Identification of Biotic Components - Evolutionary Biogeography - page 86

Figure 4.5 Graphic representation of tracks and nodes. (a) Individual tracks; (b)
generalized tracks and node.
Generalized Tracks
Generalized or standard tracks result from the significant superposition of
different individual tracks (Zunino and Zullini 1995). They indicate the preex-
istence of ancestral biotic components that became fragmented by geolo-
gical or tectonic events (Craw 1988a). Generalized tracks are the result of a
comparative analysis of the individual tracks ( fig. 4.5b ). When we compare
oriented individual tracks, we can determine that they belong to the same
generalized track when they agree in both their structure and their direc-
tion (Craw 1988a). Nihei and de Carvalho (2005) suggested that general-
ized tracks could be recognized only when there is phylogenetic evidence
supporting them (e.g., they consist of sister clades). I consider generalized
tracks and areas of endemism to be different representations of biotic com-
ponents ( fig. 4.6 ) .
The generalized trackisthe mostimportant concept inpanbiogeography.
However, McDowall (1978) noted that there are still some questions re-
search should address: How many individual tracks must coincide in order
for a generalized track to be identified? How good must the coincidence be
for an individual track to be considered part of a generalized track? How
does one interpret and weigh the patterns indicated by noncongruent or
conflicting generalized tracks? Graphic representation of generalized tracks
has been analyzed by Fortino and Morrone (1997), who suggested the use
of lines twice as thick as those used for individual tracks ( fig. 4.5b ) . When
two or more generalized tracks have to be represented on the same map,
double or triple lines could be used.
From an epistemological perspective, identifying generalized tracks is an
inductive process. Although inductivism seems to be a crude and primitive
way to conceive scientific knowledge (Ball 1976; Reig 1981), it can play a
basic part of pattern seeking, as recognized by Rosen (1988a, 1988c). Gen-
eralizedtracksandareasofendemismrepresentvalidconjectures,themost
basic hypothetical statements, which may be falsified by cladistic biogeo-
graphic analyses (Morrone 2001c).