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
With Pisaster (control) 20 15 Number of species present 10 Without Pisaster (experimental) 5 0 1963 ´70 ´71 ´73 ´64 ´65 ´69 ´66 ´72 ´67 ´68 (a) The sea star Pisaster ochraceous feeds preferentially on mussels but will consume other invertebrates. (b) When Pisaster was removed from an intertidal zone, mussels 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. Dr. Robert T. Paine’s Work
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
Keystone or Foundation? • Keystone (engineer) • Pdog 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.
Keystone or Foundation? • Foundation • Dominant primary producer that provides food and shelter for many other species Kelp
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 at lower levels. Example: Gray Wolf in Yellowstone National Park (Wolf -> Elk -> Cottonwood/Aspen/Willow --> Bird Populations)
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.
Sources • http://www.washington.edu/research/pathbreakers/1969g.html (starfish) • http://query.nytimes.com/gst/fullpage.html?res=9C0CE1DB1530F936A15751C1A966958260 (kangaroo rats) • http://www.prairiedogs.org/keystone.html (praire dogs) • http://www.eoearth.org/article/Global_marine_biodiversity_trends (kelp)