OOS 80-4
Biology, chance, and environment: Three contrasting perspectives on community structure and composition

Thursday, August 13, 2015: 2:30 PM
340, Baltimore Convention Center
Stephen T. Jackson, DOI Southwest Climate Science Center, U.S. Geological Survey, Tucson, AZ

Determinants of community structure and composition have long been sought in three contrasting domains:  ecological interactions (‘biology’), random or contingent events and processes (‘chance’), and the physical environment, particularly climate (‘environment’).  Each has deep historical roots in ecology and natural history.  Biological explanations date explicitly to the 16th and early 17th Century natural history of William Derham, John Ray, and other naturalists, who sought evidence for natural theology in ecological balance.  Biological explanations proliferated in the 19th Century, and came to dominate in much of the 20th .  Ecological attributions to chance are most closely associated with H.A. Gleason in the 1920s, and with Andrewartha and Birch in the 1950s.  However, Darwin introduced the broader notion of historical contingency to natural history, and other and earlier naturalists attributed biogeographic patterns to historical events.  Travelers and naturalists long noted ecological and vegetational changes with latitude, and Georg Forster and Alexander von Humboldt systematized the relationships between climate and biota near the turn of the 19th Century.


Ecological explanations continue to fall into one of these three modes.  Biological explanations emphasize the Eltonian niche, and consider communities to be strongly structured by interactions among species.  Chance is at the heart of the neutral theory in ecology, with communities structured by random processes of dispersal, recruitment, and mortality.  Environmental explanations emphasize species’ physiological and demographic responses to the prevailing physical environment (i.e., the Grinnellian niche).  All three of these loci of explanation are necessary, but none are sufficient to explain community composition and structure.  Climate change and variability continually alter and redirect processes within all three loci to reshape community properties.  All three loci need to be integrated if ecologists are to provide accurate and useful forecasts of ecological responses to ongoing and future environmental change.