Introduction

Remnants of natural ecosystems in urban environments are at the centre of an emerging discipline in ecology, reflecting population shifts towards towns and cities and the urgent need to understand the ecology of the environments in which most of the world's population live (McDonnell and Pickett, 1993b; Grimm et al., 2000). Major themes focus on understanding the way in which these landscapes have responded to the effects of urbanisation and how these impacts can be ameliorated (Kendle and Forbes, 1997). The importance of urban ecosystems is further enhanced by their social implications; these systems are a first connection with nature for much of the world's population and as such are important tools for education and contributions to emotional wellbeing (Kaplan, 1995). There are dramatic shifts in biodiversity in urban habitats, driven by local extinctions and invasions by exotic species. Terrestrial arthropods, the drivers of many ecological processes in urban environments, are underrepresented in the emerging field of urban ecology, despite their abundance, diversity and importance (Kremen et al., 1993; Natuhara and Hashimoto, Chapter 12; McIntyre and Rango, Chapter 14).

The development of a conceptual framework of urban ecology is crucial to the development of this emerging field (Peters, 1991; Ford, 2000; Bastian, 2001; Niemelä et al., Chapter 2; Pickett et al., Chapter 3). The main emphasis of urban ecology, as with much of landscape ecology, is on the descriptive, with the search for general principles and patterns hampered by the enormous variation in systems and methodological approaches adopted.