jueves, 31 de julio de 2008

"Pattern-based" methods

Ronquist and Nylin (1990) introduced the idea of “pattern-based” methods to refer to the plethora of techniques of cladistic biogeography that have as aim finding general patterns of area relationships without taking into account the evolutionary processes that configured those patterns. Except Brooks and his collaborators “pattern advocates” regard as the main point of biogeographic analysis what causes the congruence among taxon-area cladograms and not in what causes ambiguity (Wiley, 1987; Nelson and Platnick, 1981; Ebach, 2001). So, only when a pattern is found the investigator could discuss about the possible vicariant events have took place between the areas. In certain way this is preferable rather than assume that incongruence is due to any other biogeographic event instead vicariance. This cloudy approach is due to a misunderstanding of the relationship between phylogenetic analysis and biogeography, that is if someone wants to introduce transversal transmission needs a method able to test it as a hypothesis (see Sober, 1998). Other methods as paralogy-free-subtree analysis (Nelson & Ladiges, 1996) when remove the paralogy dismissed evidence in order to fix the data into the idea of what biogeographic history behaves. This constitutes a problem in order that it removes other possible vicariant sceneries. Although, any of the denominated “pattern-based” methods allow a clear evaluation of the biogeographical history it is preferable to assume as the only plausible explanation vicariance rather than create sentimental relates based on the incongruence.

lunes, 28 de julio de 2008

Historical Biogeography and pattern

The study of Historical Biogeography is divided in two items. The pattern and Procces approaches. The objective of pattern approaches is elucidate the hierarchy (relationships) among areas (biotes, areas of endemism).

Several methodologies has been proposed to identify these relationships. Brooks Parsimony Analysis - BPA - (Brooks, 1981, 1988), Component Analysis (Nelson & Platnick, 1978, 1981), Component Compatibility Analysis - CCA - (Zandee & Roos, 1987), and Paralogy-Free Subtrees - TASS - (Nelson & Ladiges, 1996), among others. However, The efficient of these methods is considered ambiguous in some issues.

The ideal approach in Historical Biogeography (pattern) must be include all available phylogenetic and distributional data. Thus, methods such as Component Analysis (Nelson & Platnick, 1978, 1981) and TASS (Nelson & Ladiges, 1996). The elimination of incongruent data is not desirable because this lost minimizes the realibility of results in the analysis.

The node analysis among area cladograms is also an debate point in Historical Biogeography. The comparison of internal nodes within area cladogram is not necessary. The area cladograms must be compared among them (area cladogram vs. area cladogram). The comparison among internal nodes is not produces relevant information about areas relationships.

Likewise, an optimization criterion is necessary to estimate the best area topology (hierarchy). Other point of debate is the inclusion of events methods in the seek of area relationships. The area topologies is a graphic representation of areas relationships. These topologies are not inferences about the evolutionary process in the areas.