Premise of the Study: There is growing interest in understanding plant–plant interactions via pollen transfer at the community level. Studies on the structure and spatial variability of pollen transfer networks have been valuable to this understanding. However, there is high variability in the intensity of sampling used to characterize pollen transfer interactions, which could influence network structure. To date, there is no knowledge of how sampling effort influences the richness of pollen on stigmas and thereby transfer interactions observed, nor how this may vary across species and study sites. Methods: We use rarefaction curves on 16 species to characterize the relationship between sampling effort (number of stigmas analyzed) and the richness of pollen transfer interactions recorded. We further assess variability in this relationship among species, plant community types, and sites within a single plant community. Key Results: We show high among-species variation in the amount of sampling required to sufficiently characterize interspecific pollen transfer. We further reveal variability in the sampling effort-interaction richness relationship among different plant communities and even for the same species growing in different sites. Conclusions: The wide heterogeneity in the sampling effort required to accurately characterize pollen transfer interactions observed has the potential to influence the characterization of pollen transfer dynamics. Thus, sampling completeness should be considered in future studies to avoid overestimation of modularity and specialization in pollen transfer networks that may bias the predicted causes and expected consequences of such processes for plant–plant interactions.

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Pollinator conservation has recently become a topic of greater interest and research around the world as native insect pollinator species increasingly face population declines. In the United States, growing concerns regarding food security and decreased biodiversity have led to the creation of programmatic and best management practices (BMPs) promotional efforts among governmental and non-governmental organizations. These efforts seek to support pollinators on public and private lands by addressing the primary causes of decline (e.g., habitat loss and increased chemical use). Although these organizations have worked diligently to increase awareness and applicability of programs to private landholders, there is still a gap in pollinator BMP adoption. The purpose of my dissertation was to address the pollinator BMP adoption gap through empirical research with two primary goals: 1) develop and test a measurement instrument to investigate the current state of adoption in Mississippi, landholder attributes, and attribute influence on adoption intentions, and 2) conduct segmentation analyses to develop preliminary recommendations for future educational and outreach efforts to increase adoption of pollinator BMPs. I used two sociological theories to develop a questionnaire consisting of constructs measuring landholder attributes, including Attitudes, Injunctive Norms, Perceived Behavioral Control, Intentions, Knowledge, and Communication Channel Use. I conducted a selfministered mail survey during summer 2018 and received a 38.5% effective response rate. Relative to the first goal, major findings from the research included evidence of reliability and validity for the measurement constructs, landholders having more favorable than unfavorable Attitudes regarding the use of pollinator BMPs on their properties, and Perceived Behavioral Control as the strongest influence on adoption intentions compared to additional landholder attributes. Relative to the second goal, major findings included the generation of four distinct clusters and three land use type segments that allowed for group comparisons and development of a recommended two-step targeted educational and outreach approach. My dissertation provided theoretical and substantive advances to the fields of adoption research and pollinator conservation from which future research and outreach efforts can grow.

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Os objetivos deste estudo foram: avaliar a fauna de polinizadores potenciais do morangueiro em campos de produçaõ comercial; verificar a contribuição de diversos agentes de polinização na produtividade do morangueiro, conhecendo a biologia floral e reprodutiva dos cultivares mais utilizados para o plantio; testar, em cultivo fechado (estufa), diversas espécies de Meliponini (abelhas sem ferrão)como polinizador do morangueiro, avaliando a sua adaptação ao cultivo e sua efetividade nesta cultura. Os resultados obtidos revelaram que as flores do dos cultivares "Sweet Charlie" e "Oso Grande" necessitam de um polinizador para a produção de frutos sem deformação pois a morfologia de suas flores e o amadurecimento de suas estruturas reprodutivas não favorecem a ocorrência da autopolinização, nem a distribuição homogênea do pólen pelos estigmas da flor, resultando em frutos deformados que não alcançam o seu potencial máximo de desenvolvimento. A abelha jataí (Tetragonisca angustula) adaptou-se bem ás condições do cultivo fechado (estufa) e mostrou-se efetiva na polinização do morangueiro, resultando em frutos mais pesados e em uma porcentagem mais elevada de frutos bem formados. / The aims of this study were: to investigate potencial pollinators of strawberry crops in commercial fields; to verify the contribution of several pollination agents on strawberry productivity, studying the floral and reproductive biology of some commercial cultivars; to evaluate the possibility of the rational use of stingless bees in strawberry pollination inside greenhouses. The results showed that the floral morphology of "Sweet Charlie" and Oso Grande" cultivars and the maturation pattern of their stamens and pistils nor favour the occurrence of self pollination neither the regular pollen distribuction among stigmata, yielding deformed fruits that don´t complete their development. Therefore these cultivars need pollinators to commercial production. Tetragonisca angustula (Apinae, Meliponini)was remarkable for its relatively quick adaptation inside greenhouses and for its effectivity as strawberry pollinator, resulting in heavier berries and high percentage of marketable fruits.

<p>I combined comparative and experimental studies in the field and in the greenhouse to examine factors influencing reproductive success in two insect-pollinated herbs, the tristylous, selfincompatible perennial <i>Lythrum salicaria</i> and the self-compatible, biennial <i>Pedicularis palustris</i>. More specifically, I explored (i) the effects of plant population characteristics on the intensity and outcome of interactions with pollinators and seed predators, (ii) whether flower morphology affects duration of stigma receptivity, and (iii) whether damage-induced reduction in floral display reduces pollinator visitation and increases pollen limitation.</p><p>As predicted, the rate of pollinator visitation tended to increase and the number of flowers probed per plant tended to decrease with increasing population size in <i>L. salicaria</i>, but these relationships only approached statistical significance. By taking advantage of the pollen size polymorphism that is typical of many heterostylous plants, I could show that the number of compatible pollen grains received increased with population size, and that this was associated with a reduction in pollen limitation and increased seed output per flower. The deposition of high numbers of incompatible conspecific and heterospecific pollen grains did not appear to reduce seed set.</p><p>In <i>P. palustris</i>, fruit set and seed predation varied markedly among populations and years, but this variation could only partly be explained by variation in population size. Fruit set was positively related to population size, and seed predation was negatively related to population size, in one of three years. Similarly, the level of pollen limitation, which was quantified in two years, varied among populations, but was not related to population size, density or isolation.</p><p>In <i>L. salicaria</i>, both the duration of stigma receptivity and the effect of prior self-pollination on seed output varied among style morphs. These differences may contribute to morph-specific differences in pollen limitation and seed production documented in the field.</p><p>The results of a field experiment demonstrated that damage to the shoot apex may markedly reduce fruit production in <i>L. salicaria</i>, and suggested that this is mainly because damage reduces flower number. I found no evidence that a reduced floral display increased the severity of pollen limitation.</p><p>Taken together, the results show that interactions with both pollinators and herbivores may markedly affect reproductive output in the two plant species, and that the intensity of both mutualistic and antagonistic interactions vary considerably in space and time. Moreover, they are consistent with the hypothesis that pollination success should depend less on population size in selfcompatible than in self-incompatible plants.</p>

I combined comparative and experimental studies in the field and in the greenhouse to examine factors influencing reproductive success in two insect-pollinated herbs, the tristylous, selfincompatible perennial Lythrum salicaria and the self-compatible, biennial Pedicularis palustris. More specifically, I explored (i) the effects of plant population characteristics on the intensity and outcome of interactions with pollinators and seed predators, (ii) whether flower morphology affects duration of stigma receptivity, and (iii) whether damage-induced reduction in floral display reduces pollinator visitation and increases pollen limitation. As predicted, the rate of pollinator visitation tended to increase and the number of flowers probed per plant tended to decrease with increasing population size in L. salicaria, but these relationships only approached statistical significance. By taking advantage of the pollen size polymorphism that is typical of many heterostylous plants, I could show that the number of compatible pollen grains received increased with population size, and that this was associated with a reduction in pollen limitation and increased seed output per flower. The deposition of high numbers of incompatible conspecific and heterospecific pollen grains did not appear to reduce seed set. In P. palustris, fruit set and seed predation varied markedly among populations and years, but this variation could only partly be explained by variation in population size. Fruit set was positively related to population size, and seed predation was negatively related to population size, in one of three years. Similarly, the level of pollen limitation, which was quantified in two years, varied among populations, but was not related to population size, density or isolation. In L. salicaria, both the duration of stigma receptivity and the effect of prior self-pollination on seed output varied among style morphs. These differences may contribute to morph-specific differences in pollen limitation and seed production documented in the field. The results of a field experiment demonstrated that damage to the shoot apex may markedly reduce fruit production in L. salicaria, and suggested that this is mainly because damage reduces flower number. I found no evidence that a reduced floral display increased the severity of pollen limitation. Taken together, the results show that interactions with both pollinators and herbivores may markedly affect reproductive output in the two plant species, and that the intensity of both mutualistic and antagonistic interactions vary considerably in space and time. Moreover, they are consistent with the hypothesis that pollination success should depend less on population size in selfcompatible than in self-incompatible plants.

Plant-pollinator interactions figure as key elements promoting the natural regeneration of terrestrial vegetation, as most plants depend on animals to transfer their gametes between flowers and produce seeds. Bees are the most common pollinators of plants and their interactions with flowers have served as model systems for the study of specialized mutualisms since Darwin's time. While most plants offer nectar as a reward and attract a variety of floral visitors, others produce distinctive types of resources which are sought by particular groups of pollinators. Such associations may involve specialization at the morphological, behavioral, or physiological levels and are especially common in tropical habitats. The interactions between oil-producing flowers of Neotropical Malpighiaceae and oil-collecting bees are an example of a specialized mutualism in which plants offer lipids to attract pollinators that use the resource to build nest cells and feed their offspring. Although several studies have focused on specialized pollination at the species level, their effects on the organization of tropical communities remain largely unexplored. This dissertation aims to help fill this gap through an analysis of the mechanisms of pollinator partitioning in multi-species assemblages of specialists as well as a study of the organization of communities in which they occur. The motivation for pursuing the study of specialized interactions using Neotropical species of Malpighiaceae as a model system is outlined in the first chapter. In Chapter 2, I present an evaluation of the structural properties of a plant-pollinator community from the Cerrado, a seasonal ecosystem that hosts a large diversity of oil flowers. The third chapter analyzes pollinator partitioning and reproductive strategies promoting the coexistence of closely related Malpighiaceae. A possible outcome for the selective pressures imposed by the coexistence of specialists is presented in Chapter 4 by a case study providing evidence for a shift from specialized to generalized pollination in a Neotropical Malpighiaceae species. The last chapter includes reports of active floral oil foraging by males of Tetrapedia and a description of an oil storage structure without precedence among bees and unique to males of this genus suggesting that floral oils may also play a role in bees mating systems. / text

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