Department of Ecology and Evolution, Stony Brook University, Stony Brook, New York 11794-5245, USA.
Q Rev Biol. 2011 Jun;86(2):75-96. doi: 10.1086/659883.
A major goal of research in ecology and evolution is to explain why species richness varies across habitats, regions, and clades. Recent reviews have argued that species richness patterns among regions and clades may be explained by "ecological limits" on diversity over time, which are said to offer an alternative explanation to those invoking speciation and extinction (diversification) and time. Further, it has been proposed that this hypothesis is best supported by failure to find a positive relationship between time (e.g., clade age) and species richness. Here, I critically review the evidence for these claims, and propose how we might better study the ecological and evolutionary origins of species richness patterns. In fact, ecological limits can only influence species richness in clades by influencing speciation and extinction, and so this new "alternative paradigm" is simply one facet of the traditional idea that ecology influences diversification. The only direct evidence for strict ecological limits on richness (i.e., constant diversity over time) is from the fossil record, but many studies cited as supporting this pattern do not, and there is evidence for increasing richness over time. Negative evidence for a relationship between clade age and richness among extant clades is not positive evidence for constant diversity over time, and many recent analyses finding no age-diversity relationship were biased to reach this conclusion. More comprehensive analyses strongly support a positive age-richness relationship. There is abundant evidence that both time and ecological influences on diversification rates are important drivers of both large-scale and small-scale species richness patterns. The major challenge for future studies is to understand the ecological and evolutionary mechanisms underpinning the relationships between time, dispersal, diversification, and species richness patterns.
生态学和进化研究的一个主要目标是解释为什么物种丰富度在栖息地、地区和进化枝之间存在差异。最近的评论认为，地区和进化枝之间的物种丰富度模式可以用多样性随时间的“生态限制”来解释，这为那些援引物种形成和灭绝（多样化）和时间的解释提供了另一种选择。此外，有人提出，这个假设最好通过未能发现时间（例如，进化枝年龄）和物种丰富度之间存在正相关关系来支持。在这里，我批判性地回顾了这些说法的证据，并提出了我们如何更好地研究物种丰富度模式的生态和进化起源。事实上，生态限制只能通过影响物种形成和灭绝来影响进化枝中的物种丰富度，因此这个新的“替代范式”只是生态学影响多样化的传统观念的一个方面。严格的生态限制对丰富度（即随时间变化的多样性）的唯一直接证据来自化石记录，但许多被引用为支持这种模式的研究并没有这样做，而且有证据表明随着时间的推移丰富度在增加。现存进化枝中进化枝年龄与丰富度之间没有关系的负证据并不是随时间变化多样性的正证据，许多最近发现没有年龄-多样性关系的分析存在偏见，以得出这一结论。更全面的分析强烈支持年龄与丰富度之间的正相关关系。有充分的证据表明，时间和对多样化率的生态影响都是大尺度和小尺度物种丰富度模式的重要驱动因素。未来研究的主要挑战是了解时间、扩散、多样化和物种丰富度模式之间关系的生态和进化机制。
