Book review: Species distribution models for species distribution modellers

Abstract

ISSN 1948‐6596 news and update book review Species distribution models for species distribution modellers Ecological niches and geographic distributions, by Townsend A. Peterson, Jorge Soberon, Richard G. Pearson, Robert P. Anderson, Enrique Martinez‐Meyer, Miguel Nakamura & Miguel B. Araujo, 2011, Monographs in Population Biology 49, Princeton University Press, 328 pp. $49.50 (paperback) ISBN: 078‐0‐691‐13688‐2; http://press.princeton.edu/ The statistical analysis of apparent environmental preferences of plants and animals is enjoying much attention in the ecological literature. Varia‐ bly known in the early days as “habitat suitability modelling” and later “niche modelling”, it is cur‐ rently most often referred to as “species distribu‐ tion modelling” (SDM). Given the extreme meth‐ odological dynamics of early research fields, it is not surprising that it took around two decades before the first synthesising book on the topic was published (Franklin 2009). Apart from some edited books of varying quality, the book by Town Peter‐ son and six co‐authors is the second book‐length synthesis. The authors develop a theoretical framework as the foundation for their review of methods and applications, which leads to a sub‐ stantial expansion beyond the mere methodologi‐ cal points usually receiving most attention in this field. The book is composed of three parts. “Theory” first defines most phrases commonly used in niche modelling, including a historical re‐ view of niche concepts. It then formalises the “BAM” concept proposed by the second author in an earlier publication. BAM stands for biotic inter‐ actions, abiotic conditions and migration as key determinants of the presence or absence of a spe‐ cies in geographic space. In this book, the BAM framework serves as an Ariadne's thread for all further discussions, from data quality to the simu‐ lation of dispersal. BAM is based on the premise that a species can occur in an abiotically suitable site only if it can migrate (disperse) there and if negative biotic interactions (e.g. competition, pre‐ dation) do not preclude its existence. The funda‐ mental challenge of SDMs is that available data on species' distributions are an unknown proportion of the species' fundamental niche and hence an intersection of B, A and M. Mathematically, B, A and M are sets of environmental conditions and the intersections are described by set theory. The authors use set theory to clarify different niche definitions and synthesise discussions on what SDMs actually analyse. While mathematically rig‐ orous, this framework is tedious and over‐defined. The usefulness of any concept suffers when it be‐ comes too vague (thus lacking stringency) or too precise (narrowing the range of cases it can be applied to). In this case, the book features a 7‐ page appendix with definitions of the various sym‐ bols representing elements of BAM sets. At the same time, a 12‐page glossary seeks definitional clarity but lacks the relevant BAM‐based defini‐ tions. Since the book also has no index, it is nigh impossible to discover the set‐theoretical defini‐ tion even of important terms such as “scenopoetic niche”. Here the clarity sought by part 1 evapo‐ rates because of a lack of editorial completeness. More problematically, the authors reveal that the BAM framework has profound weaknesses, such as a possibly fundamentally inestimable set B (p. 38), or the observation in coarse‐scale data that biotic interactions are largely irrelevant for distri‐ butional patterns (p. 40). With respect to M, dis‐ persal processes, the book remains completely (and incomprehensibly) silent. Also, the frame‐ work does not consider within‐species variability of niches, nor adaptability (physiological or evolu‐ tionary sense) of individuals and populations. Overall, the conceptual value of the BAM frame‐ work is, in my opinion, questionable. Part 2, “Practice”, reviews data and statisti‐ cal methods related to SDM. While covering es‐ sentially the same ground as Franklin (2009), this part is clearer in what the actual target of an analysis is, profiting from the BAM framework of part 1. “Practice” touches on many important sta‐ tistical and interpretational points of SDMs (e.g. whether actual habitat preferences of a species are detected, or only those different from avail‐ frontiers of biogeography 4.2, 2012 — © 2012 the authors; journal compilation © 2012 The International Biogeography Society