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| Author(s): |
Fabiana Curtopassi Pioker
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2011-08-24 |
| Examining board members: |
Astrid de Matos Peixoto Kleinert;
Maria Cristina Arias;
Vera Lucia Imperatriz Fonseca;
Tiago Mauricio Francoy;
Márcia Maria Corrêa Rêgo
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| Advisor: | Astrid de Matos Peixoto Kleinert |
| Abstract | |
The antropic pressure over the Cerrado has been transforming its landscape into a mosaic of fragments surrounded by an antropized matrix. The quality of the vegetation of the remaining fragments largely depends on the pollinators populations, which the bees are the most representative. The stingless bees (Apidae: Meliponini) compound the biggest biomass of this biome. Their nests are usually made inside trunk or soil cavities, but some species make exposed nests. The factors that lead Meliponini to nest in a given region are, at first, the resources availability (nest sites and food) and the intra- and interspecific competitive behavior. However, these are not the sole determinants, because the factors that lead to maintain, expand or reduce populations sizes are also related to the response of each species to the landscape antropization degree. The main general goal of this thesis was to investigate how natural and antropic factors affect the Meliponini nesting in Cerrado areas, seeking to answer the following questions: a) Do structure differences among cerrado phytophysiognomies reflect in Meliponini species composition? b) How do the reduction of Cerrado natural areas and their replacement by rural and urban landscapes affect the Meliponini nest populations? and c) How do the genetic relationship and the obtaintion of food resources affect colony distribution in a Cerrado area? To answer these questions, this thesis was split in three chapters: In chapter 1, the objective was to understand if and how the Meliponini nest distribution would vary among three Cerrado phytophysiognomies, namely campo sujo, campo cerrado and cerradão in Itirapina, SP, and how this variation would be related to differences in nesting sites and food availability in each one of them. A nest survey and an evaluation of the trees amount and species composition were undertaken in each phytophysiognomie, besides flowering plants count over 20 months. We found 50 Meliponini nests, being 17 in campo sujo (all belonging to Trigona spinipes), 19 in campo cerrado (18 of T. spinipes and one of Melipona quadrifasciata), 12 in cerradão (five of T. spinipes, three of Tetragonisca angustula, two of Leurotrigona muelleri, one of Trigona hyalinata and one of Plebeia droryana) and two nests of T. spinipes outside the sampled area. The highest amount of threes was found in cerradão while the highest amount of flowered plants was found in campo sujo. In chapter 2, the objective was to evaluate the effect of replacement of natural Cerrado areas by rural and urban landscapes over general Meliponini populations and particularly over Melípona bees. The results of 31 nests surveys in Cerrado areas besides those conducted in Itirapina were correlated to the antropization degree of the landscape. Landscape evaluation was undertaken by analysis and classification of satellite images from the surveyed surrounding areas. The Meliponini species richness was negatively related to the proportion of rural areas, but species composition was positively related. Species composition was positive related to vegetation size too. I turn, both Melípona nests density and Melípona species composition were negatively related to the proportion of rural areas. In chapter 3, the objective was to verify the degree of genetic relationship and its influence over T. spinipes colony distribution in the landscape, the foraging distance and if there was or was not sharing food among colonies. To accomplish this, a microsatellite markers study was undertaken among colonies found in chapter 1, plus a foraging range experiment. Neighbor nests shown a low genetic relationship degree among them, but workers collected at the same flower showed a high degree of genetic relationship. Foraging distance was farther than the distance between neighbor colonies. We conclude that: a) Grassland phytophysiognomies may show a nest abundance higher than forest phytophysiognomies, but these can show a higher species richness. Sample size can underestimate species richness in forest phytophysiognomies. The positive relationship between Meliponini species composition and vegetation size indicates that there are preferences of some species to some phytophysiognomies. However, the ubiquity of species with a plastic behavior may difficult the finding of a pattern. b) Antropization may have a negative effect over Meliponini population, leading to species loss. To the species with a more plastic behavior, antropized areas do not offer resources limitation, but to species with a more restrictive behavior, the replacement of natural areas may have a deleterious effect on their populations. c) The low degree of genetic relationship among neighbor nests indicates that there is no genetic flow limitation to T. spinipes. The ability of T. spinipes workers to dominate a flower resource may competitively exclude less aggressive bees. If the antropized matrix presents resource limitation, less aggressive species may not obtain food resources, becoming isolated in fragments of natural areas. The isolation may lead to loss of genetic variability and consequentially to species loss. Thus, conservation policies aiming at Meliponini species protection must take in account not only the amount of trees of a given region, but also the quality and heterogeneity of vegetation, as much in areas of environmental protection as the areas among them. (AU) | |