MACROINVERTEBRATE FUNCTIONAL FEEDING GROUPS IN THE MIDDLE AND LOWER REACHES OF THE BUFFALO RIVER, EASTERN CAPE, SOUTH-AFRICA .2. FUNCTIONAL-MORPHOLOGY AND BEHAVIOR

1. While it was impossible to assign twelve taxa from the middle and l ower reaches of the Buffalo River, eastern Cape, South Africa to funct ional feeding groups (FFGs) on the basis of their foregut contents alo ne, we were able to assign these taxa to FFGs, with varying degrees of certainty, on the basis of their mouthpart morphology and feeding beh aviour. 2. The two Hydropsychidae were identified as passive filterers on the basis of their feeding behaviour. The ultrastructure of the la bia and maxillae of the ten Ephemeroptera, and observation of the feed ing behaviour of five of these, were used to assign them to FFGs. 3. O nly mayfly species whose morphology and behaviour were recorded could be positively assigned to the FFGs active or passive filterer, gathere r, brusher, and scraper. The FFG designation described the predominant feeding behaviour, and all observed taxa exhibited a range of feeding activities. 4. FFGs are useful descriptive categories which clarify b oth the nature and distribution of the food eaten, and the role of the organism in the ecosystem. FFGs affect a variety of stream processes, and the role of the FFG concept in understanding stream functions is discussed.