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521.
物种灭绝的若干种可能的序 总被引:4,自引:0,他引:4
利用集合种群共存动力模式,研究了由于栖息地毁坏而导致物种灭绝的顺序问题.研究结果表明:在群落里各物种种群具有相等的死亡率的假设下,栖息地毁坏而导致物种的灭绝存在3种最基本可能的顺序,既最弱物种与最强物种相伴灭绝,最强物种与最弱物种是强弱交替灭绝,以及由强而弱依次灭绝.参7 相似文献
522.
Effect of Vegetation Matrix on Animal Dispersal: Genetic Evidence from a Study of Endangered Skinks 总被引:4,自引:0,他引:4
OLIVER BERRY†† MANDY D. TOCHER† DIANNE M. GLEESON‡ STEPHEN D. SARRE§ 《Conservation biology》2005,19(3):855-864
Abstract: Maintaining connectivity in fragmented landscapes is a key principle of biological conservation. Although corridors are a widely accepted approach to connecting populations, their merits are still debated, and they may be impractical in many situations. A focus on management of the vegetation matrix between populations has been advocated as an alternative way to deal with habitat fragmentation and has theoretical support. We combined microsatellite DNA and demographic data to provide an empirical account of how two forms of agricultural land use affect the connectivity of insular populations of an endangered skink in southern New Zealand. The grand skink ( Oligosoma grande ) lives in small populations (approximately 20 individuals) on rock outcrops separated from one another by 50–150 m of inhospitable matrix vegetation (either native tussock grassland or exotic pasture). Skinks typically dispersed short distances, and the nature of the matrix both quantitatively and qualitatively affected dispersal dynamics. Skink populations in pasture were significantly more genetically structured and had less genetic variation than similar populations in tussock, implying less dispersal between populations in pasture than tussock. Furthermore, although female-biased dispersal was a feature of populations in tussock, no sex bias was evident in pasture. In addition, Bayesian individual-based genetic assignment tests that incorporated prior mark-recapture information revealed that some populations produced many emigrants but received few immigrants, whereas other populations were relatively insular. Patterns of dispersal and response to matrix vegetation were complex, and the causes of these patterns deserve attention in future studies of habitat fragmentation. Managing the vegetation matrix may be a practical way to connect animal populations in some situations. 相似文献
523.
524.
Appreciating Ecological Complexity: Habitat Contours as a Conceptual Landscape Model 总被引:4,自引:0,他引:4
Abstract: Organisms respond to their surroundings at multiple spatial scales, and different organisms respond differently to the same environment. Existing landscape models, such as the "fragmentation model" (or patch-matrix-corridor model) and the "variegation model," can be limited in their ability to explain complex patterns for different species and across multiple scales. An alternative approach is to conceptualize landscapes as overlaid species-specific habitat contour maps. Key characteristics of this approach are that different species may respond differently to the same environmental conditions and at different spatial scales. Although similar approaches are being used in ecological modeling, there is much room for habitat contours as a useful conceptual tool. By providing an alternative view of landscapes, a contour model may stimulate more field investigations stratified on the basis of ecological variables other than human-defined patches and patch boundaries. A conceptual model of habitat contours may also help to communicate ecological complexity to land managers. Finally, by incorporating additional ecological complexity, a conceptual model based on habitat contours may help to bridge the perceived gap between pattern and process in landscape ecology. Habitat contours do not preclude the use of existing landscape models and should be seen as a complementary approach most suited to heterogeneous human-modified landscapes. 相似文献
525.
KENICHI OZAKI† MASAHIRO ISONO† TAKAYUKI KAWAHARA† SHIGEO IIDA† TAKUMA KUDO† KENJI FUKUYAMA† 《Conservation biology》2006,20(5):1507-1515
Abstract: Although species with large area requirements are sometimes used as umbrella species, their general utility as conservation tools is uncertain. We surveyed the species diversity of birds, butterflies, carabids, and forest-floor plants in forest sites across an area (1600 km2 ) in which we delineated large breeding home ranges of Northern Goshawk ( Accipiter gentilis ). We tested whether protection of the home ranges could serve as an effective umbrella to protect sympatric species of the four taxa. We also used an empirical habitat model of occupancy of home range to examine mechanisms by which the Northern Goshawk acts as an umbrella species. Among species richness, abundance, and species composition of the four taxa, only abundance and species composition of birds differed between sites located inside and outside home ranges, which was due to greater abundance of bird species that were prey of Northern Goshawks inside the home ranges. Thus, although home range indicated areas with high abundance of certain bird prey species, it was not effective as an indicator of the species diversity of all four taxa. We also did not find any difference in species richness, abundance, and species composition between sites predicted as occupied and unoccupied using the habitat model. In contrast, when we selected sites on the basis of each habitat variable in the model, habitat variables that selected sites either in agricultural or forested landscapes encompassed sites with high species richness or particular species composition. This result suggests that the low performance of the Northern Goshawk as an umbrella species is due to this species' preference for habitat in both agricultural and forested landscapes. Species that can adjust to changes in habitat conditions may not act as effective umbrella species despite having large home ranges. 相似文献
526.
Evaluating stream restoration projects 总被引:2,自引:3,他引:2
River and stream restoration projects are increasingly numerous but rarely subjected to systematic postproject evaluation.
Without conducting such evaluation and widely disseminating the results, lessons will not be learned from successes and failures,
and the field of river restoration cannot advance. Postproject evaluation must be incorporated into the initial design of
each project, with the choice of evaluation technique based directly upon the specific project goals against which performance
will be evaluated. We emphasize measurement of geomorphic characteristics, as these constitute the physical framework supporting
riparian and aquatic ecosystems. Techniques for evaluating other components are briefly discussed, especially as they relate
to geomorphic variables. Where possible, geomorphic, hydrologic, and ecological variables should be measured along the same
transects. In general, postproject monitoring should continue for at least a decade, with surveys conducted after each flood
above a predetermined threshold. Project design should be preceded by a historical study documenting former channel conditions
to provide insights into the processes suggest earlier, potentially stable channel configurations as possible design models. 相似文献
527.
Spatial analysis of habitat selection by Sitka black-tailed deer in Southeast Alaska,USA 总被引:1,自引:0,他引:1
We used a vector-based geographic information system (GIS) to examine habitat selection by radiocollared Sitka black-tailed
deer (Odocoileus hemionus sitkensis) in logged forests of southeast Alaska. Our main objective was to explain deer habitat selection relative to old-growth/clear-cut
edges and edge habitats at two different spatial scales. Deer home ranges contained higher percentages of recent clear-cuts
(50–69%) than the study area (37%;P<0.01) and had higher old-growth/clear-cut edge densities than expected by chance (P<0.01). Deer relocation points were closer to old-growth/clear-cut edges (average=135 m) than random points located within
each deer's relocation area (average=168 m;P=0.05). Likewise, deer relocations were closer to old-growth/clear-cut edges than points randomly located within old-growth
stands or recent clear-cuts (P<0.01). As the size of clear-cuts increased, both deer relocation density and the proportion of a clear-cut occupied by deer
home ranges decreased. Because old growth is important deer habitat and clear-cuts can produce deer forage for only 20–30
years after logging in southeast Alaska, deer management plans such as preserving entire watersheds and maintaining mixes
of old growth and recent clear-cut have been proposed. Our data suggest that deer need a diversity of habitats near each other
within their home ranges. 相似文献
528.
Thomas J. Myers Sherman Swanson 《Journal of the American Water Resources Association》1991,27(4):667-677
ABSTRACT: The quality of stream habitat varies for a variety of natural and anthropogenic reasons not identified by a condition index. However, many people use condition indices to indicate management needs or even direction. To better sort natural from livestock influences, stream types and levels of ungulate bank damage were regulated to estimates of aquatic habitat condition index and stream width parameters in a large existing stream inventory data base. Pool/riffle ratio, pool structure, stream bottom materials, soil stability, and vegetation type varied significantly with stream type. Pool/riffle ratio, soil and vegetation stability varied significantly with ungulate bank damage level. Soil and vegetation stability were highly cross-correlated. Riparian area width did not vary significantly with either stream type or ungulate bank damage. Variation among stream types indicates that riparian management and monitoring should be stream type and reach specific. 相似文献
529.
We compared the composition and structural characteristics of reclaimed and native woody plant communities near Fairfield,
Texas, to evaluate the effectiveness of woodland reclamation 3–11 years since establishment. Species composition, foliage
density, canopy cover, and woody plant densities were recorded in plots randomly placed along transects bisecting blocks of
reclaimed and native woodlands. During summer, vertical foliage densities at heights ≤2 m were similar among native and reclaimed
areas. Foliage density and canopy cover declined in reclaimed blocks during winter, but remained relatively constant in native
woodlands, where evergreens and vines were more common. Canopy cover was absent in reclaimed woodlands <6 years old but increased
with age in 6 to 11-year-old blocks. These data indicated that approximately 27 years will be needed before trees in reclaimed
blocks will achieve the stature of canopy trees in native woodlands. Reclaimed woodlands contained different woody plant species
and had lower woody stem densities compared to native woodlands. On average, stem densities in reclaimed blocks were six times
lower than densities in native woodlands. Comparisons with planting records indicate that survival of most commonly planted
woody species was low. Only green ash(Fraxinus pennsylvanica), Russian oliver(Elaeagnus commutata), smooth sumac(Rhus glabra), and redbud(Cercis canadensis) had estimated survival rates >50%. Reclamation procedures used at Big Brown Mine (BBM) during 1981–1988 have not produced
woodland habitats with vegetative characteristics comparable to premined woodlands and may not be providing the cover needed
to encourage use by certain wildlife species. Procedures for improving woodland reclamation are recommended. 相似文献
530.
Linking Multiple Accounts with GIS as Decision Support System to Resolve Forestry/Wildlife Conflicts
Sandra Brown Hans Schreier William A. Thompson Ilan Vertinsky 《Journal of environmental management》1994,42(4)
With shrinking forest resources and increasing demands for timber, conflicts between forestry and wildlife become more contentious and more frequent. New decision support methods are needed to address complex multiple land use conflicts. Multiple accounts methods linked with GIS and production models enable us to address trade-offs between timber and non-timber values, thus facilitating the evaluation and comparison of different management scenarios in a rapid and spatially referenced manner. The approach is documented in a case study in the trans-boundary zone between two national parks in British Columbia, where caribou/logging conflicts are widespread. 相似文献