首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Forested landscapes in Southeast Asia are becoming increasingly fragmented, making this region a conservation and research priority. Despite its importance, few empirical studies of effects of fragmentation on biodiversity have been undertaken in the region, limiting our ability to inform land-use regimes at a time of increased pressure on forests. We estimated the biodiversity value of forest fragments in peninsular Malaysia by studying fragmentation impacts on insectivorous bat species that vary in dependence of forest. We sampled bats at seven continuous forest sites and 27 forest fragments, and tested the influence of fragment isolation and area on the abundance, species richness, diversity, composition and nestedness of assemblages, and the abundance of the ten most common species. Overall, isolation was a poor predictor of these variables. Conversely, forest area was positively related with abundance and species richness of cavity/foliage-roosting bats, but not for that of cave-roosting or edge/open space foraging species. The smallest of fragments (<150 ha) were more variable in species composition than larger fragments or continuous forest, and larger fragments retained substantial bat diversity, comparable to continuous forest. Some fragments exhibited higher bat abundance and species richness than continuous forest, though declines might occur in the future because of time lags in the manifestation of fragmentation effects. Our findings suggest that fragments >300 ha contribute substantially to landscape-level bat diversity, and that small fragments also have some value. However, large tracts are needed to support rare, forest specialist species and should be the conservation priority in landscape-level planning. Species that roost in tree cavities or foliage may be more vulnerable to habitat fragmentation than those that roost in caves.  相似文献   

2.
Large mammal faunas in tropical forest landscapes are widely affected by habitat fragmentation and hunting, yet the environmental determinants of their patterns of abundance remain poorly understood at large spatial scales. We analysed population abundance and biomass of 31 species of medium to large-bodied mammal species at 38 Atlantic forest sites (including three islands, 26 forest fragments and six continuous forest sites) as related to forest type, level of hunting pressure and forest fragment size using ANCOVAs. We also derived a novel measure of mammal conservation importance for each site based on a “Mammalian Conservation Priority index” (MPi) which incorporates information on species richness, population abundance, body size distribution, conservation status, and forest patch area. Mammal abundance was affected by hunting pressure, whereas mammalian biomass of which was largely driven by ungulates, was significantly influenced by both forest type and hunting pressure. The MPi index, when separated into its two main components (i.e. site forest area and species-based conservation index Ci), ordered sites along a gradient of management priorities that balances species-focused and habitat-focused conservation actions. Areas with the highest conservation priority were located in semi-deciduous forest fragments, followed by lowland forests. Many of these fragments, which are often embedded within large private landholdings including biofuel and citrus or coffee crops, cattle ranches and pulpwood plantations, could be used not only to comply with environmental legislation, but also enhance the prospects for biodiversity conservation, and reduce edge effects and hunting.  相似文献   

3.
Species response to forest fragmentation may strongly vary according to ecological requirements, shape, spatial configuration and connectivity of fragments, and the structure of the surrounding matrix. Bats are natural candidates for studies on forest fragmentation. However, the conclusions of such studies are often contradictory. We present the results of a study on the effects of forest fragmentation on bat communities in Alter do Chão, Santarém area, in Central Amazonia, Brazil, an area composed by forests and fragments surrounded by savanna-like vegetation. We compared the species composition between habitats, tested the effect of size, shape and density of trees of forested areas on the presence species and their relative frequency of captures, and investigated the savannas as an ecological barrier for the dispersion of bats. With an effort of 5678 mistnet-hours, we captured 3740 bats (64 species). Multidimensional Scaling indicated no strong separation between the habitats sampled, however, savanna sites were grouped distinctly of fragments and forest sites. Multiple linear regressions indicated no significant correlation between the number of bat species recorded and the size, shape or tree density in forest sites and fragments. There was a significant correlation between the number of captures and the variables tested, explained by the shape of the sites, but not by size or tree density. In general, sites with bigger shape indices had fewer captures. Ten of the 20 most captured species showed no significant difference between the three habitats. The bat communities in Alter do Chão were not strongly affected by forest fragmentation, and the savannas did not appear to act as an ecological barrier to bats.  相似文献   

4.
Neotropic bats comprise a highly species-rich group and are considered important regulators of complex ecological processes. Resource partitioning of roosts and food is considered a key element in shaping bat communities. In this paper we examine the roosting patterns of 10 bat species belonging to a neotropical bat community in a Bolivian savanna. Roosts were more common in open woodlands than in forest islands and human settlements. In open woodlands, Tabebuia heptaphylla comprised the largest proportion of roosting trees, whereas in forest islands, Gallesia integrifolia was the most important roosting tree for phyllostomid bats. By comparing active roosts with control holes in Tabebuia heptaphylla, we found that roost site selection by Noctilio albiventris was mainly based on tree diameter and inner width of the cavities. The earlier results are discussed in view of resource partitioning within savanna bat communities and their practical conservation.  相似文献   

5.
In order to document the responses of bats to destruction and fragmentation of their natural habitat and the value of different types of man-made vegetation for bat conservation in the Neotropics, bats were sampled with mist nets to compare species richness and species composition in a tract of continuous forest, forest fragments and a habitat-island consisting of a mosaic of forest and arboreal crops in Los Tuxtlas, southern Mexico. We captured 3835 bats representing 39 species: 76% were captured in continuous forest, 74% in the mosaic habitat and 87% in forest fragments. In the mosaic habitat we captured 43% of the total number of bats, 33% in the forest fragments and 24% in continuous forest. On average the habitats studied had 64% species in common. Evidence of continuous breeding activity was determined for a high number of species at the three habitats (> 70% lactating and 65% with embryos). A few bat species (Carollia brevicauda, Pteronotus parnelli, Sturnira lilium, Artibeus jamaicensis, Dermanura phaeotis, Vampyrodes caraccioli, Glossophaga soricina, Dermanuta toltecus, Cheoroniscus godmani, Platyrrhinus helleri) dominated the sample, but their relative dominance varied among habitats. Recapture of bats provided evidence for inter-habitat movement. The co-occurrence of the three habitats helps conserve a diverse assemblage of bat species in the local landscape.  相似文献   

6.
Because global timber demands continue to threaten tropical rain forests, identification of sustainable-use forest management protocols that meet human needs while preserving biodiversity is critical. Reduced-impact logging (RIL) protocols are increasingly common in the tropics and may be a viable option for sustainable forest use; however, few studies have documented faunal responses to RIL. Moreover, evaluations of abundance or diversity may not be sufficient for a comprehensive understanding of faunal responses to human activities, especially in the short-term. We assessed the effects of RIL on the temporal activity patterns of abundant bats in lowland Amazonian rain forest. More specifically, we characterized temporal patterns of activity, overlap of temporal activity, and dispersion of activity modes for seven abundant bat species and for four common bat guilds in RIL forest and in undisturbed forest in Tapajós National Forest, Pará, Brazil. Temporal activity of aerial insectivores, nectarivores, and gleaning animalivores did not change in response to RIL. In contrast, three of five species of frugivores and frugivores as a group changed their patterns of temporal activity in response to RIL. RIL had a greater effect on temporal activity of frugivores that foraged in the understorey than on frugivores that foraged in multiple forest strata. Overlap of temporal activity of frugivores was greater than expected by chance in undisturbed forest, but was random in RIL forest. Changes in activity may be a response to a combination of increased predation risk and reduced distances of early evening flights between day roosts and feeding areas in RIL forest compared to undisturbed forest.  相似文献   

7.
Limestone karst landscapes are important for biodiversity yet are increasingly threatened by development activities such as mining. Furthermore, karsts are often scattered and isolated by agriculture, and are rarely considered in landscape planning because of a paucity of biodiversity data. We determined the conservation significance of an isolated limestone karst outcrop for insectivorous bats by quantifying the influence of this roosting resource on local assemblage structure across a fragmented landscape in peninsular Malaysia. Using a combination of rank abundance, gradient and randomisation analyses, we demonstrate that bat assemblages at nine forest sites are structured following a spatial gradient of increasing distance from a karst roosting resource. The assemblage at our karst site was dominated by a superabundance of three cave-roosting species, two of which were also found to dominate assemblages up to 11 km away. Cave-roosting bats exhibited a significant decay in abundance related to the distance from karst, with sites closest to karst also characterised by a rarity of tree cavity/foliage-roosting species that were otherwise common. Gradient analysis revealed that differences in assemblage composition were largely associated with the distance from the karst and, to a lesser extent, forest isolation and area. Our findings suggest that isolated karst outcrops can serve as important population reservoirs for cave-roosting bats, which subsidise diversity levels in forest fragments that might otherwise be expected to decline over time. While conservation efforts need to focus on maintaining large areas of connected forest, landscape management needs to ensure protection of karsts as point resources for cave-roosting bats.  相似文献   

8.
In the Yucatan, cenotes or water sinkholes formed by the dissolution of limestone and surrounded with a characteristic dense layer of heterogeneous vegetation, are the main sources of water for plant and animal assemblages. We investigated their importance to bats by comparing the assemblage structure and diversity between tropical forest and pastureland, with and without cenotes. We set ground level mist nets, sub-canopy nets and harp traps for 96 nights and caught 2819 bats of 26 species and six families. Forest had a greater bat species diversity and abundance than pastureland, as well as rare and threatened species. In forest, sites with and without cenotes had a similar bat assemblage structure and diversity, whereas in pastureland there was a greater species diversity and abundance and number of rare and threatened species at cenotes than sites without cenotes. Chrotopterus auritus and Micronycteris schmidtorum, both threatened in Mexico, and Eptesicus furinalis, were exclusively captured at cenotes. We suggest that it may be the vegetation around cenotes rather than the water bodies per se that attracts many bat species in pastureland. Cenotes are threatened by nitrate contamination from untreated domestic and animal waste and fertilizers and the removal of vegetation to allow livestock access to water. In Yucatan’s agricultural landscapes, protection of cenotes and their characteristic vegetation is key not only for bat conservation but also because they represent potential seed sources for the regeneration of the lowland forest, in which bats play key roles as pollinators and seed dispersers.  相似文献   

9.
Literature searches and recent surveys of the bat fauna of Singapore indicate that of the 24 species of Microchiroptera and six species of Megachiroptera documented for this small equatorial island just 15 and 5, respectively, are still present. These recorded declines in chiropteran species richness almost certainly understate the true losses as extensive land transformation/habitat loss (>95%) and biota loss occurred early in Singapore’s colonial history before comprehensive surveys of bats were made. In an effort to reconstruct the pre-settlement bat fauna, we inferred an upper bound of pre-settlement species richness using a checklist from a well-known bat assemblage in neighbouring Peninsular Malaysia, and a lower bound based on species common to Peninsular Malaysia, Borneo and Sumatra. The Singapore records were compared with these two species list predictions. Based on this analysis, we infer that between 60 and 72 species would have inhabited Singapore before 1819. We also estimate that between 33% (based on the confirmed inventory) and 72% of the species (based on the upper-bound estimate of species richness) are now locally extinct. For Microchiroptera the data suggest that the documented local extinction rate of 38% may project to between 69% and 75%. Forest-dependant bats are particularly affected and comprise a much lower proportion of the bat fauna than is seen in intact forest in Peninsular Malaysia. All hipposiderids and 40% of the documented rhinolophid taxa have been lost and almost half (6) of the surviving microchiropteran species are locally endangered. Projected local extinction rates for Megachiroptera raise the documented value (17%) to about 60%, with most of the survivors being widespread species known to forage in cultivated or secondary forest habitats or to commute long distances between fragmented resources. The dramatic decline in Singapore bat species richness and a concomitant change in chiropteran guild and trophic structure (Microchiroptera vs. Megachiroptera) reflect patterns of diversity change seen elsewhere in the region in response to loss of forest habitat. In Singapore, the decline in diversity (species richness and abundances) for both mega- and microbats may also relate to urbanisation and deliberate or accidental destruction of bats and their roost sites in a land that has one of the highest human population densities on the planet. Although these losses (actual and inferred) represent a microcosm of mainly local extinctions, a wider geographical extrapolation over the 21st century indicates that heavy deforestation in progress in Southeast Asia might be expected to lead to extinction of many bat taxa, with upper-bound estimates of regional species losses exceeding 40% and global extirpation anticipated for at least 23% of Southeast Asia’s bat fauna by 2100.  相似文献   

10.
Scattered trees and small patches of vegetation among farmland are typical of rural landscapes throughout the world, often comprising a significant proportion of remaining habitats for native fauna. Insectivorous bats can use such isolated resources owing to the high mobility of most species, but little is known of the relationship between bats and tree density, or of the impact of incremental loss of trees in the landscape. Bats were surveyed at 30 sites in south-eastern Australia, in five habitat categories representing a range of tree densities from remnant woodland blocks (>35 trees/ha) to sparsely scattered trees (<1 tree/ha), and open paddocks devoid of trees. Sampling was undertaken by using harp traps and ultrasonic bat detectors. The abundance of potential arthropod prey was assessed by using light traps. Eleven species of insectivorous bats were recorded and bats were widespread in all habitat categories; all species were recorded around scattered trees. Overall activity, as revealed by detectors, did not differ significantly between the four treed categories, but in open paddocks there was a lower level of activity and a different community composition. However, a regression model revealed a significant quadratic relationship between activity of bats and tree density, with highest activity at 20-30 trees/ha. All species were recorded in open paddocks, but for eight of the ten species this represented <7% of their total activity recorded across all habitat categories. For six species, significant positive correlations were found between activity levels and the abundance of potential arthropod prey. In contrast to bat detectors, trapping results showed a significant difference in overall abundance of bats between wooded habitats, with decreased abundance as tree density declined. This study highlights the value of scattered trees as foraging habitat for bats, and emphasizes that, in rural land mosaics, such small and isolated habitat components have value for the conservation of biodiversity, and require greater recognition and protection.  相似文献   

11.
Bats are ecologically important mammals in tropical ecosystems; however, their populations face numerous environmental threats related to climate change, habitat loss, fragmentation, hunting, and emerging diseases. Thus, there is a pressing need to develop and implement large-scale networks to monitor trends in bat populations over extended time periods. Using data from a range of Neotropical and Paleotropical bat assemblages, we assessed the ability for long-term monitoring programs to reliably detect temporal trends in species abundance. We explored the magnitude of within-site temporal variation in abundance and evaluated the statistical power of a suite of different sampling designs for several different bat species and ensembles. Despite pronounced temporal variation in abundance of most tropical bat species, power simulations suggest that long-term monitoring programs (?20 years) can detect population trends of 5% per year or more with adequate statistical power (?0.9). However, shorter monitoring programs (?10 years) have insufficient power for trend detection. Overall, our analyses demonstrate that a monitoring program extending over 20 years with four surveys conducted biennially on five plots per monitoring site would have the potential for detecting a 5% annual change in abundance for a suite of bat species from different ensembles. The likelihood of reaching adequate statistical power was sensitive to initial species abundance and the magnitude of count variation, stressing that only the most abundant species in an assemblage and those with generally low variation in abundance should be considered for detailed population monitoring.  相似文献   

12.
Forest fragmentation by the expansion of human activities is acknowledged as an important factor driving declines of forest species worldwide and quantitatively characterizing this trend is essential to understanding the response of populations of forest-dependent species. To examine the impacts of forest cover loss and changes in composition on forest-dependent bats, we examined the effects of these factors on the distribution of the northern long-eared bat (Myotis septentrionalis) in a case study. We surveyed forest fragments in the forest-agricultural landscape of Prince Edward Island, Canada, to assess the occupancy of bats in fragments. Logistic regression and multimodel inference using Akaike’s information criteria were used to identify potentially important predictor variables influencing the distribution of the northern long-eared bat at the fragment and landscape level and quantified their effects. A compositional variable, area of deciduous stands, was found to be the best predictor of the presence of M. septentrionalis. We found the effects of fragmentation were greatest at the fragment level for females and at the landscape level for males. This case study emphasizes the importance of examining intra-specific resource selection in how it affects the response of a forest-dependent species to fragmentation.  相似文献   

13.
The disproportionate value of scattered trees   总被引:1,自引:0,他引:1  
Scattered trees are declining in agricultural landscapes worldwide. They are considered keystone structures because their effect on ecosystem functioning is believed to be disproportionate relative to the small area occupied by any individual tree. We empirically demonstrate the disproportionate value of scattered trees for birds and bats in an Australian livestock grazing landscape. We surveyed birds at 108 sites and bats at 63 sites. Sites spanned the full range of tree densities in the study area, from zero to over 100 trees per hectare. The marginal value of individual trees was highest when trees occurred at low densities. Compared to treeless sites, bird richness doubled with the presence of the first tree; bat richness tripled with the presence of 3-5 trees; and bat activity increased by a factor of 100 with the presence of 3-5 trees. Thereafter, the marginal effect of additional trees on birds and bats diminished rapidly. Although specialist species were restricted to large areas of dense tree cover, scattered trees effectively maintained moderate levels of bird and bat activity throughout largely cleared parts of the landscape. Future management activities should recognize the disproportionate value of scattered trees.  相似文献   

14.
Habitat fragmentation has been shown to influence the abundance, movements and persistence of many species. Here, we examine the effects of forest patch and landscape metrics, and levels of forest disturbance on the patterns of local extinction of five primate and 14 carnivore species within 129 forest patches in a highly fragmented forest landscape of southern Brazilian Amazonia. Classic habitat area effects were the strongest predictors of species persistence, explaining between 42% and 55% of the overall variation in primate and carnivore species richness. Logistic regression models showed that anthropogenic disturbance, including surface wildfires, timber extraction and hunting pressure, had detrimental effects on the persistence of some species over and above those of fragment size. Different species ranged in their responses from highly sensitive to highly tolerant to forest fragmentation. Patterns of local extinction documented here were by no means chance events, and the nestedness of the overall species-by-site matrix was highly nonrandom in terms of the sets of species extirpated from the most to the least species-rich forest patches.  相似文献   

15.
The consequences of fragmentation for communities of mutualist partners are for the most part unknown; moreover, most studies addressing this issue have been conducted on plant-pollinator communities. We evaluated how the experimental fragmentation of lowland Amazonian rain forest influenced a community of ant-plant mutualists. We inventoried a total of 1057 myrmecophytes in four fragments and four continuous forest sites; the twelve plant species recorded were occupied by 33 ant morphospecies, of which 11 were obligate plant inhabitants. Neither plant species richness, ant species richness, nor total ant-plant density were significantly lower in forest fragments. However, eight of the plant species, including three of the four most common, had higher mean densities in continuous forest than fragments. Of these four species, only one (Cordia nodosa) had significantly different colonization rates between habitat types, with higher colonization rates of plants in fragments. This may be because the Azteca species it is associated with increases in abundance in forest isolates. Although our results suggest that communities of ant-plant mutualists are likely to persist in fragmented tropical landscapes 25 years after fragment isolation, most species are rare and populations sizes in fragments are extremely low. Environmental and demographic stochasticity could therefore limit long-term population viability. We suggest future studies focus on evaluating how fragmentation has altered herbivore pressure and the dispersal of ants and plants to fragments, since the interaction of these factors is likely to have the greatest impact on long-term patterns of population persistence.  相似文献   

16.
17.
In the Argentine Chaco, the three species of peccaries (Artiodactyla) are likely affected by habitat destruction and hunting, yet basic information on peccary distribution and status in this region is poorly known. This study identifies human factors associated with relative abundance and distribution of each species. Estimation of relative abundance was based on interviews with local hunters, and variables potentially related to distribution and relative abundance of peccaries were estimated for 153 circular sample sites of 10 km diameter in the Argentine Chaco. Peccaries were found in sites of high forest cover, low human density, far from towns and with low density of roads. After accounting for forest cover and other variables, number of settlements was identified as the main variable negatively associated with relative abundance of the three species, which may be a result of local hunting. Density of roads was also negatively associated with presence of chacoan peccaries. Collared peccary seems to be the least susceptible to human perturbations. It was the most widely distributed and found in a wider range of conditions than the other species. Chacoan peccary was relatively rare. Because colonization and development programs are increasing in the region, areas still uninhabited should be protected, construction of roads controlled, and hunting managed.  相似文献   

18.
An inventory of the understory forest epiphyte and epiphyllous bryophyte floras was carried out in eight Atlantic rain forest fragments. The fragments were between 7 and 500 ha in size and belonged to two areas (lowland and submontane) of the state of Pernambuco, northeastern Brazil. The aim of this study was to investigate the effect of habitat fragmentation and changes in the natural landscape on community structure (composition, richness, diversity, and abundance). Although the influence of altitude was noted in this study by increasing richness, diversity, and abundance, it was clear that in some fragments the influence of fragment size and isolation can be more important than this positive environmental factor. Fragment size and isolation affect both communities but the last one seems to be a stronger threatening factor for the epiphylls. The least isolated and the largest fragments housed the richest floras - especially in relation to the epiphylls - and had the greatest proportion of shade species. Habitat fragmentation negatively affected epiphytic and epiphyllous bryophytes and increased the representation of species with larger niches (generalists) while decreasing the representation of species with smaller niches (typically found in shady or in sunny areas). The results suggests that the critical fragment size necessary for bryophyte preservation must be correlated with insularity levels; for epiphytes, however, it is likely that low levels of isolation cannot compensate borderline effects as with the epiphyllous bryophytes.  相似文献   

19.
To guide tree planting for restoration in southern Australia bats were sampled in revegetation from a wide variety of shapes, sizes, age and isolation. Young and old age-classes were sampled and these were stratified by size and shape. Where possible, revegetated categories were compared to remnant native vegetation with the same patch sizes, as well as very large remnants (>1000 ha) and grazed paddocks. In total 120 sites were surveyed, with 10 replicates in each stratum. All bat species used revegetation sites, often with high activity (passes/night) levels. However, activity and species richness in revegetation was not greater than that recorded in the paddock matrix and activity in revegetation was less than a third of that recorded in remnants. Old, large plantings were an exception, recording twice the activity of paddocks, indicating that this was the only revegetation treatment that was used by bats more frequently than paddocks. The tree stand structure of old plantings was usually patchy, including the presence of gaps induced by drought and grazing associated mortality. Bats were generally insensitive to the effects of patch size and shape as well as the amount of remnant vegetation in the landscape. A negative relationship with understorey cover (including eucalypts if <5 m high) was the most consistent predictor of total activity and species richness. The avoidance of clutter by many species of bats suggests that efforts to restore woodland communities should use lower stem densities. Improvements to revegetation programs to benefit bats are recommended and more broad-based studies that consider the varied requirements of a diverse fauna are encouraged.  相似文献   

20.
Large flying-foxes in insular Southeast Asia are the most threatened of the Old World fruit bats due to high levels of deforestation and hunting and effectively little local conservation commitment. The forest at Subic Bay, Philippines, supports a rare, large colony of vulnerable Philippine giant fruit bats (Pteropus vampyrus lanensis) and endangered and endemic golden-crowned flying-foxes (Acerodon jubatus). These large flying-foxes are optimal for conservation focus, because in addition to being keystone, flagship, and umbrella species, the bats are important to Subic Bay’s economy and its indigenous cultures. Habitat selection information streamlines management’s efforts to protect and conserve these popular but threatened animals. We used radio telemetry to describe the bats’ nighttime use of habitat on two ecological scales: vegetation and microhabitat. The fruit bats used the entire 14,000 ha study area, including all of Subic Bay Watershed Reserve, as well as neighboring forests just outside the protected area boundaries. Their recorded foraging locations ranged between 0.4 and 12 km from the roost. We compared the bats’ use to the availability of vegetative habitat types, riparian areas, and bat trees. The fruit bats’ locations showed a preference for undisturbed forest types and selection against disturbed and agricultural areas. Bat locations also showed selection for particular fruiting/flowering bat trees. The bats showed strong preference for riparian areas; locations were in riparian areas over four times more than expected. From these results we recommend that management focus flying-fox conservation efforts on undisturbed forest and riparian areas.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号