A Comment on the Use of the Term Emergent Properties

The term emergent properties appears today with increasing frequency in ecological writings. It is a valuable term and, as will be discussed, applies to an important issue in ecology. It is also what may be termed a "pseudocognate" in that each individual who uses it feels that all readers share his own intuitive definition. The word nichle is another pseudocognate. We are all well aware of the difficulties which its use has generated. See the article by Hurlbert (1977) for a recent example. If emergent properties is not to be lost in the same semantic miasma into which nlichle disappeared, we must have early agreement on its meaning. Harre's (1972) explanation and definition are: "Many groups or aggregates have properties that are not properties of the individuals of which they are a collection. Such properties are called 'emergent' properties. ... Emergence: the property of the whole is produced by properties of the parts but is not qualitatively similar. " For ecologists, I suggest the following operational definition: "An emergent property of an ecological unit is one which is wholly unpredictable from observation of the components of that unit." The corollary is: "An emergent property of an ecological unit is only discernable by observation of that unit itself." A large proportion of the characteristics which are used in ecological studies represent statistical, algebraic, or categorical summarizations of the behavior of the components of the unit being studied--individuals in the case of populations, and species populations in the case of communities. For example, the age-class structure of a population is a result of the combined ages of all the individuals which make up the population. Similar remarks could be made about such other properties as the birth rate and death rate of a population. For communities, the species diversity index represents a summation of the proportional contribution of each of the individual species populations. In all these cases, the property is determined through an examination of the characteristics of the components of the ecological unit. Such properties are therefore not emergent, but collective. On the other hand, populations and communities may have characteristics which are expressions of the behavior of the population or community behaving as a unit. The response of Didiniium populations to the combined factors of starvation and increased density reported in the preceeding article is a particularly clear-cut example of a behavior of an ecological unit, a population in this case, which could not be predicted from a study of the component individuals. No amount of study or