Increased functional diversity has been linked to an increase in ecosystem level processes (ELPs), such as productivity, ecosystem reliability and invasion resistance. However, there has been no exact definition of functional diversity and it is not known which indices are appropriate for its measurement. Consequently, continuous indices have rarely been applied in examination of relationships between functional diversity and ELPs and little is known of the mechanisms linking functional diversity to ELPs. This thesis begins by providing an exact definition of functional diversity, identifying its primary components and devising appropriate continuous indices for the measurement of these components. These indices are used to examine relationships between functional diversity and three ELPs - biomass production, the reliability of biomass production and invasion resistance. Initially these examinations are conducted using a mechanistic community assembly and dynamic model. This model is based on physiological and morphological character data for species occurring in the short-tussock grassland communities of the Luggate field experiment, in the southern South Island, New Zealand. Finally, relationships between functional diversity, mean annual community cover and the reliability of cover are examined in the Luggate field experiment. Functional composition (i.e. the actual functional characters of the species within a community) appeared to exercise the greatest influence on ecosystem reliability in the community assembly and dynamic model. However, there was evidence that functional diversity increased the reliability of productivity via the co-variance effect. Functional composition also exercised the greatest influence over mean annual productivity in the model, almost completely accounting for the negative relationship between functional diversity and mean annual productivity. These results are respectively analogous to the positive and negative selection effects seen in species richness / ELP relationships. Both functional diversity and functional composition influenced community invasion resistance in the model. Here, increased functional diversity acted to increase community resistance to invasion. In the Luggate field experiment, neither functional diversity nor functional composition was related to mean annual cover, though species richness was positively related to it. Increased functional diversity acted to increase the reliability of cover. However, this did not appear to occur via the co-variance effect, but as a result of increased functional diversity increasing consistency in the species composition of experimental plots through time. These results demonstrate that studies examining functional diversity must account for the effects of species identity. A framework is proposed to accommodate selection effects associated with functional diversity / ELP relationships. The usefulness of the co-variance effect as a testable mechanism linking functional diversity to ecosystem reliability in the field is questionable, as there is no objective way of measuring it.

This thesis set out to examine the soils, plants, lichens, invertebrates and common skinks along a gradient of habitat modification. This gradient was represented by ten study sites, of varying management histories, in a mid altitude tall tussock (Chionochloa spp.) grassland in eastern Central Otago. One extreme of the gradient was represented by intact tall tussock plants with a high density of inter tussock vegetation. The other extreme was represented by intensively managed exotic pasture. Native plants, invertebrates and reptiles were present along the entire gradient of modification and there was a clear threshold in the diversity of native plants along the gradient. This threshold was reached after the management practice of ploughing was applied to a site. Sites that had not been ploughed were found to be similar in their native plant diversity, and all unploughed sites had significantly higher native plant diversity than unploughed sites. There was considerable variation in the abundance of individual plant and Coleoptera species along the modification gradient. The most intensively modified sites had the lowest plant diversity, the lowest abundance and diversity of Orthoptera, as well as the lowest abundance of common skinks. Sites with low levels of modification contained a higher abundance of common skinks, and, native forbs, lichens and bryophytes than the more intensively modified sites. With regard to individual plant and Coleoptera species recorded, there were generally not clear thresholds for their presence and absence along the modification gradient. Rather, there was a gradual turnover for most species along the gradient such that the plant and Coleoptera community at opposing ends of the gradient had less species in common sites of similar modification levels. A high proportion of the Coleoptera species observed were present in all sites, suggesting that disturbance has selected for an adaptive generalist life trait, and that the species remaining comprise the resilient portion of the Coleoptera fauna. The relationship between Coleoptera communities and the gradient of modification was scale dependent, with the strongest relationship being observed at the largest scale measured. The hypothesis that faunal diversity and abundance would be best predicted by the structural diversity of the vegetation rather than by plant species diversity was tested. Structural diversity was strongly correlated (p < 0.01) with Coleoptera diversity, and Coleoptera abundance whereas plant species diversity was not. However, plant species diversity was a stronger correlate of common skink abundance than plant structural diversity. The structural diversity of the vegetation has the potential to be measured remotely and could be a correlate for faunal diversity and abundance when undertaking landscape scale studies. This thesis demonstrates that native biota exists within the agricultural environment of the mid-altitude tall tussock (Chionochloa rigida) grasslands of eastern Central Otago despite intensive modification in some areas. The findings suggest that it is possible to integrate the objectives of agriculture and the conservation of some faunal groups especially for the more resilient species. However, this study also indicates that relatively unmodified sites are valuable reservoirs of biodiversity in the mid altitude zone and it is recommended that the limited number of lightly modified sites that remain in the mid altitude zone be conserved.