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

Body size of island taxa
Body size of island taxa
No island rule, no insular size extremes
the more dramatic cases of insular size evolution, where
changes are drastic enough to merit different specific status.
Thus intra-specific studies will omit from consideration, for
example, Elephas falconeri, which evolved to just 1% of the
mass of its mainland ancestor (Roth, 1992), and even studies
conducted on species within genera will miss members of
insular endemic genera such as the c. 100 kg insular rodent
Amblyrhiza inundata (Biknevicius et al., 1993) and the largest
gecko, Hoplodactylus delcourti (Russell & Bauer, 1986).
Here we examine, in a purely inter-specific fashion, whether:
(1) species with extreme body sizes (i.e. the largest and smallest
species) in a subclade are more often insular endemics than
expected by chance given the number of insular endemics in
the subclade; and (2) if there is evidence for a pattern
consistent with the island rule above the species level using
mean sizes of insular and mainland species within clades.
No island rule, insular size extremes
(a) (b) (c)
Body size of mainland taxa
Island rule, insular size extremes No island rule, insular size extremes
(d) (e) (f)
Body size of mainland taxa
We use nearly complete datasets of species body sizes of
mammals, birds and lizards. For mammals (only) a comprehensive
species-level phylogeny and an excellent late Pleistocene
fossil record exist. This meant that we were also able to
use a sister-clade comparison, and include data for species
that went extinct since the end of the last glacial, which
include some of the most pronounced cases of insular size
evolution.
MATERIALS AND METHODS
Data
Island vertebrates and body size extremes
Island rule, no insular size extremes
Reversed island rule, insular size extremes
Figure 1 Schemes showing possible ways in which patterns of body size on islands and mainland within taxa (size extremes or average
sizes) can combine to produce patterns of body size across taxa (slope 1). x-axis, mainland body size; y-axis,
island body size; dashed line, a line with an intercept of 0 and a slope of 1; solid line, slope returned by standardized major axis regression
(can mask the dashed line). The body size frequency distributions depict insular (top) and mainland members of a clade (bottom). The
mainland mean size is indicated by the vertical, dashed line. (a) The null distribution. No insular size extremes, no island rule (slope of 1,
similar insular and mainland size ranges). (b) There are size extremes because island taxa have wider size distributions, but no island
rule because mean sizes are similar (slope of 1). (c) The island rule holds (small animals evolve larger size and large ones dwarf, slope