From Populations to Ecosystems: Theoretical Foundations for a New Ecological Synthesis

Research into the potential consequences of changes in biodiversity on ecosystem functioning and on the delivery of ecosystem services has been prominent in fostering cross-fertilization between community ecology and ecosystem ecology during the last decade. This research has shown that biodiversity loss can have adverse effects on the average rates of ecosystem processes such as primary production and nutrient retention in temperate grassland ecosystems (chapter 3). Most of the evidence for this conclusion, however, comes from relatively short-term theoretical and experimental studies under controlled conditions, which do not address the long-term sustainability of ecosystems. The last chapter (chapter 4) extended this body of theory to more complex food webs and interaction webs but focused again on their functioning under equilibrium conditions.

It is of considerable interest to further understand how biodiversity loss will affect long-term temporal patterns in ecosystem functioning. Will ecosystem functional properties and services become more variable and less predictable as species diversity is reduced? Are species-rich ecosystems more capable of buffering environmental variability and maintaining ecosystem processes within acceptable bounds than species-poor ecosystems? These are fundamental questions that have considerable implications for our ability to understand, predict, and manage ecosystems in a changing world. In this chapter I synthesize recent theory that seeks to answer these questions.

As a matter of fact, these questions address in a new form a longstanding debate in ecology about the relationship between the complexity and stability of ecological systems. The study of this relationship has had a long and controversial history (May 1973; Pimm 1984, 1991; McCann 2000). It is therefore useful to understand the ins and outs of this debate before attempting to provide fresh answers to these questions. Accordingly, I first briefly summarize the central components of this debate to identify

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