sábado, 15 de septiembre de 2007

The Species Concepts in Aves: Rebuttal

The Cracraft's concept states that a "desirable" Phylogenetic Species Concept must have a "parental pattern of ancestry and descent" component. However, this component is not a rule in other views on the Phylogenetic Species Concept (Wheeler & Platnick, 2000). Because its theorical and practical content, the Phylogenetic Species Concept (Wheeler & Platnick, 2000) is more adequate approach in the debate of species, the diagnosibility by unique combinations of characters-states is a good method in the recognition and delimitation of species. The combination of characters shown the homologies between the groups and it is a good estimate of your relationships. Other Cracraft's requeriment (a criterion for ranking populations at the species-level) is not important in the definition of species, it is a way to organize the names and groups within the Linnaean rank.

The Amadon's rule is a statistical approach to delimit subspecies (Amadon, 1949), the logic of the 75% rule is that the differences among two populations can be statistically measured using the quantity of variation in the populations (Patten & Unitt, 2002). However, the rule is not applicable in many issues because its instability when it is applied to molecular data. Therefore, the 75% rule is "wrong" to delimit subspecies. Wilson and Brown (1953), and Mallet (2001) have been criticized the qualitative definitions as arbitrary because some groups classified qualitatively as subspecies are not differentiated based on multiple characters.

In many studies, the subspecies have functioned as units in at least three roles, namely in classifications, evolutionary theories and, more recently, conservation plans. So, the Linnaean rank of subspecies became prevalent with the emergence of the Biological Species Concept “BSC” (Zink, 2004). In Aves, the ornithologists have spent considerable effort refining and debating subspecies concepts (Wiens 1982). Traditionally, subspecies have been defined by morphological traits or color variations, but recent critics are concerned that these traits may not reflect underlying genetic structure and phylogenies (Haig et al, 2006). Despite the criticisms ( the incongruence among dataset or between molecular and morphological characters), recent studies in which researchers used multiple criteria (e.g., morphological, behavioral, and genetic characters) have confirmed that many subspecies are evolutionarily definable entities. Thus, although subspecies definitions may have been too liberally applied by some early taxonomists, this does not invalidate the concept of subspecies as meaningful biological entities. The subspecies are a useful hierarchy to identify and fit the variable populations within a species.

In the real life, the ornithologists used the coloration pattern to identify different groups. Some strategies are not easy applicable, or they are inconsistent. For example, within the BSC might lead one to assume that partial reproductive isolation would be an appropriate criterion for subspecies recognition. Nevertheless, there is little evidence outside of Drosophila that this criterion has been routinely employed (Haig et al, 2006), Others strategies are difficult because your methodological requirement. Generally, the TSC is "useful" to identify taxa in early approaches, but the character's recognition is essential to delimit and analyze species.