Meeting Abstract
Climatic fluctuations in the Mojave Desert of California include extended drought periods that have resulted in the demographic collapse of populations of the western fence lizard (Sceloporus occidentalis) found on desert sky-islands. Over a 6 year period (2010-2015), which coincided with a severe 3-year drought, we carried out a mark-recapture study of two lizard populations (1450m and 1850m). The high elevation population was up to four times more dense than the low elevation population, which is at the lower elevation limit of the species in the Mojave Desert. Both populations experienced demographic collapse during the 2012 and 2013 seasons due to the lack of juvenile recruitment. The frequency of first-year lizards dropped from highs of 55-83% of all lizards captured per hectare during the 2011-2012 sampling periods down to 0% in 2013 as no (i.e., zero) first-year lizards were found either on the sampling grids or anywhere on the mountain (10 sampling days and 225 person-hours of searching). Population densities declined by 50% (1850m) and 30% (1450m) over this period. In both localities, inter-annual adult recapture frequency (survivorship) increased following the severest drought year (2012-2013). Although the drought in southern California has continued through 2014 and 2015, sporadic summer monsoonal rains in 2013 and 2014 resulted in successful juvenile recruitment to both populations due to increases in insect activity following late summer and fall blooms of both annual and perennial plants. The low elevation population was rescued from likely extinction by these monsoonal rain events which are uncorrelated with winter rainfall drought conditions.
