Slaying dragons: limited evidence for unusual body size evolution ...

S. Meiri et al.
Insular mean SVL (log 10 scale)
Insular mean mass (log 10 scale)
Birds
(a) (b)
Continental mean SVL (log 10 scale)
(a) (b) (c)
Of 8069 bird species in our dataset, 1347 are insular endemics
(we have maximum mass data for all, and for 7552, including
1268 insular endemic species, we have data on mean size;
Appendix S1b). In 90 out of 223 avian genera the largest
member of the clade is an insular endemic. This is significantly
more than expected under our randomizations (median
expected = 71; P < 0.01, Table 1). However, at the family
and order levels (see size frequency histograms in Appendix
S3b) the largest member of a clade is no more often an
insular endemic than expected at random. The frequency with
which the smallest member of a clade is an insular endemic
does not depart from the null expectation for any taxonomic
level. Moreover, when we repeated the analysis at the genus
level using the maximum rather than mean body size (data are
the maximum reported for a species in Dunning, 2008),
neither the frequency of gigantism nor dwarfism departed
from the null expectation (67 observed insular maxima across
219 genera, median expected = 71, P = 0.53).
There was no evidence for the island rule at the genus and
family level in birds, with slopes equal to 1.00 and 0.98,
Continental mean mass (log 10 scale)
respectively (Fig. 3a,b). The slope at the order level, however,
was significantly shallower than 1 (SMA slope = 0.76, 95%
CI = 0.66–0.88, r = )0.70, P < 0.01; P randomization < 0.01;
Fig. 3c), even when ratites are excluded (SMA slope = 0.78,
95% CI = 0.64–0.95, r = )0.56, P < 0.05; Prandomization <
0.05).
Mammals
Figure 2 Standardized major axis regression
of mean body size [log 10-transformed
snout–vent length (SVL) in mm] on islands
versus continents for species in lizard genera
(a) and families (b). The dashed line has a
slope of 1 and an intercept of 0. The solid line
represents the standardized major axis
regression slope estimate.
Figure 3 Standardized major axis regression of mean body size (log 10-transformed mass, in g) on islands versus continents for species in
bird genera (a), families (b) and orders (c). The dashed line has a slope of 1 and an intercept of 0. The solid line represents the standardized
major axis regression slope estimate.
Of 3961 extant mammal species, 670 are insular endemics (778
of 4213 when extinct species are included). The frequency of
insular endemics that are either the largest or smallest
members of their clades does not depart from the null
expectation derived by randomization at any taxonomic level,
either including or excluding extinct taxa (Table 1, Appendix
S3c).
In agreement with the results from randomizations, the
frequency of gigantism and dwarfism tended not to exceed the
null expectation generated under a single-rate Brownian model
on the mammalian phylogeny. This was true for all taxonomic
levels, both including and excluding extinct species, except for
6 Journal of Biogeography
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