Revisiting Darwin's naturalization conundrum: explaining invasion success of non‐native trees and shrubs in southern Africa

Abstract

Summary 1.Invasive species are detrimental ecologically and economically. Their negative impacts in Africa are extensive and call for a renewed commitment to better understand the correlates of invasion success. 2. Here, we explored several putative drivers of species invasion among woody non-native trees and shrubs in southern Africa, a region of high floristic diversity. We tested for differences in functional traits between plant categories using a combination of phylogenetic independent contrasts and a simulation-based phylogenetic ANOVA. 3. We found that non-native species generally have longer flowering duration compared with native species and are generally hermaphroditic, and their dispersal is mostly abiotically mediated. We also revealed that non-native trees and shrubs that have become invasive are less closely related to native trees and shrubs than their non-invasive non-native counterparts. Non-natives that are more closely related to the native species pool may be more likely to possess traits suited to the new environment in which they find themselves and thus have greater chance of establishment. However, successful invaders are less closely related to the native pool, indicating evidence for competitive release or support for the vacant niche theory. 4. Synthesis. Non-native trees and shrubs in southern Africa are characterized by a suite of traits, including long flowering times, a hermaphroditic sexual system and abiotic dispersal, which may represent important adaptations promoting establishment. We suggest that differences in the evolutionary distances separating the native species pool from invasive and non-invasive species might help resolve Darwin's naturalization conundrum.

The effects of phylogenetic relatedness on invasion success and impact: deconstructing Darwin's naturalisation conundrum

“…; Bezeng et al . ). Most studies have interpreted this pattern as evidence for Darwin's naturalisation hypothesis based on the assumption that strong competition from close native relatives could hinder the success of the invaders.…”

“…; Park & Potter ; Bezeng et al . ). However, the vast majority of studies to date have comprised large‐scale observations at a single snapshot in time, and have supported the opposing hypotheses in roughly equal proportions (see Table S1 in Supporting Information for a summary).…”

Comparing traits of native and alien plants: Can we do better?

“…The infrequent application of such approaches (Cross et al., ; Dainese & Bragazza, ) suggests we are still a long‐way from developing robust generalisations about plant invasions. For example, comparisons of trait differences between native and alien species are still undertaken at regional scales (Bezeng, Davies, Yessoufou, Maurin, & Van der Bank, ; Kuester, Conner, Culley, & Baucom, ; Marx, Giblin, Dunwiddie, & Tank, ) even though the relevance of such analyses for understanding the vulnerability of plant communities to plant invasion is debatable. The increasing availability of plot‐scale data world‐wide (Chytry et al., ; Rutherford, Mucina, & Powrie, ; Walker et al., ) has the potential to herald considerable new insights into the role that trait differences between native and alien species may play in plant invasions and facilitate the application of methods that account for spatial scale dependence, environmental gradients and even temporal variation in species composition.…”

The community ecology of invasive species: where are we and what's next?

“…Nonetheless, in at least two case studies the presence of native congeners was shown to have only a weak effect on invasion success (for invasive plants and fish, Lambdon and Hulme , Ricciardi and Mottiar ) suggesting rather a weak influence of the environment in filtering invasive species. Moreover, two other case studies in the Southern Hemisphere concluded that competition was involved in filtering invaders regionally given that invasion success was found to increase with phylogenetic (invasive plants, Bezeng et al ) and functional distances to natives (invasive fish, Skóra et al ). Patterns such as these – which are consistent with the signature of competitive interactions – have been observed much more commonly at local scales, where invasive species have generally been found to have higher establishment success when they were functionally (Petermann et al , Price and Pärtel ) or phylogenetically distant from natives (e.g.…”