Death of a Disturbance Ecologist

Robert Paine (source)

Robert Paine, the founder of the "keystone species" idea in ecology, died last week at the age of 83. Paine published his first paper on the disproportionate role of certain species in ecosystem self-regulation in 1966, looking at a marine predator species (a starfish) and its prey (a mussel) on the Olympic Peninsula in Washington state. He systematically removed the starfish from the environment, and observed that the mussels took over and several other species disappeared in what he called a "trophic cascade" of effects. The starfish was the keystone species that regulated the mussel population and allowed other species to thrive. At the time, very few were scientists involved in experimenting with ecology, such as the removal of a keystone species, and ecologists proceeded mainly through observation. Since then, ecological experiments such as temperature manipulations, drought simulation, and CO2 enrichment have really taken off.

To a landscape ecologist, the idea of a keystone species is fascinating, and as with any good idea it brings up more questions than answers. Are all ecosystems characterised by these star players (pun intended), or is it possible to be less dependent on a single species? We know that redundancy in ecosystems, or the ability for a function to be performed in multiple ways, is key to ecosystem resilience, or the ability to "bounce back" from disturbance. This happens at scales from the cellular to the global. Being heavily reliant on a single species at an ecosystem level is a risky strategy, given how easy it would be to "tip" a system into some other state.

And I'm somewhat suspicious that keystone species always seemed to be rather charismatic, like a starfish or a prairie dog or a tiger, and not ectomycorrhizal fungi (that help plants fix important nutrients like nitrogen). If we take into account of all the species in an ecosystem, there may be more or less dependence on any of them, but highlighting some as keystone species almost makes it sound like we can safely ignore the other ones. And, of course, scale matters. What might be a highly important species in terms of its impact on other species (most importantly, homo sapiens), may not have any impact at all on others (say, protozoa). It's always helpful to ask "Who benefits?" when we want to know if something is "good" or "bad" for an ecosystem.

Dr Paine has a long academic legacy, (seriously, check out this tree) and his ideas about the ecological role of different species helped to form the basis of current ideas about ecological resilience. I'm sure that I haven't raised anything here that he didn't think of himself over his long years, and for which he likely had very good answers. His lifelong elaboration of the idea that minor shifts, like the loss of a single species, can dramatically change an ecosystem has been a massive contribution to disturbance ecology.