A phylogenetically controlled analysis of the roles of reproductive traits in plant invasions

Abstract

Reproductive traits are tightly linked to plant fitness and may therefore be mechanisms driving biological invasions, including the greater success of more phylogenetically novel introduced species in some systems. We present a phylogenetic comparative analysis of "Baker's law'', that introduced plants with the ability to reproduce autogamous or asexually may be better able to establish on introduction. We gathered data from both published and unpublished sources on pollen limitation of 141 species, including 26 introduced species and 115 native species. Our analysis compared differences in the proportion of autonomous autogamy, asexual reproduction, and pollen limitation among native, introduced noninvasive, and introduced invasive plant species, and included the phylogenetic novelty of the introduced species to the native species in that community. Introduced species were more likely to be autogamous than native species, consistent with Baker's law. On the other hand, introduced species were less likely to have the ability to reproduce asexually. Further, among species with no autonomous autogamy, pollen limitation was greater for introduced compared to native species. Such a result is consistent with the idea that plants entering a new continent receive lower quality or quantity of services from resident pollinators than species native to that continent. Finally, more phylogenetically novel invasive species had lower pollen limitation than less novel invasive species, potentially because they experience less competition for pollinators. This is the first evidence that enhanced pollination may be one mechanism driving the greater invasiveness of phylogenetically novel introduced species observed in some systems.

Hybridization can facilitate species invasions, even without enhancing local adaptation

“…Allee effects or, more specifically, pollen-limited seed production, are expected to be common, because more than 80% of plants rely on pollen transfer for reproduction (23) and ∼50% of plant species are obligate outcrossers (24). Pollen limitation, resulting from low availability of both compatible mates and pollinators, seems to be more common in introduced species than their native counterparts (25,26). First, our model shows that the presence of another species can alleviate such pollen limitation and reduce Allee effects through hybridization with related species.…”

Revisiting Darwin's conundrum reveals a twist on the relationship between phylogenetic distance and invasibility

“…Third, we predict that evolution of phenotype matching between native mutualists should also increase the match to related, newly introduced species, thereby increasing facilitation and establishment probability with phylogenetic distance. This added benefit could be offset in nature, however, by strong competition for shared mutualists (46).…”

Not all weeds are created equal: A database approach uncovers differences in the sexual system of native and introduced weeds

“…Native species, on the other hand, may be more likely to retain an association with their native pollinators during establishment, and thus may be less influenced by pollinator limitation. However, some studies suggest that most invasive species (included in our introduced weed category) are generalist‐pollinated (Richardson, Allsopp, D'Antonio, Milton, & Rejmanek, 2000) and are not more pollen‐limited than native species (but see Burns et al., 2011; Razanajatovo & Van Kleunen, 2016), in which case autonomous self‐pollination would not be beneficial.…”

“…These comparisons provide support for Baker's law, but are limited to particular taxonomic groups (Iridaceae: Van Kleunen, Manning, Pasqualetto, & Johnson, 2008; Asteraceae: Hao, Qiang, Chrobock, van Kleunen, & Liu, 2011), a restricted geographic region (South African invasives: Rambuda & Johnson, 2004; European invasives: Van Kleunen & Johnson, 2007), or work that compares invasives (hereafter “introduced weeds”) to native species (Burns, Ashman, Steets, Harmon‐Threatt, & Knight, 2011). While it is surprising that few studies of introduced weeds consider Baker's law—especially since much of its development centered around weedy plants—it is also remarkable that there are no large‐scale examinations, to our knowledge, of the potential that native weeds (plants that are native to a particular habitat and deemed weedy or problematic) are more likely to exhibit an increased capacity for self‐fertilization compared with native nonweeds.…”