Aim Reproductive traits are important mediators of establishment and spread of introduced species, both directly and through interactions with other life-history traits and extrinsic factors. We identify features of the reproductive biology of Australian acacias associated with invasiveness.Location Global.Methods We reviewed the pollination biology, seed biology and alternative modes of reproduction of Australian acacias using primary literature, online searches and unpublished data. We used comparative analyses incorporating an Acacia phylogeny to test for associations between invasiveness and eight reproductive traits in a group of introduced and invasive (23) and non-invasive (129) species. We also explore the distribution of groups of trait 'syndromes' between invasive and non-invasive species.Results Reproductive trait data were only available for 126 of 152 introduced species in our data set, representing 23/23 invasive and 103/129 non-invasive species. These data suggest that invasives reach reproductive maturity earlier (10/ 13 within 2 years vs. 7/26 for non-invasives) and are more commonly able to resprout (11/21 vs. 13/54), although only time to reproductive maturity was significant when phylogenetic relationships were controlled for. Our qualitative survey of the literature suggests that invasive species in general tend to have generalist pollination systems, prolific seed production, efficient seed dispersal and the accumulation of large and persistent seed banks that often have fire-, heat-or disturbance-triggered germination cues.Conclusions Invasive species respond quicker to disturbance than non-invasive taxa. Traits found to be significant in our study require more in-depth analysis involving data for a broader array of species given how little is known of the reproductive biology of so many taxa in this species-rich genus. Sets of reproductive traits characteristic of invasive species and a general ability to reproduce effectively in new locations are widespread in Australian acacias. Unless there is substantial evidence to the contrary, care should be taken with all introductions.

When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata. Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area.

Dispersal is thought to be a key process underlying the high spatial diversity of tropical forests. Just how important dispersal is in structuring plant communities is nevertheless an open question because it is very difficult to isolate dispersal from other processes, and thereby measure its effect. Using a unique situation, the loss of vertebrate seed dispersers on the island of Guam and their presence on the neighboring islands of Saipan and Rota, we quantify the contribution of vertebrate seed dispersal to spatial patterns of diversity of tree seedlings in treefall gaps. The presence of vertebrate seed dispersers approximately doubled seedling species richness within canopy gaps and halved species turnover among gaps. Our study demonstrates that dispersal plays a key role in maintaining local and regional patterns of diversity, and highlights the potential for ongoing declines in vertebrate seed dispersers to profoundly alter tropical forest composition.biodiversity loss | biotic homogenization | frugivory | mutualisms | tropical conservation T ropical forests typically have both high numbers of species per unit area and highly variable patterns of community composition through space (1, 2). Dispersal is thought to be a key process underlying this diversity, contributing to high local species richness by allowing the seeds arriving at a site to be drawn from a wide species pool (3, 4) and influencing the spatial arrangement of species by moving seeds away from parent trees, reducing conspecific aggregation (4-8). However, it has proven extremely difficult to quantify the contribution of seed dispersal to local diversity and spatial patterning in forests because it is confounded with other processes, including environmental variation, to which species differentially respond (2, 9); historical legacies, such as past disturbance (10); other biotic interactions, such as competition and predation (11, 12); and stochastic variation (13). Isolating the role of seed dispersal in maintaining diversity in tropical forests has nevertheless taken on new urgency due to widespread declines in populations of vertebrate dispersers throughout tropical regions (14-17). If vertebrate seed dispersal contributes substantially to the diversity and spatial patterning of trees in tropical forests, then declining vertebrate populations could lead to irrevocable changes in forest composition and structure.To separate the role of dispersal from other processes structuring tree communities, we would ideally manipulate dispersal while keeping other factors constant. For vertebrate dispersal, one approach would be to remove populations of vertebrate dispersers in treatment areas and compare these with untreated areas. However, vertebrate dispersal can occur over long distances (often up to several kilometers) (18), which requires manipulating vertebrate densities over areas larger than is logistically or ethically feasible. To overcome this, studies have used large-scale, unplanned manipulations (19) of vertebrate populations, comparing,...

Summary1. The ability to form effective mutualisms with nitrogen-fixing bacteria (rhizobia) is implicated in the success of introduced leguminous plant species, such as Acacia. While Acacia appear to associate with rhizobia where introduced, there is evidence that the extent of this may limit success during early stages of colonization.