Abrams P A
Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada.
Am Nat. 2001 Nov;158(5):459-70. doi: 10.1086/323113.
Many ecologists believe that higher mortality imposed on competing species increases the probability that they will coexist. This belief has persisted in spite of many theoretical counterarguments. However, few of those counterarguments have been based on models having explicit representation of the resources for which competition is occurring. This article analyzes a series of consumer-resource models of competition for nutritionally substitutable renewable resources and determines the range of relative resource requirements that allow coexistence. In most cases, if consumers are initially efficient at reducing resource densities, increasing density-independent mortality widens the range of resource requirements of the consumers that allow coexistence, provided the increase in mortality is not too great. The coexistence-promoting effects of mortality occur because a very efficient consumer species usually reduces the diversity of the set of resources it consumes. This lessens the extent to which resource utilization differences between consumer species can be expressed. Mortality, in this case, increases the diversity of resource types, widening the conditions for coexistence. However, sufficiently high mortality will usually reduce the range of parameters allowing coexistence, in agreement with much previous theory. The results presented here also predict maximal diversity at intermediate levels of productivity. Previous empirical studies and theory are reviewed in light of the theory developed here.
许多生态学家认为，对竞争物种施加更高的死亡率会增加它们共存的可能性。尽管存在许多理论上的反对观点，但这种观点仍然存在。然而，这些反对观点中很少有基于对竞争所涉及资源进行明确表示的模型。本文分析了一系列针对营养可替代可再生资源的消费者 - 资源竞争模型，并确定了允许共存的相对资源需求范围。在大多数情况下，如果消费者最初在降低资源密度方面效率较高，那么在不使死亡率增加过大的前提下，增加与密度无关的死亡率会扩大允许共存的消费者资源需求范围。死亡率促进共存的作用之所以会出现，是因为一个非常高效的消费者物种通常会降低其消耗的资源种类的多样性。这就减少了消费者物种之间资源利用差异得以体现的程度。在这种情况下，死亡率增加了资源类型的多样性，拓宽了共存的条件。然而，与许多先前的理论一致，足够高的死亡率通常会缩小允许共存的参数范围。这里给出的结果还预测了在中等生产力水平下的最大多样性。本文根据在此提出的理论对先前的实证研究和理论进行了综述。
