Yurkowski David J, Ferguson Steve, Choy Emily S, Loseto Lisa L, Brown Tanya M, Muir Derek C G, Semeniuk Christina A D, Fisk Aaron T
Great Lakes Institute for Environmental Research University of Windsor Windsor ON N9B 3P4 Canada.
Freshwater Institute Fisheries and Oceans Canada Winnipeg MB R3T 2N6 Canada.
Ecol Evol. 2016 Feb 14;6(6):1666-78. doi: 10.1002/ece3.1980. eCollection 2016 Mar.
Individual specialization (IS), where individuals within populations irrespective of age, sex, and body size are either specialized or generalized in terms of resource use, has implications on ecological niches and food web structure. Niche size and degree of IS of near-top trophic-level marine predators have been little studied in polar regions or with latitude. We quantified the large-scale latitudinal variation of population- and individual-level niche size and IS in ringed seals (Pusa hispida) and beluga whales (Delphinapterus leucas) using stable carbon and nitrogen isotope analysis on 379 paired ringed seal liver and muscle samples and 124 paired beluga skin and muscle samples from eight locations ranging from the low to high Arctic. We characterized both within- and between-individual variation in predator niche size at each location as well as accounting for spatial differences in the isotopic ranges of potential prey. Total isotopic niche width (TINW) for populations of ringed seals and beluga decreased with increasing latitude. Higher TINW values were associated with greater ecological opportunity (i.e., prey diversity) in the prey fish community which mainly consists of Capelin (Mallotus villosus) and Sand lance (Ammodytes sp.) at lower latitudes and Arctic cod (Boreogadus saida) at high latitudes. In beluga, their dietary consistency between tissues also known as the within-individual component (WIC) increased in a near 1:1 ratio with TINW (slope = 0.84), suggesting dietary generalization, whereas the slope (0.18) of WIC relative to TINW in ringed seals indicated a high degree of individual specialization in ringed seal populations with higher TINWs. Our findings highlight the differences in TINW and level of IS for ringed seals and beluga relative to latitude as a likely response to large-scale spatial variation in ecological opportunity, suggesting species-specific variation in dietary plasticity to spatial differences in prey resources and environmental conditions in a rapidly changing ecosystem.
个体专业化（IS）是指种群中的个体，无论年龄、性别和体型大小，在资源利用方面要么是专业化的，要么是泛化的，这对生态位和食物网结构有影响。在极地地区或随纬度变化，近顶级营养级海洋捕食者的生态位大小和个体专业化程度鲜有研究。我们对来自北极低纬度到高纬度八个地点的379对环斑海豹肝脏和肌肉样本以及124对白鲸皮肤和肌肉样本进行稳定碳氮同位素分析，以量化环斑海豹（Pusa hispida）和白鲸（Delphinapterus leucas）种群和个体水平生态位大小及个体专业化的大规模纬度变化。我们刻画了每个地点捕食者生态位大小的个体内和个体间变异，并考虑了潜在猎物同位素范围的空间差异。环斑海豹和白鲸种群的总同位素生态位宽度（TINW）随纬度增加而减小。较高的TINW值与较低纬度主要由毛鳞鱼（Mallotus villosus）和沙鳗（Ammodytes sp.）以及高纬度北极鳕鱼（Boreogadus saida）组成的猎物鱼类群落中更大的生态机会（即猎物多样性）相关。在白鲸中，它们组织间的饮食一致性，即个体内成分（WIC）与TINW以近1:1的比例增加（斜率 = 0.84），表明饮食泛化，而环斑海豹中WIC相对于TINW的斜率（0.18）表明TINW较高的环斑海豹种群具有高度的个体专业化。我们的研究结果突出了环斑海豹和白鲸的TINW和个体专业化水平相对于纬度的差异，这可能是对生态机会大规模空间变化的一种响应，表明在快速变化的生态系统中，物种在饮食可塑性方面对猎物资源和环境条件空间差异的特异性变化。
