Differential pollinator responses to disturbance can ensure plant success even in plants with only two functionally similar pollinators. This highlights the importance of pollinator replacement and dynamics for the resilience of interactions and ultimately of plant reproduction in disturbance-prone ecosystems.

Differences in morphological or ecological traits expressed by exotic species between their native and non-native ranges are often interpreted as evidence for adaptation to new conditions in the non-native ranges. In turn this adaptation is often hypothesized to contribute to the successful invasion of these species. There is good evidence for rapid evolution by many exotic invasives, but the extent to which these evolutionary changes actually drive invasiveness is unclear. One approach to resolving the relationship between adaptive responses and successful invasion is to compare traits between populations from the native and non-native ranges for both exotic invaders and congeners that are exotic but not invasive. We compared a suite of morphological traits that are commonly tested in the literature in the context of invasion for three very closely related species of Centaurea, all of which are sympatric in the same native and non-native ranges in Europe and North America. Of these, C. solstitialis is highly invasive whereas C. calcitrapa and C. sulphurea are not. For all three species, plants from non-native populations showed similar shifts in key traits that have been identified in other studies as important putative adaptive responses to post-introduction invasion. For example, for all three species plants from populations in non-native ranges were (i) larger and (ii) produced seeds that germinated at higher rates. In fact, the non-invasive C. calcitrapa showed the strongest trait shift between ranges. Centaurea solstitialis was the only species for which plants from the non-native range increased allocation to defensive spines, and allocated proportionally less resources to reproduction, patterns contrary to what would be predicted by theory and other empirical studies to enhance invasion. Our results suggest caution when interpreting the commonly observed increase in size and reproductive capacity as factors that cause exotics to become invaders.

Differences in plant and herbivore community assemblages between exotic and native ranges may select for different levels of plant traits in invasive and native populations of plant species. Little is currently known of how herbivores may mediate competitive and facilitative interactions between invasive and native populations of plant species and their plant neighbors. Here, we conducted a common-garden field experiment to test whether invasive and native populations of Brassica nigra differ in phenotypic expressions of growth (biomass and plant height) and reproductive (seed yield) traits under different plant neighbor treatments and ambient vs. reduced level of insect herbivore damage on the B. nigra plants. We found significant interactive effects of plant neighbor treatments, level of insect herbivore damage on B. nigra plants, and invasive status of B. nigra on the phenotypic trait expressions. Plant neighbor treatments had minimal effects on phenotypic trait expressions by invasive populations of B. nigra under either level of insect herbivore damage. In contrast, for native populations of B. nigra, ambient level of insect herbivore damage resulted in plant neighbors facilitating expression of the traits above, while reduced damage resulted in plant neighbors competitively suppressing trait expression. Our results suggest that insect herbivores and plant neighbors interactively shape expression of plant traits in native and exotic ranges of invasive plants. Such interactions could potentially lead to different selection pressures on traits that determine antiherbivore defenses and plant-plant interactions.

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Floral scent is considered an important long-distance signal that attracts pollinators, but also has been suggested to function at shorter distances such as within-flower nectar guides or as a defense against antagonists. Indeed, in some species floral scent production and emission show spatial patterns of variation within flowers, as certain compounds are exclusively emitted from specific floral tissues. In other species, the different volatile organic compounds that constitute the floral bouquet are emitted evenly from the entire flower. Here, we summarize the current evidence on floral scent variation within flowers by combining a literature review of published data on tissue-level floral scent variation (41 species) with floral scent dissections (17 species). For each species, we recorded the total number of volatile compounds separately and grouped in major chemical classes. To facilitate comparisons across diverse species, we compared volatiles emitted by 1) the whole flower, 2) the visual floral tissues (i.e. petals and colored structures), 3) non-visual floral tissues (i.e. green parts and reproductive structures), as well as 4) the compounds emitted by both visual and nonvisual tissues. Results show that floral scent variation is frequent, but by no means ubiquitous, occurring in species from distantly related groups. We discuss the two main functional hypotheses promoting floral scent variation within flowers, i.e. as a pollinator attractant at short-distances or a defensive function against antagonists, together with non-functional hypotheses (e.g. pleiotropic effects, ecological costs). We point out further directions on this topic and suggest experimental approaches testing the attractiveness of compounds emitted by different floral parts alone and in combination with other floral signals. Our synthesis provides a foundation for future studies on the functional ecology of floral scent and reinforces the idea of high complexity in floral chemical signals.