Ecology and Evolutionary Biology, School of Biological Sciences, University of Reading, Reading, UK.
Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, México, México.
J Anim Ecol. 2021 Mar;90(3):653-661. doi: 10.1111/1365-2656.13397. Epub 2020 Dec 22.
The local abundance or population density of different organisms often varies widely. Understanding what determines this variation is an important, but not yet fully resolved question in ecology. Differences in population density are partly driven by variation in body size and diet among organisms. Here we propose that the size of an organism' brain could be an additional, overlooked, driver of mammalian population densities. We explore two possible contrasting mechanisms by which brain size, measured by its mass, could affect population density. First, because of the energetic demands of larger brains and their influence on life history, we predict mammals with larger relative brain masses would occur at lower population densities. Alternatively, larger brains are generally associated with a greater ability to exploit new resources, which would provide a competitive advantage leading to higher population densities among large-brained mammals. We tested these predictions using phylogenetic path analysis, modelling hypothesized direct and indirect relationships between diet, body mass, brain mass and population density for 656 non-volant terrestrial mammalian species. We analysed all data together and separately for marsupials and the four taxonomic orders with most species in the dataset (Carnivora, Cetartiodactyla, Primates, Rodentia). For all species combined, a single model was supported showing lower population density associated with larger brains, larger bodies and more specialized diets. The negative effect of brain mass was also supported for separate analyses in Primates and Carnivora. In other groups (Rodentia, Cetartiodactyla and marsupials) the relationship was less clear: supported models included a direct link from brain mass to population density but 95% confidence intervals of the path coefficients overlapped zero. Results support our hypothesis that brain mass can explain variation in species' average population density, with large-brained species having greater area requirements, although the relationship may vary across taxonomic groups. Future research is needed to clarify whether the role of brain mass on population density varies as a function of environmental (e.g. environmental stability) and biotic conditions (e.g. level of competition).
不同生物的局部丰度或种群密度通常差异很大。了解是什么决定了这种变化是生态学中的一个重要但尚未完全解决的问题。种群密度的差异部分是由生物体之间的体型和饮食差异驱动的。在这里，我们提出生物体大脑的大小可能是哺乳动物种群密度的另一个被忽视的驱动因素。我们探讨了大脑大小（通过其质量来衡量）影响种群密度的两种可能的相反机制。首先，由于大脑较大的能量需求及其对生活史的影响，我们预测相对大脑质量较大的哺乳动物的种群密度会较低。或者，较大的大脑通常与利用新资源的更大能力相关联，这将为具有较大大脑的哺乳动物提供竞争优势，从而导致其种群密度更高。我们使用系统发育路径分析来检验这些预测，为 656 种非飞行陆地哺乳动物物种的饮食、体重、脑质量和种群密度之间的假设直接和间接关系建立模型。我们一起分析了所有数据，以及为数据集中物种最多的四个分类阶元（食肉目、偶蹄目、灵长目、啮齿目）分别进行了分析。对于所有物种的综合分析，支持了一个单一的模型，表明较大的大脑、较大的体型和更专门的饮食与较低的种群密度相关。在灵长目和食肉目单独分析中也支持了大脑质量的负面影响。在其他群体（啮齿目、偶蹄目和有袋目）中，这种关系不太明确：支持的模型包括从大脑质量到种群密度的直接联系，但路径系数的 95%置信区间与零重叠。研究结果支持我们的假设，即大脑质量可以解释物种平均种群密度的变化，大脑较大的物种需要更大的区域，但这种关系可能因分类群而异。未来的研究需要阐明大脑质量对种群密度的作用是否随着环境（例如环境稳定性）和生物条件（例如竞争水平）的变化而变化。
