Balza Ulises, Lois Nicolás A, Polito Michael J, Pütz Klemens, Salom Amira, Raya Rey Andrea
Laboratorio de Ecología y Conservación de Vida Silvestre Centro Austral de Investigaciones Científicas (CADIC-CONICET) Ushuaia Argentina.
Departamento de Ecología, Genética y Evolución Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires Buenos Aires Argentina.
Ecol Evol. 2020 Oct 3;10(21):12264-12276. doi: 10.1002/ece3.6856. eCollection 2020 Nov.
Optimal foraging theory predicts an inverse relationship between the availability of preferred prey and niche width in animals. Moreover, when individuals within a population have identical prey preferences and preferred prey is scarce, a nested pattern of trophic niche is expected if opportunistic and selective individuals can be identified. Here, we examined intraspecific variation in the trophic niche of a resident population of striated caracara () on Isla de los Estados (Staten Island), Argentina, using pellet and stable isotope analyses. While this raptor specializes on seabird prey, we assessed this population's potential to forage on terrestrial prey, especially invasive herbivores as carrion, when seabirds are less accessible. We found that the isotopic niche of this species varies with season, age, breeding status, and, to a lesser extent, year. Our results were in general consistent with classic predictions of the optimal foraging theory, but we also explore other possible explanations for the observed pattern. Isotopic niche was broader for groups identified a priori as opportunistic (i.e., nonbreeding adults during the breeding season and the whole population during the nonbreeding season) than it was for individuals identified a priori as selective. Results suggested that terrestrial input was relatively low, and invasive mammals accounted for no more than 5% of the input. The seasonal pulse of rockhopper penguins likely interacts with caracara's reproductive status by constraining the spatial scale on which individuals forage. Niche expansion in spatially flexible individuals did not reflect an increase in terrestrial prey input; rather, it may be driven by a greater variation in the types of marine prey items consumed.
最优觅食理论预测，动物偏好猎物的可获得性与生态位宽度之间存在反比关系。此外，当种群中的个体具有相同的猎物偏好且偏好的猎物稀缺时，如果能够识别出机会主义者和选择性个体，那么营养生态位预计会呈现嵌套模式。在这里，我们利用食丸和稳定同位素分析，研究了阿根廷洛斯埃斯塔多斯岛（斯塔滕岛）条纹卡拉鹰（）定居种群营养生态位的种内变异。虽然这种猛禽专门捕食海鸟猎物，但我们评估了该种群在海鸟较难获取时捕食陆地猎物的潜力，特别是作为腐肉的入侵食草动物。我们发现，该物种的同位素生态位随季节、年龄、繁殖状态以及在较小程度上随年份而变化。我们的结果总体上与最优觅食理论的经典预测一致，但我们也探讨了对观察到的模式的其他可能解释。先验确定为机会主义者的群体（即繁殖季节的非繁殖成年个体和非繁殖季节的整个种群）的同位素生态位比先验确定为选择性个体的同位素生态位更宽。结果表明，陆地输入相对较低，入侵哺乳动物占输入量不超过5%。凤头黄眉企鹅的季节性脉冲可能通过限制个体觅食的空间尺度，与卡拉鹰的繁殖状态相互作用。空间灵活性个体的生态位扩展并不反映陆地猎物输入的增加；相反，它可能是由所消耗的海洋猎物种类的更大变化驱动的。
