Document: SEB-3-514-202

Effects of enrichment on a 3-level food chain with omnivory.

DIEHL, S.* and M.FEISSEL

University of Munich, 80333 Munich, Germany ¹

Abstract:
We investigated enrichment effects on a system of a resource (R), an intermediate consumer (N), and an omnivore (P, feeding on R and N) using a general model. We then tested the relevance of four major predictions to a laboratory system of bacteria (= R) and the ciliates Tetrahymena (= N) and Blepharisma (= P): 1) Stable persistence of all three species is only possible, if N can persist on R alone at lower levels of enrichment than can P. This was true for the ciliate system. 2) N may facilitate or inhibit P. Enrichment may revert the effect of N on P from facilitation to inhibition. Tetrahymena always facilitated Blepharisma. Facilitation was highest at low enrichment. 3) Along an enrichment gradient, up to four regions of invasibility and coexistence of N and P may exist. At low enrichment, only R persists. At somewhat higher enrichment, R coexists with N. At intermediate enrichment, either N and P can coexist or either consumer excludes the other. At high enrichment, P can subsist on R alone and N may be excluded. The persistence pattern of Tetrahymena and Blepharisma conformed largely to this scenario. 4) Where all three species coexist stably, R always increases and N always decreases with enrichment. This was true for the ciliate system. The results caution that patterns of trophic level abundances along enrichment gradients predicted by food chain theory are not to be expected in systems with significant omnivory.

Keywords: ciliate,enrichment

This abstract is being presented at: 2:45 PM in session:
Oral Session #11: Trophic Cascades.