INTRODUCTION

Research on island organisms has contributed much to
our understanding of the selective pressures that shape
phenotypic diversity (Losos & Ricklefs 2009, Schluter
2000, Wallace 1902, Whittaker & Fern´andez-Palacios
2007). Modern comparative studies emphasize the
importance of using phylogenetically distinct taxonomic
units in an effort to eliminate pseudoreplication
(Harvey & Pagel 1991, Hurlbert 1984). Thus, the
majority of comparative studies of insular biota have
concentrated on endemic species and multi-species
radiations (Roughgarden 1995, Schluter 2000), which
have often been isolated for hundreds of thousands,

or even millions, of years. While studies that consider
phylogenetically independent taxa are useful, they have
an often overlooked drawback: the determination of
selective mechanisms that have shaped phenotypic
diversity in populations over long periods of time
(geological scales) is difficult because the role that past
ecological conditions play in current morphological or
genetic divergence is unknown (Huey & Bennett 1987).
By examining multiple populations of one species that
have been recently isolated on islands which vary in
their ecological conditions, we may reasonably assume
that observed differences between these populations are
related to current conditions (Garland et al. 1991, Grant
& Grant 2002, 2003, Schluter 2000, Whittaker &
Fern´andez-Palacios 2007).