Introduction

There has been a controversy raging for the last several decades over whether diverse ecosystems are more stable than simpler ecosystems. Initially, observations by ecologists on the response of complex and diverse ecosystems lead to the conclusion that ecosystems with more links and more pathways were more resistant to change from perturbations in the amount of any one species. The generality of this conclusion was challenged with models that showed that there was no mathematical backing that would prove that diverse systems were inherently any more stable than simpler systems. More recently, specific field examples and more sophisticated models show that in some situations diversity does lead to types of stability.

In a world where many of our ecosystems are stressed, it is very important to understand whether the complex and highly diverse natural systems are better able to handle continued stress than the simplified ecosystems that we see as a result of human interaction. Is a natural meadow with a variety of species actually more stable than a fertilized and plowed agricultural pasture? Is a forest with a mosaic of trees and undergrowth able to withstand changes in climate better than a plantation of fast growing pine trees? Are eutrophic urban lakes more resistant to invasion by nuisance species than a more natural, and less productive, lake ecosystem?

We are going to explore this problem with a case study that focuses on the ability of natural grassland ecosystems to deal with drought. We will look at this system using a "network" framework that will describe the network as a whole, integrated system.

Resources

There are three parts to this case study:

1. A copy of the case study on the link between biodiversity and ecosystem function will be handed out in class.

2. A more complete description of the "network" framework or view of a problem -

http://web.pdx.edu/~rueterj/courses/viewers/network/network.html

3. The assignment you are to turn in -

http://web.pdx.edu/~rueterj/courses/esr101/assignments/unit2_app.html