The Humped-back theory of plant species richness, a theory related to Grime's C-S-R 'triangular' model, has been widely discussed, and some evidence has been claimed in support of it. The theory suggests that species richness is maximal at intermediate levels of productivity, i.e., at intermediate positions on a stress/favourability gradient. We sought evidence for the theory from 90 stands of native podocarp/broadleaved and beech forest in the Coastal Otago region, with an adjustment made for the effect of stand area on species richness.
The anti-predator behaviours of a New Zealand freshwater crayfish (Paranephrops zealandicus) to the native long-finned eel (Anguilla dieffenbachii) and the introduced brown trout (Salmo trutta) were investigated. Crayfish modified their behaviour in the presence of both trout and eels. However, a significantly greater number of defensive chela displays and swimming responses were made to eels than trout. Crayfish were able to use chemical cues from skin mucus to detect eels but not trout.