Johan T. du Toit

The return of the giants: ecological effects of an increasing elephant population.

Abstract Northern Botswana and adjacent areas, have the worlds largest population of African elephant (Loxodonta africana). However, a 100 years ago elephants were rare following excessive hunting. Simultaneously, ungulate populations were severely reduced by decease. The ecological effects of the reduction in large herbivores must have been substantial, but are little known. Today, however, ecosystem changes following the increase in elephant numbers cause considerable concern in Botswana. This was the background for the “BONIC” project, investigating the interactions between the increasing elephant population and other ecosystem components and processes. Results confirm that the ecosystem is changing following the increase in elephant and ungulate populations, and, presumably, developing towards a situation resembling that before the reduction of large herbivores. We see no ecological reasons to artificially change elephant numbers. There are, however, economic and social reasons to control elephants, and their range in northern Botswana may have to be artificially restricted.

Ecological implications of bovine tuberculosis in African buffalo herds

Following the recent invasion of bovine tuberculosis (BTB) into the Kruger National Park, South Africa, we conducted a study on the maintenance host, African buffalo, to investigate associations between BTB prevalence and calf:cow ratio, age structure, body condition, and endoparasite load. Statistical analyses compared herds of zero, medium (1- 40%), and high (.40%) BTB prevalence. To control for ecological variation across the park we collected data in northern, central, and southern regions and restricted some analyses to particular regions of the park. Body condition declined over the course of the 2001 dry season, and buffaloes in the southern region of the park, with the highest BTB prevalence, were in worse condition than buffaloes in the northern region (which receives less annual rainfall but is still virtually BTB-free). Herd-level analyses of the entire park, the south and central regions, and just the southern region all indicated that herds of higher BTB prevalence were in worse condition and lost condition faster through the dry season than herds of lower BTB prevalence. Fecal endoparasite egg counts increased during the dry season and were associated with both decreased body condition and increased BTB prev- alence. Although we did not detect any obvious effect of BTB on the age structure of the buffalo population, our findings indicate early symptoms of wider scale BTB-related eco- logical disturbances: buffalo herds with high BTB prevalence appear more vulnerable to drought (because of a decrease in body condition and an increase in endoparasite load), and because lions selectively kill weak buffaloes their prey base is accumulating a dispro- portionately high prevalence of BTB, to which lions are susceptible.

Winning by a Neck: Tall Giraffes Avoid Competing with Shorter Browsers

With their vertically elongated body form, giraffes generally feed above the level of other browsers within the savanna browsing guild, despite having access to foliage at lower levels. They ingest more leaf mass per bite when foraging high in the tree, perhaps because smaller, more selective browsers deplete shoots at lower levels or because trees differentially allocate resources to promote shoot growth in the upper canopy. We erected exclosures around individual Acacia nigrescens trees in the greater Kruger ecosystem, South Africa. After a complete growing season, we found no differences in leaf biomass per shoot across height zones in excluded trees but significant differences in control trees. We conclude that giraffes preferentially browse at high levels in the canopy to avoid competition with smaller browsers. Our findings are analogous with those from studies of grazing guilds and demonstrate that resource partitioning can be driven by competition when smaller foragers displace larger foragers from shared resources. This provides the first experimental support for the classic evolutionary hypothesis that vertical elongation of the giraffe body is an outcome of competition within the browsing ungulate guild.

Wildlife harvesting guidelines for community-based wildlife management: a southern African perspective.

African wildlife populations and their habitats are dwindling outside ofstate-protected areas due to escalating human demands on natural resources,while the effective enforcement of conservation legislation is impracticableacross most of the continent. A particular conservation crisis is looming insouthern Africa, where extensive wildlife areas are rapidly giving way tosubsistence agropastoralism. The concept of community-based wildlife management(CBWM) has been embraced by donor agencies as a hopeful solution in areas whereadequate wildlife resources persist and agricultural potential is marginal. Theconservation value of CBWM depends, however, on communities having specificinformation to evaluate the sustainable benefits of wildlife in comparison withalternative landuse options. Furthermore, simple but scientifically soundmonitoring procedures are required to ensure that the offtake from wildlifepopulations is kept within sustainable limits. This paper draws together keyecological issues of relevance to CBWM in southern African savannas andidentifies topics requiring further attention from ecologists. The aim is toassist conservation and development agencies in providing prompt and appropriatetechnical support to communities in areas where opportunities for CBWM stillexist but could soon be foreclosed.African wildlife populations and their habitats are dwindling outside ofstate-protected areas due to escalating human demands on natural resources,while the effective enforcement of conservation legislation is impracticableacross most of the continent. A particular conservation crisis is looming insouthern Africa, where extensive wildlife areas are rapidly giving way tosubsistence agropastoralism. The concept of community-based wildlife management(CBWM) has been embraced by donor agencies as a hopeful solution in areas whereadequate wildlife resources persist and agricultural potential is marginal. Theconservation value of CBWM depends, however, on communities having specificinformation to evaluate the sustainable benefits of wildlife in comparison withalternative landuse options. Furthermore, simple but scientifically soundmonitoring procedures are required to ensure that the offtake from wildlifepopulations is kept within sustainable limits. This paper draws together keyecological issues of relevance to CBWM in southern African savannas andidentifies topics requiring further attention from ecologists. The aim is toassist conservation and development agencies in providing prompt and appropriatetechnical support to communities in areas where opportunities for CBWM stillexist but could soon be foreclosed.

Methods for Locating African Lion Kills Using Global Positioning System Movement Data

Abstract Knowledge of the range, behavior, and feeding habits of large carnivores is fundamental to their successful conservation. Traditionally, the best method to obtain feeding data is through continuous observation, which is not always feasible. Reliable automated methods are needed to obtain sample sizes sufficient for statistical inference. Identification of large carnivore kill sites using Global Positioning System (GPS) data is gaining popularity. We assessed performance of generalized linear regression models (GLM) versus classification trees (CT) in a multipredator, multiprey African savanna ecosystem. We applied GLMs and CTs to various combinations of distance-traveled data, cluster durations, and environmental factors to predict occurrence of 234 female African lion (Panthera leo) kill sites from 1,477 investigated GPS clusters. Ratio of distance moved 24 hours before versus 24 hours after a cluster was the most important predictor variable in both GLM and CT analysis. In all cases, GLMs outperformed our cost-complexity-pruned CTs in their discriminative ability to separate kill from nonkill sites. Generalized linear models provided a good framework for kill-site identification that incorporates a hierarchal ordering of cluster investigation and measures to assess trade-offs between classification accuracy and time constraints. Implementation of GLMs within an adaptive sampling framework can considerably increase efficiency of locating kill sites, providing a cost-effective method for increasing sample sizes of kill data.

Differential effects of defoliation by mopane caterpillars and pruning by African elephants on the regrowth of Colophospermum mopane foliage

Plant responses to herbivory vary depending on herbivory type, yet the comparative effects of defoliation (e.g. by insects) and pruning (e.g. by large mammals) on a single tree species are poorly documented. We investigated this in the Northern Province of South Africa by comparing the regrowth of Colophospermum mopane trees previously defoliated by caterpillars or pruned by elephants, the two main browsers of C. mopane foliage. Shoots were up to 160% and 125% longer after natural (elephant) and simulated pruning and leaves ∼25% longer in regrowth after natural pruning (n = 13-15 trees per treatment). Shoot density and chemical defences in leaves (tannin:protein ratio and total polyphenolic concentration) were, however, no different from control trees. Simulated defoliation resulted in statisticallyinsignificantchangestoregrowthintermsofleafandshootsize(bothslightlydecreased)andshootdensity (slightly increased). Natural (caterpillar) defoliation, however, resulted in regrowth with significantly decreased shoot and leaf size (about 50% and 20% of control lengths, respectively), as well as decreased leaf chemical defence. Shoot and leaf length were longer on trees flushing for the first time after pruning and late-season defoliation had a greater negative impact than mid-season defoliation. Despite the differences in regrowth characteristics after pruning and defoliation, mopane plants showed no apparent trade-off in investment between tolerance and resistance after either herbivory type, as neither regrowth nor chemical defence occurred at the expense of the other.

Dynamics of a protected black rhino (Diceros bicornis) population: Pilanesberg National Park, South Africa

Achieving maximum productivity in remnant populations of black rhinoceros is crucial to the persistence of this species. It was, therefore, investigated whether the black rhino population of Pilanesberg National Park had become regulated by resource limitation 22 years after introduction in 1979. Inter-calving intervals (which are not restricted to yearly time increments, due to asynchronous reproduction) decreased with an increase in rainfall, while the percentage of male calves born increased with increasing rainfall. The percentage of reproductive cows achieving maternal success increased with increasing density until 0.085 rhinos/km2, after which it decreased. This positive relationship at low densities is largely due to changes in the female age structure and the adult female/male ratio. The age at first calving tended to increase with increasing density, while mortality was not related to rainfall or density. It is concluded that the Pilanesberg black rhino population is showing the first signs of density dependence. It is proposed that black rhino conservators should monitor the percentage of cows achieving maternal success to detect early indications of density dependent resource limitation and use this as a criteria for decisions regarding metapopulation management.

Coexisting with Cattle

In East Africa, large wild herbivores both compete with and benefit cattle. Many large plant-eating mammals have evolved to live in multispecies assemblages, with species competing for food and other resources. Through domestication and animal husbandry, however, humans have enabled a few species of livestock, such as cattle, to dominate such assemblages. One standard practice in livestock production on rangelands, espoused by commercial ranchers and subsistence pastoralists alike, is the eradication of large, indigenous herbivores that are believed to compete with livestock for food. These eradication efforts have increasingly problematic implications for biodiversity conservation (1). So it is timely that on page 1753 of this issue, Odadi et al. (2) report on a relatively simple experiment that tested the assumption that cattle and wildlife compete for food. Their study, conducted in an East African savanna renowned for its large herbivore diversity, revealed that cattle do compete with herbivores such as zebras and gazelles during the dry season, when food quantity is low. In contrast, during the wet season, when food quantity is high, grazing by wildlife benefits cattle by improving the quality of forage. The findings highlight ecological processes that promote coexistence among large herbivores in grasslands and savannas, and hence could be useful for conservation.

Climate and density-dependent drivers of recruitment in plains bison

Abstract In semiarid ecosystems ungulate densities can compound the effects of drought on forage availability, which can feed back to regulate reproduction and offspring recruitment. Climatic changes in the frequency and severity of drought could thus exacerbate these effects. Here, we use long-term data sets to examine the dual influences of population density, cohort, and climatic variation on recruitment in the Henry Mountains bison (Bison bison bison) population. We found that 1-year lagged annual precipitation had a positive effect on recruitment (&bgr; u200a=u200a 0.032, SE u200a=u200a 0.009) and population density had a negative effect (&bgr; u200a=u200a −0.0023, SE u200a=u200a 0.0004), but did not detect cohort effects. Furthermore, the effect of population density seemed to be more severe in dry relative to wet conditions, indicating that competition for forage could be severe in drought conditions. These results could help managers gain insight into the effects of climate change on bison population dynamics, and help guide the management of bison abundance on rangelands shared with cattle.

Anthropogenic factors affecting wild dog Lycaon pictus reintroductions: a case study in Zimbabwe

In 1997 a pack of African wild dogs Lycaon pictus was reintroduced to Matusadona National Park in north-western Zimbabwe. Here we use this case study to consider anthropogenic factors likely to affect the success of wild dog reintroductions in southern Africa. Potential wild dog-human conflict was investigated using a questionnaire, administered to communal farm- ers near the Park, that recorded the incidence of livestock predation, snaring, traditional uses and attitudes of local people towards wild dogs. Predation on livestock was negligible, with wild dogs being responsible for <2% of goat losses to wild predators. Twenty-four different tra- ditional uses for wild dogs and their body parts were described by 54% of survey respondents. Less than 25%