. An ecogeographic analysis of the herpetofauna of the Yucatan Peninsula . Fig. 4.—Cluster analysis of 108 grid squares on the basis of presence or absence of lizard species. Squares clustered at the level of similarity or higher are united, assigned a number, and cir- cumscribed by a dotted line. On the map a solid line encloses major areas of faunal homogeneity. The cophenetic correlation coefficient is excess of squares with few distribution limits, and an excess of squares with many limits, indicating that the limits of distribution are contagious (clumped). The coeflBcients of
. An ecogeographic analysis of the herpetofauna of the Yucatan Peninsula . Fig. 4.—Cluster analysis of 108 grid squares on the basis of presence or absence of lizard species. Squares clustered at the level of similarity or higher are united, assigned a number, and cir- cumscribed by a dotted line. On the map a solid line encloses major areas of faunal homogeneity. The cophenetic correlation coefficient is excess of squares with few distribution limits, and an excess of squares with many limits, indicating that the limits of distribution are contagious (clumped). The coeflBcients of dispersion (CD.) in- dicate this also, for in all cases they sub- stantially exceed unity. Faunal areas.—Contagious distribu- tion limits indicate the existence of areas where distribution limits are concordant, , areas of rapid faunal transition. These in turn imply the existence of areas of faunal homogeneity, the loca- tions of which are indicated in Figures 3, 4 and 5, which summarize the results of separate cluster analyses for frogs, lizards, and snakes. What constitutes a major cluster depends upon the level of similarity used to define it, and in this I have followed no particular rule; rather I have identified clusters, and the faunal areas they represent, by inspection of the phenograms. Some might disagree with my interpretations, but this is not a serious issue, for the clusters are usually easily recognizable. Thus, in Figure 3 four areas of faunal homogeneity are in- dicated for frogs: one in the northwest corner, one in the northern half of the peninsula exclusive of the northwest cor- ner, a central area, and a southern area. A similar pattern exists for lizards, al- though the picture is less clear. In Fig- ure 4 I recognize essentially the same four faunal areas identified for frogs, plus one small area in north-central Belize. A somewhat different pattern emerges for snakes, where only three major areas are apparent: a northern, central, and southern
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