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1.
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   

2.
Tropical savannas are an important reservoir of global biodiversity. Australia’s extensive savannas, although still largely intact, are experiencing substantial declines in terrestrial biodiversity due to a variety of interrelated effects of altered fire regimes, grazing and increases in invasive species. These disturbance processes are spatially variable, combine to increase landscape to local-scale landscape heterogeneity, but rarely result in well-defined patch boundaries. We quantified the importance of this heterogeneity for native reptile and small mammal species in a tropical savanna landscape of Queensland, Australia. We used high resolution remote sensing imagery (IKONOS) to map habitat pattern at a 4 m spatial resolution and at variable extents. We found that landscapes dominated by grass or bare ground had low reptile and small mammal diversity, while landscapes with a heterogeneous mix of grass, bare ground and trees had high species diversity and relative abundance of most species. Landscape heterogeneity may increase reptile and small mammal species richness by: (i) increasing the variety and abundance of foraging resources such as seeds and invertebrates; (ii) providing cover from predators and high summer temperatures; and (iii) increasing functional connectivity and dispersal success. The importance of these resources and processes varies among individual species and at different spatial scales, reiterating the need to consider habitat requirements of multiple species in landscape management and conservation planning.  相似文献   

3.
Urban and agricultural land uses have caused documented declines in diversity of many organisms. However, responses of stream- and riparian-dwelling amphibians and reptiles to anthropogenic land development are collectively understudied and, when studied, are often grouped together as though these two taxa respond in a similar fashion. We surveyed watersheds in four land use categories (reference, pasture, developing, and urban) for amphibian and reptile species richness over a two-year period in the southeastern United States. Total herpetofauna species richness was equivalent among all watershed types, but amphibians and reptiles responded differently to urbanization when analyzed separately. Urban watersheds had significantly fewer amphibian species than all other watershed types, but these losses were counterbalanced by significant increases in reptile species richness in these same watersheds. We also found that local, riparian-scale, habitat differences were strongly correlated with species composition differences between pasture and developing watersheds. While the difference in species composition between pasture and developing sites may have multiple, species-specific explanations, the dramatic differences between amphibian and reptile species richness in urban watersheds suggest broad trends that may be important to conservation planning. Specifically, our observations suggest that urbanization in the studied watersheds alters small streams from closed-canopy, shallow-water features of the forested landscape likely present before settlement by Europeans and favored by many salamanders and frogs to features associated with open vegetation and deeper, warmer waters favored by riverine turtles and snakes. We conclude that amphibians and reptiles, despite some physiological similarities, are not equivalent for monitoring purposes. Additionally, if future development in the Piedmont mirrors current urbanization, then significant faunal shifts seem assured.  相似文献   

4.
We report the impact of human-induced desertification on the species richness, abundance, and composition of sand dune flora and herpetofauna of North Sinai, Egypt. Our hypothesis was that degraded habitats would have reduced vegetation complexity, richness, and abundance, and consequently lower reptile species richness and abundance. We also hypothesized that desert lizards would not follow the typical generalist/specialist responses to habitat degradation found in other biomes. Instead, we predicted that because vegetation loss intensifies the environmental extremity of deserts, those species specialized for open and sandy environments would be more likely to persist in desertified habitats than would desert generalists. Our results showed that areas protected from vegetation loss did not have significantly higher vegetation richness or abundance except for only a few species. However, protected sites did have significantly higher percent vegetation cover and height. Habitat protection clearly had strong effects on the reptile community as species richness and abundances were significantly higher in protected sites. The composition of the reptile community between protected and unprotected sites differed significantly. Contrary to past studies in other environments, desert generalist species were not able to persist in degraded sites and were only found in protected sites. Specialist species were ubiquitous in that they occurred in both areas protected and unprotected from vegetation loss. We propose that the effects of disturbance on species composition (specialists or generalists) depends on whether the disturbance exacerbates or reduces environmental harshness and the conditions that favor specialization. In extreme environments, specialist and generalist responses to habitat degradation are opposite to that of more productive environments.  相似文献   

5.
The commercial trading and private collecting of amphibians and reptiles is intensive and widespread in Britain and other European countries. In some circumstances and in the case of certain species the keeping of these animals in captivity seems to be justified, particularly where education and/or serious research is the objective. However, the removal of amphibians and reptile specimens from the wild may well place another factor on the loss side of the population equation and in some cases collecting already uncommon and fragmented populations has led to the extinction of colonies. Whereas it would be irrational to suggest that all private collecting be stopped, suggestions are made which might act to moderate it and safeguard the populations and their habitats.  相似文献   

6.
Secondary vegetation, associated with changes in land use, presents a conservation issue in the preservation of biological diversity in agricultural landscapes. We examine the interactive effect of eucalypt regrowth and rock habitat on reptile species richness and assemblage structure in fragmented agricultural landscapes in south-eastern Australia. Zoogeographic and geomorphic factors influenced species richness and community composition. Saxicolous and arboreal species were less abundant in grassy woodland regrowth, whereas Bassian and fossorial species responded positively to forest regrowth (and tree plantings). Regrowth with rock habitat had higher reptile richness, and more old growth-associated taxa, than regrowth without rock habitat. Thus, the presence of saxicolous habitat can reduce the time required for regrowth to attain a climax community structure and elements of old growth fauna. However, in the absence of vegetation management, secondary vegetation can reduce habitat suitability for a broad range of reptiles. In agricultural landscapes historically supporting savannah-like vegetation, habitat manipulation may be necessary to maintain reptile diversity. Furthermore, tree plantings in temperate agricultural landscapes should aim to restore historical vegetation composition and structure, thereby reflecting the habitat requirements of extant species and facilitating evolutionary processes. In grassy woodland ecosystems, this may involve heterogeneous plantings which emulate natural levels of canopy cover and solar penetration. Maintaining biodiversity in agricultural landscapes will therefore involve managing trade-offs to preserve areas of dense regeneration for regrowth-dependant fauna, while at the same time, creating open-canopy environments to enhance habitat for ectothermic organisms.  相似文献   

7.
Understanding the process animals follow to select habitat, rather than just documenting the habitat they use, will improve our ability to predict how the animals use habitat in other locations and how they will respond to changes in habitat. Animals are usually assumed to select habitats hierarchically, preferentially using specific macrohabitats at a landscape scale and specific microhabitats within the preferred macrohabitats. We used four years of telemetry data from 34 individuals to test this hierarchical model of habitat selection with eastern massasauga rattlesnakes (Sistrurus c. catenatus) in Ontario. Snakes were selective at the microhabitat scale, preferentially using locations with closer retreat sites and shrubs than random. Gravid females were most selective, using sites with more rock cover and less canopy closure than sites used by males and nongravid females. Snakes preferred forested habitats for hibernation and steadily increased their use of open, wetland, and edge habitats to a peak in mid-summer. Landscape-scale habitat preferences were generally mild and could be explained by the relative availability of suitable microhabitat within habitats, suggesting habitat selection was primarily driven by microhabitat preferences. The lack of selectivity at the landscape scale may be a consequence of fine-grained differences between habitats that allow massasauga rattlesnakes to find suitable microhabitats in all available macrohabitats. For species that select habitat primarily at the microhabitat scale (e.g., the rattlesnakes we studied), landscape-scale modeling of habitat use will only be effective to the extent habitats reflect the availability of suitable microhabitat within.  相似文献   

8.
Britain's native reptile fauna consists of three lizard species and three snake species, some of which may be unique physiological races (evidence is so far based only on their Critical Minimum Temperatures). Three species (Anguis fragilis, Lacerta vivipara, Vipera berus) are widely distributed although the populations are fragmented. The other three (Coronella austriaca, Lacerta agilis, Natrix natrix) are more or less limited in distribution to southern England (although N. natrix does reach Latitude 56°N) and most of the populations are small, scattered and geographically isolated from each other. Pressures such as land development, collecting and habitat destruction by fire are great. The snake Coronella austriaca and the lizard Lacerta agilis are now rare and several colonies and/or habitats of these two species are destroyed each year. As the survival of Britain's rarer reptiles may depend on well managed nature reserves and on the relocation of endangered colonies it is imperative that much more basic herpetological research be completed during the next few years. Fundamental eco-physiological requirements (e.g. food, heat, water) and behavioural requirements (e.g. space) of these animals are being examined in order to maintain or develop optimum habitats on nature reserves and in the hope of establishing viable reptile colonies. One example of this procedure is discussed with particular reference to the construction of an island habitat for Lacerta agilis, and suggestions for future management are outlined.  相似文献   

9.
Habitat remnants on urban green-space areas (i.e. parks, gardens and golf courses) sometimes provide refuge to urban-avoiding wildlife, leading some to suggest these areas may play a role in wildlife conservation if they are appropriately designed and managed. The high densities observed on some green-space areas may however be attributed to external influences. Localised efforts to enhance the habitat value of urban green-space areas may therefore have little more than a cosmetic effect. This study investigated environmental factors influencing bird, reptile, mammal and amphibian diversity on Australian golf courses to assess the efficacy of small-scale conservation efforts. Abundance and species richness did not simply reflect local habitat qualities but were instead, partly determined by the nature of the surrounding landscape (i.e. the area of adjacent built land, native vegetation and the number of connecting streams). Vertebrate abundance and species richness were however, also associated with on-site habitat characteristics, increasing with the area of native vegetation (all vertebrates), foliage height diversity and native grass cover (birds), tree density, native grass cover and the number of hollows (mammals), woody debris, patch width and canopy cover (reptiles), waterbody heterogeneity and aquatic vegetation complexity (frogs). Localised conservation efforts on small land types can benefit urban-avoiding wildlife. Urban green-space areas can provide refuge to urban-avoiding vertebrates provided combined efforts are made at patch (management), local (design) and landscape (planning) scales.  相似文献   

10.
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   

11.
Nonnative fishes have been introduced into naturally fishless mountain lakes worldwide, often with negative consequences for native fauna. In this study, I used data collected during a census of native herpetofauna, nonnative trout, and habitat characteristics at all lentic water bodies in Yosemite National Park (n=2655) to quantify the effect of trout introductions and habitat on the distribution of four amphibian species and two reptile species. Impacts of trout on amphibians and reptiles were characterized using generalized additive models that included as predictor variables fish presence/absence, amphibian presence/absence (only in models for the two reptile species), elevation, water depth, littoral zone and shoreline substrate composition, relative survey date, and location. All species showed significant associations with habitat characteristics, and elevation and water depth appeared particularly important in influencing distributions. In addition, distributions of the mountain yellow-legged frog (Rana muscosa) and Pacific treefrog (Hyla regilla) were strongly negatively associated with the presence of nonnative trout while those of the Yosemite toad (Bufo canorus) and Sierra newt (Taricha torosa sierrae) were unrelated to trout presence. The distribution of the mountain garter snake (Thamnophis elegans elegans) was strongly negatively associated with the presence of nonnative trout and positively associated with the presence of native amphibians. Regression results for the Sierra garter snake (Thamnophis couchi couchi) were similar except that the direct effect of nonnative trout was considerably weaker. Together, these results indicate that trout introductions have resulted in considerable alteration of Yosemite's herpetofauna. Long-term studies will be necessary to determine whether removal of nonnative trout populations, where possible, would allow these impacts to be partially reversed.  相似文献   

12.
13.
This study investigated associations between the relative abundance of the threatened ngwayir (western ringtail possum, Pseudocheirus occidentalis) and anthropogenic disturbances at local and landscape scales within the publicly-managed jarrah (Eucalyptus marginata) forests of south-western Australia. Logging, fire, fox (Vulpes vulpes) control and forest fragmentation were investigated in relation to the relative abundance of ngwayir at 90 sites within an area of 285,000 ha east of Manjimup; the location of the last remaining substantial population of ngwayir in jarrah forest. Overall, ngwayir abundance was greatest in areas with limited anthropogenic disturbance. At the local-scale, ngwayir abundance was negatively associated with greater fire intensity. At the landscape-scale, it was positively associated with fox control and negatively associated with forest fragmentation and distance from non-remnant vegetation (i.e., agriculture and tree plantations). Abundance was also greatest in predominantly unlogged landscapes and in forests that had been regrowing for an average of 40 years since the landscape was most recently logged, in other words, where logging was historically least intense. Interactions between fox control efforts and forest fragmentation were also important. This study emphasises the importance of conducting research at appropriate spatial scales and to account for the synergistic effects of the causes of decline. An adaptive management approach to the mitigation of the agents of decline is recommended.Indirect evidence indicates that high value habitat for ngwayir has in all likelihood been selectively cleared for agriculture, owing to its fertile and productive nature. Habitat loss is, therefore, also likely to be a major cause of the modern decline of the species. While many jarrah forest areas that support remaining high abundances of the ngwayir have been incorporated into reserves, conservation of ngwayir habitat and populations outside reserves also will be essential for the recovery and long-term viability of the species.  相似文献   

14.
Species with strong preferences for early or late successional stages after fire may be extinction prone under current fire regimes. However, the extent of specialisation to time since fire is poorly understood, and, for reptiles, succession models for predicting responses are in the development phase. In this study we tested predictions of a reptile succession model, and identified species that may be fire specialists. Reptiles were sampled in five burnt and unburnt mallee Eucalyptus woodlands, Australia. Two, 400 m transects within each burn treatment were sampled using 11 pairs of pitfall-traps that were opened for five weeks over two summers. A habitat accommodation model of succession that was previously developed for mallee reptiles correctly predicted the observed responses of three of 16 common reptile species. A further four species showed non-significant trends in the predicted direction. However, eight other species showed unexpected responses. One species showed a strong interaction between burn age and location, requiring a two-dimensional successional model in contrast with the usual linear models explaining reptile responses to fire. One third of common species were not affected by fire and so may not have increased risks of extinction due to the fire suppression/incineration cycle. However, approximately half to two-thirds of common reptiles did have a fire response, so the risk of deterministic extinction in small fragments may be substantial. Further model development is needed to better predict fire responses and to assist the design of fire mosaics that can accommodate early and late successional fire specialists.  相似文献   

15.
Recent studies in population dynamics suggest that landscape processes and habitat quality act at different scales on population abundances, but very few have modelled their simultaneous effects. However, at a time of large declines in natural populations, it is essential to understand such multivariate components. We tested the hypothesis that natural populations of palmate newts (Triturus helveticus) are affected on three scales: breeding patch (pond), habitat complementation (terrestrial cover), and metapopulation structure (density of ponds, surrounding populations). We conducted our survey in 130 ponds from southern France (Larzac) and analysed data with generalized additive models (GAM). Two main novel results emerge from these models: (1) the three landscape scales have significant effects on newt abundance, with more newts in deep, vegetated ponds, devoid of fish and surrounded by wooded areas and inhabited ponds; (2) the quality of the surrounding breeding patches is of primary importance in determining the abundance at core sites in a complex way: high abundances are associated positively with high densities of inhabited ponds, but negatively with the number of surrounding ponds. Deforestation, invasive species and abandonment of ponds all have negative impacts on the persistence of palmate newt populations. Future studies should encompass landscapes at different scales and incorporate the habitat quality in surrounding sites to better understand population dynamics and provide adequate conservation measures.  相似文献   

16.
Throughout North America, bird population declines may be attributable to loss of habitat on the breeding grounds. Human land uses such as residential development, greatly impact landscapes and biota, particularly breeding birds. Riparian areas, which are essential to breeding birds, are particularly vulnerable to development pressures. In North America, most studies have focused on eastern birds and it is unclear how western bird assemblages respond to the effects of residential development. We sampled bird community parameters and habitat variables at three spatial scales (microhabitat, macrohabitat, and landscape) along a residential development gradient within the Snake River riparian corridor in Jackson Hole, WY, USA. Principal component analysis and multiple linear regression statistical tests were used to determine the effects of housing densities on avian community parameters, guilds, individual species distributions, and environmental variables. Landscape-level features were most affected by residential development and trends associated with increasing housing densities, such as anthropogenic habitat fragmentation primarily structured local bird communities. Overall species richness and diversity declined with increasing residential development. Neotropical migrant species were most negatively impacted and consistently declined in proportional representation on forested plots as residential development densities increased. Food generalists, ground gleaners, and avian nest predators all increased with increasing residential development. Brood parasites, on the other hand, did not increase with increasing housing densities and their distribution may reflect the availability of nest host species. These results suggest that residential development within riparian habitats may be exerting a strong negative influence on western bird communities and at high densities may lead to a depauperate avian biota. The results of our study indicate that preserving forest structure may benefit certain species but will not likely conserve as diverse and rich an avian assemblage as minimizing fragmentation associated with residential development.  相似文献   

17.
‘Rare’ frogs and reptiles on Cape York Peninsula are those which are not found elsewhere in Australia, and which are known from either 20 or fewer museum records or from five or less localities. The six rare frog species and 22 rare reptile species are listed. Detailed data on their habitat requirements, distribution, and preservation through habitat protection in reserves are presented. Seven species inhabit areas which are not protected in any National Parks, State Forests, or Timber Reserves.  相似文献   

18.
We conducted a systematic global review of differences between timber plantations and pasture lands in terms of animal and plant species richness and abundance, and assessed the results using meta-analysis techniques. Our principal aim was to test the hypothesis that plantations contain higher species richness or abundance than pasture. Of the 1967 studies of potential relevance, 66 provided biological monitoring information and 36 met the requirements for meta-analyses. Sufficient data were available for meta-analyses to be conducted comparing the species richness and abundance of plantations and pasture lands for five taxonomic groups: plants, invertebrates, reptiles/amphibians, mammals, and birds. Within each taxon there was considerable variation in the difference between species richness and abundance between plantations and pasture lands. Birds and reptile/amphibians exhibited significantly higher species richness, and mammals exhibited significantly higher abundance, in plantations than in pasture lands which lacked remnant vegetation. Reptile/amphibian species richness was significantly higher in plantations in general. No significant differences in species richness were found for mammals, plants, or invertebrates, and no significant differences in abundance were found for birds, reptiles/amphibians, invertebrates, or plants. It is only within the presence of taxonomic caveats (i.e. reptiles/amphibians), or specific landscape features (i.e. absence of remnant vegetation within pasture), that it can be concluded that plantations support higher species richness or abundance than pasture land. We emphasize that caution is warranted when making general statements about the inherent biodiversity value of diverse and broadly-defined land-uses.  相似文献   

19.
Loose surface rocks on sandstone outcrops in coastal eastern Australia are subject to high levels of anthropogenic disturbance. The endangered reptiles that use these rocks as shelter-sites have attracted considerable research, but the invertebrate fauna under the same rocks has been neglected. We surveyed four sites in the Sydney region, to record the invertebrate fauna under a total of 240 rocks and quantify habitat associations of these animals. Fauna were present under almost 90% of surveyed rocks, with high overall abundance and species richness (up to seven species per rock). Our sampling regime was inadequate to fully characterise the sandstone invertebrate fauna, and thus substantially underestimates diversity on a broader spatial scale. The taxa covered a broad phylogenetic range, with ants and spiders the most abundant, widespread and species-rich lineages. The assemblage was dominated by predators and opportunistic scavengers, possibly reflecting the characteristic low productivity of these systems. Canonical correspondence analysis identified consistent linkages between specific faunal groups and microhabitat features (mainly substrate, also degree of shading and characteristics of the overlying rock). We conclude that surface rocks on Hawkesbury sandstone outcrops shelter a diverse and abundant invertebrate fauna, that microhabitat features influence faunal composition, and that our ignorance of this component of biodiversity will severely hamper any rational plan to conserve these distinctive and highly threatened ecosystems.  相似文献   

20.
A major challenge in conservation biology is to understand species’ responses to habitat loss. In Fennoscandia, the ongoing decline in aspen in forests is of particular concern, since aspen is the boreal forest tree species that supports the most host-specific species of cryptogams and invertebrates. In order to predict the potential effects of aspen decline we compared the occurrence of three epiphytic cyanolichens in old-growth stands of the same habitat quality, in four aspen-rich and four aspen-poor landscapes. Collemacurtisporum and Collemafurfuraceum were, on average, five and six times more frequent, respectively, in the aspen-rich than in the aspen-poor landscapes. Leptogiumsaturninum was not affected by the abundance of aspen stands at the landscape level. Our data suggests that lichen species with poor dispersal abilities may be more sensitive to habitat loss than more easily dispersed species and that species with broader habitat amplitude may be less sensitive to habitat loss than more specialized species, even if they have inferior dispersal ability. We conclude that (i) predictions of species occurrences at the stand level have to take account of the amount of suitable habitat at the landscape level, and (ii) predicting the responses of individual species based on life-history traits can be crucial, but cannot be based on single traits. Thus our study shows that biological value cannot be assessed on the basis of habitat quality alone and that a landscape perspective is needed for the sustainable management of specialist species.  相似文献   

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