Biology Reference
In-Depth Information
0.04
0.02
0
-0.02
-0.04
-0.06
-0.08
6
7
8
9
10
11
12
13
14
Centroid size
0.004
0.003
0.002
0.001
0.000
-0.001
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Positivized size contrast
FIGURE 10.4
Comparison of regression on means to regression on contrasts. (A) Mean shape regressed on
mean centroid size for jaws of 23 sciurine squirrel species. Triangles: Tamiasciurus: squares: Old World
Sciurus
;
diamonds: North American
Sciurus
; circles: South American
Sciurus
; gray circles: South American dwarf species.
(B) Regression on contrasts for the same species. Black symbols are within group contrasts for same taxa as in A;
white symbols are contrasts between that group and its sister group; gray circles are contrasts between the dwarf
species and their respective South America sister groups.
For both PGLS and PIC, errors in phylogenetic inference (both branching pattern and
branch lengths) have the potential to produce misleading results. These phylogenetic
errors increase the standard errors of the estimated statistical parameters, but the estimates
are still unbiased (
Rohlf, 2006
). Numerous studies have demonstrated that these methods
