PHENOMENA ASSOCIATED WITH POPULATION DENSITY
PHENOMENA ASSOCIATED WITH POPULATION DENSITY
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DOI：
10.1073/pnas.47.4.428
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发表时间：
1961-01-01
影响因子：
11.1
通讯作者：
CHRISTIAN, J
中科院分区：
文献类型：
--
作者：
CHRISTIAN, J
作为本次讨论的主题的哺乳动物及其种群可能已经进化出足够的方法来适应它们的环境，并具有足够的生理灵活性来满足环境中的日常和季节性变化。他们还必须建立人口控制机制，防止过度利用和破坏他们的环境，从而防止他们自己的灭绝。哺乳动物种群的增长通常在这一点上停止；然而，哺乳动物种群的下降广泛而松散地归因于食物短缺。批判性研究普遍未能将这些下降与高度贫瘠地区以外的食物供应枯竭联系起来。任何可靠、广泛有效的人口控制系统肯定都是直接或间接依赖密度的，因此对人口本身是不可或缺的。几年前，我们提出，种群的增长和下降受到一系列反馈机制的调节，特别是涉及垂体-肾上腺皮质和垂体-性腺系统，而这些反馈机制反过来又被种群内的社会心理因素(种内竞争)激活。13 14现有证据表明，相互作用的行为和内分泌机制至少构成了种群中个体的这种系统的一个重要部分：该系统对动物数量的变化作出反应，从而使种群的增长是自我限制和自我调节的。这篇论文将总结这种机制的证据，很大程度上是通过从迄今尚未发表的数据中提取的例子来说明的，这些数据的细节将在其他地方公布。在对证据进行总结之前，应当提到产仔数，因为选择调节种群增长的生理机制无疑涉及选择最佳产仔数，其定义是每窝产仔的平均数量足以以对母体最小的代价维持种群。生殖功能的调节是导致调节种群增长的适应性反应的一个组成部分，因为它们在很大程度上调节生殖。在正常情况下，维持生命的功能和繁殖并不是相互排斥的，而是当生存所需的能量超过动物满足它们和繁殖的能力时，才会相互排斥。正如我们将看到的，繁殖是被牺牲的。证据--如所述，人口增长的调节涉及行为和生理机制，后者重要的包括垂体-肾上腺皮质系统以及垂体-性腺功能。关于肾上腺皮质功能的研究已经写得太多了，所以这里不再对其进行回顾，只是说它在调节正常代谢过程中至关重要，也许更重要的是在紧急情况下。当面临环境变化或生理需求显著增加时，肾上腺皮质功能增强是保证生存的重要手段之一。值得注意的是，它增加了它的大小和功能，以应对情绪压力、流浪、伤害、寒冷和许多其他潜在的有害刺激，因此提供
The mammals and their populations which are the topic of this discussion presumably have evolved adequate means of adapting to their environment and possess sufficient physiologic flexibility to meet-daily and seasonal changes in their environment. They also must have developed mechanisms of population control which have prevented overutilization and destruction of their environment and therefore their own extinction. The growth of mammalian populations usually ceases short of this point; yet declines in mammalian populations are widely and loosely attributed to shortages of food. Critical studies generally have failed to associate these declines with exhaustion of the food supply other than in highly lo-calized areas. Any dependable, extensively effective system of population control surely must be density dependent, directly or indirectly, and therefore would be integral to the population itself. Some years ago we proposed that population growth and decline were regulated by series of feed-back mechanisms, particularly involving the pituitary-adrenocortical and pituitary-gonadal systems, and that these in turn were activated by socio-psychological factors (intraspecific competition) within the population. 13 14 Present evidence indicates that interacting behavioral and endocrine mechanisms comprise at least an important part of such a system in the individuals in a population: a system responding to changes in the number of animals in such a way that population growth is self-limiting and self-regulating. This paper will summarize the evidence for such a mechanism, illustrated to a large degree by examples drawn from data so far unpublished, the details of which will be published elsewhere. Before proceeding to a summary of the evidence, litter size should be mentioned, since selection for physiological mechanisms regulating population growth un-doubtedly involved selection for optimum litter size, defined as the mean number of young per litter sufficient to maintain the population with the least cost to the maternal organism. Regulation of reproductive function is an integral part of the adaptive responses which result in regulating population growth because, to a large degree, they regulate reproductionYs Normally, life-maintaining functions and reproduction are not mutually exclusive, but become so when the energy re-quirements for survival exceed the capacity of the animal to meet themand to reproduce. Reproduction is sacrificed, as we shall see. The Evidence.-The regulation of population growth, as outlined, involves behavioral and physiological mechanisms, the latter importantly including the pituitary-adrenocortical system as well as pituitary-gonadal function. So much has been written on adrenocortical function that it will not be reviewed here, other than to say that it is vitally important in the regulation of normal metabolic processes, and perhaps more particularly in emergencies. Increased adrenocortical function provides one of the important means of insuring survival when confronted with environmental change or markedly increased physiological demands. Notably, it increases its size and function in response to emotional stress, bums, injury, cold, anda number of other potentially harmful stimuli and therefore provides