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1.
Landscape connectivity is considered important for species persistence, but linkages among landscape populations (metalandscape connectivity) may be necessary to ensure the long-term viability of some migratory songbirds at a broader regional scale. Because of regional
source-sink dynamics, these species can maintain steady populations within extensively fragmented landscapes (landscape sinks)
owing to high levels of immigration from source landscapes. We undertook a modeling study to identify the conditions under
which immigration, an index of metalandscape connectivity, could rescue declining populations of songbirds in heavily disturbed
landscapes. In general, low to moderate levels of immigration (m = 0–20%) were sufficient to rescue species with low edge-sensitivity in landscapes where<70% habitat had been destroyed.
At the other extreme, moderate to high levels of immigration (m = 11–40%) were usually required to rescue highly edge-sensitive species in these same landscapes. Very high levels of immigration
(m>40%) were required to rescue highly edge-sensitive species in extensively fragmented landscapes that had lost >50% habitat,
or when any landscape lost ≥50% habitat gradually over a period of 100 or more years (r = 0.5% habitat lost/year). Paradoxically higher levels of immigration were thus necessary to offset population declines when
habitat was lost gradually than when it was lost quickly, where population response lagged behind landscape change. This implies
that the importance of metalandscape connectivity for population viability may not be fully appreciated in landscapes undergoing
rapid rates of change. Natural immigration rates for migratory songbirds match the very high levels (>40%) we found necessary
to sustain populations in heavily disturbed landscapes, which underscores the importance of metalandscape connectivity for
the continued persistence of many migratory songbirds in the face of widespread habitat loss and fragmentation. 相似文献
2.
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
3.
Can landscape indices predict ecological processes consistently? 总被引：36，自引：0，他引：36
The ecological interpretation of landscape patterns is one of the major objectives in landscape ecology. Both landscape patterns and ecological processes need to be quantified before statistical relationships between these variables can be examined. Landscape indices provide quantitative information about landscape pattern. Response variables or process rates quantify the outcome of ecological processes (e.g., dispersal success for landscape connectivity or Morisita's index for the spatial distribution of individuals). While the principal potential of this approach has been demonstrated in several studies, the robustness of the statistical relationships against variations in landscape structure or against variations of the ecological process itself has never been explicitly investigated. This paper investigates the consistency of correlations between a set of landscape indices (calculated with Fragstats) and three response variables from a simulated dispersal process across heterogeneous landscapes (cell immigration, dispersal success and search time) against variation in three experimental treatments (control variables): habitat amount, habitat fragmentation and dispersal behavior. I found strong correlations between some landscape indices and all three response variables. However, 68% of the statistical relationships were highly inconsistent and sometimes ambiguous for different landscape structures and for differences in dispersal behavior. Correlations between one landscape index and one response variable could range from highly positive to highly negative when derived from different spatial patterns. I furthermore compared correlation coefficients obtained from artificially generated (neutral) landscape models with those obtained from Landsat TM images. Both landscape representations produced equally strong and weak statistical relationships between landscape indices and response variables. This result supports the use of neutral landscape models in theoretical analyses of pattern-process relationships. 相似文献
4.
Since the fragmentation of natural habitats is one of the most serious problems for many endangered species, it is highly interesting to study the properties of fragmented landscapes. As a basic property, landscape connectivity and its effects on various ecological processes are frequently in focus. First, we discuss the relevance of some graph properties in quantifying connectivity. Then, we propose a method how to quantify the relative importance of habitat patches and corridors in maintaining landscape connectivity. Our combined index explicitly considers pure topological properties and topographical measures, like the quality of both patches (local population size) and corridors (permeability). Finally, for illustration, we analyze the landscape graph of the endangered, brachypterous bush-cricket Pholidoptera transsylvanica. The landscape contains 11 patches and 13 corridors and is situated on the Aggtelek Karst, NE-Hungary. We characterize the importance of each node and link of the graph by local and global network indices. We show how different measures of connectivity may suggest different conservation preferences. We conclude, accordingly to our present index, by identifying one specific habitat patch and one specific corridor being in the most critical positions in maintaining connectivity.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
5.
Comparison and development of new graph-based landscape connectivity indices: towards the priorization of habitat patches and corridors for conservation 总被引：11，自引：3，他引：11
The loss of connectivity of natural areas is a major threat for wildlife dispersal and survival and for the conservation of
biodiversity in general. Thus, there is an increasing interest in considering connectivity in landscape planning and habitat
conservation. In this context, graph structures have been shown to be a powerful and effective way of both representing the
landscape pattern as a network and performing complex analysis regarding landscape connectivity. Many indices have been used
for connectivity analyses so far but comparatively very little efforts have been made to understand their behaviour and sensitivity
to spatial changes, which seriously undermines their adequate interpretation and usefulness. We systematically compare a set
of ten graph-based connectivity indices, evaluating their reaction to different types of change that can occur in the landscape
(habitat patches loss, corridors loss, etc.) and their effectiveness for identifying which landscape elements are more critical
for habitat conservation. Many of the available indices were found to present serious limitations that make them inadequate
as a basis for conservation planning. We present a new index (IIC) that achieves all the properties of an ideal index according
to our analysis. We suggest that the connectivity problem should be considered within the wider concept of habitat availability,
which considers a habitat patch itself as a space where connectivity exists, integrating habitat amount and connectivity between
habitat patches in a single measure. 相似文献
6.
Uroy Léa Alignier Audrey Mony Cendrine Foltête Jean-Christophe Ernoult Aude 《Landscape Ecology》2021,36(9):2487-2504
Landscape Ecology - Landscape connectivity plays a key role in determining the persistence of species inhabiting fragmented habitat patches. In dynamic landscapes, most studies measure connectivity... 相似文献
7.
Metapopulation models are frequently used for analysing species–landscape interactions and their effect on structure and dynamic
of populations in fragmented landscapes. They especially support a better understanding of the viability of metapopulations.
In such models, the processes determining metapopulation viability are often modelled in a simple way. Animals’ dispersal
between habitat fragments is mostly taken into account by using a simple dispersal function that assumes the underlying process
of dispersal to be random movement. Species-specific dispersal behaviour such as a systematic search for habitat patches is
likely to influence the viability of a metapopulation. Using a model for metapopulation viability analysis, we investigate
whether such specific dispersal behaviour affects the predictions of ranking orders among alternative landscape configurations
rated regarding their ability to carry viable metapopulations. To incorporate dispersal behaviour in the model, we use a submodel
for the colonisation rates which allows different movement patterns to be considered (uncorrelated random walk, correlated
random walk with various degrees of correlation, and loops). For each movement pattern, the landscape order is determined
by comparing the resulting mean metapopulation lifetime Tm of different landscape configurations. Results show that landscape orders can change considerably between different movement
patterns. We analyse whether and under what circumstances dispersal behaviour influences the ranking orders of landscapes.
We find that the ‘competition between patches for migrants’ – i.e. the fact that dispersers immigrating into one patch are
not longer available as colonisers for other patches – is an important factor driving the change in landscape ranks. The implications
of our results for metapopulation modelling, planning and conservation are discussed. 相似文献
8.
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
9.
Ferenc Jordán Tibor Magura Béla Tóthmérész Vera Vasas Viktor Ködöböcz 《Landscape Ecology》2007,22(10):1527-1539
For many species, one important key to persistence is maintaining connectivity among local populations that allow for dispersal
and gene flow. This is probably true for carabid species (Coleoptera:Carabidae) living in the fragmented forests of the Bereg
Plain (NE Hungary and W Ukraine). Based on field data, we have drafted a landscape graph of the area representing the habitat
network of these species. Graph nodes and links represented two kinds of landscape elements: habitat (forest) patches and
corridors, respectively. The quality of habitat patches and corridors were ranked (from low (1) to high (4)), reflecting local
population sizes in the case of patches and estimated permeability in the case of corridors. We analysed (1) the positional
importance of landscape elements in maintaining the connectivity of the intact network, (2) the effect of inserting hypothetical
corridors into the network, (3) the effects of improving the quality of the existing corridors, and (4) how to connect every
patch in a cost-effective way. Our results set quantitative priorities for conservation practice by identifying important
corridors: what to protect, what to build and what to improve. Several network analytical techniques were used to account
for the directed (source-sink) and highly fragmented nature of the landscape graph. We provide conservation priority ranks
for the landscape elements and discuss the conditions for the use of particular network indices. Our study could be of extreme
relevance, since a new highway is being planned through the area. 相似文献
10.
Connectivity measures: a review 总被引：8，自引：3，他引：5
One of the central problems in contemporary ecology and conservation biology is the drastic change of landscapes induced by
anthropogenic activities, resulting in habitat loss and fragmentation. For many wild living species, local extinctions of
fragmented populations are common and recolonization is critical for regional survival. Successful recolonization depends
on the availability of dispersing individuals and the degree of landscape connectivity. The obvious implications of landscape
connectivity for conservation biology have led to a proliferation of connectivity measures. However, general relationships
between landscape connectivity and landscape structure are lacking, and so are the relationships between different connectivity
metrics. Consequently, there is a need to develop landscape metrics that more accurately characterize the landscape with an
emphasis on the underlying processes. Here we review various definitions of landscape connectivity, explain their mathematical
connotations, and make some unifying conclusions and suggestions for future research. 相似文献
11.
Landscape connectivity and animal behavior: functional grain as a key determinant for dispersal 总被引：2，自引：0，他引：2
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
12.
Yu-Huang Wang Kuoh-Cheng Yang Cara Lin Bridgman Liang-Kong Lin 《Landscape Ecology》2008,23(8):989-1000
Landscape connectivity is important in designing corridor and reserve networks. Combining genetic distances among individuals
with least-cost path (LCP) modelling helps to correlate indirect measures of gene flow with landscape connectivity. Applicability
of LCP modelling, however, is reduced if knowledge on dispersal pathways or routes is lacking. Therefore, we integrated habitat
suitability modelling into LCP analysis to avoid the subjectivity common in LCP analyses lacking knowledge on dispersal pathways
or routes. We used presence-only data and ecological niche factor analysis to model habitat suitability for the spiny rat,
Niviventer coninga, in a fragmented landscape of western Taiwan. We adapted the resultant habitat suitability map for incorporation into LCP
analyses. Slightly increased Mantel correlations indicated that a class-weighted suitability map better explained genetic
distances among individuals than did geographical distances. The integration of habitat suitability modelling into LCP analysis
can thus generate information on distribution of suitable habitats, on potential routes of dispersal, for placement of corridors,
and evaluate landscape connectivity.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
A comparison of metrics predicting landscape connectivity for a highly interactive species along an urban gradient in Colorado, USA 总被引：1，自引：1，他引：0
Many organisms persist in fragmented habitat where movement between patches is essential for long-term demographic and genetic
stability. In the absence of direct observation of movement, connectivity or isolation metrics are useful to characterize
potential patch-level connectivity. However, multiple metrics exist at varying levels of complexity, and empirical data on
species distribution are rarely used to compare performance of metrics. We compared 12 connectivity metrics of varying degrees
of complexity to determine which metric best predicts the distribution of prairie dog colonies along an urban gradient of
385 isolated habitat patches in Denver, Colorado, USA. We found that a modified version of the incidence function model including
area-weighting of patches and a cost-weighted distance surface best predicted occupancy, where we assumed roads were fairly
impermeable to movement, and low-lying drainages provided dispersal corridors. We also found this result to be robust to a
range of cost weight parameters. Our results suggest that metrics should incorporate both patch area and the composition of
the surrounding matrix. These results provide guidance for improved landscape habitat modeling in fragmented landscapes and
can help identify target habitat for conservation and management of prairie dogs in urban systems. 相似文献
14.
Temporal variability of connectivity in agricultural landscapes: do farming activities help? 总被引：5，自引：0，他引：5
Baudry Jacques Burel Françoise Aviron Stéphanie Martin Manuel Ouin Annie Pain Guillaume Thenail Claudine 《Landscape Ecology》2003,18(3):303-314
Landscape Ecology - In landscapes where natural habitats have been severely fragmented by intensive farming, survival of many species depends on connectivity among habitat patches. Spatio-temporal... 相似文献
15.
16.
Landscape cohesion: an index for the conservation potential of landscapes for biodiversity 总被引：14，自引：6，他引：14
In urbanising landscapes, planning for sustainable biodiversity occurs in a context of multifunctional land use. Important
conditions for species persistence are habitat quality, the amount and configuration of habitat and the permeability of the
landscape matrix. For planning purposes, these determinants should be integrated into simple indicators for spatial conditions
of persistence probability. We propose a framework of three related indices. The cohesion index is based on the ecology of
metapopulations in a habitat network. We discuss how an indicator for species persistence in such a network could be developed.
To translate this network index into an area index, we propose the concept of spatial cohesion. Habitat cohesion and spatial
cohesion are defined and measured for single species or, at best, for species profiles. Since species differ in their perception
of the same landscape, different species will rate different values of these indices for the same landscape. Because landscapes
are rarely planned for single species, we further propose the index of landscape cohesion, which integrates the spatial cohesion
indices of different species. Indices based on these concepts can be built into GIS tools for landscape assessment. We illustrate
different applications of these indices, and emphasise the distinction between ecological and political decisions in developing
and applying such tools.
This revised version was published online in August 2006 with corrections to the Cover Date. 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.
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
19.
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
20.
Although the role of habitat fragmentation in species declines is well recognised, the effect of habitat quality on species
distributions is often studied using presence–absence models that ignore metapopulation dynamics. We compared three approaches
to model the presence–absence of North Island robins in 400 sites among 74 fragments of native forest in a 15,000-ha agricultural
landscape in New Zealand. The first approach only considered local habitat characteristics, the second approach only considered
metapopulation factors (patch size and isolation), and the third approach combined these two types of factors. The distribution
of North Island robins was best predicted by patch isolation, as their probability of occurrence was negatively correlated
with isolation from neighbouring patches and from the closest major forests, which probably acted as a source of immigrants.
The inclusion of habitat factors gave only a slight increase in predictive power and indicated that robins were more likely
to occur in areas with tall canopy, tall understory and low density of young trees. We modelled the effect of isolation using
an index of functional patch connectivity based on dispersal behaviour of radio-tracked juveniles, and this functional index
greatly improved the models in comparison to classical indices relying on Euclidean distances. This study highlights the need
to incorporate functional indices of isolation in presence–absence models in fragmented landscapes, as species occurrence
can otherwise be a misleading predictor of habitat quality and lead to wrong interpretations and management recommendations. 相似文献