Abstract
Distribution patterns of herpetofauna of Mexican Nayarit-Guerrero Biotic Province indicate that a gradual change of limiting factors (usually climatic rather than physiographic) will result in a step-wise or clinal loss of spp. from a fauna. This negates likelihood of using percentage of distinctiveness as a means of delimiting biotic provinces. Biotic province concept is misused when a new subsp. is even partially characterized by its occurrence in a different province than its nearest relative, and when a sp. range is descr. by biotic province rather than by actual specimen records, which often leads to that sp. being used to substantiate provincial limits.

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