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941.
JINLIANG WANG 《Conservation biology》2004,18(2):332-343
Abstract: Endangered species are commonly found in several (partially) isolated populations dispersed on different fragments of a habitat, natural reserve, or zoo. A certain level of connectivity among such populations is essential for maintaining genetic variation within and between populations to allow local and global adaptation and for preventing inbreeding depression. A rule of thumb widely accepted by the conservation community is that one migrant per generation (OMPG) into a population is the appropriate level of gene flow. This rule is based on Wright's study of his island model under a long list of simplifying assumptions. I examined the robustness of the OMPG rule to the violation of each of the many assumptions, quantifying the effect with population genetics theory. I showed that, when interpreted as one effective migrant per generation, OMPG is generally valid for real populations departing from the ideal model in the discrepancies of actual ( N ) and effective ( Ne ) population sizes and actual ( m ) and effective ( me ) migration rates. I also addressed the issue of converting the effective number of migrants ( Me = Ne me ) into the actual number of migrants ( M = Nm ) of a certain age and sex. In particular, Ne < N , a case common for natural populations, did not necessarily require M > Me to maintain a certain level of differentiation among populations. Rather, translating the elusive Me into the manageable M depends on the specific causes (e.g., biased sex ratio, reproductive skew) that lead to Ne < N . 相似文献
942.
Mihailovic Dragutin T. Rao S. Trivikrama Hogrefe Christian Clark Richard D. 《Environmental Fluid Mechanics》2002,2(4):315-337
Experimental evidence indicates that there is a significant departure of the wind profile above the underlying surface consisting of patches of solid and liquid parts, and plant communities with different morphological from that predicted by the logarithmic relationship, which gives the values larger than those observed. This situation can seriously affect the transfer of momentum, heat and water vapor from the surface fluxes into the atmosphere.The object of this paper is to generalize the calculation of the exchange of momentum between the atmosphere and a very heterogeneous surface, find a general equation for the wind speed profile in a roughness sublayer under neutral conditions, and, then, derive aggregated roughness length and displacement height over the grid cell. The suggested expression for the wind profile is compared with some earlier approaches, using a common parameterization of aerodynamic parameters over the grid cell, and the observations obtained at an experimental site in Philadelphia, PA. 相似文献
943.
Environmental and Ecological Statistics - It is shown that community dynamics is neither haphazard nor completely directed. This is quite clear from our examination of a concrete example where... 相似文献
944.
Using Gall Wasps on Oaks to Test Broad Ecological Concepts 总被引:1,自引:0,他引:1
PETER W. PRICE WARREN G. ABRAHAMSON† MARK D. HUNTER‡ GEORGE MELIKA§ 《Conservation biology》2004,18(5):1405-1416
Abstract: Planning conservation of insect herbivores requires knowing what needs to be conserved and developing a set of predictor variables that aid management. We conducted a state-wide survey to examine the species richness of gall wasps (Hymenoptera: Cynipidae) on six oak species dominant in the threatened scrub-oak vegetation in peninsular Florida. Eighty-eight cynipid species were recorded; 23 were new species to Florida (a 35% increase), including 17 species new to science and 6 species newly recorded in the state. The cynipid species represented 68% of cynipids of Florida, on only 24% of oak species sampled. This fauna represents a hotspot of richness, justifying conservation initiatives in scrub-oak habitat and throughout the state. We derived predictor variables from general ecological concepts: (1) the theory of island biogeography that insect species richness increases as host plant geographic area increases and as local abundance increases, (2) the plant-architecture hypothesis that insect species richness increases with increased plant size, and (3) phytochemical patterns in leaves, including nutrients and digestibility reducers predicting suitability for insect herbivores. Concepts 1 and 2, developed for large scales and species numbers, were tested at smaller scales relevant to much conservation research and management. A stepwise multiple regression including all predictor variables accounted for 99% of the variance in cynipid species richness with three variables: foliar hemicellulose concentration (81%), host geographic area (16%), and tree height (2%). The trends were negative, however, and opposite to those predicted by concepts 1 and 2. Ecological theory was not applicable to discovery of predictors of cynipid species richness on six oak species. Thus, we promote caution in applying ecological theory to a narrow set of species without specific testing of how patterns conform to theoretical predictions. 相似文献
945.
本文在分析了生态系统进化的热力学理论(最大能量、最大功率、最大优势原理)的基础上,综述了能量、功率和优势值在国内外湖泊富营养化研究中的应用,说明生态系统进化的热力学理论为认识和研究复杂的湖泊生态系统提供了整体性的途径,并指出为把热力学理论有效地用于湖泊富营养化的研究而应加强的科研工作。 相似文献
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949.
Restoring habitat corridors in fragmented landscapes using optimization and percolation models 总被引:2,自引:0,他引:2
Justin?C.?WilliamsEmail author Stephanie?A.?Snyder 《Environmental Modeling and Assessment》2005,10(3):239-250
Landscape fragmentation and habitat loss are significant threats to the conservation of biological diversity. Creating and
restoring corridors between isolated habitat patches can help mitigate or reverse the impacts of fragmentation. It is important
that restoration and protection efforts be undertaken in the most efficient and effective way possible because conservation
budgets are often severely limited. We address the question of where restoration should take place to efficiently reconnect
habitat with a landscape-spanning corridor. Building upon findings in percolation theory, we develop a shortest-path optimization
methodology for assessing the minimum amount of restoration needed to establish such corridors. This methodology is applied
to large numbers of simulated fragmented landscapes to generate mean and variance statistics for the amount of restoration
needed. The results provide new information about the expected level of resources needed to realize different corridor configurations
under different degrees of fragmentation and different characterizations of habitat connectivity (“neighbor rules”). These
results are expected to be of interest to conservation planners and managers in the allocation of conservation resources to
restoration projects. 相似文献
950.
Richard S.J. Tol 《Environmental Modeling and Assessment》1997,2(3):151-163
This paper presents the Climate Framework for Uncertainty, Negotiation and Distribution (FUND), an integrated assessment model
of climate change, and discusses selected results. FUND is a nine‐region model of the world economy and its interactions with
climate, running in time steps of one year from 1990 to 2200. The model consists of scenarios for economy and population,
which are perturbed by climate change and greenhouse gas emission reduction policy. Each region optimizes its net present
welfare. Policy variables are energy and carbon efficiency improvement, and sequestering carbon dioxide in forests. It is
found that reducing conventional air pollution is a major reason to abate carbon dioxide emissions. Climate change is an additional
reason to abate emissions. Reducing and changing energy use is preferred as an option over sequestering carbon. Under non‐cooperation,
free riding as well as assurance behaviour is observed in the model. The scope for joint implementation is limited. Under
cooperation, optimal emission abatement is (slightly) higher than under non‐cooperation, but the global coalition is not self‐enforcing
while side payments are insufficient. Optimal emission control under non‐cooperation is less than currently discussed under
the Framework Convention on Climate Change, but higher than observed in practice.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献