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1.
The reliability of ants as bioindicators of ecosystem condition is dependent on the consistency of their response to localised
habitat characteristics, which may be modified by larger-scale effects of habitat fragmentation and loss. We assessed the
relative contribution of habitat fragmentation, habitat loss and within-patch habitat characteristics in determining ant assemblages
in semi-arid woodland in Queensland, Australia. Species and functional group abundance were recorded using pitfall traps across
20 woodland patches in landscapes that exhibited a range of fragmentation states. Of fragmentation measures, changes in patch
area and patch edge contrast exerted the greatest influence on species assemblages, after accounting for differences in habitat
loss. However, 35% of fragmentation effects on species were confounded by the effects of habitat characteristics and habitat
loss. Within-patch habitat characteristics explained more than twice the amount of species variation attributable to fragmentation
and four times the variation explained by habitat loss. The study indicates that within-patch habitat characteristics are
the predominant drivers of ant composition. We suggest that caution should be exercised in interpreting the independent effects
of habitat fragmentation and loss on ant assemblages without jointly considering localised habitat attributes and associated
joint effects.
The State of Queensland's right to retain a non-exclusive, royalty free license in and to any copyright is acknowledged. 相似文献
2.
The distribution of plant species in urban vegetation fragments 总被引:21,自引:4,他引:17
(1) The presence and absence of 22 plant species of various growth forms and habitat associations were analysed in 423 habitat fragments totalling 10.4 km2 in a 268 km2 urban and suburban region, in Birmingham, UK. (2) Multivariate logistic regressions were used to assess the effects of patch geometry and quality on the species distributions. Measures of geometry were area, shape (S-factor), distance from open countryside and various measures of isolation from other patches. Potential habitat for each species was determined quantitatively, and the distribution of each species was considered within a subset of patches containing potentially suitable habitat types. There was found to be a significant positive correlation between the density of patches available to a species and the proportion of these patches which were occupied. (3) Logistic analyses and incidence functions revealed that, for many of the species, occupancy increased with site age, area, habitat number and similarity of adjacent habitats, while increasing distance to the nearest recorded population of the same species decreased the likelihood that a species would be found in a patch. (4) Patterns of occupancy are consistent with increased extinction from small sites, and colonisation of nearby habitats, coupled with an important role for site history. We conclude that spatial dynamics at the scale of the landscape are of importance to the long-term persistence of many plant species in fragmented landscapes, and must be seriously considered in conservation planning and management. These results have direct implications for the siting and connectivity of urban habitat reserves. 相似文献
3.
Rune H. Økland Harald Bratli Wenche E. Dramstad Anette Edvardsen Gunnar Engan Wendy Fjellstad Einar Heegaard Oddvar Pedersen Heidi Solstad 《Landscape Ecology》2006,21(7):969-987
Knowledge of variation in vascular plant species richness and species composition in modern agricultural landscapes is important
for appropriate biodiversity management. From species lists for 2201 land-type patches in 16 1-km2 plots five data sets differing in sampling-unit size from patch to plot were prepared. Variation in each data set was partitioned
into seven sources: patch geometry, patch type, geographic location, plot affiliation, habitat diversity, ecological factors,
and land-use intensity. Patch species richness was highly predictable (75% of variance explained) by patch area, within-patch
heterogeneity and patch type. Plot species richness was, however, not predictable by any explanatory variable, most likely
because all studied landscapes contained all main patch types – ploughed land, woodland, grassland and other open land – and
hence had a large core of common species. Patch species composition was explained by variation along major environmental complex
gradients but appeared nested to lower degrees in modern than in traditional agricultural landscapes because species-poor
parts of the landscape do not contain well-defined subsets of the species pool of species-rich parts. Variation in species
composition was scale dependent because the relative importance of specific complex gradients changed with increasing sampling-unit
size, and because the amount of randomness in data sets decreased with increasing sampling-unit size. Our results indicate
that broad landscape structural changes will have consequences for landscape-scale species richness that are hard or impossible
to predict by simple surrogate variables. 相似文献
4.
Classical metapopulation models do not account for temporal changes in the suitability of habitat patches. In reality, however,
the carrying capacity of most habitat types is not constant in time due to natural succession processes. In this study, we
modeled plant metapopulation persistence in a successional landscape with disappearing and emerging habitat patches, based
on a realistic dune slack landscape at the Belgian–French coast. We focused on the effects of the variation of different plant
traits on metapopulation persistence in this changing landscape. Therefore, we used a stage based stochastic metapopulation
model implemented in RAMAS/Metapop, simulating a large variation in plant traits but keeping landscape characteristics such
as patch turnover rate and patch lifespan constant. The results confirm the conclusions of earlier modeling work that seed
dispersal distance and seed emigration rate both have an important effect on metapopulation persistence. We also found that
high population growth rate or high recruitment considerably decreased the extinction risk of the metapopulation. Additionally,
a long plant life span had a strong positive effect on metapopulation persistence, irrespective of the plant's dispersal capacity
and population growth rate. Plant species that invest in life span require less investment in offspring and dispersal capacity
to avoid extinction, even in dynamic landscapes with deterministic changes in habitat quality. Moreover, metapopulations of
long-lived plant species were found to be much less sensitive to high levels of environmental stochasticity than short-lived
species. 相似文献
5.
The landscape matrix modifies the effect of habitat fragmentation in grassland butterflies 总被引:1,自引:0,他引:1
Erik ?ckinger Karl-Olof Bergman Markus Franzén Tomá? Kadlec Jochen Krauss Mikko Kuussaari Juha P?yry Henrik G. Smith Ingolf Steffan-Dewenter Riccardo Bommarco 《Landscape Ecology》2012,27(1):121-131
The landscape matrix is suggested to influence the effect of habitat fragmentation on species richness, but the generality
of this prediction has not been tested. Here, we used data from 10 independent studies on butterfly species richness, where
the matrix surrounding grassland patches was dominated by either forest or arable land to test if matrix land use influenced
the response of species richness to patch area and connectivity. To account for the possibility that some of the observed
species use the matrix as their main or complementary habitat, we analysed the effects on total species richness and on the
richness of grassland specialist and non-specialist (generalists and specialists on other habitat types) butterflies separately.
Specialists and non-specialists were defined separately for each dataset. Total species richness and the richness of grassland
specialist butterflies were positively related to patch area and forest cover in the matrix, and negatively to patch isolation.
The strength of the species-area relationship was modified by matrix land use and had a slope that decreased with increasing
forest cover in the matrix. Potential mechanisms for the weaker effect of grassland fragmentation in forest-dominated landscapes
are (1) that the forest matrix is more heterogeneous and contains more resources, (2) that small grassland patches in a matrix
dominated by arable land suffer more from negative edge effects or (3) that the arable matrix constitutes a stronger barrier
to dispersal between populations. Regardless of the mechanisms, our results show that there are general effects of matrix
land use across landscapes and regions, and that landscape management that increases matrix quality can be a complement to
habitat restoration and re-creation in fragmented landscapes. 相似文献
6.
Effects of patch attributes, barriers, and distance between patches on the distribution of a rock-dwelling rodent (Lagidium viscacia) 总被引:1,自引:0,他引:1
We tested whether size of habitat patches and distance between patches are sufficient to predict the distribution of the mountain
vizcacha Lagidium viscacia a large, rock-dwelling rodent of the Patagonian steppe Argentina, or whether information on other patch and landscape characteristics
also is required. A logistic regression model including the distance between rock crevices and depth of crevices, distance
between a patch and the nearest occupied patch, and whether or not there was a river separating it from the nearest occupied
patch was a better predictor of patch occupancy by mountain vizcachas than was a model based only on patch size and distance
between patches. Our results indicate that a simple metapopulation analysis based on size of habitat patches and distance
between patches may not provide an accurate representation of regional population dynamics if patches vary in habitat quality
independently of patch size and features in the matrix alter connectivity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
Anette Edvardsen Rune Halvorsen Ann Norderhaug Oddvar Pedersen Knut Rydgren 《Landscape Ecology》2010,25(7):1071-1083
Habitat specificity analysis provides a tool for partitioning landscape species diversity on landscape elements by separating
patches with many rare specialist species from patches with the same number of species, all of which are common generalists
and thus provide information of relevance to conservation goals at regional and national levels. Our analyses were based upon
species data from 2201 patch elements in SE Norwegian modern agricultural landscapes. The context used for measuring habitat
specificity strongly influences the results. In general the gamma diversity contribution and core habitat specificity calculated
from the patch data set were correlated. High values for both measures were observed for woodland, pastures and road verges
whereas midfield islets and boundary transitional types were ranked low, as opposed to findings in traditional, extensively
managed agricultural landscapes. This is due to our study area representing intensively used agricultural landscape elements
holding a more trivial species composition, in addition to ruderals being favoured by fertility and disturbance, a finding
also being supported by the semi-natural affiliation index. Results obtained by use of checklist data from the same study
area diverged from patch data. Caution is needed in interpretation of habitat specificity results obtained from checklist
data, because modern agricultural landscapes contain several land types which are seldom surveyed by botanists, thus being
under-represented in the data set. We propose the use of core habitat specificity and gamma diversity contribution in parallel
to obtain a value neutral diversity assessment that addresses patch uniqueness and other properties of conservation interests. 相似文献
8.
Bradley J. Cosentino Robert L. Schooley Christopher A. Phillips 《Landscape Ecology》2010,25(10):1589-1600
Habitat area and isolation have been useful predictors of species occupancy and turnover in highly fragmented systems. However,
habitat quality also can influence occupancy dynamics, especially in patchy systems where habitat selection can be as important
as stochastic demographic processes. We studied the spatial population dynamics of Chrysemys picta (painted turtle) in a network of 90 wetlands in Illinois, USA from 2007 to 2009. We first evaluated the relative influence
of metapopulation factors (area, isolation) and habitat quality of focal patches on occupancy and turnover. Next, we tested
the effect of habitat quality of source patches on occupancy and turnover at focal patches. Turnover was common with colonizations
(n = 16) outnumbering extinctions (n = 10) between the first 2 years, and extinctions (n = 16) outnumbering colonizations (n = 3) between the second 2 years. Both metapopulation and habitat quality factors influenced C. picta occupancy dynamics. Colonization probability was related positively to spatial connectivity, wetland area, and habitat quality
(wetland inundation, emergent vegetation cover). Extinction probability was related negatively to wetland area and emergent
vegetation cover. Habitat quality of source patches strongly influenced initial occupancy but not turnover patterns. Because
habitat quality for freshwater turtles is related to wetland hydrology, a change from drought to wet conditions during our
study likely influenced distributional shifts. Thus, effects of habitat quality of source and focal patches on occupancy can
vary in space and time. Both metapopulation and habitat quality factors may be needed to understand occupancy dynamics, even
for species exhibiting patchy population structures. 相似文献
9.
Conservationists, managers, and land planners are faced with the difficult task of balancing many issues regarding humans
impacts on natural systems. Many of these potential impacts arise from local-scale and landscape-scale changes, but such changes
often covary, which makes it difficult to isolate and compare independent effects arising from humans. We partition multi-scale
impacts on riparian forest bird distribution in 105 patches along approximately 500 km of the Madison and Missouri Rivers,
Montana, USA. To do so, we coupled environmental information from local (within-patch), patch, and landscape scales reflecting
potential human impacts from grazing, invasive plant species, habitat loss and fragmentation, and human development with the
distribution of 28 terrestrial breeding bird species in 2004 and 2005. Variation partitioning of the influence of different
spatial scales suggested that local-scale vegetation gradients explained more unique variation in bird distribution than did
information from patch and landscape scales. Partitioning potential human impacts revealed, however, that riparian habitat
loss and fragmentation at the patch and landscape scales explained more unique variation than did local disturbances or landscape-scale
development (i.e., building density in the surrounding landscape). When distribution was correlated with human disturbance,
local-scale disturbance had more consistent impacts than other scales, with species showing consistent negative correlations
with grazing but positive correlations with invasives. We conclude that while local vegetation structure best explains bird
distribution, managers concerned with ongoing human influences in this system need to focus more on mitigating the effects
of large-scale disturbances than on more local land use issues.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Modeling patch occupancy: Relative performance of ecologically scaled landscape indices 总被引:1,自引:1,他引:0
In fragmented landscapes, the likelihood that a species occupies a particular habitat patch is thought to be a function of
both patch area and patch isolation. Ecologically scaled landscape indices (ESLIs) combine a species’ ecological profile,
i.e., area requirements and dispersal ability, with indices of patch area and connectivity. Since their introduction, ESLIs
for area have been modified to incorporate patch quality. ESLIs for connectivity have been modified to incorporate niche breadth,
which may influence a species’ ease in crossing the non-habitat matrix between patches. We evaluated the ability of 4 ESLIs,
the original and modified indices of area and connectivity, to explain patterns in patch occupancy of 5 forest rodents. Occupancy
of eastern gray squirrels (Sciurus carolinensis), North American red squirrels (Tamiasciurus hudsconicus), fox squirrels (Sciurus niger), white-footed mice (Peromyscus leucopus), and eastern chipmunks (Tamias striatus) was modeled at 471 sites in 35 landscapes sampled from the upper Wabash River basin in Indiana. Models containing ESLIs
received support for gray squirrels, red squirrels, and chipmunks. Modified ESLIs were important in models for red squirrels.
However, none of the models demonstrated high predictive ability. Incorporating habitat quality and using surrogate measures
of dispersal can have important effects on model results. Additionally, different responses of species to area, isolation,
and habitat quality suggest that generalizing patterns of metapopulation dynamics was not justified, even across closely related
species. 相似文献
11.
James C. Beasley Zachary H. Olson Guha Dharmarajan Timothy S. EaganII Olin E. RhodesJr. 《Landscape Ecology》2011,26(7):937-950
Human land-use practices have dramatically altered the composition and configuration of native habitats throughout many ecosystems.
Within heterogeneous landscapes generalist predators often thrive, causing cascading effects on local biological communities,
yet there are few data to suggest how attributes of fragmentation influence local population dynamics of these species. We
monitored 25 raccoon (Procyon lotor) populations from 2004 to 2009 in a fragmented agricultural landscape to evaluate the influence of local and landscape habitat
attributes on spatial and temporal variation in demography. Our results indicate that agricultural ecosystems support increased
densities of raccoons relative to many other rural landscapes, but that spatial and temporal variation in demography exists
that is driven by non-agricultural habitat attributes rather than the availability of crops. At the landscape scale, both
density and population stability were positively associated with the size and contiguity of forest patches, while at the local
scale density was positively correlated with plant diversity and the density of tree cavities. In addition, populations occupying
forest patches with greater levels of plant diversity and stable water resources exhibited less temporal variability than
populations with limited plant species complexity or water availability. The proportion of populations comprised of females
was most strongly influenced by the availability of tree cavities and soft mast. Despite the abundance of mesopredators in
heterogeneous landscapes, our results indicate that all patches do not contribute equally to the regional abundance and persistence
of these species. Thus, a clear understanding of how landscape attributes contribute to variation in demography is critical
to the optimization of management strategies. 相似文献
12.
In fragmented landscapes, plant species persistence depends on functional connectivity in terms of pollen flow to maintain
genetic diversity within populations, and seed dispersal to re-colonize habitat patches following local extinction. Connectivity
in plants is commonly modeled as a function of the physical distance between patches, without testing alternative dispersal
vectors. In addition, pre- and post-dispersal processes such as seed production and establishment are likely to affect patch
colonization rates. Here, we test alternative models of potential functional connectivity with different assumptions on source
patch effects (patch area and species occupancy) and dispersal (relating to distance among patches, matrix composition, and
sheep grazing routes) against empirical patch colonization rates at the community level (actual functional connectivity),
accounting for post-dispersal effects in terms of structural elements providing regeneration niches for establishment. Our
analyses are based on two surveys in 1989 and in 2009 of 48 habitat specialist plants in 62 previously abandoned calcareous
grassland patches in the Southern Franconian Alb in Bavaria, Germany. The best connectivity model S
i
, as identified by multi-model inference, combined distance along sheep grazing routes including consistently and intermittently
grazed patches with mean species occupancy in 1989 as a proxy for pre-dispersal effects. Community-level patch colonization
rates depended to equal degrees on connectivity and post-dispersal process. Our study highlights that actual functional connectivity
of calcareous grassland communities cannot be approximated by structural connectivity based on physical distance alone, and
modeling of functional connectivity needs to consider pre- and post-dispersal processes. 相似文献
13.
Context
The habitat amount hypothesis has rarely been tested on plant communities. It remains unclear how habitat amount affect species richness in habitat fragments compared to island effects such as isolation and patch size.Objectives
How do patch size and spatial distribution compared to habitat amount predict plant species richness and grassland specialist plant species in small grassland remnants? How does sampling area affect the prediction of spatial variables on species richness?Methods
We recorded plant species density and richness on 131 midfield islets (small remnants of semi-natural grassland) situated in 27 landscapes in Sweden. Further, we tested how habitat amount, compared to focal patch size and distance to nearest neighbor predicted species density and richness of plants and of grassland specialists.Results
A total of 381 plant species were recorded (including 85 grassland specialist species). A combination of patch size and isolation was better in predicting both density and richness of species compared to habitat amount. Almost 45% of species richness and 23% of specialist species were explained by island biogeography parameters compared to 19 and 11% by the amount of habitat. A scaled sampling method increased the explanation level of island biogeography parameters and habitat amount.Conclusions
Habitat amount as a concept is not as good as island biogeography to predict species richness in small habitats. Priority in landscape planning should be on larger patches rather than several small, even if they are close together. We recommend a sampling area scaled to patch size in small habitats.14.
Threshold levels of habitat composition for the presence of the long-tailed tit (Aegithalos caudatus) in a boreal landscape 总被引:4,自引:0,他引:4
We assessed the habitat patch occupancy of a deciduous-mixed forest specialist, the long-tailed tit (Aegithalos caudatus), in a 1000 km2 conifer dominated landscape in relation to two landscape parameters, namely proportion and isolation of suitable habitat. Data from five consecutive spring seasons were used and within habitat variation controlled for. The occurrence of long-tailed tits was positively related to the amount of habitat within 1 km2 (p=0.0007) and negatively related to the distance between habitat patches (p<0.0001). When combined, the two variables explained >78% of the variation in local patch occupancy. There were distinct thresholds in these landscape variables for the probability of local long-tailed tit presence. In the model the probability increased from 0.1 to 0.8 when interpatch distance decreased from 500 to 100 m with 5% total habitat coverage. With a total proportion of 15% suitable habitat, the same probability jump occurred when interpatch distance changed from 900 to 500 m. The general importance of defined measurements and quantified threshold levels for species conservation and landscape management is discussed. 相似文献
15.
We evaluated the effects of aspen patch area and orientation (relative to North and an elevational gradient) on the early
breeding season abundance and species richness of migratory and resident birds in the northern ungulate winter range of the
Yellowstone ecosystem, USA. Using an information-theoretic model selection approach, we found patch area and basal area of
aspen to be the most important covariates for long distance migrants, and patch orientation relative to elevational gradient
the most important covariate for residents/short-distance migrants. Basal area of live aspen and aspen snags was marginally
important for both migratory strategies, likely because aspen snags are an important habitat for most cavity-nesting species.
Landscape ecological theory postulates passive interception of dispersing or migrating organisms by patches of suitable habitat.
Our results suggest that residents/short-distance migrants are intercepted by patches that are oriented perpendicular to the
elevational gradient of our study region resulting in greater abundances and species richness in those patches. However, long-distance
migrants appear to use aspen patches without regard to orientation, but rather to patch area. 相似文献
16.
John L. Orrock Gregory R. Curler Brent J. Danielson David R. Coyle 《Landscape Ecology》2011,26(10):1361-1372
The size, shape, and isolation of habitat patches can affect organism behavior and population dynamics, but little is known
about the relative role of shape and connectivity in affecting ecological communities at large spatial scales. Using six sampling
sessions from July 2001 until August 2002, we collected 33,685 arthropods throughout seven 12-ha experimental landscapes consisting
of clear-cut patches surrounded by a matrix of mature pine forest. Patches were explicitly designed to manipulate connectivity
(via habitat corridors) independently of area and edge effects. We found that patch shape, rather than connectivity, affected
ground-dwelling arthropod richness and beta diversity (i.e. turnover of genera among patches). Arthropod communities contained
fewer genera and exhibited less turnover in high-edge connected and high-edge unconnected patches relative to low-edge unconnected
patches of similar area. Connectivity, rather than patch shape, affected the evenness of ground-dwelling arthropod communities;
regardless of patch shape, high-edge connected patches had lower evenness than low- or high-edge unconnected patches. Among
the most abundant arthropod orders, increased richness in low-edge unconnected patches was largely due to increased richness
of Coleoptera, whereas Hymenoptera played an important role in the lower evenness in connected patches and patterns of turnover.
These findings suggest that anthropogenic habitat alteration can have distinct effects on ground-dwelling arthropod communities
that arise due to changes in shape and connectivity. Moreover, this work suggests that corridors, which are common conservation
tools that change both patch shape and connectivity, can have multiple effects on arthropod communities via different mechanisms,
and each effect may alter components of community structure. 相似文献
17.
Responses of Chilean forest birds to anthropogenic habitat fragmentation across spatial scales 总被引:1,自引:1,他引:0
Although it is recognized that anthropogenic forest fragmentation affects habitat use by organisms across multiple spatial
scales, there is uncertainty about these effects. We used a hierarchical sampling design spanning three spatial scales of
habitat variability (landscape > patch > within-patch) and generalized mixed-effect models to assess the scale-dependent responses
of bird species to fragmentation in temperate forests of southern Chile. The abundances of nine of 20 bird species were affected
by interactions across spatial scales. These interactions resulted in a limited effect of within-patch habitat structure on
the abundance of birds in landscapes with low forest cover, suggesting that suitable local habitats, such as sites with dense
understory cover or large trees, are underutilized or remain unused in highly fragmented landscapes. Habitat specialists and
cavity-nesters, such as tree-trunk foragers and tapaculos, were most likely to exhibit interactions across spatial scales.
Because providing additional sites with dense understory vegetation or large habitat trees does not compensate the negative
effect of the loss of forest area on bird species, conservation strategies should ensure the retention of native forest patches
in the mixed-use landscapes. 相似文献
18.
We conducted two studies on how highways affect their adjacent habitats by sampling carabid beetles (Coleoptera, Carabidae)
in patches of formerly continuous forest next to highways. (1) We sampled carabids at 14 highway intersections near Helsinki,
Finland. Each intersection (constructed 2–40 years ago) had two forested patches to study: a remnant (0.5–37.4 ha) and, isolated
from the remnant by an intersection lane, an islet (size 0.2–1.8 ha). Pitfall trap catch data (2301 carabids, 25 species)
showed that remnants hosted higher catches of three carabid species, and slightly higher species richness, than islets (patch-size
effect). Time since intersection construction had no apparent effect on carabids. Traffic volume along the intersection lane
determined the assemblage structure of carabids in dry patches, and the abundance of a forest carabid Calathus micropterus. Compared to moist patches, drier patches hosted lower catches of four generalist species; they also had different assemblages
of carabids (habitat-type effect). An interaction between patch size and habitat type for a forest generalist Pterostichus oblongopunctatus indicated that the patch-size effect was dependent on habitat type. (2) We examined possible dispersal of carabids among
forested patches that were separated by highway lanes in Drenthe, the Netherlands. We released 2696 marked individuals of
10 species, and recaptured 376 using dry pitfall traps. We found no evidence for inter-patch movement for nine forest species,
but 22 of 225 recaptured individuals of Poecilus versicolor, an eurytopic open-habitat species, had crossed the highway. Catches of seven forest species were also significantly lower
in the road verges, compared to the adjacent forests. These two studies suggest that (i) decreasing patch size negatively
affects forest-carabid catch and overall species richness, (ii) habitat type can affect the intensity of the patch-size effect,
(iii) carabid assemblages of forest fragments vary with traffic volume (which may be linked with urbanization), (iv) forest
carabids rarely cross highways, and (v) open habitats associated with road margins are dispersal barriers for forest carabids. 相似文献
19.
Effects of area and isolation of woodland patches on herbaceous plant species richness across Great Britain 总被引:5,自引:2,他引:5
Petit Sandrine Griffiths Leila Smart Simon S. Smith Geoff M. Stuart Rick C. Wright Simon M. 《Landscape Ecology》2004,19(5):463-471
Richness of Ancient Woodland Indicator plant species was analysed in 308 woodland patches that were surveyed during the Countryside Survey of Great Britain carried out in 1998. The Countryside Survey recorded vegetation plots and landscape structure in 569 stratified 1 km sample squares and developed a remotely-sensed land cover map of the UK. Using these datasets, we tested the hypothesis that Ancient Woodland Indicator species richness in woodland fragments was limited by patch area, shape and spatial isolation and that woodland patches located in the lowland region of Great Britain would respond differently than those in the upland region. The variation in Ancient Woodland Indicator species richness in the British lowlands (n = 218) was mainly explained by patch area and two measures of connectivity, the length of hedgerows and lines of trees in the 1 km square and the area of woodland within 500 m of the vegetation plot. By contrast, variation in Ancient Woodland Indicator species richness in the British uplands (n = 90) was related to Ellenberg scores of the vegetation communities sampled – a surrogate for habitat quality – and no significant effect of spatial structure was detected. It therefore appears that the degree of fragmentation of woodland in the British lowlands limits the distribution of Ancient Woodland Indicator species, while in the uplands, failed colonisation is a matter of habitat quality rather than a result of landscape structure.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
20.