Efeitos climáticos, ecológicos e evolutivos sobre os padrões de interação entre polinizadores e plantas

Abstract

Plant-pollinator interactions can be affected by factors operating at different spatial and temporal scales, from historical and contemporary macroclimatic conditions to the seasonal availability of resources at the local level. Given the complexity involved in the structure of these interactions, one of the major challenges in Ecology is to understand how evolutionary, ecological, and climatic aspects influence such relationships. In this context, this thesis seeks to answer how historical and current climatic conditions are related to the architecture of interaction networks between bees and plants in the American continent (Chapter 1). To achieve this, we built a database from published studies on bee-plant interactions at the community level in the Americas and calculated network-level and species-level metrics for each network found. We used historical and current bioclimatic variables to assess the relationship with the observed metrics. We compiled a total of 42 studies, from which we obtained 64 plant-bee interaction networks, composed by 13 to 532 species. Apis mellifera L. was the most recurrent species in the studies, present in 71% of the observed networks; in modular networks, this species acted mainly as a connector, linking species from different modules. The results further revealed that connectance and network asymmetry showed no relationship with the evaluated climatic characteristics. On the other hand, precipitation seasonality during the Last Glacial Maximum (LGM) negatively affected plant richness, bee richness, network size; and positively influenced network nestedness. The temperature increase since the LGM had a positive effect on network structure, enhancing both modularity and nestedness. Thus, we demonstrate that historical climatic variation is the main factor influencing bee-plant interaction networks at the continental scale. In Chapter 2, in a smaller scale approach, we investigated whether the interactions between floral visitors and plants in the Pantanal are more related to ecological factors or to the evolutionary characteristics of these plants. For this purpose, we searched for studies on these interactions conducted in this ecosystem and categorized plant attributes based on specialized literature. Subsequently, to evaluate whether these attributes are associated with evolutionary and/or ecological factors, we tested the phylogenetic signal of the evaluated species. We compiled a total of 38 studies, with 1659 interaction records involving nine pollinator groups and 312 plant species. Most plants recorded occur in terrestrial environments, have an herbaceous habit, predominantly white, dish-shaped flowers, and are native. Bees were the group with the highest number of records, with A. mellifera L. and Trigona spinipes (Fabricius) being the species involved in the majority of recorded interactions. We found a significant association between the frequency of records of certain pollinator groups and terrestrial plants, aquatic plants, or plants occurring in both habitats. Aquatic plants or those occurring in both environments were more associated with herbaceous habit, dish-shaped and gullet-shaped flowers, and cooler colors. In contrast, terrestrial plants were more associated with characteristics such as tree, shrub, and liana habits, white, or yellow flowers with inconspicuous, brush and tube floral types. Regarding the phylogenetic signal, the attributes of flower color, environment of occurrence (terrestrial, aquatic or both), and floral type proved to be phylogenetically significant. These findings reinforce the idea that both phylogenetic and ecological characteristics act to determine the structure of plant-pollinator interactions in the Pantanal. The high specificity related to some pollinator groups and the environment of plant occurrence highlights the need for conservation measures that consider maintaining the habitat variability existing in the Pantanal. These patterns have important implications for the maintenance of biodiversity and the ecosystem functioning of Pantanal, especially in a scenario of environmental changes.