keystone species

Kelly Cassidy lostriver at
Sun Jan 13 10:13:03 PST 2002

Kevin Li is correct. "Keystone species" was coined by Paine. He found that removal of Pisaster (the starfish and top predator in the intertidal community he studied) caused a decrease in diversity of intermediate predators. Paine concluded that Pisaster had a disproportionate influence on community composition. The use of the term "keystone" ballooned and it soon seemed that almost any species one picked could be termed a keystone species for some reason or another.

In the 90s, there was an effort to restrict the term "keystone" to a species that had an effect disproportionate to its biomass in the community. Thus a dominant species (like Douglas-fir or Western Hemlock in west-side forests) exerts a large influence because it comprises a large proportion of the biomass in the community. That is, its influence is proportionate to its biomass. A grizzly bear on the other hand would be a keystone species because, although bears have a low total biomass, they exert a disproportionate influence on the species below them.

My problem with the more recent definition is that, the further up a species is on the food chain, the more disproportionate its effect compared to its biomass simply because of the loss of energy with each trophic level. The biomass at each trophic level is only a maximum of about 1-2% (for warm-blooded animals) or 10-20% (for cold-blooded animals) of the biomass of the trophic level below it. Hence, you could argue that keystone species is merely a synonym for top predator.

At any rate, my sense is that, because of overuse, the term has fallen out of favor in the ecological community. I've never heard the term "keynote" species.

Kelly Cassidy
Pullman, WA

My impression is that the term "keystone species" was first coined around the early 1970s by Prof. emeritus Robert Paine of the University of WA Zoology Dept., with regard to the starfish Pisaster and its role in the structure of intertidal communities at Tatoosh Island. I'm not familiar with use of the term "keynote" in regard to a species.

Kevin Li
Ballard, USA
kdli at

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