30.3 Thursday, Jan. 5 Ecological cost of growth in a free-ranging lizard ANDERSON, R A*; KARASOV, W H; NAGY, K A; Western Washington Univ.; Univ. Wisconsin, Madison; Univ. California, Los Angeles Roger.Anderson@wwu.edu
The doubly labeled water (DLW) method can be used to measure respiration, compare metabolizable energy intake among individuals with different growth rates, and estimate ecological cost of growth in free-living animals. We used DLW to study field energetics of adults and juveniles in the wide foraging desert lizard, Aspidoscelis tigris. The cost for these insectivores to secure the extra food that powers growth was predicted to result in a cost of growth that is substantially higher than the consensus estimate for cost of growth (0.33 J respired per J deposited) in constrained animals. Positive correlations were predicted for respiration v. growth rate and for growth rate v. metabolizable energy intake. Daily rates of metabolism, feeding and growth were expected to be higher in A. tigris than in syntopic ambush predators. Juveniles had longer daily activity periods, adults moved more, juveniles and adults had similar time proportions in locomotion during the activity period, and their diets were similar. All juveniles and most adults increased in body mass during the 3 week study. There were no significant differences among groups in mass-corrected FMR, but mass-corrected water influxes in juveniles and adult females were higher than in adult males. Analysis of mass residuals of mass gain, FMR, and food water influx for all lizards with positive mass gains yielded significant positive correlations for FMR v. mass gain and for mass gain v. food water influx. There were no significant differences in slopes or intercepts of these relationships with sex or age when analyzed by ANCOVA. The ecological cost of growth was high in this wide forager (> 2.6 J/J), and it did have higher rates than syntopic ambushers in the parameters predicted.