Offering floral rewards to pollinators such as nectar and pollen may not mean reproductive success. Some plant species present strategies to minimize this cost and dupe their pollinators. Begonia cucullata presents a mimicry system characterized by female rewardless flowers (mimic) that mimic male flowers (model) with a large amount of pollen. For the perfect functioning of mimetism, the proportion of mimics should not be higher than models. We tested different arrays of mimic-model flower proportions to test the efficacy of this system. We observed that bees avoided rewardless female flowers, although fruit set did not indicate pollen limitation.
Several South American species of Iridaceae, especially those of Tigridieae, produce floral oils as rewards to oil-bee pollinators. The present study aimed to contribute to a deeper understanding of the reproductive biology, pollination ecology and level of specialization of the interactions of species encompassed in Tigridieae. Data on breeding and pollination systems were acquired from six species native to Southern Brazil. The visitation frequency and pollen load of pollen- and oil-collecting bees were also investigated. The results strongly suggest that the studied species are distributed along a specialization–generalization continuum. Three oil-producing taxa, Cypella herbertii, Cypella pusilla and Cypella amplimaculata, were pollinated effectively by oil-bees, whereas in the other two studied species, Kelissa brasiliensis and Herbertia pulchella, the oil-bees appeared to function as oil thieves, owing to failure to contact the plant reproductive parts during oil-foraging behaviour. New insights into aspects of the specialization–generalization continuum of pollination systems, differences in pollinator behaviour during oil and pollen foraging, and reproductive outputs of the studied species are provided. Taken together, our results provide a significant contribution towards a better understanding of reproductive biology and plant–pollinator interactions between Iridaceae and oil-collecting bees.
Diverse ecological factors (top-down and bottom-up) act on the richness and abundance patterns of insect galls. Host plant density is a kind of bottom-up factor and is related to ''resource concentration hypothesis.'' In this study, we analyzed forest patches that differ in vegetational structure and host plant abundance: homogeneous forest patches (Schinus-dominated) and more complex forest patches, to determine whether there are differences in the intensity of gall infestation among individual trees. Insect galls were sampled from 15 Schinus polygamus trees along five transects in each forest (150 trees in total). Two galler species, a psyllid leaf galler and cecidomyiid shoot galler, were recorded. We found that Psyllidae gall infestation in S. polygamus presents higher values of galls per individual tree in Schinus-dominated forest patches than forest patches that are more diverse in plant species. Cecidomyiidae galls did not differ between areas and were not related to host plant abundance. We did not observe any variation in gall infestation within individual. Our study demonstrated that density-dependence effect could be more important for some galls species than others. The results suggest that biological attributes of galling insects' infestation could be associated with susceptibility to host plant density.
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