Coleoptera Diversity and Assemblage Structure on Acacia Host Plants Along an Environmental Gradient

Abstract

<p>Global biodiversity is under threat from climate change as well as current and future modification to the environment. In order to accurately assess the risks facing ecological communities and predict possible responses to these changes, it is essential to understand drivers of diversity patterns. In ecology, gradient analysis is a methodology using transects of environmental change at varying spatial scales to measure the influence of environmental factors on ecological communities. This thesis investigates the use of gradients in association with Coleoptera, as beetles are one of the most species-rich taxa on Earth, are ubiquitous in almost all habitats and have considerable ecological and economic importance.</p> <p>In order to expand understanding of beetle responses to environmental change I first systematically review published literature that uses gradient analysis techniques to measure responses in beetle taxa. In doing this, I reveal important trends, biases and gaps in the global knowledge and offer suggestions for future directions of research. Further, an assessment of beetle communities on <i>Acacia</i> host plants along a gradient of decreasing rainfall across New South Wales is conducted. This assessment provides crucial information about these understudied Australian taxa and gives insight into how they may respond to future climate change.</p> <p>A systematic review of the literature revealed 223 papers studying beetles along gradients. These papers were published over a 45-year period between 1971 and 2016, increasing in frequency over time, with more than 90% of the work being produced after the year 2000. An investigation of the ecological methods used in association with gradient analysis revealed that 78% of these studies reported on general concepts of diversity (species richness and/ or abundance). Regional trends emerged, showing that 78.6% of papers originated from the Northern Hemisphere with Europe producing the largest portion (44.4%). Beetle species from seventeen families were represented and there was a strong bias toward taxonomically well-studied beetle groups, with the most common beetle families targeted being ground-dwelling species, especially those from the family Carabidae which made up 30.5% of studies. Trends in the use of Carabidae in the literature showed that this family was the primary focus in studies using urbanisation gradients (89.3%) and pollution gradients (63.6%).</p> <p>The gradient types that were most frequently utilised across the literature were disturbance/ landuse gradients and altitudinal/ elevational gradients. Regional trends emerged in the usage of gradient types as well as with the beetle families studied. In northern Europe, disturbance/ landuse gradients were most commonly used and Carabidae was the most-studied beetle family, while in South America elevational gradients were preferentially used and the beetle family targeted most often in this region was Scarabaeidae. The results of the systematic review revealed that highly biodiverse regions, such as Asia, Africa and Oceania were critically underrepresented in the literature, as were many important beetle families. Future research should consider incorporating regions outside of the temperate Northern Hemisphere as well as a wider selection of beetle taxa, in order to fill the current gaps in the knowledge. </p> <p>According to the results of the systematic review, little is known about how beetles respond along environmental gradients within Australia. Moreover, our understanding of how beetles will respond to future climate change is also limited. Therefore, to investigate the potential effects of a warming climate on beetle communities across New South Wales, we conducted one of the first studies assessing beetle diversity and assemblage structure along a large gradient of decreasing rainfall, while also giving consideration to the influence of <i>Acacia</i> host plant phylogeny. The effects of regional climate, season, and host plant on beetle communities were assessed along a 970km transect. Sampling sites were located in either subtropical, temperate, semi-arid or arid climate zones and <i>Acacia</i> host plants were selected from the Botrycephalae, Juliflorae, Phyllodineae, and Plurinerves sections. Regional climate zones were defined by average annual rainfall, therefore changes in temperature and aridity along the gradient were used as a proxy for the changes predicted under a warming climate</p> <p>Beetle diversity increased slightly along the gradient toward areas of higher rainfall, however richness was highest in the temperate zone and abundance was higher in the semi-arid zone. There was a significant difference in beetle species richness between climate zones and seasons but not <i>Acacia</i> sections. Additionally, abundance within beetle communities differed significantly between <i>Acacia</i> section and season but not between climate zones. Assemblages along the gradient were made up predominantly by species from four beetle families, Chrysomelidae, Curculionidae, Coccinellidae and Staphylinidae. Staphylinidae diversity increased toward tropical regions, while Curculionidae diversity increased in arid regions. Hump-shaped diversity patterns were revealed in Chrysomelidae and Coccinellidae, which were more common at semi-arid and temperate sites. </p> <p>This study showed that the environmental factors with the highest influence on beetle communities along the gradient were season and climate (mean temperate, average annual rainfall). Therefore, we can predict that beetle diversity will be negatively impacted by the changes that have been predicted for the region under climate change (mean temperature rises and decreasing annual rainfall). Semi-arid and arid communities may show some resilience to climate change, however temperate and subtropical species may need to adapt or shift ranges to avoid extinction. These results are important in the identification of at-risk communities and may be useful to inform on future conservation management strategies. </p> <p>This gradient study, along with the systematic review have revealed important information on previously unexplored ecological questions concerning beetle diversity and gradient analysis techniques. This thesis has provided information on the current state of the literature, broadened our knowledge and provided new insights into how beetles may respond to environmental change along gradients. The information provided herein has also permitted the opportunity to identify crucial gaps in the collective knowledge and suggest areas suitable for future work. </p>