COLONIZATION AND SUCCESSION OF STREAM COMMUNITIES IN GLACIER BAY, ALASKA; WHAT HAS IT CONTRIBUTED TO GENERAL SUCCESSIONAL THEORY?

Succession is a key concept in ecology and its study has generated well known and highly debated theories on mechanisms by which communities are assembled, including the relative role of deterministic and stochastic pathways. The contribution of stream ecosystems to general successional theory, particularly primary succession, has been extremely limited due to the lack of long-term studies on stream channels at a large enough spatial scale. We suggest that the study of succession in streams in Glacier Bay, southeast Alaska where rapid ice recession has occurred may offer one of the few examples of the tolerance model as a major mechanism of macroinvertebrate community assembly; the majority of macroinvertebrate taxa, with the exception of the cold-tolerant first colonizers, have persisted within the community following colonization. Relative abundance has however changed markedly over time. In contrast, a meiofaunal component of the invertebrate community exhibited poor persistence with numerous extinctions. Stream successional processes may be unique in being closely linked to, and markedly influenced by, processes in other ecosystems, particularly the terrestrial environment. Stream succession in Glacier Bay also demonstrates differences from terrestrial succession in the number of reset mechanisms that can cause communities to significantly shift to an earlier successional stage or at least allow the persistence of early colonizers, including the loss of flow buffering lakes, floods and redd construction by spawning salmon. We suggest in these streams community assembly initially follows deterministic pathways due to the overriding influence of water temperature but as temperatures exceed 7 degrees C then stochastic mechanisms influence succession and community assembly. Copyright (C) 2009 John Wiley & Sons, Ltd.