Spiders as potential indicators of elephant‐induced habitat changes in endemic sand forest,Maputaland, South Africa

Elephant impacts on spider assemblages, and the potential use of spiders as indicators of habitat changes was assessed in central Maputaland, South Africa. Three habitats, namely undisturbed sand forest, elephant disturbed sand forest and mixed woodland, were sampled. To ensure a thorough representation of all spider guilds, spiders were collected by tree beating, sweep netting, active searching, leaf litter sifting and pitfall traps. In total, 2808 individual spiders, representing 36 families, 144 determined genera and 251 species were collected. Spider abundance was highest in the undisturbed sand forest (n = 1129, S = 179), followed by elephant disturbed sand forest (n = 1006, S = 165) and mixed woodland (n = 673, S = 171). Assemblages of the two sand forests were more similar than to the mixed woodland assemblage. Active hunting species were indicators of the more open vegetation of elephant disturbed sand forest (six active hunters, no web‐builders) and mixed woodland (ten active hunters, one web‐builder), whereas web‐builders are indicators of the dense, complex vegetation structure of undisturbed sand forest (six web‐builders, three active hunters). Elephant‐induced changes to the vegetation structure in this high diversity, high endemism region result in changes in the composition of spider assemblages, and may need to be mitigated by management intervention.     

Understanding Long-Term Variations in an Elephant Piosphere Effect to Manage Impacts

Surface water availability is a key driver of elephant impacts on biological diversity. Thus, understanding the spatio-temporal variations of these impacts in relation to water is critical to their management. However, elephant piosphere effects (i.e. the radial pattern of attenuating impact) are poorly described, with few long-term quantitative studies. Our understanding is further confounded by the complexity of systems with elephant (i.e. fenced, multiple water points, seasonal water availability, varying population densities) that likely limit the use of conceptual models to predict these impacts. Using 31 years of data on shrub structure in the succulent thickets of the Addo Elephant National Park, South Africa, we tested elephant effects at a single water point. Shrub structure showed a clear sigmoid response with distance from water, declining at both the upper and lower limits of sampling. Adjacent to water, this decline caused a roughly 300-m radial expansion of the grass-dominated habitats that replace shrub communities. Despite the clear relationship between shrub structure and ecological functioning in thicket, the extent of elephant effects varied between these features with distance from water. Moreover, these patterns co-varied with other confounding variables (e.g. the location of neighboring water points), which limits our ability to predict such effects in the absence of long-term data. We predict that elephant have the ability to cause severe transformation in succulent thicket habitats with abundant water supply and elevated elephant numbers. However, these piosphere effects are complex, suggesting that a more integrated understanding of elephant impacts on ecological heterogeneity may be required before water availability is used as a tool to manage impacts. We caution against the establishment of water points in novel succulent thicket habitats, and advocate a significant reduction in water provisioning at our study site, albeit with greater impacts at each water point.     

Home range and ranging behaviour of Bornean elephant (Elephas maximus borneensis) females

Background

Home range is defined as the extent and location of the area covered annually by a wild animal in its natural habitat. Studies of African and Indian elephants in landscapes of largely open habitats have indicated that the sizes of the home range are determined not only by the food supplies and seasonal changes, but also by numerous other factors including availability of water sources, habitat loss and the existence of man-made barriers. The home range size for the Bornean elephant had never been investigated before.

Methodology/Principal Findings

The first satellite tracking program to investigate the movement of wild Bornean elephants in Sabah was initiated in 2005. Five adult female elephants were immobilized and neck collars were fitted with tracking devices. The sizes of their home range and movement patterns were determined using location data gathered from a satellite tracking system and analyzed by using the Minimum Convex Polygon and Harmonic Mean methods. Home range size was estimated to be 250 to 400 km² in a non-fragmented forest and 600 km² in a fragmented forest. The ranging behavior was influenced by the size of the natural forest habitat and the availability of permanent water sources. The movement pattern was influenced by human disturbance and the need to move from one feeding site to another.

Conclusions/Significance

Home range and movement rate were influenced by the degree of habitat fragmentation. Once habitat was cleared or converted, the availability of food plants and water sources were reduced, forcing the elephants to travel to adjacent forest areas. Therefore movement rate in fragmented forest was higher than in the non-fragmented forest. Finally, in fragmented habitat human and elephant conflict occurrences were likely to be higher, due to increased movement bringing elephants into contact more often with humans.     

The influence of wave exposure on the foraging activity of marine otter, <Emphasis Type="Italic">Lontra felina</Emphasis> (Molina, 1782) (Carnivora: Mustelidae) in northern Chile

The marine otter Lontra felina has been said to prefer wave-exposed habitats over more protected sites in response to a greater prey abundance in exposed habitat. We examined how the foraging activity of L. felina is affected by the regime of wave exposure and prey availability at Isla Choros, northern Chile. Through focal sampling we recorded time spent by otters in foraging, the duration of dives, and the hunting success on a wave-exposed and a wave-protected site on the island. In addition, we quantified the abundance of prey in both habitats. Marine otters spent more time foraging in the wave-protected site compared with the wave-exposed habitat. Successful dives reached 26.9% in the wave-exposed habitats, and 38.2% in the wave-protected habitat. Foraging dives were 18% shorter in wave-exposed as compared with wave-protected habitat. Numerically, available prey did not differ significantly with habitat. Our results are more consistent with the hypothesis that wave-exposed habitats represent a sub-optimal habitat to foraging marine otters. Marine otters’ use of wave-exposed patches through northern and central Chile coastal areas probably reflects a low availability of suitable protected areas and greater human disturbance of more protected habitat.     

普洱市亚洲象栖息地适宜度评价

亚洲象(Elephas maximus)属于我国Ⅰ级保护动物,在中国仅分布于云南省西双版纳国家级自然保护区、普洱市的思茅区、澜沧县和江城县,以及临沧南滚河国家级自然保护区。将普洱全境作为研究区域,利用野外调查数据,结合遥感与地理信息系统技术,运用生态位因子分析(ENFA)模型对普洱市亚洲象的栖息地适宜度进行了评价,并预测了适宜栖息地的分布。发现:普洱市亚洲象栖息地的边际值为0.991,表明亚洲象在普洱市境内对环境变量的选择不是随机的;耐受值为0.315,表明亚洲象在普洱市境内生态位较窄,受环境条件的制约。根据模型计算得到的栖息地适宜度指数,将普洱市的亚洲象栖息地分为最适栖息地,较适栖息地,边际栖息地和非栖息地4个等级,面积分别为409.32、574.32、2909.48、38722.32 km2。最适栖息地仅占全市面积的0.96%,而非栖息地占90.86%。利用GIS和Biomapper 4.0生成亚洲象栖息地分布图,发现普洱境内最适栖息地和较适栖息地面积狭小。对最适栖息地、较适栖息地和边际栖息地进行景观格局分析的结果表明,3种类型的栖息地破碎化均十分严重,连通度较低,栖息地内受到较大程度的人类活动的干扰。因此建议在普洱和西双版纳间尽快建立野生动物生态廊道,以加强亚洲象各种群间的交流。     

Effect of fire on northern bettong (Bettongia tropica) foraging behaviour

An examination of movement paths, foraging patterns and habitat use of an endangered mycophagous marsupial, the northern bettong (Bettongia tropica), was undertaken in fire‐prone forest in north‐eastern Australia before and after experimentally induced fires. Fungal biomass remaining at bettong foraging points was similar across the study area prior to burning, but increased significantly on burnt ground during the period after fire. After burning, significantly more bettongs chose to forage in burnt habitat and those that did experienced higher probabilities of truffle recovery. Using data from spool‐and‐line tracking, observed movement patterns of bettongs were compared with those expected from a simple null model of animal movement (a correlated random walk). Analysis of mean‐squared displacement revealed that 22% of observations fell beyond the model’s 95% prediction interval. Further analysis revealed the reasons for the model’s inadequacy: bettongs exhibited area‐restricted search behaviour by taking significantly more frequent and more acute turns immediately prior to and following recovery of hypogeous fungi (truffles), and by taking significantly more frequent and more acute turns following any other foraging activity. In general ecological terms, the results indicate a flexible response by the northern bettong to habitat alteration and increased food availability brought about by low intensity fires.     

Samango Monkeys (<Emphasis Type="Italic">Cercopithecus albogularis labiatus</Emphasis>) Manage Risk in a Highly Seasonal,Human-Modified Landscape in Amathole Mountains,South Africa

Wild species use habitats that vary in risk across space and time. This risk can derive from natural predators and also from direct and indirect human pressures. A starving forager will often take risks that a less hungry forager would not. At a highly seasonal and human-modified site, we predicted that arboreal samango monkeys (Cercopithecus albogularis labiatus) would show highly flexible, responsive, risk-sensitive foraging. We first determined how monkeys use horizontal and vertical space across seasons to evaluate if high-risk decisions (use of gardens and ground) changed with season, a proxy for starvation risk. Then, during a subsequent winter, we offered equal feeding opportunities (in the form of high-value, raw peanuts) in both gardens and forest to see if this short-term change in food availability and starvation risk affected monkeys’ foraging decisions. We found that during the food-scarce winter, monkeys foraged outside indigenous forest and in gardens, where they fed on exotic species, especially fallen acorns (Quercus spp.), despite potential threats from humans. Nevertheless, and as predicted, when given the choice of foraging on high-value foods in gardens vs. forest during our artificial foraging experiment, monkeys showed a preference for a safer forest habitat. Our experiment also indicated monkeys’ sensitivity to risk in the lower vertical strata of both habitats, despite their previous extensive use of the ground. Our findings support one of the central tenets of optimal foraging theory: that risk of starvation and sensitivity to the variation in food availability can be as important drivers of behavior as risk of predation.     

Ontogenetic niche partitioning in southern elephant seals from Argentine Patagonia

Elephant seals, Mirounga spp., are highly dimorphic, having different energetic requirements according to age and sex, and foraging in various ecological and oceanographic contexts. Resource partitioning has been shown for the sub-Antarctic populations of southern elephant seals, M. leonina, where colonies are surrounded by narrow shelves that deepen abruptly. In contrast, seals from Península Valdés (Argentina), in the northernmost extent of the breeding range, face an extended, shallow, temperate, and productive continental shelf. We integrated tracking data from 98 animals (juveniles and adults, males and females) gathered over more than two decades, and found that although all available habitats were used, individuals segregated by age and sex. Juvenile males favored shelf habitats, whereas subadult and adult males also used the shelf break. Juvenile females preferred the shelf and the more distant Argentine Basin used by postbreeding and postmolt adult females. Males showed the highest proportion of area-restricted search locations, suggesting more spatially concentrated feeding activity, and likely reflecting a preference for foraging habitat and prey. Our results are consistent with those from other populations, implying that elephant seals show remarkable similarities in habitat use by age and sex classes, despite broad differences in the offshore habitats between sub-Antarctic and temperate ecosystems.     

Modeling foraging behavior of piping plovers to evaluate habitat restoration success

Habitat restoration projects are often deemed successful based on the presence of the target species within the habitat; however, in some cases the restored habitat acts as an ecological trap and does not help to improve the reproductive success of the target species. Understanding wildlife–habitat relationships through precise measurements of animal behavior can identify critical resources that contribute to high quality habitat and improve habitat restoration practice. We evaluated the success of a restored piping plover (Charadrius melodus) breeding habitat in New Jersey, USA. We identified the major factors influencing foraging rates, compared foraging activity budgets over 3 yr at restored and natural habitats, and explored the potential of artificial tidal ponds as a viable restoration alternative. Adult foraging rates were higher in artificial pond and ephemeral pool habitats, during low tide, and after breeding activity ended. Adult foraging rates were impeded by the presence of people and vehicles within 50 m. Chick foraging rates were highest at artificial ponds and bay shores and lowest in dunes and on sand flats. Chick foraging rates were strongly hindered by the presence of corvids and the number of people within 50 m. In addition, at artificial tidal ponds, piping plovers spent more time foraging and less time engaged in defensive behaviors (vigilance, crouching, and fleeing) compared to other potential habitats. Our findings support the hypothesis that artificial tidal ponds are a valuable, perhaps superior, foraging habitat. Future beach restoration projects should include this feature to maximize habitat quality and restoration success. © 2011 The Wildlife Society.     

Multiple habitat use by declining migratory birds necessitates joined‐up conservation

Many species depend on multiple habitats at different points in space and time. Their effective conservation requires an understanding of how and when each habitat is used, coupled with adequate protection. Migratory shorebirds use intertidal and supratidal wetlands, both of which are affected by coastal landscape change. Yet the extent to which shorebirds use artificial supratidal habitats, particularly at highly developed stopover sites, remains poorly understood leading to potential deficiencies in habitat management. We surveyed shorebirds on their southward migration in southern Jiangsu, a critical stopover region in the East Asian Australasian Flyway (EAAF), to measure their use of artificial supratidal habitats and assess linkages between intertidal and supratidal habitat use. To inform management, we examined how biophysical features influenced occupancy of supratidal habitats, and whether these habitats were used for roosting or foraging. We found that shorebirds at four of five sites were limited to artificial supratidal habitats at high tide for ~11–25 days per month because natural intertidal flats were completely covered by seawater. Within the supratidal landscape, at least 37 shorebird species aggregated on artificial wetlands, and shorebirds were more abundant on larger ponds with less water cover, less vegetation, at least one unvegetated bund, and fewer built structures nearby. Artificial supratidal habitats were rarely used for foraging and rarely occupied when intertidal flats were available, underscoring the complementarity between supratidal roosting habitat and intertidal foraging habitat. Joined‐up artificial supratidal management and natural intertidal habitat conservation are clearly required at our study site given the simultaneous dependence by over 35,000 migrating shorebirds on both habitats. Guided by observed patterns of habitat use, there is a clear opportunity to improve habitat condition by working with local land custodians to consider shorebird habitat requirements when managing supratidal ponds. This approach is likely applicable to shorebird sites throughout the EAAF.     

Environmental factors affecting the distribution of African elephants in the Kasigau wildlife corridor,SE Kenya

The African elephant, Loxodonta africana, is under threat from habitat loss, poaching and human–elephant conflict. To mitigate for impact of habitat loss and reduce conflict, connectivity between elephant habitats can be improved through the protection of corridor areas. This study looks at elephant distribution and movement patterns within the Kasigau Wildlife Corridor (KWC) within the Tsavo Conservation Area in South‐east Kenya. Elephant presence data were obtained from observations by rangers during routine patrols across KWC, and were analysed in MaxEnt. The environmental factors predicting elephant distribution and density were tested, as well as the relationship between elephant maximum entropy and the presence and abundance of other wildlife. Seasonal variations in temperature and precipitation, plus presence of waterholes were found to play significant roles in elephant distribution across KWC. Higher elephant densities were not found to correlate with lower densities of other wildlife species; indeed, during the dry seasons, elephant presence was associated with greater wild herbivore densities. Besides illustrating the importance of the KWC for elephant conservation in the Tsavo ecosystem, both as a key corridor and habitat, this study also hopes to highlight the untapped utility of routine ranger patrol data, and encourage the use of such presence‐only data for deducing important knowledge for conservation of biodiversity.     

Forest elephant paths and movements at the Odzala National Park, Congo: the role of clearings and Marantaceae forests

The role of forest clearings and Marantaceae forest on elephant movement at the Odzala National Park was studied by describing and mapping elephant paths. Three types of paths were distinguished based on their direction, length, width, elephant activity and the types of forests they cross. They were called boulevards, foraging paths, and clearing alleys. All paths explored were heavily used. Boulevards are used for travelling over long distances (up to 34 km) and for linking up rapidly favourite sites such as clearings. Foraging paths mainly run through the medium-density Marantaceae forests which provide elephants with both herbaceous foods and tree fruit. Clearing alleys form a dense network of tracks around clearings. This network could be a result of an anti-predatory monitoring behaviour of elephants before entering the clearings where they have long experienced heavy poaching. The heavy trampling which results from the elephant activity could contribute to the maintenance of clearings by preventing germination and seedling survival of the numerous seeds dispersed in their dung.     

Functional responses in polar bear habitat selection

Habitat selection may occur in situations in which animals experience a trade-off, e.g. between the use of habitats with abundant forage and the use of safer retreat habitats with little forage. Such trade-offs may yield relative habitat use conditional on the relative availability of the different habitat types, as proportional use of foraging habitat may exceed proportional availability when foraging habitat is scarce, but be less than availability when foraging habitat is abundant. Hence, trade-offs in habitat use may result in functional responses in habitat use (i.e. change in relative use with changing availability). We used logistic and log-linear models to model functional responses in female polar bear habitat use based on satellite telemetry data from two contiguous populations; one near shore inhabiting sea ice within fjords, and one inhabiting pelagic drift ice. Open ice, near the ice edge, is a highly dynamic habitat hypothesised to be important polar bear habitat due to high prey availability. In open ice-polar bears may experience a high energetic cost of movements and risk drifting away from the main ice field (i.e. trade off between feeding and energy saving or safety). If polar bears were constrained by ice dynamics we therefore predicted use of retreat habitats with greater ice coverage relative to habitats used for hunting. The polar bears demonstrated season and population specific functional responses in habitat use, likely reflecting seasonal and regional variation in use of retreat and foraging habitats. We suggest that in seasons with functional responses in habitat use, polar bear space use and population distribution may not be a mere reflection of prey availability but rather reflect the alternate allocation of time in hunting and retreat habitats.     

云南西双版纳尚勇保护区亚洲象对栖息地的选择

以西双版纳国家级自然保护区尚勇子保护区内的亚洲象种群为研究对象, 利用村寨调查、样线调查和3S(GIS、GPS、RS) 技术对该地区野生亚洲象的栖息地状况和亚洲象对栖息地选择利用进行了初步的研究。结果表明亚洲象喜欢海拔1 000 m以下的区域, 坡度小于10°的区域, 坡位为平坦的沟谷和山坡的下部, 坡向为南、北两个方向。偏好的植被类型有竹阔混交林、灌丛和高山草甸。研究还发现尚勇保护区及周边区域亚洲象栖息地的丧失和日益增加的非法盗猎活动已经严重威胁到该地区野生亚洲象种群的生存。     

Northern pigtailed macaques rely on old growth plantations to offset low fruit availability in a degraded forest fragment

Space-use and foraging strategies are important facets to consider in regard to the ecology and conservation of primates. For this study, we documented movement, ranging, and foraging patterns of northern pigtailed macaques (Macaca leonina) for 14 months in a degraded habitat with old growth Acacia and Eucalyptus plantations at the Sakaerat Biosphere Reserve in northeastern Thailand. We used hidden Markov models and characteristic hull polygons to analyze these patterns in regard to fruit availability. Macaques' home range (HR) was 599 ha and spanned through a natural dry-evergreen forest (DEF), and plantation forest. Our results showed that active foraging increased with higher fruit availability in DEF. Macaques changed to a less continuous behavioral state during periods of lower fruit availability in DEF, repeatedly moving from foraging to transiting behavior, while extending their HR further into plantation forest and surrounding edge areas. Concomitantly, macaques shifted their diet from fleshy to dry fruit such as the introduced Acacia species. Our results showed that the diet and movement ecology adaptations of northern pigtailed macaques were largely dependent on availability of native fruits, and reflected a “high-cost, high-yield” foraging strategy when fresh food was scarce and dry fruit was available in plantation forest. Conversely, wild-feeding northern pigtailed macaque populations inhabiting pristine habitat approached a “low-cost, low-yield” foraging strategy. Our results outline the effects of habitat degradation on foraging strategies and show how a flexible species can cope with its nutritional requirements.     

The impact of tree modification by African elephant (Loxodonta africana) on herpetofaunal species richness in northern Tanzania

In Africa, no other nonhuman animal fulfils the role of ecosystem engineers to the extent of the elephant. However, little is known about the relationship between elephant modified habitats and species composition of other animals. Our objective was to sample the herpetofauna within an Acacia habitat that varied in the degree of elephant impact. If elephant foraging was only modifying but not degrading or enriching the habitat, then herpetofauna species abundance and richness were predicted to be similar in elephant damaged and elephant excluded areas. We conducted this study at Endarakwai Ranch in northeastern Tanzania for 6 months in 2007 and 2008. We sampled herpetofaunal species richness and abundance within high, medium and low elephant damaged areas and in a plot that excluded elephants. Areas of heavy damage yielded higher species richness than the exclusion plot. Species diversity did not differ between the damaged areas and the exclusion plot. Frogs were more abundant in areas of high damage; in contrast, toads were found the least in high damage areas. The results support the notion that free ranging elephants influence herpetofaunal species distribution by creating habitat complexity through modifying the woodland area.     

Soil nutrient status determines how elephant utilize trees and shape environments

1. Elucidation of the mechanism determining the spatial scale of patch selection by herbivores has been complicated by the way in which resource availability at a specific scale is measured and by vigilance behaviour of the herbivores themselves. To reduce these complications, we studied patch selection by an animal with negligible predation risk, the African elephant. 2. We introduce the concept of nutrient load as the product of patch size, number of patches and local patch nutrient concentration. Nutrient load provides a novel spatially explicit expression of the total available nutrients a herbivore can select from. 3. We hypothesized that elephant would select nutrient-rich patches, based on the nutrient load per 2500 m(2) down to the individual plant scale, and that this selection will depend on the nitrogen and phosphorous contents of plants. 4. We predicted that elephant would cause more adverse impact to trees of lower value to them in order to reach plant parts with higher nutrient concentrations such as bark and root. However, elephant should maintain nutrient-rich trees by inducing coppicing of trees through re-utilization of leaves. 5. Elephant patch selection was measured in a homogenous tree species stand by manipulating the spatial distribution of soil nutrients in a large field experiment using NPK fertilizer. 6. Elephant were able to select nutrient-rich patches and utilized Colophospermum mopane trees inside these patches more than outside, at scales ranging from 2500 down to 100 m(2) . 7. Although both nitrogen and phosphorus contents of leaves from C. mopane trees were higher in fertilized and selected patches, patch choice correlated most strongly with nitrogen content. As predicted, stripping of leaves occurred more in nutrient-rich patches, while adverse impact such as uprooting of trees occurred more in nutrient-poor areas. 8. Our results emphasize the necessity of including scale-dependent selectivity in foraging studies and how elephant foraging behaviour can be used as indicators of change in the availability of nutrients.     

Using presence‐only modelling to predict Asian elephant habitat use in a tropical forest landscape: implications for conservation

Aim Asian elephants, Elephas maximus, are threatened throughout their range by a combination of logging, large scale forest conversion and conflict with humans. We investigate which environmental factors, both biotic and abiotic, constrain the current distribution of elephants. A spatially explicit habitat model is constructed to find core areas for conservation and to assess current threats. Location Ulu Masen Ecosystem in the province of Nanggroe Aceh Darussalam on the island of Sumatra, Indonesia. Methods A stratified survey was conducted at 12 sites (300 transects) to establish the presence of elephants. Presence records formed the basis to model potential habitat use. Ecological niche factor analysis (ENFA) is used to describe their niche and to identify key factors shaping elephant distribution. An initial niche model was constructed to describe elephant niche structure, and a second model focused on identifying core areas only. To assess the threat of habitat encroachment, overlap between the elephants’ optimal niche and the occurrence of forest encroachment is computed. Results Elephants were recorded throughout the study area from sea level to 1600 m a.s.l. The results show that the elephant niche and consequently habitat use markedly deviates from the available environment. Elephant presence was positively related to forest cover and vegetation productivity, and elephants were largely confined to valleys. A spatially explicit model showed that elephants mainly utilize forest edges. Forest encroachment occurs throughout the elephants range and was found within 80% of the elephants’ ecological niche. Main conclusions In contrast to general opinion, elephant distribution proved to be weakly constrained by altitude, possibly because of movement routes running through mountainous areas. Elephants were often found to occupy habitat patches in and near human‐dominated areas. This pattern is believed to reflect the displacement of elephants from their former habitat.     

基于InVEST-图论模型的西双版纳州亚洲象生境网络评价

在大力推进生物多样性保护工作的背景下,亚洲象的活动范围与人类生产生活空间不断重叠,人象冲突矛盾日益严重,对物种栖息地生境网络进行优化能从源头缓解这一矛盾。在亚洲象国家公园建设之际,研究以西双版纳州为例,提出了一种基于InVEST-图论复合模型识别并优化生境网络的方法:即以土地利用数据为基础,结合亚洲象生活习性与栖息地偏好,通过海拔、坡度、距水源距离3个约束因子矫正生境质量数据,运用Graphab软件识别潜在生境网络,结合最小累积阻力模型理念与景观图论的分析方法,从"源地-廊道"角度定量化分析西双版纳州国家级亚洲象保护区的保护空缺,探讨保护区的空间布局优化策略与生境分级保护策略,以期为亚洲象国家公园的建设与西双版纳州国土空间规划提供新视角。结果表明,西双版纳州共识别出生态源地335个,总面积4595.60km²,总体上高质量生境分布较为均衡,连通性较好的生境网络集中分布在北部与东部区域,中部B4勐仑片区存在较为显著的生态孤岛现象,西南部高质量生境斑块小而破碎,联系紧密但缺少作为核心栖息地的大面积生境。保护空缺方面,国家级保护区范围内的生态源地仅占总源地面积的31.68%,大型保护空缺集中分布于B3勐养片区东北部;优化后的生境网络能形成以B3勐养片区为核心,以国家自然保护区为主的"B5-A-B3-B4-B1-B2"生物迁徙廊道。     

Shift in Black Rhinoceros Diet in the Presence of Elephant: Evidence for Competition?

In African large herbivore assemblages, megaherbivores dominate the biomass and utilise the greatest share of available resources. Consequently, they are considered a separate trophic guild that structures the food niches of coexisting large herbivores. However, there exists little empirical evidence on how food resources are shared within this guild, and none for direct competition for food between megaherbivores. Using the histological analysis of faeces, we explore this phenomenon for African elephant Loxodonta africana and black rhinoceros Diceros bicornis in the Addo Elephant National Park, South Africa, where the accumulated impacts of elephant have reduced browse availability. Despite being unable to generalise beyond our study sites, our observations support the predictions of competition theory (as opposed to optimality theory) by showing (1) a clear seasonal separation in resource use between these megaherbivores that increased as resource availability declined, and (2) rhinoceros changed their selectivity in the absence of elephant (using an adjacent site) by expanding and shifting their diet along the grass-browse continuum, and in relation to availability. Although black rhinoceros are generally considered strict browsers, the most significant shift in diet occurred as rhinoceros increased their preferences for grasses in the presence of elephant. We speculate that the lack of specialised grazing adaptations may increase foraging costs in rhinoceros, through reduced harvest- and handling-efficiencies of grasses. In the short-term, this may be off-set by an enhanced tolerance for low quality food and by seasonally mobilising fat reserves; however, the long-term fitness consequences require further study. Our data suggest that managing elephant at high densities may compromise the foraging opportunities of coexisting browsers. This may be particularly important in small, fenced areas and overlapping preferred habitats where impacts intensify.