Leaf-eating invertebrates as competitors of aquatic hyphomycetes.

Leaf-eating invertebrates selectively ingest leaf areas rich in fungal cells. The effect of this process on coincident and cumulative species diversity (species numbers and evenness) of the fungi was studied on 3 substrates (oak leaves, larch and spruce needles) in 2 hardwater and 2 softwater streams. Cumulative species number of colonizing fungi follows the equation S=k·A (A=area below decay curve of the substrate, k=substrate-specific constant, Z=0.47). Higher feeding activity means faster weight loss of the substrate which leads to lower species richness of the fungi. The opposite is true for early successional stages on larch needles. Evenness of the fungi (distribution of individuals among species) is negatively correlated with feeding intensity by invertebrates, as measured by increased decay rates. The overall effect of leaf-eating invertebrates on aquatic hyphomycetes resembles that of potent competitors preempting substrate otherwise used by a late successional tail of relatively rare fungi.