DIPTERA: SPATIAL DISTRIBUTION AND ABUNDANCE IN A TROPICAL RIVER IN NIGERIAM.O. Omoigberale and A.B.O. OgedegbeAbstract This study contains results of an investigation of the spatial distribution and abundance of Diptera larvae at five different sites in a fourth order river in southern Nigeria, between March 2009 and August, 2009. Thirteen taxa comprising three families were encountered from a total of 3,516 individuals recorded. The dominant taxa were Chironomus transvaalensis (19.65%), C. fractilobus (13.48%), Pseudochironomus sp (11.72%), Pentaneura sp (10.3%) and Polypedium sp (10.28%). The overall fauna abundance varies significantly (P<0.05) among the five study sites which received varying degrees of anthropogenic input from human activities along the stretch of the river. A Posteriori Duncan Multiple Range (DMR) test revealed that the mean abundance of stations 5 was significantly higher (P<0.05) than that of other stations. The family Chironomidae dominated at all stations. The taxon richness (d), general diversity (H), Hill index (N) and evenness (E) calculated for the study stations supported the pattern observed in the number of taxa encountered and their abundance. The influence of level of urban and industrial discharges and the presence of aquatic macrophytes on the spatial distribution and abundance at the study station is reported.
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