生态学中的尺度问题：内涵与分析方法

尺度问题已成为现代生态学的核心问题之一.尺度问题主要涉及3个方面：尺度概念、尺度分析和尺度推绎.主要评述前两个方面.生态学尺度有三重概念：维数、种类和组分,其中每重概念又包含了多个定义,有必要进行澄清、分类和统一.尺度分析涉及尺度效应分析和多尺度空间格局分析.格局、过程及它们之间的关系,以及某些景观特性均表现出尺度效应,因此多尺度研究非常必要和重要.多尺度空间格局分析（尤其是特征尺度的识别）是进行尺度效应分析和跨尺度推绎的基础.多尺度分析需要特定的方法,景观指数法是最常用和最简单的方法,但也常产生误导;空间统计学方法（如半方差分析法、尺度方差分析法、空隙度指数法和小波分析法等）和分维分析法在最近十几年发展起来,并逐渐应用于生态学,在尺度分析上具有很大的应用潜力.各种方法在尺度分析上各有优势和不足,有必要同时使用两种或两种以上方法进行比较和评估.总之,有关尺度分析的研究需要进一步加强,从而为下一步的尺度推绎提供可靠的依据.

Scale issues in ecology: concepts of scale and scale analysis

Scale issues are fundamental to all ecological investigations,and have become a central topic in ecology in recent decades with the increasing recognition of broad-scale environmental issues(such as global warming) and land-management problems,rapid development of digital technologies(remote sensing,GIS, desktop computers,etc.),and emergence of landscape ecology.However,there are still many ecological studies in which scale is treated simplistically or superficially.Scale issues remain a key challenge for ecologists in the 21~(st) century.Scale issues include conceptualization of scale,scale analysis and scaling.This paper focuses on the former two issues.A three-tiered conceptualization of scale is introduced: dimensions,kinds,and components.Dimensions of scale are most general,including space,time,and organizational levels.Kings of scales can be distinguished among phenomenon scale(including structure and process scale,also referred to as characteristic or intrinsic scale),observation scale(also referred to as sampling or measurement scale),analysis or modeling scale and policy scale.The most specific and measurable definitions are components of scale,including grain,extent,spacing(or lag),coverage,cartographic scale,and support.Scale is often expressed as grain and extent in landscape ecology.Because each type of scale concept includes multiple terms and definitions, it is necessary to carefully discriminate,classify and unify them.Scale analysis is to analyze scale effects and identify multiple-scale spatial patterns(especially characteristic scale(s)).Scale effects may occur in each of the following three situations: changing grain size only,changing extent only,and changing both grain and extent.When scale of observation,analysis,modeling,or experimentation change,statistical results(for example,mean,variance and multivariate relationships) are expected to change.Scale influences the results of examining spatial pattern,such as spatial heterogeneity,spatial distribution,spatial autocorrelation,spatial anisotropy,and patch and gap sizes. When scale changes,new ecological processes and patterns may occur,and the rate or frequency of processes,control factors,and correlations between processes may also change.Some landscape properties(for example,landscape openness, equilibrium,predictability,species richness and diversity) also exhibit scale effects.Because of scale effects,it is extremely important to conduct research at multiple scales.Identifying characteristic scale(s) means examining hierarchical structure of pattern or process,and distribution of patch sizes and spacing between patches,which are the basis for studying scale effects and scaling.Some specific methods need to be developed for scale analysis,mainly including spatial statistics methods,landscape metrics and fractal analysis.Landscape metrics are the most popular methods which are both simple and potentially misleading.Spatial statistics methods and fractal analysis have been developed and applied in ecology during the past decades,and have a great potential in scale analysis and scaling.Spatial statistics methods include semivariance,scale variance,lacunarity,wavelet,representative elementary volume analysis,and so on.Each of them has its own advantages and disadvantages in identifying characteristic scale(s) and analyzing scale effects,thus it is essential to compare and evaluate two or more methods in the same study.In summary,to provide a reliable foundations for scaling,scale analysis must be conducted thoroughly first.Research focusing on characteristic scales of landscape pattern or process and establishing scaling relations should be followed. Finally,a better understanding and thus explanation of the dependence of pattern and process on scale may be achieved.