Urban Ecosystems, 7: 241–265, 2004 c  2004 Kluwer Academic Publishers. Manufactured in The Netherlands. Ecological resilience in urban ecosystems: Linking urban patterns to human and ecological functions MARINA ALBERTI malberti@u.washington.edu Department of Urban Design and Planning, University of Washington, Box 355740, Seattle, Washington 98195, USA JOHN M. MARZLUFF College of Forest Resources, University of Washington, Box 352100, Seattle, Washington 98195, USA Abstract. Urban ecosystems evolve over time and space as the outcome of dynamic interactions between socio-economic and biophysical processes operating over multiple scales. The ecological resilience of urban ecosystems—the degree to which they tolerate alteration before reorganizing around a new set of structures and processes—is influenced by these interactions. In cities and urbanizing areas fragmentation of natural habitats, simplification and homogenization of species composition, disruption of hydrological systems, and alteration of energy flow and nutrient cycling reduce cross-scale resilience, leaving systems increasingly vulnerable to shifts in system control and structure. Because varied urban development patterns affect the amount and interspersion of built and natural land cover, as well as the human demands on ecosystems differently, we argue that alternative urban patterns (i.e., urban form, land use distribution, and connectivity) generate varied effects on ecosystem dynamics and their ecological resilience. We build on urban economics, landscape ecology, population dynamics, and complex system science to propose a conceptual model and a set of hypotheses that explicitly link urban pattern to human and ecosystem functions in urban ecosystems. Drawing on preliminary results from an empirical study of the relationships between urban pattern and bird and aquatic macroinvertebrate diversity in the Puget Sound region, we propose that resilience in urban ecosystems is a function of the patterns of human activities and natural habitats that control and are controlled by both socio-economic and biophysical processes operating at various scales. We discuss the implications of this conceptual model for urban planning and design. Keywords: aquatic macroinvertebrates, birds, fragmentation, land cover, resilience, urban sprawl, urbanization Introduction The environmental changes associated with urbanization have been significant during the last century and are expected to continue through the next several decades. Urban devel- opment fragments, isolates, and degrades natural habitats (Marzluff, 2001), simplifies and homogenizes species composition (Blair, 2001), disrupts hydrological systems (Arnold and Gibbons, 1996; Booth and Jackson, 1997), and modifies energy flow and nutrient cycling (McDonnell and Pickett, 1990; Medley et al., 1995; McDonnell et al., 1997; Vitousek et al., 1997; Grimm et al., 2000). Urbanized area accounts only for ∼1 to 6 percent of the total earth surface (Meyer and Turner, 1992), but cities appropriate a large share of earth’s carrying capacity in terms of resource input and waste sinks (Rees, 1996). Cities import ecological services from distant regions and depend on the ecological transformations that occur on the global scale. Changes in ecological conditions associated with urbanization—such as the contamination of watersheds, loss of biodiversity, and change in climate—affect local