COMMUNITY EQUILIBRIA AND STABILITY, AND AN EXTENSION OF COMPETITIVE EXCLUSION PRINCIPLE
COMMUNITY EQUILIBRIA AND STABILITY, AND AN EXTENSION OF COMPETITIVE EXCLUSION PRINCIPLE
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DOI：
10.1086/282676
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发表时间：
1970-01-01
影响因子：
2.9
通讯作者：
LEVIN, SA
中科院分区：
文献类型：
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作者：
LEVIN, SA
本文证明了在一个生态群落中，如果某些r个组分受小于r个限制因子的限制，则不可能达到稳定的平衡。因此，限制因素被提出作为那些方面的生态位决定物种是否可以共存的关键。例如，考虑以下简单的食物网：尽管两个被捕食物种在这个网络中占据相似的位置，但如果每个物种都受到捕食和资源限制的独立组合的限制，那么它们就有可能共存，因为两个独立的因素限制了两个物种。另一方面，如果两个物种以不同但过剩的食物来源为食，但受到同一个捕食者的限制，它们就不能无限期地共存。因此，这两个物种，虽然显然填补不同的生态位，不能生存在一起。一般来说，如果捕食者变得稀少，每个物种都会增加，如果捕食者丰富，就会减少，并且会有一个特征阈值捕食者水平，在这个阈值上它会稳定下来。阈值水平高的物种在其他物种不高的情况下会逐渐增加，并有取代其他物种的趋势。如果两者具有可比的阈值（这当然是可能的），则两者之间达到的任何均衡都将是高度可变的，不会产生稳定的均衡状况。这并不等同于将这种情况视为“无限不可能”，这在这种情况下是不可接受的论点。哈钦森在前一节中的观点生动地说明了这一点。本文的结果在三个方面改进了已有的结果。首先，它们消除了所有物种都是资源有限的限制，这是文献中持续存在的限制。第二，结果一般涉及到周期平衡，而不是常数平衡。第三，证明的性质与提议的平衡点附近的轨迹行为的关键问题有关，并提供了对限制因素数量不足时系统行为的洞察。
It is shown in this paper that no stable equilibrium can be attained in an ecological community in which some r of the components are limited by less than r limiting factors. The limiting factors are thus put forward as those aspects of the niche crucial in the determination of whether species can coexist. For example, consider the following simple food web: Despite the similar positions occupied by the two prey species in this web, it is possible for them to coexist if each is limited by an independent combination of predation and resource limitation, since then two independent factors are serving to limit two species. On the other hand, if two species feed on distinct but superabundant food sources, but are limited by the same single predator, they cannot continue to coexist indefinitely. Thus these two species, although apparently filling distinct ecological niches, cannot survive together. In general, each species will increase if the predator becomes scarce, will decrease where it is abundant, and will have a characteristic threshold predator level at which it stabilizes. That species with the higher threshold level will be on the increase when the other is not, and will tend to replace the other in the community. If the two have comparable threshold values, which is certainly possible, any equilibrium reached between the two will be highly variable, and no stable equilibrium situation will result. This is not the same as dismissing this situation as "infinitely unlikely," which is not an acceptable argument in this case. Hutchinson's point of the preceding section vividly illustrates this. The results of this paper improve on existing results in three ways. First, they eliminate the restriction that all species are resource-limited, a restriction persistent in the literature. Second, the results relate in general to periodic equilibria rather than to constant equilibria. Third, the nature of the proof relates to the crucial question of the behavior of trajectories near the proposed equilibrium, and provides insight into the behavior of the system when there is an insufficient number of limiting factors.