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1.
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   

2.
Rivers and streams lined by narrow forest strips are common in the lowland countryside of south-western Costa Rica. We studied the importance of these gallery forests for understorey birds, especially forest species. Using mist-nets, we captured 1110 birds belonging to 90 species between June and September 2007 at 16 sites spread equally over four habitat types: forest interior, forest margin, gallery forest connected to closed forest, and isolated gallery forest. Though isolated gallery forests had the greatest number of expected species in total, they supported the lowest number of forest-specialist species, lower even than connected gallery forests. Granivorous birds showed an increase from forest to isolated gallery forest, all other feeding guilds however showed no change. The studied habitats differed from each other in their faunal composition. Assemblages of three species groups categorised by their habitat preferences (forest specialists, forest generalists, non-forest species) showed nested distribution patterns across the four habitats. There was no significant difference in the proportion of birds with brood patches or of recaptures across the studied habitat types, leading to the assumption that birds not only use gallery forests for movement and foraging but also for reproduction. Though of limited conservation value for most forest understorey birds, at least for a small fraction of forest species gallery forests constitute an important secondary habitat. More significantly, they can form corridors or stepping stones that allow movements within the matrix of human-dominated habitats, and represent an important landscape component benefiting total bird species richness in the Costa Rican countryside.  相似文献   

3.
Avifaunal responses to understorey fire disturbance and subsequent changes in habitat structure were examined within 20 burnt and unburnt forest plots of 0.25 ha (10×250 m), 10-15 months after an unprecedented understorey fire swept through the Tapajós-Arapiuns Extractive Reserve of central Brazilian Amazonia following the severe 1997-1998 El-Niño dry season. Although these surface fires in the previously undisturbed primary forest were relatively mild, they resulted in dramatic changes in forest structure consistent with those found elsewhere in Amazonia. Bird species negatively affected by these changes tended to be the least common, the most disturbance-sensitive, and habitat specialists. Considering different guilds, ant followers, dead-leaf gleaners, terrestrial gleaners, and arboreal sallying insectivores were the most negatively affected, whereas nectivores and arboreal granivores became more abundant in the burnt forest. The results highlight the severe consequences of even relatively mild surface fires in neotropical forests, and the importance of controlling haphazard frontier expansion for the conservation of susceptible species that are endemic to fire-prone regions.  相似文献   

4.
We compared the composition and structure of primary forest avifauna among primary forests, selectively logged forests and mixed-rural areas (e.g. villages and agricultural areas) of Peninsular Malaysia. We found that forests that were selectively logged at least 30 years ago contained only 73-75% of the 159 species of extant primary forest birds, with an increased proportion of dominant species. We estimated that only 28-32% of the primary forest species utilized the mixed-rural habitat, and that the number of species that bred in the agricultural landscapes might be even lower. The microhabitat of different species most affected their vulnerability to disturbance. Most small, arboreal frugivores and omnivores, and insectivores that fed from tree trunks, showed greater persistence in the mixed-rural habitat than ground dwelling bird species, which were affected most by disturbance. Resource abundance and variables that were closely related to forest disturbance such as the density of large trees, density of dead trees, canopy cover density and shrub volume influenced the distribution of the primary forest birds. Large primary forest reserves and a revision of short-cycle logging regimes (ca. 30 years) are needed if we are to conserve the lowland rainforest avifauna of Peninsular Malaysia and other parts of Southeast Asia.  相似文献   

5.
Despite the loss of 83% of native forests in the Philippines, little is known on the effects of this massive habitat loss and degradation on its forest biotas. This is a cause for concern because of the threat posed to the country’s large number of endemic taxa. To investigate the impacts of anthropogenic disturbance, forest birds and butterflies were surveyed in closed and open canopy forests, as well as suburban, rural and urban areas within the Subic Bay Watershed Reserve and Olongapo City in western Luzon. Measures of forest species richness and population densities for both taxa were similar in the two forest types, but showed different patterns in the other habitats. Indirect gradient analysis showed that forest bird species were positively correlated with vegetation variables (i.e., canopy cover, tree density, height to inversion and ground cover), while forest butterflies were not strongly correlated to any of the measured habitat variables. Community composition of birds in forests was distinct from those in modified habitats, while butterfly communities were more similar. A simulation showed that canopy cover of 60% or higher was required by 24 of the 26 bird species that were sensitive to canopy loss. Endemicity and nesting strata were the significant predictors of vulnerability to habitat disturbance for birds, while endemicity and larval hostplant specificity were significant for butterflies. Both taxa were negatively affected by anthropogenic disturbance but may respond to different components in the habitat (i.e., structure and resources), and thus cannot be used as surrogates of each other. Conservation of forests with contiguous canopy cover should be prioritized, and more ecological research is needed to improve the knowledge on the effects of disturbance on Philippine biodiversity.  相似文献   

6.
In view of the continued decline in tropical forest cover around the globe, forest restoration has become a key tool in tropical rainforest conservation. One of the main - and least expensive - restoration strategies is natural forest regeneration. By aiding forest seed influx both into disturbed and undisturbed habitats, frugivorous birds facilitate forest regeneration. This study focuses on the tolerance of a frugivorous bird community to anthropogenic habitat disturbance within the broader context of natural forest regeneration with conservation purposes. It was carried out in the tropical cloud forest of Costa Rica’s Talamanca Mountains. Bird community response and tolerance to habitat disturbance was assessed by comparing bird presence and densities along a disturbance gradient, ranging from open pastures to closed mature forests. Birds were censused along nine transects applying the variable width line transect procedure. Forty relevant frugivorous bird species were observed during 102 h of survey time. Densities were calculated for 33 species; nine species responded negatively to increasing level of disturbance and nine others positively. Results indicate that large frugivores are generally moderately tolerant to intermediate, but intolerant to severe habitat disturbance, and that tolerance is often higher for medium and small frugivores. It appears that moderately disturbed habitats in tropical cloud forests are highly suitable for restoration through natural regeneration aided by frugivorous birds. Due to a lack of large forest seed dispersers, severely disturbed habitats appear less suitable.  相似文献   

7.
I examined the lingering effects of past timber management practices on the vegetation structure and bird community of Kibale National Park, Uganda. I compared four forest treatments: unlogged native forest (UL), two that were selectively logged at low (LL) and high (HL) intensities in the 1960s, and a conifer plantation (PL). Forest-dependent birds were best represented at UL. LL was similar to UL in both vegetation structure and bird community composition, although some forest-dependent bird species were missing from the former. HL had significantly less canopy closure and lower tree density than other plots as a result of the combination of extensive secondary damage and natural disturbance patterns that prevented the reclosure of the forest canopy. Thirty-one percent of the forest-dependent bird species observed during the study were not detected at HL. At PL, bird species richness and bird abundance were about a third of those observed in other plots. There were significant correlations between heterogeneity of tree distribution (horizontal heterogeneity) and abundance and species richness of birds across plots. Abundance and species richness of all, forest-dependent, and forest generalist birds were highest in plots with intermediate measures of horizontal heterogeneity, which were mostly unlogged or lightly logged. If reduced-impact logging practices are not implemented during selective logging operations in tropical forests, consequent long-term changes in vegetation structure may result in significant declines in the populations of some forest-dependent species, as was observed in Kibale National Park.  相似文献   

8.
We examined the effects of forest disturbance and fragmentation on diversity and composition of canopy arthropod fauna in six oak species in central Mexico. Canopy fogging of 54 trees during rainy and dry seasons was conducted on three temperate forests with different levels of disturbance and habitat fragmentation. In total, we found 831 morphospecies belonging to 20 arthropod orders. Diversity of arthropods was higher in the rainy season. Acari, Hymenoptera and Diptera orders dominated during the dry season, and Acari and Collembola during the rainy season. Oak species distributed in sites with lower disturbance had significantly higher arthropod diversity than those distributed in disturbed and fragmented sites. Mean density of arthropod fauna ranged from 47.0 individuals m−2 in the dry season to 375.5 m−2 in the rainy season. Forest disturbance and fragmentation reduced the number of arthropod morphospecies and modified the relative abundance of arthropods at order level.  相似文献   

9.
Mitigating the effects of habitat loss requires estimating the minimum amount of habitat necessary for the persistence of wildlife populations in a changing landscape. Assessing minimum habitat amounts, however, relies on identifying ecological thresholds in species’ responses to landscape change. Using two repeated state-wide atlases, our objective was to investigate the responses of 25 forest birds to a range of forest cover and fragmentation. Repeat atlases allow for the analysis of four population dynamics including: (1) colonization, (2) persistence, (3) extinction, and (4) absence. Our objective was to test the hypothesis that forest birds demonstrated thresholds in these four basic dynamics to varying amounts of forest cover and fragmentation.We found thresholds to be a common, though not pervasive, characteristic of how forest birds respond to forest cover and pattern. We found that the probability of persistence was positively correlated with forest cover and 22 species demonstrated threshold responses. In addition, 15 of 25 birds demonstrated discrete thresholds in extinction dynamics. The existence of a colonization threshold has received significantly less attention in ecology. We also found that 17 out of 25 species demonstrated thresholds in their colonization response to a greater amount of forest cover. The effects of forest fragmentation, independent of forest amount, were less clear. We found support for incorporating the effects of fragmentation, but this fragmentation effect was found both below and above threshold points. We conclude that incorporating ecological thresholds in environmental planning should be species-specific and focus on populations on the verge of rapid ecological change.  相似文献   

10.
Madagascar is a global biodiversity hotspot threatened by forest loss, degradation and fragmentation, all of which are detrimental to the future survival of forest-dwelling organisms. For conservation purposes it is essential to determine how species respond to habitat disturbance, specifically deforestation. In this study we investigated the impacts of deforestation on three vertebrate communities, lizards, small mammals and birds, in an area of spiny forest subjected to anthropogenic forest clearance. Spiny forest has high levels of endemism, but conservation in this unique ecosystem is hindered by the lack of research. We undertook standardised trapping, time-constrained and timed species searches to assess species richness, species abundance and community composition of lizards, small mammals and birds in six areas of ‘forest’ and six ‘cleared’ areas. From surveys and opportunistic sightings we recorded a total of 70 species of birds, 14 species of mammals and 38 species of reptiles and amphibians. We found forest clearing to have a negative effect on species richness and community structure of all groups and identified loss of canopy cover as a driving factor behind this. However, the response and sensitivity to clearing varied between groups and species. Lizards (50%) and small mammals (40%) had the greatest decline in species richness in response to clearing as compared to birds (26%), although birds showed the greatest shift in community structure. The community in cleared areas contained more generalist and introduced species that have wider geographic ranges and habitat preferences, than those unique to the spiny forest. We found the first suite of species to suffer from forest clearance were those of high conservation priority due to their restricted geographic range. Our findings are discussed in relation to future spiny forest conservation and management.  相似文献   

11.
Throughout the world, but particularly in tropical regions habitat loss and disturbance are considered detrimental to biodiversity. We examine the effects of disturbance by harvesting, burning and habitat fragmentation on six bird species associated with papyrus (Cyperus papyrus) swamps. The presence or absence of these species was verified in 93 wetlands in southern Uganda between June and August 2003. Disturbance was estimated directly by observation and indirectly from examining vegetation structure. Habitat fragmentation was quantified by delineating swamps on Landsat ETM images and applying ‘Fragstats’ to calculate relevant patch metrics. The occurrence of all six species was affected positively by increased swamp size, but birds were more likely to occur in small swamps at high altitude. The shape and proximity of swamps to neighbouring wetlands had little effect on occurrence. As altitude, habitat fragmentation and disturbance were correlated, determining avian responses to disturbance was problematic. However, the occurrence of all species was affected by disturbance, often showing unimodal responses, if disturbance was not considered in conjunction with habitat fragmentation. When the effects of habitat fragmentation and disturbance were analysed together, only the occurrences of papyrus yellow warbler and white-winged warbler were affected (positively) by disturbance. Results suggest that papyrus-dwelling passerines, except papyrus gonolek, are tolerant of low intensities of disturbance, a novel finding in the tropics. We recommend that policy-makers do not prohibit harvesting, thus generating good will and encouraging rural householders to comply with additional conservation policy.  相似文献   

12.
We evaluated the relationship between amphibian and reptile diversity and microhabitat dynamics along pasture-edge-interior ecotones in a tropical rainforest in Veracruz, Mexico. To evaluate the main correlation patterns among microhabitat variables and species composition and richness, 14 ecotones were each divided into three habitats (pasture, forest edge and forest interior) with three transects per habitat, and sampled four times between June 2003 and May 2004 using equal day and night efforts. We measured 12 environmental variables describing the microclimate, vegetation structure, topography and distance to forest edge and streams.After sampling 126 transects (672 man-hours effort) we recorded 1256 amphibians belonging to 21 species (pasture: 12, edge: 14, and interior: 13 species), and 623 reptiles belonging to 33 species (pasture: 11, edge: 25, and interior: 22 species). There was a difference in species composition between pasture and both forest edge and interior habitats. A high correlation between distance to forest edge and temperature, understorey density, canopy cover, leaf litter cover, and leaf litter depth was found. There was also a strong relationship between the composition of amphibian and reptile ensembles and the measured environmental variables. The most important variables related to amphibian and reptile ensembles were canopy cover, understorey density, leaf litter cover and temperature.Based on amphibian and reptile affinity for the habitats along the ecotone, species were classified into five ensembles (generalist, pasture, forest, forest edge and forest interior species). We detected six species that could indicate good habitat quality of forest interior and their disappearance may be an indication of habitat degradation within a fragment, or that a fragment is not large enough to exclude edge effects. Different responses to spatial and environmental gradients and different degrees of tolerance to microclimatic changes indicated that each ensemble requires a different conservation strategy. We propose to maintain in the Los Tuxtlas Biosphere Reserve the forest remnants in the lowlands that have gentler slopes and a deep cover of leaf litter, a dense understorey, and high relative humidity and low temperature, to buffer the effects of edge related environmental changes and the invasion of species from the matrix.  相似文献   

13.
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   

14.
The effects of habitat fragmentation on forest bird assemblages were analysed in 214 holm oak (Quercus ilex) remnants spread across the northern and southern plateaux of central Spain. Bird richness was highly dependent on fragment area for all species regardless of isolation, and barely affected by habitat traits. Geographical location was associated with high differences in richness of bird assemblages, which included 17 species exclusive to northern remnants and one exclusive to southern remnants. This supports the hypothesis that habitat suitability deteriorates sharply from north to south for forest birds in Spain. The species-area relationships of bird assemblages sampled in fragmented forests along a broad continental gradient (from Norway to southern Spain) showed that true forest birds only nest in woodlands >100 ha in southern Spain, whereas the full complement of forest species occurs in much smaller fragments in central-western Europe. Loss of species that are particularly sensitive to habitat fragmentation accounts for these differences between dry Spanish and mesic European woodlands. These results are explained by the low habitat suitability of Spanish woodlands, associated with the restrictive conditions for plant regeneration in the Mediterranean climate and long-standing human usage. There is, therefore, a particular need to develop management strategies that conserve birds, and probably other forest organisms, in Mediterranean regions by preventing habitat deterioration and decreases in fragment size, and by conserving all woods >100 ha.  相似文献   

15.
We studied bird community composition and abundance within the logged and unlogged forest areas of a certified forestry concession in lowland Bolivia. The logged forest was harvested using reduced-impact logging techniques between one and four years previously. We used canonical correspondence analysis to describe the relationship between selected environmental variables and bird species abundance data, and the Indicator Value procedure to test for associations between bird species and the logged and unlogged habitats. Approximately one-third of birds were restricted to either the logged or unlogged areas, with 20% of all species only encountered in, or significantly more abundant in, the unlogged areas of the concession. The majority of birds found in significantly higher abundance in the unlogged areas of the concession were associated with forest habitats dominated by large trees, or a high diversity of trees, providing dense canopy cover and deep leaf litter, with an understorey dominated by ferns. Over 40% of bird species that were significantly associated with the unlogged areas of the concession are of conservation concern. In contrast, the majority of birds associated with the logged areas of the concession are known to be relatively resilient to human disturbance. The majority of species which exhibited significant lower abundances in the logged areas of the concession belonged to insectivorous or frugivorous feeding guilds. We discuss whether current management practices within this certified concession are sustainable and how our results can be used to guide future research and inform better practice.  相似文献   

16.
Habitat fragmentation fundamentally affects trophic interactions and ecosystem function. Understanding how the landscape matrix modulates such interactions can improve our understanding of fragmentation ecology. Studies of breeding birds provide clear examples of the consequences of habitat fragmentation, but the landscape context of these effects are unclear. We sampled avian nesting success in 12 moderately-large forest patches (>250 ha) embedded in different types of landscapes in southern Illinois, USA. We then evaluated eight models that predicted the probability of nest success and brood parasitism by Brown-headed Cowbirds. These models incorporated landscape composition (% grassland, % agriculture, fragmentation), year and seasonal effects, conspecific density, predator density, and combinations of these variables. Temporal factors (stage of nesting cycle, seasonal effects, annual variation) had the most effect on nesting success; landscape factors had little influence on nesting success. The rate and intensity of brood parasitism were significantly influenced by the amount of grassland for the Wood Thrush, but not for the Acadian Flycatcher. Fine-scale management of the matrix surrounding the patches may dictate the local abundance and movements of nest predators and parasites. Other major nest predators may prefer the forest interior and at least partially compensate for the lower abundance of nest predators that depend upon the matrix. Overall, landscape metrics were weak predictors of avian nesting success in complex landscapes that have diverse predator communities.  相似文献   

17.
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   

18.
Remnant forest strips are frequently proposed as valuable conservation tools in fragmented tropical landscapes, yet we currently lack evidence to evaluate their potential conservation value for native biota. We examined the potential value for understorey forest birds of 30-year-old riparian and terra firme (unflooded) primary forest strips within a large silvicultural landscape in the north-east Brazilian Amazon, where the matrix is dominated by Eucalyptus plantations. We conducted mist-netting in eight forest strips connected to continuous forest (four of each forest type), with a total of 24 replicate sampling sites located near to (<1 km), far from (2.5-9 km), and within undisturbed forest controls (i.e. 16 samples within the strips, and 8 in controls). Bird communities in both strip types changed with increasing distance along forest remnants into the plantation matrix. Matrix-embedded samples were characterised by a higher representation of birds typical of secondary growth forest but not those typical of the Eucalyptus-dominated matrix. While the long-term viability of the bird populations in these remnants remains unclear, our data demonstrate that forest strips can provide important habitat for many bird species that are otherwise rarely found outside primary forest. Forest strips therefore provide an important tool to enhance biodiversity conservation in plantation landscapes. The relative practical ease with which these areas can be selected and maintained means that the protection of forest strips as part of a wider conservation strategy is likely to have particular appeal to policy makers and landscape managers working in the human-dominated tropics.  相似文献   

19.
Habitat loss and fragmentation are recognized as major threats to biodiversity. Their respective effects, however, are sometimes not well distinguished, even though habitat loss is recognized as the most important source of variation affecting species abundance and richness at the landscape scale. As ‘habitat’ is a species-specific concept (based on species perception of its environment), habitat loss and fragmentation studies should be conducted on a species-specific basis. We here assessed the influence of habitat loss and fragmentation in the context of a boreal forest considering forest clearcutting as an anthropogenic disturbance inducing mature forest loss and fragmentation that has a potential impact on wildlife. Using 16 simulated patterns of mature forest loss and fragmentation and three natural landscapes as replicates, we assessed the respective influence of forest loss and fragmentation on the abundance of 10 bird species common in the boreal forest of eastern Canada. Species–habitat relationships were modeled through habitat use models that were utilized to predict abundance of the 10 species within each combination of loss and fragmentation patterns (3 landscapes × 16 patterns). We used three-way ANOVAs to assess the effects of mature forest loss, fragmentation and replicates (random effect) on species abundance. Our results indicated that: (1) variation in species abundance mostly depended on mature forest loss, followed by static landscape attributes other than cutovers (e.g. streams, lakes, roads) and finally by fragmentation and (2) responses to mature forest loss and fragmentation differed among species, not necessary in relation to the successional status but in relation to their perception of their environment. Decreasing detrimental effects of mature forest loss through conservation of large continuous patches of forest may be suitable to maintain abundances of mature forest bird species. Our results highlight that studies aiming to quantify effects of habitat loss and fragmentation on wildlife should be conducted on a species-specific basis and use several landscape replicates to avoid potentially biased results.  相似文献   

20.
Understorey gaps are common in subtropical forests where pole-size trees are harvested for building materials. The creation of artificial understorey gaps has the potential to affect tree regeneration and the maintenance of forest tree diversity by locally increasing resource availability (light, nutrients, moisture). Understorey tree gaps had significantly lower foliage density in the 3-10-m stratum and higher soil moisture. However, fine root biomass and nutrient availability (N, P, K, Corg) were not different to controls in the intact understorey. Light intensity at the forest floor was a function of the age of the understorey gap, being greater in recent gaps but was not different between older gaps and the controls in intact understorey. The early regeneration community in gaps was different in composition from under intact understorey. Understorey gaps appeared to promote the regeneration of understorey species (density and species richness) by increasing community-wide seedling establishment of understorey species. However, understorey gaps had no effect on the early regeneration of canopy species. We argue that under low harvesting intensity (11.6% of the available pole-size stems), understorey gaps have a neutral role in the long-term maintenance of understorey species diversity and no apparent role in the long-term maintenance of canopy tree species diversity. These results suggest that low levels of subsistence harvesting of understorey species will not detrimentally affect the overall species composition of scarp forest.  相似文献   

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