Globally, habitats are becoming more stressful and less predictable. We have a poor understanding of how these changes in environmental conditions are influencing organisms living in modern ecosystems. Among different global change drivers, urbanization is among the most multifaceted; organisms living in cities must simultaneously cope with fragmentation, urban heat islands, changing water dynamics, and pollution. In this study we asked: (i) how does the food-for-protection mutualism between Tree Cholla (Cylindropuntia imbricata) and its ant bodyguards vary along an urbanization gradient? And (ii) how do nectar and ant aggression traits change as urbanization increases? In July 2018, we performed a plant and arthropod survey along an urbanized gradient from Albuquerque to the Sevilleta National Wildlife Refuge.
Results/Conclusions
We found that C. imbricata were 72.56% and 174.22% more variable in urban sites (open spaces) than cholla cacti in suburban and desert wildland sites, respectively. Ants were more distinct (PERMANOVA: P=0.0001) and had higher activity (Kruskal Wallis: P= 0.0084) in desert wildlands than they were in either urban or suburban sites. Nectar production and ant aggression also varied along this urbanization gradient. When taking all of this into consideration, it is likely that the dynamics of this mutualism change as sites become increasingly urban. By understanding the ways that species interactions change with urbanization we will be able to better predict community-wide responses to a rapidly urbanizing world.