Sexual selection may contribute to the evolution of plant sexual dimorphism by favoring architectural traits in males that improve pollen dispersal to mates. In both sexes, larger individuals may be favored by allowing the allocation of more resources to gamete production (a “budget” effect of size). In wind‐pollinated plants, large size may also benefit males by allowing the liberation of pollen from a greater height, fostering its dispersal (a “direct” effect of size). To assess these effects and their implications for trait selection, we measured selection on plant morphology in both males and females of the wind‐pollinated dioecious herb Mercurialis annua in two separate experimental common gardens at contrasting density. In both gardens, selection strongly favored males that disperse their pollen further. Selection for pollen production was observed in the high‐density garden only, and was weak. In addition, male morphologies associated with increased mean pollen dispersal differed between the two gardens, as elongated branches were favored in the high‐density garden, whereas shorter plants with longer inflorescence stalks were favored in the low‐density garden. Larger females were selected in both gardens. Our results point to the importance of both a direct effect of selection on male traits that affect pollen dispersal, and, to a lesser extent, a budget effect of selection on pollen production.

The differential plasticity hypothesis suggests that sexual dimorphism in dioecious plants could evolve in response to sex-specific resource requirements for reproduction (i.e., high carbon requirements for ovules and high nitrogen demands for pollen). When resources become limiting during growth, males and females should, therefore, adjust their allocation to resource-harvesting organs differently. To investigate the potential for plants to respond to resource limitation late in life and to test the differential plasticity hypothesis, we grew male and female individuals of the annual wind-pollinated plant Mercurialis annua in a common garden. Late in the growth season, we simulated a change in competition by decreasing plant density in half of the replicates. We measured both allocation to vegetative and reproductive traits and analyzed the relative allocation to reproduction vs. growth. Males and females differentially adjusted their resource allocation in response to varying plant densities, despite the fact that they were reproductively mature. Males maintained the same relative allocation of resource to reproductive vs. vegetative tissues at both densities. In contrast, females reduced vegetative growth proportionally less than seed production at the higher density. Our results highlight the dynamic nature of allocation decisions taken by plants, which respond quickly and in a sexually dimorphic way to changes in their competitive circumstances. The existence of resource ‘currencies’ limiting male and female functions differently have potentially led to the evolution of sex-specific strategies of resource acquisition and deployment, with females conserving resources for vegetative organs to ensure their future carbon-rich reproduction.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-017-3966-5) contains supplementary material, which is available to authorized users.

Bateman's principles posit that male fitness varies more, and relies more on mate acquisition, than female fitness. While Bateman's principles should apply to any organism producing gametes of variable sizes, their application to plants is potentially complicated by the high levels of polyandry suspected for plants, and by variation in the spatial distribution of prospective mates. Here we quantify the intensity of sexual selection by classical Bateman metrics using two common gardens of the wind-pollinated dioecious plant Mercurialis annua . Consistent with Bateman's principles, males displayed significantly positive Bateman gradients (a regression of fitness on mate number), whereas the reproductive success of females was independent of their ability to access mates. A large part of male fitness was explained by their mate number, which in turn was associated with males' abilities to disperse pollen. Our results suggest that sexual selection can act in plant species in much the same way as in many animals, increasing the number of mates through traits that promote pollen dispersal.

The ecological niche of a species describes the variation in population growth rates along environmental gradients that drives geographic range dynamics. Niches are thus central for understanding and forecasting species’ geographic distributions. However, theory predicts that migration limitation, source–sink dynamics, and time-lagged local extinction can cause mismatches between niches and geographic distributions. It is still unclear how relevant these niche–distribution mismatches are for biodiversity dynamics and how they depend on species life-history traits. This is mainly due to a lack of the comprehensive, range-wide demographic data needed to directly infer ecological niches for multiple species. Here we quantify niches from extensive demographic measurements along environmental gradients across the geographic ranges of 26 plant species (Proteaceae; South Africa). We then test whether life history explains variation in species’ niches and niche–distribution mismatches. Niches are generally wider for species with high seed dispersal or persistence abilities. Life-history traits also explain the considerable interspecific variation in niche–distribution mismatches: poorer dispersers are absent from larger parts of their potential geographic ranges, whereas species with higher persistence ability more frequently occupy environments outside their ecological niche. Our study thus identifies major demographic and functional determinants of species’ niches and geographic distributions. It highlights that the inference of ecological niches from geographical distributions is most problematic for poorly dispersed and highly persistent species. We conclude that the direct quantification of ecological niches from demographic responses to environmental variation is a crucial step toward a better predictive understanding of biodiversity dynamics under environmental change.

Aim:The Hutchinsonian niche is a foundational concept in ecology and evolutionary biology that describes fundamental characteristics of any species: the global maximum population growth rate (r max ); the niche optimum (the environment for which r max is reached); and the niche width (the environmental range for which intrinsic population growth rates are positive). We examine whether these characteristics are related to inter-and intraspecific variation in functional traits.Location: Cape Floristic Region, South Africa. Time period: Present day.Major taxa studied: Twenty-six plant species (Proteaceae). Methods:We measured leaf, plant-architectural and seed traits across species geographical ranges. We then examined how species-mean traits are related to demographically derived niche characteristics of r max , in addition to niche optima and widths in five environmental dimensions, and how intraspecific trait variation is related to niche widths. Results:Interspecific trait variation generally exceeded range-wide intraspecific trait variation. Species-mean trait values were associated with variation in r max (R 2 = 0.27) but were more strongly related to niche optima (mean R 2 = 0.56). These relationships generally matched trait-environment associations described in the literature. Both species-mean traits and intraspecific trait variability were strongly related to niche widths (R 2 = 0.66 and 0.59, respectively). Moreover, niche widths increased with intraspecific trait variability. Overall, the different niche characteristics were associated with few, largely non-overlapping sets of traits. Main conclusions:Our study relating functional traits to Hutchinsonian niches demonstrates that key demographic properties of species relate to few traits with relatively strong effects. Our results further support the hypothesis that intraspecific trait variation increases species niche widths. Given that niche characteristics were related to distinct sets of traits, different aspects of environmental change might affect axes of trait variation independently. Trait-based studies of Hutchinsonian | 535 TREURNICHT ET al.