Keystone species
Although the concept is valued as a descriptor for particularly strong inter-species interactions, and has allowed easier communication between ecologists and conservation policy-makers, it has been criticized for oversimplifying complex ecological systems.
[1][2] Paine developed the concept to explain his observations and experiments on the relationships between marine invertebrates of the intertidal zone (between the high and low tide lines), including starfish and mussels.
[3] In his 1966 paper, Food Web Complexity and Species Diversity, Paine had described such a system in Makah Bay in Washington.
[1] The ochre starfish is a generalist predator and feeds on chitons, limpets, snails, barnacles, echinoids, and even decapod crustacea.
Yet without the predators, the herbivorous prey would explode in numbers, wipe out the dominant plants, and dramatically alter the character of the ecosystem.
The exact scenario changes in each example, but the central idea remains that through a chain of interactions, a non-abundant species has an outsized impact on ecosystem functions.
For example, the herbivorous weevil Euhrychiopsis lecontei is thought to have keystone effects on aquatic plant diversity by foraging on nuisance Eurasian watermilfoil in North American waters.
[17] Without predation, herbivores began to over-graze many woody browse species, affecting the area's plant populations.
In addition, wolves often kept animals from grazing in riparian areas, which protected beavers from having their food sources encroached upon.
Increased browsing on willows and conifers along Blacktail Creek due to a lack of predation caused channel incision because the beavers helped slow the water down, allowing soil to stay in place.
[20] The jaguar, whose numbers in Central and South America have been classified as near threatened, acts as a keystone predator by its widely varied diet, helping to balance the mammalian jungle ecosystem with its consumption of 87 different species of prey.
[22] Keystone mutualists are organisms that participate in mutually beneficial interaction, the loss of which would have a profound impact upon the ecosystem as a whole.
Therefore, the loss of this one species of tree would probably cause the honeyeater population to collapse, with profound implications for the entire ecosystem.
Depending on topography, soils, and many factors, these dams change the riparian edges of streams and rivers into wetlands, meadows, or riverine forests.
[30] In the Amazon river basin, peccaries produce and maintain wallows that are utilized by a wide variety of species.
[33] In the Serengeti, the presence of sufficient gnus in these grasslands reduces wildfire likelihood, which in turn promotes tree growth.
That stretching can be quantified: the researcher Ishana Shukla has listed 230 species identified as keystones in some 157 studies in the 50 years since Paine's paper.
Paine had indeed stated that in Alaska, without the relevant mussel species as prey, the predatory Pisaster was "just another sea star".
[7] Although the concept of the keystone species has a value in describing particularly strong inter-species interactions, and for allowing easier communication between ecologists and conservation policy-makers, it has been criticized by L. S. Mills and colleagues for oversimplifying complex ecological systems.
