Efeitos da paisagem sobre as interações e a diversidade funcional de plantas e polinizadores em remanescentes urbanos de Cerrado

Abstract

Urbanization modifies the natural landscape through fragmentation and isolation of habitats. The consequences of these processes reflect on the structure of the vegetation, on pollinator communities and, consequently, on pollination services. Human disturbances are variable across the length of cities and, for this reason, they are excellent models for examining effects on organisms, including pollinating insects and plants. In the first chapter of this thesis, we evaluated the effects of land cover types around 14 Cerrado remnants in Campo Grande, MS at different scales (500 m, 1 km and 2 km), on richnees of plants and pollinators, as well as on network and species level metrics. We also evaluated if the beta diversity of species and interactions differs between remnants with higher and lower degrees of urbanization (semi-natural and urban areas). We also evaluated whether remnants’ isolation affects changes in interactions between local networks and the meta-network. The networks were nested, presented low modularity and predominance of generalist interactions, which was expected, since the studied remnants occur in urban areas. The different land covers had effects on plant-pollinator interactions, since all of them, at least on one scale, led to increased richness of interactions. Furthermore, the change in the composition of plants and pollinators was the determining factor for the replacement of interactions among remnants, reinforcing that the city's phytophysiognomies favor the diversity existing in the city. Isolation only led to changes in interactions among shared species between the local networks and the meta-network, indicating that connectivity between the remnants of Cerrado is necessary for the maintenance of these interactions. In the second chapter, we analyzed whether the functional traits of plants and bees, as well as functional richness (FRic), functional equitability (FEve) and functional divergence (Fdiv) of these groups are affected by remnants’ isolation and by landascape cover in three spatial scales. Richness of bees was positively affected by the richness and by the functional richness of plants. Furthermore, the functional richness of plants was related to the species richness of this group, but the species richness of bees was not related to their functional richness. This shows that patterns of functional diversity are much more variable than patterns related to species diversity and reinforces the importance of conserving natural areas within urban spaces. The increased coverage of green areas on a larger scale reduced the uniformity and functional divergence of plants. The pasture/open field areas were associated with a lower functional richness of plants, which may have led to a lower functional diversity of bees. The isolation of the remnants, in turn, did not influence the components of the functional diversity of bees and plants. The expansion of urban coverage led to an increase in the body size of bees, suggesting that the dispersion and establishment of these insects can be influenced by the quality of the habitat, both in the Cerrado remnants sampled and in the surrounding areas. In the third chapter we evaluated how remnants’ isolation and land cover at three spatial scales affected the abundance of Apis mellifera, as well as the richness of visited plant species and pollen grains carried by these bees (zoocentric and phytocentric sampling). Based on these two approaches, we analyzed whether plants’ richness and diversity correlates with the number of species visited in the remnants. Apis mellifera explored a wide variety of floral species. Asteraceae was the most representative family of plants, both in pollen sampling and in focal observations of bees on flowers. The richness of plants visited in these two approaches was positively affected by the richness of plants in the Cerrado remnants, demonstrating the importance of these areas for bees. Isolation and the abundance of bees did not affect the richness of visited plants recorded in both approaches. Several types of land cover in different scales favored the richness of plants visited, probably because A. mellifera is a generalist species that can handle various types of environments and degrees of disturbance. The results obtained throughout this study showed that landscapes altered by man are capable of harboring a wide range of species and interactions, even maintaining certain types of ecosystem functions. The distinct land covers around the remnants of Cerrado can influence the communities of plants and insects in different ways. Therefore, we suggest to expand the studies including sampling also in different matrices of the landscape.