There is a great need to understand how and why biodiversity, which we define as the variety of organisms found in a given place, changes over time. Current estimates suggest strikingly slow change in traditional measures of biodiversity. These estimates seem to contradict rapid shifts in the abundance of individual species and have led to a rethinking of the mechanisms shaping biodiversity. Conceptual models emphasise the role of competition among species or, more recently, selection on species identity (i.e. selection that favours some species at the expense of others). However, it is difficult to quantify how these mechanisms contribute to biodiversity change. To illustrate this point, we present cases where strong competition or selection on species identity leads to no biodiversity change. In view of this disconnect, we develop a new approach to studying biodiversity change using the Price equation. We show that biodiversity change responds to selection on species’ rarity, rather than to either competition or selection on species identity. We then show how this insight can be used to quantify the effects of the mechanisms previously thought to influence biodiversity: (1) selection, (2) (ecological) drift, (3) immigration and (4) speciation. Our results suggest the connection between species’ fates and their rarity is fundamental to understanding biodiversity change.

非常需要了解生物多样性（我们将其定义为在给定地点发现的各种生物）如何以及为什么会随着时间发生变化。目前的估计表明，生物多样性的传统衡量标准发生了惊人的缓慢变化。这些估计似乎与单个物种丰富度的快速变化相矛盾，并导致重新思考塑造生物多样性的机制。概念模型强调物种之间竞争的作用，或者最近强调物种特性选择（即选择以牺牲其他物种为代价偏爱某些物种）。然而，很难量化这些机制如何促进生物多样性变化。为了说明这一点，我们展示了对物种身份的激烈竞争或选择导致生物多样性没有变化的案例。鉴于这种脱节，我们开发了一种使用价格方程研究生物多样性变化的新方法。我们表明，生物多样性变化对物种稀有性的选择做出反应，而不是对竞争或对物种身份的选择做出反应。然后我们展示了如何使用这种见解来量化以前认为影响生物多样性的机制的影响：（1）选择，（2）（生态）漂移，（3）移民和（4）物种形成。我们的研究结果表明，物种命运与其稀有性之间的联系是理解生物多样性变化的基础。然后我们展示了如何使用这种见解来量化以前认为影响生物多样性的机制的影响：（1）选择，（2）（生态）漂移，（3）移民和（4）物种形成。我们的研究结果表明，物种命运与其稀有性之间的联系是理解生物多样性变化的基础。然后我们展示了如何使用这种见解来量化以前认为影响生物多样性的机制的影响：（1）选择，（2）（生态）漂移，（3）移民和（4）物种形成。我们的研究结果表明，物种命运与其稀有性之间的联系是理解生物多样性变化的基础。