Abstract:
The speed of range expansion in many invasive species is often accelerating because individuals with stronger dispersal
abilities are more likely to be found at the range front. This ‘spatial sorting’ of strong dispersers will drive the acceleration of
range expansion. In this study, we test whether the process of spatial sorting is at work in an invasive bird population
(Common myna, Acridotheris tristis) in South Africa. Specifically, we sampled individuals across its invasive range and
compared morphometric measurements relevant and non-relevant to the dispersal ability. Besides testing for signals of
spatial sorting, we further examined the effect of environmental factors on morphological variations. Our results showed
that dispersal-relevant traits are significantly correlated with distance from the range core, with strong sexual dimorphism,
indicative of sex-biased dispersal. Morphological variations were significant in wing and head traits of females, suggesting
females as the primary dispersing sex. In contrast, traits not related to dispersal such as those associated with foraging
showed no signs of spatial sorting but were significantly affected by environmental variables such as the vegetation and the
intensity of urbanisation. When taken together, our results support the role of spatial sorting in facilitating the expansion of
Common myna in South Africa despite its low propensity to disperse in the native range.
