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1.
Habitat loss and fragmentation promote relatively predicable shifts in the functional signature of tropical forest tree assemblages, but the full extent of cascading effects to biodiversity persistence remains poorly understood. Here we test the hypotheses that habitat fragmentation (a) alters the relative contribution of tree species exhibiting different reproductive traits; (b) reduces the diversity of pollination systems; and (c) facilitates the functional convergence of reproductive traits between edge-affected and early-secondary forest habitats (5-32 years old). This study was carried out in a severely fragmented 670-km2 forest landscape of the Atlantic forest of northeastern Brazil. We assigned 35 categories of reproductive traits to 3552 trees (DBH ? 10 cm) belonging to 179 species, which described their pollination system, floral biology, and sexual system. Trait abundance was calculated for 55 plots of 0.1 ha across four habitats: forest edges, small forest fragments (3.4-83.6 ha), second-growth patches, and core tracts of forest interior within the largest available primary forest fragment (3500 ha) in the region. Edge-affected and secondary habitats showed a species-poor assemblage of trees exhibiting particular pollination systems, a reduced diversity of pollination systems, a higher abundance of reproductive traits associated with pollination by generalist diurnal vectors, and an elevated abundance of hermaphroditic trees. As expected, the reproductive signature of tree assemblages in forest edges and small fragments (edge-affected habitats), which was very similar to that of early second-growth patches, was greatly affected by both habitat type and plot distance to the nearest forest edge. In hyper-fragmented Atlantic forest landscapes, we predict that narrow forest corridors and small fragments will become increasingly dominated by edge-affected habitats that can no longer retain the full complement of tree life-history diversity and its attendant mutualists.  相似文献   

2.
Recent global assessments have shown the limited coverage of protected areas across tropical biotas, fuelling a growing interest in the potential conservation services provided by anthropogenic landscapes. Here we examine the geographic distribution of biological diversity in the Atlantic Forest of South America, synthesize the most conspicuous forest biodiversity responses to human disturbances, propose further conservation initiatives for this biota, and offer a range of general insights into the prospects of forest species persistence in human-modified tropical forest landscapes worldwide. At the biome scale, the most extensive pre-Columbian habitats across the Atlantic Forest ranged across elevations below 800 masl, which still concentrate most areas within the major centers of species endemism. Unfortunately, up to 88% of the original forest habitat has been lost, mainly across these low to intermediate elevations, whereas protected areas are clearly skewed towards high elevations above 1200 masl. At the landscape scale, most remaining Atlantic Forest cover is embedded within dynamic agro-mosaics including elements such as small forest fragments, early-to-late secondary forest patches and exotic tree monocultures. In this sort of aging or long-term modified landscapes, habitat fragmentation appears to effectively drive edge-dominated portions of forest fragments towards an early-successional system, greatly limiting the long-term persistence of forest-obligate and forest-dependent species. However, the extent to which forest habitats approach early-successional systems, thereby threatening the bulk of the Atlantic Forest biodiversity, depends on both past and present landscape configuration. Many elements of human-modified landscapes (e.g. patches of early-secondary forests and tree monocultures) may offer excellent conservation opportunities, but they cannot replace the conservation value of protected areas and hitherto unprotected large patches of old-growth forests. Finally, the biodiversity conservation services provided by anthropogenic landscapes across Atlantic Forest and other tropical forest regions can be significantly augmented by coupling biodiversity corridor initiatives with biota-scale attempts to plug existing gaps in the representativeness of protected areas.  相似文献   

3.
In this study we compared ground beetles (Carabidae) from a range of different forest fragments along an urbanization gradient in Brussels, Belgium. We address the following questions: (i) How does the degree of urbanization in the surrounding habitat affect forest beetles, and does it interact with the effects of patch size and distance to forest edge? (ii) Do these factors have a different effect at the level of individual species, habitat affinity groups or total community? During 2002 we sampled 13 forest plots in 10 forest patches, ranging in size from 5.27 to 4383 ha. The beetles were captured using transects of pitfall traps from the edge to a distance of 100 m into each woodland and identified to species level. Effects of urbanization, forest size and forest edge were evaluated on total species number, abundance and habitat affinity groups and ten abundant, widespread model carabid species. Overall, the effects of urbanization, forest size and edge effects slightly influenced total species richness and abundance but appeared to have a major effect on ground beetle assemblages through species specific responses. More urbanized sites had significantly fewer forest specialists and more generalist species. Large forest fragments were favoured by forest specialist species while generalist species and species frequently associated with forest (forest generalists) dominated the smaller forests. Forest edges mainly harboured generalist species while forest specialist species were more frequent into the forests if the forest patches were large enough, otherwise they disappeared due to the destruction or impoverishment of their habitat. Our results show the importance of differentiating between habitat affinity, especially habitat generalists versus specialists, the latter having a higher value in nature conservation, and merely the quantity of species represented in human-dominated areas.  相似文献   

4.
Like most ecosystems of the world, tropical dry forests of the central coast of the Gulf of Mexico are inadequately preserved. Given that reserve expansion is unlikely, it is imperative that the conservation capacity of the matrix surrounding reserves is enhanced. Here, we examine the habitat value of isolated pasture trees and patches of secondary regrowth in terms of their terrestrial and arboreal ant assemblages in both a wet and dry season. These simplified wooded systems increase species densities within the agricultural matrix and provide habitat for some forest ant species. Estimated species richness of arboreal ants was particularly low on isolated trees, highlighting an important limitation. This was not the case for terrestrial ants, which were particularly species rich under isolated trees. We also found that the inter-site variations in species densities and similarity to the forest ant assemblage for terrestrial and arboreal strata were not correlated, suggesting that responses to restoration may not be as uniform as often thought. This has important implications for the use of indicator taxa in suggesting the response of other taxa. In terms of species composition, neither secondary regrowth nor isolated trees were appropriate replacements for forest fragments, even though the studied forest fragments were small (13-32 ha). The ant assemblages did not exhibit a seasonal change in composition. However, season influenced the contrast between habitats, with isolated trees being more distinct from pasture, and regrowth more closely resembling forests, during the wet season. Microclimatic variables indicate that the forests were least affected by the tropical dry season, and this may contribute to their characteristic fauna. We conclude that even small forest patches make a unique contribution to landscape conservation and that, where reserves are limited, conscientious management of the landscape matrix may provide some species with sufficient new habitat to survive outside of reserve systems. These conclusions are influenced by both season and strata studied.  相似文献   

5.
Unprecedented deforestation is currently underway in Southeast Asia. Since this trend is likely to continue, it is critical to determine the value of human-modified habitats (e.g., mixed-rural habitat) for conserving the regional native forest avifauna. The impacts of ongoing deforestation on the highly endemic avifauna (33%) of Sulawesi (Indonesia) are poorly understood. We sampled birds in primary and secondary forests in the Lore Lindu National Park in central Sulawesi, as well as the surrounding plantation and mixed-rural habitats. Species richness, species density and population density of forest birds showed a consistent decreasing trend in the following order: primary forests > secondary forests > mixed-rural habitat > plantations. Although primary forests contained the highest proportion (85%) of a total of 34 forest species recorded from our point count surveys, 40-yr old secondary forests and the mixed-rural habitat showed high conservation potential, containing 82% and 76% of the forest species, respectively. Plantations recorded only 32% of the forest bird species. Fifteen forest species had the highest abundance in primary forests, while two species had higher abundance outside primary forests. Our simulations revealed that all forest birds that were sensitive to native tree cover could be found in areas with at least 20% continuous native tree cover. Our study shows that although primary forests have the highest conservation value for forest avifauna, the potential of degraded habitats, such as secondary forests and the mixed-rural habitat, for conserving forest species can be enhanced with appropriate land use and management decisions.  相似文献   

6.
We examined the influence of habitat characteristics at the microhabitat, macrohabitat, and landscape spatial scales on small mammals occurring in 12 forest patches within four agricultural landscapes of Prince Edward Island (Canada). Landscape features were important determinants of small mammal variables at all levels, but especially at the community level, whereas microhabitat characteristics tended to influence small mammals at the population level. Macrohabitat characteristics had only minor effects on small mammals occurring in our study sites. Species richness was most strongly influenced by patch area, reaching a threshold at forest patches of roughly 8-10 ha. The proportions of both forest and hedgerow cover within 400 m from the study site were also significant determinants of small mammals species diversity, possibly reflecting their ability to perceive suitable habitats, forage in areas outside the forest patches, and/or disperse in agricultural landscapes. At least one small mammal species (Napaeozapus insignis) benefitted from the presence of agricultural fields at distances up to 1000 m. Tamias striatus benefitted from the presence of hedgerow cover within 400 m from forest patches, possibly allowing them to move between forest patches. Clearly, the maintenance of forest patches of 8-10 ha and of forest cover within 400 m from them is fundamental for the conservation of small mammals inhabiting agricultural landscapes on the Island. Conservation strategies should also consider the establishment of more effective regulations to prevent and/or reduce hedgerow removal on Prince Edward Island.  相似文献   

7.
Forest fragmentation is a common disturbance affecting biological diversity, yet the impacts of fragmentation on many forest processes remain poorly understood. Forest restoration is likely to be more successful when it proceeds with an understanding of how native and exotic vertebrates utilize forest patches of different size. We used a system of forest fragments isolated by volcanic activity 153 years ago in Hawaii to examine how long-term fragmentation, as well as fragment size and structural features affect the richness of native and exotic bird species. The total number of bird species increased rapidly with forest fragment size, with most of the native species pool found in patches <3 ha. Smaller fragments were dominated by native bird species with several exotic bird species found only in the largest fragments, suggesting that exotic bird species in this landscape show greater area-sensitivity than native species. We used airborne scanning light detection and ranging (LiDAR) to assess whether fragment area was correlated with estimates of fragment vegetation volume as well as measures of tree height. Fragment area was highly correlated with vegetation volume, maximum tree height, and canopy height heterogeneity, and these variables were strong predictors of bird richness, demonstrating that remote sensing can provide key insights into the relationship between fragment structural attributes and biodiversity indicators. Overall, this work demonstrates the value of conserving small remnant mid-elevation forest patches for native birds in Hawaii. This work also provides insight into how newly created forest patches might be used by native and exotic bird species in Hawaii.  相似文献   

8.
Saproxylic Coleoptera are diverse insects that depend on dead wood in some or all of their life stages. In even-aged boreal forest management, remnant habitats left as strips and patches contain most of the dead wood available in managed landscapes and are expected to act as refuges for mature forest species during the regeneration phase. However, use of remnant habitats by the saproxylic fauna has rarely been investigated. Our objective was to characterize the saproxylic beetle assemblages using clearcuts and forest remnants in western Québec, Canada, and to explore the effects of forest remnant stand characteristics on saproxylic beetle assemblages. We sampled both beetle adults and larvae, using Lindgren funnels and snag dissection, in five habitat locations (clearcuts, forest interiors of large patches, edges of large patches, small patches and cut-block separators) from three distinct landscapes. Adult saproxylic beetles (all feeding guilds combined) had significantly higher species richness and catch rates in small patches compared to forest interiors of large patches; the phloeophagous/xylophagous group had significantly higher species richness only. Small patches, cut-block separators and edges of large patches also had the highest snag density and basal area, increasing habitat for many saproxylic beetles. No significant differences in density of saproxylic larvae were found between habitat patches, but snag dissection nevertheless suggests that snags in forest remnants are used by comparable densities of insects. Saproxylic beetles appear to readily use habitat remnants in even-aged managed landscapes suggesting that forest remnants can insure the local persistence of these species, at least in the timeframe investigated in our study.  相似文献   

9.
Staphylinid beetle assemblages from coniferous foothills forest in west-central Alberta, Canada were studied via pitfall trapping to examine the effects of stand age and possible edge effects. Sites included a chronosequence of stands from 1 to 27 years post-harvest, and four types of mature forest that had not been disturbed by fire for at least 80 years. In all, 19 sites were sampled between 1989 and 1991. A total of 98 species were identified, nine of which are reported for the first time in Alberta. Staphylinids were more abundant in mature forest stands but assemblages were more diverse in regenerating stands. Thirty-four rove beetle species showed significant indicator value for particular stands or groups of stands, including mature forest, young forest, and open ground specialists. After harvesting, the catch rate of many forest species decreased dramatically, and open ground species were more commonly collected. Populations of some forest species remained active on logged sites for one or 2 years before disappearing. As stands regenerated, they were colonized by species characteristic of young stands, but true forest species were found only in older unharvested stands. The beetle assemblages from regenerating stands became more similar to those from mature stands as they aged, but still differed considerably from them 27 years after harvesting. Transects across forest-clearcut edges revealed a significant beetle response to habitat edges. Staphylinids assemblages were compared to the ground beetle (Carabidae) assemblage sampled via the same pitfall trapping regime. Mature forest specialists are threatened by fragmentation and loss of habitat. In order to conserve these beetle assemblages, forest managers should retain adequate patches of older successional stages on working landscapes.  相似文献   

10.
Recent developments have highlighted the importance of forest amount at large spatial scales and of matrix quality for ecological processes in remnants. These developments, in turn, suggest the potential for reducing biodiversity loss through the maintenance of a high percentage of forest combined with sensitive management of anthropogenic areas. We conducted a multi-taxa survey to evaluate the potential for biodiversity maintenance in an Atlantic forest landscape that presented a favorable context from a theoretical perspective (high proportion of mature forest partly surrounded by structurally complex matrices). We sampled ferns, butterflies, frogs, lizards, bats, small mammals and birds in interiors and edges of large and small mature forest remnants and two matrices (second-growth forests and shade cacao plantations), as well as trees in interiors of small and large remnants. By considering richness, abundance and composition of forest specialists and generalists, we investigated the biodiversity value of matrix habitats (comparing them with interiors of large remnants for all groups except tree), and evaluated area (for all groups) and edge effects (for all groups except trees) in mature forest remnants. Our results suggest that in landscapes comprising high amounts of mature forest and low contrasting matrices: (1) shade cacao plantations and second-growth forests harbor an appreciable number of forest specialists; (2) most forest specialist assemblages are not affected by area or edge effects, while most generalist assemblages proliferate at edges of small remnants. Nevertheless, differences in tree assemblages, especially among smaller trees, suggest that observed patterns are unlikely to be stable over time.  相似文献   

11.
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   

12.
Phyllomedusa tarsius is a hylid frog that breeds in ponds located in a range of habitats from continuous forests to severely disturbed matrix habitats in Central Amazon. During three reproductive seasons, we followed the movement patterns, measured body size and registered abundance and residency time of this species in five habitats: pasture, Vismia regrowth, Cecropia regrowth, 1 and 10 ha forest fragments, and continuous forest. The frog captures were strongly correlated with rainfall in all disturbed habitats, but not in continuous forest, probably because individuals respond more directly to rainfall patterns in more open habitats. Males in disturbed habitats were smaller than those found in continuous forest, perhaps as a result of differences in habitat quality. Males remained at sites for longer periods in fragments and continuous forest compared to matrix habitats. Here again, the quality and suitability of breeding sites in matrix habitats may be lower than in continuous forest resulting in the need for more movement. We found bigger subpopulations in matrix habitat ponds and a higher percentage of individuals moving among them when compared to continuous forest ponds. Constant movement of individuals among disturbed subpopulations decreases population isolation and increases interbreeding among different subpopulations. No movement between individuals from continuous forest ponds and disturbed habitats was observed. This suggests that the disturbed habitat subpopulations are not acting as sink subpopulations for continuous forest populations. The maintenance of individuals in fragments is more dependent on local conditions for reproduction and on subpopulations in the matrix habitat than on recruitment of individuals from populations in continuous forest.  相似文献   

13.
We sampled the carabid beetles in 22 forests managed by six different silvicultural systems, defined by treatment and tree species composition: even-aged conifer, even-aged beech, even-aged oak, uneven-aged conifer, uneven-aged beech and group mixed (beech + conifer). In each of these forests, we placed pitfall traps in young, medium-aged and mature stands (3 stages). We evaluated the effect of treatment, tree species composition, silvicultural system, stage and habitat type (silvicultural system + stage) on indicators of community conservation value and ecological structure. The species composition and the ecological structure of carabid beetles of the managed stands were then compared to that of nine unmanaged stands (without tree exploitation). In the managed forests, species richness was highest in large young stands (3-10 years old) and in forests managed by even-aged systems (with large clear-cuts), mainly due to eurytopic and opportunist carabid species with high dispersal abilities. Oak and beech, uneven-aged, and mature stands were mainly inhabited by typical forest species, and even-aged conifer stands mainly by ubiquitous species. Several typical forest species recorded in unmanaged stands were lacking from the managed forests. Large scale clear-cutting allows open-habitat species to enter the forest, which increases the species richness at a landscape level but can disfavour typical forest species by competition. Long rotations should be implemented and more areas left unmanaged in Belgium, in order to help typical forest species to re-colonise managed forests.  相似文献   

14.
Many threatened primates now exist in fragmented forest habitats. The survival of these populations may depend on their ability to utilise agricultural or other matrix habitats between forest fragments, but this is poorly known. Here, we systematically investigate an arboreal primate’s use of a heterogeneous matrix in a fragmented forest landscape: the Angola black-and-white colobus (Colobus angolensis palliatus) in southern Kenya. We used a novel technique, based on semi-structured interviews with local informants, to address the difficulty of sampling relatively rare but important events, such as dispersal between fragments. We found that colobus frequently travelled and foraged in indigenous matrix vegetation (such as mangrove, wooded shrubland and shrubland) up to 4 km from the nearest forest fragments. Agricultural habitats, such as perennial plantation (coconut, mango and cashew nut) were also used by colobus for travelling and foraging (in remnant indigenous trees). The probability of sighting colobus in the matrix increased with the proportion of both tall (>6 m) vegetation cover and food tree cover, but declined with distance from forest habitat. Our findings suggest that certain matrix habitats are important for C. a. palliatus, and that future primate conservation initiatives might benefit from adopting a ‘landscape-level’ approach to habitat management, particularly in fragmented forest systems.  相似文献   

15.
Secondary forests and exotic tree plantations are rapidly expanding across tropical landscapes, yet we currently have a very poor understanding of the value of these human-dominated forest landscapes for biodiversity conservation. Mist netting, point counts and transect walks were used to compare the bird communities of these habitats and neighboring primary forest in north-east Brazilian Amazonia. The extensive spatial scale of plantations and second-growth in our study area enabled us to implement a robust replicated design, with survey plots approximately two to three orders of magnitude larger than most previous studies of land-use change in the tropics, thus minimising the influence of the surrounding landscape. Species richness was highest in primary forest and lowest in Eucalyptus plantations, and community turnover between habitats was very high whether based upon matrices of relative abundance or species presence-absence data, and for both point count and mist net data. Monthly line-transect censuses conducted over an annual cycle showed an increase in the detection of canopy frugivores and seed predators during the peak of flower and fruit availability in primary forest, but failed to suggest that second-growth or Eucalyptus stands provide suitable foraging habitat at any time of the year. The conservation value of both secondary forest and plantations was low compared to conclusions from previous studies. Our results indicate that while large-scale reforestation of degraded land can increase regional levels of diversity, it is unlikely to conserve most primary forest species, such as understorey insectivores and canopy frugivores.  相似文献   

16.
The species richness and frequency of occurrence of bryophytes within taxonomic and functional groups was examined in relation to the size of 20 old-growth patches (size range: 0.6-63.6 ha) remaining after logging in temperate rainforests of coastal British Columbia. At the centre of each remnant patch, bryophytes were sampled in sixty-three 10 cm × 30 cm microplots on three substrate-types (forest floor, downed logs and tree bases). Generalized linear models demonstrated that the species richness and frequencies of some bryophyte functional groups were related to patch size. In particular, some dispersal-limited groups (perennial stayers) and microclimate-sensitive groups (closed canopy species, epixylic (log-dwelling) species, and liverworts) showed significant declines in either richness or frequency as patch size decreased. In contrast, colonists and open canopy species showed little association with patch size. Many, but not all, of the significant patch size relationships disappeared when the three smallest patches (0.6-1.8 ha) were eliminated from the analysis. These results suggest that patches sized 3.5 ha or larger may provide habitat capable of sustaining a diverse array of bryophyte functional groups in temperate rainforest landscapes.  相似文献   

17.
Studies of habitat fragmentation have been restricted primarily to anthropogenically-altered habitats, with most research conducted 60-90 years post-fragmentation. It is unclear whether patterns in older systems concur with results from these dynamic landscapes, and hence the long-term viability of populations inhabiting habitat fragments remains largely unexplored. I focused on resident birds in fragments of humid pine-oak forest in Oaxaca, southern Mexico, isolated over 5000 years ago by climate-change. Seventeen fragments, ranging from 2 ha to over 150,000 ha were sampled in 1997 and 1998 yielding 141 species, of which 60 residents were used for analysis. Avian assemblages exhibited a highly nested structure and, with several notable exceptions, assemblages of birds in low-richness fragments were predictable subsets of those in more diverse fragments. Patch-scale factors—area, shape, elevation, habitat diversity and fractal dimension of edge—all exerted strong univariate influence on avian richness but were so closely inter-related that none had a significant independent effect. Thus, larger fragments were more complex in shape, included higher peaks, supported more diverse forests, and contained higher diversities of resident species. In contrast, the landscape-scale index used—distance from nearest large fragment (>50,000 ha)—had little effect on richness. This was reinforced by species-level analyses—one species was significantly influenced by isolation, compared with 31 species that displayed significant minimum-area distributions, restricted to patches larger than a particular threshold value. In terms of autecology, vagility, relative abundance and elevational breadth were closely related to distribution—those species with greater mobility, higher abundances and broader elevational tolerances were consistently more widespread. I suggest that more abundant species were less prone to extinction initially, more vagile species were better dispersers and species with broader elevational tolerances more likely to be successful colonists. As with previous research from older landscapes, patch-scale factors were consistently found to be influential, with high quality fragments supporting diverse communities regardless of landscape context. This suggests that the influence of landscape-scale factors noted in younger, anthropogenically fragmented systems may be transitory, overwhelmed by patch-scale factors with time. Which patch attributes are most influential could not be resolved, however, indicating that even thousands of years after fragmentation, they affect diversity patterns in concert. Rather than differentiating effects of area from habitat heterogeneity and other patch-level factors, I advocate resource-based approaches to understand and manage diversity in habitat fragments.  相似文献   

18.
Fragmentation of natural forests is a major threat to forest biodiversity. In areas with a long history of forestry, the remaining patches of old forests constitute only a minor part of the landscape. In such situations small stands may be valuable and important for conservation. However, as they may suffer from strong edge effects and isolation, their value may be lower than anticipated. In Sweden a national inventory of woodland key habitats (WKHs) has identified about 1% of the forest landscape as sites where red-listed species occur or may occur. Most are small (national median 1.4 ha) and isolated stands within an intensively managed landscape. The present analyses calculate WKH core area based on a range of depths of edge influence, and isolation based on both distance to nearest WKH and a weighted isolation measure that includes all neighboring WKHs and protected forest. These analyses are done on the WKHs in Norrbotten County in northern Sweden and include almost 5000 stands. The actual core area in the WKHs is about 30% given a 50 m edge influence. The degree of isolation is species dependent but the results indicate that only species with high dispersal abilities may effectively utilize the network of WKHs. For species with effective dispersal distances of less than 2 km the network is probably insufficient. The results emphasize the need to create buffer zones, to increase reserve areas and to manage the matrix so that species dispersal is promoted. This likely includes a necessity to aggregate biodiversity efforts on the landscape scale.  相似文献   

19.
Bird species composition (61 species) of Afromontane forest fragments (n = 19) embedded in a natural grassland matrix or a plantation forestry matrix were compared. Forest bird assemblages in a natural grassland matrix displayed a nested non-random species distribution. Species loss was significantly area-dependent and predictable. Assemblages in the plantation-dominated matrix were also nested but were neither area- nor isolation-dependent and these potential processes had equal influence over bird species composition. Forests patches <50 ha in plantation were more species rich than those in a grassland matrix and visa versa for patches >50 ha. The effect of the matrix is revealed here with arboreal plantation cover promoting dispersal across the landscape, favouring abundant generalist bird species in smaller patches than expected in the plantation matrix, and the loss of some specialists and species living at low densities from large (>50 ha) patches. Because of a significant species-area relationship and possible area-dependent extinction, the largest forest patch in the nested series in a grassland matrix protects most bird species (89%). However, in a plantation matrix the absence of a species-area relationship requires the combination of many larger forest patches to protect most bird species. Plantation forests in the matrix significantly alter forest bird assemblage structure and composition. To avoid the effects of insularisation and to maintain the viability of bird communities in Afromontane forests requires conservation of the larger forests in a natural matrix. However, for forests in a plantation matrix, the management of dispersal processes by manipulation of the matrix may be as important to conserving species and communities as is minimising extinctions. Avoiding placing plantations near large forests, increasing the size of small patches, and where afforestation is unavoidable, placing plantations in the vicinity of small rather than large forest patches, are preferable management practices.  相似文献   

20.
The combined effects of rapid habitat loss, fragmentation and disturbance on tropical forest avifaunas have not been examined to date. The southern Amazonian ‘arc of deforestation’ marks the boundary of the most aggressive agricultural frontier in tropical forests worldwide. We sampled 21 disturbed and undisturbed primary forest patches, ranging in size from 1.2 to 14,476 ha, to elucidate the synergistic effects of both forest disturbance and fragmentation on bird community structure, and pinpoint which species were the “winners” and “losers” from this process. A number of forest patch metrics, derived from an independent remote sensing approach, explained much of the resulting presence/absence matrix. The bird community exhibited a highly nested structure, with small patches being most dissimilar from one another. Bird species differed in their response to both forest patch size and forest canopy perforation according to their dependence on closed-canopy primary forest. Forest patch geometry, which clearly modulated the shape of species-area relationships accounted for 83-96% of the variation in species richness, but forest habitat quality resulting from logging and surface-fire disturbance was also a significant predictor of species richness for the most forest-dependent taxa.  相似文献   

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