The ecology and behaviour of coastal Diptera communities in Aotearoa|New Zealand

Abstract

This thesis aims to explore the biogeography, ecology, behaviour, and temporal patterns of a community that occupies the land-sea interface. Coastal communities present an interesting opportunity for exploring patterns of change as there are numerous factors imposed by both the terrestrial and marine environments which may create a complex interplay of conditions that species and communities respond to. The Diptera are recognised as having many coastal specialists, including most notably the species that rely on wrack - organic marine debris such as macroalgae which is washed ashore, as their primary resource and habitat. In Aotearoa|New Zealand there is a diverse but little known coastal Diptera community which the thesis aims to describe and explore. Overall, I visited 110 coastal sites, and collected a total of 275 species identified from 46,956 specimens. One site was visited each month for a period of two years to explore temporal variation, with the other 109 sites each visited once to investigate geographic variation in coastal Diptera communities throughout Aotearoa|New Zealand. In addition, I studied the sexual size dimorphism, allometry, and mating behaviour in two endemic kelp fly species (Coelopidae). I have found that overall coastal Diptera communities show large-scale spatial variation both with latitude and between the east and west coasts. However, wrack communities are predominantly driven by variation in the local wrack conditions, and do not display notable patterns of geographic variation. Previously delineated marine and terrestrial regions of Aotearoa|New Zealand help to describe how coastal communities vary, a topic of particular importance as local anthropogenic changes were found to cause shifts in community structure and negatively impact species richness. Furthermore, there is some evidence of temporal variation in communities, but this is driven by changes in the abundance or presence of a small number of common wrack species. Finally, endemic species of kelp flies show significant sexual dimorphism, and positive allometry in male traits associated with coercive mating, with a large-male mating advantage, but also potential for significant variation in response to an ephemeral habitat.