Consistent effects of productivity and disturbance on diversity between landscapes

Productivity and disturbance have a strong role in determining diversity patterns in nature yet whether they operate individually or interact to determine diversity is unclear. Moreover, what effect land-use change has on this relationship has not been assessed. We tested whether land use influenced the relationship between productivity, disturbance and diversity, and assessed the fit of three productivity-disturbance-diversity models, using data from multiple samplings of 16 streams in two contrasting regions of the North Island of New Zealand. As the Dynamic Equilibrium Model (DEM) has received inconsistent support in all ecosystems and little favorable applications in lotic systems, we applied this along with two previously developed for stream communities. Although the community structure differed between the two regions, the response of taxonomic richness to productivity and disturbance was consistent. That is, richness was log-linearly related to productivity and declined monotonically with disturbance. However, there was no evidence of an interactive effect of productivity and disturbance. When accounting for density ( rarefaction) the results were inconsistent, exhibiting no relationship with productivity but declining with disturbance. Our results suggest both the Death and Tonkin productivity-disturbance-diversity models are the most applicable in these communities where disturbance simply removes taxa and productivity controls the upper limit to richness.