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

gilaman@comcast.net

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.


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