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1.
With expansion of urban areas worldwide, migrating songbirds increasingly encounter fragmented landscapes where habitat patches
are embedded in an urban matrix, yet how migrating birds respond to urbanization is poorly understood. Our research evaluated
the relative importance of patch-level effects and body condition to movement behaviour of songbirds during migratory stopover
within an urban landscape. We experimentally relocated 91 migrant Swainson’s thrushes (Catharus ustulatus) fitted with 0.66 g radio-transmitters to seven forest patches that differed in area (0.7–38.4 ha) and degree of urbanization
within central Ohio, USA, May 2004–2007. Fine-scale movement rate of thrushes (n = 55) did not differ among urban forest sites, but birds in low energetic condition moved at higher rates, indicating an
energetically mediated influence on movement behaviour. In larger sites, Swainson’s thrushes (n = 59) had greater coarse-level movement during the first 3 days and utilized areas farther from forest edge, indicating stronger
influence by patch-level factors. Thrushes exhibited strong site tenacity, with only five individuals (7%) leaving release
patches prior to migratory departure. Movement outside the release patch only occurred at the smallest forest patches (0.7
and 4.5 ha), suggesting that these sites were too small to meet needs of some individuals. Swainson’s thrushes exhibited edge
avoidance and apparent area sensitivity within urban forest patches during stopover, implying that conservation of larger
patches within urban and other fragmented landscapes may benefit this species and other migrant forest birds. 相似文献
2.
Landscape pattern indices are common tools of landscape ecologists, affording comparisons of different study areas, or the
same study area at different times. Since the advent of popular index-calculating software, more landscapes can be analyzed
in short amounts of time, yet the behaviour of landscape pattern indices can vary for different contexts or data characteristics,
complicating interpretation. I applied a selected set of landscape pattern indices to fine-resolution (3 m) data representing
a highly fragmented landscape – Corn Belt Iowa agriculture – to investigate the performance of landscape pattern indices.
Indices measured pattern attributes that affect the viability of small mammal populations, namely habitat proportion and connectivity
and landscape grain size and heterogeneity. Results showed that the performance of indices for fine-resolution data can be
highly variable, depending upon data and contextual issues like the presence of linear elements and the amount of habitat.
For these Corn Belt landscapes good habitat proportions and patch sizes were small (commonly less than 10% and less than 1 ha,
respectively), and connectivity was variable depending on the measure. Aggregation and mean nearest neighbour indices performed
better than other connectivity indices. Fine-resolution data representing highly fragmented landscapes can raise difficulties
for indices of landscape configuration. Landscape pattern indices require improvement to perform better for increasingly available
fine-resolution data representing common landscape types. 相似文献
3.
Individual movement is a key process affecting the distribution of animals in heterogeneous landscapes. For specialist species in patchy habitat, a central issue is how dispersal distances are related to landscape structure. We compared dispersal distances for cactus bugs (Chelinidea vittiger) on two naturally fragmented landscapes (≤ 4% suitable habitat) with different matrix structures (i.e., vegetation height of nonsuitable habitat between suitable patches). Using mark-release-recapture studies, we determined that most transfers between cactus patches occurred during the mating season. Dispersal distances were reduced by > 50% on the landscape that had reduced structural connectivity due to relatively high matrix structure and low patch density. An experiment with detailed movement pathways demonstrated that greater matrix structure decreased mean step lengths, reduced directionality, and thus decreased net displacement by > 60%. However, habitat edges between two matrix elements that differed substantially in resistance to movement were completely permeable. Therefore, the difference in distributions of dispersal distances between the two landscapes mainly reflected the average resistance of matrix habitat and not the level of matrix heterogeneity per se. Our study highlights the merits of combining estimates of dispersal distances with insights on mechanisms from detailed movement pathways, and emphasizes the difficulty of treating dispersal distances of species as fixed traits independent of landscape structure. 相似文献
4.
Loss of connectivity is one of the main causes of decreases in habitat availability and, thus, in species abundance and occurrence
in fragmented landscapes. It is therefore important to measure habitat connectivity for conservation purposes, but there are
several difficulties in quantifying connectivity, including the need for species movement behavioral data and the existence
of few consistent indices to describe such data. In the present study, we used a graph theoretical framework to measure habitat
availability, and we evaluate whether this variable is adequate to explain the occurrence pattern of an Atlantic rainforest
bird (Pyriglena leucoptera, Thamnophilidae). The playback technique was used to parameterize the connectivity component of habitat availability indices
and to determine the presence or absence of the study species in forest patches. Patch- and landscape-level habitat availability
indices were considered as explanatory variables. Two of these were landscape-level indices, which varied in terms of how
inter-patch connections are defined, using either a binary or probabilistic approach. This study produced four striking results.
First, even short open gaps may disrupt habitat continuity for P. leucoptera. Second, the occurrence of P. leucoptera was positively affected by habitat availability. Third, proper measures of this explanatory variable should account for the
landscape context around the focal patch, emphasizing the importance of habitat connectivity. Finally, habitat availability
indices should consider probabilistic and not binary inter-patch connections when intending to explain the occurrence of bird
species in fragmented landscapes. We discuss some conservation implications of our results, stressing the advantages of an
ecologically scaled graph theoretical framework. 相似文献
5.
How should we measure landscape connectivity? 总被引：9，自引：0，他引：9
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
6.
Context
Theory predicts that habitat loss and fragmentation may have drastic consequences on species’ interactions. To date, however, little empirical evidence exists on the strength of interspecific competition in shaping animal communities in fragmented landscapes.Objectives
Our aim was to measure the degree of ongoing competitive interference between species in fragmented landscapes. Our model system was the community of ground-dwelling rodents in deciduous woodlands in central Italy, composed of a habitat generalist species (Apodemus sylvaticus) and two forest specialists (Apodemus flavicollis and Myodes glareolus). Our objectives were to test whether species were segregated among forest patches and whether spatial segregation was determined by interspecific competition or habitat and resource availability.Methods
We surveyed the populations inhabiting 29 woodland patches in a highly fragmented landscape using a capture-mark-recapture protocol, capturing >4500 individuals. First we modelled species’ distribution as a function of habitat, resource availability and landscape variables. The second stage of our analyses involved measuring the response of vital rate parameters (body mass, reproduction, survival, recruitment, population density) to competitor density.Results
The relative distribution of species reflected a spatial segregation of habitat generalists and specialists according to habitat quality, cover and connectivity. Interspecific competition mainly affected individual level vital rates, whereas we found no substantial effects at the population level.Conclusions
Competitive exclusion of specialist species by generalist species was occurring. However, when compared to other factors such as habitat connectivity and resource availability, interspecific competition played a relatively minor role in shaping the studied community.7.
Landscape features that promote animal movement contribute to functional habitat connectivity. Factors that affect the use of landscape features, such as predation risk, may alter functional connectivity. We identify factors important to functional habitat connectivity by quantifying movement patterns of the Santa Rosa beach mouse (Peromyscus polionotus leucocephalus) in relation to landscape features and by examining how ambient perceived predation risk, which is altered by moon phase, interacts with landscape features. We use track paths across the sand to relate the probability that beach mice cross gaps between vegetation patches to gap width, patch quality, landscape context and moon phase. Overall activity levels were lower during full versus new moon nights, demonstrating that beach mice respond negatively to moonlight. Gap crossing was more likely during new moon nights (25 % of gaps crossed vs. 7 % during full moon nights), and across narrower gaps (<8.38 m) that led to larger vegetation patches (>11.75 m2). This study suggests that vegetation recovery is necessary for functional connectivity in post-hurricane landscapes commonly inhabited by beach mice and provides initial guidelines for restoring landscape connectivity. More broadly, this study highlights the importance of considering predation risk when quantifying landscape connectivity, as landscape features that facilitate connectivity when predation risk is low may be ineffective if predation risk increases over time or across space. 相似文献
8.
Roland F. Graf Stephanie Kramer-Schadt Néstor Fernández Volker Grimm 《Landscape Ecology》2007,22(6):853-866
Inter-patch connectivity can be strongly influenced by topography and matrix heterogeneity, particularly when dealing with
species with high cognitive abilities. To estimate dispersal in such systems, simulation models need to incorporate a behavioral
component of matrix effects to result in more realistic connectivity measures. Inter-patch dispersal is important for the
persistence of capercaillie (Tetrao urogallus) in central Europe, where this endangered grouse species lives in patchy populations embedded in a mountainous landscape.
We simulated capercaillie movements with an individual-based, spatially explicit dispersal model (IBM) and compared the resulting
connectivity measure with distance and an expert estimation. We used a landscape comprising discrete habitat patches, temporary
habitat, non-habitat forests, and non-habitat open land. First, we assumed that dispersing individuals have perfect knowledge
of habitat cells within the perceptual range (null model). Then, we included constraints to perception and accessibility,
i.e., mountain chains, open area and valleys (three sub-models). In a full model, all sub-models were included at once. Correlations
between the different connectivity measures were high (Spearman’s ρ > 0.7) and connectivity based on the full IBM was closer
to expert estimation than distance. For selected cases, simple distance differed strongly from the full IBM measure and the
expert estimation. Connectivity based on the IBM was strongly sensitive to the size of perceptual range with higher sensitivity
for the null model compared to the full model that included context dependent perceptual ranges. Our heuristic approach is
adequate for simulating movements of species with high cognitive abilities in strongly structured landscapes that influence
perception and permeability. 相似文献
9.
Graph-based analysis is a promising approach for analyzing the functional and structural connectivity of landscapes. In human-shaped
landscapes, species have become vulnerable to land degradation and connectivity loss between habitat patches. Movement across
the landscape is a key process for species survival that needs to be further investigated for heterogeneous human-dominated
landscapes. The common frog (Rana temporaria) was used as a case study to explore and provide a graph connectivity analysis framework that integrates habitat suitability
and dispersal responses to landscape permeability. The main habitat patches influencing habitat availability and connectivity
were highlighted by using the software Conefor Sensinode 2.2. One of the main advantages of the presented graph-theoretical
approach is its ability to provide a large choice of variables to be used based on the study’s assumptions and knowledge about
target species. Based on dispersal simulation modelling in potential suitable habitat corridors, three distinct patterns of
nodes connections of differing importance were revealed. These patterns are locally influenced by anthropogenic barriers,
landscape permeability, and habitat suitability. And they are affected by different suitability and availability gradients
to maximize the best possible settlement by the common frog within a terrestrial habitat continuum. The study determined the
key role of landscape-based approaches for identifying the “availability-suitability-connectivity” patterns from a local to
regional approach to provide an operational tool for landscape planning. 相似文献
10.
Context
Many connectivity metrics have been used to measure the connectivity of a landscape and to evaluate the effects of land-use changes and potential mitigation measures. However, there are still gaps in our understanding of how to accurately quantify landscape connectivity.
ObjectivesA number of metrics only measure between-patch connectivity, i.e. the connectivity between different habitat patches, which can produce misleading results. This paper demonstrates that the inclusion of within-patch connectivity is important for accurate results.
MethodsThe behavior of two metrics is compared: the Connectance Index (CONNECT), which measures only between-patch connectivity, and the effective mesh size (meff), which includes both within-patch and between-patch connectivity. The connectivity values of both metrics were calculated on a set of simulated landscapes. Twenty cities were then added to these landscapes to calculate the resulting changes in connectivity.
ResultsWe found that when using CONNECT counter-intuitive results occurred due to not including within-patch connectivity, such as scenarios where connectivity increased with increasing habitat loss and fragmentation. These counter-intuitive results were resolved when using meff. For example, landscapes with low habitat amount may be particularly sensitive to urban development, but this is not reflected by CONNECT.
ConclusionsApplying misleading results from metrics like CONNECT can have detrimental effects on natural ecosystems, because reductions in within-patch connectivity by human activities are neglected. Therefore, this paper provides evidence for the crucial need to consider the balance between within-patch connectivity and between-patch connectivity when calculating the connectivity of landscapes.
相似文献11.
Strong relations between population trends and spatial distribution have been suggested at the regional scale: declining species
should have more fragmented distributions because decline causes range retractions towards optimal habitats, whereas increasing
species should have more aggregated distributions, because colonization processes are constrained by distance. Most analyses
of the effects of land use changes on animal populations are diachronic studies of population dynamics or synchronic studies
of species habitat selection. Few studies take simultaneously into account temporal changes in habitat distribution and changes
in species spatial distribution. We applied the above rationale to the landscape scale and analysed how population declines,
increases or stability, as diagnosed in a long term study, correlate with population connectivity or fragmentation at that
scale. We used data on changes in faunal distribution and information on temporal changes in the vegetation in a Mediterranean
area that had been subjected to land abandonment. We found that species declining at the landscape scale had retracting fragmented
distributions and that expanding species had expanding continuous distributions. However, for the latter, we suggest that
the factors involved are related to landscape structure and not to dispersal mediated meta-population processes, which are
of little relevance at this local scale. We also show that even species that are numerically stable can show fragmentation
of their distribution and major spatial distribution shifts in response to land use changes, especially in species that have
low occurrence levels or that are associated with transitory habitats such as heterogeneous shrublands (e.g. Sylvia melanocephala). Studying the spatial structure of species distribution patterns at the landscape scale may provide information about population
declines and increases both at the regional and the landscape scale and can improve our understanding of short-term risks
of local extinction. 相似文献
12.
Habitat fragmentation often has negative consequences for genetic diversity, and thereby for the viability of populations.
However, these negative consequences might be counteracted by gene flow as the latter provides functional connectivity between
apparently isolated habitat fragments. Gene flow is itself influenced by landscape structure and composition, and it is therefore
important to understand the relationship between gene flow and landscape structure and composition. We used linear LAD regression
models to investigate the relationship between contemporary gene flow by pollen in the rare, insect-pollinated forest tree
Sorbus domestica and several landscape features. None of the landscape components—which included closed forest, deep valleys, open land and
settlements—proved to be an impermeable barrier to gene flow by pollen. We found evidence that settlements, large open areas,
and a pronounced topography increased long-distance gene flow in the landscape as compared to a random model including all
possible gene flow trajectories. These results are encouraging from a conservation view, as gene flow in species pollinated
by generalist insects seems to provide functional connectivity and may help to maintain genetic diversity in rare plant species
in fragmented landscapes. 相似文献
13.
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
14.
We studied the effects of anthropogenic edges on predation and parasitism of forest bird nests in an agriculturally fragmented
landscape and a continuously forested landscape in Ontario, Canada. Nesting data were collected at 1937 nests across 10 species
in the fragmented landscape from 2002–2008, and 464 nests across 4 species in the continuously forested landscape from 2006–2008.
Brood parasitism only occurred in the fragmented landscape, and was positively related to the proportion of rural grassland
and row crop habitats within 500-m of nests. Daily nest survival was negatively related to the density of roads within 500-m
of nests in the fragmented landscape, but was not influenced by distance to anthropogenic edge in either landscape. Predation
rates were higher in the fragmented landscape for Ovenbird and Rose-breasted Grosbeak nests, but did not differ between landscapes
for Veery and American Redstart nests. Uniformly high predation in the fragmented landscape may be a result of (1) matrix
predators that penetrate deep (>300 m) into the forest interior, or (2) the additive effect of forest-dependent and matrix-associated
predators that results in high predation pressure in both edge and interior habitats. Further research focused on the identification
of nest predators, their population dynamics, and habitat use is required to understand the underlying mechanisms leading
to uniformly high nest predation in fragmented landscapes. 相似文献
15.
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
16.
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
17.
Studies on the distribution of mammalian carnivores in fragmented landscapes have focused mainly on structural aspects such
as patch and landscape features; similarly, habitat connectivity is usually associated with landscape structure. The influence
of food resources on carnivore patch use and the important effect on habitat connectivity have been overlooked. The aim of
this study is to evaluate the relative importance of food resources on patch use patterns and to test if food availability
can overcome structural constraints on patch use. We carried out a patch-use survey of two carnivores: the beech marten (Martes foina) and the badger (Meles meles) in a sample of 39 woodland patches in a fragmented landscape in central Italy. We used the logistic model to investigate
the relative effects on carnivore distribution of patch, patch neighbourhood and landscape scale variables as well as the
relative abundance of food resources. Our results show how carnivore movements in fragmented landscapes are determined not
only by patch/landscape structure but also by the relative abundance of food resources. The important take-home message of
our research is that, within certain structural limits (e.g. within certain limits of patch isolation), by modifying the relative
amount of resources and their distribution, it is possible to increase suitability in smaller/relatively isolated patches.
Conversely, however, there are certain thresholds above which an increase in resources will not achieve high probability of
presence. Our findings have important and generalizable consequences for highly fragmented landscapes in areas where it may
not be possible to increase patch sizes and/or reduce isolation so, for instance, forest regimes that will increase resource
availability could be implemented.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
18.
In agricultural landscapes many plant species are limited to the network of landscape elements that are not used for agricultural
production. This habitat is fragmented in space and time due to anthropogenic, biotic and abiotic factors. Therefore, plant
populations are spatially sub-divided and their persistence might be dependent on the spatial dynamics in the network of local
populations. Dispersal characteristics and seed bank persistence are main determinants of colonization ability which in turn
is a key determinant of metapopulation viability. We propose a conceptual model that relates plant population dynamics to
habitat quality, configuration and dynamics. In this model, the habitat is arranged as a network of suitable and unsuitable
patches,and the distribution of the patches is assumed to be dynamic in time. Based on dispersal and seed bank characteristics
four plant strategies are distinguished:species having either long (> 100 m) or short (< 100m) distance dispersal and either
a long (> 5 yr)or short (< 5 yr) term persistent seed bank. We expect that species with contrasting strategies have different
survival probabilities in landscapes with contrasting habitat arrangement in space and time. We found few empirical studies
for testing the hypotheses based on the model. Therefore the relation between landscapes and plant survival needs to be further
explored,especially the quantitative aspects. We propose an iterative process of empirical and modelling research to determine
this relation and to define management options for multifunctional farms in which biodiversity is one of the land use aims.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Matthew J. Smith Matthew G. Betts Graham J. Forbes Daniel G. Kehler Maryse C. Bourgeois Stephen P. Flemming 《Landscape Ecology》2011,26(5):709-721
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
20.
Ecological processes such as plant–animal interactions have a critical role in shaping the structure and function of ecosystems,
but little is known of how such processes are modified by changes in landscape structure. We investigated the effect of landscape
change on mistletoe parasitism in fragmented agricultural environments by surveying mistletoes on eucalypt host trees in 24
landscapes, each 100 km2 in size, in south-eastern Australia. Landscapes were selected to represent a gradient in extent (from 60% to 2% cover) and
spatial pattern of remnant wooded vegetation. Mistletoes were surveyed at 15 sites in each landscape, stratified to sample
five types of wooded elements in proportion to their relative cover. The incidence per landscape of box mistletoe (Amyema miquelii), the most common species, was best explained by the extent of wooded cover (non-linear relationship) and mean annual rainfall.
Higher incidence occurred in landscapes with intermediate levels of cover (15–30%) and higher rainfall (>500 mm). Importantly,
a marked non-linear decline in the incidence of A. miquelii in low-cover landscapes implies a disproportionate loss of this species in remaining wooded vegetation, greater than that
attributable to decreasing forest cover. The most likely mechanism is the effect of landscape change on the mistletoebird
(Dicaeum hirundinaceum), the primary seed-dispersal vector for A. miquelii. Our results are consistent with observations that habitat fragmentation initially enhances mistletoe occurrence in agricultural
environments; but in this region, when wooded vegetation fell below a threshold of ~15% landscape cover, the incidence of
A. miquelii declined precipitously. Conservation management will benefit from greater understanding of the components of landscape structure
that most influence ecological processes, such as mistletoe parasitism and other plant–animal mutualisms, and the critical
stages in such relationships. This will facilitate action before critical thresholds are crossed and cascading effects extend
to other aspects of ecosystem function. 相似文献