Trophic dynamics and effects of urbanization: A complex field experiment compared to a simple mathematical model

Water is usually the limiting resource for plant productivity in the Sonoran Desert. In the Central Arizona Phoenix (CAP) area, urbanization generally leads to increased and more stable water availability, resulting in increased plant productivity. We are conducting a large scale field experiment to explore how this changing water availability affects ecological communities, with emphasis on guild composition, plant productivity, and arthropod and bird species diversity. Data from the first year are grouped into trophic level biomass and compared to a simple tri-trophic Lotka-Volterra system with a type II functional response. The model assumes water as the limiting resource, thereby directly influencing plant carrying capacity. The model provides a good fit to the data presently available and is compared to a more familiar theory of exploitation ecosystems. This work provides a good foundation for further exploration of the effects of urbanization on ecosystems.