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1.
ContextIn heterogeneous landscapes, local patterns of community structure are a product of the habitat size and condition within a patch interacting with adjacent habitat patches of varying composition and quantity. While evidence for local versus landscape factors have been found in terrestrial biomes, support for such multi-scale effects shaping marine ecological communities is equivocal.ObjectivesWe investigated whether within-patch habitat condition can override seascape context to explain the community structure of macroalgae-associated reef fishes across a tropical seascape.MethodsWe mapped the distribution and abundance of a diverse family of reef fishes (Labridae) occupying macroalgae meadows within a tropical reef ecosystem, and using best-subsets model selection, investigated the potential for habitat structural connectivity and/or local habitat quality for predicting variations in fish community structure across the seascape.ResultsLocal habitat quality (canopy structure, hard habitat complexity) and area of coral-dominated habitat within 500 m of a macroalgal meadow provided the best predictors of fish community structure. However, the specific importance of a given predictor varied with fish life history stage and functional trophic group. Interestingly, macroalgae meadow area was among the least important predictors.ConclusionsGiven the complex interplay between local habitat quality and spatial context effects on fish biodiversity, our study reveals the multi-scale predictors that should be used in spatial conservation and management approaches for tropical fish diversity. Moreover, our findings question the ubiquity of habitat area effects in patchy landscapes, and cautions against a sole reliance on habitat quantity in spatial management. 相似文献
2.
The methods for measuring landscape connectivity have never been compared or tested for their responses to habitat fragmentation. We simulated movement, mortality and boundary reactions across a wide range of landscape structures to analyze the response of landscape connectivity measures to habitat fragmentation. Landscape connectivity was measured as either dispersal success or search time, based on immigration into all habitat patches in the landscape. Both measures indicated higher connectivity in more fragmented landscapes, a potential for problematic conclusions for conservation plans. We introduce cell immigration as a new measure for landscape connectivity. Cell immigration is the rate of immigration into equal-sized habitat cells in the landscape. It includes both within- and between-patch movement, and shows a negative response to habitat fragmentation. This complies with intuition and existing theoretical work. This method for measuring connectivity is highly robust to reductions in sample size (i.e., number of habitat cells included in the estimate), and we hypothesize that it therefore should be amenable to use in empirical studies. The connectivity measures were weakly correlated to each other and are therefore generally not comparable. We also tested immigration into a single patch as an index of connectivity by comparing it to cell immigration over the landscape. This is essentially a comparison between patch-scale and landscape-scale measurement, and revealed some potential for patch immigration to predict connectivity at the landscape scale. However, this relationship depends on the size of the single patch, the dispersal characteristics of the species, and the amount of habitat in the landscape. We conclude that the response of connectivity measures to habitat fragmentation should be understood before deriving conclusions for conservation management. 相似文献
3.
Habitat loss and associated fragmentation effects are well-recognised threats to biodiversity. Loss of functional connectivity (mobility, gene flow and demographic continuity) could result in population decline in altered habitat, because smaller, isolated populations are more vulnerable to extinction. We tested whether substantial habitat reduction plus fragmentation is associated with reduced gene flow in three ??decliner?? woodland-dependent bird species (eastern yellow robin , weebill and spotted pardalote) identified in earlier work to have declined disproportionately in heavily fragmented landscapes in the Box-Ironbark forest region in north-central Victoria, Australia. For these three decliners, and one ??tolerant?? species (striated pardalote) , we compared patterns of genetic diversity, relatedness, effective population size, sex-ratios and genic (allele frequency) differentiation among landscapes of different total tree cover, identified population subdivision at the regional scale, and explored fine-scale genotypic (individual-based genetic signature) structure. Unexpectedly high genetic connectivity across the study region was detected for ??decliner?? and ??tolerant?? species. Power analysis simulations suggest that moderate reductions in gene flow should have been detectable. However, there was evidence of local negative effects of reduced habitat extent and structural connectivity: slightly lower effective population sizes, lower genetic diversity, higher within-site relatedness and altered sex-ratios (for weebill and eastern yellow robin) in 10 × 10?km ??landscapes?? with low vegetation cover. We conclude that reduced structural connectivity in the Box-Ironbark ecosystem may still allow sufficient gene flow to avoid the harmful effects of inbreeding in our study species. Although there may still be negative consequences of fragmentation for demographic connectivity, the high genetic connectivity of mobile bird species in this system suggests that reconnecting isolated habitat patches may be less important than increasing habitat extent and/or quality if these need to be traded off. 相似文献
4.
Landscape connectivity is critical to species persistence in the face of habitat loss and fragmentation. Graph theory is a
well-defined method for quantifying connectivity that has tremendous potential for ecology, but its application has been limited
to a small number of conservation scenarios, each with a fixed proportion of habitat. Because it is important to distinguish
changes in habitat configuration from changes in habitat area in assessing the potential impacts of fragmentation, we investigated
two metrics that measure these different influences on connectivity. The first metric, graph diameter, has been advocated
as a useful measure of habitat configuration. We propose a second area-based metric that combines information on the amount
of connected habitat and the amount of habitat in the largest patch. We calculated each metric across gradients in habitat
area and configuration using multifractal neutral landscapes. The results identify critical connectivity thresholds as a function
of the level of fragmentation and a parallel is drawn between the behavior of graph theory metrics and those of percolation
theory. The combination of the two metrics provides a means for targeting sites most at risk of suffering low potential connectivity
as a result of habitat fragmentation. 相似文献
5.
ContextHabitat characteristics are often equated with habitat function for animals. However, in heterogeneous landscapes, similar habitat types occur in different environmental contexts. In the marine realm, landscape studies have been confined to particular environments, rather than encompassing entire seascapes, due to incompatible sampling methods required in different situations. ObjectivesWe examined the interactive structuring effects of local habitat characteristics and environmental context on assemblage composition. MethodsWe used a single technique—remote underwater video census—to explore the importance of habitat type (biotic structural components, substrate, and depth) and environmental context (marine vs estuarine) in structuring juvenile fish assemblages throughout an entire coastal region. In this model system, a range of structural habitat types were present in both estuarine and marine contexts. ResultsThe 1315 video surveys collected show a clear hierarchy in the organisation of juvenile fish communities, with assemblages first distinguished by environmental context, then by habitat type. Marine and estuarine mangroves contained entirely different assemblages, and likewise for rocky reefs and submerged aquatic vegetation. Our results suggest that two functionally different ‘seascape nursery’ types exist at local scales within a single region, defined by their context. ConclusionsThe context of a location can be of greater significance in determining potential habitat function than what habitat-forming biota and substrates are present, and apparently similar habitat types in different contexts may be functionally distinct. These findings have important implications for local-scale management and conservation of juvenile fish habitats, particularly in regard to offsetting and restoration. 相似文献
6.
Maintaining and restoring connectivity among high-quality habitat patches is recognized as an important goal for the conservation
of animal populations. To provide an efficient measure of potential connectivity pathways in heterogeneous landscapes, least-cost
route analysis has been combined with graph-theoretical techniques. In this study we use spatially explicit least-cost habitat
graphs to examine how matrix quality and spatial configuration influence assessments of habitat connectivity. We generated
artificial landscapes comprised of three landcover types ranked consistently from low to high quality: inhospitable matrix,
hospitable matrix, and habitat. We controlled the area and degree of fragmentation of each landcover in a factorial experiment
for a total of 20 combinations replicated 100 times. In each landscape we compared eight sets of relative landcover qualities
(cost values of 1 for habitat, between 1.5 and 150 for hospitable matrix, and 3–10,000 for inhospitable matrix). We found
that the spatial location of least-cost routes was sensitive to differences in relative cost values assigned to landcover
types and that the degree of sensitivity depended on the spatial structure of the landscape. Highest sensitivity was found
in landscapes with fragmented habitat and between 20 and 50% hospitable matrix; sensitivity decreased as habitat fragmentation
decreased and the amount of hospitable matrix increased. As a means of coping with this sensitivity, we propose identifying
multiple low-cost routes between pairs of habitat patches that collectively delineate probable movement zones. These probable
movement zones account for uncertainty in least-cost routes and may be more robust to variation in landcover cost values. 相似文献
7.
In marine systems, seagrass meadows, which serve as essential nursery and adult habitat for numerous species, experience fragmentation through both human activity and environmental processes. Results from studies involving seagrass patch size and edge effects on associated fauna have shown that patchy seagrass habitats can be either beneficial or detrimental. One reason for the variable results might be the existence of ecological trade-offs for species that associate with seagrass habitats. Bay scallops, Argopecten irradians, are useful model organisms for studying the response of a semi-mobile bivalve to changes in seagrass seascapes—they exhibit a strong habitat association and seagrass offers a predation refuge at a cost of reduced growth. This study investigated the potential ecological survival–growth trade-off for bay scallops living within a seagrass seascape. Scallop growth was consistently fastest in bare sand and slowest at patch centers, and survival showed the opposite trend. Scallops in patch edges displayed intermediate growth and survival. Using models for minimizing mortality ( μ) to foraging ( f) ratios, the data suggests seagrass edge habitat offered similar value to patch centers. Further, investigations of core-area index suggest that small, complex patches might offer scallops a balance between predation risk and maximized growth. Taken in sum, these results suggest that edge habitats may benefit organisms like bay scallops by maximizing risk versus reward and maximizing edge habitat. 相似文献
8.
The erection of dams alters habitat and longitudinal stream connectivity for migratory diadromous and potamodromous fish species
and interrupts much of organismal exchange between freshwater and marine ecosystems. In the US, this disruption began with
colonial settlement in the seventeenth century but little quantitative assessment of historical impact on accessible habitat
and population size has been conducted. We used published surveys, GIS layers and historical documents to create a database
of 1356 dams, which was then analyzed to determine the historical timeline of construction, use and resultant fragmentation
of watersheds in Maine, US. Historical information on the anadromous river herring was used to determine natural upstream
boundaries to migration and establish total potential alewife spawning habitat in nine watersheds with historic populations.
Dams in Maine were constructed beginning in 1634 and by 1850 had reduced accessible lake area to less than 5% of the virgin
892 km 2 habitat and 20% of virgin stream habitat. There is a near total loss of accessible habitat by 1860 that followed a west-east
pattern of European migration and settlement. Understanding historic trends allows current restoration targets to be assessed
and prioritized within an ecosystem-based perspective and may inform expectations for future management of oceanic and freshwater
living resources. 相似文献
9.
Habitat connectivity is an important element of functioning landscapes for mobile organisms. Maintenance or creation of movement
corridors is one conservation strategy for reducing the negative effects of habitat fragmentation. Numerous spatial models
exist to predict the location of movement corridors. Few studies, however, have investigated the effectiveness of these methods
for predicting actual movement paths. We used an expert-based model and a resource selection function (RSF) to predict least-cost
paths of woodland caribou. Using independent data for model evaluation, we found that the expert-based model was a poor predictor
of long-distance animal movements; in comparison, the RSF model was effective at predicting habitat selection by caribou.
We used the Path Deviation Index (PDI), cumulative path cost, and sinuosity to quantitatively compare the spatial differences
between inferred caribou movement paths and predicted least-cost paths, and quasi-random null models of directional movement.
Predicted movement paths were on average straighter than inferred movement paths for collared caribou. The PDI indicated that
the least-cost paths were no better at predicting the inferred paths than either of two null models—straight line paths and
randomly generated paths. We found statistically significant differences in cumulative cost scores for the main effects of
model and path type; however, post-hoc comparisons were non-significant suggesting no difference among inferred, random, and
predicted least cost paths. Paths generated from an expert based cost surface were more sinuous than those premised on the
RSF model, but neither differed from the inferred path. Although our results are specific to one species, they highlight the
importance of model evaluation when planning for habitat connectivity. We recommend that conservation planners adopt similar
techniques when validating the effectiveness of movement corridors for other populations and species. 相似文献
10.
Habitat fragmentation is expected to disrupt dispersal, and thus we explored how patch metrics of landscape structure, such as percolation thresholds used to define landscape connectivity, corresponded with dispersal success on neutral landscapes. We simulated dispersal as either a purely random process (random direction and random step lengths) or as an area-limited random walk (random direction, but movement limited to an adjacent cell at each dispersal step) and quantified dispersal success for 1000 individuals on random and fractal landscape maps across a range of habitat abundance and fragmentation. Dispersal success increased with the number of cells a disperser could search (m), but poor dispersers (m<5) searching via area-limited dispersal on fractal landscapes were more successful at locating suitable habitat than random dispersers on either random or fractal landscapes. Dispersal success was enhanced on fractal landscapes relative to random ones because of the greater spatial contagion of habitat. Dispersal success decreased proportionate to habitat loss for poor dispersers (m=1) on random landscapes, but exhibited an abrupt threshold at low levels of habitat abundance (p<0.1) for area-limited dispersers (m<10) on fractal landscapes. Conventional metrics of patch structure, including percolation, did not exhibit threshold behavior in the region of the dispersal threshold. A lacunarity analysis of the gap structure of landscape patterns, however, revealed a strong threshold in the variability of gap sizes at low levels of habitat abundance (p<0.1) in fractal landscapes, the same region in which abrupt declines in dispersal success were observed. The interpatch distances or gaps across which dispersers must move in search of suitable habitat should influence dispersal success, and our results suggest that there is a critical gap-size structure to fractal landscapes that interferes with the ability of dispersers to locate suitable habitat when habitat is rare. We suggest that the gap structure of landscapes is a more important determinant of dispersal than patch structure, although both are ultimately required to predict the ecological consequences of habitat fragmentation. 相似文献
11.
Although abrupt changes (i.e. thresholds) have been precisely defined in simulated landscapes, such changes in the structure
of real landscapes are not well understood. We tested for threshold occurrence in three common deforestation patterns in the
Brazilian Amazon: small properties regularly distributed along roads (fishbone), irregularly distributed small properties
(independent settlements), and large properties. We analyzed differences between real deforestation patterns, and tested the
capacity of simulated landscape with different aggregation degrees to predict threshold occurrence. Three 8×8 km sites (replicates)
with more than 90% of forest in 1984 and less than 30% in 1998 were selected/simulated for each deforestation pattern. Thresholds
were observed for fishbone and large property patterns, especially when considering the connectivity index, although threshold
incidences were more frequently observed in simulated landscapes. The capacity of simulated landscapes to predict the exact
threshold point in real landscapes was limited, even when considering highly aggregate simulations. However, the general trend
in landscape structural changes was similar in real and simulated landscapes. Thresholds occurred at the beginning of the
deforestation for mean patch size and at an intermediate stage, corresponding to the percolation threshold, for connectivity,
isolation and fragmentation. Threshold behavior for connectivity index might suggest that the survival of strictly forest
species will sharply decrease when the proportion of forest reach values <0.60, indicating that conservation efforts should
be done to maintain forest cover above this limit. Significant differences observed among the real deforestation patterns,
especially in patch isolation and number of fragments, can have significant consequences for conservation. The independent
settlement pattern is, without a doubt, the least favorable of them, resulting in a higher level of fragmentation, whereas
the large property and fishbone patterns may be less detrimental if connectivity among the remnant forest patches is preserved. 相似文献
12.
Management of tropical marine environments calls for interdisciplinary studies and innovative methodologies that consider processes occurring over broad spatial scales. We investigated relationships between landscape structure and reef fish assemblage structure in the US Virgin Islands. Measures of landscape structure were transformed into a reduced set of composite indices using principal component analyses (PCA) to synthesize data on the spatial patterning of the landscape structure of the study reefs. However, composite indices (e.g., habitat diversity) were not particularly informative for predicting reef fish assemblage structure. Rather, relationships were interpreted more easily when functional groups of fishes were related to individual habitat features. In particular, multiple reef fish parameters were strongly associated with reef context. Fishes responded to benthic habitat structure at multiple spatial scales, with various groups of fishes each correlated to a unique suite of variables. Accordingly, future experiments should be designed to test functional relationships based on the ecology of the organisms of interest. Our study demonstrates that landscape-scale habitat features influence reef fish communities, illustrating promise in applying a landscape ecology approach to better understand factors that structure coral reef ecosystems. Furthermore, our findings may prove useful in design of spatially-based conservation approaches such as marine protected areas (MPAs), because landscape-scale metrics may serve as proxies for areas with high species diversity and abundance within the coral reef landscape. 相似文献
13.
Landscape composition and configuration, often termed as habitat loss and fragmentation, are predicted to reduce species population
viability, partly due to the restriction of movement in the landscape. Unfortunately, measuring the effects of habitat loss
and fragmentation on functional connectivity is challenging because these variables are confounded, and often the motivation
for movement by target species is unknown. Our objective was to determine the independent effects of landscape connectivity
from the perspective of a mature forest specialist—the northern flying squirrel ( Glaucomys sabrinus). To standardize movement motivation, we translocated 119 squirrels, at varying distances (0.18–3.8 km) from their home range
across landscapes representing gradients in both habitat loss and fragmentation. We measured the physical connectedness of
mature forest using an index of connectivity (landscape coincidence probability). Patches were considered connected if they
were within the mean gliding distance of a flying squirrel. Homing success increased in landscapes with a higher connectivity
index. However, homing time was not strongly predicted by habitat amount, connectivity index, or mean nearest neighbour and
was best explained as a simple function of sex and distance translocated. Our study shows support for the independent effects
of landscape configuration on animal movement at a spatial scale that encompasses several home ranges. We conclude that connectivity
of mature forest should be considered for the conservation of some mature forest specialists, even in forest mosaics where
the distinction between habitat and movement corridors are less distinct. 相似文献
14.
The distribution of the northern brown bandicoot ( Isoodon macrourus), a medium-sized ground-dwelling marsupial, was examined in habitat fragments within the urban landscape of the city of Brisbane,
Australia. From surveys conducted in 68 fragments, bandicoots were found to be present in 33 (49%) despite widespread habitat
loss and fragmentation. Logistic regression analysis revealed that of 13 measured independent variables, functional connectivity
was the only factor that significantly predicted the presence of bandicoots within fragments, with connectivity positively
correlated with the likelihood of occupation. Functional connectivity was equated to the likelihood of bandicoot immigration
into the focal fragment from the nearest occupied fragment, based on the estimated resistance to movement offered by the intervening
matrix. Within Brisbane, riparian habitat fragments typically have a relatively high level of functional connectivity, as
thin strips of vegetation fringing waterways serve as corridors between larger riparian areas and facilitate the movement
of bandicoots between patches. Analyses based on the Akaike Information Criterion revealed that the optimal model based on
landscape context variables was convincingly better supported by the data than the optimal model produced from fragment characteristics.
However, it is important to examine both internal attributes of habitat fragments and external features of the surrounding
landscape when modelling the distribution of ground-dwelling fauna in urban environments, or other landscapes with a highly
variable matrix. As urban centres throughout the world expand, it is crucial that the ecology of local wildlife be considered
to ensure functional connection is maintained between habitat patches, especially for the conservation of species that are
highly susceptible to fragmentation. 相似文献
15.
Management of tropical marine environments calls for interdisciplinary studies and innovative methodologies that consider processes occurring over broad spatial scales. We investigated relationships between landscape structure and reef fish assemblage structure in the US Virgin Islands. Measures of landscape structure were transformed into a reduced set of composite indices using principal component analyses (PCA) to synthesize data on the spatial patterning of the landscape structure of the study reefs. However, composite indices (e.g., habitat diversity) were not particularly informative for predicting reef fish assemblage structure. Rather, relationships were interpreted more easily when functional groups of fishes were related to individual habitat features. In particular, multiple reef fish parameters were strongly associated with reef context. Fishes responded to benthic habitat structure at multiple spatial scales, with various groups of fishes each correlated to a unique suite of variables. Accordingly, future experiments should be designed to test functional relationships based on the ecology of the organisms of interest. Our study demonstrates that landscape-scale habitat features influence reef fish communities, illustrating promise in applying a landscape ecology approach to better understand factors that structure coral reef ecosystems. Furthermore, our findings may prove useful in design of spatially-based conservation approaches such as marine protected areas (MPAs), because landscape-scale metrics may serve as proxies for areas with high species diversity and abundance within the coral reef landscape. 相似文献
16.
We introduce a novel approach to building corridors in spatial conservation prioritization. The underlying working principle is the use of a penalty structure in an iterative algorithm used for producing a spatial priority ranking. The penalty term aims to prevent loss or degradation of structural connections, or, equivalently, to promote to a higher rank landscape elements that are required to keep networks connected. The proposed method shows several convenient properties: (1) it does not require a priori specification of habitat patches, end points or related thresholds, (2) it does not rely on resistance coefficients for different habitats, (3) it does not require species targets, and (4) the cost of additional connectivity via corridors can be quantified in terms of habitat quality lost across species. Corridor strength and width parameters control the trade-off between increased structural connectivity via corridors and other considerations relevant to conservation planning. Habitat suitability or dispersal suitability layers used in the analysis can be species specific, thus allowing analysis both in terms of structural and functional connectivity. The proposed method can also be used for targeting habitat restoration, by identifying areas of low habitat quality included in corridors. These methods have been implemented in the Zonation software, and can be applied to large scale and high resolution spatial prioritization, effectively integrating corridor design and spatial conservation prioritization. Since the method operates on novel principles and combines with a large number of features already operational in Zonation, we expect it to be of utility in spatial conservation planning. 相似文献
17.
Landscape connectivity can be viewed from two perspectives that could be considered as extremes of a gradient: functional
connectivity (refers to how the behavior of a dispersing organism is affected by landscape structure and elements) and structural
connectivity (depends on the spatial configuration of habitat patches in the landscape like vicinity or presence of barriers).
Here we argue that dispersal behavior changes with landscape configuration stressing the evolutionary dimension that has often
been ignored in landscape ecology. Our working hypothesis is that the functional grain of resource patches in the landscape
is a crucial factor shaping individual movements, and therefore influencing landscape connectivity. Such changes are likely
to occur on the short-term (some generations). We review empirical studies comparing dispersal behavior in landscapes differing
in their fragmentation level, i.e., with variable resource grain. We show that behavioral variation affecting each of the
three stages of the dispersal process (emigration, displacement or transfer in the matrix, and immigration) is indeed likely
to occur according to selective pressures resulting from changes in the grain of the landscape (mortality or deferred costs).
Accordingly, landscape connectivity results from the interaction between the dispersal behavior of individuals and the grain
of each particular landscape. The existence of this interaction requires that connectivity estimates (being based on individual-based
models, least cost distance algorithms, and structural connectivity metrics or even Euclidian distance) should be carefully
evaluated for their applicability with respect to the required level of precision in species-specific and landscape information. 相似文献
18.
Although many empirical and theoretical studies have elucidated the effects of habitat fragmentation on the third trophic level, little attention has been paid to the impacts of this driver on more generalist groups of non-hymenopteran parasitoids. Here, we used the highly-diverse group of tachinid flies as an alternative model to test the effects of landscape fragmentation on insect parasitoids. Our aims were: (i) to evaluate the relative importance of habitat area and connectivity losses and their potential interaction on tachinid diversity, (ii) to test whether the effects of habitat fragmentation changes seasonally, and (iii) to further assess the effect of habitat diversity on tachinid diversity and whether different parasitoid-host associations modify the species richness response to fragmentation. In 2012 a pan-trap sampling was conducted in 18 semi-natural grasslands embedded in intensive agricultural landscapes along statistically orthogonal gradients of habitat area, connectivity and habitat diversity. We found an interaction between habitat area and connectivity indicating that tachinid abundance and species richness were more negatively affected by habitat loss in landscapes with low rather than with relatively large habitat connectivity. Although tachinid communities exhibited large within-year species turnover, we found that the effects of landscape fragmentation did not change seasonally. We found that habitat diversity and host association did not affect tachinid species diversity. Our results have important implications for biodiversity conservation as any attempts to mitigate the negative effects of habitat loss need to take the general level of habitat connectivity in the landscape into account. 相似文献
19.
Habitat fragmentation is considered a major cause of biodiversity loss, both on terrestrial and marine environments. Understanding the effects of habitat fragmentation on the structure and dynamics of natural communities is extremely important to support management actions for biodiversity conservation. However, the effects of habitat fragmentation on marine communities are still poorly understood. Here we evaluated whether habitat fragmentation affects the structure of epifaunal communities in the sublittoral zone, in the northern coast of São Paulo state, Brazil. Five experimental landscapes were constructed, each one forming a large continuous patch. After 4 weeks, each landscape was cut on three patches of different sizes. Epifaunal macroinvertebrate communities were sampled at the edge and interior of experimental landscapes before manipulation to evaluate edge effects. After four more weeks, communities from the three patch sizes were also sampled to evaluate patch size effects. We compared the diversity of communities at different levels of fragmentation by total abundance, rarefied taxon richness, Shannon–Wiener diversity index, Simpson’s dominance index, and abundance of dominant taxa. Higher taxon richness and gastropod abundance were recorded in the patch edges, but no significant differences were found among patch sizes. We found a significant effect of habitat fragmentation, with lower abundances of Gammaridea (the dominant taxon), Ophyuroidea, and Pycnogonida after the experimental fragmentation. Lower abundances of dominant taxa resulted in higher diversity and lower dominance in fragmented landscapes when compared to integral, pre-manipulation landscapes. Our results suggest that fragmentation of landscapes in the system studied can reduce dominance, and that even small patch sizes can be important for the conservation of macroinvertebrate diversity. 相似文献
20.
Habitat amount and fragmentation usually covary in natural and simulated landscapes. A common way of distinguishing between
their effects is to take the residuals of the fragmentation index or indices regressed on habitat amount, as the index of
habitat fragmentation. We used data on prairie songbird relative abundances from southern Alberta, Canada to compare this
approach with the reverse: taking the residuals of habitat amount regressed on habitat fragmentation as the index of habitat
amount. We used generalized additive models (GAMs) to derive residuals, and modeled relative abundances using linear mixed-effects
models. The modeling approach used strongly influenced the statistical results. Using residuals as an index of fragmentation
resulted in an apparently stronger effect of habitat amount relative to habitat fragmentation. In contrast, habitat fragmentation
appeared more influential than habitat amount when residuals were used as an index of habitat amount. Regression of residuals
may eliminate statistical collinearity, but cannot distinguish between the ecological effects of habitat amount and fragmentation.
Habitat fragmentation may therefore have a larger effect on species than previously studies have shown, but experimental manipulations
of underlying mechanisms are ultimately required to address this debate. 相似文献
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