The Maku are a linguistically distinct indigenous population of hunter-gatherers living deep within the tropical forest of northwestern Amazonia. Their geographical range greatly overlaps that of another indigenous population, the Tukanoans, riparian fisher -gardeners. In ecological terms, the two populations can be viewed as occupying different niches within their equatorial forest biome. A quantitative examination of the Maku diet indicates that calories may at times pose a dietary problem for the Maku. In contrast, the Tukanoans may occasionally face seasonal shortages of fish, their major protein source. Traditional exchanges of food and labor between members of the two populations may help avert potential dietary problems and increase overall human biomass in this geographical region.