Biology Reference
In-Depth Information
FIGURE 10.10
Cladogram of the piranhas ana-
lyzed in this chapter; nodes are numbered to des-
ignate clades.
TABLE 10.1
Disparities of Clades (Numbered as in
Figure 10.10
), Measured at Two Ontogenetic Stages
Taxon
Juvenile Disparity
Standard Error
Adult Disparity
Standard Error
Clade 1
0.00543
0.0003
0.00398
0.0002
Clade 2
0.00575
0.0003
0.00405
0.0002
Clade 3
0.00431
0.0004
0.00550
0.0003
Clade 4
0.00229
0.0002
0.00603
0.0004
Clade 5
0.00116
0.0002
0.00151
0.0001
Clade 6
0.00073
0.0002
0.00051
0.0002
Disparities of juveniles are measured at the transition from larval to juvenile growth; those of adults are measured at maximum
body size attained by each species.
whole (Clade 1), which may seem impossible, but disparities measured this way are not
additive. In these analyses, we are measuring the disparity of each clade relative to that
clade's own mean
hence a low disparity indicates that few species differ by much from
the mean of that clade. Consequently, a group comprising three or four species that differ
a great deal from each other (and from the group mean) can have a much higher disparity
than a larger group that includes those species. That is because the additional species in
the larger group may all be much closer to the grand mean. Consequently, their values of
D
j
are small and contribute relatively less to
P
D
1
whereas the addition of each species
increases
N
1 by one. The net effect is that
MD
decreases. For that reason, a large group
containing only a few species that are far from the grand mean can be less disparate than
a small group with the same number of species far from the mean. That is one reason why
morphological disparity can decrease while taxonomic diversity increases.
2
Partial Disparity
When we want to quantify the contribution that a particular taxon makes to the overall
disparity of a larger group, we want a metric that allows us to partition disparity
