Approximately 90% of flowering plants depend on pollinators for reproduction. The stability and effectiveness of plant-pollinator interactions are crucial for ecosystem function. Increasing numbers of non-native plants are naturalized in plant communities and may alter pollination success of native plant species. Thus, invasive species have the potential to alter community function and stability. However, the effects of invasive species on community-wide plant-pollinator interactions are poorly understood. While the effects of invasive species on the structure of plant-pollinator networks are well studied. However, these studies have relied on pollinator visitation data that is only one component of the pollination process. Thus, the effects of invasive species on pollen transport and pollen transfer dynamics remain unknown and this may misrepresent the true nature of invasive effects on community-wide plant-pollinator interactions. Pollen transport networks may give more accurate representations of plant-pollinator interactions by providing information on pollen collection by floral visitors. Therefore, in this study I evaluate the effect of the invasive Cirsium arvense on pollen transport networks to improve our understanding of the impact that invasive plants have on community-wide plant-pollinator interactions. Pollinators were collected on one invaded and one non-invaded site once weekly throughout the flowering season (May- August of 2017). Pollen was isolated for each insect and pollen samples were identified with a pollen reference library and counted using a hemocytometer. 154 insect morphospecies were collected carrying 73 pollen species. Preliminary results indicate that Cirsium arvense has no impact on network structure: connectance (0.15 and 0.18), link density (3.01 and 2.23), and weighted nestedness (0.68 and 0.75), for invaded and non-invaded respectively. However, the role of individual species within the network seems to vary between sites suggesting that Cirsium arvense may change community dynamics (identity of species-pair interactions). Future analysis will evaluate invasive species effects at the species level.

BACKGROUND: Studies that aim to understand the processes that generate and organize plant diversity in nature have a long history in ecology. Among these, the study of plant-plant interactions that take place indirectly via pollinator choice and floral visitation has been paramount. Current evidence, however, indicates that plants can interact more directly via heterospecific pollen (HP) transfer and that these interactions are ubiquitous and can have strong fitness effects. The intensity of HP interactions can also vary spatially, with important implications for floral evolution and community assembly. SCOPE: Interest in understanding the role of heterospecific pollen transfer in the diversification and organization of plant communities is rapidly rising. The existence of spatial variation in the intensity of species interactions and their role in shaping patterns of diversity is also well recognized. However, after 40 years of research, the importance of spatial variation in HP transfer intensity and effects remains poorly known, and thus we have ignored its potential in shaping patterns of diversity at local and global scales. Here, I develop a conceptual framework and summarize existing evidence for the ecological and evolutionary consequences of spatial variation in HP transfer interactions and outline future directions in this field. CONCLUSIONS: The drivers of variation in HP transfer discussed here illustrate the high potential for geographic variation in HP intensity and its effects, as well as in the evolutionary responses to HP receipt. So far, the study of pollinator-mediated plant-plant interactions has been almost entirely dominated by studies of pre-pollination interactions even though their outcomes can be influenced by plant-plant interactions that take place on the stigma. It is hence critical that we fully evaluate the consequences and context-dependency of HP transfer interactions in order to gain a more complete understanding of the role that plant-pollinator interactions play in generating and organizing plant biodiversity.

Evaluation of pollen transfer in wild plant communities revealing heterospecific pollen receipt is common, yet experimental hand pollinations have revealed high among-species variation in the magnitude of its effect on recipient fitness. The causes of this among-species variation are unknown, however, prompting the investigation of underlying factors. Here, we conducted a hand-pollination experiment with ten co-flowering species to determine whether the effects of heterospecific pollen receipt are mediated by the pollen donor or recipient species alone, or whether the effects are determined by the interaction between them. We further assessed species traits potentially mediating interactive effects in heterospecific pollen receipt by evaluating the relationship between heterospecific pollen effect size and three different predictors reflecting a unique combination of pollen donor and recipient characteristics. Our results show, for the first time, that the magnitude of the heterospecific pollen receipt effect is determined by the specific combination of donor and recipient species (i.e., interactive effects). However, we were unable to uncover the specific combination of traits mediating these effects. Overall, our study provides strong evidence that an understanding of heterospecific pollen receipt effects based on recipient or donor characteristics alone may be insufficient. This study is an important step toward an understanding of consequences of heterospecific pollen receipt in co-flowering communities.

The myriad ways species interact with each other have always captivated biologists. These interactions—predation, competition, parasitism, and mutualism—are fundamental to the stability of ecological communities and drive the evolution of species they contain. Some mutualistic systems consist of mutually dependent partners that strongly influence each other’s survival, while other mutualistic systems consist of many, diffuse relationships between large assemblages of partners. Critical ecological processes like pollination and seed dispersal are prime examples of such complex systems. Plant-pollinator communities are characterized by extensive pollinator sharing among plant species. My dissertation explores some of the consequences of this reliance on shared pollinators on the structure of plant-pollinator interaction networks, the foraging decisions of pollinators, and the fitness outcomes of plant species. Through several comprehensive field studies, I contribute to our understanding of mutualist interaction patterns at multiple levels of biological hierarchy: the community, species, and individuals. My first chapter examines the forces driving the change in interaction patterns of an entire plant-pollinator community and individual species throughout the flowering season. Nearly all studies of plant-pollinator interaction networks ignore potential intra-annual variation, and in doing so may be missing critical mechanisms contributing to overall community stability. I find that the overall turnover of interactions is high and driven by a process of interaction rewiring in which species frequently shuffle between available partners. Furthermore, I distinguish pollinator species whose interactions are driven by an abundance-based neutral process versus those that change their interactions beyond what is predicted by a neutral, abundance-driven null model. My second chapter uses a network-based framework to consider the fitness consequences for plants participating in a diffuse plant-pollinator network. I analyze the relationship between plant species’ network metrics and pollen deposition. Empirical examples that link patterns of interactions and functional outcomes (e.g., pollination) are scarce, but necessary to establish the utility of characterizing species interaction patterns. My final chapter explores how pollinator composition, local floral neighborhoods, and timing of flowering influence the pollination outcomes of individual Oenothera fruticosa flowers. I demonstrate extensive intraspecific variation in receipt of pollen from other species (‘heterospecific pollen receipt’) and find that this heterospecific pollen has a negative fitness effect if present in sufficiently high amounts. Together, the chapters of my thesis provide novel insights into the consequences of pollinator sharing among co-flowering plant species. / Biology

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.

No description available.

Orientador: Marlies Sazima / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-20T00:54:41Z (GMT). No. of bitstreams: 1 Fonseca_LorenaCoutinhoNeryda_D.pdf: 15688849 bytes, checksum: 5ab648e9c0a851952dff287bd487d46e (MD5) Previous issue date: 2012 / Resumo: O estudo das relações entre beija-flores e plantas, do fluxo polínico entre as espécies polinizadas e da área utilizada por estas aves é importante para melhor entendimento dos processos evolutivos que levaram a estas interações, além de fornecer subsídios para a conservação das espécies envolvidas. O presente estudo fornece informações sobre a distribuição temporal do recurso alimentar (néctar), a disponibilidade de energia no néctar e o transporte de pólen de espécies polinizadas por beija-flores em área de Mata Atlântica. O estudo foi realizado no Parque Estadual da Serra do Mar, sudeste do Brasil, em área de Mata Atlântica de terras baixas. Os beija-flores foram capturados mensalmente com redes de neblina, anilhados e os grãos de pólen foram retirados com fita adesiva para análise em laboratório. Para verificar a distribuição do recurso alimentar ao longo do ano, foi registrada a fenologia floral das espécies ornitófilas de uma área com 5000m2. O volume e a concentração de açúcares do néctar das espécies foram medidos para o cálculo da quantidade de calorias disponíveis na área. Foram coletados estigmas de duas espécies de plantas (Canistropsis seidelii e Psychotria nuda) para verificar se há transporte de pólen interespecífico mediado por beija-flores. Foram capturadas seis espécies de beija-flores: Amazilia fimbriata, Florisuga fusca, Phaethornis ruber, Phaethornis squalidus, Ramphodon naevius e Thalurania glaucopis. Ramphodon naevius foi a espécie mais abundante e os dados de recaptura demonstraram que esta espécie permanece na área ao longo do ano. Foram registradas oito famílias com espécies ornitófilas: Bromeliaceae com 15 espécies, Gesneriaceae com três espécies, Rubiaceae com duas espécies e Acanthaceae, Fabaceae, Heliconiaceae, Loranthaceae e Orchidaceae com uma espécie cada. A disponibilidade de recursos variou ao longo do ano, o que influencia as áreas de forrageamento dos beija-flores. Segundo as estimativas realizadas, um beija-flor precisaria ao menos entre 0,37 ha e 4,7 ha para obter recurso (néctar) suficiente na área de estudo. Foram encontrados 31 morfotipos polínicos nos beija-flores, sendo Bromeliaceae a família que apresentou maior quantidade de morfotipos. As amostras apresentavam entre um e seis morfotipos de pólen e a maioria apresentou dois ou mais. Foram encontrados 29 morfotipos polínicos em Ramphodon naevius, cinco em Thalurania glaucopis e quatro em Florisuga fusca. Nos indivíduos de Ramphodon naevius que apresentaram sobreposição de grãos interespecíficos, houve predominância de um morfotipo por local de deposição. Houve deposição de grãos interespecíficos de pólen nos estigmas das duas espécies de plantas, porém o número de grãos interespecíficos foi baixo. Apesar de Ramphodon naevius transportar com freqüência grãos de pólen entre as espécies de plantas, na maior parte das vezes os grãos transportados em determinado local da cabeça pertencem, em sua maioria, a apenas uma espécie. O transporte de pólen entre espécies é baixo, embora seja frequente. É sugerido que este transporte interfira pouco no sucesso reprodutivo das plantas que participam desta interação / Abstract: Studies about bird and plant interaction, pollen transfer between bird-pollinated plants and the area used by hummingbirds are needed to improve our knowledge about the processes involved in bird-plant interactions and about their conservation. In this study, we provide information about temporal distribution of food resources (nectar), energy availability on nectar and pollen transfer between hummingbird-pollinated species in a lowland Atlantic Forest area. The study was conducted at Parque Estadual da Serra do Mar, southeastern Brazil. Hummingbirds were captured monthly and received metallic bands. Pollen grains were collected from hummingbirds'bill and head with transparent tapes and then placed on a glass microscope slide for latter analyses. Records on the floral phenology of the ornithophilous species were made monthly in a 5000 m2 area. The quantity of calories in the nectar was estimated from the values of volume and sugar concentration. We collected stigmas from two species (Canistropsis seidelii and Psychotria nuda) in order to quantify the pollen transfer between the species. We captured six hummingbird species: Amazilia fimbriata, Florisuga fusca, Phaethornis ruber, Phaethornis squalidus, Ramphodon naevius and Thalurania glaucopis. Ramphodon naevius was the most abundant species and the data about recaptures through the year indicate that it is a resident species. We registered ornithophilous species from eight families: Bromeliaceae (15 species), Gesneriaceae (3 species), Rubiaceae (2 species) and Acanthaceae, Fabaceae, Heliconiaceae, Loranthaceae and Orchidaceae (one species each). The food resource availability varied through the year, influencing the size of the area used by hummingbirds. According to the estimations, a hummingbird would need an area of, at least, 0,37 ha to 4,7 ha to obtain enough resources. Hummingbirds carried 31 morphospecies of pollen grains and Bromeliaceae had many morphospecies. Each hummingbird carried from one to six morphospecies of pollen grains and most of them carried two or more of them. There were 29 morphospecies in Ramphodon naevius, five in Thalurania glaucopis and four in Florisuga fusca. Individuals of Ramphodon naevius that carried two or more morphospecies at the same place of its body had one morphospecies more abundant than the others. There was deposition of interespecific pollen grains on the stigmas of the studied species, but the number of interespeficif pollen grains was low. Despite transporting often pollen grains between species, Ramphodon naevius transported mainly one morphospecies on each part of its head or bill. The pollen transfer between species was low, although it was frequent. We suggest that the interespecific pollen transfer between these hummingbird-pollinated species may have little effect on its reproductive assurance / Doutorado / Biologia Vegetal / Doutor em Biologia Vegetal

Background: Pollen transfer via animals is necessary for reproduction by ~80 % of flowering plants, and most of these plants live in multispecies communities where they can share pollinators. While diffuse plant-pollinator interactions are increasingly recognized as the rule rather than the exception, their fitness consequences cannot be deduced from flower visitation alone, so other proxies, functionally closer to seed production and amenable for use in a broad variety of diverse communities, are necessary. Scope: We conceptually summarize how the study of pollen on stigmas of spent flowers can reflect key drivers and functional aspects of the plant-pollinator interaction (e.g. competition, facilitation or commensalism). We critically evaluate how variable visitation rates and other factors (pollinator pool and floral avoidance) can give rise to different relationships between heterospecific pollen and (1) conspecific pollen on the stigma and (2) conspecific tubes/grain in the style, revealing the complexity of potential interpretations. We advise on best practices for using these proxies, noting the assumptions and caveats involved in their use, and explicate what additional data are required to verify interpretation of given patterns. Conclusions: We conclude that characterizing pollen on stigmas of spent flowers provides an attainable indirect measure of pollination interactions, but given the complex processes of pollen transfer that generate patterns of conspecific-heterospecific pollen on stigmas these cannot alone determine whether competition or facilitation are the underlying drivers. Thus, functional tests are also needed to validate these hypotheses.