Omnivory (feeding at different trophic levels) is frequently invoked as being important in tropical stream food webs. Ontogenetic omnivory is certainly common, but within a life stage omnivory may not be common. C-N stable isotope biplots typically show a continuum of species with little separation of trophic levels. However, basal resources in tropical streams show a very wide C-N isotope footprint, so an alternative explanation could be that there are multiple food chains starting from diverse basal resources. We examined these alternatives using C-N stable isotope niche biplots for macroinvertebrates and tadpoles in upland streams in Panama. Results showed very clear niche diversification among species within trophic categories, suggesting that food resource partitioning is occurring at fine scales. It appears that species have finely partitioned their food resources. Given the apparent high level of competition for resources in these systems, we examine the question of whether omnivory is an evolutionary stable strategy for species in tropical stream food