Selous Game Reserve Research Articles

Six ecological factors that may limit African wild dogs, Lycaon pictus

AbstractAfrican wild dogs (Lycaon pictus) always live at low population densities relative to sympatric large carnivores. This suggests that there are basic ecological reasons for the wild dog's endangered status. We examined the effects of intraspecific and interspecific competition, infectious diseases, foraging success, genetics and human activities on wild dogs. We present data from wild dogs in the Selous Game Reserve, and make comparisons with other populations to identify the limiting factors that are broadly important. The high density of wild dogs in Selous (40 adults/1000 km2) is associated with weak competition from lions and spotted hyenas. Across ecosystems, population density is negatively related to the intensity of interference competition with larger carnivores. Predation by lions and hyenas accounted for 13% of known‐cause deaths in Selous and 33–50% in other populations. Intraspecific competition caused 69% of known‐cause deaths in Selous, through infanticide and fights between packs, although most of the victims were juveniles with low reproductive value. Infectious diseases had little apparent impact in Selous (4% of deaths) or Kruger National Park (5%), but did play a role in the extinction of a small population in Serengeti. Infectious diseases and competition will generally interact because competitors harbor and transmit the diseases that affect wild dogs. Human activities caused 12% of deaths in Selous, even though it is large (43 000 km2) and does not border large human or livestock populations. Humans were the major agent of mortality in some populations. Foraging success varied little across ecosystems and was not apparently limiting. Mitochondrial DNA (mtDNA) genotypes revealed clinal variation between Selous and distant populations (rather than geographically isolated subspecies, as previously suggested). All wild dog populations have a genetically effective size (Ne) less than 500, so gene flow is necessary to maintain genetic diversity within populations.

Six ecological factors that may limit African wild dogs, Lycaon pictus

African wild dogs (Lycaon pictus) always live at low population densities relative to sympatric large carnivores. This suggests that there are basic ecological reasons for the wild dog's endangered status. We examined the effects of intraspecific and interspecific competition, infectious diseases, foraging success, genetics and human activities on wild dogs. We present data from wild dogs in the Selous Game Reserve, and make comparisons with other populations to identify the limiting factors that are broadly important. The high density of wild dogs in Selous (40 adults/1000 km2) is associated with weak competition from lions and spotted hyenas. Across ecosystems, population density is negatively related to the intensity of interference competition with larger carnivores. Predation by lions and hyenas accounted for 13% of known-cause deaths in Selous and 33–50% in other populations. Intraspecific competition caused 69% of known-cause deaths in Selous, through infanticide and fights between packs, although most of the victims were juveniles with low reproductive value. Infectious diseases had little apparent impact in Selous (4% of deaths) or Kruger National Park (5%), but did play a role in the extinction of a small population in Serengeti. Infectious diseases and competition will generally interact because competitors harbor and transmit the diseases that affect wild dogs. Human activities caused 12% of deaths in Selous, even though it is large (43 000 km2) and does not border large human or livestock populations. Humans were the major agent of mortality in some populations. Foraging success varied little across ecosystems and was not apparently limiting. Mitochondrial DNA (mtDNA) genotypes revealed clinal variation between Selous and distant populations (rather than geographically isolated subspecies, as previously suggested). All wild dog populations have a genetically effective size (Ne) less than 500, so gene flow is necessary to maintain genetic diversity within populations.

Serosurvey for selected viral diseases and demography of African wild dogs in Tanzania.

African wild dogs (Lycaon pictus) are endangered, with only 3,000-5,000 remaining in the wild. It is believed that wild dogs are unusually vulnerable to viral diseases, particularly rabies and canine distemper (CDV). However, canine distemper has been confirmed by laboratory diagnosis in only one free-living wild dog. The 43,000 km2 Selous Game Reserve (SGR; Tanzania) holds approximately 900 adult wild dogs. In a study area of 2,600 km2, the population maintained high density (> or = 1 dog/20.5 km2) from 1991 to 1996. The population was stable, varying 18% below and 9% above the mean density over the 6-yr period. Serum samples (n = 22) collected over 3 yr showed that most individuals were exposed to CDV (59%:95% confidence interval = 43-76% seropositive) and canine parvovirus (68%:95% CI = 54-81% seropositive), although none were seropositive for rabies (0%:95% CI = 0-17%). CDV titers were positively related to age, with no seropositive dogs younger than 1.9 yr. At least five of 13 dogs positive for CDV seroconverted during the study. Dogs with high CDV titers did not survive better in the years after sampling (mean survival +/- SE for those that died = 638 +/- 92 days,). Variation in mean litter size was inversely related to CPV exposure in the SGR and elsewhere. Annual mortality rates were low in comparison to other populations for all age classes (pups: 31 +/- 8%, n = 127, yearlings: 22 +/- 10%, n = 93, adults: 20 +/- 6%, n = 235). Annual mortality rates fluctuated little between 1992 and 1996. These data show that wild dog populations, like those of other canids, can remain stable and demographically healthy despite exposure to CDV and CPV.

Lion density and population structure in the Selous Game Reserve: evaluation of hunting quotas and offtake

In 1992, tourist hunting in the Selous Game Reserve generated 1.28 million dollars for the Tanzanian government, of which 0·96 million dollars were returned to wildlife conservation. Lions (Panthera leo) are one of three critical species for tourist hunting, consistently generating 12%–13% of hunting revenue from 1988 to 1992. Because of their ecological and economic importance (and intrinsic value), it is important that lion quotas be set so that offtake is sustainable. The population density of lions in Selous ranges from 0·08 to 0·13 adults km−2, comparable to unhunted ecosystems. The adult sex ratio (36–41% male) and the ratio of cubs to adults (29% cubs) are similar to those of unhunted populations. The ratio of lions to hyaenas is lower in heavily hunted areas (0·17 lions/hyena) than in unhunted areas (0·43 lions/hyena). Hunting levels between 1989 and 1994 took 2·7–4·3% of adult males annually, which is sustainable. The current quota is 10–16% of the adult male population, which exceeds natural mortality rates for male lions. To remain stable if the quota was filled, the population would have to compensate via increased fecundity, increased juvenile survival, or an altered sex‐ratio. Compensation occurs in Selous by producing (or raising) more male than female cubs (66–81% of juveniles are male). Only 28% of the Selous quota was filled in 1992. The percentage of quota filled (both in Selous and nationwide) has dropped since 1988 as quotas have increased. The current intensity of lion hunting in Selous is sustainable, but the quota cannot be filled sustainably.

Rank and reproduction in cooperatively breeding African wild dogs: behavioral and endocrine correlates

African wild dogs (Lycaon pictus) live in cooperative packs with a clear-cut dominance hierarchy in each sex. Reproduction is largely monopolized by the dominant male and female. Alpha females produced 76% of all litters in the Selous Game Reserve and 81% in Kruger National Park. Only 6-17% of subordinate females gave birth each year, compared to 82% of dominant females. In nonmating periods, subordinate females had higher estrogen levels and higher estrogen/progestin ratios than alpha females, apparently preventing ovulation. During mating periods, subordinate females had lower estrogen levels than dominants, mated less often, and were less aggressive. Subordinate males mated at low rates, wore less aggressive than dominants, and had lower testosterone levels. Beta males were similar to alpha males behavioraDy and hormonaUy, suggesting that alpha males may share paternity with beta males. If paternity is more evenly shared than maternity, then subordinate males have a larger incentive than subordinate females to remain in the pack. Following this expectation, dispersal in Selous was female biased (49% versus 24% dispersing annually). Perhaps as a result of mortality associated with dispersal, the adult sex ratio was male biased, although the pup sex ratio was unbiased. In Kruger, neither dispersal nor the adult sex-ratio was biased. Reproductive suppression is widely thought to be caused by social stress in subordinates, but basal cortkosterone levels were higher in dominants than in subordinates

Limitation of African Wild Dogs by Competition with Larger Carnivores

African wild dogs (Lycaon pictus) are endangered largely because their population‐density is low under all conditions. Interspecific competition with larger carnivores may be a factor limiting wild dog density. The density of wild dogs on a 2600‐km2 area of the Selous Game Reserve (Tanzania) was 0.04 adults/km2. Spotted hyaena (Crocuta crocuta) density for the same area was estimated by audio playbacks as 0.32 hyaenas/km2. Lion (Panthera leo) density, determined from the ratio of hyaenas to lions, was 0.11 lions/km2. Across six ecosystems including Selous, there were strong negative correlations between wild dog and hyaena densities (r = −0.92; p = 0.01) and between wild dog and lion densities (r = −0.91; p = 0.03). Hyaenas out‐numbered wild dogs by ratios ranging from 8:1 to 122:1. Ratios of lions to wild dogs ranged from 3:1 to 21:1. The diets of hyaenas and wild dogs overlap extensively; those of wild dogs and lions show less overlap. Where hyaenas are common and visibility is good, interference competition from hyaenas at wild dog kills is common and reduces wild dogs’ feeding time. Where hyaena density is lower and visibility is poor, interference competition at wild dog kills is rare. Wild dogs are commonly killed by lions and occasionally by hyaenas. These data suggest that competition with spotted hyaenas may limit or exclude wild dogs when hyaena density is high. Competition with lions appears less intense, but direct predation by lions on wild dogs is important. Competition and predation by larger carnivores may be of broad importance to the conservation of wild dogs and other medium‐sized carnivores.

Endangered primates in the Selous Game Reserve and an imminent threat to their habitat : B. S. Decker, Oryx, 28(3), 1994, pp 183–190

Endangered primates in the Selous Game Reserve and an imminent threat to their habitat : B. S. Decker, Oryx, 28(3), 1994, pp 183–190

The effects of anthrax on endangered African wild dogs (Lycaon pictus)

African wild dogs (Lycaon pictus) are large, social canids formerly found throughout sub‐Saharan Africa. Wild dogs are now endangered; only six nations hold populations larger than 100 individuals. Considerable evidence suggests that disease plays a central role in the regulation of some wild dog populations. In particular, it has been suggested that epizootics of rabies, canine distemper and anthrax can have strong local effects on wild dog numbers. Resolution of the regulatory importance of these diseases has been hampered by lack of data from wild populations. Here we report on an outbreak of anthrax among wild dogs in the Selous Game Reserve in southern Tanzania, describing clinical signs and diagnosis, measuring mortality, and testing for effects on hunting success and movements. Only one of five packs under study was affected. Immediate mortality was mild, with none of 18 adults (0%) and four of 24 pups (17%) dying. Mortality was significantly higher among puppies (<1 year old) than among adults. Mortality of individuals that showed signs of disease but did not die immediately was not significantly elevated over the following six months. The hunting success and movement patterns of the pack were not affected by the outbreak. Collectively, these data suggest that African wild dogs possess a degree of resistance to anthrax.

Communal hunting and pack size in African wild dogs, Lycaon pictus

African wild dogs are 20–25 kg social carnivores whose major prey are ungulates ranging from 15 to 200 kg. In the Selous Game Reserve, Tanzania, wild dog pack size ranged from three to 20 adults (3–44 including yearlings and pups). Data from 905 hunts and 404 kills showed that hunting success, prey mass and the probability of multiple kills increased with number of adults. Chase distance decreased with number of adults. None the less, the distribution of per capita food intake across adult pack size was U-shaped, with a minimum close to the modal pack size. A similar result has been used to conclude that cooperative hunting does not favour sociality in lions (Packer et al. 1990, Am. Nat., 136, 1–19), and to argue that cooperative hunting is not responsible for group living in any carnivore (Caro 1994, Cheetahs of the Serengeti Plains: Group Living in an Asocial Species). Daily per capita food intake only accounts for variation in the benefits to cooperative hunting, ignoring variation in costs. For Selous wild dogs, per capita food intake per km chased peaked close to the modal adult pack size (where per capita food intake per day was near its minimum). Thus, the energetics of cooperative hunting favour sociality in Selous wild dogs. Analyses that incorporate variation in both costs and benefits of hunting may show that cooperative hunting favours sociality in other species where its influence has previously been rejected.

Endangered primates in the Selous Game Reserve and an imminent threat to their habitat

The Magombera Forest in Tanzania contains the most viable population of the endangered Uhehe red colobus monkey, three other primates, and rare and endemic plants and animals. In 1980 almost half of the Magombera Forest Reserve was surrendered for settlement in exchange for the southern part being incorporated into the Selous Game Reserve. Due to an oversight, the southern part was not legally annexed into the Selous and now the Kilombero Sugar Company has claimed a portion of it. The forest is currently in good condition and offers the best opportunity to conserve the Uhehe red colobus. The author recommends a number of measures to save the forest and its wildlife and to ensure that the needs of the local people are met.

The Conflict between Wildlife and Local People Living Adjacent to Protected Areas in Tanzania: Human Density as a Predictor

A questionnaire survey was conducted in Tanzania of 1396 local people living adjacent to Arusha, Kilimanjaro, Tarangire, Lake Manyara, and Mikumi National Parks and the Selous Game Reserve. Over 71% of local people surveyed reported problems with wildlife. The relative frequency of reported conflict with wildlife was significantly and inversely related to human density on lands adjacent to a protected area. Of those local people who reported having problems with wildlife, 86% reported crop damage, while 10% reported the killing of livestock and poultry. The problematic wildlife species also varied significantly with human density. Large animals were more problematic at low human densities, while small animals were more problematic at high human densities. Local people were generally less effective in controlling small‐bodied species than large‐bodied species. The relative frequency of reported success in controlling wildlife varied significantly with human density and was bimodal: local people were less effective in controlling wildlife at lower and higher human densities. This bimodal relationship suggests that, even if all protected areas in Tanzania were abolished, local people would continue to experience problems with wildlife at high human densities. To minimize the conflict between wildlife and local people, land uses associated with low human density that are non‐attractive to wildlife should be encouraged on lands adjacent to protected areas in Tanzania.

Conservation attitudes of local people living adjacent to five protected areas in Tanzania

A questionnaire survey of conservation attitudes of 1190 people living adjacent to Arusha, Tarangire, Lake Manyara, and Mikumi National Parks and the Selous Game Reserve showed that over 71% were opposed to the suggested abolishment of the adjacent protected area. However, when local people were asked, ‘What good things do people from the adjacent park do?’, 47% reported ‘nothing’. If these same individuals are combined with those who did not answer this question over 71% also held negative or neutral attitudes towards protected area employees. Over 74% of local people felt that poachers are law-breakers. Using a three-way log linear analysis we examined how resource use patterns and problems, and past interactions with the protected area and protected area employees, influence conservation attitudes. Past problems with wildlife, a lack of perceived effectiveness in its control, a shortage of grazing and farming land, problems with flooding, and long-term residency were significantly correlated with support or neutral attitudes toward the abolishment of the adjoining park or reserve. The absence of perceived visitation to a village by a protected area employee, the lack of effectiveness in controlling wildlife, small farm size, problems with flooding, and long-term residency were related to negative attitudes towards protected area employees. Finally, the frequency with which an individual ate meat per month was related to opinions about whether poachers are law-breakers.

Environmental Impacts of the Proposed Stiegler's Gorge Hydropower Project, Tanzania

Establishment of a planned reservoir at Stiegler's Gorge on the Rufiji River would enable a large amount of highlyvalued energy to be produced. This would represent an important national asset. But although such a large net amount of energy would be realized on a short- to mediumterm basis, its production would be negatively influenced by a variety of reservoir operation options that would be related mainly to irrigated agriculture, fisheries, and water quality, which form trade-offs with hydropower generation.The most significant effect of the dam would be drastic reduction, by controlled discharge, in the frequency of severe floods in the lower Rufiji valley. Floods in excess of 2,500 cubic metres of discharge per second could be reduced in number from some 14 to 3 in 24 years, or from 167 to 13 during 300 years. The most devastating floods would also be reduced—from once in about 8 years to once in maybe 40 years.The STIGO Project impact area contains a major wildlife resource in terms of size, density, and diversity. Its accessibility to Dar es Salaam gives it a great potential for tourism development. As an access road to the dam-site would be a necessary prerequisite to implementation of the STIGO Project, it would indirectly help to open up the Selous Game Reserve to tourism, which is currently being hampered by poor communications. Also, a substantial amount of the forest resources identified along this road could be exploited.No complete populations of animal wildlife would be in danger from direct ecological consequences of river impoundment and dam construction. However, significant proportions of the populations in the STIGO Project impact area of three species (Giraffe, Wildebeest, and Zebra) would be potentially at risk, owing to their need for habitats of restricted range. On the other hand some species, including Crocodile and Hippopotamus, would increase in numbers following creation of the reservoir and improvement of their habitat downstream of the dam (due to swamp drainage).Not withstanding that the ecological impacts of dam construction are relatively minor, the socio-economic impacts on wildlife and conservation values are potentially great—resulting, for instance, from facilitated access to the heart of the Selous Game Reserve and concomitantly increased conflict between wild animals and Man. These circumstances would reduce wilderness values and disturb animal wildlife, so that, especially, commercially valuable species may be expected to decline unless strict regulations are made and enforced.*River impoundment would have very negative impacts on floodplain fisheries and agriculture, the latter of which would probably be changed to irrigated agriculture with artificial fertilization, while floodplain fisheries would totally collapse. Some mangrove stands in the Delta would probably be displaced by reeds. Delta fisheries would be very negatively affected, because of changes in the water regime as well as in salinity levels.Water quality in the planned reservoir and in the downstream area would be negatively affected by the project. The water would often be unfit for human and animal consumption and use, as well as unfavourable for fisheries. The project would also have negative effects on the health of the riparian population, owing to increased potentials for disease vectors.Overall, a high degree of uncertainty is involved in the project. The effect of the primary project (hydropower) would be negative owing to its drastic consequences for the immediate and more distant impact areas. Its image might improve and probably become positive if development in the Basin were carefully controlled and managed. This would require reliable prediction of the impacts and a thorough analysis of the remedial and/or additional measures to arrive at an integrated development strategy for the Basin. Although several measures are planned to eliminate and/or minimize the negative impacts, their implementation may be difficult in view of the bad economic situation of the country.

Chairman's report

Notes the ongoing work of the AERSG relating to elephants which includes monitoring status in Mali, Mauritania and Namibia, supporting studies focused on the forest elephant, a census in Selous Game Reserve and supporting conservation initiatives throughout west and central Africa.

Rhino and elephant poaching trends in the Selous Game Reserve

In 1981 the Selous Game Reserve, the largest in Africa, harboured the largest elephant and black rhino populations on the continent. The elephant population density was calculated to be very similar during 1976 and 1981 surveys. During the seventies, poaching was minimal due to the inaccessibility of the reserve, but construction of Shell Company oil exploration roads beginning in 1981 can be linked with an increased poaching activity in the area. The depressed economic situation of the country coupled with the rising international prices for ivory and rhino horn contributed to poaching. Results of a survey based on interviews with hunters, staff and clients of the Tanzania Wildlife Corporation and Wildlife Divison staff carried out in 1984 are discuss along with reasons for increased poaching and recommendations to remedy the situation.

Demographic characteristics of the warthog population of the eastern Selous Game Reserve, Tanzania

SummaryDemographic characteristics of warthog (Phacochoerus aethiopicus) were studied in the Selous Game Reserve. Samples of both animals and skull collections were used to construct static life tables and mortality rate curves. The animal sample comprised specimens between 0 and 7 years old, but skull sample had specimens representative of ages from 1 to 11.A characterstic mortality rate curve was obtained which can be divided into a juvenile phase where the rate of mortality is initially high but rapidly decreases, followed by a post‐juvenile phase characterized by an initial low but steadily increasing rate of mortality.The significance of the work to effective management of the species in the area is stressed.RésuméLes caractéristiques démographiques du phacochère (Phacochoerus aethiopicus) ont étéétudiées au Selous Game Reserve. Un échantillonage d'animaux et de crânes a permis la construction d'une table de survie et de courbes de taux de mortalité. L'échantillonage d'animaux comprend des individus entre 0 et 7 ans et celui des crânes compte des spécimens représentant des âges de 0 à 11 ans.La courbe de taux de mortalité obtenue peut être divisée en une phase juvénile où la mortalité est d'abord élevée puis décroit rapidement, et une phase postjuvénile caractérisée par un taux de mortalité d'abord faible, puis augmentant rapidement.La signification de ce travail pour la gestion efficace de l'espèce dans cette région est mise en évidence.

Chairman's report

Reviews the background behind the decision to develop the AERSG by combining the African Elephant and Rhino Specialist Groups into one body focused on the conservation of both species. Notes assistance to Selous Game Reserve and Garamba National Park, studies updating infromation the volume, source and destination of African ivory including analysis of the recent large consignments out of Sudan, analysis of ivory statistics in relation to elephant population, and forthcoming research focused on the forest elephant (Loxodonta africana cyclotis)

A riverside count in Africa's Selous Game Reserve

The Selous contains a wealth of animals but monitoring the populations is difficult because motorable tracks are few and aerial surveys are expensive. The author gained access to the heart of the reserve along its rivers and during a 12-day raft journey he recorded the large animals he saw. He was impressed by the pristine condition of the riverside habitat and he found no evidence of poaching there.

Reproductive ecology of the warthog Phacochoerus aethiopicus and its significance for management in the Eastern Selous Game Reserve, Tanzania

The study examines the reproductive potential of the warthog Phacochoerus aethiopicus in the eastern Selous Game Reserve, Tanzania, and establishes the recruitment pattern of the population. The methods involved animal collection and field observations. Results showed that female warthogs reached sexual maturity at about two years of age. There was a fairly high reproductive rate, with 87% of sexually mature females producing an average of 2·6 hoglets each a year. Breeding occurred in April and May, farrowing in September, October and November. This suggested a gestation period of about five months. Females of 4 and 5 years of age were found to be more productive than either younger or older ones. Pre-natal sex ratio was 1:1, but post-natal deviated from unity. Mortality was highest in younger and very old animals. The importance of data on reproductive ecology to efficient game management is stressed.

The Railway and a Rare Colobus Monkey

The Tanzania-Zambia railway now bisects the Magombera Forest Reserve in Tanzania, and as a result the most viable surviving population of the rare endemic Iringa red colobus is seriously threatened. The railway has facilitated tree-felling, settlement and cultivation, and the colobus habitat is already seriously damaged. The authors conducted a survey of the forest in 1979, and recommended that the southern part, which has a viable colobus population, be included in the neighbouring Selous Game Reserve, thus giving that part the stronger protection of a game reserve, and that the local people be compensated by the release to them of a small area of the Selous.