Leaf preference and choice of the macroinvertebrate shredder Potomonautes emini in Gombe Stream National Park, Tanzania

Stream ecosystems rely heavily on the input of allochthonous organic matter, such as leaves, as a primary source of nutrients. Within the macroinvertebrate community, shredders are an essential component in the process of leaf litter breakdown in streams and are largely responsible for the conversion of coarse particulate organic matter (CPOM) into fine particulate organic matter (FPOM) (Rincon and Martinez 2006). Many other chemical and biological factors, including water temperature, nutrient concentrations in the leaf, and microbial activity, influence the rate at which particular leaf species break down in a stream (Peterson and Cummins 1972). Furthermore, these factors have a direct relationship to the subsequent colonization of leaf litter by macroinvertebrate shredders (Peterson and Cummins 1972). In particular, it has been observed that shredders feed preferentially on certain leaf species according to the microbial community established on a leaf (Peterson and Cummins 1972). The rate at which leaves are conditioned by microbes in a stream is dependent on the composition of different nutrients and compounds in the leaf (Rincon and Martinez 2006). In temperate streams, colonization of different leaf species by invertebrate shredders varies substantially, depending on the rate at which available leaves breakdown (Peterson and Cummins 1972). However, little experimental support exists for preferential feeding of different leaf species by the macroinvertebrate community in tropical stream ecosystems. Rincon and Martinez (2006), found that Phylloicus sp. larvae actively discriminate between various native leaf species differing in chemical composition in a second order stream located in northwestern Venezuela. Phylloicus larvae selected leaves with high N and P concentrations and low polyphenol and lignin concentrations, while rejecting leaves having low N and P levels and high amounts of polyphenols and lignin (Rincon and Martinez 2006).