Biology Reference
In-Depth Information
Using Comparisons Between Interspecific Vectors to Find Characters
The basic idea of this approach is to compare all species to one other species (which is
held constant). These pairwise contrasts can then be examined for similarities. By compar-
ing the differences between one species and each of the others, we can then inspect the dif-
ferences for similarities. The logic of the method is that we are looking for similarities in
the differences
i.e. similarities among taxa in features specific to them. To exemplify this
approach, we will continue the analysis of piranha juvenile body shape, comparing each
species to the outgroup (Figure 13.7). Of course, it is not necessary to use the outgroup in
these comparisons; any species could be used as that “other,” and it may be useful to use
more than one before drawing conclusions.
From these comparisons, it is obvious that
S. elongatus
,
S. gouldingi
and
S. manueli
are
shallow-bodied compared to all other piranhas. They differ profoundly from
P. denticulata
in this, whereas none of the other species do. This is the feature that dominated the PCA
(and it is obvious by qualitative visual
inspection as well). Additionally, these three
P. denticulata vs S. altuvei
P. denticulata vs S. elongatus
P. denticulata vs S. gouldingi
P. denticulata vs S. spilopleura
P. denticulata vs S. manueli
P. denticulata vs P. piraya
FIGURE 13.7
Pairwise comparisons between mean juvenile body shapes of
P. denticulata
and six other spe-
cies. Comparisons to
P. nattereri
and
P. cariba
are not distinct from the comparison to
P. piraya
.
