Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
Oecologia. 2011 Apr;165(4):877-89. doi: 10.1007/s00442-010-1869-9. Epub 2010 Dec 12.
Categorizing animal populations by diet can mask important intrapopulation variation, which is crucial to understanding a species' trophic niche width. To test hypotheses related to intrapopulation variation in foraging or the presence of diet specialization, we conducted stable isotope analysis (δ(13)C, δ(15)N) on hair and claw samples from 51 grizzly bears (Ursus arctos) collected from 2003 to 2006 in the Mackenzie Delta region of the Canadian Arctic. We examined within-population differences in the foraging patterns of males and females and the relationship between trophic position (derived from δ(15)N measurements) and individual movement. The range of δ(15)N values in hair and claw (2.0-11.0‰) suggested a wide niche width and cluster analyses indicated the presence of three foraging groups within the population, ranging from near-complete herbivory to near-complete carnivory. We found no linear relationship between home range size and trophic position when the data were continuous or when grouped by foraging behavior. However, the movement rate of females increased linearly with trophic position. We used multisource dual-isotope mixing models to determine the relative contributions of seven prey sources within each foraging group for both males and females. The mean bear dietary endpoint across all foraging groups for each sex fell toward the center of the mixing polygon, which suggested relatively well-mixed diets. The primary dietary difference across foraging groups was the proportional contribution of herbaceous foods, which decreased for both males and females from 42-76 to 0-27% and 62-81 to 0-44%, respectively. Grizzlies of the Mackenzie Delta live in extremely harsh conditions and identifying within-population diet specialization has improved our understanding of varying habitat requirements within the population.
根据饮食对动物种群进行分类可能会掩盖种群内的重要变异，而这对于了解物种的营养生态位宽度至关重要。为了检验与觅食行为或饮食特化有关的种群内变异假说，我们对 2003 年至 2006 年间在加拿大北极麦肯齐三角洲地区采集的 51 只灰熊（Ursus arctos）的毛发和爪子样本进行了稳定同位素分析（δ¹³C，δ¹⁵N）。我们研究了雄性和雌性觅食模式的种群内差异，以及营养位（根据 δ¹⁵N 测量值得出）与个体运动之间的关系。毛发和爪子中 δ¹⁵N 值的范围（2.0-11.0‰）表明营养生态位宽度较宽，聚类分析表明种群内存在三种觅食群体，从接近完全的食草到接近完全的食肉。我们发现，当数据连续或按觅食行为分组时，栖息地大小与营养位之间没有线性关系。然而，雌性的运动速度与营养位呈线性增加。我们使用多源双同位素混合模型来确定每个觅食群体中七种猎物来源的相对贡献，包括雄性和雌性。所有觅食群体中，雄性和雌性的熊饮食端点平均值都落在混合多边形的中心附近，这表明饮食相对混合。不同觅食群体之间的主要饮食差异是草本食物的比例贡献，雄性和雌性的比例分别从 42-76%降至 0-27%和 62-81%降至 0-44%。麦肯齐三角洲的灰熊生活在极其恶劣的条件下，确定种群内的饮食特化有助于我们更好地了解种群内不同的栖息地需求。
