Physiological ecology of desert tortoises in southern Nevada

摘要: Seasonal changes in water balance, energetics, food consumption, daily behavior, diet, osmoregulation and body mass were measured using doubly labeled water, radiotelemeters, field behavior observations of tortoises (Gopherus agassizii) through a year (1976-1977) Rock Valley, Nevada. Aboveground activity extended over the warm seasons (between March November), hibernated burrows winter. In spring, active for about 3 h every fourth day. Some drank rainwater they all gained weight while eating succulent annual plants, which provided excess potassium that stored urinary bladder, but energy intake was less than required to meet expenses via respiration, solids declined. As plants dried late eventually achieved positive balance grasses, masses declined due negative balance. Bladder urine became isosmotic with blood plasma, both more concentrated. summer drought continued, feeding diminished spent progressively time estivating burrows. Thundershowers July triggered emergence from estivation, much rainwater, voided concentrated urine, accumulated dilute restored normal plasma osmotic concentration, resumed on still-dry grasses forbs, surplus energy. However, during this concentrations bladder increased. More rain September again relieved stress as drank, urinated, urine. Energy remained strongly until began new sprouts germinated September, returned spring-like physiological situation mid-November when hibernation began. Tortoises apparently relinquish maintenance internal homeostasis basis most year, tolerating large imbalances their salt budgets. This ability enables them exploit resources are only available periodically, balancing budgets an showing energetic profit. The environmental properties rainfall (beneficial tortoises) dietary content (deleterious) appear have major effects health these impressive reptiles.