Biology Reference
In-Depth Information
FIGURE 1.4
4
The 16 landmarks, stripped
of the line segments connecting them.
3
5
2
6
14
15
1
7
16
13
8
12
11
10
9
4
3
5
2
6
14
15
1
7
13
16
8
11
12
10
9
the variance), size explains 72.3% of the variance in shape in one species but only 21.7%
in the other.
An important advantage of analyzing landmark coordinates is that it is relatively easy
to draw informative pictures to illustrate the results. In
Figure 1.5
, the shape changes
that occur during the ontogeny of one species of piranha are shown as vectors of relative
landmark displacement and as a deformed grid that shows the changes between those
vectors. In both representations, it is quite clear that the middle of the body becomes rela-
tively deeper while the postanal region becomes relatively short, especially the caudal
peduncle (between landmarks 6 and 7). Both pictures also show that the posterodorsal
region of the head (above and behind the eye) becomes relatively longer and deeper while
other regions of the head become relatively shorter. (We emphasize that these are
relative
changes, because the piranha becomes
absolutely
larger in every dimension and region
mentioned.)
It is possible to present traditional morphometric results in graphic form by placing
the values of the allometric coefficients on the organisms, as in
Figure 1.6
. This, like
