Development of resource-rich patches by soil-disturbing animals in arid environments
In arid landscapes limited resources are concentrated into fertile patches that allow greater productivity than would otherwise be expected. Fertile patches are created and maintained by processes that modify soil topography and interrupt the flow of resources across the landscape. These processes may be abiotic or biotic in origin. Species that modify, maintain or create habitat have been termed ecosystem engineers. One group of soil disturbing ecosystem engineers creates fertile patches by modifying soil microtopography through foraging for food and creating habitat. This thesis examines the effects of soil foraging animals on resource concentration in arid environments and how effects are moderated by species and landscape. Chapter 1 provides an overview of the importance of fertile patches in arid systems and describes previous research on the effects of ecosystem engineers in arid environments. Chapter 2 examines how fertile patch creation by a well-studied arid zone engineer, the ant, varies between ant species and landforms, demonstrating that while we can generalise about the effects of ant nests on water flow and nutrient levels, differences in soil type, nest density and ant species across sites are likely to moderate these effects. Chapters 3, 4 and 5 compare the engineering effects of reintroduced native species, the Greater bilby (Macrotis lagotis) and Burrowing bettong (Bettongia lesueur) with the Sand goanna (Varanus gouldii) and the invasive European rabbit (Oryctolagus cuniculus) across three Australian landforms, revealing differences between reintroduced and invasive engineers at the both patch and landscape scales. At the landscape scale, differences in pit densities and resource concentration in foraging pits between landforms suggest that fertile patch development is not uniform. Chapter 6 examines whether the structure of the pit or the presence of litter per se explains observed increases in plant germination in foraging pits, and compares temperature and soil moisture conditions in bilby and bettong pits to the soil surface. Chapter 7 is a review that builds upon previous chapters, published and unpublished literature of the potential for reintroductions of ecosystem engineers to restore ecosystem function in degraded environments. Chapter 8 summarises the research presented in this thesis and its implications, and suggests directions for future work.
Ecosystem engineer, Arid, Ecology, Disturbance, Fertile patch, Mammal, Bilby
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