Cities have always been sites where resources are concentrated and diverse individuals come together, and rats and other “pests” and “vermin” have thrived in the interstices of urban food systems for millennia. Over the past two centuries, however, cities have grown to unprecedented sizes, whether one measures them by population, geographical extent, energy consumption, waste production, or other metrics. As of 2014, approximately 82 percent of North Americans lived in urban areas; globally, the proportion was 54 percent. On a per-capita basis, people living in cities may have a smaller environmental footprint than those living outside of cities, but in the aggregate they constitute one of the driving forces of the Anthropocene.
The increasing centrality of urban metabolisms to the functioning of Earth systems casts new light on the encounters between human and nonhuman life that take place within the city’s borders. Oceanic ecosystems offer a useful metaphor. The phenomenon of upwelling occurs along coastlines and around seamounts where wind and currents bring cold, nutrient-rich water to the surface. Such upwellings can support extraordinary biological productivity, as phytoplankton use nitrates, phosphates, and other nutrients to create energy-rich organic matter, which then serves as the basis of diverse food chains. Resources are rarely “wasted” in such systems; instead they are concentrated and dispersed, stored and circulated. In the natural economies of abundance that emerge around upwellings, examples of inter- and intraspecies predation, parasitism, competition, symbiosis, and cooperation abound. Off the coast of Peru, for example, dolphins herd schools of small fish toward the surface, where they are also consumed by seabirds, whose blood nourishes ticks and other parasites and whose guano can be harvested for human agriculture.
So it is in modern cities, where the vast flows of energy and materials that have been harnessed for human purposes have also generated opportunities for other forms of life, even as the ecologies of the rural hinterlands that support them have become increasingly depauperate. Cities are artificial upwellings, driven by the winds of human commerce and providing occasions for multispecies encounters of almost every imaginable form. Once we recognize that these flows of energy and nutrients are only partially captured and controlled by their human residents, new questions about some well-known episodes in the history of human-animal relations in the American city arise.