Dr L.D.J. (Lothar) Kuijper

Room: B154
Phone: 020-4447246
Email: kuijper@bio.vu.nl
Project: Role of food web structures
Publications:

The Role of Food Web Structures in the Dynamics of Ecosystems

Introduction

Ecosystems can be regarded as complex dynamics systems. Some of them consist of only a few species, but most are incredibly large and very difficult to get a grip on. In spite of decades of research in field and laboratory, the reaction of even the simplest of ecosystems upon changes in environmental conditions is still largely unknown. Ecological problems, such as global warming or the hole in the ozone layer, have forced us to put more concentration to the understanding of dynamic behaviour of ecosystems.

Aim of Study

The aim of this study is to investigate whether a simple model, based on a few basic assumptions, can explain commonly found characteristics of ecosystems. Two issues are of main interest:
  1. Complexity vs. diversity; can a higher diversity of species stabilise an ecosystem?
  2. Paradox of enrichment; what are the influences of environmental conditions on species diversity?

Research

A number of simple ecosystems will be modelled and these models will be analysed. The ecosystems are modelled using the DEB-theory of Kooijman (Dynamic Energy Budgets). The theory assumes that nutrients are assimilated and added to generalised reserves. From these reserves, the costs for structural maintenance, growth and reproduction are paid.

First, long term behaviour of ecosystems with increasing complexity (see figures) will be investigated, using a chemostat model and simple hyperbolic functional responses. The models will be analysed using bifurcation analysis, with the throughput rate and food density in the supply as bifurcation parameters. This will be done using advanced computer software (AUTO, LOCBIF, CONTENT).


Food chains of increasing complexity, to be modelled in a chemostat system model.

Later on, systems in batch cultures will be examined. These systems are open for energy and closed for mass. Real ecosystems can often be regarded as batch-alike systems. For this reason, a batch-culture model has a more evident connection to real ecosystems than a chemostat model. In a batch system, mass conservation requires an appropriate description of nutrient cycling. Decomposers are added to the model. In the advanced DEB-theory, the nutrient uptake and release of an organism is governed by a number of Synthesising Units (SU's). SU can be regarded as enzyme complexes that link substrate concentrations in the medium to assimilation and cellular processes to reserve density. In the course of the study batch cultures of increasing complexity will be modelled.

During the research, the coupling of the results to their ecological meaning has a high priority. It will be attempted to maintain a high level of co-operation with experimental ecologists.