Age-based differential host acceptability and human mediated disturbance prevent establishment of an invasive species and displacement of a native competitor.

Establishment failure by immigrant species, while believed to be a common occurrence, is difficult to observe and so factors contributing to failure are poorly explored. Human mediated disturbance is a key element in facilitating biological invasions, but its role in preventing establishment is rarely considered. In Australia, the whitefly, Bemisia tabaci biotype B was first detected in 1994 and has since spread widely and displaced an indigenous competitor. However, in one location it has failed to establish permitting an indigenous competitor to persist. In this area, the dominant plant host is Euphorbia cyathophora. Through a combination of laboratory and field experimentation we show that while both can utilise the young, upper leaves only the indigenous competitor can use the older lower leaves. We then demonstrate that the removal of the upper leaves as part of foreshore vegetation management is the key factor in preventing the establishment of the invader and subsequent displacement of its competitor. While human mediated disturbance coupled with complex biological interactions may promote invasion they may equally well retard rather than facilitate invasion, a factor that appears to have been largely ignored. Complexities of this kind must be conceived in our thinking to achieve a comprehensive understanding of biological invasion. [ABSTRACT FROM AUTHOR]