Differences in phenotypic variance between old and young congeneric species on a small island

Abstract

AbstractAimInsular environments theoretically promote within‐species phenotypic variance, in part but not only because insular species enjoy a lower number of trophic interactions than their mainland counterparts. However, environmental factors apparently confound empirical comparisons between insular and mainland systems. To address this issue, we studied sympatric, congeneric species from the same small island, but that stemmed from separate colonization events. We predicted that the time since the species had colonized the island would correlate positively with the within‐species variance in morphometrics.LocationLifu island, New Caledonia, South Pacific.TaxaZosterops inornatus, Z. minutus, Z. lateralis (Passeriformes).MethodsWe measured seven morphological traits and used principal component analysis to compute axes of variation.ResultsThe within‐species variance in bill size and in feet/tail ratio corrected for body size increased with the estimated time since the species had been on the island. A similar but non‐significant trend existed for body size and bill width.Main ConclusionsThe morphometrics of the three species of Zosterops birds from Lifu supported the hypothesis that insular environments promote within‐species phenotypic variance, and cast a new light on the role of competition in the erosion of phenotypic variance.