Assessing biodiversity in farming landscapes: a cross-taxonomic approach to conservation planning

Abstract

Surrogates of biodiversity are necessary tools for guiding the effective conservation of biodiversity. One of the best known approaches to assessing biodiversity is cross-taxonomic surrogacy, which is underpinned by the hypothesis that selected taxa (i.e. the surrogate) can provide useful and commensurate information on other components of biodiversity (i.e. the target). In this thesis, I examined the effectiveness of cross-taxonomic surrogacy by assessing cross-taxonomic patterns of congruence among ecologically important vertebrate and invertebrate taxa, and with respect to time and different landscape contexts. Using a long-term dataset, I first assessed patterns of cross-taxonomic congruence between three vertebrate groups over a 15-year period. My analyses revealed that patterns of cross-taxonomic congruency were inconsistent over time, varied among the taxa compared, and across different landscape contexts. Bird and mammal diversity were weakly concordant, but strengthened with time. However, there was little association between either birds or mammals, and reptiles. My findings suggested that cross-taxonomic surrogacy has limited effectiveness in heavily disturbed landscapes such as Nanangroe where ecological communities are expected to exhibit high temporal variation. Second, I examined the responses of two ecologically important insect groups (wild bees, beetles) to landscape context. Here, I found that species richness of bee assemblages showed no clear responses to different landscape contexts, unlike beetle assemblages. These patterns persisted even when both insect assemblage was partitioned into functionally-defined groups. Further analyses showed that both groups were responding to different landscape and vegetation components. My findings here demonstrated that wild bee diversity is weakly congruent with beetle diversity, and that surrogacy relationships between even charismatic insects should not be assumed without rigorous testing. Third, I examined how sets of woodland patches prioritised to best conserve each surrogate group (bird, herpetofauna, bee, beetle, tree) represented the other four groups using a complementarity-based approach. Thereafter, I compared these findings with correlation-based analysis to determine patterns of cross-taxonomic congruence. I found that patch sets selected to optimise representation of the surrogate varied in how it incidentally represented other taxa. Beetles achieved the highest incidental representation of other taxa while bees and trees performed the worst. Yet, beetles were the most costly taxa to conserve given the large number of patches needed to meet beetle targets, an ecological consequence of the high diversity and compositional turnover of beetle assemblages. My findings show that species diversity of any taxa should be a pertinent consideration in identifying cross-taxonomic surrogates to prioritise sites for biodiversity conservation. Fourth, I performed a meta-analytical review of the global surrogate literature to assess the effects of anthropogenic disturbance on cross-taxonomic surrogacy in terrestrial systems. Drawing from a dataset compiled from 146 studies, my analyses revealed that anthropogenic disturbance plays an important role in shaping patterns of cross-taxonomic congruence, especially at landscape and regional scales. Spatial scale was an important predictor of cross-taxonomic patterns, but only at very large scales. In conclusion, my findings caution against extrapolating cross-taxonomic surrogates across landscapes subjected to different levels of disturbance and spatial scales to assess biodiversity. Focusing on ubiquitous, human-modified landscapes, my work underscores a number of practical and theoretical issues concerning the use of cross-taxonomic surrogacy. By collectively or individually examining the roles of time, landscape context and habitat structure with respect to diverse groups of vertebrate and invertebrate taxa, my thesis makes explicit the need to consider important ecological processes that can better guide the use of biodiversity surrogates in conservation.