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991.
David J. Augustine Stephen J. Dinsmore Michael B. Wunder Victoria J. Dreitz Fritz L. Knopf 《Landscape Ecology》2008,23(6):689-697
Sylvatic plague is a major factor influencing the dynamics of black-tailed prairie dog (Cynomys ludovicianus) colonies in the western Great Plains. We studied the nesting response of the mountain plover (Charadrius montanus), a grassland bird that nests on prairie dog colonies, to plague-driven dynamics of prairie dog colonies at three sites in
the western Great Plains. First, we examined plover nest distribution on colonies that were previously affected by plague,
but that had been recovering (expanding) for at least 6 years. Plovers consistently nested in both young (colonized in the
past 1–2 years) and old (colonized for 6 or more years) portions of prairie dog colonies in proportion to their availability.
Second, we examined changes in plover nest frequency at two sites following plague epizootics, and found that mountain plover
nest numbers declined relatively rapidly (≤2 years) on plague-affected colonies. Taken together, our findings indicate that
available plover nesting habitat associated with prairie dog colonies closely tracks the area actively occupied by prairie
dogs each year. Given the presence of plague throughout most of the mountain plover’s breeding range in the western Great
Plains, important factors affecting plover populations likely include landscape features that determine the scale of plague
outbreaks, the distance that plovers move in response to changing breeding habitat conditions, and the availability and quality
of alternate breeding habitat within the landscape. 相似文献
992.
Chris S. Duvall 《Landscape Ecology》2008,23(6):699-716
Customary land-use practices create distinctive cultural landscapes, including landscapes where abandoned settlements host
vegetation that attracts wild animals. Understanding how landscape patterns relate to land-use history can help clarify the
ecological effects of particular land uses. This study examines relationships between chimpanzee habitat selection and Maninka
settlement practice, to determine how settlement history has affected chimpanzee habitat in Mali’s Bafing Biosphere Reserve,
where conservation practitioners assume that the characteristic settlement pattern reflects a process of settlement expansion
into undisturbed habitat. Three types of data are reported: (1) ethnographic interviews on settlement history and practice;
(2) systematic sampling of chimpanzee habitat use; and (3) ground-based mapping of settlement sites, surface water, and fruit-tree
patches. These data show that the Maninka have a shifting settlement system, meaning that most sites are occupied for only
relatively brief periods; and that some abandoned settlement sites host fruit-tree patches that are seasonally important chimpanzee
habitat. Two main conclusions are: (1) settlement expansion has not occurred; instead, historic settlement has created habitat
that is both attractive and available to chimpanzees. Anthropogenic habitat does not appear to be vital for chimpanzee survival,
but it spatially and temporally supplements natural habitats. (2) Conservation policies meant to reduce the presumed threat
of settlement expansion may have initiated an unintended, long-term threat of habitat loss for chimpanzees. While settlement
practices may be a component of short-term threats to chimpanzees, such as hunting, when addressing these threats conservation
practitioners should consider long-term settlement processes to avoid creating new threats. 相似文献
993.
Invasions resulting in the transformation of one ecosystem to another are an increasingly widespread phenomenon. While it
is clear that these conversions, particularly between grassland and shrubland systems, have severe consequences, it is often
less clear which factors are associated with these conversions. We resampled plots from the 1930s (Weislander VTMs) to test
whether two widely assumed factors, changes in fire frequency and nitrogen deposition, are associated with the conversion
of coastal sage scrublands to exotic grasslands in southern California. Over the 76-year period, coastal sage scrub cover
declined by 49%, being replaced predominantly by exotic grassland species. Grassland encroachment was positively correlated
with increased fire frequency and, in areas with low fire frequencies, air pollution (percent fossil carbon as indicated by
∂14C, likely correlated with nitrogen deposition). We conclude that increases in fire frequency and air pollution over the last
several decades in southern California may have facilitated the conversion of coastal sage shrubland to exotic grassland systems. 相似文献
994.
Seagrasses, which form critical subtidal habitats for marine organisms worldwide, are fragmented via natural processes but are increasingly being fragmented and degraded by boating, fishing, and coastal development. We constructed an individual-based model to test how habitat fragmentation and loss influenced predator–prey interactions and cohort size for a group of settling juvenile blue crabs (Callinectes sapidus Rathbun) in seagrass landscapes. Using results from field studies suggesting that strong top-down processes influence the relationship between cannibalistic blue crab populations and seagrass landscape structure, we constructed a model in which prey (juvenile blue crabs) are eaten by mesopredators (larger blue crabs) which in turn are eaten by top-level predators (e.g., large fishes). In our model, we varied the following parameters within four increasingly fragmented seagrass landscapes to test for their relative effects on cohort size: juvenile blue crab (prey) predator avoidance response, hunting ability of mesopredators and predators, the presence of a top-level predator, and prey settlement routines. Generally, prey cohort size was maximized in the presence of top-level predators and when mesopredators and predators exhibited random searching behavior vs. directed hunting. Cohort size for stationary (tethered) prey was maximized in fragmented landscapes, which corresponds to results from field experiments, whereas mobile prey able to detect and avoid predators had higher survival in continuous landscapes. Prey settlement patterns had relatively small influences on cohort size. We conclude that the effects of seagrass fragmentation and loss on organisms such as blue crabs will depend heavily on behaviors of prey and predatory organisms and how these behaviors change with landscape structure. 相似文献
995.
996.
The urban region: natural systems in our place,our nourishment,our home range,our future 总被引:1,自引:1,他引:0
Richard T. T. Forman 《Landscape Ecology》2008,23(3):251-253
997.
A significant challenge facing forestry today is managing private forests sustainably in the face of continued ownership fragmentation
(i.e., parcelization). Cross-boundary coordination––where forest practices are coordinated across multiple properties––has
been proposed as a mechanism by which landscape-level ecological and economic benefits may be accrued in privately-owned landscapes,
but few tests of the concept exist. Using a case study approach, we quantify the extent to which ownership-centric forest
management is constrained by economies of scale and misses opportunities to achieve ecological objectives in three landscapes
in Wisconsin, USA. Methods are based on existing forest management plans and include spatial analysis of patch distributions
and shapes, simulation of forest practices, and calculation of net present value over a 20-year horizon. Our results indicate
substantial opportunity for cross-boundary coordination: between 62% and 88% of the managed properties within our study landscapes
were adjacent to other properties with forest management plans. At a patch scale, coordination can result in ecological benefits
that can be accrued into the future (e.g., maintenance of large patches and natural ecosystem boundaries). Because these landscapes
are already highly parcelized, however, coordination offers little opportunity to impact the overall landscape-scale structure.
Greater economies of scale can also be gained by coordinating forest practices, including increases in the size (16–99%) and
volume of timber sales (16–94%), and a modest economic advantage (3–6%). As first steps, investment in data infrastructure
and professional training are required to support cross-boundary multi-ownership forest management. More broadly is the need
to shift from policies and practices that are largely ownership-centric to those that include and better incorporate landscape-centric
perspectives. 相似文献
998.
Relationships of dead wood patterns with biophysical characteristics and ownership according to scale in Coastal Oregon,USA 总被引:1,自引:0,他引:1
Dead wood patterns and dynamics vary with biophysical factors, disturbance history, ownership, and management practices; the
relative importance of these factors is poorly understood, especially at landscape to regional scales. This study examined
current dead wood amounts in the Coastal Province of Oregon, USA, at multiple spatial scales. Objectives were to: (1) describe
current regional amounts of several characteristics of dead wood; (2) compare dead wood amounts across ownerships; (3) determine
the relative importance, according to spatial scale, of biophysical and ownership characteristics, to regional dead wood abundance.
Dead wood plot data were evaluated with respect to explanatory variables at four spatial scales of resolution: plots, subwatersheds,
watersheds and subbasins. The relationships of dead wood characteristics with biophysical attributes and ownership were diverse
and scale-specific. Region-wide dead wood abundance and types varied among ownerships, with public lands typically having
higher amounts of dead wood and more large dead wood than private lands. Regression analysis of total dead wood volume indicated
that ownership was important at the subbasin scale. Growing season moisture stress was important at plot, subwatershed, and
watershed scales. Topography was important at the two coarser scales. Multivariate analysis of dead wood gradients showed
that ownership was important at all scales, topography at the subbasin scale, historical vegetation at watershed and subbasin
scales, and current vegetation at plot and subwatershed scales. Management for dead wood and related biodiversity at watershed
to landscape scales should consider the distinct dynamics of snags and logs, the importance of historical effects, and the
relevance of ownership patterns. 相似文献
999.
In reply to the critique of Baird and Kerr, we emphasize that our model is a generalized vulnerability model, built from easily
acquired data from anywhere in the world, to identify areas with probable susceptibility to large tsunamis—and discuss their
other criticisms in detail. We also show that a rejection of the role of trees in helping protect vulnerable areas is not
justified in light of existing evidence. 相似文献
1000.
Kirtland’s warblers (Dendroica kirtlandii) persist in a naturally patchy environment of young, regenerating jack pine forests (i.e., 5–23 years old) created after
wildfires and human logging activities. We examined how changing landscape structure from 26 years of forest management and
wildfire disturbances influenced population size and spatial dispersion of male Kirtland’s warblers within their restricted
breeding range in northern Lower Michigan, USA. The male Kirtland’s warbler population was six times larger in 2004 (1,322)
compared to 1979 (205); the change was nonlinear with 1987 and 1994 identified as significant points of change. In 1987, the
population trend began increasing after a slowly declining trend prior to 1987, and the rate of increase appeared to slow
after 1994. Total amount of suitable habitat and the relative area of wildfire-regenerated habitat were the most important
factors explaining population trend. Suitable habitat increased 149% primarily due to increasing plantations from forest management.
The relative amount and location of wildfire-regenerated habitat modified the distribution of males among various habitat
types, and the spatial variation in their abundance across the primary breeding range. These findings indicate that the Kirtland’s
warbler male population shifted its use of habitat types temporally and spatially as the population increased and as the relative
availability of habitats changed through time. We demonstrate that researchers and managers need to consider not only habitat
quality, but the temporal and the spatial context of habitat availability and population levels when making habitat restoration
decisions. 相似文献