Macroinvertebrados associados a pedras em riachos : padrões de diversidades ao longo de uma bacia hidrografica

Orientador: Claudio Gilberto FroehlichDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de BiologiaResumo: Neste trabalho estudei alguns aspectos da estrutura de comunidades de macro invertebrados aquáticos em 10 riachos dentro de uma mesma bacia hidrográfica. Especificamente, investiguei 3 hipóteses: (1) a existência de um gradiente de diversidade ao longo da bacia, tendo seus maiores valores em riachos de tamanho médio; (2) o fato da estrutura da comunidade poder estar mais perturbada durante o verão em relacão ao inverno, devido a enchentes e a (3) hipótese de que riachos tropicais possuem maior diversidade em relação a riachos de regiões temperadas. o local de estudo foi o Parque Estadual Intervales, localizado no Vale do Rio Ribeira, Estado de São Paulo durante duas épocas do ano: no verão (época de maiorAbstract: Some aspects of the community structure of the aquatic macroinvertebrates in 10 streams in the same basin were investigated. I looked specificalIy into 3 hypothesis: (1) the presence of a diversity gradient along the basin, with higher values in mid-sized streams; (2) higher perturbation of the community structure in summer than in winter, because of frequent spates and (3) that tropical streams support a more diversified assemblage than the temperate counterparts. The study site was the Parque Estadual Intervales, in the Ribeira River Basin, São Paulo State, in two periods: summer (the more rainy period) and winter. The colIections were done in a quantitative way, each sample unit consisting of alI macroinvertebrates associated with individual stones about 18 cm. long, superficialIy embedded in riffies. For the data analysis, I used values of the observed and extrapolated richness and the alpha diversity index. For analysis of the community structure in summer and winter, I used an index proposed in the literature and also methods ofMultivariate Analysis. Two out of the 10 studied streams, have a different physical structure (many sediments on stones) and presented lower richness and diversity. In relation to a diversity gradient along the basin, the result differ from current theories. The main difference is that the highest richness was found in streams smaller than those proposed by the theory and previous empirical work. With the index used to evaluate the community structure, I have not found differences betwen summer and winter. With Multivariate Analysis, the position ofthe same stream in the two periods (summer and winter) was very close, showing that the community structure did not undergo major changes. Richness and diversity values obtained in this study agree with other tropical studies and are larger than those of temperate counterparts. I eonclude that small streams around first (exeept in sites near their sourees) and third orders, have higher riehness and diversity of maeroinvertebrates than larger streams. Although spates are frequent and heavy throughout summer, it seem that they do not ehange signifieantly the eommunity strueture. The high predietability of spates in this period may have promoted the evolution of resistanee meehanisms for these disturbanees. The spates in the year of the study were close in frequeney and intensity to those expeeted. However, larger spates, that oeeur in eycles over 1 year, probably eould ehange eommunity strueture, a faet reported in several papers in the literatureMestradoMestre em Ciências Biológica