Expanding the Definition of an Urban Ecosystem Through Stable Isotope Analysis

The question of defining ecosystem boundaries is important in creating management policies, conservation guidelines, and continuing accurate research. In the case of urban ecosystems, boundaries cannot be defined by strictly cultural or physical methods. Approaching boundary definitions in this manner ignores the importance of energy movement through an ecosystem. Part of the energy budget of an urban ecosystem is the anthropogenic food input, which can serve to attract wildlife to the city. It is proposed that this attraction to urban centers due to food resources influences surrounding classically defined natural ecosystems to such an extent that the urban ecosystem should be redefined to include the environment surrounding cities. The research technique that is the most time and cost effective, least invasive, and allows multiple species to be compared at once is stable isotope analysis. Isotope compositions have been commonly used for decades, and among the most important isotopes for deciphering ecosystem functions are carbon and nitrogen. Through the use of stable isotope analysis, urban wildlife can be differentiated from wildlife that is not influenced by human inputs to the ecosystem by the carbon value. The isotope ratio of anthropogenic foods is unique enough from natural sources of food that it can be used as a marker for human influence on the food chain. Previous work supports that species and individuals within a species can be differentiated using stable isotope analysis. It is proposed that stable isotope analysis be used to analyze samples of wildlife for carbon and nitrogen values in an attempt to measure the impact that people are having on urban and non-urban species.