Spatial and Temporal Aspects of Surface Activity and Relative Abundance in a Lizard Assemblage in So

Jones, Lawrence L. C.

Southwest Zoologists’ League

Tucson, AZ

Rorabaugh, James C.

Saint David, AZ

Murphy, John C.

Green Valley, AZ 85614

In an ongoing study, we quantified surface activity patterns in a lizard community in southeastern Arizona over nine years. The Marijilda study area is located near Safford, Arizona, in a transition zone between grasslands, oak woodlands, and both the Sonoran and Chihuahuan deserts. A total of 20 species have been detected in the immediate vicinity. This is arguably the highest reported diversity of lizards in the U.S. for such a small area, although only 5-9 species were encountered frequently enough for analyses; and two of these are grouped into the Desert Spiny Lizard complex (Sceloporus magister + S. bimaculosus), as this appears to be a hybrid zone. During 208 site-visits, we detected 12,503 lizards of 16 species. Mean encounter rate was 60.1 lizards per the 2.6 mile transect. By far the most abundant species was Urosaurus ornatus, which accounted for 48% of all detections, the other commonly encountered species were: Uta stansburiana (17%), S. magister complex (12%), Cophosaurus texanus (6%), Aspidoscelis tigris (5%), and Crotaphytus collaris (4%). Lizard activity was seasonally bimodal, with activity peaking in the spring (late March to early May) and the monsoon (late June or early July through mid-September). One species (U. ornatus) was most active during the spring, while most others were more active during or after the monsoon. Some were active throughout April-September. Most taxa responded positively to sunny periods following rainfall. Detections during the first survey of the monsoon were generally 2-3 times greater than the last pre-monsoon survey. Total numbers were fairly consistent during 2003 and 2010-2014, and then the number of detections declined. Possible reasons for the apparent decline in abundance will be discussed.