Monday, August 6, 2007

PS 6-68: Influence of dispersal on disturbance and recovery dynamics in a marine benthic landscape

Carolyn J. Lundquist, Simon F. Thrush, and Judi E. Hewitt. National Institute of Water & Atmospheric Research Ltd.

In landscapes that represent a mosaic of patches in different states of recovery from disturbance, dispersal between patches will influence recovery and landscape-scale community responses to changes in the disturbance regime.  We model a mosaic patch landscape to illustrate how disturbance and dispersal interact to determine recovery and stability in a marine benthic community.  We simulate recovery of three marine benthic communities characterized by species with different population dynamics, chosen to represent realistic benthic community dynamics.  We vary the spatial extent and frequency of disturbance events which reduce the community to a pioneer state, assuming that communities age through a series of successional stages toward a mature or climax community.  Disturbance frequencies include realistic combinations of spatial and temporal extent, from small, frequent disturbances like ray pits, to large infrequent disturbances like hurricanes.  The relative importance of dispersal is demonstrated by varying the size of the local neighborhood through which colonists are available, i.e., the dispersal distance. The model predicts a profound effect of disturbance frequency on recovery dynamics, indicating functional extinction of later successional community stages under many combinations of temporal and spatial frequencies of disturbance. Communities were strongly dependent on dispersal for recovery, demonstrating rates of disturbance that are tolerable (i.e., did not result in functional extinction of mature climax communities) with respect to each dispersal distance.  System stability also decreased as dispersal distance decreased, exhibiting thresholds in disturbance for which even pioneer communities were unable to persist due to the dependence of recovery on minimum distances for dispersal and thus colonization. We demonstrate that the scale of dispersal, interacting with the disturbance regime, can lead to radical shifts in the ability of organisms to colonize patches and persist within the landscape.

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