COS 77-3 - Does connectivity enhance or decrease stability?  Effects of system size and scales of dynamics on variability in aquatic microcosms

Wednesday, August 10, 2011: 2:10 PM
10A, Austin Convention Center
Matthew P. Hammond and Jurek Kolasa, Biology, McMaster University, Hamilton, ON, Canada

Studies have shown increased connectivity in ecological systems to attenuate local variance (enhance stability) of populations, communities and ecosystem metrics.  However, connectivity can also decrease local stability when variance of the whole system increases via coherence/synchrony of patches or populations.  We investigated the mechanisms behind this apparent contradiction in multiple ecosystem and community variables by manipulating two aspects of connectivity; (i) the number of local patches connected and (ii) the degree of exchange among patches.  In particular, we hypothesized that increases in either number of patches connected and/or degree of interaction would attenuate variance differently for a range of variables (e.g. NEP, GPP, P/B, community biomass).  Connectivity was manipulated by connecting aquatic microcosms, containing three semi-stable communities (including several invertebrate species, phytoplankton and microbes), into arrays and adjusting connecting tube number (extent) or diameter over twenty weeks.


Preliminary results indicate that increases in connectivity can indeed either promote local stability or decrease global stability.  Specifically, the attenuating effect of connectivity on system variance depends on the variable or community component examined.  Whether local stability of a given variable is enhanced or compromised appears to hinge upon three closely related factors; (a) the relative “speed” or maximal rate of change for that variable, (b) the physical ease with which components (e.g. individuals, nutrients) are allowed to propagate though the system’s extent, and (c) the characteristic rate of temporal or spatial dynamics (e.g. turnover rate, patchiness) endowed by the community structure of a patch.  We will discuss how these intrinsic drivers of variability might be useful for predicting the multivariate effects of size-mediated phenomena, such as habitat fragmentation.

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