| Popis: |
Ectotherms which survive for more than one year in the desert must be able to cope with a variety of seasonal changes, such as temperature regimes and food availability. As temperature and food availability vary, the organism must adjust its activity and energetic expenditure in response to these external influences. Two sympatric tenebrionid beetles (Eleodes armata and Cryptoglossa verrucosa ) of the Mojave Desert of North America were studied in both laboratory and field to determine how energy requirements varied over a year. By combining laboratory and field measurements of metabolic rate, the cost of activity was determined for these two species of beetles. In all seasons, E. armata had higher daily energy expenditure (DEE) and higher daily maintenance (resting) energy expenditure (DREE) than C. verrucosa, although the daily cost of activity (difference between DEE and DREE) was often similar. Increasing temperature and body mass increased laboratory oxygen consumption rates and field metabolic rates for both species. Metabolic rate of C. verrucosa did appear to be more sensitive to temperature than that of E. armata, as indicated by a multiple regression. This data suggests that E. armata can exploit a wider range of temperature regimes than C. verrucosa. The metabolic responses may reflect a phylogenetic or historical difference, as E. armata is thought to have evolved in montane habitats with a 'recent' invasion of deserts and C. verrucosa is considered to be endemic to deserts. |
