INTRODUCTION

As the focus of ecological research has broadened from site-level observations and experiments to landscape-scale studies, interest among ecologists in connectivity among habitat patches has increased (Turner et al. 1995; Wiens 1995; Gustafson and Gardner 1996; Hanski and Gilpin 1997; Haddad and Baum 1999). From a conservation perspective, concern with the maintenance of connectivity has grown as habitat loss and fragmentation continue worldwide (Rosenberg et al. 1997; de Lima and Gascon 1999; Haddad and Baum 1999). Typically, both basic and applied studies consider connectivity among patches of the same habitat type, such as a set of forest fragments embedded in a matrix of agricultural land uses. These studies, reviewed throughout this volume, focus on measuring patch isolation and examining the utility of corridors to restore connectivity among patches.

However, another type of connectivity, although less well studied and understood, is of equal importance in these complex landscapes: the connectivity among patches of different habitat types (Daily et al. 2001; Ricketts et al. 2001; Talley et al. Chapter 5). Many species require different habitat types for different resources or life-history stages. The proximity and availability of different habitat types, therefore, can affect the population dynamics and persistence of individual species and the diversity of communities. For example, bees often nest in one habitat type (e.g, tree cavities in forest) but require other types for forage (e.g., wildflower meadows).