Odonatological Abstracts

(18062) DE MARCO, P., Jr, 1992. Community structure and co-occurrence of larval odonate species: a morphological approach. Tese Mestre Cien. Biol., Univ. Campinas, ix+80 pp. (Port., with Engl. s.). — (Lab. Ecol. Teoretica, Depto Biol, Geral, Univ. Fed. de Goias, BR-74001-970 Goiania, GO). Studies on odon. larvae have shown the existence of feeding territories, suggesting that competition for foraging patches may be an important factor in community structuring. Field studies however have failed to demonstrate competition, and have suggested that fish predation and cannibalism among larvae are important regulating factors. Here, the co-occurrence patterns among larvae in several aquatic plants are examined in order to evaluate the importance of these interactive processes to the explanation of the observed patterns. Odon. were sampled on aquatic plants in the states of Minas Gerais and Sao Paulo (Brazil). 14 measures were taken of the body, head and labium of each individual. Cluster analysis showed 2 types of communities associated with macrophytes of distinct architecture. The submerged Egeria densa, Myriophyllum brasiliense and the emergent Eleocharis mutata had Ischnura fluviatilis, Micrathyria hesperis, Erythrodiplax sp. and Acanthagrion sp. as dominants, whereas the floating Eichhomia crassipes and Salvinia sp. were dominated by Miathyria simplex and Telebasis filiola. The morphometry data demonstrated convergence within the sets. The spp. characteristic of floating plants have greater eye width and smaller anterior, medium and posterior femur length, when compared to the spp. living in submerged and emergent macrophytes. In order to test the importance of interactive processes as determinants of the morphological patterns of cooccurring spp. (limited similarity hypothesis), null models were built representing the expected patterns if the communities were assembled through random selection from the sampled spp. The Egeria densa community showed smaller morphometric distances among spp. than that expected by chance, suggesting convergence mechanisms in relation to possible colonizing morphologies. The larvae in Myriophyllum brasiliense tended to separate more than expected by chance, suggesting an effect of interspecific competition. The consistency between 2 different null model constructions was an interesting way to evaluate the behaviour of the statistical test, in the identification of non-random patterns, ft is suggested as an important methodological approach.