Interregional comparison of the size-structure of populations of Melaleuca quinquenervia in its native and exotic range, with and without biocontrol agents

摘要

We compare size structure and rates of recruitment and mortality in populations of Melaleuca quinquenervia in its native and exotic ranges. In the exotic range study sites were chosen to include contrasts in presence and abundance of two biological control agents. We tagged and measured (DBH) all the individuals in permanent plots and revisited them annually to record growth, mortality and recruitment. DBH varied among sites, the largest trees were found in the native populations. Per capita mortality (% deaths between years) was highest in Florida, where both insects are present; and lowest in the Bahamas where no insects are present. In Australia, even though the full range of natural enemies comprising approximately 450 species is present, deathrate on average, and recruitment were quite low. Annual per capita recruitment is difficult to quantify in our study plots because it is episodic and mostly restricted to newly colonised sites. Since observed mortality was nonzero and recruitment was low, local populations seem to be declining.