CONTINENT-WIDE PATTERNS OF SONG VARIATION PREDICTED BY CLASSICAL RULES
OF BIOGEOGRAPHY
Abstract
Physiological constraints related to atmospheric temperature pose a
limit to body size in endothermic animals. This relationship has been
summarized by two classical principles of biogeography: Bergmann’s and
Allen’s rules. Body size may also constrain other phenotypic traits
important in ecology, evolution and behaviour, and such effects have
seldom been investigated at a continental scale. Through a
multilevel-modelling approach, we demonstrate that continent-wide
morphology of related African barbets follows predictions of both
ecogeographic rules, and that body size mirrors variation in song pitch,
an acoustic trait important in species recognition and sexual selection.
Bergmann’s rule effects on song dwarf those of acoustic adaptation at a
continental scale. Our findings suggest that macroecological patterns of
body size can influence phenotypic traits important in ecology and
evolution, and provide a baseline for further studies on the effects of
environmental change on bird song.