The stability-diversity-complexity debate of theoretical community ecology: a philosophical analysis

The stability-diversity-complexity debate has persisted as a central focus of theoretical ecology for half a century. The debate concerns the deceptively simple question of whether there is a causal relationship between the complexity and/or diversity of biological communities and their stability. Historical analysis of the debate shows that conflicting claims different studies seem to support indicate an underlying lack of conceptual clarity about the three concepts. The problem of defining these concepts is thus at the debate's core, and finding adequate definitions is one objective of the dissertation. The absence of consensus about how ecological stability should be defined, for instance, reflects uncertainty about what properties of a community should be considered its stability, resulting in studies that suggest conflicting conclusions based on different senses of the concept. For this reason, some philosophers have claimed that proposed definitions of ecological stability are incompatible and that the concept is itself problematic. I argue, however, that three unproblematic concepts are jointly sufficient and individually necessary for ecological stability. Another issue concerns whether the mathematical concept of Lyapunov stability utilized in physics adequately defines ecological stability, as many theoretical ecologists assume. I argue that it does not because it cannot adequately represent perturbations against which community stability must be assessed. The project of defining these particular concepts raises a more fundamental issue: what adequacy criteria should definitions in general satisfy? Against the prevailing view that definitions must preserve meaning exactly, I argue there are good reasons to require definitions preserve only similarity of meaning with the defined concept. Following Carnap, I call such definitions 'explicative'. The prevailing view is clearly unproblematic if the definitional goal is simply to clarify the actual meaning of concepts. It is problematic, however, if the objective is to provide normative guidance about concepts. Concepts play an indispensable role in the acquisition of knowledge. As such, definitional modifications of our conceptual apparatus should be evaluated by epistemic advantages or disadvantages they procure. I argue the advantages afforded by an explicative definition --such as enhancing precision, testability, theoretical unification, etc.-- justify forgoing strong similarity with the concept being defined.