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71.
我国旱涝空间型的马尔科夫概型分析 总被引:13,自引:2,他引:13
旱涝灾害在我国是影响最大、也最为频繁的气候灾害。本文利用马尔科夫概型分析的原理和方法,在验证了我国旱涝空间型序列具有马尔科夫性质的基础上,计算出各状态的转移概率,进而分析了旱涝空间型序列的静态和动态结构,并揭示出旱涝空间型各状态演化的优势倾向。 相似文献
72.
Spatial-econometric analysis of attraction and repulsion of private conservation by public reserves 总被引:1,自引:0,他引:1
Heidi J. Albers Amy W. Ando Xiaoxuan Chen 《Journal of Environmental Economics and Management》2008,56(1):33-49
It is difficult for public agencies to make optimal reserve-site selections without knowing how new public reserves might influence the configuration of private conservation. Private land trusts protect much land in the USA, but little is known about how private groups respond to conservation decisions made by other conservation agents. To fill that gap, we analyze township-level spatial data on conservation in California, Illinois, and Massachusetts to explore relationships between the location of private and public conservation land. Using linear spatial-econometric models and Bayesian spatial probit models, we find evidence that private-protected acres are clustered together in space. In California, it appears that private land conservation is attracted towards places where the government has reserves. In Illinois and Massachusetts, however, it appears that private conservation shifts away from townships with government reserves due to a mixture of spatial repulsion and simple acreage displacement. 相似文献
73.
Modelling habitat suitability of semi-aquatic vertebrates for large scale conservation purposes is a particularly challenging task, due to the fine-scale linearity of riverine habitats, and to the ecological continuum represented by the riparian and the aquatic ecosystems, on one side, and by a river and its tributaries, on the other. 相似文献
74.
Rarefaction estimates how many species are expected in a random sample of individuals from a larger collection and allows
meaningful comparisons among collections of different sizes. It assumes random spatial dispersion. However, two common dispersion
patterns, within-species clumping and segregation among species, can cause rarefaction to overestimate the species richness
of a smaller continuous area. We use field studies and computer simulations to determine (1) how robust rarefaction is to
nonrandom spatial dispersion and (2) whether simple measures of spatial autocorrelation can predict the bias in rarefaction
estimates. Rarefaction does not estimate species richness accurately for many communities, especially at small sample sizes.
Measures of spatial autocorrelation of the more abundant species do not reliably predict amount of bias. Survey sites should
be standardized to equal-sized areas before sampling. When sites are of equal area but differ in number of individuals sampled,
rarefaction can standardize collections. When communities are sampled from different-sized areas, the mean and confidence
intervals of species accumulation curves allow more meaningful comparisons among sites.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
Daniel SimberloffEmail: |
75.
Jan Peters Niko E.C. Verhoest Roeland Samson Marc Van Meirvenne Liesbet Cockx Bernard De Baets 《Ecological modelling》2009
Ensemble learning techniques are increasingly applied for species and vegetation distribution modelling, often resulting in more accurate predictions. At the same time, uncertainty assessment of distribution models is gaining attention. In this study, Random Forests, an ensemble learning technique, is selected for vegetation distribution modelling based on environmental variables. The impact of two important sources of uncertainty, that is the uncertainty on spatial interpolation of environmental variables and the uncertainty on species clustering into vegetation types, is quantified based on sequential Gaussian simulation and pseudo-randomization tests, respectively. An empirical assessment of the uncertainty propagation to the distribution modelling results indicated a gradual decrease in performance with increasing input uncertainty. The test set error ranged from 30.83% to 52.63% and from 30.83% to 83.62%, when the uncertainty ranges on spatial interpolation and on vegetation clustering, respectively, were fully covered. Shannon’s entropy, which is proposed as a measure for uncertainty of ensemble predictions, revealed a similar increasing trend in prediction uncertainty. The implications of these results in an empirical distribution modelling framework are further discussed with respect to monitoring setup, spatial interpolation and species clustering. 相似文献
76.
Bea Merckx Peter Goethals Maaike Steyaert Ann Vanreusel Magda Vincx Jan Vanaverbeke 《Ecological modelling》2009
In this paper, we investigated: (1) the predictability of different aspects of biodiversity, (2) the effect of spatial autocorrelation on the predictability and (3) the environmental variables affecting the biodiversity of free-living marine nematodes on the Belgian Continental Shelf. An extensive historical database of free-living marine nematodes was employed to model different aspects of biodiversity: species richness, evenness, and taxonomic diversity. Artificial neural networks (ANNs), often considered as “black boxes”, were applied as a modeling tool. Three methods were used to reveal these “black boxes” and to identify the contributions of each environmental variable to the diversity indices. Since spatial autocorrelation is known to introduce bias in spatial analyses, Moran's I was used to test the spatial dependency of the diversity indices and the residuals of the model. The best predictions were made for evenness. Although species richness was quite accurately predicted as well, the residuals indicated a lack of performance of the model. Pure taxonomic diversity shows high spatial variability and is difficult to model. The biodiversity indices show a strong spatial dependency, opposed to the residuals of the models, indicating that the environmental variables explain the spatial variability of the diversity indices adequately. The most important environmental variables structuring evenness are clay and sand fraction, and the minimum annual total suspended matter. Species richness is also affected by the intensity of sand extraction and the amount of gravel of the sea bed. 相似文献
77.
Christine R. Maher 《Behavioral ecology and sociobiology》2009,63(6):857-868
Solitary species show several patterns of space use and relatedness. Individuals may associate randomly or may live near female
or male kin, often as a result of natal philopatry or dispersal patterns. Although usually described as solitary or asocial,
woodchucks (Marmota monax) are behaviorally flexible marmots that exhibit greater sociality in some populations than others. I examined relationships
between kinship, geographic distance, and home range overlap, as well as dispersal and philopatry, to determine the extent
to which kin associated spatially. I used a combination of microsatellite DNA analysis, long-term behavioral observations,
and radiotelemetry to test predictions that females, but not males, would associate with kin. Indeed, woodchucks lived closer
and shared a greater proportion of their home range with more closely related animals. Overlap of females' and males' home
ranges was positively correlated with kinship, and male–female dyads shared more area with closer kin. Most juveniles delayed
dispersal beyond their first summer. Females often remained philopatric and settled near their natal range. Although males
often dispersed as yearlings, some males also established territories within or immediately adjacent to their natal home ranges.
A combination of factors can explain these spatial patterns, including high population density associated with the study site's
location within a suburban environment, high dispersal costs, and abundant food. Thus, despite their asocial and solitary
reputation, woodchucks displayed spatial patterns seen in other, more social species of ground-dwelling sciurids. 相似文献
78.
Douglas G. Sprugel Katherine G. Rascher Rolf Gersonde Martin Dovčiak James A. Lutz Charles B. Halpern 《Ecological modelling》2009
Young forests can be manipulated in diverse ways to enhance their ecological values. We used stem maps from two dense, second-growth stands in western Washington and a spatially explicit light model (tRAYci) to simulate effects of five silvicultural manipulations on diameter distribution, species composition, spatial patterning, and light availability. Each treatment removed 30% of the basal area, but differed in how trees were selected for removal. Three primary treatments were thin from below (removing the smallest trees), random thin (removing trees randomly), and gap creation (removing all trees in circles ∼1 tree height in diameter). Two additional treatments combined elements of these approaches: random ecological thin (a mixture of thin from below and random thin) and structured ecological thin (a mixture of thin from below and gap creation). 相似文献
79.
F. Le Ber C. Lavigne K. Adamczyk F. Angevin N. Colbach J.-F. Mari H. Monod 《Ecological modelling》2009
Neutral landscape models are not frequently used in the agronomical domain, whereas they would be very useful for studying given agro-ecological or physical processes. Contrary to ecological neutral landscape models, agricultural models have to represent and manage geometrical patches and thus should rely on tessellation methods. We present a three steps approach that aimed at simulating such landscapes. Firstly, we characterized the geometry of three real field patterns; secondly, we generated simulated field patterns with two tessellation methods attempting to control the value of some of the observed characteristics and, thirdly, we evaluated the simulated field patterns. For this evaluation, we considered that good simulated field patterns should capture characteristics of real landscapes that are important for the targeted agro-ecological process. Real landscapes and landscapes simulated using either a Voronoi or a rectangular tessellation were thus compared when used as input data within a gene flow model. The results showed that neither tessellation method captured field shapes correctly, thus leading to over or (small) under estimation of gene flow. The Voronoi tessellation, though, performed better than the rectangular tessellation. Possible research directions are proposed to improve the simulated patterns, including the use of post-processing, the control of cell orientation or the implementation of other tessellation techniques. 相似文献
80.
Slope,aspect and climate: Spatially explicit and implicit models of topographic microclimate in chalk grassland 总被引:2,自引:0,他引:2
Jonathan Bennie Brian Huntley Andrew Wiltshire Mark O. Hill Robert Baxter 《Ecological modelling》2008
The slope and aspect of a vegetated surface strongly affects the amount of solar radiation intercepted by that surface. Solar radiation is the dominant component of the surface energy balance and influences ecologically critical factors of microclimate, including near-surface temperatures, evaporative demand and soil moisture content. It also determines the exposure of vegetation to photosynthetically active and ultra-violet wavelengths. Spatial variation in slope and aspect is therefore a key determinant of vegetation pattern, species distribution and ecosystem processes in many environments. Slope and aspect angle may vary considerably over distances of a few metres, and fine-scale species’ distribution patterns frequently follow these topographic patterns. The availability of suitable microclimate at such scales may be critical for the response of species distributions to climatic change at much larger spatial scales. However, quantifying the relevant microclimatic gradients is not straightforward, as the potential variation in solar radiation flux under clear-sky conditions is modified by local and regional variations in cloud cover, and interacts with long-wave radiation exchange, local meteorology and surface characteristics. 相似文献