November first, 2013 at 11.00hr there is a colloquium on
Tipping points in food web stability
By Cassandra van Altena, together with Jan Kuiper from NIOO.
Shallow lakes are typically in one of two contrasting states: a clear state with submerged macrophytes, or a turbid state dominated by phytoplankton. Between these two alternative states, rapid regime shifts (or catastrophic transitions) can occur, often associated with non-trophic interactions, e.g. (interference) competition for light and nutrients between macrophytes and phytoplankton. Trophic interactions, however, and especially the strength and patterning of these interactions, are more generally considered to be an important feature regulating the state and functioning of ecosystems. Our goal was to investigate if specific patterns in trophic interactions, in terms of interaction strengths, are related to the two alternative states. We modeled a lake food web along an eutrophication axis, focusing only on trophic interactions by using the ‘community matrix’ approach. We here show that the pattern in interaction strengths differs between the two alternative states, and that food web stability decreases gradually preceding a regime shift. Our results indicate that the structure of the food web, either expressed in terms of interaction strength patterning or the resulting food web stability, can serve as an ‘early warning signal’ of an impending regime shift in lakes.
All are cordially invited.