PARENT SESSION
Oral Session #87: Ecosystem Ecology.
Presiding: B. Currie
Thursday, August 8. 1:00 PM to 3:45 PM. Graham Meeting Room, TCC.

Quantity defies quality - A new approach to food web analysis.

BANASEK-RICHTER, CAROLIN^*,1, BERSIER, LOUIS-FELIX^1,2, CATTIN, MARIE-FRANCE¹, ¹ University of Neuchatel, Neuchatel, Switzerland² Swiss federal Institute of Technology, Lausanne, Switzerland

ABSTRACT- Food web descriptors have been devised to extract ecologically meaningful information from food web matrices, e.g., vulnerability, the average number of predators per species. Analyses of collections of webs based on these properties have revealed regularities that fostered the formulation of models of food web structure. However, it has been shown that most of these binary descriptors are highly sensitive to varying levels of sampling effort. The main problem is that webs described extensively include trophic links of highly uneven magnitude, with typically few important links and a wealth of weak ones; with binary descriptors, the same weight is given to all trophic interactions. To overcome this problem, food webs should be described and analysed quantitatively. Consequently, we propose a suite of quantitative food web descriptors, which are built on information theory indices. We define descriptors intended to have a similar meaning as the classical binary indices. The quantitative counterpart of the link density property serves as an example of how these descriptors were devised. We demonstrate that quantitative properties are less sensitive to sampling effort than qualitative ones. Quantitative food webs are used to illustrate how these descriptors yield new insights into food web structure.

KEY WORDS: connectance, sampling effort, Shannon index, community structure