Resource partitioning along three niche dimensions in a size-structured tropical fish assemblage

In Tissawewa, a tropical reservoir, the size-specific resource use of the 1 0 most important fish species was determined along three dimensions: trophi c, spatial, and temporal. During this study, a drought occurred distinguish ing two periods before and after the drought that differed markedly in avai lability of resources and fish biomass. In this study, differences in resou rce use between the two periods are presented together with their consequen ce on the partitioning of resources. A different approach is introduced int o the calculation of niche breadth and niche overlap incorporating size-spe cific differences in resource use and interactions between resource dimensi ons. Comparison with conventional measures of niche breadth and niche overl ap shows that conventional measures often misrepresent interactions between species. Condition and biomass were used as indicators of a species' fitne ss, and it is shown that fitness of most species is governed by the availab ility of resources and partitioning of these resources is an important mech anism allowing potential competitors to coexist. Resource partitioning alon g the trophic dimension was more important than along the spatial or tempor al dimension.