Leaf litter diversity and shredder preferences in an Australian tropical rain-forest stream

Consumption of terrestrial leaf litter by stream invertebrates is an important process, but little attention has been paid to the influence of leaf diversity on the process. Tropical forests are known to have much greater diversity of plant species than their temperate counterparts, but studies of litter processing in tropical streams have not explicitly addressed this issue. This paper documents the streambed leaf litter composition and diversity of an Australian tropical rain-forest stream and the leaf preferences of consumers in the stream. We hypothesized that there would be high diversity of litter in the stream and that the shredders would have broad preferences, given that litterfall of any one species would occur over a restricted period. Leaf litter was characterized by high species diversity (81 species from one stream reach sampled on two occasions). Leaf consumers ('shredders') were associated with a relatively broad suite of leaf species (38 species) and did not indicate clear leaf preferences. However, in a laboratory feeding experiment, using the three most common shredder species and some of the most abundant leaf species in the stream, all shredder species exhibited clear preference for a single leaf species (Endiandra bessaphila). Preference for this and other species was affected by the conditioning age of leaves (i.e. the length of time leaves were exposed to leaching and microbial colonization), with conditioned leaves usually being preferred, and previously non-selected leaves becoming more palatable with conditioning. Thus, different successional stages were more important than the identity of leaf species in determining the distribution of shredders among the leaves.