Original paper

Patchy resources in a heterogeneous environment: effects of leaf litter and forest cover on colonisation patterns of invertebrates in a British Columbian stream

Gjerløv, Charlotte; Richardson, John S.

Abstract

We tested experimentally the hypotheses that leaves are colonised for their value as food and not as microhabitat, and that colonisation of leaves would be faster in a clearcut reach due to food limitation. During weekly trials in a forested and a clearcut reach of a small stream in the continental interior of British Columbia, Canada, we provided colonisation cages with one of three leaf treatments (no leaves, artificial, red alder). Shredder-detritivores preferentially colonised the alder leaf packs in both reaches (densities 3.9 times greater in alder leaf treatments), but there was no difference between the artificial and no leaf treatments. Preferential colonisation of alder leaves suggests they were being colonised for their value as food and not microhabitat. Colonisation was faster in the forested reach for all treatments (cage: benthos ratio for densities greater than 2.3 times those of the clearcut reach), contrary to predictions. Faster colonisation in the forested reach may be a response to lower UV radiation, a more patchy food source (leaf litter vs. algae) or greater habitat heterogeneity. These results suggest forest harvesting can affect community dynamics of streams, primarily through shifts in community composition.

Keywords

leaf colonizationmicrohabitatfood limitationleaf packs