Time as an ecological dimension: the historical threads in ecological thinking in the 19th and 20th centuries

Background/Question/Methods

Time has been treated by ecologists in three contrasting and often non-overlapping ways:  steady-state, changing environment, and historical contingency.  Steady-state, where time is perceived as an axis along which ecological processes culminate in some static or dynamic equilibrium, has long been central to ecological thinking in such diverse realms as ecological succession, population and community dynamics, ecosystem development, and evolution.  Steady-state treatment of time has a strong theoretical and conceptual framework, owing in part to mathematical tractability and in part to analogies of ecological processes with simple physical, chemical, and physiological processes.  Changing environment has roots in 19^th century development of historical geology and paleontology; environmental changes ranging from climate variation of recent centuries and millennia to deep-time changes in climate, sea-level, and continental configurations have been elaborated in numerous paleoecological and other geohistorical studies of the past century.  Paleoecologists in the 20^thcentury, for instance, provided diverse case studies and regional syntheses of ecological changes driven by environmental changes.  With rare exceptions, paleoecological studies were strongly empirical, and little synthesis was attempted between steady-state and environmental-change views.  Historical contingency traces back to Darwin’s evolutionary thinking, emerging more explicitly in arguments by Gleason and others concerning alternative successional trajectories and endpoints. 

Results/Conclusions

Historical contingency gained traction in ecology in the late 20^th century, with acceptance of Gleason’s insights and recognition of historical-legacy effects following disturbances and climate episodes.  At the same time, renewed focus among ecologists on the physical environment, particularly climate, as an ecological determinant led to attempts at embedding steady-state processes within a context of environmental change, and to fusion of these ideas with historical contingency.  Conceptual synthesis remains incomplete.  Particular challenges, both conceptual and empirical, include linking ecological processes and dynamics across temporal scales, and disentangling cross-scale interactions in space and time.  These are not easy challenges, but confronting them should open opportunities for advancing the science of ecology and for informing resource management and policy in a time of rapid environmental change.