The city of Phoenix, AZ is one of the largest and fastest growing cities in the U.S. My lab studies how this urbanization changes soil ecology, but one thing we didn't know much about was how it will change herbivores in the Sonoran Desert. We have a lot of small herbivores who rely on the plants growing in the soil. We know a bit about how plants and soils change... but what about the animals that eat them?
One of my students, Jessica, decided to find out the answer to that question for a particular group of herbivores: small rodents. There are many species of small rodents in the Sonoran Desert that eat either plants or their seeds. These include cute critters like kangaroo rats, pocket mice, and ground squirrels!
For two years, she conducted population surveys of small rodent populations at four sites inside urban Phoenix and four sites outside in the rural, non-urbanized areas. She wanted to find out whether abundances and diversity of small rodents are different when you compare the urban and rural areas. That matters, because small rodents are common vertebrate herbivores who can impact the plants in the desert. Jessica hypothesized that rodents will be more abundant inside the city, because there would be more food for them and fewer predators than out in the rural desert, but that there would be more biodiversity of rodents out in the non-urbanized rural desert, because some species wouldn't have the necessary habitat to survive inside the city.
Jessica used a capture & release method, where she caught mice in humane live-traps, identified their species, and then let them go. In order to do this, we had to have a lot of permits to verify that we were not causing any harm to the rodents. She carefully avoided bad weather and protected them from predators. She became an expert rodent handler and identifier! The surveys were conducted at desert sites inside and outside the city.
We learned from these surveys that abundance is actually the same inside and outside the city. We expected more rodents inside the city, but in fact they are the same inside and out! We did notice, though, that the communities inside the city were very different from outside the city. The rodents inside the city were mostly from just a couple of groups of pocket mice and deer mice, with only a few rodents from other groups present. Outside the city, though, there were pocket mice, kangaroo rats, woodrats, grasshopper mice, and many other types!
We think that this difference is probably related to the food available. The species we found outside the city have particular plants or habitat types that they need to survive which might not be available inside the city. However, we didn't specifically measure their food sources yet, so that is work for another future study!
The results of this study are
published in: Alvarez Guevara & Ball 2018. Urbanization alters small rodent community composition but not abundance.. PeerJ 6:e4885. DOI 10.7717/peerj.4885
