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Abstract

When an area is brought under protection, current animal populations and their habitat preferences need to be assessed to predict population trends and future habitat availability. Using data from walking transects, we estimated the size of native ungulate populations on an abandoned cattle ranch in a coastal savannah in Tanzania, now included in the new Saadani National Park. Data were analysed with DISTANCE sampling and conventional strip transect techniques and were compared with results of previous wildlife counts. Few individuals of mainly browsing species were present in former cattle grazing areas exhibiting high bush-encroachment while a ten times higher biomass of browsers and grazers was found in the cattle-unmodified savannah. Population sizes of some species increased twofold between 1991 and 2001 within the entire area but neither population size nor species richness increased in the abandoned rangeland during our 3-year study period from 2001 to 2003. We conclude that the former ranch has potential for future recolonization by wild ungulates. Resettlement will take place gradually with 'pioneer-species' facilitating the entry of more demanding species. Habitat restoration through wildlife can be observed and quantified on Mkwaja Ranch which will be of importance for future management of native ungulates reclaiming abandoned rangeland.

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... That these two methodologies are not systematically implemented in the field 4 comes from serious practical limitations. CR requires a substantial proportion of the population to be recognizable (Strandgaard (1972) advised up to 2/3 of a roe 6 deer population to be marked) achieved by the physical capture of animals to mark them (physically or visually). In addition the capture and marking of wild 8 animals can raise ethical questions for endangered species. ...
... 2 Giraffe (Giraffa camelopardalis) is a charismatic species of conservation significance with decreasing populations in many parts of Africa (O'connor et al. 4 2019). The assessment of local conservation status of populations and their long-term viability are however hampered by the many different ways abundance 6 has been estimated between study areas. Here, we propose to take advantage of the waterhole monitoring with camera traps on Ongava Game Reserve, Namibia, 8 to compare six population size estimators of giraffe population to characterize the biases associated with spatial, temporal and individual variability in detection 10 rates. ...
... The weather zone for the reserve is typical for semi-arid northern Namibia, with an average annual rainfall of 380mm (see Stratford & Stratford 4 2011, for further details)). There are several natural dams on the reserve, although most of these only contain water during the rainy season (January - 6 March). During the dry season (May to December) water is only available at 12 artificial waterholes. ...
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Camera-traps are a versatile and widely adopted tool to collect biological data in wildlife conservation and management. If estimating population abundance from camera-trap data is the primarily goal of many projects, what population estimator is suitable for such data needs to be investigated. We took advantage of a 21 days camera-trap monitoring on giraffes at Onvaga Game Reserve, Namibia to compare capture-recapture (CR), saturation curves and N-mixture estimators of population abundance. A marked variation in detection probability of giraffes was observed in time and between individuals. Giraffes were also less likely to be detected after they were seen at a waterhole with cameras (visit frequency of f = 0.25). We estimated population size to 119 giraffes with a Cv = 0.10 with the best CR estimator. All other estimators we a applied over-estimated population size by ca. -20 to >+80%, because they did not account for the main sources of heterogeneity in detection probability. We found that modelling choices was much less forgiving for N-mixture than CR estimators. Double counts were problematic for N-mixture models, challenging the use of raw counts at waterholes to monitor giraffes abundance.
... An example of the increased recent conservation efforts in coastal Tanzania is the incorporation of Saadani Game Reserve, Mkwaja Ranch, and Zaraninge forest into a national park. Since its gazettement in 2005, Saadani National Park has been the subject of several ecological studies focusing on large ungulate populations and plants, for example, [9][10][11]. Thus, the existing knowledge about this area is limited and arguably biased towards large mammals. ...
... Thus, the existing knowledge about this area is limited and arguably biased towards large mammals. Thus increased understanding of the other biodiversity present in this recently gazetted protected area is important for predicting future population trends and assessing the required level of habitat management [9]. This is especially important as the area had experienced large scale decrease in the cover of bushland and a significant encroachment of bushes in some parts due to cattle grazing that persisted for nearly 50 years [12,13]. ...
... This is especially important as the area had experienced large scale decrease in the cover of bushland and a significant encroachment of bushes in some parts due to cattle grazing that persisted for nearly 50 years [12,13]. The reduction of such pressures may have resulted in significant turnover leading to high species richness and/or altered community assemblages [9,11]. Despite the fact that many external sources of anthropogenic pressure have been minimized following protection, the area continues to receive some internally generated disturbance such as intentional or accidental fires and illegal resource extraction persists. ...
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Our current understanding of the vertebrate communities of a newly gazetted Tanzanian coastal national park is limited and strongly taxonomically biased towards large mammals. We conducted bird assessments in three sites in Saadani National Park using species lists to analyze some parameters to inform biodiversity conservation in the area. We recorded 3112 individuals in 268 species falling in 66 families, including 2 endangered, 2 vulnerable, and 6 near threatened species. Both species richness and species diversity varied between sites. Species relative abundances were not different between the sites although some functional groups, especially granivores, were more abundant than others. Bird assemblages included 21 forest specialists (FF-species), 35 forest generalists (F-species), and 68 forest visitors (f-species) overlapping among bushland, wooded grassland, grassland, and thickets suggesting presence of important microhabitats for the forest-associated species in this ecosystem. Bird species richness in a feeding guild also showed marked overlap between habitats suggesting availability of rich food resources for the birds. This paper highlights the importance of maintaining a structurally heterogeneous landscape to sustain diverse bird communities in the area.
... The entire national park is grazed by wild herbivores such as warthog, waterbuck, reedbuck, buffalo, wildebeest, giraffe and elephant. Densities and diversity of wild herbivores are much higher in the southern part of the park, and no increase in ungulate abundance was observed in the former ranch area during the first three years after abandonment of the ranch (Treydte et al. 2005). ...
... The area is grazed by wild herbivores including warthog, waterbuck, reedbuck, buffalo, wildebeest, giraffe and elephant. Densities and diversity of wild herbivores are much higher in the southern part of the park compared to the former ranch area (Treydte et al. 2005). Mean annual temperature recorded at the former ranch complex is 25° C . ...
... For phosphorus, balances tended to be negative in paddock centres and in grazed areas, and zero or positive in the other vegetation types (Table 5). Herbivore dung and urine: for the sites along the paddock gradients in the former ranch area we divided dung input rates measured in the Saadani area by a factor 10 since it has c. 10 times lower densities of wild herbivores (Treydte et al. 2005); we assumed PC to receive similar dung input rates like tallgrass sites (TG M ); grazed patches are assumed to be grazed for 1.5-2.5 years before being abandoned temporarily for one growing season (6 months) during which input rates are equal to those in tallgrass savanna (TG S ). ...
... There is a growing concern that many wild African mammal and bird species today survive poorly outside protected areas due to human-related activities like habitat modification, hunting and poaching, and livestock feeding (Caro 1999, Caro et al. 1998, Prins 1992, Sinclair et al. 2002, Treydte et al. 2005, Young et al. 2005. ...
... Some studies indicate competition between livestock and wild ungulates (Fritz et al. 1996, Mishra et al. 2002, Perkin 1995, Prins 1992, Runyoro et al. 1995, Voeten & Prins 1999. Commonly an increase in wild ungulate populations has been reported when livestock is removed, and this indicates the presence of diffuse competition between domestic and wild species (Prins 2000, Treydte et al. 2005. The expansion of rangelands to accommodate livestock grazing has reduced grazing areas for many wild ungulates (Bagchi et al. 2004, Darkoh & Mbaiwa 2002. ...
Article
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The small size of many African protected areas makes adjacent rangelands potentially important in the local survival of wild animals. In order to assess the importance of pastoral areas to wild ungulates, we studied density and habitat choice of wild ungulates and cattle in Lake Mburo National Park, Uganda, the adjacent exclusively pastoral Nshara Dairy Ranch and on private land consisting of a mixture of ranching and subsistence farms. Transects, in the three land-use zones, were walked during the wet season and the data were analysed by DISTANCE sampling technique. We found significantly higher total density of wild ungulates on the dairy ranch compared with the National Park and private land. There was no significant difference in total wild animal density between the National Park and private land. Impala (Aepyceros melampus), zebra (Equus quagga), bushbuck (Tragelaphus scriptus) and waterbuck (Kobus ellipsiprymnus) had significantly higher densities on the dairy ranch compared to the National Park. Only eland (Taurotragus oryx) density was higher in the National Park compared to private land. Wild ungulates and cattle showed a high degree of habitat overlap, generally preferring open grassland. Our study shows that high densities of wild ungulates are not necessarily associated with protected areas. Pastoral areas may be important for populations of wild herbivores during the growing season despite a pronounced presence of livestock.
... These forms of human activities are known to affect population sizes or densities of wild ungulates negatively (Norton-Griffiths 1979, Newby 1990, Sodeinde 1992, Prins 1992, Treydte et al. 2005, Holmern et al. 2006, Fischer & Linsenmair 2007, Hassan 2007. Still, where protected areas with a self-sustaining population of a given species exist in close proximity to areas that are affected by human activities, source-sink dynamics may occur, whereby an apparently stable population in the disturbed area depends on continuous immigration from the protected (source) habitat (Watkinson & Sutherland 1995, Gundersen et al. 2001). ...
... A situation as outlined above is found in some ungulate species inhabiting Lake Mburo National Park (LMNP) and the adjacent unprotected ranchland of the Ankole Ranching Scheme (ARS) in Uganda, which are part of the Akagera Ecosystem (Averbeck et al. , 2010. Livestock keeping and burning of the vegetation in areas subjected to pastoralism are often accompanied by shifts in landscape structuring and habitat modifications, which can be followed by pronounced changes in the communities of ungulates (de Boer & Prins 1990, Prins 2000, Treydte et al. 2005, Lamprey & Mugisha 2009). Although landscape structures in the ARS have been modified to a relatively small extent (Hoag & Clements 1993), some vegetation types have clearly changed; e.g. the proportion of mixed Brachariawoodlands declined in the ARS (Hoag & Clements 1993). ...
Article
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Most ungulates in East African savannahs experience some form of human disturbance, such as direct pursuit (e.g. hunting and poaching), habitat degradation and competition with livestock. In many studies, the impact of human activities on wildlife is assessed through census counts, i.e. by estimating population sizes or densities, but also the social organisation of gregarious species can be affected. Using seven species of ungulates occurring in the Akagera Ecosystem, we compared grouping patterns (i.e. group sizes and compositions) of different group types (e.g. bachelor, all-female and mixed-sex groups) between sites situated inside a protected area, i.e. Lake Mburo National Park in Uganda and the adjacent Ankole Ranching Scheme (ARS), an unprotected area with intense human pursuit. Differences in group sizes were detectible in only a few cases, e.g. bachelor group size in common eland Tragelaphus oryx pattersonianus increased in the ARS, which may be advantageous due to increased vigilance. However, we found pronounced differences in group compositions in numerous species and for different group types, for example, in eland and waterbuck Kobus ellipsiprymnus defassa (i.e. in all group types), and topi Damaliscus lunatus jimela, oribi Ourebia ourebi and warthog Phacochoerus aetiopicus (all-female and mixed-sex groups). We discuss that continuous monitoring of grouping patterns of these (and other) species may be a valuable approach to detect 'subtle' effects of human nuisance even before an overall population decline can be observed.
... Densities are not known precisely but are estimated at 7.5-12.4 individuals km −1 for Bohor reedbuck, 2.4-2.7 for waterbuck and 1.3-3.1 for wildebeest (Treydte et al. 2005). Bohor reedbuck (36-55 kg) is considerably smaller than waterbuck (means 180-240 kg) and the similarly sized wildebeest (means 160-200 kg), whereas in terms of muzzle width, Bohor reedbuck (incisor arcade width about 30 mm according to measurements in very similar Redunca arundinum) and waterbuck (47.5 mm) are closer to each other than they are to wildebeest (73.1 mm; weights from Kingdon 1982 and muzzle widths from Gordon & Illius 1988). ...
... This somewhat unusual grazer assemblage lacks most of the 'classical plains game' associated with drier savannas further inland such as impala (Aepyceros melampus), gazelles, topi (Damaliscus lunatus), Coke's hartebeest (Alcelaphus buselaphus) and plains zebra (Equus quagga). A few zebra were introduced at the same time as wildebeest but, unlike wildebeest, did not establish a sustained population (Treydte et al. 2005). Instead, the Saadani herbivore community resembles those of other wet tallgrass savannas as far away as West Africa (East 1984;de Iongh et al. 2011) that are also numerically dominated by species of the tribe Reduncini (Bohor reedbuck and waterbuck). ...
Article
We studied how grazing intensity by small and mid-sized ungulate grazers varied with nutritional quality and grass species composition in wet oligotrophic tallgrass savanna of coastal northern Tanzania. Average grazing intensity was low (3–15% by cover), and most grass species were scarcely used by herbivores. Only two grasses, Panicum infestum and Digitaria milanjiana, had nitrogen and phosphorus concentrations that were consistently above the minimum levels (e.g. nitrogen concentrations <7 mg g−1) required by the three commonest grazers, Bohor reedbuck, waterbuck and wildebeest. The best predictors of grazing intensity were cover of P. infestum (the most abundant grass, with a mean cover of 15%) and canopy height of ungrazed vegetation. Models did not contain separate predictors for nutritional quality, presumably because quality varied mainly at the grass species level and therefore was fully represented by the variable ‘cover of P. infestum’. Given that the three grazers differed greatly in body size and muzzle width (parameters known to influence nutrient requirements and the ability of grazers to feed selectively at the smallest spatial scale), we expected there to be strong resource partitioning that would be detectable in terms of grazing strategies and feeding sites. However, apart from minor differences in canopy height, greenness and diameter of grazed patches (albeit consistent with our expectations), feeding stations of the three grazers were similar and strongly dominated by P. infestum. We conclude that the low quality of herbage in wet oligotrophic savannas restricts foraging choices, which produces a characteristic yet impoverished grazing community that exhibits only limited resource partitioning.
... Due to their differing management histories, the density and diversity of herbivores is much lower in Mkwaja than Saadani (Treydte et al. 2005). Annual precipitation is sufficient to allow for a high percentage of woody cover (Sankaran et al. 2005), and the fact that vegetation is now mainly savanna probably reflects a long history of deliberate burning in the dry months (cf., Bond et al. 2005). ...
... Our results show that the relative importance of litter and dung deposition from browsing herbivores as pathways for nutrient return vary with tree density (Fig. 3). For example, the return of N and P through excreta was highest where tree densities were low, especially in the Saadani area where herbivores were more common (Treydte et al. 2005). Since browsing animals, mainly giraffe, were observed to feed across the range of tree densities, we conclude that they probably bring about some redistribution of nutrients from Acacia-to grass-dominated areas (Fig. 3a, b). ...
Article
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Studies of nutrient cycling in savanna ecosystems rarely consider how fluxes are affected by local variations in tree density and nutrient redistribution by herbivores. We studied how the density of Acacia zanzibarica trees in a humid savanna ecosystem affected the input of nitrogen (N) through N2-fixation and N and phosphorus (P) outputs through fire and also internal pathways of N and P return through herbivores. We found that N inputs and P outputs both increased with increasing density of N2-fixing trees, the N effect being due to tree density rather than to differences in the rate of N2-fixation. However, total N outputs due to fire did not vary with tree density because losses from the herb layer decreased as losses from the tree layer increased. In contrast, total P outputs did increase with tree density because P losses from the tree layer exceeded those from the herb layer. We suggest that variation in the density of N2-fixing trees coupled with the effects of fire can cause substantial differences in the local N and P balances in savanna vegetation. To some extent, these differences may be evened out by the tendency for browsing herbivores to transfer nutrients from Acacia- to grass-dominated areas. We conclude that encroachment by N2-fixing trees and shrubs has important consequences for ecosystem properties such as N and P dynamics.
... Indeed, the present savanna vegetation at Mkwaja Ranch appears to be maintained by fire, with wildlife playing only a secondary role (cf. East 1984;Sankaran et al. 2005;Treydte et al. 2005;Cochard & Edwards 2011a). Due to poaching, numbers of wildlife on Mkwaja Ranch were particularly low between 2000, when ranching was discontinued, and 2005, when the area was incorporated into Saadani National Park (cf. ...
... Due to poaching, numbers of wildlife on Mkwaja Ranch were particularly low between 2000, when ranching was discontinued, and 2005, when the area was incorporated into Saadani National Park (cf. Treydte et al. 2005). The soils in the study area are mostly grey vertisols derived from coral sands, and are relatively uniform and unstructured to a depth of more than 1.5 m. ...
Article
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Questions We studied a humid savanna rangeland, abandoned in 2000, where intensive cattle grazing had led to widespread encroachment by Acacia zanzibarica . We asked whether the acacia trees were able to regenerate in the absence of domestic livestock, either beneath acacia canopies or in artificial clearings. Location Tropical coastal Tanzania (former Mkwaja Ranch, now in Saadani National Park). Methods We set out a total of 48 plots on four sites in November 2001, and assigned them to three treatments: trees felled ( FN ), trees felled and the stumps poisoned ( FP ) with Triclopyr, and no intervention (controls, NN ). We analysed soils of plots for texture and nutrients. In two wet (July 2002 and 2003) and one dry (February 2003) seasons we assessed grass and tree leaf biomass and transpiration rates, and counted acacia seedlings and resprouts. The effects of treatments (controlled for site and other co‐variables) on grass growth and acacia recruitment were determined statistically using general linear models ( GLM ). Results Acacia leaves had a much higher stomatal conductance than grasses, with the consequence that total evapotranspiration in woodland was higher than in clearings. In the wet seasons, grass biomass and seedling densities were significantly higher in clearings than in control plots, which we attributed to more favourable moisture conditions. In the dry season, by contrast, we found no differences, and all seedlings had died. On FN plots, 71% of stumps, and on FP plots, 11% resprouted (coppicing), but only a quarter of these shoots survived until July 2003. Root suckering occurred spontaneously at low densities. No root suckers or resprouts grew beyond the grass layer. Conclusions Acacia woodlands do not regenerate in the absence of cattle grazing, and tree cutting – in combination with appropriate fire management – could potentially accelerate re‐establishment of open grassland. However, regeneration might occur in the future due to the increasing wildlife populations within the new national park.
... There is a growing concern that many wild African mammal and bird species today survive poorly outside protected areas due to human-related activities like habitat modification, hunting and poaching, and livestock feeding (Caro 1999, Caro et al. 1998, Prins 1992, Sinclair et al. 2002, Treydte et al. 2005, Young et al. 2005. ...
... Some studies indicate competition between livestock and wild ungulates (Fritz et al. 1996, Mishra et al. 2002, Perkin 1995, Prins 1992, Runyoro et al. 1995, Voeten & Prins 1999. Commonly an increase in wild ungulate populations has been reported when livestock is removed, and this indicates the presence of diffuse competition between domestic and wild species (Prins 2000, Treydte et al. 2005. The expansion of rangelands to accommodate livestock grazing has reduced grazing areas for many wild ungulates (Bagchi et al. 2004, Darkoh & Mbaiwa 2002. ...
Article
Full-text available
The small size of many African protected areas makes adjacent rangelands potentially important in the local survival of wild animals. In order to assess the importance of pastoral areas to wild ungulates, we studied density and habitat choice of wild ungulates and cattle in Lake Mburo National Park, Uganda, the adjacent exclusively pastoral Nshara Dairy Ranch and on private land consisting of a mixture of ranching and subsistence farms. Transects, in the three land-use zones, were walked during the wet season and the data were analysed by DISTANCE sampling technique. We found significantly higher total density of wild ungulates on the dairy ranch compared with the National Park and private land. There was no significant difference in total wild animal density between the National Park and private land. Impala (Aepyceros melampus), zebra (Equus quagga), bushbuck (Tragelaphus scriptus) and waterbuck (Kobus ellipsiprymnus) had significantly higher densities on the dairy ranch compared to the National Park. Only eland (Taurotragus oryx) density was higher in the National Park compared to private land. Wild ungulates and cattle showed a high degree of habitat overlap, generally preferring open grassland. Our study shows that high densities of wild ungulates are not necessarily associated with protected areas. Pastoral areas may be important for populations of wild herbivores during the growing season despite a pronounced presence of livestock.
... We determined the density of eland in the two zones using the walking transect method (Treydte, Edwards & Suter, 2005). Four transects of 3 km each were walked in each density zone. ...
... Eland density was 1.92 and 0.86 km )2 for high-and lowdensity zones respectively. Styles & Skinner (2000) reported a density of 0.34 km )2 from an aerial survey, while Treydte et al. (2005) reported a density of 0.7 km )2 from walking transects. Aerial survey methods give low population estimates compared with ground methods. ...
Article
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We studied the impacts of eland density on the physiognomy of Combretum apiculatum. We divided the study area into two zones: high eland density zone (≤8 km from watering point) and low eland density zone (≥8 km from watering point). Eland density was determined in each zone using walking transects. Combretum apiculatum height and diameter and levels of eland damage were measured in each zone. Eland density was 1.92 and 0.86 km⁻² for high and low-density zones respectively. We recorded 239 C. apiculatum trees, 138 in low-density zone and 101 in high-density zone. Mean C. apiculatum height was 2.88 ± 0.67 m and 5.05 ± 1.04 m for high and low eland density zones respectively. High eland density prevented the recruitment of C. apiculatum from the 2.6–5.5 m height class to the >5.6 m height class. Although extensive tree damage occurred at <2.5 m height stratum, C. apiculatum showed resilience as recruitment into the 2.6–5.5 m height class continued. We concluded that high eland density prevents recruitment of C. apiculatum to higher height classes while at the same time causing extensive tree damage at lower height strata.
... The wide forage palate of native herbivores contributes to a more complete utilization of resources, compared to domestic livestock (Taylor and Walker 1978). Wild herbivores play an important role in grassland/savanna maintenance by reducing invasion by woody species (Hudak 1999; Augustine and McNaughton 2004;Treydte et al. 2005). ...
... Theoretically, herbivore diversity allows the producer an adaptive way to respond to a wide range of environmental conditions across the farm and over time (Richardson 1998). Additionally, the browser community has been shown to control woody species in African savannas (Dublin et al. 1990;Prins and van der Jeugd 1993;Augustine and McNaughton 2004;Wiseman et al. 2004;Treydte et al. 2005), and many species are compatible with domestic livestock when sharing the same farm (Fritz et al. 1996). Thus, managing native browser communities not only provides marketable products, but also helps control woody species in the process. ...
Article
The private game industry has grown across Africa since the mid-20th century. While considerable research has documented wildlife production on commercial land in many eastern and southern African countries, few studies have focused specifically on the integration of livestock and game production in Namibia and Zambia. This paper reports a survey of 43 commercial conservancy members in Namibia and 23 game farmers in Zambia conducted between September 2004 and June 2005. The survey was based on inductive sampling theory and queried farmers on how they have integrated wildlife production into their management practices. Farmers in each country reported considerable integration of wildlife conservation and agricultural production. Namibian farmers reported substantial problems with bush encroachment, whereas none of their Zambian counterparts raised similar complaints. This paper describes the state of rangeland management on commercial farms in Namibia and Zambia and identifies important areas where further research can contribute to the enhancement of this conservation-production system. KeywordsGame farming-Game ranching-Wildlife production-Sustainable grazing-Veld management-Veld ecology-Bush encroachment-Namibia-Zambia
... From 1969, much of the southern part was managed as a game reserve (Figure 1). Wild herbivores include warthog, waterbuck , reedbuck, buffalo, wildebeest, giraffe, and elephant, which continue to be much more abundant in the southern part than in the former ranch (Treydte and others 2005). Mean annual temperature recorded at the former ranch complex was 25°C (1973–1998). ...
... Such a heterogeneous pattern of offtake, which has also been demonstrated in semi-arid savanna (Van de Vijver and others 1999), probably develops because regrowth contains higher concentrations of nutrients and is therefore grazed repeatedly (Hobbs 1996). Even though nutrient concentrations were highest in vegetation of the former paddocks (Table 1), there were only very few signs of grazing (Cech, personal observation), probably due to the low density of wild herbivores on the area of the former cattle ranch (Treydte and others 2005). ...
Article
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Availabilities of nitrogen (N) and phosphorus (P) have a strong influence on plant growth and the species composition of savannas, but it is not clear how these availabilities depend on factors such as fire, N2-fixation, and activities of wild herbivores and cattle. We quantified soil N and P availabilities in various ways (extractable pools, mineralization, resin adsorption) along vegetation gradients within a recently abandoned cattle ranch and a former game reserve in Tanzania (both areas now part of the Saadani National Park). We also assessed annual N and P balances to evaluate how long-term availabilities of N and P are affected by large herbivores, symbiotic N2-fixation, and fire. The results show that cattle ranching led to a spatial re-distribution of nutrients, with the local accumulation of P being stronger and more persistent than that of N. In the former game reserve, intensively grazed patches of short grass tended to have elevated soil N and P availabilities; however, because quantities of nutrients removed through grazing exceeded returns in dung and urine, the nutrient balances of these patches were negative. In dense Acacia stands, N2-fixation increased N availability and caused a net annual N input. Fire was the major cause for nutrient losses from tallgrass savanna, and estimated N inputs from the atmosphere and symbiotic N2-fixation were insufficient to compensate for these losses. Our results call into question the common assumption that N budgets in annually burned savanna are balanced; rather, these ecosystems are a mosaic of patches with both N enrichment and impoverishment, which vary according to the vegetation type. Keywordsfire-herbivory-N-fixation-N:P stoichiometry-nutrient balances-mineralization
... Savanna ecosystems cover 50% of the southern continents (Mordelet and Menaut, 1995). As a biome of unparalleled beauty, African savannas are characterised by a continuous grass layer interspersed by trees, maintained by characteristic patterns of rainfall and soil fertility (Olff et al., 2002;Sankaran et al., 2005), but also shaped by human influences (Tobler et al., 2003;Treydte et al., 2005). Trees in these ecosystems have been referred to as 'islands of fertility' (Belsky et al., 1989), because elevated soil nutrients are found beneath their crowns, together with decreased solar radiation, reduced evapotranspiration and reduced soil temperatures (Ludwig et al., 2004). ...
... The areas had similar tree densities of o200 trees ha À1 , i.e. an intermediate density at which their tendency to intercept rain, decrease soil temperature and light, and reduce evapotranspiration have been shown to be most pronounced (Belsky and Amundson, 1992). They also had similar tree and grass species, being Acacia-Terminalia savannas, as well as having several large herbivore species in common, such as warthog Phacochoerus africanus Gmelin, wildebeest Connochaetes taurinus Buchell, zebra Equus burchelli Boddaert, and buffalo Syncerus caffer Sparrman (Ben-Shahar and Coe, 1992;Treydte et al., 2005;Looringh van Beeck, 2005). ...
Article
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The tree-grass interactions of African savannas are mainly determined by varying rainfall patterns and soil fertility. Large savanna trees are known to modify soil nutrient conditions, but whether this has an impact on the quality of herbaceous vegetation is unclear. However, if this were the case, then the removal of trees might also affect the structure and quality of the grass layer. We studied the impact of large nitrogen- and non-nitrogen fixing trees on the sub-canopy (SC) grass layer in low- and high-rainfall areas of differing soil fertility in eastern and southern Africa. We compared the structure and nutrient levels of SC grasses with those outside the canopy. Grass leaf nitrogen and phosphorus contents beneath tree canopies were elevated at all study sites and were up to 25% higher than those outside the canopy in the site of lowest rainfall and soil fertility. Grass leaf fibre and organic matter (OM) contents were slightly enhanced beneath tree canopies. At the site of highest rainfall and soil fertility, grasses beneath the canopy had significantly lower ratios of stem:leaf biomass and dead:living leaf material. Grass species composition differed significantly, with the highly nutritious Panicum spp. being most abundant underneath tree crowns. In the two drier study sites, soil nitrogen and OM contents were enhanced by 30% beneath trees. N-fixation capacity of trees did not contribute to the improved quality of grass under the canopy. We conclude that trees improve grass quality, especially in dry savannas. In otherwise nutrient-poor savanna grasslands, the greater abundance of high-quality grass species with higher contents of N and P and favourable grass structure beneath trees could attract grazing ungulates. As these benefits may be lost with tree clearance, trees should be protected in low fertility savannas and their benefits for grazing wildlife recognised in conservation strategies.
... However, densities of Thomson's gazelles in the Serengeti ecosystem are approximately 10× greater compared to MR (Dublin et al., 1990). In contrast, other wildlife species (e.g., elephants, warthogs) may only occur at relatively low densities in livestockdominated areas (Bhola et al., 2012;Ogutu et al., 2016;Treydte, Edwards, & Suter, 2005). Although these spatial wildlife density comparisons provide some insights in the overall conservation value of MR, they do not provide causal inference for assessing the impact of livestock grazing on wildlife population densities. ...
Article
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Facilitating coexistence between people and wildlife is a major conservation challenge in East Africa. Some conservation models aim to balance the needs of people and wildlife, but the effectiveness of these models is rarely assessed. Using a case‐study approach, we assessed the ecological performance of a pastoral area in northern Tanzania (Manyara Ranch) and established a long‐term wildlife population monitoring program (carried out intermittently from 2003 to 2008 and regularly from 2011 to 2019) embedded in a distance sampling framework. By comparing density estimates of the road transect‐based long‐term monitoring to estimates derived from systematically distributed transects, we found that the bias associated with nonrandom placement of transects was nonsignificant. Overall, cattle and sheep and goat reached the greatest densities and several wildlife species occurred at densities similar (zebra, wildebeest, waterbuck, Kirk's dik‐dik) or possibly even greater (giraffe, eland, lesser kudu, Grant's gazelle, Thomson's gazelle) than in adjacent national parks in the same ecosystem. Generalized linear mixed models suggested that most wildlife species (8 out of 14) reached greatest densities during the dry season, that wildlife population densities either remained constant or increased over the 17‐year period, and that herbivorous livestock species remained constant, while domestic dog population decreased over time. Cross‐species correlations did not provide evidence for interference competition between grazing or mixed livestock species and wildlife species but indicate possible negative relationships between domestic dog and warthog populations. Overall, wildlife and livestock populations in Manyara Ranch appear to coexist over the 17‐year span. Most likely, this is facilitated by existing connectivity to adjacent protected areas, effective anti‐poaching efforts, spatio‐temporal grazing restrictions, favorable environmental conditions of the ranch, and spatial heterogeneity of surface water and habitats. This long‐term case study illustrates the potential of rangelands to simultaneously support wildlife conservation and human livelihood goals if livestock grazing is restricted in space, time, and numbers.
... When wildlife is readily observable, assessing, and estimating species richness of large mammal assemblages and population densities of specific species over time can be performed simultaneously Kiffner, Nagar, Kollmar, & Kioko, 2016;Schuette et al., 2018). This combined approach offers advantages over focusing solely on species richness (Cromsigt, van Rensburg, Etienne, & Olff, 2009;Msuha, Carbone, Pettorelli, & Durant, 2012;Treydte, Edwards, & Suter, 2005), on one or few snapshot assessments of species' densities (Caro, 1999;Waltert, Meyer, & Kiffner, 2009), or on population trends of selected species Ogutu et al., 2017). This is because (a) mammal communities are sensitive to different levels of human impact (Kiffner, Wenner, LaViolet, Yeh, & Kioko, 2015;Msuha et al., 2012;Riggio et al., 2018); (b) focusing on one snapshot assessment in time may yield biased conclusions if animals move across the landscape in response to seasonal variation of natural resources (Rannestad, Danielsen, & Stokke, 2006); focusing on a single species may not represent population trajectories of other species (Caro, 2016;Caro, Gardner, Stoner, Fitzherbert, & Davenport, 2009;Kiffner, Hopper, & Kioko, 2016;Riggio et al., 2018). ...
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Community‐based conservation models have been widely implemented across Africa to improve wildlife conservation and livelihoods of rural communities. In Tanzania, communities can set aside land and formally register it as Wildlife Management Area (WMA), which allows them to generate revenue via consumptive or nonconsumptive utilization of wildlife. The key, yet often untested, assumption of this model is that economic benefits accrued from wildlife motivate sustainable management of wildlife. To test the ecological effectiveness (here defined as persistence of wildlife populations) of Burunge Wildlife Management Area (BWMA), we employed a participatory monitoring approach involving WMA personnel. At intermittent intervals between 2011 and 2018, we estimated mammal species richness and population densities of ten mammal species (African elephant, giraffe, buffalo, zebra, wildebeest, waterbuck, warthog, impala, Kirk's dik‐dik, and vervet monkey) along line transects. We compared mammal species accumulation curves and density estimates with those of time‐matched road transect surveys conducted in adjacent Tarangire National Park (TNP). Mammal species richness estimates were similar in both areas, yet observed species richness per transect was greater in TNP compared to BWMA. Species‐specific density estimates of time‐matched surveys were mostly not significantly different between BWMA and TNP, but elephants occasionally reached greater densities in TNP compared to BWMA. In BWMA, elephant, wildebeest, and impala populations showed significant increases from 2011 to 2018. These results suggest that community‐based conservation models can support mammal communities and densities that are similar to national park baselines. In light of the ecological success of this case study, we emphasize the need for continued efforts to ensure that the BWMA is effective. This will require adaptive management to counteract potential negative repercussions of wildlife populations on peoples' livelihoods. This study can be used as a model to evaluate the effectiveness of wildlife management areas across Tanzania.
... The vegetation of the Saadani National Park and neighboring landscape portray varied levels of ecosystem succession following the differential shifts in previous land use regimes. The land use systems the park has gone through before being gazetted into a national park include being managed as a cattle ranch and sisal plantation [20,21] and the ongoing fishery along the Indian Ocean shoreline. Indeed, the repercussion brought about by the former two land use regimes on bird species composition could be enormous, including negatively impacting species richness or causing local extinction in some of the species, for example. ...
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The East African coastal forests are subject of haphazard modification following anthropogenic pressures including tree cutting and clearing for agriculture. These activities, which are leading cause of habitat disturbance and species loss, are the major challenge in the management of sensitive wildlife species such as forest understory birds. This study investigated species composition of understory birds in the coastal forests of northeastern Tanzania to generate information for the management of the landscape and biodiversity in the area. Using mist nets, birds were trapped from core and edge habitats of representative forest patches. Trapped birds were classified to species level and categorized into bird guilds based on their levels of forest dependence. It was found out that species richness was influenced by forest patch size rather than level of habitat disturbance. Edge habitat was also found to be important in hosting higher number of forest understory birds, especially generalists—but this should be treated with caution because following habitat destruction that is ongoing in the study area, there is a danger of generalist wiping out specialist species due to competitive exclusion. Strict control measures to stop illegal tree cutting and agricultural activities near the forests were recommended for sustainable conservation of the understory birds in the forests.
... The savanna grassland vegetation is characterized by a continuous grass layer and a discontinuous woody layer , composed of widely scattered trees or shrubs (Scholes and Archer, 1997). The vegetation is maintained by characteristic patterns of rainfall and soil fertility (Olff et al., 2002;Sankaran et al., 2005), but also shaped by anthropogenic activities (Tobler et al., 2003;Treydte et al., 2005). Although trees have been viewed as competitors with grasses and hence regarded as having a negative impact on understory herbaceous production (Ludwig et al., 2004), a flood of literature (e.g. ...
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The productivity, sustainability and ecological integrity of grassland ecosystems in Uganda is hugely threatened by the alarming levels of ecosystem degradation attributed mainly to anthropogenic activities. Mitigating grassland degradation in Uganda requires adequate understanding of both the primary and secondary drivers of grassland degradation. In this paper, we carefully categorize the drivers of grassland deterioration into two classes (primary and secondary causes) and employ concepts and theories in landscape; terrestrial, behavioral and restoration ecology to elucidate the contribution of various factors on degradation of grassland ecosystems in Uganda. . Overgrazing and tree removal are key primary causes of deterioration that result in demolition of vegetation cover, loss of surface litter, increase in erosion and run-off, loss of soil fertility and consequently reduced grassland productivity. The negative consequences of overgrazing and tree removal facilitate encroachment and/or invasion of alien species and surges in termite activity. Mitigation of grassland deterioration therefore calls elucidation of appropriate areaspecific stocking rates in equilibrium grassland ecosystems; development of sustainable grazing management interventions in non-equilbrium grassland systems where the concept of stocking rate is less practical; generation of ecologically sound and sustainable termite management interventions; development of appropriate species-specific management of noxious weeds in grassland ecosystems.
... The savanna grassland vegetation is characterized by a continuous grass layer and a discontinuous woody layer , composed of widely scattered trees or shrubs (Scholes and Archer, 1997). The vegetation is maintained by characteristic patterns of rainfall and soil fertility (Olff et al., 2002;Sankaran et al., 2005), but also shaped by anthropogenic activities (Tobler et al., 2003;Treydte et al., 2005). Although trees have been viewed as competitors with grasses and hence regarded as having a negative impact on understory herbaceous production (Ludwig et al., 2004), a flood of literature (e.g. ...
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The productivity, sustainability and ecological integrity of grassland ecosystems in Uganda is hugely threatened by the alarming levels of ecosystem degradation attributed mainly to anthropogenic activities. Mitigating grassland degradation in Uganda requires adequate understanding of both the primary and secondary drivers of grassland degradation. In this paper, we carefully categorize the drivers of grassland deterioration into two classes (primary and secondary causes) and employ concepts and theories in landscape; terrestrial, behavioral and restoration ecology to elucidate the contribution of various factors on degradation of grassland ecosystems in Uganda.. Overgrazing and tree removal are key primary causes of deterioration that result in demolition of vegetation cover, loss of surface litter, increase in erosion and runoff , loss of soil fertility and consequently reduced grassland productivity. The negative consequences of overgrazing and tree removal facilitate encroachment and/or invasion of alien species and surges in termite activity. Mitigation of grassland deterioration therefore calls elucidation of appropriate area-specific stocking rates in equilibrium grassland ecosystems; development of sustainable grazing management interventions in non-equilbrium grassland systems where the concept of stocking rate is less practical; generation of ecologically sound and sustainable termite management interventions; development of appropriate species-specific management of noxious weeds in grassland ecosystems.
... We studied the diet of warthogs on a former ranch in Tanzania recently abandoned after 50 years of intensive use (Treydte et al. 2005). Warthogs were most abundant around former paddock enclosures (bomas) where cattle had been kept at night (Treydte 2004), and we hypothesized that nutrient enrichment made these areas particularly attractive to recolonizing wildlife. ...
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In otherwise nutrient-poor savannas, fertile vegetation patches are particularly attractive to ungulates because of the higher-quality food they provide. We investigated forage plants and diet of the common warthog (Phacochoerus africanus) on an abandoned cattle ranch in coastal Tanzania. The forage grasses of highest nutritional quality occurred in former paddock enclosures (bomas) where cattle had been herded at night. In the dry season, grass samples from bomas contained approximately 4 times as much nitrogen and phosphorus as those of the surrounding vegetation. δ15N values of soil and plants also were highest in bomas and decreased significantly with distance, and high δ15N values in feces suggest that warthogs preferentially fed in the vicinity of the former bomas. δ13C values of warthog feces indicate that warthogs ingested on average 83% (77-98%) C4 grasses, with this proportion varying regionally but not seasonally. We conclude that, for medium-sized selective grazers such as warthogs, bomas represent attractive feeding grounds. We also hypothesize that by promoting nutrient turnover in these patchily distributed areas, grazing animals help to maintain them as sources of high-quality forage.
... The northern part (Mkwaja area: c. 470 km 2 ) was managed as a cattle ranch until 2000, while the southern part (Saadani area: c. 210 km 2 ) has been a wildlife reserve since the 1960s. Although the entire park is accessible to wildlife, the northern part still has a lower density and diversity of large herbivores (Treydte, Edwards & Suter 2005), probably because of its former use as a ranch and the bush encroachment that ensued (Tobler, Cochard & Edwards 2003). ...
Article
Although dung of mammalian herbivores is an important pathway for nutrient return in savanna ecosystems, differences in dung decomposition rates among species have been little studied. We measured the rates of dung deposition and decomposition for various herbivores in a moist T anzanian savanna and the related differences among species to nutrient concentrations and the activities of soil macrofauna (e.g. different mesh sizes of decomposition bags, or presence and absence of dung beetles). Dung C : N : P stoichiometry varied widely among species, which could in part be explained by differences in feeding strategy (browsers vs. grazers) and digestive physiology (ruminants vs. non‐ruminants). Rates of both decomposition and nutrient release were influenced by the C : N : P stoichiometry of dung, with lower relative losses of the least abundant nutrient in the dung. Surprisingly, soil macrofauna increased the relative losses of the least abundant nutrient, thereby stabilizing the ratio of N loss to P loss. Dung beetles increased rates of N and P release from wildebeest dung significantly and also increased N availability in the soil. We conclude that rates of nutrient return in dung depend not only on where herbivores deposit their dung, but also on its C : N : P stoichiometry, the activity of soil macrofauna and interactions between these factors. These factors may therefore influence the relative availabilities of N and P in the soil and hence the functioning of savanna ecosystems.
... But existing research shows that a breadth of native herbivores match the spatial pattern of grazing to the spatial pattern of fire in when burns occur as patches on the landscape [28,70]. Managers across Southern Africa have sought to accommodate a breadth of herbivores-native and domestic, small and large, grazers and browsers-as a management tool to increase utilization of grazing and browsing resources, control woody plant encroachment, and diversify revenue [29,71,72]. ...
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Residents of Southern Africa depend on rangeland for food, livelihoods, and ecosystem services. Sustainable management of rangeland ecosystems requires attention to interactive effects of fire and grazing in a changing climate. It is essential to compare rangeland responses to fire and grazing across space and through time to understand the effects of rangeland management practices on biodiversity and ecosystem services in an era of global climate change. We propose a paradigm of ecologically-analogous rangeland management within the context of multifunctional landscapes to guide design and application of ecosystem-based rangeland research in Southern Africa. We synthesize range science from the North American Great Plains and Southern African savannas into a proposal for fire and grazing research on rangeland in Southern Africa. We discuss how management for the fire-grazing interaction might advance multiple goals including agricultural productivity, biodiversity conservation, and resilience to increased variability under global change. Finally, we discuss several ecological and social issues important to the effective development of sustainable rangeland practices especially within the context of global climate change. The associated literature review serves as a comprehensive bibliography for sustainable rangeland management and development across the savanna biomes of Southern Africa.
... Mean annual temperature is 25°C. Due to their differing management histories, Saadani supports a much higher density and diversity of wild herbivores than Mkwaja (Treydte and others 2005). Annual precipitation in the region is sufficient to support woodland (Sankaran and others 2005), and the fact that vegetation is now mainly savanna probably reflects a long history of anthropogenic fire in the dry months (compare Bond and others 2005). ...
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Nitrogen (N) fixing trees including many species of Acacia are an important though variable component of savanna ecosystems. It is known that these trees enrich the soil with carbon (C) and N, but their effect on the combined C:N:P stoichiometry in soil is less well understood. Theory suggests that they might reduce available phosphorus (P), creating a shift from more N-limited conditions in grass-dominated to more P-limited conditions in tree-dominated sites, which in turn could feed back negatively on the trees’ capacity to fix N. We studied the effects of Acacia zanzibarica tree density upon soil and foliar N:P stoichiometry, and the N2-fixation rates of trees and leguminous herbs in a humid Tanzanian savanna. Foliar N:P ratios and N2-fixation rates of trees remained constant across the density gradient, whereas soil C, N and organic P pools increased. In contrast, the N:P ratio of grasses increased and N2-fixation rates of leguminous herbs decreased with increasing tree density, indicating a shift towards more P-limited conditions for the understory vegetation. These contrasting responses suggest that trees and grasses have access to different sources of N and P, with trees being able to access P from deeper soil layers and perhaps also utilizing organic forms more efficiently.
... Densities and diversity of wild herbivores are much higher in the southern part of the park compared to the former ranch area (Treydte and others 2005). Mean annual temperature recorded at the former ranch complex is 25°C (1973–1998). ...
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The quantities and spatial distribution of nutrients in savanna ecosystems are affected by many factors, of which fire, herbivory and symbiotic N2-fixation are particularly important. We measured soil nitrogen (N) pools and the relative abundance of N and phosphorus (P) in herbaceous vegetation in five vegetation types in a humid savanna in Tanzania. We also performed a factorial fertilization experiment to investigate which nutrients most limit herbaceous production. N pools in the top 10 cm of soil were low at sites where fires were frequent, and higher in areas with woody legume encroachment, or high herbivore excretion. Biomass production was co-limited by N and P at sites that were frequently burnt or heavily grazed by native herbivores. In contrast, aboveground production was limited by N in areas receiving large amounts of excreta from livestock. N2-fixation by woody legumes did not lead to P-limitation, but did increase the availability of N relative to P. We conclude that the effects of fire, herbivory and N2-fixation upon soil N pools and N:P-stoichiometry in savanna ecosystems are, to a large extent, predictable.
... The collection of spatially referenced biological data is generally at the most detailed level possible given available funding levels and purpose of the collected data. Collection measures may include a variety of approaches including animal counts in georegistered aerial photos (Jachmann, 2002) and line transects on the ground (Treydte, Edwards & Suter, 2005). A common theme in nearly all such data is that geographic location is of principle importance. ...
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Information on the distribution of animal populations is essential for conservation planning and management. Unfortunately, shared coordinate-level data may have the potential to compromise sensitive species and generalized data are often shared instead to facilitate knowledge discovery and communication regarding species distributions. Sharing of generalized data is, unfortunately, often ad hoc and lacks scalable conventions that permit consistent sharing at larger scales and varying resolutions. One common convention in African applications is the Quarter Degree Grid Cells (QDGC) system. However, the current standard does not support unique references across the Equator and Prime Meridian. We present a method for extending QDGC nomenclature to support unique references at a continental scale for Africa. The extended QDGC provides an instrument for sharing generalized biodiversity data where laws, regulations or other formal considerations prevent or prohibit distribution of coordinate-level information. We recommend how the extended QDGC may be used as a standard, scalable solution for exchange of biodiversity information through development of tools for the conversion and presentation of multi-scale data at a variety of resolutions. In doing so, the extended QDGC represents an important alternative to existing approaches for generalized mapping and can help planners and researchers address conservation issues more efficiently.
... A major challenge for environmental monitoring programs in African protected areas is accurate assessment of populations of larger mammals, which is crucial both for monitoring success of existing management actions and for formulating future management strategies. One important option to assess large mammal abundance are line transects carried out from the ground, but there are only few published examples that could help conservation managers design and conduct such surveys adequately (but see Karanth and Sunquist 1992, Jathanna et al. 2003, Brugière et al. 2005, Treydte et al. 2005, Ogutu et al. 2006. ...
Article
Reliable assessments of large mammal population sizes are crucial for the management of protected areas. We tested feasibility of foot surveys for population assessments of large mammals in western Tanzanian woodland, comparing estimates of herbivore densities from line-transect data from a National Park with those from an adjacent Game Reserve (GR). We used a Geographic Information System (GIS) and Global Positioning System—supported field design, consisting of systematically distributed closed-circuit transects, and recorded sighting distances and angles. Total survey effort was 1,032 km, conducted within the dry season. We fitted detection functions to distance data with the help of DISTANCE 4.1, using the 3 habitat categories woodland, grassland, and swamp as covariates for detection probability. We found estimates of density and abundance to be reliable for 19 out of 20 larger mammalian herbivores and found significant differences in density between the Park and the GR for 5 species, of which 4 had a higher density in the Park and one had a higher density in the GR. Our results show that, using GIS support and modern navigation methods, foot-transect surveys can be effective in providing accurate data on woodland herbivore populations even in large study areas. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):603–610; 2008)
... These include habitat-deterioration (Saleh, 1987) or fragmentation (Banks et al., 2007), regular burning of the vegetation (Glover, 1968; Sodeinde, 1992), reduced access to natural resources through fencing (e.g. water ponds; Bedunah & Schmidt, 2004), competition between livestock and game (Prins, 1992; Treydte, Edwards & Suter, 2005), and hunting (Newby, 1990; Fischer & Linsenmair , 2006; Setsaas et al., 2007). However, where protected areas with a self-sustaining population of a given species exist in close proximity to areas that are negatively affected by human activities, source-sink dynamics may occur, whereby an apparently stable population in the area affected by hunting depends on immigration from the protected (source) habitat (Watkinson & Sutherland , 1995; Gundersen et al., 2001). ...
Article
We investigated herd-sizes and herd-compositions of Impala (Aepyceros melampus) inside a protected area [Lake Mburo National Park (LMNP) in western Uganda] and the unprotected adjacent ranchland [the Ankole Ranching Scheme (ARS)]. Impala experience intense hunting and poaching in the study area, and poaching is especially strong on the ARS. We found evidence for changes in overall group-sizes in both mixed-sex and pure bachelor herds between areas in and outside LMNP. Mixed-sex herds strongly decreased in size outside the National Park, but bachelor herds even slightly increased in size. While the group-composition of mixed-sex herds was very similar in areas in and outside LMNP, bachelor herds comprised more yearlings and subadult males on the ARS. Our study suggests that effects of hunting and other human nuisance may differ between herd types: mixed herds probably decrease in size because females are more strongly hunted. Around LMNP, impala are usually hunted using nets and spears, thereby increasing the hunters' chance of being injured. Poachers therefore prefer hornless females (and their calves), as it is less dangerous to handle net-caught females than males. As a result, males are less hunted, but increased vigilance and, therefore, reduced aggression among the members of a bachelor herd, may account for the observed increase in herd sizes and changes in group-compositions. © 2009 The Authors. Journal compilation
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Full-text available at: http://rdcu.be/ErWC ___________________________________________________________________________ Large-mammal populations are ecological linchpins1, and their worldwide decline2 and extinction3 disrupts many ecosystem functions and services4. Reversing this trend requires understanding the determinants of population decline, to predict when and where collapses will occur and to guide effective, cost-efficient conservation and restoration policies2,5. Many correlates of large-mammal declines are known, including slow life histories, overhunting, and habitat destruction2,6,7. However, persistent uncertainty about the effects of one widespread factor—armed conflict—complicates conservation-planning and priority-setting efforts5,8. Case studies reveal that conflict can have either positive or negative local impacts on wildlife8–10, but the direction and magnitude of its net effect over large spatiotemporal scales have not previously been quantified5. Here we show that conflict frequency predicts the occurrence and severity of population declines among wild large herbivores in African protected areas from 1946–2010. Conflict was extensive during this interval, occurring in 71% of protected areas, and conflict frequency was the single most important predictor of wildlife population trends among the variables analyzed. Population trajectories were stable (λ≈1.0) in peacetime, fell significantly below replacement with only slight increases in conflict frequency (≥1 conflict-year every 2–5 decades), and were almost-invariably negative in high-conflict sites, both in the full 65-year dataset and in an analysis restricted to recent decades (1989–2010). Yet total population collapse was infrequent, indicating that war-torn faunas can often recover. Human population density was also correlated (positively) with wildlife population trajectories in recent years; however, we found no significant effect in either interval of species’ body mass, protected-area size, conflict intensity (i.e., human fatalities), drought frequency, presence of extractable mineral resources, or various metrics of development and governance. Our results suggest that sustained conservation activity in conflict zones—and rapid interventions following ceasefires—may help to save many at-risk populations and species.
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Various complex trade-offs determine the vitality and survival of acacias in dynamic savannas. Recently, T. M. Palmer et al. (“Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna,” Reports, 11 January, p. [192][1]) illustrated how exclusion of large
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Loss of habitat is one of the most significant problems facing elephants worldwide, leading to clashes over resources between wildlife and humans where elephants receive the largest part of blame - defined as Human Elephant Conflict (HEC). The sub-Saharan region of Africa contains an approximate population of 500,000 elephants that occupy 37 range countries. The African Elephant (Loxodonta africana) is categorized as Vulnerable in the Red List of Threatened Species; they are listed there as two distinct subspecies: the Savanna Elephant (L. a. africana) and the Forest Elephant (L. a. cyclotis). The Red List of Threatened Species categorizes the Asian Elephant (Elephas maximus) as endangered, and today they are found in 13 range states. The Asian Elephant population is estimated to be 30,000 to 50,000 with approximately 60% of the population being present in India. Due to threats of poaching, the elephant ivory debate has been an important part of recent meetings of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) as Parties have debated proposals for one-time sales of legal government stockpiles of elephant tusks. To maintain elephant populations into the future, long-term and large-scale planning is necessary to ensure adequate space and protection for elephants and people living in elephant habitats.
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Some plants respond to browsing with compensatory regrowth of plant tissues and with increased thorn growth. Associations between browsers and their preferred forage were examined through wandering quarter vegetation sampling and observational studies in an effort to understand how some plants respond to browsing by large African herbivores. Acacia seyal (n = 2680) A. drepanolobium (n = 1850), and Balanites glabra (n = 960) were three species of frequently browsed indigenous plants examined on Game Ranching Ltd. in Kenya. There were several statistically significant associations revealed. Individual A. seyal exposed to intensive browser utilization were observed to lose shoot tips, produce long thorns, and have relatively few flowers and fruits. Browser utilization was associated with increased lateral branching in A. drepanolobium and with an increased occurrence of short, thickened spines in B. glabra. Thorns, spines and flowers were measurable indicators of relative browser utilization, and may be useful features to monitor in the management of large African mammals and their prickly forage.
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Ungulate populations in African conservation areas (CAs) are in widespread decline, which can largely be attributed to a lack of functionality of the area encompassed by the CAs themselves. We present evidence from a wide range of African CAs showing that they do not encompass both the functional wet- and dry-season resources that ungulates traditionally migrated between. Before human populations and economic development had grown to levels where they interfered with migrations outside the CAs, ungulates were able to make use of their traditional seasonal resources but this is becoming increasingly difficult and we are now seeing the effects of this restriction of movement on ungulate population numbers. New innovative strategies are required for the conservation of African wildlife. An urgent Africa-wide survey is needed to establish past and present functional resources in and around CAs and to prioritize conservation regions that are most functional. In addition, innovative attempts need to be made to reconsolidate functional seasonal resources within revised expanded protected areas.
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1. The spatial distribution of two wild ungulates, impala and kudu, and of domestic cattle, was monitored across seasons in a 9400 ha ranch of the 'highveld' of Zimbabwe. Habitat use, preference, selectivity and overlap were estimated. Predation was negligible and the study concentrated on interspecific competition. 2. Cattle were contained in paddocks, and were moved regularly, while wild ungulates moved freely. Wild ungulate habitat use, preference and selectivity between paddocks with and without cattle were compared, as was the variation in broad diet, group size and densities. 3. All herbivores were selective, with a marked preference for the nutrient-rich Acacia/Dichrostachys vegetation type. Terminalia communities were almost completely avoided. Selectivity increased as the dry season progressed. Habitat overlap was always high. 4. Interspecific competition occurred between cattle and impala, especially during the wet season and the hot dry season. Impala showed a switch in habitat preference and an increase in selectivity and started to concentrate on 'refuge habitat'. Some also switched in their diet composition. During the hot dry season, when resources were at their lowest, most impala stopped using paddocks with cattle. 5. Kudu seemed relatively unaffected by the presence of cattle: the variations observed in kudu spatial behaviour may have been caused by competition with impala.
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We provide stable carbon isotope data from 37 species of African bovids to document dietary preferences for C3 browse (or fruits) or C4 grass. These data provide a quantitative measure of the fraction of C4 grass in bovid diets, can be applied on regional to local scales, can be derived from tooth enamel and hair or other tissues, and permit the diets of bovids to be considered in the context of a grazer - browser continuum. We recognize hypergrazers (>95% C4 grass), grazers (70-95% C4 grass), mixed feeders (>30% C4 grass and >30% C3 browse), browsers (70-95% C3 browse), and hyperbrowsers or frugivores (>95% C3 browse or fruit). Our results suggest that, of the extant East African Bovidae, impala (Aepyceros melampus), Thomson's gazelle (Gazella thomsonii), and oribi (Ourebia ourebi) can be construed as mixed feeders. Dietary estimates based on stable isotope analysis are in broad agreement with other measures of diet such as hypsodonty index, mass relationships, and wear scratches on enamel.
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Offers a comprehensive introduction to distance sampling, a statistical method used by many biologists and conservationists to estimate animal abundance. The text discusses point transect sampling and line transect sampling and also describes several other related techniques. There are updates on study design and field methods, laser range finders, theodolites and the GPS and advice is given on a wide range of survey methods. Analysis methods have also been generalized, through the use of various types of multiplier and exercises for students in wildlife and conservation management are included.
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Large mammalian herbivores not only depend on plant communities for their existence but cause major changes in plant community composition and structure. These changes have direct consequences for ecosystem processes, but recent studies of ungulate-ecosystem relations show widely divergent ungulate effects in different ecosystems. We reviewed studies of ungulate effects on plant community composition to gain insight into potential mechanisms of ungulate-induced changes in both community composition and ecosystem processes. Our analysis of these studies is based on the premise that the effect ungulates exert on plant communities depends on the balance between (1) feeding selectivity of herbivores (i.e., degree to which different plant species or ecotypes experience different levels of tissue loss), and (2) differences among plant species in their ability to recover from tissue loss. A large number of studies clearly show that selective ungulate herbivory leads to the dominance of unpalatable, chemically defended plant species in communities. However, many studies have also demonstrated that intensive long-term herbivory does not lead to the invasion of unpalatable species into the community, and can even increase the dominance of highly palatable species. Our review indicates that high levels of nutrient inputs or recycling and an intermittent temporal pattern of herbivory (often due to migration) are key factors increasing the regrowth capacity of palatable species and hence maintaining their dominance in plant communities supporting abundant herbivores. Key factors limiting ungulate foraging selectivity, again limiting herbivore-induced dominance of slow-growing, unpalatable species, include herding behavior, early growing season and postfire herbivory, asynchronous phenology of palatable versus unpalatable species, and low relative abundance of unpalatable species. Our review indicates differences among ecosystems in the role played by ungulate herbivory result from the relative strength of these factors enhancing plant tolerance to herbivory and limiting foraging selectivity. Anthropogenic changes in these factors (e.g., alteration of migration patterns) therefore have the potential to significantly alter the effects of ungulates on plant communities and ecosystem processes.
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The success of large‐scale cattle ranching in African savanna vegetation has often been limited by problems of bush encroachment and disease (in particular trypanosomiasis spread by tsetse flies). Mkwaja Ranch, occupying an area of 462 km ² on the coast of Tanzania, is a recent example of a large ranching enterprise that failed within the savanna environment. It was closed in 2000 after 48 years of operation. In this paper we describe the main vegetation types of the area (excluding closed forest vegetation) and relate their patterns of distribution to the former use of the ranch for cattle. The study area comprised the former ranch and parts of the adjacent Saadani Game Reserve, which had not been grazed by cattle for many years and had never been used for large‐scale ranching. Following field surveys, 15 distinct types of grassland and bush vegetation were defined and a vegetation map was created using a Landsat TM satellite image. A multispectral classification using the maximum likelihood algorithm gave good results and enabled all 15 vegetation types to be distinguished on the map. Two main spatial trends were detected in the vegetation. One was a large‐scale decrease in the cover of bushland from the most intensively used parts of the ranch through more extensively used areas to the game reserve; this trend was attributed to differences in management history as well as to climatic and topographic factors. A second trend was a radial vegetation pattern associated with the enclosures where cattle were herded at night. High amounts of three bushland types [dominated by (i) Acacia zanzibarica , (ii) Dichrostachys cinerea , Acacia nilotica or Acacia mellifera and (iii) Terminalia spinosa ] occurred in a zone between 300 and 2500 m from the paddocks, with a peak in bush density at about 900 m (mean value for 18 paddocks). In contrast, bushland dominated by Hyphaene compressa was scarce close to the paddocks and became more abundant with distance. There was also a radial trend in the grassland communities: close to the paddocks there was short grass vegetation containing many ruderals and invasive weedy species, while the tall grassland types with species such as Hyperthelia dissoluta and Cymbopogon caesius occurred further away in the areas less affected by cattle. Synthesis and applications. The intensive modern livestock ranching as practised on Mkwaja Ranch proved to be unsustainable both economically and ecologically. In the end, the biggest problem faced by the ranch managers was not controlling disease, as had originally been feared, but preventing the spread of bush on pasture land. The results of our study demonstrate just how severe the problem of bush encroachment was, especially in areas close to paddocks. An important lesson for management is that grazing patterns need to be taken into consideration when determining the sustainable stocking rate for an area. To reduce the risk of bush encroachment in grazing systems with focal points such as paddocks or watering points, stocking rates need to be lower than in systems with a more uniform grazing distribution.
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The effect of the introduction of an exotic species (cattle) into a native African herbivore assemblage was investigated by studying resource partitioning between zebu cattle, wildebeest and zebra. Resource partitioning was investigated by analysing grass sward characteristics (such as sward height and percentage nitrogen in leaves) of feeding sites selected by the different herbivore species. Linear discriminant analysis was used to determine whether a distinction could be made between feeding sites selected by the different animal species or whether the animal species showed overlap in resource use by selecting similar feeding sites. Wildebeest and zebra did not show overlap in resource use except in the wet season when resources were ample. Cattle showed overlap in resource use with zebra in the early wet season and with wildebeest in the early dry season, seasons when food limitation is likely. In the wet season, cattle showed overlap in resource use with both zebra and wildebeest. Implications of these results for competitive relationships between livestock and wildlife are discussed. We suggest that interpretation of overlap in resource use may be different for an assemblage of long-term coexisting native species as compared to an assemblage of native and exotic species. Among native herbivores, overlap in resource use is not expected based on evolutionary segregation. In a native assemblage to which an exotic species has been introduced, however, overlap in resource use can occur under food-limited conditions and consequently implies competition.
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Grazing in patches of Cynodon dactylon and of Sporobolus spicatus by four large herbivores, and the interaction between these sedentary herbivores was studied in Lake Manyara National Park, northern Tanzania. The herbivores were the African buffalo, Syncerus caffer; the African elephan, Loxodonta africana; the Burchell's zebra, Equus burchelli; and the wildebeest, Connochaetus taurinus. Four different hypotheses of the interactions between the herbivores were tested, viz., increased predator detection/protection through association of species, facilitation of the food intake through the influence of other species, use by other species of the food manipulation strategy of buffalo, and interspecific competition for food. On the level of a single day, zebra and wildebeest were symbiotic, which could have been caused by an increased chance of predator detection. A similar association between buffalo and wildebeest or zebra was also detected on C. dactylon grasslands. There was no indication of facilitation between any of the herbivores. Buffalo had a despotic relationship with elephant, that is the elephant's consumption was lowered when buffalo had visited a patch prior to their arrival. When elephant and buffalo arrived at the same time there appeared to be scramble competition between them. Habitat overlap was calculated for four pairs of species. In conjunction with the analyses of the patch visits, it was concluded that a small overlap was associated with interspecific competition and a large habitat overlap was associated with symbiosis.
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Current hypotheses to explain dynamic transitions between savanna grasslands and woodlands in Africa focus on grazing by elephant or the influence of fire. Using a simple mathematical model, this paper argues that interactions between small herbivores such as impala or buffalo and large herbivores such as elephant or giraffe may provide a plausible alternative hypothesis. The interplay of competition and facilitation between these types of herbivores could explain transitions between grassland and woodland and vice versa. A review of the literat- ure is presented in support of this hypothesis.
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Difficulties imposed by dense vegetation in conducting population density estimates of forest dwelling mammals are well documented. Six methods, ie drive counts, line transects, variable and fixed width transects, dung-heap counts, and territory mapping, were compared to evaluate their suitability in estimating population densities of forest duikers. The variable width transect method appears most suitable for estimating forest duiker population densities. -from Authors
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Discusses 'carrying capacity' and derivative notions of overpopulation, overharvesting and overgrazing, outlining the traditional understanding of these terms, identifying problems that arise from traditional views, and suggesting ways of resolving some of the problems. -from Author
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The avifauna within the willow Salix community on the Arapaho National Wildlife Refuge, N Colorado, was dominated by 11 species of passerine birds during summer. A eurytopic response guild (habitat generalist) included yellow warbler Dendroica petechia, savannah sparrow Passerculus sandwichensis and song sparrow Melospiza melodia. A stenotopic response guild (habitat specialists) included willow flycatcher Empidonax traillii, Lincoln's sparrow Melospiza lincolnii and white-crowned sparrow Zonotrichia leucophrys. The intermediate, mesotopic response guild included American robin Turdus migratorius, red-winged blackbird Agelaius phoeniceus and brown-headed cowbird Molothrus ater. Population densities of the euryptopic response guild differed little between healthy (historically winter-grazed) and decadent (historically summer-grazed) willow communities within a year. Densities of species in the mesotopic response guild differed more dramatically, and stenotopic response-guild species were absent or accidental in decadent willows. The response-guild structure appears primarily to reflect the impact of cattle upon the horizontal patterning of the vegetative community. -from Authors
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The conservation of species requires preservation of natural habitats. Where the integrity of natural habitats has been upset, species go extinct. All natural habitats are continuing to decline, both inside and outside of reserves. Habitat change is partly a natural process (e.g., succession), but human activities have accelerated the process of decay so that natural rates of renewal are insufficient to maintain natural habitats. We argue that our only recourse, in light of these scenarios, is to adopt a new conservation strategy that considers the importance of habitat renewal in addition to habitat preservation. Accordingly, in our management decisions we must not only choose the size of area to preserve but also the size of area that balances habitat loss with habitat renewal. We also suggest that this habitat equilibrium point, H*, needs to be decided upon urgently, otherwise many species will become extinct in the next 50 yr according to numerous predictions. There are two ways to achieve H*. The first is to set habitats aside in protected areas in perpetuity. There are two reasons why this protection alone is insufficient: (1) protected areas continue to decline, albeit at a slower rate than outside of their boundaries, and (2) achieving H* simply by setting aside protected areas is no longer an option in many areas where severe habitat degradation or fragmentation has already occurred. The other way to achieve H* is to promote the restablishment of natural habitats, or ''habitat renewal.'' This concept is illustrated using a simple trade-off model that balances habitat decay and habitat renewal. We then provide examples of habitat loss outside and inside of protected areas and discuss the potential for habitat renewal to offset these losses. We conclude that continued emphasis needs to be placed on setting aside natural habitat in protected areas. However, our examples of habitat loss show that this policy alone is most likely doomed to failure, so a policy of habitat renewal is also required.
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Birth seasons of ungulates in tropical regions show a complex pattern varying from asynchronous to highly synchronous and at different times of year. We examine the factors determining the phenology and synchrony of birth seasons of 13 species of ungulates in the Serengeti ecosystem, Tanzania. We propose that phenology of births (time of year) is determined by food supply, whereas birth synchrony (degree of coordination or spread) is an antipredator adaptation that functions in two different ways. High synchrony may occur through 'predator satiation' in species with precocious newborn ('followers'), whereas asynchrony may occur through 'predator avoidance' in species with nonprecocial young ('hiders'). We used green biomass of grass or tree shoots and percentage crude protein as measures of food supply. Births were determined from monthly sample counts covering the period 1967-1997. The frequency distribution of births was compared to that predicted by the abundance of green biomass and percentage protein, and by an even (asynchronous) monthly distribution. Wildebeest, topi, warthog, and Grant's gazelle births differed from all predicted distributions. Another group showed birth distributions similar to that of green biomass food (buffalo, oribi) or the distribution of percentage protein (giraffe, waterbuck, kongoni, zebra). Also giraffe, waterbuck, and Thomson's gazelle showed births spread more evenly through the year, For grazing species the lag in months between birth peak and protein peak is a positive function of metabolic body size whereas the lag with biomass is a negative function of body size. We suggest that small grazers produce their young early in the wet season ahead of the high protein peak, whereas large species produce their young in phase with high biomass and after the protein peak consistent with metabolic requirements. In terms of synchrony, large species in large herds with precocial young (wildebeest, topi, buffalo) have highly synchronized birth seasons consistent with the 'predator satiation' hypothesis. Small species living in small groups with nonprecocial young (impala, Thomson's and Grant's gazelle, waterbuck, oribi) have births less synchronized than the food supply, as predicted by the 'predator avoidance' hypothesis. In general, food supply determines the phenology of the birth season. Predation appears to shape the synchrony of births through two opposite adaptations. However, no single feature predicts all species' birth distributions. A combination of the phenology of food supply plus antipredator adaptations accounts for most but not all these distributions.
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This field guide begins with a checklist. The main part of the volume consists of entries for each species. Each entry provides information on common names, measurements, recognition, geographical distribution (plus map), habitat, diet, behaviour, adaptations and conservation status. Illustrations are also included. Brief notes are also provided on the African environment (physical, climate and vegetation) and palaeoecology (habitats and species). Finally a short section examines African wildlife conservation.
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The problem of estimating animal abundance is common in wildlife management and environmental impact asessment. Capture-recapture and removal methods are often used to estimate population size. Statistical Inference From Capture Data On Closed Animal Populations, a monograph by Otis et al. (1978), provides a comprehensive synthesis of much of the wildlife and statistical literature on the methods, as well as some extensions of the general theory. In our primer, we focus on capture-recapture and removal methods for trapping studies in which a population is assumed to be closed and do not treat open-population models, such as the Jolly-Seber model, or catch-effort methods in any detail. The primer, written for students interested in population estimation, is intended for use with the more theoretical monograph.
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Both aerial transect sample counts and total counts of elephant and buffalo were conducted in the study area during the wet season. The results from the two counting methods were tested for significant difference. The test showed that the results were not significantly different for both the elephant (P > 0.05) and buffalo (P > 0.05). Pendant la saison des pluies, on a réalisé des comptages aériens par transects échantillons et des comptages totaux des éléphants et des buffles. On a testé les résultats des deux méthodes de comptage pour découvrir des différences significatives. Les tests montrent que les résultats n’étaient significativement différents ni pour les éléphants (P > 0,05), ni pour les buffles (P > 0,05).
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Between April 1981 and December 1984 aerial surveys were conducted in the northern Central Kalahari Game Reserve, the Lake Xau area and a larger area in southwestern Botswana. Range conditions were monitored in the northern Central Kalah, ri Game Reserve. The migration of wildebeest to surface water at Lake Xau was documented. Since the Kalahari wildebeest population has had severely restricted access to surface water for decades and this access is steadily diminishing, it is inferred that the existing population is smaller than it used to be and can be expected to decline further in the future.
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Summary 1. The effect of livestock on African rangelands has been a major focus of recent research, but little attention has been paid to the way livestock affects the distribution and availability of soil nutrients. In East African savannas, overnight containment of livestock in thorn-scrub corrals or 'bomas' concentrates large quantities of nutrients into small areas, potentially altering the landscape distribution of nitrogen (N) and phosphorus (P) in soils and plants. 2. This study was designed to (i) measure the density, turnover rates and soil nutrient concentrations of abandoned cattle bomas on nutrient-poor rangeland in central Kenya; (ii) determine whether long-term glades dominated by Cynodon plectostachyus are derived from abandoned bomas; and (iii) evaluate the effect of cattle bomas on the landscape-level distribution of N and P. 3. In the study area, glades (> 39 years old) averaged 0·71 ha in size and occurred at a density of 0·71 km - 2 . Abandoned bomas (1-39 years since abandonment) averaged 0·39 ha and occurred at a density of 1·21 km - 2 . During 1961-2000, no glades reverted to bushland vegetation, while 53 bomas were abandoned. 4. All characteristics of soils measured across a boma-glade chronosequence indicated glades were indeed derived from abandoned bomas. Soil N, P and organic matter qual- ity in the surface (0-15 cm) layer were similar for glades and 30-39-year-old bomas, but were significantly enriched relative to surrounding bushland. In contrast, at 40-65 cm depth beneath bomas, glades and bushland, soil N was similar. The texture of surface soils from bomas, glades and bushland was similar, indicating glades were not derived from a unique parent material. 5. Leaves of C. plectostachyus from 12-24-year bomas and long-term glades were enriched in P, calcium (Ca) and N relative to leaves of Cynodon dactylon from nearby bushland sites. In particular, P in boma and glade grass was above recommended levels for growing and lactating livestock, while P content of bushland grass was lower than recommended levels. 6. Cattle management via bomas exerts a greater effect on the distribution of P relative to N within the landscape. For cattle grazing an area of 20-25 km 2 boma - 1 , an estimated 0·24-0·30 g N m - 2 year - 1 is removed from the rangeland and deposited into bomas. Within 1·5 years of boma abandonment, 70% of this N is already lost from the manure and upper soil layer. Permanent N loss does occur via leaching, but the majority is probably volatilized and redistributed in rainfall. N deposition in rainfall (0·43 g N m - 2 year - 1 ) is more than sufficient to offset losses due to cattle grazing and deposition in bomas. In contrast, P deposited in bomas is more tightly retained, creating small P-enriched 'hotspots' while causing a permanent loss of the order of 0·021-0·026 g P m - 2 year - 1 from the surrounding bushland landscape. 7. Synthesis and applications. Results indicate that abandoned bomas persist as nutrient- enriched patches for at least four decades. Rangeland managers should recognize that the placement and relocation rate of current bomas influences the long-term distribu- tion and availability of nutritionally important forage for livestock and wildlife. Future assessments of African rangeland stability should incorporate not only direct effects of
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The African savanna biome supports a higher diversity of ungulate species than is found in any other biome or continent. This exceptional faunal diversity and herbivore biomass density is directly linked to the high spatial heterogeneity of African savanna ecosystems. The dependence of herbivore dietary tolerance on body size translates into important size-related differences between savanna ungulate species in terms of habitat specificity, geographical range, and the share of community resources exploited. Intact savanna ungulate communities, with species distributed across body size classes and feeding guilds (grazer/browser), have strong regulatory influences on savanna ecosystem structure and function. Replacement with livestock systems of low diversity and high biomass density within a narrow body size range has occurred through the removal of competitors, pathogens, and predators, and the widespread provisioning of water. Overgrazing by livestock, coupled with episodic droughts, has caused widespread rangeland degradation and loss of floristic and faunal diversity which, by current models, is unlikely to recover to ‘climax’ conditions even with destocking. In selected regions where potential still exists, African savanna biodiversity and human economic development will both be best served by the integration of sustainable wildlife utilization into multispecies animal production systems.
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Immunocompetence (i.e., the ability to produce an immune response to pathogens) can be predicted to influence the chances that organisms have to survive and reproduce. In this study we simulated a challenge to the immune systems of male barn swallows (Hirundo rustica) by injecting them intraperitoneally with a multigenic antigen, sheep red blood cells, and we analyzed long-term survival in relation to their immunocompetence. Males were assigned to four groups that differed for the treatment of the length of the outermost tail feathers, a sexually dimorphic ornamental character that is currently under directional sexual selection. Immunocompetence was measured as change of concentration of gamma globulins relative to plasma proteins. The intensity of the immune response was independent of age. Males that showed the highest short-term response to sheep red blood cells were more likely to survive until the breeding season following that in which they had been inoculated, a pattern consistently observed within each experimental group. Males with comparatively long tails were more likely to survive than those with short tails. To our knowledge, the results of this study are the first to demonstrate that immunocompetence can predict long-term survival in a free-ranging vertebrate. Moreover, they are compatible with current models of parasite-mediated sexual selection because long-tailed males are more immunocompetent than short-tailed ones, and females, by preferring to mate with the most ornamented males, may acquire the "good genes" for high immunocompetence and, hence, for high viability of their offspring.
Saadani and Bagamoyo – Published for Tanzania National Parks
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Johnson, P., Mccullum, H. & Boyd, J. (2002) Saadani and Bagamoyo – Published for Tanzania National Parks. African Publishing Group (International), Harare, Zimbabwe.
CRC Handbook of Census Methods for Terrestrial Vertebrates. Library of congress cataloging in publication data Large herbivores that strive mightily but eat and drink as friends
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Davis, D.E. (1982) CRC Handbook of Census Methods for Terrestrial Vertebrates. Library of congress cataloging in publication data, Boca Raton, Florida, USA. De Boer, W.F. & Prins, H.H.T. (1990) Large herbivores that strive mightily but eat and drink as friends. Oecologia 82, 264–274.
Report on the Ground Census of Large Mammals in Saadani Game Reserve. GTZ Wildlife Programme in Tanzania (GTZ: 35) Dar Es Salaam JMP User's Guide The Estimation of Animal Abundance and Related Parameters
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Estimating the number of animals in wildlife populations In: Research Man-agement Techniques for Wildlife and Habitats Carrying capacity and related slippery shibbo-leths
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Mkwaja Ranch: A Management's Perspective of Cattle Ranching in a Tsetse Infested Area in Tanzania Between
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Introduction to Distance Sampling Diets of East African bovidae based on stable isotope analysis
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Habitat Use of Wildlife and Fodder Preferences of the Common Warthog (Phacochoerus africanus) on a Former Cattle Ranch in a Tanzanian Savanna Tanzania Wildlife Conservation Monitoring: Aerial Wildlfie Census Saadani Ecosystem
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