a b s t r a c tScientists use models to understand the natural world, and it is important not to conflate model and nature. As an illustration, we distinguish three different kinds of populations in studies of ecology and evolution: theoretical, laboratory, and natural populations, exemplified by the work of R. A. Fisher, Thomas Park, and David Lack, respectively. Biologists are rightly concerned with all three types of populations. We examine the interplay between these different kinds of populations, and their pertinent models, in three examples: the notion of "effective" population size, the work of Thomas Park on Tribolium populations, and model-based clustering algorithms such as Structure. Finally, we discuss ways to move safely between three distinct population types while avoiding confusing models and reality.Ó 2015 Elsevier Ltd. All rights reserved.
When citing this paper, please use the full journal title Studies in History and Philosophy of Biological and Biomedical SciencesWhat are the relationships among the populations that biologists postulate in idealized theoretical models, the populations they set up in experimental laboratories, and the populations they survey and sample in the wild? We describe three qualitatively different kinds of populations at the heart of distinct styles of scientific practice in ecology and evolution, viz., theoretical, laboratory, and field investigations. Distinguishing three types of populationsdtheoretical, laboratory, and naturaldprovides a useful lens for viewing both past and contemporary work in ecology and evolutionary biology.Three examples illustrate the value of distinguishing theoretical, laboratory, and natural populations: the concept of "effective" population size, the work of Thomas Park on flour beetle populations, and the use of model-based genetic clustering algorithms such as Structure. In keeping with the "Genomics and Philosophy of Race" theme of the special issue in which this article appears, our trichotomy can assist analyses of the implications of genomic studies for claims about the existence (or the non-existence) of human races. In the conclusion, we suggest ways to avoid conflating the three kinds of populations. Researchers can cycle through natural, laboratory, and theoretical populations, expressing genuine interest in each population type. Theoretical, laboratory, and natural populations also pertain to fields beyond ecology and evolution, including statistics.We analyze scientific practice. Although questions regarding realism and anti-realism, the concepteworld relation, and the general ontology of science lurk, our trichotomy is not intended as a rubric for determining how much a model does or does not correspond to reality. Admittedly, an overarching aim of population biology is to understand the complex structure and dynamics of populations "in the wild." Even so, the multiple ontologies of scientific practice are complexdarguably there is a world in a theoretical model (e.g., Morgan, 2012) or in an experimental system (e.g., Leon...