Describes labels given to species of critical importance in an ecosystem.

1. Keystone or Foundation
Species?

2. Keystone or Foundation?
• Keystone
• Pisaster ochraceus is an
efficient predator of the
common mussel, Mytilus
californicus.
• It reduces abundance of
M. californicus, allowing
other macroinvertebrates
to persist.
• If Pisaster present =
diverse intertidal
community.
Based on the research of Dr. Robert T. Paine

3. Dr. Robert T. Paine’s Work
With Pisaster (control)
20
Number of species
15
present 10 Without Pisaster (experimental)
5
0
1963 ´64 ´65 ´66 ´67 ´68 ´69 ´70 ´71 ´72 ´73
(a) The sea star Pisaster ochraceous feeds
preferentially on mussels but will consume other (b) When Pisaster was removed from an intertidal zone, mussels
invertebrates. eventually took over the rock face and eliminated most other
invertebrates and algae. In a control area from which Pisaster was not
removed, there was little change in species diversity.

4. Keystone or Foundation?
• Keystone
• Removing three species of
kangaroo rats changed a
desert plain into an arid
grassland. In areas without
kangaroo rats, grasses filled
in between the shrubs,
stems and other plant litter
accumulated, large-seeded
plants replaced those with
smaller seeds, snow melted
more slowly and the
numbers of the other rodents
increased significantly.
Based on the research of Dr. James H. Brown

5. Keystone or Foundation?
• Keystone
• Their burrows act as homes to
other creatures, including
burrowing owls, badgers,
rabbits, black-footed ferrets,
snakes, salamanders, and
insects.
• Their burrowing activity works to
loosen and churn up the soil,
increasing its ability to sustain
plant life.
• Their foraging and feeding
practices enable a more
nutritious, diverse and nitrogen-
rich mixture of grasses and
forbs (broad-leafed vegetation)
to grow.

6. Keystone or Foundation?
• Foundation
• Dominant primary producer
that provides food and
shelter for many other
species
*Note: Some authors,
including Miller, equate
this with “engineer” type
keystone species

7. Effects of losing the
“keystone” predator…
• A trophic cascade-
in a food web, the
cascading effect that a
change in the size of one
population (usually an
apex predator) in the
web has on the
populations below it
Example: Gray Wolf in Yellowstone National Park
(Wolf -> Elk -> Cottonwood/Aspen/Willow -> Bird Populations)

8. Don’t forget…
• A keystone species is one that has a
disproportionate impact on its ecosystem when
compared to its abundance.
• A foundation species is usually a primary producer
that dominates an ecosystem in abundance and
influence.

9. Sources
• http://www.washington.edu/research/
pathbreakers/1969g.html (starfish)
• http://query.nytimes.com/gst/fullpage.html?
res=9C0CE1DB1530F936A15751C1A966958
260 (kangaroo rats)
• http://www.prairiedogs.org/keystone.html
(praire dogs)
• http://www.eoearth.org/article/
Global_marine_biodiversity_trends (kelp)