Abstract
A number of ecologists have put forward various proposals that ecology has laws, yet they have not explicated what role laws play in ecological explanations. Marcel Weber (1999), Lev Ginzburg and Mark Colyvan (2004) correct this deficiency and also make their case for laws of ecology: the principle of competitive exclusion and Malthus’s law of exponential growth respectively. According to Weber, the principle of competitive exclusion explains phenomena (1) by direct application, or (2) by describing a default state from which observed phenomena deviate and mechanisms are called to account for the discrepancy. Independently of Weber, Ginzburg and Colyvan articulate a role similar to (2) for Malthus’s law. I argue that Weber’s proposition of explanation by direct application is not consistent with Gause’s account of “bottle experiments” that he uses to support it and does not do justice to ecologists’ explanatory practice. To address these problems, I articulate an alternative account of explanation by direct application—the covering-law model—based on a proposal by Elgin and Sober (2002) and show that even in this proposal mechanisms play a key explanatory role. I also demonstrate how the covering-law model accounts for how Malthus’s law can explain by direct application and for its role of descriptor of a default state. Finally, I argue that the views on laws as components in covering-law model explanations or as descriptors of default states do not give sufficient attention to the prominent explanatory role of mechanisms and to the demanding task of identifying and describing them, and ought to be corrected.
Highlights
In contrast to the students of physics, students of ecology are not taught that their science offers an unequivocal set of laws that should be used to explain and predict ecological phenomena
It is more appropriate to conceive of the explanation of competitive exclusion not in terms of application of a law that produces an effect by causal necessity, but in terms of the fit between a model incorporating that law and experimentally obtained data, plus an empirical study of the factors limiting growth
That laws of ecology play a central role in explanations by direct application or by describing a contrast class does not minimize the role of mechanism descriptions
Summary
In contrast to the students of physics, students of ecology are not taught that their science offers an unequivocal set of laws that should be used to explain and predict ecological phenomena. In addition to Malthus’s law, Berryman (1999, 2003) showed that ecology uses laws that cover intraspecific cooperation, competition, predator-prey interaction, and limiting factors acting on a population, such as Liebig’s law of the minimum He is one of the few that claims that these laws are not specific to ecology, but are reformulations of principles from general systems theory, physics and chemistry. The goal of ecologists to show that ecology has genuine laws is typically tied to their concern to demonstrate that it is a science on a par with physics and not just a historical investigation This endeavor is incomplete because it does not show how the identified laws, or regularities, perform their work in explanations and predictions. In light of (i), (ii) and (iii), I conclude that the case for laws in ecological explanations makes the case for the centrality of mechanisms in ecological explanations, and further work should be directed toward their analysis and classification
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