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The Debate on Determinants of Species Richness Author(s): Trevor Price Source: The American Naturalist, Vol. 185, No. 5 (May 2015), p. 571 Published by: The University of Chicago Press for The American Society of Naturalists Stable URL: . Accessed: 21/09/2015 10:05 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .

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vol. 185, no. 5

the american naturalist

may 2015

American Society of Naturalists Debate

The Debate on Determinants of Species Richness Trevor Price* Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637

Why are more species found in some places of the world than others? This question, so basic to ecology, has been surprisingly difficult to answer. But recent advances in our understanding of earth’s history and of phylogenetic relationships among species and their geographical distributions, as well as better, well-developed theory, have led to a continuum of more or less well-defined perspectives. At one extreme, the world is full to carrying capacity, so, for example, temperate areas can simply hold fewer species than tropical ones. At the other extreme, many more species could fit in everywhere, but, continuing with the example, temperate areas are constantly being subject to disturbance over all timescales, which slows species accumulation to a greater extent than in the tropics. While no one adheres to one or other of these extremes, we thought that a debate between proponents who lie toward different ends of this scale would be informative in laying out the groundwork for where we are and where to go next. The idea was to follow the style of the University of Oxford debate, which is famous among biologists for the intense confrontation it hosted in 1860 between Bishop Samuel Wilberforce (“Soapy Sam”) and Thomas Henry Huxley (“Darwin’s Bulldog”) on the Origin of Species. Our debate was held at the American Society of Naturalists meeting in Asilomar, California (January 2014), a conference specifically designed to bring together ecologists, evolutionary biologists, and others interested in bridging disciplines. The debate was entitled “This House Believes That Species Richness on Continents Is Dominated

by Ecological Limits,” with the word continent inserted because dispersal limitation is less of an issue for terrestrial species on continents than it is on islands. Following the Oxford format, the proponent and opponent of the motion were asked to speak for about 20 minutes, followed by a seconder from each side. Most of the 200 attendees at the meeting were present, despite the attraction of refreshments elsewhere. Much discussion ensued after the debate, without a vote being taken. Unlike Huxley versus Wilberforce, our debate was not heated, suggesting signs of synthesis. In consequence, we asked the debaters to prepare articles contrasting the alternative viewpoints. The essays are well worth reading for their points of agreement and disagreement and for where the same data are interpreted differently. There are surely creative analyses waiting to be done that might resolve some of these differences. But both sides agree on one important issue, which is that local communities may be far from equilibrium, regardless of whether regional species richness is strongly dependent on ecological factors such as productivity (D. L. Rabosky and A. H. Hurlbert) or largely independent of such factors (L. J. Harmon and S. Harrison). At local scales, Rabosky and Hurlbert note that succession and metapopulation dynamics place communities out of equilibrium. But how many more species could a relatively small region in which this local patch is embedded hold? I suggest, at least in some places, not many at all. Rabosky and Hurlbert perhaps have a more middling position, and Harmon and Harrison are on the other side. The debate continues.

* As the 2014 President of the American Society of Naturalists, Trevor Price organized an Oxford-style debate as part of the ASN’s stand-alone meeting in Asilomar, California. He then invited the participants to write up their positions for this special section, which he has edited for The American Naturalist. Am. Nat. 2015. Vol. 185, p. 571. q 2015 by The University of Chicago. 0003-0147/2015/18505-56020$15.00. All rights reserved. DOI: 10.1086/680858

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The debate on determinants of species richness.

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