The size of pollination neighbourhoods has important consequences for mating patterns, seed production, gene flow, and patterns of genetic variation across populations. We examined the size of the pollination neighbourhood in a stand of a wind-pollinated clonal plant (Typha latifolia L.; broadleaf cattail) by evaluating spatial patterns of pollen production and seed set by individual shoots. We then simulated spatial patterns of pollen availability to investigate the shape of the pollen dispersal curve. We detected significant positive spatial autocorrelations in seed set over distances up to 5 m. This spatial variation in patterns of seed set appeared to be driven by the local availability of pollen: we found significant cross-correlations between pollen production and seed set over distances of approximately 2 m. The simulations supported this inference; simulated pollen dispersal curves fit observed patterns of seed set when ∼99% of pollen was assumed to disperse over distances less than 2 m. Together, these results indicate that the majority of pollination events occur within very close proximity of pollen sources in T. latifolia. Although within-shoot selfing has long been assumed to be a major pollination mode in T. latifolia, our data indicate that pollination events in the stand were more likely to have involved between-shoot pollination.

Aralia nudicaulis L. is a clonal dioecious herb common to forested ecosystems in eastern North America. Across 15 sites, the frequency of female ramets ranged between 5% and 95%. This variation was used to examine hypotheses involving the life history and pollination biology of A. nudicaulis. Because female reproductive function is thought to incur greater resource costs than male function, we predicted that female ramets should (i) be more common where resources (and light in particular) are more abundant and (ii) have lower rates of survival than male ramets. However, there was (i) no significant association between light availability (measured as canopy closure) and female frequencies across sites and (ii) ramet ages were skewed towards older ages for females, not males. Female A. nudicaulis produce staminodes that render female inflorescences visually similar to male inflorescences. We experimentally manipulated the presence-absence of staminodes and found that pollen receipt by females without staminodes was substantially lower than for plants with intact staminodes. Finally, pollinators tend to prefer visiting male over female flowers. We were interested in evaluating whether such preferences might scale up to the population level, with higher pollinator abundances at male-dominated sites. However, we instead found a strong positive association between pollinator abundances and female frequencies. Although there is unlikely to be a causal relationship between them, the identification of a common variable underlying variation in female frequencies and pollinator abundances might reveal key insights into the factors regulating the life history and pollination of forest understory plants.Résumé : L'Aralia nudicaulisL. est une plante clonale herbacée dioïque des écosystèmes forestiers de l'est de l'Amérique du Nord. Sur les 50 sites observés la fréquence des genets femelles va 5 à 95 %. Les auteurs ont utilisé cette variation pour examiner des hypothèses impliquant le cycle vital et la biologie de la pollinisation de l'A. nudicaulis. Parce que l'on croit que la fonction reproductive femelle nécessite un coût plus élevé en ressources que la fonction mâle, les auteurs ont prédit que les genets femelles devraient (i) être plus communs là où les ressources (et en particulier la lumière) sont plus abondantes et (ii) avoir des taux de survie plus faibles que les genets mâles. Cependant, il n'y a pas (i) d'association significative entre la disponibilité de la lumière (mesurée comme fermeture de la canopée) et les fréquences des femelles sur l'ensemble du site et (ii) les âges des genets présentent une curtose des âges avancés en faveur des femelles et non des mâles. Les femelles de l'A. nudicaulis produisent des staminodes qui rendent les inflorescences femelles visuellement similaires aux inflorescences mâles. Les auteurs ont manipulé expérimentalement la présence/absence des staminodes et ont constaté une réduction substantielle de la quantité de pollen reçu par les plantes femelles sans staminodes par rapport aux ...

Pollination success in dioecious plants is expected to be regulated by the ratio of female:male plants and the distances between plants of each sex. These factors have received considerable attention in studies of dioecious and other gender dimorphic plants, yet their effects have rarely been jointly considered. We documented sex ratios in 26 populations of Cirsium arvense (L.) Scop. (creeping thistle), a widely distributed clonal dioecious plant, and show that population sex ratios are generally female biased (∼60% of shoots were female, and 15 of 26 populations were female biased). We found clear evidence for a negative association between pollen loads and distances between females and males within populations. In contrast, and in spite of broad variation in sex ratios among populations (range: 0.11–0.99 female), we found no relationship between sex ratios and pollen receipt by females. However, both sex ratios and interplant distances were associated with female seed production: seed production declined with distances between females and males and increased with the proportion of male shoots. Our data suggest that female plants of C. arvense might often be pollen limited and that distances between individual females and males drive pollen limitation more strongly than the overall frequency of males within sites.