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Field Energetics and Foraging Mode of Kalahari Lacertid Lizards
Author(s) -
Nagy Kenneth A.,
Huey Raymond B.,
Bennett Albert F.
Publication year - 1984
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1941421
Subject(s) - foraging , energetics , lizard , sauria , biology , ecology , sympatric speciation , energy budget , nocturnal , burrow , basal metabolic rate , zoology , biochemistry
We examined the energetic costs associated with foraging mode in the widely foraging lizard Eremias lugubris (mean mass 3.83 g) and the sit—and—wait lizard Eremias lineoocellata (3.27 g). These lizards are broadly sympatric in the Kalahari desert. Individuals of both species were probably abroad every day, but the wide forager was abroad for much shorter periods (2.75 h/d vs. 10.25 h/d). Nevertheless, the widely foraging species had significantly higher field metabolic rates (800 vs. 544 J/d, as measured with doubly labeled water), feeding rates (metabolizable energy of 1165 vs. 739 J/d), production rates (365 vs. 195 J/d) and water influx rates (0.285 vs 0.156 mL/d). Measurements were made before the productive season began; there were no significant differences in these measures between sexes within either species. Resting metabolic rates (measured as O 2 consumed) were similar at 37°C (0.240 vs 0.252 mL°g — 1 °h — 1 ) and at 26° (0.094 vs. 0.103 mL°g — 2 °h — 1 ), the field active and nocturnal burrow temperatures, respectively, of both species. Field metabolic rates, on a 24—h basis, were 3.1 x resting in E. lugubris and 2.2 x resting in E. lineoocellata. Energy expenditures during the activity period were 12.0 x resting in the wide forager and 2.8 x resting in the sit—and—wait predator. Foraging efficiency (metabolizable energy gained while foraging/total energy spent while foraging) was higher in the wide forager (2.0) than in the sit—and—wait predation (1.6). However, when foraging efficiency is expressed as metabolizable energy gained/activity cost (above resting cost), the wide forager (2.2) was less effective than the ambush predator (2.6), apparently because the cost of searching is substantial for E. lugubris but negligible for E. lineoocellata. The hourly cost of foraging was much higher for E. lugubris (almost 5 x that of E. lineoocellata) but the hourly benefit of foraging for E. lugubris was even higher (nearly 6 x that of E. lineoocellata). Thus E. lugubris made a greater profit on its investment (46 vs. 36% each day), and the wide forager grew nearly twice as fast as did the sit—and—wait predator during this study. On an annual basis, variation in food availability of differences in predation rate may alter the relative fitness of these foraging modes.