This quote captures the spirit of the new urban emphasis in the US Long-Term Ecological Research (LTER) network. We know now that Earth abounds with both subtle and pronounced evidence of the influence of people on natural ecosystems (Russell 1993, Turner and Meyer 1993). Arguably, cities are the most human dominated of all ecosystems. Recent calls for studies on “human-dominated ecosystems” (Vitousek et al. 1997) finally have been heeded, over 60 years after Tansley penned his warning, with the addition of two metropolises (Phoenix and Baltimore) to the LTER network. In this article, we describe an emerging approach to understanding the ecology of urban areas by contrasting these two metropolises, and we present a call to action for ecologists to integrate their science with that of social scientists to achieve a more realistic and useful understanding of the natural world in general and its ecology in particular (Pickett and McDonnell 1993, Ehrlich 1997). We begin by framing a conceptual basis for the study of urban ecological systems: the rationale, contrasting approaches, and special considerations for including human interactions at different scales and in a spatial context. We then discuss the application of our conceptual approach by comparing site conditions and initial research results in Baltimore and Phoenix. We conclude with a summary and synthesis of implications for the integration of social and ecological sciences.
