Page 9 - Renaud_Michaux_2007

Mandibles and molars of the wood mouse, Apodemus sylvaticus (L.)

(a) 0.5
IBIZ
0.4
ELBA
Distance to
mainland
0.3
D < 10 km
FR-Y 10 < D < 200 km
Md size (Area H1) 0.1 FR-RE CO D > 200 km
0.2

0.0
SIC-FIC
FR-OL
12
FR-PORQ Ln(island area)
FR-PTCR 10
–0.1
SIC-GRAT
FR-NM 8
6
–0.2
4
SARD 2
–0.3 0
–0.5 0.0 0.5 1.0
M1 Size (A0)
(b) 0.07
FR-Y
0.06

Figure 4 Insularity effect on size (a) and 0.05
shape (b) of molar vs. mandible of the wood Md shape (Dist. FCs EFT7)
mouse. (a) The size divergence is estimated as IBIZ
the difference between the mean value of the 0.04 FR-RE
size estimator (A 0 for molars and area H1 for CO SIC-FIC
the mandible) on one island and its closest FR-PTCR
mainland relative. (b) The divergence in SIC-GRAT
0.03 FR-NM FR-PORQ
shape is estimated as the Euclidean distance
between the mean values of the FCs (RFT9
FR-OL
for the molar and EFT7 for the mandible) of ELBA
SARD
one island and its closest mainland relative. 0.02
The size of each symbol is proportional to the 0.00 0.01 0.02 0.03
logarithm of the island area. M1 Shape (Dist. FCs RFT9)

Ecological parameters such as competition and predation, the island may counterbalance its remoteness, possibly leading
however, are known to play an important role in island to a decrease in mandible size.
evolution. These parameters are difficult to assess reliably for The amount of shape divergence of M1 was related to island
all the islands, because predators and competitors may vary area but was minimal on islands of intermediate size (Elba,
greatly from one island to another, and density is also a Corsica, Ibiza). The shape of the mandible varied with the
crucial factors that cannot be easily quantified. Quantitative remoteness of the island. As in the case of mandible size,
comparisons were performed between morphological estima- intermediate levels of remoteness (Yeu, Ibiza, Corsica) pro-
tors and these various parameters of the islands, but moted divergence of mandible shape. Finally, the number of
comparisons with ecological factors should be considered competitors on the island was also related to divergence of
with caution. mandible shape, with maximal divergence for three compet-
The size of M1 did not correlate with any investigated itors (Yeu, Ibiza, Re ´).
parameter (Table 6). The size of the mandible was related to
island area, although in a nonlinear fashion. Mandibular size
DISCUSSION
increased on islands of intermediate size (Ibiza, Corsica, Elba)
and/or at intermediate distances to the mainland (Yeu, The most striking result from this study is the discrepancy
Corsica, Ibiza). In the case of Sardinia, the very large size of between a latitudinal mainland gradient in size and shape of

Journal of Biogeography 34, 339–355 347
ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd