Festa-Bianchet Marco, Gaillard Jean-Michel, Côté Steeve D
Groupe de recherche en écologie, nutrition et énergétique, Département de biologie, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1.
Unité Mixte de Recherche No.5558 'Biométrie et Biologie Evolutive', 43 boulevard du 11 novembre 1918, 69622 Villeurbanne Cedex, France, and ‡Département de biologie et Centres d'Études Nordiques, Université Laval, Sainte-Foy, Québec, Canada G1K 7P4.
J Anim Ecol. 2003 Jul;72(4):640-649. doi: 10.1046/j.1365-2656.2003.00735.x.
Large herbivores have strongly age-structured populations. Because recruitment often decreases as population density increases, in unexploited populations the proportion of older adults may increase with density. Because survival senescence is typical of ungulates, ignoring density-dependent changes in age structure could lead to apparent density-dependence in adult survival. To test for density dependence in adult survival, we used data from three populations that underwent considerable changes in density. Bighorn sheep (Ovis canadensis) on Ram Mountain, Alberta, ranged from 94 to 232, mountain goats (Oreamnos americanus) on Caw Ridge, Alberta, varied from 81 to 147, and estimates of roe deer (Capreolus capreolus) older than 1 year at Chizé, France, ranged from 157 to 569. We used recent developments of capture-mark-recapture modelling to assess the response of adult survival to changes in density when age structure was and was not taken into account. Survival rates were 10-15% higher during the prime-age stage than during the senescent stage for all sex-species combinations. When adults were pooled into a single age class there was an apparent negative effect of density on female survival in bighorns and roe deer, and negative trends for female mountain goats, male roe deer and male bighorn sheep. When age class was taken into account, there were no significant effects of density on adult survival. Except for male mountain goats, the strength of density dependence was lower when age was taken into account. In ungulate populations, age structure is an important determinant of adult survival. Most reports of density dependence in adult survival may have been confounded by changes in age structure.
大型食草动物种群具有明显的年龄结构。由于随着种群密度增加，补充率往往会下降，在未受开发的种群中，老年个体的比例可能会随着密度增加而上升。由于有蹄类动物普遍存在生存衰老现象，忽视年龄结构中密度依赖的变化可能会导致成年个体生存出现明显的密度依赖性。为了检验成年个体生存的密度依赖性，我们使用了来自三个密度发生显著变化的种群的数据。艾伯塔省拉姆山的加拿大盘羊（Ovis canadensis）数量从94只到232只不等，艾伯塔省考岭的美洲野山羊（Oreamnos americanus）数量从81只到147只不等，法国奇泽年龄超过1岁的狍（Capreolus capreolus）数量估计从157只到569只不等。我们利用捕获-标记-重捕模型的最新进展，评估在考虑和不考虑年龄结构时成年个体生存对密度变化的反应。对于所有性别-物种组合，壮年阶段的存活率比衰老阶段高10%-15%。当将成年个体合并为一个年龄组时，密度对加拿大盘羊和狍的雌性生存有明显的负面影响，对雌性美洲野山羊、雄性狍和雄性加拿大盘羊有负面趋势。当考虑年龄组时，密度对成年个体生存没有显著影响。除了雄性美洲野山羊外，考虑年龄时密度依赖的强度较低。在有蹄类动物种群中，年龄结构是成年个体生存的重要决定因素。大多数关于成年个体生存密度依赖性的报告可能因年龄结构的变化而混淆。
