Forchhammer Mads C, Boomsma Jacobus J
Department of Ecology and Genetics, University of Aarhus, Bld. 540, Ny Munkegade, DK-8000, Aarhus C, Denmark.
Oecologia. 1995 Oct;104(2):169-180. doi: 10.1007/BF00328582.
Various aspects of optimal foraging and seasonal diet composition of bulls (bachelor and dominant), cows, subadults, and yearlings of muskoxen Ovibos moschatus were investigated in West Greenland during the following seasons: calving, post-calving, summer, rut and mid-winter. The following hypotheses were tested: (1) muskoxen maximize daily energy intake during spring and summer, (2) dominant bulls monopolizing cows during the rutting season shift from an energy maximizing to a time minimizing foraging strategy in order to maximize the time available for reproductive activities, and (3) muskoxen employ a time minimizing foraging strategy during winter to conserve energy. As forage quality changed throughout the short Arctic growing season, muskoxen responded by changing the proportions of daily time spent feeding on graminoids (Cyperaceae, Poaceae) and dicots (Salix, Betula), respectively. This seasonal variation in the relative proportion of daily feeding time spent ingesting graminoids followed approximately the energy maximization prediction over the periods calving to rut. Neither time minimizing nor random foraging could explain the observed diets in this period, thus confirming hypothesis 1. Dominant bulls did not shift to the time minimizing strategy as predicted by hypothesis 2. However, during the pre-rutting and rutting seasons bulls deviated from the other sex/age classes by failing to obtain the daily maximum energy predicted by the model, as a result of a higher proportion of time allocated to agonistic and sexual behaviour. During winter, none of the sex/age classes employed a time minimizing strategy, so rejecting hypothesis 3. Instead, muskoxen were found to maximize Na intake, indicating that Na is of major importance for winter survival. The results emerging from a linear programming model with constraint settings varying over seasons confirm that the constraint parameters applied are indeed important limiting factors for muskoxen in natural populations.
在西格陵兰岛，对麝牛（Ovibos moschatus）的单身公牛、成年公牛、母牛、亚成体和一岁小牛在产犊、产后、夏季、发情期和冬季中期等季节的最佳觅食和季节性饮食组成的各个方面进行了调查。测试了以下假设：（1）麝牛在春季和夏季将每日能量摄入最大化；（2）在发情季节独占母牛的成年公牛从能量最大化觅食策略转变为时间最小化觅食策略，以最大化可用于繁殖活动的时间；（3）麝牛在冬季采用时间最小化觅食策略以保存能量。由于在北极短暂的生长季节中草料质量发生变化，麝牛通过改变每日分别以禾本科植物（莎草科、禾本科）和双子叶植物（柳属、桦属）为食的时间比例做出反应。在产犊到发情期期间，每日进食时间中摄入禾本科植物的相对比例的这种季节性变化大致遵循能量最大化预测。在这个时期，时间最小化觅食或随机觅食都无法解释观察到的饮食情况，从而证实了假设1。成年公牛并没有如假设2所预测的那样转变为时间最小化策略。然而，在发情前期和发情期，公牛由于分配给争斗和性行为的时间比例较高，未能获得模型预测的每日最大能量，从而与其他性别/年龄组有所不同。在冬季，没有一个性别/年龄组采用时间最小化策略，因此否定了假设3。相反，发现麝牛会最大化钠的摄入量，这表明钠对冬季生存至关重要。一个线性规划模型的结果表明，随着季节变化约束设置也会变化，这证实了所应用的约束参数确实是自然种群中麝牛的重要限制因素。
