Ritchie Mark E
School of Natural Resources, University of Michigan, 48109-1115, Ann Arbor, MI, USA.
Oecologia. 1990 Jan;82(1):56-67. doi: 10.1007/BF00318534.
Optimal diets were determined for each of 109 individual Columbian ground squirrels (Spermophilus columbianus) at two sites in northwestern Montana. Body mass, daily activity time, and vegetation consumption rates for individuals were measured in the field, along with the average water content of vegetation at each ground squirrel colony. I also measured stomach and caecal capacity and turnover rate of plant food through the digestive tract for individuals in the laboratory to construct regressions of digestive capacity as a function of individual body mass. Finally, I obtained literature estimates of average daily energy requirements as a function of body mass and digestible energy content of vegetation. These data were used to construct a linear programming diet model for each individual. The model for each individual was used to predict the proportion of two food types (monocots and dicots) that maximized daily energy intake, given time and digestive constraints on foraging. Individuals were classified as "optimal" or "deviating", depending on whether their observed diet was significantly different from their predicted optimal diet. I determined the consequences of selecting an optimal diet for energy intake and fitness. As expected, daily energy intake calculated for deviators (based on their observed diet proportion) was less than that for optimal foragers. Deviating foragers do not appear to compensate for their lower calculated energy intake through other factors such as body size or physiological efficiency of processing food. Growth rate, yearly survivorship, and litter size increase with calculated energy intake, and optimal foragers have six times the reproductive success of deviators by age three. Optimal foraging behavior, therefore, appears to confer a considerable fitness advantage.
在蒙大拿州西北部的两个地点，为109只哥伦比亚地松鼠（Spermophilus columbianus）个体分别确定了最优饮食。在野外测量了个体的体重、每日活动时间和植被消耗率，以及每个地松鼠群落中植被的平均含水量。我还在实验室中测量了个体的胃和盲肠容量以及植物性食物在消化道中的周转率，以构建消化能力与个体体重之间的回归关系。最后，我获得了根据体重和植被可消化能量含量估算的平均每日能量需求的文献数据。这些数据被用于为每个个体构建线性规划饮食模型。每个个体的模型用于预测在觅食时间和消化限制条件下，两种食物类型（单子叶植物和双子叶植物）的比例，该比例能使每日能量摄入最大化。根据观察到的饮食与预测的最优饮食是否存在显著差异，个体被分为“最优”或“偏离”两类。我确定了选择最优饮食对能量摄入和适合度的影响。正如预期的那样，偏离者（根据其观察到的饮食比例）计算出的每日能量摄入量低于最优觅食者。偏离的觅食者似乎无法通过其他因素（如体型或处理食物的生理效率）来弥补其较低的计算能量摄入量。生长率、年存活率和窝仔数随着计算能量摄入量的增加而增加，到三岁时，最优觅食者的繁殖成功率是偏离者的六倍。因此，最优觅食行为似乎赋予了相当大的适合度优势。
