Jesmer Brett R, Kauffman Matthew J, Murphy Melanie A, Goheen Jacob R
Program in Ecology, University of Wyoming, Laramie, WY, USA.
Department of Zoology and Physiology, University of Wyoming, Laramie, WY, USA.
J Anim Ecol. 2020 Dec;89(12):2825-2839. doi: 10.1111/1365-2656.13351. Epub 2020 Oct 19.
Despite the shared prediction that the width of a population's dietary niche expands as food becomes limiting, the Niche Variation Hypothesis (NVH) and Optimal Foraging Theory (OFT) offer contrasting views about how individuals alter diet selection when food is limited. Classical OFT predicts that dietary preferences do not change as food becomes limiting, so individuals expand their diets as they compensate for a lack of preferred foods. In contrast, the NVH predicts that among-individual variation in cognition, physiology or morphology create functional trade-offs in foraging efficiency, thereby causing individuals to specialize on different subsets of food as food becomes limiting. To evaluate (a) the predictions of the NVH and OFT and (b) evidence for physiological and cognitive-based functional trade-offs, we used DNA microsatellites and metabarcoding to quantify the diet, microbiome and genetic relatedness (a proxy for social learning) of 218 moose Alces alces across six populations that varied in their degree of food limitation. Consistent with both the NVH and OFT, dietary niche breadth increased with food limitation. Increased diet breadth of individuals-rather than increased diet specialization-was strongly correlated with both food limitation and dietary niche breadth of populations, indicating that moose foraged in accordance with OFT. Diets were not constrained by inheritance of the microbiome or inheritance of diet selection, offering support for the little-tested hypothesis that functional trade-offs in food use (or lack thereof) determine whether populations adhere to the predictions of the NVH or OFT. Our results indicate that both the absence of strong functional trade-offs and the digestive physiology of ruminants provide contexts under which populations should forage in accordance with OFT rather than the NVH. Also, because dietary niche width increased with increased food limitation, OFT and the NVH provide theoretical support for the notion that plant-herbivore interaction networks are plastic rather than static, which has important implications for understanding interspecific niche partitioning. Lastly, because population-level dietary niche breadth and calf recruitment are correlated, and because calf recruitment can be a proxy for food limitation, our work demonstrates how diet data can be employed to understand a populations' proximity to carrying capacity.
尽管有共同的预测认为，随着食物变得有限，种群饮食生态位的宽度会扩大，但生态位变异假说（NVH）和最优觅食理论（OFT）对于食物有限时个体如何改变饮食选择提出了截然不同的观点。经典的最优觅食理论预测，随着食物变得有限，饮食偏好不会改变，因此个体通过补偿缺乏偏好食物的方式来扩大饮食范围。相比之下，生态位变异假说预测，个体在认知、生理或形态上存在的差异会在觅食效率上产生功能权衡，从而导致个体在食物有限时专门食用不同的食物子集。为了评估（a）生态位变异假说和最优觅食理论所做的预测，以及（b）基于生理和认知功能权衡的证据，我们使用DNA微卫星和代谢条形码技术，量化了六个食物限制程度不同的种群中218头驼鹿（Alces alces）的饮食、微生物组和遗传相关性（社会学习的一个指标）。与生态位变异假说和最优觅食理论均一致的是，饮食生态位宽度随着食物限制程度增加而增大。个体饮食范围的扩大——而非饮食专门化程度的提高——与食物限制以及种群的饮食生态位宽度都密切相关，这表明驼鹿的觅食行为符合最优觅食理论。饮食不受微生物组遗传或饮食选择遗传的限制，这为一个较少被检验的假说提供了支持，即食物利用中的功能权衡（或缺乏这种权衡）决定了种群是否符合生态位变异假说或最优觅食理论的预测。我们的结果表明，既不存在强烈的功能权衡，反刍动物的消化生理也为种群应根据最优觅食理论而非生态位变异假说进行觅食提供了背景条件。此外，由于饮食生态位宽度随着食物限制程度的增加而增大，最优觅食理论和生态位变异假说为植物 - 食草动物相互作用网络具有可塑性而非静态这一观点提供了理论支持，这对于理解种间生态位划分具有重要意义。最后，由于种群水平的饮食生态位宽度与幼崽数量相关，并且由于幼崽数量可以作为食物限制的一个指标，我们的研究展示了饮食数据如何能够用于理解种群接近承载能力的程度。
