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A Computer Approach to the Comparison and Identification of Species in Difficult Taxonomic Groups

Ernest E. Williams
Hugh Rand
A. Stanley Rand
Robert J. O’Hara

{Abstract}

A computer program for the identification of unknown taxa in “difficult groups” based on matching rather than sequential exclusion is proposed as a substitute for both the conventional dichotomous key and for the random entry matrix that has been suggested as a replacement for the dichotomous key. The matching program is modeled after the steps that a practicing taxonomist would employ in the identification of an unknown specimen:

1. Data for the unknown are compiled.
2. Data for the unknown are compared with those of relevant known taxa.
3. On the basis of the comparison, certain of the named taxa are considered possible matches with the unknown.
4. Final choice of the named taxon best matching the unknown is made and confirmed from additional data. If there is no match, the possibility of an undescribed species must be confronted. {page 2}

The program enables a computer to follow these steps:

1. It first enters the states of selected characters for the unknown individual or series. For each character of the unknown individual or series, two numbers are recorded, a minimum and a maximum; in the case of the series allowing for variation within the sample, and in the case of the individual allowing for differences between its two sides and also obscurities and ambiguities in counts or coding.
2. Once these data are entered, the program compares them against the ranges recorded in a reference matrix for selected known species. The user specifies the maximum number of characters in which a taxon in the reference matrix is allowed to differ from the unknown before being accepted as a “match.”
3. The resulting report lists all the matching taxa and, for each, the number of characters not matched, the specific characters not matched, and by how much.
4. Included in the report for each matching taxon is a “descriptor” that cites characters that are not coded for the computer as well as characters regarded as “diagnostic” for the taxon. The descriptors assist in the final choice of the most plausible identification for the unknown. In certain cases (e.g., a new taxon), evaluation of the descriptors may require the user to reject all matches.

While the program was inspired by problems encountered during exploration of the systematics of anoline lizards, it does not deal with phylogeny at all. It is only—in our eyes—a better substitute for the dichotomous key. It aids in the identification of animals. As such, it has been customized for the anoles. The reference matrices, character descriptions, and “descriptors” provided as examples in the second and succeeding sections of this paper are for anoline lizards only. The concept of the matching program is, however, applicable to taxa of any sort.