Meeting Abstract

P1.184  Friday, Jan. 4  Energetics of Blainville’s Horned Lizards, Phrynosoma blainvillii, in Disturbed and Undisturbed Habitats BROWN, T.K.*; MERSCHEIM, M.; DAVIDSON, E.; CSU San Marcos traceyb@csusm.edu

Blainville’s Horned Lizard, Phrynosoma blainvillii, is considered a California state species of special concern. The distribution of this species has declined dramatically in so. Cal. largely because of habitat disturbance, human development, and the introduced Argentine ant. Previous work indicated that the body size, diet, and movements of this species living in disturbed (long-term grazing & fire) habitats were adversely affected. These findings suggest that anthropogenic disturbance may result in higher energy expenditure in the lizards stemming from increased foraging costs. The present study was aimed at estimating the energetics of individual Blainville’s horned lizards to help elucidate the physiological mechanisms driving population decline in suboptimal habitats. Twelve horned lizards (six each in undisturbed and disturbed CSS/chaparral habitat) were captured and fitted with radio-transmitters in Riverside Co., CA. Doubly labeled water was used to study the field metabolic rates (FMR) during two, two-week periods representing late spring and early summer; data on growth, habitat use and movements were also collected. Overall, season had a significant effect on FMR (P = 0.006), but there was also a significant season-site interaction (P = 0.002) and nearly a season-sex-site interaction (P = 0.057). At the undisturbed site, female FMRs increased 13 to 27% while male FMRs decreased by 9 to 40% between the first and second study period. At the disturbed site, all lizard FMRs decreased 20 to 76%. Overall, FMR at the disturbed site appeared to be lower than at the undisturbed site, but this tendency was overshadowed by the large proportion of study animals who were male (only one female followed there) and beginning aestivation. Mean FMR for both sexes combined in the late spring was 0.158 ml CO₂ per gram hour for lizards with a mean body mass of 42.8 g.