Dimensions of ecosystem complexity: Heterogeneity, connectivity, and history

Biocomplexity was introduced to most ecologists through the National Science Foundation’s grant program, and the literature intended to introduce that program. The generalities of that literature contrast with the abstract and mathematical sophistication of literature from physics, systems theory, and indeed even of pioneering ecologists who have translated the concept intoecology.Thissituation leavesamiddleground, that isbothaccessible toecologists in general, and cognizant of the fundamentals of complexity, to bemore completely explored. To help scope thismiddle ground, and to promote empirical explorations thatmay be located there, we propose a non-exclusive framework for the conceptual territory.While recognizing the deep foundations in the studies of complex behavior, we take ecological structure as the entry point for framework development. This framework is based on a definition of biocomplexity as the degree to which ecological systems comprising biological, social and physical components incorporate spatially explicit heterogeneity, organizational connectivity, and historical contingency through time. These three dimensions of biocomplexity – heterogeneity, connectivity, and history – will be explored as axes of increasing complexity. Basing the description of spatial heterogeneity on either patch or continuous quantification, complexity of spatial structure increases as quantification moves from simple discrimination of patch typesandthenumberofeachtypetoassessmentofconfigurationandthechangeinthemosaic through time.Organizational complexity reflects the increasing connectivityof thebasicunits that control system dynamics. At the simple end of the axis, the functional connectivity between units is low, and the processes within a unit are determined by structures or other processeswithin that unit. At thehighest level of complexity along this axis, units in amosaic interact through fluxes of energy, matter, organisms, or information, and the structure and dynamics of the mosaic can be altered by those fluxes. Temporal relationships in the system range from direct contemporary ones to indirect and historically contingent ones. The influence of indirect effects, legacies, the existence of lagged effects, and the presence of slowly appearing indirect effects constitute increasing temporal complexity. This framework embodies some features of both the structural approach to complexity and the approach of complexity of explanations that we extracted from the literature. It leaves the issue of what levels of each axis result in complex behavior as an important question for further research. # 2006 Published by Elsevier B.V. avai lab le at www.sc iencedi rect .com journal homepage: ht tp : / /www.e lsev ier .com/ locate /ecocom * Corresponding author. E-mail address: [email protected] (M.L. Cadenasso). 1476-945X/$ – see front matter # 2006 Published by Elsevier B.V. doi:10.1016/j.ecocom.2005.07.002 e c o l o g i c a l c om p l e x i t y 3 ( 2 0 0 6 ) 1 – 1 2 2