[Coral-List] What is a keystone species?

John McManus jmcmanus at rsmas.miami.edu
Tue Sep 16 12:27:28 EDT 2014

Yes, it is good to think back on the origins of the terms.

Note that wolves, sea otters, and other classically labelled keystone
species are usually apex predators in upright food pyramids.  Many present
day reefs are upright pyramids, and so one could look for apex predators
there as well. For natural reefs that were inverted pyramids, the small
biomass criteria would result in much different conclusions. 

Regardless, I find these old ecological concepts good for introductory
classes, but a bit limiting in the modern context. If one uses a trophic
network analysis, one can find various species groups that, if their
populations are reduced,  will likely have cascading impacts. That can
happen at any trophic level. Additionally, once that group has been reduced,
the trophic network will shift, and perhaps new groups will be the ones with
potentially strong cascading effects. Of course, trophic pyramids do not
well account for space competition among species and refuge volumes provided
by certain species. I believe we should shift more towards a multivariate
approach for issues including cascade impacts, succession, foundation
species, phase shifts, etc., and not rely too heavily on simplifications we
see in textbooks. It would be good to read recent work from Jordi Bascompte,
Marten Scheffers, etc. who are among those setting a foundation for modern
ecological community analysis approaches.  



-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov
[mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Sarah
Sent: Sunday, September 14, 2014 9:14 AM
To: John Bruno; coral list
Subject: Re: [Coral-List] What is a keystone species?

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,
and-Research CollaboratorSmithsonian-National Museum of Natural Historyat
Smithsonian Marine Station, Fort Pierce, FL, USATwitter: @GrouperDocBlog:

> 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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