Effect of low rainfall and browsing by large herbivores on an enclosed savannah habitat in Kenya

Savannah ecosystems in East Africa are rarely stable and can experience rapid local changes from dense woodlands to open plains. In this 3‐year study there was a reduction of 16.3% in a height‐stratified sample of nearly 1000 individually marked Acacia drepanolobium trees. The study was carried out in an enclosed fire‐free wooded grassland habitat in the Laikipia region of Kenya. The trees were monitored from 1998 to 2001, a period that included 12 months when rainfall was 60% below average. Elephants were responsible for the loss of 40% of the trees, black rhinos 33% and 27% died from the effects of the drought. Low rainfall was correlated with increased damage as elephants switched diet from grass to trees. Heavy browsing by giraffes reduced tree growth rates and increased their susceptibility to drought. Hence the combination of low rainfall and heavy browsing by elephants, black rhinos and giraffes led to the rapid tree loss. These findings have implications for research into the causes of instability in savannah ecosystems and the management of enclosed reserves.     

The impact of giraffe, rhino and elephant on the habitat of a black rhino sanctuary in Kenya

The habitat in an enclosed black rhino sanctuary, the Sweetwaters Game Reserve in Kenya, is being altered as populations of elephant, giraffe and black rhino increase. Height‐specific browse impact data were recorded for 1075 trees of the dominant species, the whistling thorn, Acacia drepanolobium. Rhinos and elephants browsed 18% of these trees in 1 year, including 5% that were killed or removed. The remaining trees were subjected to high levels of giraffe browse and low rainfall and grew by only 7.5 cm in a year. A mathematical model has been constructed that predicts how the number of trees ha^?1 will change with time under different browsing impacts. The model compares recruitment rate with removal rate and estimates that the number of trees ha^?1 will fall by 2% per year under the current browsing impact of black rhino (0.27 per km²), elephant (1.1 per km²) and giraffe (1.9 per km²). In 7 years, if the rhino and elephant populations continue to increase at the current rates, tree density will be falling by 5% per year and nearly one‐third of the trees will have been removed. These conditions are unsustainable and will result in habitat change and may affect rhino breeding. Several ways of alleviating the problem are discussed.     

Browsing impact of large herbivores on Acacia xanthophloea Benth in Lake Nakuru National Park, Kenya

Significant differences ( P <0.05) were found in growth of plant height, canopy cover and stem diameter of Acacia xanthophloea trees in fenced plot as compared with unfenced plot both in the wet and in the dry seasons. Finding of this study showed that although heavy browsing reduced the height and canopy of trees, it did not kill any trees and seedling regeneration took place simultaneously. Despite the presence of large herbivores that impact some considerable browsing pressure results indicate that the A. xanthophloea habitat type would continue to remain in balance in the presence of recruitment of seedlings and saplings. The conditions at the time of study indicate that the browsing on A. xanthophloea was not significant and was not serious enough to warrant management intervention at present.     

Human impact on wildlife populations within a protected Central African forest

This paper addresses the effect of human activities on the density of large mammals in the Dzanga‐Ndoki National Park and the adjacent Dzanga‐Sangha Reserve in the Central African Republic. Between six and eight 20 km long permanent transects were walked on a monthly basis from January 1997 to August 1999 to assess large mammal populations as well as human intrusion. There were no obvious seasonal or monthly trends in elephant, gorilla or non‐human primate densities. Overall, it appears that human activities negatively influence the distribution of most of the large forest animals in Dzanga‐Sangha. Elephants in particular were significantly less common in areas used by humans, but also other species such as non‐human primates showed lower densities closer to the main road and the town of Bayanga. This study confirms the findings of previous studies that roads have a negative impact on wildlife populations. Results of this study stress the need for conservation of large uninterrupted forest blocks to maintain wildlife populations at normal levels. Simply creating roads, even within a protected Central African forest, is likely to have negative impacts on wildlife populations.     

Structure and composition of Acacia xanthophloea woodland in Lake Nakuru National Park, Kenya

The woody vegetation of Lake Nakuru National Park occurs along rivers, lakeshores and flood plains. Four different sites within the Acacia xanthophloea woodlands were selected for the study. Vegetation structure was not significantly different in the four woodlands used for the study, but these sites differed in the relative density of Acacia trees. Regeneration of A. xanthophloea differed in each site, with the highest regeneration rates found in the nonfenced plots where browsing took place.     

Strong but opposing effects of associational resistance and susceptibility on defense phenotype in an African savanna plant

The susceptibility of plants to herbivores can be strongly influenced by the identity, morphology and palatability of neighboring plants. While the defensive traits of neighbors often determine the mechanism and strength of associational resistance and susceptibility, the effect of neighbors on plant defense phenotype remains poorly understood. We used field surveys and a prickle‐removal experiment in a semi‐arid Kenyan savanna to evaluate the efficacy of physical defenses against large mammalian herbivores in a common understory plant, Solanum campylacanthum. We then quantified the respective effects of spinescent Acacia trees and short‐statured grasses on browsing damage and prickle density in S. campylacanthum. We paired measurements of prickle density beneath and outside tree canopies with long‐term herbivore‐exclusion experiments to evaluate whether associational resistance reduced defense investment by decreasing browsing damage. Likewise, we compared defense phenotype within and outside pre‐existing and experimentally created clearings to determine whether grass neighbors increased defense investment via associational susceptibility. Removing prickles increased the frequency of browsing by ~25%, and surveys of herbivory damage on defended leaves suggested that herbivores tended to avoid prickles. As predicted, associational resistance and susceptibility had opposing effects on plant phenotype: individuals growing beneath Acacia canopies (or, analogously, within large‐herbivore exclosures) had a significantly lower proportion of their leaves browsed and produced ~ 70–80% fewer prickles than those outside refuges, whereas plants in grass‐dominated clearings were more heavily browsed and produced nearly twice as many prickles as plants outside clearings. Our results demonstrate that associational resistance and susceptibility have strong, but opposing, effects on plant defense phenotype, and that variable herbivore damage is a major source of intraspecific variation in defense phenotype in this system.     

Impact of land use and tenure changes on the Kitenden wildlife corridor,Amboseli Ecosystem,Kenya

This study assesses the ecological pressure exerted by changing land use and tenure on the Kitenden wildlife corridor, a critical cross‐border link between the Amboseli and Kilimanjaro national parks. The implications on viability of the two high‐value protected areas and their respective dispersal areas are both negative and serious. The extent of land use change and its impacts were assessed through household and vegetation surveys, while wildlife abundance was measured using transect walks. Approximately 30% of the study area has shifted from community to private land ownership over the last two decades. Except for baboon and vervet monkey, most wildlife avoided the cultivated area. Vegetation composition on the noncultivated area has been greatly altered by intense wildlife and livestock use, where mean herbaceous vegetation cover differed significantly among range‐plant categories (F_{3, 524} = 29.015, p < 0.05). The frequency of increaser I (21.4%) differs greatly from that of decreaser and forbs, at 8.3% and 7.4%, respectively Tree recruitment was low, with a significant difference in mean density among age classes (F_{2, 110} = 3.663, p < 0.05). Only through land leasing agreements between landowners and conservation organisations, and a widely supported land use plan, can the spread of cultivation be controlled and complete cessation of wildlife movement be prevented.     

Roadside conditions as predictor for wildlife crossing probability in a Central African rainforest

The negative effects of roads on wildlife in tropical rainforests are poorly understood. Road construction has high priority in Africa, while negative impacts of roads on wildlife movement often are neglected. This study aims at providing information on the effects of roads on crossing behaviour of rainforest wildlife. The probability that wildlife would cross forest roads was analysed for association with ten different factors that were linked to road presence or construction. Factors were divided into three classes: vegetation cover, topography and human influence. A trackplot survey was done in southern Cameroon, Africa. Trackplots were laid along a 32 km unpaved logging road that intersects Campo‐Ma’an National Park. Tracks of several species were found frequently (e.g. genets and porcupines); while others were found only sporadically (e.g. forest duikers and apes). The actual physical obstacles found along the road (e.g. logs, banks, etc.) were highly negatively correlated with crossing probabilities. For all wildlife species high vegetation cover was positively correlated to crossing probability. This study indicates that roads have a large impact on wildlife, and suggests which factors could be altered during road construction and maintenance in order to mitigate these impacts.     

人与野生动物冲突研究现状及经验启示

人与野生动物冲突是人与自然耦合系统不可避免的负向产物,对冲突的治理是实现保护与发展协调的重要路径。国内外学者对此展开了大量的研究。本文从冲突生成、影响、成本和治理四个方面对现有研究进行梳理,结果表明人与野生动物冲突对保护与发展都造成负面影响,包括社区直接经济损失、人身安全受威胁、福祉降低以及野生动物被伤害、栖息地被挤占。现有研究还存在缺乏跨学科系统研究框架、忽视冲突隐性成本以及对冲突影响研究不深入等不足,未来在科学测度冲突成本、从生态和社会经济视角对冲突影响进行评估以及冲突治理措施多元化方面研究需要深入。在此基础上,从建立中央政府为主、地方政府为辅的野生动物冲突补偿专项基金;政府为主导,企业、社区、国际组织和高校多方利益群体参与机制;人与野生动物冲突分区管理制度;冲突损失核算和申报管理系统;多元化冲突治理模式;冲突减缓土地利用规划体系方面提出现有研究对治理我国人与野生动物冲突的启示。     

Human–wildlife conflicts in a fragmented Amazonian forest landscape: determinants of large felid depredation on livestock

Most large carnivore species are in global decline. Conflicts with people, particularly over depredation on small and large livestock, is one of the major causes of this decline. Along tropical deforestation frontiers, large felids often shift from natural to livestock prey because of their increased proximity to human agriculture, thus increasing the likelihood of conflicts with humans. On the basis of data from 236 cattle ranches, we describe levels of depredation by jaguars Panthera onca and pumas Puma concolor on bovine herd stocks and examine the effects of both landscape structure and cattle management on the spatial patterns and levels of predation in a highly fragmented forest landscape of southern Brazilian Amazonia. Generalized linear models showed that landscape variables, including proportion of forest area remaining and distance to the nearest riparian forest corridor, were key positive and negative determinants of predation events, respectively. We detected clear peaks of depredation during the peak calving period at the end of the dry season. Bovine herd size and proportion of forest area had positive effects on predation rates in 60 cattle ranches investigated in more detail. On the other hand, distance from the nearest riparian forest corridor was negatively correlated with the number of cattle predated. The mean proportion of cattle lost to large felids in 24 months for the region varied according to the herd class size (<500: 0.82%; 500–1500: 1.24%; >1500: 0.26%) but was never greater than 1.24%. The highest annual monetary costs were detected in large cattle ranches (>1500 head of cattle), reaching US$ 885.40. Patterns of depredation can be explained by a combination of landscape and livestock management variables such as proportion of forest area, distance to the nearest riparian corridor, annual calving peak and bovine herd size.     

Effects of human–livestock–wildlife interactions on habitat in an eastern Kenya rangeland

Human–livestock–wildlife interactions have increased in Kenyan rangelands in recent years, but few attempts have been made to evaluate their impact on the rangeland habitat. This study identified drivers of increased human–livestock–wildlife interactions in the Meru Conservation Area between 1980 and 2000 and their effects on the vegetation community structure. The drivers were habitat fragmentation, decline in pastoral grazing range, loss of wildlife dispersal areas and increase in livestock population density. Agricultural encroachment increased by over 76% in the western zone adjoining Nyambene ranges and the southern Tharaka area, substantially reducing the pastoral grazing range and wildlife dispersal areas. Livestock population increased by 41%, subjecting areas left for pastoral grazing in the northern dispersal area to prolonged heavy grazing that gave woody plant species a competitive edge over herbaceous life‐forms. Consequently, open wooded grassland, which was the dominant vegetation community in 1980, decreased by c. 40% as bushland vegetation increased by 42%. A substantial proportion of agro pastoralists were encountered around Kinna and Rapsu, areas that were predominantly occupied by pastoralists three decades ago, indicating a possible shift in land use in order to spread risks associated with habitat alterations.     

Survival,recruitment and dynamics of Acacia drepanolobium Sjøstedt seedlings at Olpejeta Conservancy,Kenya, between 1999 and 2009

Survival and recruitment of the whistling thorn (Acacia drepanolobium Sjøstedt) seedlings was studied in Olpejeta Conservancy, Kenya, between 1999 and 2009. Seedlings were monitored for damage by drought and herbivores as well as survival and recruitment into adult trees. We determined variability in seedling damage, survival and recruitment before and after two management interventions; the elephant translocation in 2001 and the expansion of the reserve in 2007. Seedling survival over 8 years was low, with mortalities being initially high between 2000 and 2001. Reduction in elephant numbers was followed by a gradual reduction in seedling mortality. We recorded a 47% survival over 8 years; 63% of the mortality having been caused by browsers, drought or other factors. Only 8 (0.75%) of the seedlings had grown into trees. Seedlings experienced greater damage at higher densities and exhibited a storage effect underneath grass cover. Survival and recruitment of A. drepanolobium seedlings is very low and of concern. The expansion of conservation area and the opening of wildlife migration corridors have, however, resulted in a steady recovery for seedlings. We recommend enclosing sections of the conservancy to exclude grazers and browsers such as elephants and to allow seedling survival and recruitment.     

Impact of leopards on a working ranch in Laikipia,Kenya

This study of leopard predation on livestock was carried out on the Lolldaiga Hills ranch (200 km²) in the Laikipia District in Kenya between September 1989 and August 1995. The aims of the study were to find out whether leopards depend on livestock as a food resource on the ranch, and to quantify the economic impact of leopards on the livestock production systems. The density of leopards was estimated in three ways, and the biomass density of potential prey for leopards, both wild and domestic. Diet analysis of leopards revealed that leopards are not relying on livestock as an important food resource. To quantify the effects of leopards, an approach used in the economic assessment of agricultural development schemes was adopted ( Gittinger, 1982 ) and models were derived by following those criteria. It was found that leopards, not being persecuted, live at a relatively high density on the ranch but have less of an adverse impact on livestock than might be expected. Wildlife as a food resource for leopards and a buffer against the killing of livestock could be of benefit on a working ranch to reduce the economic impact of predators on the production system.     

Population trends of large non-migratory wild herbivores and livestock in the Masai Mara ecosystem, Kenya, between 1977 and 1997

The total of all non-migratory wildlife species in the Masai Mara ecosystem has declined by 58% in the last 20 years. This decline ranges from 49% in small brown antelopes to 72% in medium brown antelopes. In individual wildlife species, the decline ranges from 52% in Grant's gazelle to 88% in the warthog. Declines of over 70% have been recorded in buffalo, giraffe, eland and waterbuck. Only elephant, impala and ostrich have not shown any significant decline or increase. Overall, there has not been any significant difference in decline of all wildlife population sizes inside and outside the reserve, except for Thomson's gazelle and warthog. Livestock have not significantly declined over the entire analysis period. However, livestock and cattle populations significantly declined during the 1983–88 period. Donkey declined by 67%, while shoats (goats and sheep) remained stable. In the case of wildlife, land use and vegetation changes, drought effects and poaching are considered to be among the potential factors that may have been responsible for the decline; the decline in livestock during the 1983–84 period was probably due to drought effects.