Identification of Biotic Components - Evolutionary Biogeography - page 82

Figure 4.3 Alternativerepresentationofaspeciesdistribution.(a)Dotmap;(b)out-
line map, where a free-form line encloses the peripheral localities; (c) application of
Rapoport's (1975) mean propinquity method; (d) individual track.
Another criterion for orienting individual tracks is the location of main
massings, which are defined as the greatest concentration of biological di-
versity in the range of the taxon, such as number of species or genetic di-
versity ( fig. 4.4c ) . In general, main massings represent areas of numerical,
genetic, or morphological diversity of a group (Page 1987), which may be
identified by a grid analysis (Craw et al. 1999). Platnick and Nelson (1988)
and Humphries and Seberg (1989) complained that Croizat referred to main
massings as “dispersal centers,” “places of origin,” “centers of emergence,”
“ancestral centers of radiation,” and “centers of origin,” and even Page
(1990c) admitted that the concept of main massing was “horribly vague.” If a
track is oriented from the main massing toward the periphery, the inference
involved would be similar to that from dispersal biogeographers (Crisci et al.
2000), so this criterion might also be inappropriate.
Of the available criteria for orienting tracks, the less problematic is the
baseline. When the analyses are undertaken on continental scale, however,
the use of geological or tectonic characteristics is somewhat more difficult