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31.
Ethanol produced from cellulosic biomass is examined as a large-scale transportation fuel. Desirable features include ethanol's fuel properties as well as benefits with respect to urban air quality, global climate change, balance of trade, and energy security. Energy balance, feedstock supply, and environmental impact considerations are not seen as significant barriers to the widespread use of fuel ethanol derived from cellulosic biomass. Conversion economics is the key obstacle to be overcome. In light of past progress and future prospects for research-driven improvements, a cost-competitive process appears possible in a decade. 相似文献
32.
Linking movement behavior and fine-scale genetic structure to model landscape connectivity for bobcats (Lynx rufus) 总被引：1，自引：0，他引：1
Dawn M. Reding Samuel A. Cushman Todd E. Gosselink William R. Clark 《Landscape Ecology》2013,28(3):471-486
Spatial heterogeneity can constrain the movement of individuals and consequently genes across a landscape, influencing demographic and genetic processes. In this study, we linked information on landscape composition, movement behavior, and genetic differentiation to gain a mechanistic understanding of how spatial heterogeneity may influence movement and gene flow of bobcats in the agricultural landscape of Iowa (USA). We analyzed movement paths of 23 animals to parameterize landscape resistance surfaces, applied least cost path analysis to generate measures of effective geographic distance between DNA collection locations of 625 bobcats, and tested the correlation between genetic distance and the different models of geographic distance. We found that bobcats showed a strong preference for forest over any other habitat type, and that incorporating information on habitat composition both along the path and in the surrounding landscape provided the best model of movement. Measures of effective geographic distance were significantly correlated with genetic distance, but not once the effects of Euclidean distance were accounted for. Thus, despite the impact of habitat composition on movement behavior, we did not detect a signature of a landscape effect in genetic structure. Our results are consistent with the issue of limiting factors: the high uniformity of forest fragmentation across southern Iowa, the primary study area, results in a landscape resistance pattern virtually indistinguishable from the isolation-by-distance pattern. The northern portion of the state, however, is predicted to pose a high level of resistance to bobcat movement, which may impede the regional genetic connectivity of populations across the Midwest. 相似文献
33.
Ahmadi Mohsen Farhadinia Mohammad S. Cushman Samuel A. Hemami Mahmoud-Reza Nezami Balouchi Bagher Jowkar Houman Macdonald David W. 《Landscape Ecology》2020,35(7):1505-1517
Landscape Ecology - With accelerating global declines in biodiversity, establishment and expansion of conservation areas (CAs) have increasingly been advocated in recent decades. Gap analysis has... 相似文献
34.
Individual-based landscape genetic analyses provide empirically based models of gene flow. It would be valuable to verify
the predictions of these models using independent data of a different type. Analyses using different data sources that produce
consistent results provide strong support for the generality of the findings. Mating and dispersal movements are the mechanisms
through which gene flow operates in animal populations. The best means to verify landscape genetic predictions would be to
use movement data to independently predict landscape resistance. We used path-level, conditional logistic regression to predict
landscape resistance for American black bear (Ursus americanus) in a landscape in which previous work predicted population connectivity using individual-based landscape genetics. We found
consistent landscape factors influence genetic differentiation and movement path selection, with strong similarities between
the predicted landscape resistance surfaces. Genetic differentiation in American black bear is driven by spring movement (mating
and dispersal) in relation to residential development, roads, elevation and forest cover. Given the limited periods of the
year when gene flow events primarily occur, models of landscape connectivity should carefully consider temporal changes in
functional landscape resistance. 相似文献
35.
Tzeidle N. Wasserman Samuel A. Cushman Michael K. Schwartz David O. Wallin 《Landscape Ecology》2010,25(10):1601-1612
Individual-based analyses relating landscape structure to genetic distances across complex landscapes enable rigorous evaluation
of multiple alternative hypotheses linking landscape structure to gene flow. We utilize two extensions to increase the rigor
of the individual-based causal modeling approach to inferring relationships between landscape patterns and gene flow processes.
First, we add a univariate scaling analysis to ensure that each landscape variable is represented in the functional form that
represents the optimal scale of its association with gene flow. Second, we use a two-step form of the causal modeling approach
to integrate model selection with null hypothesis testing in individual-based landscape genetic analysis. This series of causal
modeling indicated that gene flow in American marten in northern Idaho was primarily related to elevation, and that alternative
hypotheses involving isolation by distance, geographical barriers, effects of canopy closure, roads, tree size class and an
empirical habitat model were not supported. Gene flow in the Northern Idaho American marten population is therefore driven
by a gradient of landscape resistance that is a function of elevation, with minimum resistance to gene flow at 1500 m. 相似文献
36.
Ecological relationships between patterns and processes are highly scale dependent. This paper reports the first formal exploration
of how changing scale of research away from the scale of the processes governing gene flow affects the results of landscape
genetic analysis. We used an individual-based, spatially explicit simulation model to generate patterns of genetic similarity
among organisms across a complex landscape that would result given a stipulated landscape resistance model. We then evaluated
how changes to the grain, extent, and thematic resolution of that landscape model affect the nature and strength of observed
landscape genetic pattern–process relationships. We evaluated three attributes of scale including thematic resolution, pixel
size, and focal window size. We observed large effects of changing thematic resolution of analysis from the stipulated continuously
scaled resistance process to a number of categorical reclassifications. Grain and window size have smaller but statistically
significant effects on landscape genetic analyses. Importantly, power in landscape genetics increases as grain of analysis
becomes finer. The analysis failed to identify the operative grain governing the process, with the general pattern of stronger
apparent relationship with finer grain, even at grains finer than the governing process. The results suggest that correct
specification of the thematic resolution of landscape resistance models dominates effects of grain and extent. This emphasizes
the importance of evaluating a range of biologically realistic resistance hypotheses in studies to associate landscape patterns
to gene flow processes. 相似文献
37.
38.
The influence of landscape characteristics and home-range size on the quantification of landscape-genetics relationships 总被引：1，自引：1，他引：0
Tabitha A. Graves Tzeidle N. Wasserman Milton Cezar Ribeiro Erin L. Landguth Stephen F. Spear Niko Balkenhol Colleen B. Higgins Marie-Josée Fortin Samuel A. Cushman Lisette P. Waits 《Landscape Ecology》2012,27(2):253-266
A common approach used to estimate landscape resistance involves comparing correlations of ecological and genetic distances
calculated among individuals of a species. However, the location of sampled individuals may contain some degree of spatial
uncertainty due to the natural variation of animals moving through their home range or measurement error in plant or animal
locations. In this study, we evaluate the ways that spatial uncertainty, landscape characteristics, and genetic stochasticity
interact to influence the strength and variability of conclusions about landscape-genetics relationships. We used a neutral
landscape model to generate 45 landscapes composed of habitat and non-habitat, varying in percent habitat, aggregation, and
structural connectivity (patch cohesion). We created true and alternate locations for 500 individuals, calculated ecological
distances (least-cost paths), and simulated genetic distances among individuals. We compared correlations between ecological
distances for true and alternate locations. We then simulated genotypes at 15 neutral loci and investigated whether the same
influences could be detected in simple Mantel tests and while controlling for the effects of isolation-by-distance using the
partial Mantel test. Spatial uncertainty interacted with the percentage of habitat in the landscape, but led to only small
reductions in correlations. Furthermore, the strongest correlations occurred with low percent habitat, high aggregation, and
low to intermediate levels of cohesion. Overall genetic stochasticity was relatively low and was influenced by landscape characteristics. 相似文献
39.
Kevin McGarigal Ho Yi Wan Kathy A. Zeller Brad C. Timm Samuel A. Cushman 《Landscape Ecology》2016,31(6):1161-1175
Context
Scale is the lens that focuses ecological relationships. Organisms select habitat at multiple hierarchical levels and at different spatial and/or temporal scales within each level. Failure to properly address scale dependence can result in incorrect inferences in multi-scale habitat selection modeling studies.Objectives
Our goals in this review are to describe the conceptual origins of multi-scale habitat selection modeling, evaluate the current state-of-the-science, and suggest ways forward to improve analysis of scale-dependent habitat selection.Methods
We reviewed more than 800 papers on habitat selection from 23 major ecological journals published between 2009 and 2014 and recorded a number of characteristics, such as whether they addressed habitat selection at multiple scales, what attributes of scale were evaluated, and what analytical methods were utilized.Results
Our results show that despite widespread recognition of the importance of multi-scale analyses of habitat relationships, a large majority of published habitat ecology papers do not address multiple spatial or temporal scales. We also found that scale optimization, which is critical to assess scale dependence, is done in less than 5 % of all habitat selection modeling papers and less than 25 % of papers that address “multi-scale” habitat analysis broadly defined.Conclusions
Our review confirms the existence of a powerful conceptual foundation for multi-scale habitat selection modeling, but that the majority of studies on wildlife habitat are still not adopting multi-scale frameworks. Most importantly, our review points to the need for wider adoption of a formal scale optimization of organism response to environmental variables.40.
Ramesh Krishnamurthy Samuel A. Cushman Mriganka S. Sarkar Manjari Malviya Moorthy Naveen Jeyaraj A. Johnson Subharanjan Sen 《Landscape Ecology》2016,31(6):1355-1368