CONSERVATION OF ARABIAN GAZELLES - Nwrc.gov.sa

conventional taxonomic characters typically have an unknown or a limited genetic basis and may be
primarily environmentally determined (A vise, 1989).
This taxonomic revolution will need a tremendous investment of time, effort and financial
resources to redefine the levels of all taxa. Effort should first concentrate on endangered taxa where
disputes about taxonomy are hampering appropriate conservation measures.
An overall approach for evaluating the validity of a subspecies
One general approach to evaluate the validity of a particular subspecies is to consider objectively all
available information resulting from the application of different analytical tools to the concerned
taxon (Ryder, 1986). If the information is convergent and reveals a taxonomic distance from other
subspecies, or not, the validity of the subspecies should then be accepted, or rejected. If the data are
inconclusive because of the lack of data or the complexity of the case, other methods should be
applied.
- Range and distribution, natural history, ecology: These simple data can be useful for
investigating speciation and geographic adaptation and thus assessing the validity of some subspecies
within a species. Because populations constituting distinct subspecies are reproductively compatible,
subspecies are normally allopatric, except in secondary hybrid zones (A vise and Ball, 1990). The
characteristics of the range will determine the different habitats to which the species become adapted.
An extended range, particularly on a north-south axis, will probably present a wide variety of climatic
conditions. The distribution of the species, continuous or in patches, and of the different subspecies
are also important factors for genetic isolation. An insular distribution will favour the speciation
process. The natural history of the populations should also be considered carefully. The longer the
geographic isolation, the greater the opportunity for genetic divergence. The problem is to determine
what constitutes a significant period of reproductive isolation (Avise and Ball, 1990). This isolation
time should of course be interpreted in terms of generation time. The founder size of the population
and the initial growth rate, when known, are also key factors in understanding the differentiation
process. It must be kept in mind that the distribution of many taxa has been recently modified due to
human factors . All the ecological differences, such as type of habitat, behaviour, reproductive
performances and physiological adaptations, between two taxa should be taken into account. Their
dispersal habits (e.g. migratory, erratic, sedentary) will also influence gene pool isolation.
- Morphometric analysis: Morphometrics, the quantification of the phenotypic similarities
of popUlations, is a powerful tool if applied on a scientific basis in which large numbers of variables
such as measurements of skulls, skeletons, horns, etc. are subjected to multivariate statistical analysis.
Before any premature judgement is reached, the whole geographic variation of the species should be
considered and genetically independent characters should be studied before grouping the different
races into valid subspecies (Wilson and Brown, 1953).
For example, Fabricius et al. (1989) developed a simple field method to distinguish the two
subspecies of Damaliscus dorcas, the bontebok D. d. dorcas, and the blesbok D. d. phillipsi, and their
hybrids. They proposed a discriminant function obtained by measurements of the white patches on
the hind quarters (based on photographs).
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