The Effects of Dung Beetles on Ecosystem Functioning: From Global Trends to New Zealand Pastures
Permanent link to Research Commons versionhttps://hdl.handle.net/10289/16071
Dung beetles are amazing. Their diverse nesting behaviours affect a suite of important biotic and abiotic ecosystem processes, or functions. However, the dynamics of these functions across different ecosystems and over time remain largely unknown. This PhD thesis investigates the relationships between dung beetles and ecosystem functions, from global-scale trends to the introduced dung beetle communities in pastures of Aotearoa New Zealand. In the first chapter, I provide an overview of the research topic. I go on to describe ecosystem functioning, and in particular the biotic drivers that shape these processes which ultimately lead to ecosystem multifunctionality and the delivery of ecosystem services that benefit humans. I then emphasise the natural history of dung beetles as a springboard to posit whether we can use dung beetles to enhance ecosystem functioning in human modified landscapes, such as agricultural livestock pastures. The ecosystem functions and services delivered by dung beetles are wide-ranging, including dung removal, nutrient cycling, plant growth enhancement, bioturbation, secondary seed dispersal and trophic regulation. In a meta-analysis of the relationships between dung beetles and ecosystem functions and services (chapter two), I reveal significant positive relationships between dung beetle presence on all measured ecosystem functions, with mixed nesting behaviours showing greater enhancement of ecosystem functioning. Additionally, the findings highlight the significant gaps in our understanding of the mechanisms by which dung beetles contribute to ecosystem functioning, particularly in relation to primary productivity and trophic regulation. Next, in a comparative analysis of dung beetle community characteristics (chapter three) I examine the potential of community structure, community-weighted functional traits, and metabolic rates in predicting dung removal. My findings show that the use of a nesting behaviour index serves as a reliable functional trait for predicting dung removal. In a mesocosm experiment (chapter four), I attempt to disentangle the mechanisms through which dung beetle temporal diversity drives direct and indirect changes in ecosystem multifunctionality. By comparing methods including individual ecosystem functions, ecosystem multifunctionality metrics, and structural equation modelling, I demonstrate that a causal inference approach best describes ecosystem multifunctionality. In the concluding chapter (chapter five), I synthesise the overarching significance of the findings obtained in the preceding chapters and examine the potential of dung beetles as a nature-based solution in agricultural landscapes. I propose that the introduction of dung beetles can be viewed as a means of ecological intensification, offering potential advantages for multitrophic diversification. Overall, the findings of this thesis have positive implications for nature-based management, offering promising prospects for fostering self-sustaining agroecosystems that can benefit future generations.
The University of Waikato
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