Two widely held notions about urbanization are: 1) diversity decreases in urban areas and 2) remnant or restored habitats will have or re-gain the same diversity as natural areas. More recent research has shown contradicting results for both ideas. For over ten years we have monitored arthropod communities with pitfall traps in the Central Arizona Phoenix area in residential areas and compared them to desert and desert remnant sites. To explore underlying mechanisms for community composition, a large scale field experiment was initiated to study potential differences in trophic dynamics. In a factorial design, we used exclosures and manipulations of limiting resources to a common shrub, and surveyed the associated arthropod communities in terms of biomass and diversity.  

Results/Conclusions

We found that diversity in mesic yards varied similar to desert sites, albeit with a different community composition, while xeric yards and desert remnants experienced a dramatic decline in diversity over the ten year period. The results from the field experiments reveal a complex dynamic pattern in trophic organization, indicating resource limiting processes in some of the natural desert areas, and top-down forces being more prominent in urban residential areas. The strength of these processes, and why they lack in some of the cases, has yet to be determined, but our combined results ultimately call for better landscape management strategies. Our results stress the complexity and seemingly unpredictable effects of urbanization on arthropod diversity superimposed on seasonal and regional climatic patterns.