Abstract:
The expansion and intensification of agriculture is one of the most prominent forms of human-mediated environmental change, and is a major driver of biodiversity loss. Biodiversity is critical for the functioning of ecosystems and the provision of ecosystem services, such as pollination. Bees are an important pollinator group in both natural and agricultural ecosystems. Worldwide, most bee species are solitary and nest in the ground. The nesting ecology and habitat requirements of ground-nesting bees are poorly understood in many parts of the world, including New Zealand. In this thesis, I describe three separate but related studies that I carried out to investigate the nesting ecology and habitat requirements of ground-nesting solitary bees in northern New Zealand. In the first study (Chapter 2), I investigated the nest-site selection of ground-nesting bees from the genus Leioproctus. I found that the chemical and physical characteristics of the soil substrate, including soil compaction, temperature, organic matter content, and rock and leaf litter cover, had a strong influence on the nest-site selection of ground-nesting bees. In the second study (Chapter 3), I explored how ground-nesting bees respond to environmental variables at multiple spatial scales. I found that ground-nesting bees in New Zealand respond most strongly to environmental variables at the smallest spatial scale analysed (250 m). In the third study (Chapter 4), I examined the effect of farm management practices on ground-nesting bee communities. I found that farm management practices, such as pesticide use and tilling, have a negative impact on ground-nesting bees in New Zealand. Altogether, my thesis shows that the nesting ecology and habitat requirements of groundnesting bees are strongly influenced by both local scale factors, such as soil substrate, and wider landscape-scale factors, including the environment and farm management. The information in this thesis is valuable for informing conservation and management decisions to protect groundnesting bees, and ensure the provision of ecosystem services needed to produce agricultural crops and maintain wild plant communities.