Ecologically Benign Invasions: The Invasion and Adaptation of Common Waxbills (Estrilda astrild) in Iberia

Abstract

Invasive species often damage the ecosystems they colonise. But non-harmful biological invasions also exist in nature, and understanding which biological invasions are ecologically benign is important for prioritizing conservation goals. As a case study, we review research on the biological invasion of the Iberian Peninsula by the common waxbill (Estrilda astrild ), a small estrildid finch from sub-Saharan Africa, with the objectives of assessing the potential for detrimental impact on Mediterranean ecosystems, and illustrating how biological invasions provide research models for diverse sub-disciplines in ecology. Common waxbills are traded as pets and, starting from birds escaped or released from captivity, have been invading the Iberian Peninsula since the 1960s. Range expansion initially used coastal areas and river valleys, and later progressed to more inhospitable sites at higher altitude or inland. Colonising those diverse ecological environments poses adaptive challenges, and phenotypic changes have accompanied this invasion. Differences in personality among populations appear adaptive to the different climatic regimens waxbills colonised, and changes in ornamentation during the invasion are best explained by ecologically-mediated differences in sexual selection among sites. These phenotypic changes show the usefulness of invasive species for research in behavioural and evolutionary ecology. The niche waxbills occupy in Iberia is marginal in relation to the ecological space occupied by native passerines, and waxbills appear not to compete strongly with natives. The differentiated ecological niche that waxbills occupy is in part due to anthropogenic influences (irrigation of agricultural areas, and food provided by exotic plants). We conclude that anthropogenic modification of the landscape creates novel niches that native species may not have filled in, and that thus can accommodate some exotic species with minimal interference on the native community.