PS 84-32
Habitat preference of Sceloporus jarrovii (Yarrow’s Spiny Lizard)

Friday, August 14, 2015
Exhibit Hall, Baltimore Convention Center
Earyn McGee, Biology Department, Howard University, Washington, DC
George Middendorf, Biology, Howard University, Washington, DC

We examined patterns of habitat use by Yarrow’s spiny lizard, Sceloporus jarrovii, in a 0.5 km stretch of Cave Creek Canyon in the Chiricahua Mountains of southeastern Arizona. Sceloporus jarrovii is found from northern Mexico to southern Arizona and southern New Mexico. As a high elevation species, they are restricted to mountain peaks in the Chihuahuan desert (so-called “sky islands”), separated by deserts. Seasonal weather, particularly the cold winters, reduces the amount of time available for foraging and growth during the remainder of the year.  They are also impacted by seasonal rains that extend from July through September. The selection of territories and over-wintering hibernacula provides opportunities to select sites with good thermal characteristics.  Unfortunately, catastrophic events also occur. In July of 2014, the area experienced a 500-year flood (a flood elevation that has a 0.2 percent chance of being equaled or exceeded each year; FEMA, 2009).  Rainfall and resulting stream flows of this magnitude occur rarely, but when they do happen, water flow is sufficient to send large debris (full trees) and boulders downstream, scouring the stream bed and both sides of the canyon. This study takes advantage of an ongoing, multi-year study looking at site selection by lizards and coupling it with changes in stream geomorphometric characteristics.


Data collected include population density, population demographics, annual changes in the lizard community structure, and changes in the distribution of lizards in their summer territory locations.   Historical observations suggest that these lizards are non-randomly distributed, and that lizard locations are affected by geology (exposed shale outcrops) and habitat structure (logs and large boulders) within the canyon. Because lizards are dependent upon sunlight for thermoregulation, we added additional components by examining canyon direction, stream bed width, aspect, and slope. Data was collected prior to the 500-year flood. Using the data we were able to divide microhabitat into three categories: rock/wall, rocky, and mixed. Microhabitat played a large role. When the canyon ran north to south, 56% of lizards were found in the rock wall microhabitat type,  27% were in the rocky microhabitat and 13% were in the mixed habitat. When the canyon ran east to west, 69% of lizards were found in the rock wall microhabitat type, 36% were in the rocky microhabitat and 8% were in the mixed habitat. A chi square analysis indicates that directionality does not play a significant role in how lizards chose their territories.