The Time is Ripe for General Theory in Community Ecology

The state in which the science of community ecology finds itself has been proclaimed a mess more than once. That such assertions might be hard to face for many of us working in that field is one thing; but to be fair, it is undeniable that the pure amount and disparity of different frameworks, concepts, and theories in community ecology, and underlying fields such as population ecology, are overwhelming and perplexing and do not seem to do justice to the scientific goal of providing a general theory of how populations, and consequently ecological communities, evolve and behave. Such a “real” theory should provide a system of axioms from which one can deduce consequences and should be both explicative (i.e., explaining observed patterns) and predictive (i.e., predicting results of situations not yet observed). In this sense, the theory should generate testable hypotheses. The Theory of Ecological Communities (Vellend) and Theory-Based Ecology: a Darwinian Approach (Pásztor et al.) attempt such a generalization, although in quite different ways. Vellend does a tremendous job, and accomplishes for the field of community ecology what few have attempted, and even fewer, if any, have achieved. The volume puts together most (because all is impossible) of the separately treated community ecological theories and concepts and boils down the myriad of suggested and formalized processes connected to community ecology into 4 main underlying pillars, which Vellend calls “high-level processes”: speciation, dispersal, drift, and selection. As he lays out in the introductory chapter, this idea is strongly based on similar concepts in population genetics and inspired by other authors who have perceived these conceptual parallels. Although many ecologists will very probably disagree on the relevance and importance of the devised high-level processes, to synthesize community ecological theory as proposed in the book is a great and worthwhile achievement. Moreover, it is up to all community ecologists to prove whether any of the 4 high-level processes can be omitted and which ones are most important. However, this is not going to be an easy task. And, the book could be criticized for taking a big broom and sweeping all the separated, system-contiguous, and scale-dependent theories of community ecology under 4 big rugs, so that in the end the effort could have no effect on one’s daily scientific work with one’s pet system under one’s pet theories. This would be a justified criticism but for the 3 chapters toward the end of the book in which Vellend presents existing empirical evidence on how high-level processes are shaping communities. This evidence is summarized in tables for each of the processes that contain potential caveats and challenges. Together with the last 2 chapters, in which the author provides his view on the what and why of future research in community ecology, approximately half the book is packed with ideas for testable hypotheses and predictions. Given the density and complexity of the matter, it is astonishing that Vellend manages to communicate his ideas with an absolute minimum of mathematical formulizations (i.e., almost none). Instead, he provides computer code (in R language) to demonstrate the application of his 4 principles. With its overall plain language and clear prose, his book is excellent material for preand postgraduate students. For the first time, Vellend offers this target group a fair chance of grasping the complexity that is community ecology because he connects and synthesizes a mountain of seemingly unrelated concepts and theories. In this regard, the table in chapter 5 is an invaluable overview of theories in community ecology, new and old, and how they connect to the proposed high-level processes. After so much praise, a few critical points also seem legitimate, although we emphasize these points do not take away from the overall positive impression this book made on us. Because it is concise and focuses on the necessary, the book cannot serve as a comprehensive introduction to all the reviewed theories. Although it is a great starting point, a reader not familiar with a particular theory will need to go to the original references (which are available in the reference list of the book and cited appropriately throughout the text). The review of the literature in chapters 8–10 is a subjective, narrative review, not a systematic one. Thus, probably every experienced reader will find some points to disagree with the author’s statements and conclusions or will be unsatisfied by the effort made to review the literature concerning a specific point. Although we think the presented simulation