Tangled banks

Darwin chose the metaphor of '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, " writes Andy Dobson of Princeton University and colleagues, in a series of papers in the Philosophical Transactions of the Royal Society B (published online) focused on food webs. Food webs represent one of the biggest ecological challenges because they are often more complex than they might first appear, many are under increasing pressure from human activity and the loss of key components can result in a much wider collapse that is often difficult to repair. " In particular, studies of food webs provide important insights into how natural ecosystems function, " Dobson says. " Real food webs are most certainly not randomly assembled. They are ultimately the winnowed products of evolutionary processes, " says Robert May at Oxford University, introducing the papers. " Early work in the 1970s helped to clear the undergrowth, refocusing the agenda to address the question of what are the structural mechanisms whereby real food webs and ecosystems reconcile complexity, " he says. Increasingly rich collections of species have a tangle of interactions among them – with persistence in the face of environmental buffering, he says. Feature The aim of the present papers is to give an " account of where we currently are in terms of data and uncertainties about the structure of real food webs on land and in the sea, and about the effects of various kinds of disturbance on them, along with theoretical ideas about how such networks of interacting species are put together and how removals or invasions affect them, " says May. Ferenc Jordan, of the Institute of Advanced Studies in Budapest, one of the authors, says " we live in the age of the sixth mass extinction. " Extinction rates may reach one to three species per hour: a rate probably never seen before, he says. " We know that biodiversity is important, but we do not yet clearly understand its functional aspects and the possible ways to maintain it, " he says. We need to know " more about Food webs are a key component of ecological systems but are often little understood and more fragile and threatened than they first may appear. Nigel Williams reports. Collapse: The decline in sea otters in southeast Alaska has led …