Caddisfly distribution in a tropical stream

Trichoptera (caddisflies) are important components of the pollution-sensitive invertebrate taxa that are commonly used for assessing water quality worldwide. Their natural distri- bution is thus modified by anthropogenic factors, notably oxygen demand, related to the presence of organic matter and other oxidising substances, and to suspended sediment. The natural factors that influence caddis distribution mean that a correct interpretation of the presence/absence of a particular taxon requires an in-depth understanding of tax- on-habitat relationships. Such knowledge exists in temperate regions (notably in Europe and in North America) after decades of research, but it is almost non-existent for tropical streams. Trichoptera occupy a number of important ecological roles within stream trophic chains and have representatives in all functional feeding groups. In particular, some caddis taxa are effective shredders found in streams worldwide. This is the also case in tropical streams, in which shredders are considered to be under-represented. We present an analysis of the distribution of Trichoptera collected in a single Afro-tropi- cal stream in Kenya. A detailed description of the in-stream biotopes from which samples were collected is linked to partition of the taxa into functional feeding groups, established through the assessment of ΔN and ΔC stable isotopes in degutted caddis larvae. We link this to analysis of the composition of larval gut contents, and to a morphological assess- ment of the shape and adaptation of their mandibles. Our results contribute to understanding the ecological role of poorly known caddis taxa and provide greater insight about the presence of shredders in tropical streams.