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1.
Neutral models for testing landscape hypotheses 总被引：5，自引：0，他引：5
Neutral landscape models were originally developed to test the hypothesis that human-induced fragmentation produces patterns
distinctly different from those associated with random processes. Other uses for neutral models have become apparent, including
the development and testing of landscape metrics to characterize landscape pattern. Although metric development proved to
be significant, the focus on metrics obscured the need for iterative hypothesis testing fundamental to the advancement of
the discipline. We present here an example of an alternative neutral model and hypothesis designed to relate the process of
landscape change to observed landscape patterns. The methods and program, QRULE, are described and options for statistical
testing outlined. The results show that human fragmentation of landscapes results in a non-random association of land-cover
types that can be describe by simple statistical methods. Options for additional landscape studies are discussed and access
to QRULE described in the hope that these methods will be employed to advance our understanding of the processes that affect
the structure and function in human dominated landscapes. 相似文献
2.
Michael C. Wimberly 《Landscape Ecology》2006,21(1):35-46
Although landscape ecology emphasizes the effects of spatial pattern on ecological processes, most neutral models of species–habitat relationships have treated habitat as a static constraint. Do the working hypotheses derived from these models extend to real landscapes where disturbances create a shifting mosaic? A spatial landscape simulator incorporating vegetation dynamics and a metapopulation model was used to compare species in static and dynamic landscapes with identical habitat amounts and spatial patterns. The main drivers of vegetation dynamics were stand-replacing disturbances, followed by gradual change from early-successional to old-growth habitats. Species dynamics were based on a simple occupancy model, with dispersal simulated as a random walk. As the proportion of available habitat (p) decreased from 1.0, species occupancy generally declined more rapidly and reached extinction at higher habitat levels in dynamic than in static landscapes. However, habitat occupancy was sometimes actually higher in dynamic landscapes than in static landscapes with similar habitat amounts and patterns. This effect was most pronounced at intermediate amounts of habitat (p = 0.3?0.6) for mobile species that had high colonization rates, but were unable to cross non-habitat patches. Differences between static and dynamic landscapes were contingent upon the initial metapopulation size and the shapes of disturbances and the resulting habitat patterns. Overall, the results demonstrate that dispersal-limited species exhibit more pronounced critical behavior in dynamic landscapes than is predicted by simple neutral models based on static landscapes. Thus, caution should be exercised in extending generalizations derived from static landscape models to disturbance-driven landscape mosaics. 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.
A hierarchical neutral model for landscape analysis 总被引：11，自引：0，他引：11
Empirical studies have revealed scaled structure on a variety of landscapes. Understanding processes that produce these structures
requires neutral models with hierarchical structure. The present study presents a method for generating random maps possessing
a variety of hierarchical structures. The properties of these scaled landscapes are analyzed and compared to patterns on totally
random, unstructured landscapes. Hierar-chical structure permits percolation (i.e., continous habitat spanning the landscape) under a greater variety of conditions than found on totally random landscapes.
Habitat clusters on structured maps tend to have smaller perimeters. The clusters tend to be less clumped on sparsely occupied
landscapes and more clumped in densely occupied conditions. Hierarchical structure changes the expected spatial properties
of the landscape, indicating a strong need for this new generation of neutral models.
Research supported by the Ecological Research Division, Office to Health and Environmental Research, U.S. Department of Energy
under contract No. DE-AC05-840R21400 with Martin Marietta, Energy Systems, Inc. Environmental Sciences Publication No. 3813,
ORNL. 相似文献
5.
Brian R. Miranda Brian R. Sturtevant Jian Yang Eric J. Gustafson 《Landscape Ecology》2009,24(5):587-598
We demonstrate a method to evaluate the degree to which a meta-model approximates spatial disturbance processes represented
by a more detailed model across a range of landscape conditions, using neutral landscapes and equivalence testing. We illustrate
this approach by comparing burn patterns produced by a relatively simple fire spread algorithm with those generated by a more
detailed fire behavior model from which the simpler algorithm was derived. Equivalence testing allows objective comparisons
of the output of simple and complex models, to determine if the results are significantly similar. Neutral landscape models
represent a range of landscape conditions that the model may encounter, allowing evaluation of the sensitivity and behavior
of the model to different landscape compositions and configurations. We first tested the model for universal applicability,
then narrowed the testing to assess the practical domain of applicability. As a whole, the calibrated simple model passed
the test for significant equivalence using the 25% threshold. When applied to a range of landscape conditions different from
the calibration scenarios, the model failed the tests for equivalence. Although our particular model failed the tests, the
neutral landscape models were helpful in determining an appropriate domain of applicability and in assessing the model sensitivity
to landscape changes. Equivalence testing provides an effective method for model comparison, and coupled with neutral landscapes,
our approach provides an objective way to assess the domain of applicability of a spatial model. 相似文献
6.
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
7.
Landscape Ecology - Neutral landscape models are useful and popular tools for exploring effects of spatial patterns on ecological processes. Most neutral landscape models mimic natural landscape... 相似文献
8.
Neutral models for the analysis of broad-scale landscape pattern 总被引：47，自引：19，他引：28
Robert H. Gardner Bruce T. Milne Monica G. Turnei Robert V. O'Neill 《Landscape Ecology》1987,1(1):19-28
The relationship between a landscape process and observed patterns can be rigorously tested only if the expected pattern in the absence of the process is known. We used methods derived from percolation theory to construct neutral landscape models,i.e., models lacking effects due to topography, contagion, disturbance history, and related ecological processes. This paper analyzes the patterns generated by these models, and compares the results with observed landscape patterns. The analysis shows that number, size, and shape of patches changes as a function of p, the fraction of the landscape occupied by the habitat type of interest, and m, the linear dimension of the map. The adaptation of percolation theory to finite scales provides a baseline for statistical comparison with landscape data. When USGS land use data (LUDA) maps are compared to random maps produced by percolation models, significant differences in the number, size distribution, and the area/perimeter (fractal dimension) indices of patches were found. These results make it possible to define the appropriate scales at which disturbance and landscape processes interact to affect landscape patterns. 相似文献
9.
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
10.
Increasing land ownership fragmentation in the United States is causing concerns with respect to its ecological implications
for forested landscapes. This is especially relevant given that human influence is one of the most significant driving forces
affecting the forest landscape. A method for generating realistic land ownership maps is needed to evaluate the effects of
ownership fragmentation on forest landscapes in combination with other natural processes captured in forest process models.
Ownership patterns from human activities usually generate landscape boundary shapes different from those arising from natural
processes. Spatial characteristics among ownership types – e.g., private, public ownership – may also differ. To address these
issues, we developed the Fragmented Land Ownership Spatial Simulator (FLOSS) to generate ownership patterns that reflect the
Public Land Survey System (PLSS) shapes and various patch size distributions among different types of ownership (e.g., private,
public). To evaluate FLOSS performance, we compared the simulated patterns with various ownership fragmentation levels to
the actual ownership patterns in the Missouri Ozarks by using selected landscape indices. FLOSS generated landscapes with
spatial characteristics similar to actual landscapes, suggesting that it can simulate different levels of ownership fragmentation.
This will allow FLOSS to serve as a feasible tool for evaluating forest management applications by spatially allocating various
management scenarios in a realistic way. The potentials and limitations of FLOSS application are discussed. 相似文献
11.
Fire and grazing are ecological processes that frequently interact to modify landscape patterns of vegetation. There is empirical
and theoretical evidence that response of herbivores to heterogeneity is scale-dependent however the relationship between
fire and scale of heterogeneity is not well defined. We examined the relationship between fire behavior and spatial scale
(i.e., patch grain) of fuel heterogeneity. We created four heterogeneous landscapes modeled after those created by a fire–grazing
interaction that differed in grain size of fuel patches. Fire spread was simulated through each model landscape from 80 independent,
randomly located ignition points. Burn area, burn shape complexity and the proportion of area burnt by different fire types
(headfire, backfire and flankfire) were all affected by the grain of fuel patch. The area fires burned in heterogeneous landscapes
interacted with the fuel load present in the patch where ignition occurred. Burn complexity was greater in landscapes with
small patch grain than in landscapes with large patch grain. The proportion of each fire type (backfire, flankfire and headfire)
was similar among all landscapes regardless of patch grain but the variance of burned area within each of the three fire types
differed among treatments of patch grain. Our landscape fire simulation supports the supposition that feedbacks between landscape
patterns and ecological processes are scale-dependent, in this case spatial scale of fuel loading altering fire spread through
the landscape. 相似文献
12.
Changing landscapes to accommodate for climate change impacts: a call for landscape ecology 总被引：2，自引：1，他引：1
Predictions of climate change suggest major changes in temperature, rainfall as well as in frequency and timing of extreme weather, all in varying degrees and patterns around the world. Although the details of these patterns changes are still uncertain, we can be sure of profound effects on ecological processes in and functioning of landscapes. The impact of climate change will affect all types of land use, ecosystem services, as well as the behavior of humans. The core business of Landscape Ecology is the interaction of landscape patterns and processes. Most of these interactions will be affected by changing climate patterns, so clearly within the focus of our science. Nevertheless, climate change received little attention from landscape ecologists. Are we missing the boat? Why is it that our science does not contribute to building a knowledge base to help solving this immense problem? Why is there so little attention paid to adaptation of landscape to climate change? With this editorial article IALE would like to receive inputs from the Landscape Ecology scientific community in related research on adaptation of landscapes to climate change, on tools or approaches to help landscape planners and stakeholders to this new challenge where landscape ecology can play a key role. 相似文献
13.
Road Density and Landscape Pattern in Relation to Housing Density,and Ownership,Land Cover,and Soils 总被引：5，自引：0，他引：5
Roads are conspicuous components of landscapes and play a substantial role in defining landscape pattern. Previous studies
have demonstrated the link between roads and their effects on ecological processes and landscape patterns. Less understood
is the placement of roads, and hence the patterns imposed by roads on the landscape in relation to factors describing land
use, land cover, and environmental heterogeneity. Our hypothesis was that variation in road density and landscape patterns
created by roads can be explained in relation to variables describing land use, land cover, and environmental factors. We
examined both road density and landscape patterns created by roads in relation to suitability of soil substrate as road subgrade,
land cover, lake area and perimeter, land ownership, and housing density across 19 predominantly forested counties in northern
Wisconsin, USA. Generalized least squares regression models showed that housing density and soils with excellent suitability
for road subgrade were positively related to road density while wetland area was negatively related. These relationships were
consistent across models for different road types. Landscape indices showed greater fragmentation by roads in areas with higher
housing density, and agriculture, grassland, and coniferous forest area, but less fragmentation with higher deciduous forest,
mixed forest, wetland, and lake area. These relationships provide insight into the complex relationships among social, institutional,
and environmental factors that influence where roads occur on the landscape. Our results are important for understanding the
impacts of roads on ecosystems and planning for their protection in the face of continued development. 相似文献
14.
Context
Quantitative grouping of similar landscape patterns is an important part of landscape ecology due to the relationship between a pattern and an underlying ecological process. One of the priorities in landscape ecology is a development of the theoretically consistent framework for quantifying, ordering and classifying landscape patterns.
ObjectiveTo demonstrate that the information theory as applied to a bivariate random variable provides a consistent framework for quantifying, ordering, and classifying landscape patterns.
MethodsAfter presenting information theory in the context of landscapes, information-theoretical metrics were calculated for an exemplar set of landscapes embodying all feasible configurations of land cover patterns. Sequences and 2D parametrization of patterns in this set were performed to demonstrate the feasibility of information theory for the analysis of landscape patterns.
ResultsUniversal classification of landscape into pattern configuration types was achieved by transforming landscapes into a 2D space of weakly correlated information-theoretical metrics. An ordering of landscapes by any single metric cannot produce a sequence of continuously changing patterns. In real-life patterns, diversity induces complexity—increasingly diverse patterns are increasingly complex.
ConclusionsInformation theory provides a consistent, theory-based framework for the analysis of landscape patterns. Information-theoretical parametrization of landscapes offers a method for their classification.
相似文献15.
Landscape dynamics in crown fire ecosystems 总被引：21，自引：3，他引：18
Crown fires create broad-scale patterns in vegetation by producing a patch mosaic of stand age classes, but the spread and behavior of crown fires also may be constrained by spatial patterns in terrain and fuels across the landscape. In this review, we address the implications of landscape heterogeneity for crown fire behavior and the ecological effects of crown fires over large areas. We suggest that fine-scale mechanisms of fire spread can be extrapolated to make broad-scale predictions of landscape pattern by coupling the knowledge obtained from mechanistic and empirical fire behavior models with spatially-explicit probabilistic models of fire spread. Climatic conditions exert a dominant control over crown fire behavior and spread, but topographic and physiographic features in the landscape and the spatial arrangement and types of fuels have a strong influence on fire spread, especially when burning conditions (e.g., fuel moisture and wind) are not extreme. General trends in crown fire regimes and stand age class distributions can be observed across continental, latitudinal, and elevational gradients. Crown fires are more frequent in regions having more frequent and/or severe droughts, and younger stands tend to dominate these landscapes. Landscapes dominated by crown fires appear to be nonequilibrium systems. This nonequilibrium condition presents a significant challenge to land managers, particularly when the implications of potential changes in the global climate are considered. Potential changes in the global climate may alter not only the frequency of crown fires but also their severity. Crown fires rarely consume the entire forest, and the spatial heterogeneity of burn severity patterns creates a wide range of local effects and is likely to influence plant reestablishment as well as many other ecological processes. Increased knowledge of ecological processes at regional scales and the effects of landscape pattern on fire dynamics should provide insight into our understanding of the behavior and consequences of crown fires. 相似文献
16.
Spatial and temporal analysis of landscape patterns 总被引：89，自引：0，他引：89
Monica G. Turner 《Landscape Ecology》1990,4(1):21-30
A variety of ecological questions now require the study of large regions and the understanding of spatial heterogeneity. Methods
for spatial-temporal analyses are becoming increasingly important for ecological studies. A grid cell based spatial analysis
program (SPAN) is described and results of landscape pattern analysis using SPAN are presentedd. Several ecological topics
in which geographic information systems (GIS) can play an important role (landscape pattern analysis, neutral models of pattern
and process, and extrapolation across spatial scales) are reviewed. To study the relationship between observed landscape patterns
and ecological processes, a neutral model approach is recommended. For example, the expected pattern (i.e., neutral model) of the spread of disturbance across a landscape can be generated and then tested using actual landscape data
that are stored in a GIS. Observed spatial or temporal patterns in ecological data may also be influenced by scale. Creating
a spatial data base frequently requires integrating data at different scales. Spatial is shown to influence landscape pattern
analyses, but extrapolation of data across spatial scales may be possible if the grain and extent of the data are specified.
The continued development and testing of new methods for spatial-temporal analysis will contribute to a general understanding
of landscape dynamics. 相似文献
17.
The ecology of urban landscapes: modeling housing starts as a density-dependent colonization process 总被引：3，自引：0，他引：3
Data on permits for new housing starts are a key source of information on recent changes in the urban landscape of central Arizona, USA. Drawing primarily on the conceptual parallels between the process of urban expansion and the spatial spread of non-human species, we outline a nested series of 'colonization' models that could be used to study changes in urban landscapes through simulations of housing starts.Within our probabilistic colonization framework, the ecological principle of density-dependence (operating simultaneously on different spatial scales) governs the positioning of new housing units. These simple models afford a great diversity of possible spatial patterns, ranging from tight clustering of houses to urban sprawl to more subtle patterns such as aversion of housing developments from (and aggregation near) different kinds of landscape features. These models can be parameterized from a variety of types of governmental housing data. Ultimately, such a framework could be used to contrast development patterns among cities and identify pertinent operational scales and factors influencing processes associated with urbanization. 相似文献
18.
Landscape metric scalograms (the response curves of landscape metrics to changing grain size) have been used to illustrate the scale effects of metrics for real landscapes. However, whether they detect the characteristic scale of hierarchically structured landscapes remains uncertain. To address this question, the scalograms of 26 class-level metrics were systematically examined for a simple random landscape, seven hierarchical neutral landscapes, and the real landscape of the Xilin River Basin of Inner Mongolia, China. The results show that when the fraction of the focal patch type (P) is below a critical value (P c), most metric scalograms are sensitive to change in single-scale and lower-level hierarchical structure and insensitive to change in higher-level hierarchical structure. The scalograms of only a few metrics measuring spatial aggregation and connectedness are sensitive to change in intermediate-level hierarchical structure. Most metric scalograms explicitly identify the characteristic scale of a single-scale landscape and fine or intermediate characteristic scales of a multi-scale landscape for both simulated and real landscapes. When P exceeds P c, only some metrics detect scale and change in structure. The scalograms of total class area and Euclidean nearest-neighbor distance cannot detect scale or change in structure in either case. Landscape metric scalograms are useful for addressing scale issues, including illustrating the scale effects of spatial patterns, detecting multi-scale patterns, and developing possible scaling relations.
相似文献19.
The influence of landscape features on the movement of an organism between two point locations is often measured as an effective distance. Typically, raster models of landscape resistance are used to calculate effective distance. Because organisms may experience landscape heterogeneity at different scales (i.e. functional grains), using a raster with too fine or too coarse a spatial grain (i.e. analysis grain) may lead to inaccurate estimates of effective distance. We adopted a simulation approach where the true functional grain and effective distance for a theoretical organism were defined and the analysis grains of landscape connectivity models were systematically changed. We used moving windows and grains of connectivity, a recently introduced landscape graph method that uses an irregular tessellation of the resistance surface to coarsen the landscape data. We then used least-cost path metrics to measure effective distance and found that matching the functional and analysis grain sizes was most accurate at recovering the expected effective distance, affirming the importance of multi-scale analysis. Moving window scaling with a maximum function (win.max) performed well when the majority of landscape structure influencing connectivity consisted of high resistance features. Moving window scaling with a minimum function (win.min) performed well when the relevant landscape structure consisted of low resistance regions. The grains of connectivity method performed well under all scenarios, avoiding an a priori choice of window function, which may be challenging in complex landscapes. Appendices are provided that demonstrate the use of grains of connectivity models. 相似文献