Patterns and drivers of biotic population and community structure in built environments
Urbanization changes both abiotic and biotic conditions, altering the physical environment, climate, and resource dynamics; these changes in turn induce alterations in species composition in urban areas. Because cities can be viewed as an ecosystem (albeit one characterized by high-density human habitation and built structures), understanding how organisms respond to the ever-increasing scope of urban development makes focusing on urban patterns and processes an important component of contemporary ecology. Organisms in urban ecosystems face selective pressures common to all ecosystems, such as acquiring resources, adapting to abiotic conditions, and coping with intra- and interspecific interactions. However, they are also subject to novel stressors, such as socioeconomic drivers and unprecedented species combinations. As part of a symposium on the emergence, rise, and future of urban ecology, my talk will provide a retrospective overview of the main foci and findings at the population and community levels in urban ecosystems and will conclude with potentially fruitful areas for future research in urban ecology. In so doing, I will discuss how urban ecology has co-opted theories from population and community ecology, and will ask whether urban ecology has any unique theories of its own.
I reviewed over 50 studies that have examined how factors diagnostic to urban ecosystems (alterations to the physical structure of the environment, human decisions, a heterogeneous socioeconomic distribution of humans and resources) lead to resource replacement and/or supplementation with dampened fluctuations (“oasis effect”), which in turn are responsible for characteristic patterns of relatively stable species richness (although with replacement of some native species with exotics), highly skewed abundances, and altered biotic interactions (e.g. trophic dynamics) that often illustrate a “luxury effect” in urban areas. These result in a biota comprised of so-called urban adapters and exploiters (at the expense of urban avoiders) that experience an altered diet, timing of reproduction and/or migration, behaviors, demography, and genetic structure. Although urban organisms tend to follow foundational ecological patterns (e.g. species-area relationship, intermediate disturbance hypothesis), the unique features of urban populations and communities of plants, animals, and microorganisms induce downstream consequences on ecosystem services, such as reduced rates of decomposition and pollination. Experiments, cross-city comparisons, and longitudinal studies are needed to determine whether urban assemblages are stable, how they are responding to climate change, and how they can be managed sustainably.