Ashok Kumar, Asst. Manager En-Vision Enviro Engineers Pvt. Ltd. Surat-395002, Gujarat (India).
Like the emperor who had no clothes, generally ecology is criticized as lacking the theoretical adornments of the physical sciences. Indeed, for many years ecologists have decried the fact that we have no general theories. A theory is a framework or system of concepts and propositions that provides causal explanations of phenomena within a particular domain. The purpose of a theory is to provide a set of linkages for observations and lower level models or theories of those observations. Confusion exists because the term theory is used in reference to a variety of kinds of systems at different levels of specificity. Moreover, the nature of theory differs at each level. At the broadest level, a general theory consists of an entire domain of science and a set of fundamental principles e.g. theory of evolution. A general theory does not make specific predictions. Rather, it provides the scaffolding on which the components of more specific, constituent theories are assembled and integrated. It exposes assumptions that are sometimes hidden at the level of models or constituent theories and identifies areas that are ripe for theoretical development. In addition, it provides the interconnections that link constituent theories to each other. A mature or fully developed general theory enhances understanding at the broadest of levels and facilitates prediction and forecasting via well articulated models and constituent theories. At the intermediate level are constituent theories, which set boundaries and identify parameters for particular interest, guiding model development. Constituent theories can overlap in domain and differ in scope. Depending on the form and domain of a constituent theory, it may make no predictions or it may make qualitative predictions. Most important, a constituent theory unifies a set of interrelated models. A general theory consists of a domain plus a set of fundamental principles. Fundamental principles are broad statements about empirical patterns and the processes that operate within a domain.
Seven Fundamental Principles
- Organisms are distributed in space and time in a heterogeneous manner. [Inclusionary Rule]
- Organisms interact with their abiotic and biotic environments. [Inclusionary Rule]
- The distributions of organisms and their interactions depend on contingencies. [Exclusionary Rule]
- Environmental conditions are heterogeneous in space and time. [Causal Rule]
- Resources are finite and heterogeneous in space and time. [Causal Rule]
- All organisms are mortal. [Causal Rule]
- The ecological properties of species are the result of evolution. [Causal Rule]
The first fundamental principle, the heterogeneous distribution of organisms, is a refinement of the domain. It encompasses the basic object of interest and its most important property. The heterogeneity of distribution is one of the most striking features of nature. All species have a heterogeneous distribution at some, if not most, spatial scales. Perhaps, the origins of ecology as a discipline and the first ecological theories can be traced to its recognition. This heterogeneous distribution is both caused by and a cause of other ecological processes. The fundamental principles are not independent causal mechanisms; rather, the mechanisms that they encompass interact.
The second fundamental principle; interactions of organisms, includes within it the vast majority of ecological processes responsible for heterogeneity in time and space. Many definitions of ecology are equivalent to this principle. Within this principle, particular interactions that are part of constituent theories act to unpack the general theory.
The third fundamental principle, contingency, represents either the inclusionary rule or the exclusionary rule, depending on views of the history of theories in ecology. Since that time, recognition of the importance of contingency in all ecological processes has increased steadily and now appears in a wide variety of constituent theories and models. Contingency is an important cause of the heterogeneous distribution of organisms, both at very large extents of time and space e.g. a particular species arose on a particular continent and at very small extents e.g. a seed lands in one spot and not another. We speculate that general theories of all domains include some version of this principle e.g. genetic drift in evolution; quantum theory in physics. Thus, it might be considered fundamental to all scientific theories. This principle demonstrates that the decision to include a fundamental principle and the type of rule that is the basis for inclusion are not always clear and may be subject to debate by scientists, historians and philosophers.
The fourth fundamental principle, environmental heterogeneity, is a consequence of processes from the domains of the earth and space sciences. For example, seasonal variation in temperature is the result of orbital properties of the Earth, whereas a variety of geophysical processes create heterogeneity in environmental stressors like salt e.g. wave action near shores) or heavy metals e.g. geologic processes that create differences in bedrocks. It is beyond the scope of this paper to detail all of those processes and their domains. Indeed, this principle encompasses many constituent theories and contains a broad class of underlying mechanisms for the heterogeneous distribution of organisms. As with the second principle, particular mechanisms pertain to particular constituent theories. Again, the fundamental principle captures a wide range of theories and mechanisms so as to provide a unifying framework.
The fifth principle, finite and heterogeneous resources, is again a consequence of processes from the domains of the earth and space sciences. Although variation in resources is similar to variation in environmental conditions, a fundamental distinction is the finite nature of these resources. Unlike an environmental condition, a resource is subject to competition. For example, seasonal variation in light and temperature are caused by the same orbital mechanisms, but light is subject to competition e.g. one plant shades another, whereas temperature is a condition and not subject to competition. This distinction in the nature of environmental factors with regard to competitive processes can result in very different ecological outcomes e.g. patterns of diversity in plant communities. Whether a particular environmental factor is a condition or a resource can be context dependent. For example, water is sometimes a resource subject to competition e.g. plants in a desert and sometimes a condition like fish in the ocean.
The sixth fundamental principle, the mortality of organisms, is the result of processes that come from the domain of organismal biology, physiology and development. By mortal we mean that no organism is invulnerable, i.e. any organism might die as the result of predation, stress or trauma. We do not mean by this principle that all organisms senesce. The senescence of organisms is a narrower version of this principle that would apply to particular constituent theories. Although the majority of multicellular species apparently senesce, this has not been demonstrated for some multicellular species. We are not aware of an articulated theory of development or physiology that predicts the necessity of or conditions for senescence, but suspect that it could be accomplished given current knowledge of organisms. We will let philosophers argue whether a bacterium that splits into two represents a single, immortal organism or (our position) the end of one individual and the creation of two new individuals. This fifth principle, either in the more general version of vulnerability or in the more narrow version of senescence, forms the basis of a large number of constituent theories concerning phenomena as wide ranging as life histories, behavior, demography and succession.
The seventh principle, the evolutionary cause of ecological properties, is the result of processes that derive from the theory of evolution. The inclusion of evolution within ecological thinking was an important outcome of Modern Synthesis. Although evolutionary thinking about ecological processes goes back at least to Darwin in 1859, evolutionary thinking had been infusing ecology more widely at least since the 1920s and its widespread acceptance occurred primarily in the latter half of the 20th century. The acceptance of this principle led to such disciplines as behavioral ecology and population biology and the termination of the Clementsian super organism theory.
Scope of Fundamental Principle
These fundamental principles are necessary and sufficient to support a general theory of ecology. One or more of the propositions of each constituent theory of ecology can be shown to be a consequence either of the fundamental principles of ecology or of principles from other domains. A proposition of a constituent theory can be a consequence of a fundamental principle in three ways. First, a proposition may be a member of a class defined by a fundamental principle. For example, competition, a type of biotic interaction (principle 2), plays a key role in plant succession. Second, a constituent theory can identify, define or refine particular patterns or mechanisms identified in a fundamental principle. For example, variation in dispersal distance, a form of contingency (principle 3), is a component of population dynamic theory. Third, a proposition in a constituent theory might be derived formally from a fundamental principle e.g. in food web theory, rules governing food chain length derive from aspects of the second law of thermodynamics. In the next section, we examine further the relationship between fundamental principles and the propositions of constituent theories. To the extent that the fields of ecology can be characterized as a collection of related or overlapping constituent theories, these principles provide the scaffolding for a mature and fully developed theory that applies to all sub disciplines of ecology. The general theory establishes relationships among constituent theories. Linkages occur when constituent theories are derived from one or more of the same fundamental principles. Constituent theories that share fundamental principles must be consistent with each other. If they are not, one or more of those theories may require revision. Some of the propositions may be the consequence of theories in other domains. To be a constituent theory within the domain of ecology, at least one of its propositions would have to be a consequence of the fundamental principles of the general theory of ecology. The fundamental principles do not include ecological entities or systems, such as populations, communities or ecosystems. Rather, those entities are a consequence of the mechanisms embodied by the principles. A population and its properties are the consequence of organisms of a single species inhabiting a particular location (principle 1) and interacting with each other (principle 2). Philosophers refer to this derivation of one object from other principles as ontological reduction. Ontological reduction is favored because it results in theory simplification and eliminates ontological primitives that require special explanation.
The fundamental principles do not specify mechanisms. It is the function of constituent theories to explicate the types and appropriateness of particular mechanisms e.g. interactions such as predation, herbivory, competition, mutualism or parasitism might be mechanisms within theories of community structure. Such lack of specificity has two causes. The first relates to the diversity of environmental and historical circumstances which determine the importance of any suite of mechanisms affecting the properties of ecological systems. Any attempt to enumerate the circumstances in which particular biotic interactions dominate would create an unwieldy theory. The second cause relates to the history of ecology, which can be characterized as the accumulation of mechanisms about and an appreciation for, the complexity of ecological systems. Rather than debates about the existence of mechanisms, disagreements mostly have been about their relative importance, a dispute that occurs at the level of constituent theories, rather than at the level of the universal presumption.