Lycaon pictus).

Recently it was suggested that the handling of wild dogs (Lycaon pictus) by researchers in the Serengeti ecosystem created stress, resulting in the reactivation of latent rabies viruses in carrier animals. We present data from ongoing studies on free-ranging and captive wild dogs elsewhere in Africa which do not support this hypothesis. Cortisol profiles suggest that immobilization of wild dogs does not cause the chronic stress required for stress-reactivation of latent viruses. Furthermore, there is no evidence of handling-related mortalities in wild dogs: the survivorship of unhandled and handled free-ranging wild dogs did not differ and no captive animals died within a year of handling (immobilization and/or vaccination against rabies). We suggest that the mortalities observed in Tanzania were due to an outbreak of a disease which rabies vaccination was unable to prevent. Intensive monitoring and active management research programmes on wild dogs are essential as without these, critically endangered wild dog populations have little hope of survival.

Social systems and behaviour of the African wild dog Lycaon pictus and the spotted hyaena Crocuta crocuta with special reference to rabies.

Differences in the social systems and behaviour of two potentially important hosts of rabies, the African wild dog and the spotted hyaena, may lead to differences in the epizootiology of the disease in the two species. Wild dogs are highly social animals in which pack members are in constant physical contact with each other, but in which inter-pack interactions are rare. Spotted hyaenas are more flexible in their social systems and behaviour. Clan members interact less frequently than do wild dogs, but inter-clan contact rates may be high in high density populations. Rabies transmission within wild dog packs should be rapid, but rare between packs. In spotted hyaenas rabies transmission between clan members may partially depend on the social status of the animals involved and between packs on the density of hyaenas in the area.

The wild dog (Lycaon pictus): a new host for Ancylostoma caninum.

Faecal nematode egg counts performed on one captive and 49 free-ranging wild dogs (Lycaon pictus) revealed the presence of eggs of Ancylostoma spp. in 12 (24%) of the animals. The captive wild dog pup showed anorexia, general malaise, pale mucous membranes and black stools. Adult male and female Ancylostoma caninum were recovered from an approximately 3-month-old pup which died of distemper-like disease and a 9-year-old severely debilitated captive wild dog. A single adult A. caninum was also recovered from the intestines of a free-ranging wild dog in the Kruger National Park. These findings confirm the wild dog to be a host for A. caninum.

An investigation into the health status and diseases of wild dogs (Lycaon pictus) in the Kruger National Park.

Many factors have been cited as possible reasons for the decline in the number of wild dogs (Lycaon pictus), but few studies have provided supportive data. Between 1990 and 1993, the dynamics of 10 wild dog packs in the southern district of the Kruger National Park in South Africa were monitored. Casual observations of the causes of disease and mortality in the entire population were also recorded. During the same period, 46 wild dogs were immobilised, weighed, and subjected to physical examination as well as the collection of blood and faecal specimens. External parasites were collected and blood smears were prepared. Serum specimens were subjected to routine blood chemistry analyses, hormone and serological assays and formalinised blood specimens and faeces were subjected to screening for endoparasites. The study population varied from 75 in 1990 to 123 in 1993 with a survival rate of 29.9% for pups, 64.3% for yearlings and 69% for adults. Eighty per cent or more of the population were under 4 years of age. The cause of death in all wild dogs in the Kruger National Park could be established only in a small number of cases. Lions were responsible for the death of 20/62 wild dogs and disease caused the death of 6/62 wild dogs. All immobilised dogs were in a good physical condition, but 85% of dogs had one or more skin lesions. Potential life-threatening lesions (bitewounds inflicted by other dogs and lesions inflicted by a snare) occurred in 4 dogs. One male dog had only one testicle in the scortum. Twenty-six (93%) blood smears were positive for gametocytes of Hepatozoon sp., presumably H. canis, and in 2 dogs trophozoites of Babesia canis were seen. Eighty-six per cent of the specimens were positive for Dipetalonema reconditum. All dogs were infested with ticks and Haemaphysalis leachi, Amblyomma hebraeum, A. marmoreum, Boophilus decoloratus, Rhipicephalus simus, R. evertsi, R. appendiculatus and R. zambesiensis were identified. Ctenocephalides sp. and Echidnophaga larina were also identified. Taenia sp., Toxascaris canis and Ancylostoma caninum were present in faecal specimens. Antibody titres to adenovirus (26/31), B. canis (6/15), canine para-influenza virus (21/31), coronavirus (20/31), Coxiella burnetti (8/29), reovirus Type 3 (9/31), Rickettsia conori/africae (27/29), rotavirus (16/31) and Toxoplasma gondii (16/16) were found. The average serum urea concentration was higher (16.4 mmol/e) than that described for captive wild dogs, but other biochemical parameters were generally in agreement with values reported for captive wild dogs.(ABSTRACT TRUNCATED AT 400 WORDS)

Patterns of population subdivision, gene flow and genetic variability in the African wild dog (Lycaon pictus).

African wild dogs are large, highly mobile carnivores that are known to disperse over considerable distances and are rare throughout much of their geographical range. Consequently, genetic variation within and differentiation between geographically separated populations is predicted to be minimal. We determined the genetic diversity of mitochondrial DNA (mtDNA) control region sequences and microsatellite loci in seven populations of African wild dogs. Analysis of mtDNA nucleotide diversity suggests that, historically, wild dog populations have been small relative to other large carnivores. However, population declines due to recent habitat loss have not caused a dramatic reduction in genetic diversity. We found one historical and eight recent mtDNA genotypes in 280 individuals that defined two highly divergent clades. In contrast to a previous, more limited, mtDNA analysis, sequences from these clades are not geographically restricted to eastern or southern African populations. Rather, we found a large admixture zone spanning populations from Botswana, Zimbabwe and south-eastern Tanzania. Mitochondrial and microsatellite differentiation between populations was significant and unique mtDNA genotypes and alleles characterized the populations. However, gene flow estimates (Nm) based on microsatellite data were generally greater than one migrant per generation. In contrast, gene flow estimates based on the mtDNA control region were lower than expected given differences in the mode of inheritance of mitochondrial and nuclear markers which suggests a male bias in long-distance dispersal.

Molecular genetic and morphological analyses of the African wild dog (Lycaon pictus).

African wild dog populations have declined precipitously during the last 100 years in eastern Africa. The possible causes of this decline include a reduction in prey abundance and habitat; disease; and loss of genetic variability accompanied by inbreeding depression. We examined the levels of genetic variability and distinctiveness among populations of African wild dogs using mitochondrial DNA (mtDNA) restriction site and sequence analyses and multivariate analysis of cranial and dental measurements. Our results indicate that the genetic variability of eastern African wild dog populations is comparable to that of southern Africa and similar to levels of variability found in other large canids. Southern and eastern populations of wild dogs show about 1% divergence in mtDNA sequence and form two monophyletic assemblages containing three mtDNA genotypes each. No genotypes are shared between the two regions. With one exception, all wild dogs examined from zoos had southern African genotypes. Morphological analysis supports the distinction of eastern and southern African wild dog populations, and we suggest they should be considered separate subspecies. An eastern African wild dog breeding program should be initiated to ensure preservation of the eastern African form and to slow the loss of genetic variability that, while not yet apparent, will inevitably occur if wild populations continue to decline. Finally, we examined the phylogenetic relationships of wild dogs to other wolf-like canids through analysis of 736 base pairs (bp) of cytochrome b sequence and showed wild dogs to belong to a phylogenetically distinct lineage of the wolf-like canids.