(Upload on June 25 2015) [ 日本語  English ]
Mount Usu / Sarobetsu postmined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily
HOME > Lecture catalog / Research summary > Glossary > Ordination
The apparent complexity of techniques for analyzing vegetation data (Kent & Coker 1992) Plant community data are multivariate in nature = raw data matrix Aims of multivariate analysis
1. Summarizing plant community data Reduction of many species/variables into a few components 
[indirect ordination, direct ordination, cluster] Data reductionClassification: Phytosociological approach, Cluster analysis (TWINSPAN)Ordination: direct gradient analysis (CCA), Indirect gradient analysis (PCA,DCA) History1901 Pearson: developed PCA as a regression1927 Spearman: applied factor analysis (to psychology) 1930 Ramensky: introduces the term 'ordnung (German)' into ecology 1954 Goodall DW: introduced PCA into ecology and proposed the term 'ordination' 1970 Whittaker RH (ホイッタカー): developd gradient analysis 1971 Gabriel KR: developd biplot graphical display 1973 Hill MO: reinvented correspondence analysis and introduced CA (as reciprocal averaging) into ecology 1986 ter Braak C: invented CCA 
ordinatio (L) ≡ multidimensional scaling, component analysis and latentstructure analysis Ordination (gradient analysis) is one of the popular multivariate analyses an analytical method of ordering samples (plots) and/or species along actual or presumed gradients Normal analysis= Ranalysis (R分析): Stand or quadrat ordinationOrdination diagram: scatter plot of the eigenvector; used both for biplots and joint plots. Biplot: an ordination diagram of two kinds of entities, e.g., species and environmental variables, which has particular rules of interpretation because it is based on a bilinear model. Interpretation proceeds by projecting points on directions defined by arrows in the biplot. 
Joint plot: an ordination diagram of two kinds of entities based on a weighted averaging method.
Ordination axis: eigenvector, latent variable, theoretical explanatory variable.Inverse analysisor transposed analysis= Qanalysis (Q分析: Species or environmentalfactors ordination
Species score (種スコア): eigenvector coefficient; loading in PCA, center of species curve in CA and DCA. eigenvalue (固有値) = latent roots, characteristic root 
To synthesize species or environmental data and to produce an ordination of quadrats based on environmental or species variables alone. Indirect gradient analysis (indirect ordination): internal analysis, "factor analysis", unconstrained ordination, unconstrained multidimensional scaling, possibly followed posthoc by an regression analysis on external variables Table. Indirect ordination (modified after Kent & Coker 1992)

Fig. 1. Algorithms for (A) correspondence analysis, (B) detrended correspondence analysis, and (C) canonical correspondence analysis, diagrammed as flowcharts. LC scores are the linear combination site scores, and WA scores are the weighted averaging site scores. (Palmer 1993) 
Table. Classification of gradient analysis techniques by type of problem, response model and method of estimation. The techniques listed under “linear/leastsquares” and “unimodal/weighted averaging” can be carried out with CANOCO.
RESPONSE MODEL: linear unimodal
Method of estimation:  leastsquare  maximum likelihood  weighted averaging 
Type of problem:  
Regression  Multiple regression  Gaussian regression  weighted averaging of site scores (WA) 
Calibration  linear calibration; "inverse regression"  Gaussian calibration  weighted averaging of species scores (WA) 
Ordination  Principal component analysis (PCA)  Gaussian ordination  correspondence analysis (CA)^{5)}; detrended correspondence analysis (DCA) 
Constrained ordination^{1)}  Redundancy analysis (RDA)^{4)}  Gaussian canonical ordination  Correspondence analysis (CCA), detrended CCA 
Partial ordination^{2)}  Partial components analysis  partial Gaussian ordination  partial correspondence analysis; partial DCA 
Partial constrained ordination^{3)}  Partial redundancy analysis  partial Gaussian canonical ordination  partial canonical correspondence analysis; partial detrended DCA 
Procedure1. make similarity matrix2. Set up two samples that are the lowest similarity on the two poles 3. Calculate scores of the other samples as follows

AZ = l = 1.0  0.2, KA = d1 = 0.4, KZ = d2 = 0.6 Eigenvaluex:y = kind of contribution rate on axis AZMeasure how much variation in the species data is explained by the particular axis and, hence, by the environmental variables. 
PCA: linear response model ↔ CA: unimodal response model Originally defined for data with multinormal distributions, thus the data should be normalized. Deviations from normality do not necessarily bias the results, however, one should be careful of the descriptors and try to ensure they are not skewed or have outliers. Four versions of PCA
Procedure: Twoway weighted summation algorithm a. Iteration process 1. Take arbitrary initial site scores (x_{i}), not all equal to zero. 2. Calculate new species scores (b_{k}) by weighted summation of the site scores (Eq 5.8). 
3. Calculate new site scores (x_{i}) by weighted summation of the species scores (Eq 5.9). 4. For the first axis go to step 5. For second and higher axes, make the site scores (x_{i}) uncorrelated with the previous axes by the orthogonalization procedure described below. 5. Standardize the site scores (x_{i}). See below for the standardization procedure. 6. Stop on convergence, i.e., when the new site scores are sufficiently close to the site scores of the previous cycle of the iteration; ELSE go to step 2. b. Orthogonalization procedure 4.1. Denote the site scores of the previous axis by f_{i} and the trial scores of the present axis by x_{i}. 4.2. Calculate v = Σ_{i=1}^{n}x_{i}f_{i}. 4.3. Calculate x_{i, new} = x_{i, old}  vf_{i}. 4.4. Repeat Steps 4.14.3 for all previous axes. c. Standardization procedure 5.1. Calculate the sum of squares of the site scores s^{2} = Σ_{i=1}^{n}x^{2}. 5.2. Calculate x_{i}, new = x_{i}, old/s Note that, upon convergence, s equals the eigenvalue. 
[ 平均 ]
Weighted averaging method: method based on a unimodal response model (= unimodal trace line) of which the optimum (mode, ideal point) is estimated by weighted averaging. Ex. correspondence analysis.
Procedure

Table. Site ordination by weighted average.
Site Species Weight 1 2 3 1 100 5 1 0 2 80 3 3 0 3 50 2 4 1 4 30 0 0 3 5 0 10 0 5 Total 21 9 12 Weighted average 84.0 30.0 15.6Ex. Site 1: (100 × 5 + 300 × 80 + 50 × 2 + 30 × 0 + 0 × 0)/10 Klinka weighted average method Dry Wet Moisture score 1 2 3 4 5 6 Total Cover 36.81 14.32 8.94 0.28 0.16 0.32 60.83 Weight 36.8 28.6 26.8 1.1 0.8 1.9 96.0 Soil moisture indicator index = Weight/Cover × 10 = 15.8 
= reciprocal averaging 1935 Hartley HO (19121980): proposed CA 1973 Benzécri JP (19322019) and colleagues: developed CA 
hump = horseshoe (PCA) + arch (CA) + …
Hump can be seen in any PCA and CA The appearance of a projected data swarm as a curve ("arch" or "horseshoe") when the data were obtained from sampling unitHow to remove hump: Do DCA or drop environmental variables highly correlated with the arch to remove the arch. Dropping variables is effective. CANOCO has an improved polynomial detrending technique 
Reciprocal averaging, RA= correspondence analysis (Hill 1973)CA is an extension of the method of weighted averaging (Whittaker 1967) → Species commonly show bellshaped response curves with respect to environmental gradients Figure 5.3. Artificial example of unimodal response curves of five species (AE) with respect to standardized variables, showing different degrees of separation of the species curves, a. real environmental factor, e.g., moisture. b: first axis of CA. c: first axis of CA folded in this middle and the response curves of the species lowered by a factor of about 2. Sites are shown as dots at y = 1 if species D is absent. Procedurea: iteration process (反復過程)1. Take arbitrary, but unequal, initial site scores (xi) 2. Calculate new species scores (uk) by weighted averaging of the site scores (Eq. 5.1). 3. Calculate new site scores (xi) by weighted averaging of the species scores (Eq 5.2). 
4. For the first axis go to step 5. For second and higher axes, make the site scores (xi) uncorrelated with the previous axes by the orthogonaliztion procedure described below. 5. Standardize the site scores (xi). See below for the standardization procedure. 6. Stop on convergence, i.e., when the new site scores are sufficiently close to the site scores of the previous cycle of the iteration; ELSE go to step 2. b: orthogonalization procedure (直交化過程) 4.1. Denote site scores of the previous axis by fi and the trial scores of the present axis by xi. 4.2. Calculate v = Σ_{i=1}^{n}y+ixifi/y_{++}, where y+i = Σ_{i=1}^{m}yki, and y++ = Σ_{i=1}^{n}y+i 4.3. Calculate xi, new = xi, old  vfi.4.4. Repeat Steps 4.14.3 for all previous axes c: Standardization procedure (標準化過程) 5.1. Calculate the centroid, z, of site scores (xi). z = Σ_{i=1}^{n}y+ixi/y++ 5.2. Calculate the dispersion of the site scores s^{2} = Σi=1^{n}y+i(xi  z)^{2}/y++ 5.3. Calculate xi, new = (xi, old  z)/s Note that, upon convergence, s equals the eigenvalue. Ex. Ecological Statistics Package Detrended correspondence analysis, DCA (Hill 1979)Fig. Method of detrending by segments (simplified). The closed circles indicate site scores before detrending; the open circles are site scores after detrending. The closed circles are obtained by subtracting, within each of five segments, the mean of the trial scores of the second axis (Hill & Gauch 1980). 
Principal coordinate analysis (主座標分析), PCO or PCoA= classical multidimensional scaling (CMDS) 
= partial correlation ordination that factors out undesirable influences (like random effects), e.g., difference in observers, phenological variation, block effect, spatial autocorrelation (or depencence) Covariates (covariables): the variables to be factored out 
Partial constrained ordinationspartial CCA, RDA, etcpollution effects × seasonal effects (→ covariables) Eliminate (partial out) effect of covariables. Relate residual variation to pollution variablesReplace environmental variables by their residuals obtained by regressing each pollution variable on the covariables 
Direct gradient analysis (direct ordination): external analysis, canonical ordination (including DCCA), ordination constrained by external variables, constrained multivariate regression, reducedrank regression. 
Canonical ordination(正準序列化, 適訳無): An ordination in which the axes are constrained to be linear combinations of environmental variables. Designed to detect patterns of variation in the species that can be best explained by the observed environmental variables. Differs from indirect ordination because it incorporates a correlation and regression between floristic data and environmental factors within the ordination analysis. Direct ordination (modified after Kent & Coker 1992) (Detrended) canonical correspondence analysis ([D]CCA)
Not strictly indirect ordination since it is a revised version of DCA with ordination axes constrained by multiple regression with environmental factors. Use CANOCO / CANOPLOT / CANODRAW (Micro$oft Windows version available) for analysis (ter Braak et al. 2002) CCA is widely used technique for direct gradient ordination (ter Braak & Smilauer 2002), assuming that species have a unimodal distribution along environmental gradients. DCCA is the detrended form of CCA, as well as relationship between DCA and CA. 
⇓ CCA (Canonical correspondence analysis) (ter Braak 1987, 1988) Gaussian curve (ガウス曲線, 正常分配曲線): curve expressing erro Distribution  The simplest model for a unimodal species response curve (see explorations in coenospace). It has only three parameters, and the equation is: y = A·exp((xB)^{2}/C), where A is the maximum height of the curve, B is the modal location of the curve, and C is a measure of the breadth of the curve (often called niche breadth, tolerance, or standard deviation). The curve is bellshaped. The difference between a Gaussian Curve and a Normal Distribution is that the latter is a statistical distribution, and hence the area under the curve is constrained to be one, and the yaxis represents frequency. TerminologyCanonical axis: an ordination axis that is constrained to be a linear combination of environmental variablesCanonical coefficients: parameters of the final regression = the best weights Linear method: method based on a linear model, e.g., linear regression, multiple regression, principal components analysis, redundancy analysis Partial CCAAll the same precautions apply as with CCAOutput will be nearly identical with the inclusion of the variance accounted for by the partial variable.
Total inertial in the ordination  same as CA Packages handling CCA

= clustering, classification
A. Hiearchical cluster analysis (階層クラスター分析)1. Aglomerative strategy (bottomup)Nearest neighbor method (単純連結法, singlelinkage method 最近隣法)Mountford averagelinkage method (Lassel & Host 1970) Farthest neighbor method (completelinkage method) Centroid method Median method Ward method (= minimum variance method) 2. Divisive strategy (topdown)Phytosociology  not recommended in generalNomenclature: Weber HE, Moravec J & Theurillat JP. 2000. International code of phytosociological nomenclature. 3rd edition. Journal of Vegetation Science 11: 739768 kmeansDIANA (divisive analysis clustering) (MacnaughtonSmith et al. 1964, reviewed by Kaufman & Rousseeuw 1990) Derivations: AGNES, CLARA, DAISY, FANNY, etc. TWINSPAN (twoway indicator species analysis) (Hill 1979)twinspanR in R 
B. Nonhiearchical cluster analysis (非階層クラスター分析) 
SITE 11 1 219807631245 sp. 9 2113 0000 sp. 5 53415 0001 sp. 3 452113 0010 sp.11 32545 0011 sp. 8 153 01 sp. 2 5414545424 100 sp. 1 2313221411 101 sp. 6 2223411 1100 sp.10 142135553 1101 sp. 7 34 1110 sp.12 54 1110 sp. 4 151 1111 000000111111 000001001111 00011 010011 00101 0101 01 Table. Output of TWINSPAN 
[ unfold plots along first axis by RA ] ← (1, 3) 
= vegetation taxonomy, or syntaxonomy A system for classifying plant communities by means of the tabulation of data collected by quadrats 
Fidelity (適合度)= the concentration of a species in a particular syntaxon and which is used both in the classification procedure and in the characterization of syntaxa 