Historical Ecology: A New Approach to Studying the Evolution of Ecological Associations

Abstract

Historical ecology is presented as a complementary approach to evolutionary ecology. The prime distinction between the two approaches is the use of direct estimates of history in explanations by the former and of indirect estimates of history by the latter. Direct estimates of history are obtained by using phylogenetic systematics. They require analysis of many species simultaneously. Indirect estimates can be applied in individual cases and include such concepts as: (1) equating number of species in an ecological association with the age of the association; (2) equating the geographic range of a species with its age; and (3) equating the specificity of ecological interactions with the length of time species have been associated. Historical ecological methods have been applied in three general areas: (1) the historical context of geographic distribution patterns; (2) the historical context of ecological associations; and (3) the historical context of particular ecological life history traits. A unified quantitative approach allows historical ecological analysis for individual clades or aggregates of clades. Among the most interesting general conclusions that are forthcoming from the historical ecological perspective are those that differ from the evolutionary ecological view. These include: (1) ecological diversification lags behind morphological diversification historically; (2) degree of specificity is not a thoroughly reliable indicator of the age of an association; (3) resource tracking models of coevolution seem to include unacceptable assumptions; and (4) maximum competition scenarios are indistinguishable from random association scenarios. Future studies promise to be fruitful. A number of fundamental and general questions have held the attention of ecologists for over a century. Why are species distributed in the manner they are? Why are certain species associated with each other ecologically, and how long have such associations existed? And, why do certain species have the ecological life history traits they do, and under what circumstances did those traits emerge? In the past 125 years, biology has operated under an evolutionary paradigm, a stance that I think has been undeniably productive. The search for causal mechanisms responsible for observed attributes has concentrated on evolutionary, that is historical, mechanisms. In ecology, this has led to the emergence of the field called evolutionary ecology. In presenting what I will call historical ecology