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1.
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.2.
Habitat fragmentation strongly affects insect species diversity and community composition, but few studies have examined landscape
effects on long term development of insect communities. As mobile consumers, insects should be sensitive to both local plant
community and landscape context. We tested this prediction using sweep-net transects to sample insect communities for 8 years
at an experimentally fragmented old-field site in northeastern Kansas, USA. The site included habitat patches undergoing secondary
succession, surrounded by a low turf matrix. During the first 5 years, plant richness and cover were measured in patches.
Insect species richness, total density, and trophic diversity increased over time on all transects. Cover of woody plants
and perennial forbs increased each year, adding structural complexity to successional patches and potentially contributing
to increased insect diversity. Within years, insect richness was significantly greater on transects through large successional
patches (5000 m2) than on transects through fragmented arrays of 6 medium-sized (total area 1728 m2) or 15 small (480 m2) patches. However, plant cover did not differ among patch types and was uncorrelated with insect richness within years. Insect
richness was strongly correlated with insect density, but trophic and α diversities did not differ among patch types, indicating
that patch insect communities were subsets of a common species pool. We argue that differences in insect richness resulted
from landscape effects on the size of these subsets, not patch succession rates. Greater insect richness on large patches
can be explained as a community-level consequence of population responses to resource concentration. 相似文献
3.
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
4.
Streambed landscapes: evidence that stream invertebrates respond to the type and spatial arrangement of patches 总被引：9，自引：1，他引：8
Palmer Margaret A. Swan Christopher M. Nelson Karen Silver Pamela Alvestad Rachel 《Landscape Ecology》2000,15(6):563-576
The availability and spatial arrangement of habitat patches are known to strongly influence fauna in terrestrial ecosystems. The importance of patch arrangement is not well-studied within running-water systems where flow-induced movements of patches and of fauna could decouple habitat characteristics and faunal habitat preferences. Using small, stream-dwelling invertebrates, we asked if fauna in such systems can distinguish among patch types and if patch arrangement at their `landscape scale' (i.e., within a streambed across which they move and forage) can be linked to faunal abundance. We quantified the spatial distribution of sand and leaf patches at multiple sites on a streambed at regular intervals over a 1
yr period, estimated faunal abundance in the two patch types, and experimentally determined if faunal colonization varied among leaf patches that were similar structurally but differed in their potential microbial food resources. We show that despite their small size and limited swimming abilities, these stream invertebrates did respond to patch type, that specific characteristics of an individual patch influenced faunal colonization, and that the spatial arrangement of patches on the streambed was linked to field abundances. Larval chironomids and adult copepods were more abundant in leaves than in sand and preferentially colonized leaf patches made with rapidly decomposing leaves that harbored higher microbial (bacteria and fungi) abundances over leaf patches with more refractory leaves and lower microbial abundances. Further, statistical models that included spatially-explicit data on patch arrangement (e.g., patch contagion, distance between patches) explained significantly more variation in faunal abundance, than models that included only nonspatial information (e.g., date, time since last flood). Despite the fact that these fauna live in a highly dynamic environment with variable flow rates during the year, unstable patch configurations, and seasonal changes in total abundance, our findings suggest a need for aquatic ecologists to test the hypothesis that small-scale landscape attributes within streams (e.g., leaf patch aggregation) may be important to faunal dynamics. If patch aggregation has negative consequences for stream biota, streambed `landscapes' may be fundamentally different from many terrestrial landscapes due to the inherent connectivity provided by the water and the over-riding importance of patch edges. Regardless of these differences, our findings suggest that the spatial configuration of patches in a landscape may have consequences for fauna even in highly dynamic systems, in which patches move and fauna periodically experience high levels of passive dispersal. 相似文献
5.
Context
A recent hypothesis, the habitat amount hypothesis, predicts that the total amount of habitat in the landscape can replace habitat patch size and isolation in studies of species richness in fragmented landscapes.Objectives
To test the habitat amount hypothesis by first evaluating at which spatial scale the relationship between species richness in equal-sized sample quadrats and habitat amount was the strongest, and then test the importance of spatial configuration of habitat—measured as local patch size and isolation—when habitat amount was taken into account.Methods
A quasi-experimental setup with 20 habitat patches of dry calcareous grasslands varying in patch size, patch isolation and habitat amount at the landscape scale was established in the inner Oslo fjord, Southern Norway. We recorded species richness of habitat specialists of vascular plants in equal-sized sample quadrats and analysed the relationship between species richness, habitat amount in the landscape and patch size and isolation.Results
Although the total amount of habitat in a 3 km-radius around the local patch was positively related to species richness in the sample quadrats, local patch size had an additional positive effect, and the effect of patch size was higher when the amount of habitat within the 3 km-radius was high than when it was low.Conclusions
In our study system of specialist vascular plants in dry calcareous grasslands, we do not find support for the habitat amount hypothesis.6.
Despite good theoretical knowledge about determinants of plant species richness in mosaic landscapes, validations based on
complete surveys are scarce. We conducted a case study in a highly fragmented, traditional agricultural landscape. In 199
patches of 20 representative multi-patch-plots (MPPs, 1 ha) we recorded a total of 371 plant species. In addition to an additive
partitioning of species diversity at the (a) patch- and (b) MPP-scale, we adopted the recently proposed ‘specificity’ measure
to quantify the contribution of a spatial subunit to landscape species richness (subunit-to-landscape-contribution, SLC).
SLC-values were calculated at both scales with respect to various spatial extents. General regression models were used to
quantify the relative importance of hypothesis-driven determinants for species richness and SLC-values.
At the patch scale, habitat type was the main determinant of species richness, followed by area and elongated shape. For SLC-values,
area was more important than habitat type, and its relevance increased with the extent of the considered landscape. Influences
of elongated shape and vegetation context were minor. Differences between habitat types were pronounced for species richness
and also partly scale-dependent for SLC-values.
Relevant predictors at the MPP-scale were nonlinear habitat richness, the gradient from anthropogenic to seminatural vegetation,
and the proportions of natural vegetation and rare habitats. Linear elements and habitat configuration did not contribute
to species richness and SLC. Results at the MPP-scale were in complete accordance with the predictions of the mosaic concept.
Hence, our study represents its first empirical validation for plant species diversity in mosaic landscapes. 相似文献
7.
Assessing and predicting the species richness of a complex landscape remains a problem because there is no simple scaling function of species richness in a heterogeneous environment. Furthermore, the potential value of an area for biodiversity conservation may depend on which, rather than how many, species the area contains. This paper shows how we can objectively evaluate the contribution of an area, e.g., a habitat patch, to larger-scale plant species richness, e.g., a landscape composed of patches of several habitat types, and how we can test hypotheses that attempt to explain this contribution. We quantified the concept of habitat specificity to assess the proportion of each observed plant population that is concentrated within a given spatial element. A case study of a biodiversity-monitoring program in the Swiss Canton of Aargau showed that the relative contribution of the three main types of land use to the overall species richness differed strongly between higher taxa (vascular plants and molluscs). However, the type of data, i.e., presence-absence or abundance, was not important. Resampling of the plant data suggested that stratification provided an unbiased estimate of relative specificity, whereas unstratified sampling caused bias even for large samples. In a second case study of vascular plants in an agricultural landscape in central Switzerland, we tested whether the type, size or shape of a landscape element can predict its contribution to the species richness of the landscape. Habitat types that were less frequently disturbed contributed more per m2 to landscape species richness than more frequently disturbed ones. Contrary to expectation, patch size was negatively correlated to specificity per m2 for arable fields, whereas patch shape appeared to be unrelated to the specificity per m2 both for arable fields and for meadows. The specificity approach provides a solution to the problem of scaling species richness and is ideally suited for testing hypotheses on the effect of landscape structure on landscape species richness. Specificity scores can easily be combined with measures of other aspects of rarity to assess the contribution of a spatial element to conservation goals formulated at regional, national or global level. 相似文献
8.
Additive partitioning of plant species diversity in an agricultural mosaic landscape 总被引：14，自引：1，他引：13
In this paper, we quantify the effects of habitat variability and habitat heterogeneity based on the partitioning of landscape species diversity into additive components and link them to patch-specific diversity. The approach is illustrated with a case study from central Switzerland, where we recorded the presence of vascular plant species in a stratified random sample of 1'280 quadrats of 1 m2 within a total area of 0.23 km2. We derived components of within- and between-community diversity at four scale levels (quadrat, patch, habitat type, and landscape) for three diversity measures (species richness, Shannon index, and Simpson diversity). The model implies that what we measure as within-community diversity at a higher scale level is the combined effect of heterogeneity at various lower levels. The results suggest that the proportions of the individual diversity components depend on the habitat type and on the chosen diversity aspect. One habitat type may be more diverse than another at patch level, but less diverse at the level of habitat type. Landscape composition apparently is a key factor for explaining landscape species richness, but affects evenness only little. Before we can test the effect of landscape structure on landscape species richness, several problems will have to be solved. These include the incorporation of neighbourhood effects, the unbiased estimation of species richness components, and the quantification of the contribution of a landscape element to landscape species richness. 相似文献
9.
Context
Habitat loss and habitat fragmentation negatively affect amphibian populations. Roads impact amphibian species through barrier effects and traffic mortality. The landscape variable ‘accessible habitat’ considers the combined effects of habitat loss and roads on populations.Objectives
The aim was to test whether accessible habitat was a better predictor of amphibian species richness than separate measures of road effects and habitat loss. I assessed how accessible habitat and local habitat variables determine species richness and community composition.Methods
Frog and tadpole surveys were conducted at 52 wetlands in a peri-urban area of eastern Australia. Accessible habitat was delineated using a highway. Regressions were used to examine relationships between species richness and eleven landscape and local habitat variables. Redundancy analysis was used to examine relationships between community composition and accessible habitat and local habitat variables.Results
Best-ranked models of species richness included both landscape and local habitat variables. There were positive relationships between species richness and accessible habitat and distance to the highway, and uncertain relationships with proportion cover of native vegetation and road density. There were negative relationships between species richness and concreted wetlands and wetland electrical conductivity. Four species were positively associated with accessible habitat, whereas all species were negatively associated with wetland type.Conclusions
Barrier effects caused by the highway and habitat loss have negatively affected the amphibian community. Local habitat variables had strong relationships with species richness and community composition, highlighting the importance of both availability and quality of habitat for amphibian conservation near major roads.10.
Bird assemblages in forest fragments within Mediterranean mosaics created by wild fires 总被引：1，自引：1，他引：0
The role of habitat heterogeneity as a key factor in determining species pools in habitat mosaics has been acknowledged, but we still know little on the relative importance of the different ecological processes acting within such complex landscapes. We compared species richness and distribution in forest fragments imbedded in shrub-lands to those in continuous forests or in continuous shrublands. We examined the consistency of our data with the predictions of two hypotheses: 1) the Habitat fragmentation hypothesis which states that fragmentation has negative effects on the species from the original continuous habitat; 2) the Habitat supplementation /complementation hypothesis which stipulates that the presence of a matrix habitat around the fragments will mitigate negative effects on the species from the original habitat (supplementation) or allow the presence of species that depend on the presence of both the fragment and matrix habitats (complementation). We show that: 1) species richness in forest fragments did not differ from species richness in segments of continuous forests of equal area; 2) the bird community of forest fragments got impoverished in some forest species but a higher proportion of species common in continuous forests were not affected by fragmentation; 3) fragment communities had a significant proportion of common species that were scarce in, or absent from both continuous forests and shrublands. While, a few forest species supported predictions from the fragmentation hypothesis, occurrence patterns observed in several other species were consistent with either the supplementation or the complementation hypotheses. Our results suggest that there is no single hypothesis that properly captures the consequences of a shift from continuous forests to a mosaic of forest fragments and shrublands and that different ecological mechanisms act in conjunction to determine species pools in habitat mosaics. Habitat heterogeneity at a local scale appears a key factor in maintaining bird diversity in fire driven Mediterranean landscapes. 相似文献
11.
Heike Kappes Kurt Jordaens Frederik Hendrickx Jean-Pierre Maelfait Luc Lens Thierry Backeljau 《Landscape Ecology》2009,24(5):685-697
Habitat fragmentation is a major cause for species loss, but its effect on invertebrates with low active dispersal power,
like terrestrial gastropods, has rarely been studied. Such species can not cross a hostile habitat matrix, for which the predictions
of island theory, such as positive relations between species richness and patch size, should apply. In order to test this
prediction, we studied gastropod species diversity by assessing gastropod assemblage characteristics from 35 sites in 19 fragments
of deciduous old-growth forests in the Lower Rhine Embayment, Germany. Assemblages differed between larger (≥700 ha) and smaller
forests (<400 ha), those of large forests held a higher percentage of forest species. Although α-diversity was similar between
the two forest size classes, small forests often comprised matrix species, resulting in a higher β-diversity. Edge effects
on the species richness of matrix species were noticeable up to 250 m into the forest. Hierarchical partitioning revealed
that distance to disturbances (external edge, internal edges like roads) explained most assemblage variables, whereas forest
size and woodland cover within a 1 km radius from the sites explained only a few assemblage variables. Densities of two forest-associated
species, Discus rotundatus and Arion fuscus, decreased with forest size. Yet, forest size was positively correlated with richness of typical forest species and densities
of Limax cinereoniger. The latter species seems to need forests of >1,000 ha, i.e., well above the size of most fragments. In conclusion, the prediction
is valid only for forest species. The response to fragmentation is species specific and seems to depend on habitat specialization
and macroclimatic conditions.
Jean-Pierre Maelfait: Deceased. 相似文献
12.
Context
Butterflies have been continuously declining for several decades in Europe due to many factors, such as farming intensification. Rural landscapes have undergone dramatic changes leading to homogenized landscapes.Objectives
In this study, we investigated how landscape composition, structure and connectivity impact butterfly communities according to their ecological and biological traits.Methods
We made use of 5669 Lepidoptera surveys performed at 4525 distinct locations in lowland Central France. We considered 19 ecological groups based on habitat specialization, mobility, diet, voltinism or overwintering strategy. Generalized linear mixed-effect models were used to relate the species richness of these groups to landscape variables defined in circular zones with radius from 250 m to 5 km.Results
Richness of most species groups co-varied with landscape variables, with the exception of mobile, imago-overwintering, monophagous and polyphagous species. Habitat proportion explained more variation in butterfly diversity than habitat connectivity or habitat diversity. Moreover, the best proportion models were generally found for the 250-m circular zones. Thirteen species groups were disfavored by cropland amount. Except for forest specialists and high mobility group, no other group was more diverse in landscapes dominated by a single land cover type. Rather, for total diversity and 14 groups, species richness peaked for forest proportions varying between 40 and 80%, and for total diversity and nine groups for grassland proportions ranging from 30 to 60%.Conclusions
These results indicate that landscape homogenization is contributing to the ongoing decline in butterflies, and support preserving and (re)creating mosaics of grasslands and forests.13.
Klaus Henle Claudia Andres Detlef Bernhard Annegret Grimm Pavel Stoev Nikolay Tzankov Martin Schlegel 《Landscape Ecology》2017,32(1):131-145
Context
Species show different sensitivity to habitat loss and fragmentation depending on their specialization. Populations of a species at the range margin are generally assumed to be more stenoecious than populations at the core of the distribution and should therefore be more sensitive to habitat fragmentation.Objectives
We evaluated the hypothesis that fragmentation effects species more strongly at the range periphery of their range compared to the core, resulting in lower genetic variability in comparable patch sizes and lower gene flow among populations.Methods
We compared the genetic diversity and structure of five sand lizard (Lacerta agilis) populations at the margin of its range in Bulgaria and of 11 populations at the core of its distribution in Germany. We based the analysis on microsatellites, comprising 15 loci in Bulgaria and 12 in Germany.Results
All diversity indices declined with patch size. For medium-sized patches all diversity indices were lower at the range periphery compared to the core, with two of them being significant. AICc based model selection showed strong support for core/periphery and patch size effects for observed and expected heterozygosity but only a patch size effect for allelic richness. There was no isolation-by-distance and each sampled population was allocated to a separate cluster with high probability for both countries, indicating that all populations are (almost) completely isolated.Conclusion
Our study indicates an increased sensitivity of a species to fragmentation at the periphery compared to the core of its distribution. This differential sensitivity should be accounted for when prioritizing species based on their fragmentation sensitivity in landscape management.14.
The study measured landscape level diversity of the understory plants of mature, upland forests in north-central Wisconsin USA. Habitat types were used to segregate the landscape along a moisture-nutrient gradient. Forty sites that had closed canopies, had been undisturbed for at least 20 years, and were at least 8 ha in size were used. The percent cover of groundlayer species was ocularly estimated in 12–18 randomly located, one meter square plots in June and August, 1995. Shrub cover was estimated by the line intercept method. Alpha, beta and gamma diversity were determined for early and late summer periods separately. Gamma diversity was quantified using a new method, affinity analysis, which generates a list of modal and outlier sites and calculates mosaic diversity, a measure of landscape complexity. Generally, communities in the middle of the moisture-nutrient gradient were modal, whereas those at the mesic end of the gradient were outlier. Mosaic diversity values were very similar for early summer and late summer (2.88±0.04, 2.95±0.03, respectively), but was much higher for both periods combined (3.95±0.07). Whittaker's Index (beta diversity) revealed varying rates of species turnover along presumed moisture and nutrient gradients, whereas species densities and richness were relatively constant among habitat types. A one-way analysis of variance of Shannon-Weaver values found no significant differences among habitat types (p0.05). Regional diversity mainly resulted from high beta values which appears to be primarily a function of the moisture gradient. The other factors influencing compositional differences among sites are variation in site history, especially disturbance, with niche partitioning and differences in seed dispersal capacity having a minor influence. The affinity analysis method indicated that sampling once per season is inadequate, and that many types of sites are modal. This method for estimating gamma (landscape) diversity shows considerable promise, but information on the processes that produce outlier sites is needed to fully understand and use the results of this method. 相似文献
15.
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
16.
Context
Patch diversity, evenness and dominance are important metrics of landscape composition. They have been traditionally measured using indices based on Shannon’s information entropy (H) and Simpson’s concentration statistic (λ).
ObjectivesThe main objectives of this study are: (1) to show that the Lorenz curve is an appropriate framework to understand and measure patch dominance, evenness and diversity; (2) to show that Lorenz-compatible indices have better mathematical behavior than H-based and λ-based indices.
MethodsThirteen different hypothetical landscapes were created to assess landscape composition with the Lorenz curve and to compare the mathematical behavior of Lorenz-compatible indices with that of H-based and λ-based indices.
ResultsThe Lorenz curve is a suitable framework to understand and measure patch dominance, evenness and diversity due to four relevant equivalences: (1) patch dominance?=?the separation of the Lorenz curve from the 45-degree line of perfect patch evenness; (2) patch evenness?=?1 ? patch dominance; (3) patch diversity (eliminated by patch dominance)?=?patch richness?×?patch dominance; (4) patch diversity (preserved by patch evenness)?=?patch richness?×?patch evenness. Accordingly, patch diversity/patch richness?=?1???patch dominance and land-cover concentration?=?1/patch diversity.
ConclusionsLorenz-compatible indices have better mathematical behavior than H-based and λ-based indices, exhibiting greater coherence and objectivity when measuring patch dominance, evenness and diversity.
相似文献17.
Elsa Aggemyr Alistair G. Auffret Love Jädergård Sara A. O. Cousins 《Landscape Ecology》2018,33(12):2273-2284
Context
Understanding how landscape patterns affect species diversity is of great importance in the fields of biogeography, landscape ecology and conservation planning, but despite the rapid advance in biodiversity analysis, investigations of spatial effects on biodiversity are still largely focused on species richness.Objectives
We wanted to know if and how species richness and species composition are differentially driven by the spatial measures dominating studies in landscape ecology and biogeography. As both measures require the same limited presence/absence information, it is important to choose an appropriate diversity measure, as differing results could have important consequences for interpreting ecological processes.Methods
We recorded plant occurrences on 112 islands in the Baltic archipelago. Species richness and composition were calculated for each island, and the explanatory power of island area and habitat heterogeneity, distance to mainland and structural connectivity at three different landscape sizes were examined.Results
A total of 354 different plant species were recorded. The influence of landscape variables differed depending on which diversity measure was used. Island area and structural connectivity determined plant species richness, while species composition revealed a more complex pattern, being influenced by island area, habitat heterogeneity and structural connectivity.Conclusions
Although both measures require the same basic input data, species composition can reveal more about the ecological processes affecting plant communities in fragmented landscapes than species richness alone. Therefore, we recommend that species community composition should be used as an additional standard measure of diversity for biogeography, landscape ecology and conservation planning.18.
Balázs Deák Orsolya Valkó Péter Török András Kelemen Ádám Bede András István Csathó Béla Tóthmérész 《Landscape Ecology》2018,33(7):1117-1132
Context
Landscape and habitat filters are major drivers of biodiversity of small habitat islands by influencing dispersal and extinction events in plant metapopulations.Objectives
We assessed the effects of landscape and habitat filters on the species richness, abundance and trait composition of grassland specialist and generalist plants in small habitat islands. We studied traits related to functional spatial connectivity (dispersal ability by wind and animals) and temporal connectivity (clonality and seed bank persistence) using model selection.Methods
We sampled herbaceous plants, landscape (local and regional isolation) and habitat filters (inclination, woody encroachment and disturbance) in 82 grassland islands in Hungary.Results
Isolation decreased the abundance of good disperser specialist plants due to the lack of directional vectors transferring seeds between suitable habitat patches. Clonality was an effective strategy, but persistent seed bank did not support the survival of specialist plants in isolated habitats. Generalist plants were unaffected by landscape filters due to their wide habitat breadth and high propagule availability. Clonal specialist plants could cope with increasing woody encroachment due to their high resistance against environmental changes; however, they could not cope with intensive disturbance. Steep slopes providing environmental heterogeneity had an overall positive effect on species richness.Conclusions
Specialist plants were influenced by the interplay of landscape filters influencing their abundance and habitat filters affecting species richness. Landscape filtering by isolation influenced the abundance of specialist plants by regulating seed dispersal. Habitat filters sorted species that could establish and persist at a site by influencing microsite availability and quality.19.
The factors responsible for widespread declines of grassland birds in the United States are not well understood. This study,
conducted in the short-grass prairie of eastern Wyoming, was designed to investigate the relationship between variation in
habitat amount, landscape heterogeneity, prey resources, and spatial variation in grassland bird species richness. We estimated
bird richness over a 5-year period (1994–1998) from 29 Breeding Bird Survey locations. Estimated bird richness was modeled
as a function of landscape structure surrounding survey routes using satellite-based imagery (1996) and grasshopper density
and richness, a potentially important prey of grassland birds. Model specification progressed from simple to complex explanations
for spatial variation in bird richness. An information-theoretic approach was used to rank and select candidate models. Our
best model included measurements of habitat amount, habitat arrangement, landscape matrix, and prey diversity. Grassland bird
richness was positively associated with grassland habitat; was negatively associated with habitat dispersion; positively associated
with edge habitats; negatively associated with landscape matrix attributes that may restrict movement of grassland bird; and
positively related to grasshopper richness. Collectively, 62% of the spatial variation in grassland bird richness was accounted
for by the model (adj-R2 = 0.514). These results suggest that the distribution of grassland bird species is influenced by a complex mixture of factors
that include habitat area affects, landscape pattern and composition, and the availability of prey. 相似文献
20.
Aafke M. Schipper Kees Koffijberg Marije van Weperen Guido Atsma Ad M. J. Ragas A. Jan Hendriks Rob S. E. W. Leuven 《Landscape Ecology》2011,26(3):397-410
Understanding the driving forces behind the distribution of threatened species is critical to set priorities for conservation
measures and spatial planning. We examined the distribution of a globally threatened bird, the corncrake (Crex crex), in the lowland floodplains of the Rhine River, which provide an important breeding habitat for the species. We related
corncrake distribution to landscape characteristics (area, shape, texture, diversity) at three spatial scales: distinct floodplain
units (“floodplain scale”), circular zones around individual observations (“home range scale”), and individual patches (“patch
scale”) using logistic regression. Potential intrinsic spatial patterns in the corncrake data were accounted for by including
geographic coordinates and an autocovariate as predictors in the regression analysis. The autocovariate was the most important
predictor of corncrake occurrence, probably reflecting the strong conspecific attraction that is characteristic of the species.
Significant landscape predictors mainly pertained to area characteristics at the patch scale and the home range scale; the
probability of corncrake occurrence increased with potential habitat area, patch area, and nature reserve area. The median
potential habitat patch size associated with corncrake occurrence was 11.3 ha; 90% of the corncrake records were associated
with patches at least 2.2 ha in size. These results indicate that the corncrake is an area-sensitive species, possibly governed
by the males’ tendency to reside near other males while maintaining distinct territories. Our results imply that corncrake
habitat conservation schemes should focus on the preservation of sufficient potential habitat area and that existing management
measures, like delayed mowing, should be implemented in relatively large, preferably contiguous areas. 相似文献