The discipline of ecology seeks to understand how ecosystems, communities, and populations are regulated. A ubiquitous mechanism of population regulation of consumers is that capturing energy and nutrients in sufficient quantities for survival and reproduction becomes more difficult as population density increases. Extensive evidence has revealed that populations of large herbivores are often regulated by density dependence, defined as the reduction in the per-capita population growth rate that occurs as populations grow large. Diminished body mass of individuals has been repeatedly observed in high-density populations, implicating compromised nutrition as the primary cause of density dependence. However, there is no general explanation for why these nutritional deficiencies occur. Recent work demonstrated that reduced food intake rates resulting from the functional response of herbivores to depleted plant biomass does not provide a sensible explanation for density dependence because rates of food intake of herbivores are often insensitive to changes in plant biomass. A new model of feedbacks from plant biomass to herbivores shows how reduced nutrition of herbivores can result from increased dilution of nutrients in the plant tissue they consume as populations grow, even when their rate of consumption of plants remains constant. The model contains parameters that can be scaled to body mass, allowing unusually general predictions. The model shows that convex, concave, and linear relationships between the per-capita growth rate and population density can arise from the effects of depletion of plant biomass by herbivore foraging. The model is the first to explicitly include spatial variance in the nutritional quality of plants as a general driver of herbivore population dynamics. I show how regulation of herbivore abundance by plant nutrients can occur, even when a large fraction of the consumable plant biomass remains uneaten, providing a simple, mechanistic explanation for bottom-up control of population dynamics of primary consumers in a “green world.”

中文翻译：

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对大型食草动物种群密度依赖性的一般性、基于资源的解释


生态学学科旨在了解生态系统、社区和人口是如何受到监管的。消费者的人口调节的普遍机制是，随着人口密度的增加，获取足够数量的能量和营养物质以维持生存和繁殖变得更加困难。大量证据表明，大型食草动物的种群数量通常受到密度依赖性的调节，密度依赖性定义为随着种群数量的增加而出现的人均人口增长率的下降。在高密度人群中反复观察到个体体重减少，这表明营养不良是密度依赖的主要原因。然而，对于为什么会出现这些营养缺乏症，还没有一般性的解释。最近的研究表明，食草动物对耗尽的植物生物量的功能反应导致的食物摄入率降低并不能为密度依赖性提供合理的解释，因为食草动物的食物摄入率通常对植物生物量的变化不敏感。植物生物量对食草动物的反馈的新模型表明，即使食草动物消耗植物的速度保持不变，随着种群的增长，食草动物消耗的植物组织中的营养物质会不断稀释，从而导致食草动物的营养减少。该模型包含可以根据体重缩放的参数，从而可以进行异常普遍的预测。该模型表明，人均增长率和人口密度之间的凸、凹和线性关系可能是由于草食动物觅食造成的植物生物量消耗的影响而产生的。 该模型是第一个明确将植物营养质量的空间差异作为草食动物种群动态的一般驱动因素的模型。我展示了即使大部分可消耗植物生物量仍未被吃掉，植物营养物质对草食动物丰度的调节也是如何发生的，为“绿色世界”中初级消费者种群动态的自下而上控制提供了一个简单的机械解释。”