Patterns of introduction, naturalisation, invasion, and impact differ between fleshy- and dry-fruited species of Myrtaceae

Recent studies on patterns of biological invasions in several plant families have confirmed general findings (e.g., taxa with larger native range sizes are more likely to become invasive; and taxa with longer residence time in new regions are more likely to naturalise) and highlighted some context-specific findings relevant for management (e.g., resistance to Phytophthora is a pre-requisite for successful naturalisation in Proteaceae). We explore these issues for the plant family Myrtaceae, specifically by contrasting taxa with fleshy fruits with those with dry fruits to develop hypotheses around the role of seed dispersal in the invasion process. To this end we: 1) compiled a comprehensive list of introduced Myrtaceae; 2) determined the degree of establishment of each species in its introduced range; 3) compared the distribution of native, introduced, and invasive ranges; 4) assessed traits associated with the degree of establishment; and 5) assessed the magnitude and types of impacts of invasive Myrtaceae. A slightly higher proportion of dry-fruited species have been introduced than fleshy-fruited species [170 out of 2257 (7.5 %) vs. 236 out of 3741 (6.7 %)], though the difference was not significant. However, introduced dry-fruited Myrtaceae have naturalised more frequently than fleshy-fruited taxa [90 out of 170 (53 %) vs. 40 out of 236 (17 %)], whereas naturalised dry-fruited taxa have become invasive at a lower rate [22 out of 90 (24 %) vs. 18 out of 40 (46 %)]. Invasions of fleshy-fruited taxa seem to be more common on islands. Although invasions by fleshy- and dry-fruited species had similar impact mechanisms and magnitudes, naturalised fleshy-fruited Myrtaceae are more likely to have impacts on islands than dry-fruited confamilials.

Synthesis Fleshy- and dry-fruited taxa of Myrtaceae differ in rates of transition along the invasion continuum and where invasions and impacts occur. We speculate that seed dispersal abilities, lack of competitors, and the availability of areas suitable for germination might explain these differences.