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Darwin chose the metaphor of a ‘tangled bank’ to conclude the ‘Origin of species’. Two centuries after Darwin's birth, we are still untangling the complex ecological networks he has pondered. In particular, studies of food webs provide important insights into how natural ecosystems function (Pascual & Dunne 2005). Although the nonlinear interactions between many species creates challenges of scale, resolution of data and significant computational constraints, the last 10 years have seen significant advances built on the earlier classic studies of Cohen, May, Pimm, Polis, Lawton and Yodzis (May 1974; Cohen 1978; Pimm 1982; Briand & Cohen 1984, 1987; Yodzis 1989; Cohen et al. 1990; Pimm et al. 1991; Yodzis & Innes 1992; Yodzis 1998). These gains stem from advances in computing power and the collation of more comprehensive data from a broader array of empirical food webs.
Increasingly, environmental disruption unravels the tangled bank (Vitousek et al. 1997). The authors of the papers collected in this synthesis were specifically requested to examine how studies and models of food webs can inform the management of natural ecosystems. A common question is what makes food webs collapse? Several authors in this synthesis also describe what food-web studies have told us about the restoration of natural ecosystems and how species composition and interactions affect the provisioning of ecosystem services.
If our understanding of food webs is to have a firm empirical basis, we need to describe and attempt to model the structure of webs for a variety of natural and human-modified ecosystems (Memmott et al. 2005). At present, a significant proportion of ecosystem management is based upon a blend of ‘conventional wisdom’, insights from single-species studies, pressure to conserve charismatic vertebrates, attempts to balance the integrity of the natural ecosystem with the benefits it is expected to provide to the local community (‘community conservation’), and occasional adaptive management (Walters & Holling 1990; Kremen 2005). While we do not suggest that food web theory should replace any of these approaches, we do make a plea for it to be more widely considered in plans for the management of national parks and the biodiversity they seek to preserve. A considerable urgency drives attempts to assemble data for webs from large undisturbed and pristine ecosystems such as tropical grasslands, forests, and coral reefs. Moreover, if the principal arguments for conserving natural ecosystems are based purely on economic benefits (Norton 1986; Lovejoy 1996; Daily et al. 1997, 2000), then we need to develop a theory that links ecosystem services to food-web structure.
To conclude, we identify some priorities for food-web research that apply to the conservation of biological diversity.
Ultimately, food webs represent deep problems in applied mathematics that involve many different populations interacting with each other at a variety of different rates on different spatial scales. We believe that these problems are as deep and as challenging as any in physics or pure mathematics. When Darwin stared at the tangled bank, he began to appreciate the complexity of this challenge. Today he would be shocked at the urgency that we need to bring into solving the many facets of this problem and applying the insights gained into the conservation of biological diversity. The time available for many species may be less than the time since Darwin published the ‘Origin’.
This Theme Issue was born of symposia held at the Society for Conservation Biology Annual Meeting in Port Elizabeth, South Africa, June 2007 and at the Ecological Society of America, Annual meeting in San Jose, CA, August 2007. Many thanks to Georgina Mace for encouraging us to collate the papers into a special issue of the proceedings and to Claire Rawlinson and James Joseph for their patience in the preparation of this issue.
One contribution of 15 to a Theme Issue ‘Food-web assembly and collapse: mathematical models and implications for conservation’.