[Coral-List] What is a keystone species?

Sarah Frias-Torres sfrias_torres at hotmail.com
Sun Sep 14 09:13:37 EDT 2014

It's helpful to remember where the word "keystone" originates.
Back in old days, arches were built with stones, starting first with a wood framework to build either side of the arch, and culminating with the placement of the keystone, the wedge-shaped stone at the apex of the arch or vault. At that time, the wooden frames will be taken apart and the arch remained in place. 
Without the keystone, the arch falls apart. Without the wolf or the sea otter, the ecosystem falls apart. I think that's the easiest way to understand what a keystone species means.
Incidentally, the chief stone mason was required to stand underneath the arch after the keystone was placed, and while the wooden frame was taken away. It was a way to ensure he had done a good job. Not a kind of work ethic we see these days...

Sarah Frias-Torres, Ph.D. Coordinator Reef Rescuers ProgramIsland Conservation Centre Nature Seychelles,Amitie, Praslin, Seychelleshttp://www.natureseychelles.org/what-we-do/coral-reef-restoration-and-Research CollaboratorSmithsonian-National Museum of Natural Historyat Smithsonian Marine Station, Fort Pierce, FL, USATwitter: @GrouperDocBlog: http://grouperluna.wordpress.comhttp://independent.academia.edu/SarahFriasTorres

> From: jbruno at unc.edu
> To: coral-list at coral.aoml.noaa.gov
> Date: Wed, 10 Sep 2014 22:06:43 +0000
> Subject: [Coral-List] What is a keystone species?
> Re, the recent posts "Keystone coral species in the Panama region”: I thought it would be useful to explain that a keystone species is defined as one that has a large effect on its community relative to its total mass.  Thus a habitat forming coral cannot, by definition, be a keystone.  Keystones have a large per captia (or biomass scaled) effect.  Their influence is not simply a result of their numerical dominance.  Given the very large proportion of biomass made up by top predators like sharks on “pristine” reefs, they too are very unlikely to be keystones.  (I also doubt that sharks have an exceptional effect even ignoring their biomass dominance when present, but that is a different argument). Generally, only very uncommon predators meet these criteria, e.g., wolves and sea otters.
> Habitat forming species like corals are instead termed “foundation species” and they have a large community effect (usually via habitat provision and the modification of environmental conditions) but their mass standardized effect is not exceptional.
> Bruno, J. F., and M. D. Bertness. 2001. Habitat modification and facilitation in benthic marine communities. Pages 201–218 Marine Community Ecology. Sinauer, Sunderland, MA.
> Power, M. E., D. Tilman, J. A. Estes, B. A. Menge, W. J. Bond, L. S. Mills, G. Daily, J. C. Castilla, J. Lubchenco, and R. T. Paine. 1996. Challenges in the quest for keystones. BioScience 46:609–620..
> Also see:
> http://en.wikipedia.org/wiki/Keystone_species
> http://en.wikipedia.org/wiki/Foundation_species
> Sincerely,
> John Bruno
> Professor, Dept of Biology
> UNC Chapel Hill
> www.johnfbruno.com<http://www.johnfbruno.com>
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