The effects of leaf toughness on feeding preference by two Tasmanian shredders

The effect of leaf toughness on the diet preference of two shredding invertebrates, Caenota plicata (Trichoptera: Calocidae) and Antipodeus wellingtoni (Amphipoda) using native leaves, Eucalyptus globulus, Eucalyptus obliqua and Pomaderris apetala, and one exotic species, Alnus glutinosa (Alder) were tested in the laboratory. We hypothesised that the softer textured leaves of P. apetala and A. glutinosa would be preferred over the tougher eucalypt leaves. Leaf toughness was measured using a penetrometer and preference was calculated based on Chesson-Manly selection index. E. globulus, E. obliqua and A. glutinosa were all consumed to some extent; however, there was a clear avoidance of P. apetala by both shredder species. Only A. wellingtoni showed a clear preference for E. globulus. This study demonstrates that the toughness of leaves does not affect the consumption of leaves by A. wellingtoni and C. plicata. Hence there is no reason to assume a priori that the tougher Australian leaves would be avoided by local shredders as have been observed in northern hemisphere studies.