Ginnett T F, Demment Montague W
Department of Agronomy and Range Science, University of California-Davis, Davis, CA 95616, USA, , , , , , US.
Oecologia. 1997 Apr;110(2):291-300. doi: 10.1007/s004420050162.
We test predictions about differences in the foraging behaviors of male and female giraffes (Giraffa camelopardalis tippelskirchi Matchie) that derive from a hypothesis linking sexual size dimorphism to foraging behavior. This body-size hypothesis predicts that males will exhibit specific behaviors that increase their dry-matter intake rate relative to females. Foraging behavior was examined at two hierarchical levels corresponding to two spatial and temporal scales, within patches and within habitats. Patches are defined as individual trees or shrubs and habitats are defined as collections of patches within plant communities. Males were predicted to increase dry-matter intake rate within patches by taking larger bites, cropping bites more quickly, chewing less, and chewing faster. Within habitats, males were expected to increase intake rate by increasing the proportion of foraging time devoted to food ingestion as opposed to inter-patch travel time and vigilance. The predictions were tested in a free-ranging population of giraffes in Mikumi National Park, Tanzania. Males spent less total time foraging than females but allocated a greater proportion of their foraging time to forage ingestion as opposed to travel between patches. There was no sex difference in rumination time but males spent more time in activities other than foraging and rumination, such as walking. Within patches, males took larger bites than females, but females cropped bites more quickly and chewed faster. Males had longer per-bite handling times than females but had shorter handling times per gram of intake. Within habitats, males had longer average patch residence times but there was no significant sex difference in inter-patch travel times. There was no overall difference between sexes in vigilance while foraging, although there were significant sex by habitat and sex by season interactions. Although not all the predictions were confirmed, overall the results agree qualitatively with the body-size hypothesis. Sex-related differences in foraging behavior led to greater estimated intake rates for males at the within-patch and within-habitat scales.
我们检验了关于雄性和雌性长颈鹿（长颈鹿指名亚种）觅食行为差异的预测，这些预测源自一个将两性体型差异与觅食行为联系起来的假说。这个体型假说预测，雄性会表现出特定行为，相对于雌性，这些行为能提高它们的干物质摄入率。觅食行为在两个层次水平上进行了研究，这两个层次水平分别对应两个空间和时间尺度，即斑块内和栖息地内。斑块被定义为单株树木或灌木，栖息地被定义为植物群落内斑块的集合。预计雄性通过大口采食、更快地啃咬、更少地咀嚼以及更快地咀嚼，来提高斑块内的干物质摄入率。在栖息地内，预计雄性通过增加用于食物摄取的觅食时间比例，而非斑块间移动时间和警戒时间，来提高摄入率。这些预测在坦桑尼亚米库米国家公园的一个自由放养的长颈鹿种群中进行了检验。雄性用于觅食的总时间比雌性少，但它们将更大比例的觅食时间用于食物摄取，而非在斑块间移动。反刍时间没有性别差异，但雄性在觅食和反刍之外的活动（如行走）上花费的时间更多。在斑块内，雄性的采食口比雌性大，但雌性啃咬更快且咀嚼更快。雄性每口的处理时间比雌性长，但每摄入一克的处理时间更短。在栖息地内，雄性的平均斑块停留时间更长，但斑块间移动时间没有显著的性别差异。觅食时的警戒在两性之间没有总体差异，尽管存在显著的性别×栖息地和性别×季节交互作用。虽然并非所有预测都得到证实，但总体而言，结果在质量上与体型假说相符。觅食行为的性别相关差异导致在斑块内和栖息地尺度上，雄性的估计摄入率更高。
