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.
Bibliographical noteFunding Information:
Mark Westoby, Thuy Nguyen, and Buck Trible, the other participants in our discussion group, whose thoughts shaped the current article. We are particularly indebted to Margaret Kosmala for creating and organising these discussions. Our paper would not have been possible without her effort. This manuscript has received thoughtful comments from several previous reviewers, and we are indebted to their work. In particular, we recognise Jeremy Fox, who reviewed the manuscript several times, along with James Rosindell and an anonymous reviewer who reviewed the text during an extremely stressful time. Helpful comments were provided by Mark Vellend, Steve Frank, Komei Kadowaki, Erol Ackay, Adrian Paterson, Bevin Brett and Robert Cruickshank. Images of rabbit and squirrel based on illustrations by Anthony Caravaggi (https://creativecommons.org/licenses/by-nc-sa/3.0/). All illustrations from phylopic (http://phylopic.org/).
© 2020, Springer Nature B.V.
- Evolutionary theory
- Price equation
- Theoretical ecology