Showing papers by "Robert R. Sokal published in 1981"

Comparing numerical taxonomic studies

Abstract: Rohlf, F. J. 1 (IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598) and R. R. Sokal (Department of Ecology and Evolution, State University of New York, Stony Brook, New York 11794) 1981. Comparing numerical taxonomic studies. Syst. Zool., 30:459-490.-Recent proposals to measure the degree to which given taxometric methods meet goals defined by the three current schools of classification have led to quantitative comparisons of the methods. To aid in understanding such comparisons, a flow chart of taxonomic procedures is presented. Optimality tests are reviewed for each type of procedure. Possibly desirable properties of classifications include: the fit of a summary representation to a similarity matrix, stability, general utility, fit to a known cladistic relationship, and optimality criteria of numerical phylogenetic methods. We examine how they relate to the professed goals of the taxonomic schools and whether they can be used for comparative evaluations between these schools. Previous attempts at comparing numerical classifications are reexamined. Such comparisons have largely been made improperly. Published comparative tests of taxonomic congruence are based on inappropriate comparisons or were improperly executed and cannot furnish evidence on relative stability of phenetic, evolutionary, and phylogenetic classifications. Reports which claim to show that numerical phylogenetic classifications result in better fits to original similarity matrices than phenetic methods and therefore retain distance information better than phenetic classifications are shown to be misleading. In the first such study, the comparison was not relevant to the question asked. In all of these studies the results were biased in favor of phylogenetic methods by retaining redundant information during the computation of matrix correlations for the phylogenetic methods. In two later studies based on ten taxonomic data sets, the comparisons for the phylogenetic methods were in terms of unrooted trees rather than hierarchic classifications. By limiting the reference OTU to OTU 1 in each data set, results were obtained in these studies, that tended to favor the phylogenetic methods considerably more than if some other reference OTUs had been employed. Only in a few cases is there a significant increase in fit with the phylogenetic methods. Interpreted as classifications, UPGMA clustering of the original dissimilarity matrix gives the best fit in the majority of cases when compared with rooted trees (minimum length and least squares fitted). For these data, there is no evidence that classifications by any "phylogenetic" technique yield better summaries of phenetic information than UPGMA. A recent study of predictivity, while correctly designed, yielded complex results with no clear preference for any one school of taxonomy. Thus there is no current acceptable evidence that numerical phylogenetic methods yield classifications which contain more information than either phenetic or evolutionary ones. [Numerical taxonomy; classification; phenetics; phylogenetics; cladistics]. In this paper, we examine the methods proposed for measuring the degree to which various numerical methods meet the differing goals proposed by the various classificatory schools. Are given numerical methods consonant with the stated goals of a given school of taxonomy and can one develop criteria which measure how well these methods meet such goals? We also discuss the validity of usI Present address: Department of Ecology and Evolution, State University of New York, Stony Brook, New York 11794. ing the same criteria to compare phenetic and cladistic approaches to taxonomy. We first describe the normal flow of procedures in a numerical taxonomic study. Next we enumerate the types of criteria that have been used to evaluate the optimality of such procedures and discuss appropriate ways by which comparisons can be made between alternative taxonomic procedures. We suggest methods for improving the evaluation of numerical techniques and outline some principles for studies comparing numerical phenetic and phylogenetic techniques. Then we examine several pub-

Geographic variation in Pemphigus populitransversus (Insecta: Aphididae)*†

Abstract: The geographic variation of 33 morphological characters of two morphs of the gall-forming aphid Pemphigus populitransversus is studied in 214 locality samples. Among-locality variation ranges from 1 to 69% in the elongate morph and from 0 to 44% in the globular morph. The design of the study permits separation of interlocality correlations from intralocality correlations. The former are partly a function of the latter, confirming early observations on another Pemphigus species and on ticks. Factor analyses of both correlation matrices for both morphs yield four factors. Within localities these factors agree for the two morphs; among localities only one factor corresponds. Multiple discriminant analyses among localities of the two data sets do not correspond. There is little correlation between characters of stem mother and alate morphotypes within localities but such correlations are strong among localities. Maps are furnished for characters representing the independent dimensions of variation for each morph. Patterns of variation are shown to be significant by spatial autocorrelation analysis for both morphs but are much more marked in the elongate morph. Significant positive autocorrelation occurs up to 1000 km in the elongate morph – mostly only up to 200 km in the globular morph. There are two to three geographic variation patterns in the elongate morph, whereas in the globular morph the classes of patterns are less well defined and involve few characters. The environmental factors to which the globular and elongate morphs are adapting would appear to have different autocorrelation patterns. In each morph the patterns are clearly different and cannot be explained by a single microevolutionary process. The findings are compared with an earlier study in the related and largely sympatric P. populicaulis.

Geographic Variation in Variability of Pemphigus Populicaulis

Abstract: Bird, J., B. Riska, and R. R. Sokal. (Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, New York 11794) 1981. Geographic variation in variability of Pemphigus populicaulis. Syst. Zool., 30:58-70.-Geographic variation of variability profiles is studied based on stem mother, alate and gall characters of the aphid Pemphigus populicaulis. Significant differences among the coefficients of variation of the suite of characters in every locality were found by two methods-Bartlett's test for homogeneity of variances (using log-transformed data) and Friedman's nonparametric test for randomize'd blocks. Nine characters are highly variable and six are consistently low in variability. Coefficients of variation show significant heterogeneity among localities for every character by Bartlett's test, and for all but two characters using a modified Friedman's test. The variability profiles of the 66 localities were clustered into three groups based on both size and shape by the k-means algorithm. A mixture of two types of profiles occurs throughout the middle latitudes of the study area, while the third type is found in its northern and southern regions. This geographic pattern may in part be due to the year of collection. Attempts to relate the magnitude of the coefficients of variation to several ecological indices were unsuccessful. [Variability, variability profiles, geographic variation, coefficients of variation, Pemphigus.] This study investigates whether relative morphological variability varies geographically. A measure of variability is a fundamental parameter in evolutionary research because of the intimate relationship between natural selection and variability. Natural selection shapes variability and is in turn limited in its potential effects by the extent of the variability of a given character. Low variability in a