ORDINATION TECHNIQUES IN ENVIRONMENTAL BIOLOGY - …：环境生物学排序技术—….ppt

CONCLUSIONS What can be done with modern ordination techniques in a combined exploratory and confirmatory way? Hallgren, Palmer, & Milberg (1999) Journal of Ecology 87, 1037-1051 2000+ plots in cereal and oil-seed crops in Sweden 1970-1994 AN INVESTIGATION OF BROAD-SCALE GRADIENTS IN SWEDISH WEED COMMUNITIES E. Hallgren, M.W. Palmer & P. Milberg (1999), Journal of Ecology 87:1037-1051 Data Diving With Cross-validation: Flow chart for the sequence of analyses employed in the study. Solid lines represent the flow of data and dashed lines the flow of ideas or analyses. Map of Sweden with the geographical regions (A-H) indicated. Environmental variables used in the analyses Nominal variables Sowing season (autumn or spring) Geographical regions: Swedish counties (A-H) Soil types (1, sandy soil; 2, fine sand soil; 3, silty soil; 4, loamy soil; 5, silty clay loam; 6, heavy to very heavy clay soil; 7, organogenic soil) Crop species (barley, wheat, rye, oats, turnip rape, rape; categorised according to season of sowing) Interval-scale variables Year of trial (1970-1994) Organic content (%; seven catgories) Continuous variables Nitrogen fetilization (N ha-1) Crop yield (kg ha-1) Techniques used 1.? Detrended correspondence analysis - reveal gradients in data 2.? Canonical correspondence analysis - Monte Carlo permutation tests on "trace" statistic 3. Partial DCA - any interpretable species patterns beyond the effects of measured environmental variables 4.? Partial CCA - can one set of variables explain variation in species composition not explained by a second set of variables 5.? Stepwise CCA Exploratory data set 1000 plots Confirmatory data set 1000 plots Display data set 2359 plots Autumn sown Spring sown Variance partitioning Partitioning of the explainable variable variation among the four groups of variables. T?U is the variation described by T but not explained by U. T?U is the variation jointly described by T and U. U?T is the variation described