Keystones,umbrellas and focal species

Keystone species Rocky intertidal Bodega bay Food web Pisaster feeds on acorn barnacles and mussels in rocky intertidal Exclosure experiment by R.

Paine (Am. Nat. 1966) Pisaster removed by hand from sections of shore for 3 yrs. Observed change in bivalve community. Pisaster maintains diversity through predation of Mytilus californiana. Otherwise competitive exclusion results

No Pisaster -> 8 species bivalve Pisaster present -> 15 species bivalve Original keystone concept Two facets to being a Keystone species: A predator preferentially eats and controls the abundance of a primary consumer The primary consumer was capable of

excluding (through competition or predation) other members of the community. Estes and Palmisano (Science 1974) Veg Urchin density Depth (m)

Contrasting kelp and urchin densities in Pacific NW Urchins Shemya Amchitka Vegetation cover Otters present

Diameter of urchins Shaded area = urchin biomass Open area = number of urchins Otters absent Diameter of urchins Sea otter impact on urchins

Otters substantially reduce populations of large urchins. Estes and Palmisano (Science 1974) Kelp density and otters 100 100 60

60 20 20 0 3 7 11 15 19 0 3 7 11 15 19

0 3 7 11 15 19 0 3 7 11 15 19 Otter effects on urchin biomass Estes (Ec. Monogr. 1995) Other Keystones?

Both the examples given are of keystone predators. Can you think of examples other than predation where one species has a large effect on a system? Paine (1966) first usage Pisaster (top predator) was identified as the species that maintained diversity in a rocky intertidal community (exclosure experiments).

Demonstrated that removal of Pisaster (top predator) led to reduction from 15 to 8 spp. in foodweb. Keystone predator may increase spp. diversity of prey by preventing competitive exclusion. 1) Keystone predator: sensu Paine (1966). Sea Otters:- limit sea-urchin

density and hence allow development of kelp beds with otters present there is a very different community (Estes and Palmisano; Science 1974). This meets the original definition in that removal of primary consumer changes environment.

More Keystone predators? Other authors have interpreted any predator with a major impact as a keystone...Risch and Carroll 1982...fire ants reduce number of arthropods harmful to agriculture. Ants are generalists preying on herbivores that are not specially competitive. Note the removal of fire ants does not change the environment and so this is a different meaning for keystone.

2) Keystone Prey (Holt 1974) Models demonstrated that if a prey species had sufficiently high reproductive output it could maintain predator popn that reduced density of other prey. i.e. rabbits support fox popn at a high level, foxes also prey on other mammals perhaps eliminating some rare ones. If this prey were removed species diversity would rise

3) Keystone mutualists (Gilbert 1980) Mobile links....pollinators and dedicated seed dispersers. Hummingbird pollinators and mammalian dispersers of mycorrhizal fungae. If these mutualists are absent the plant composition would change radically. 4) Keystone hosts: Hosts of the mobile links must also be

keystones. Terborgh suggested palm nuts, figs and nectar sources are critical to the survival of 50-75% of tropical forest mammal and bird biomass. 5) Keystone modifiers: Beavers alter the hydrology of large areas, create wetlands and may be the cause of the majority of

high elevation wetlands in the Rockies. Pleistocene megafauna may have been modifiers and as they started to be lost there was a snowball effect that led to the elimination of about half the mammalian genera with bodymass between 5 and 1000 kg at end of Pleistocene. Pocket gophers slow aspen invasion in mountain meadows. Keystones and importance Classic food web theory assumes either

that species-by-species interactions are uniform, or that their interaction strengths are drawn from symmetrical distributions. Keystone concepts demand that we quantify another measure.Community importance. Keystone is a species that is disproportionately important relative

to its BIOMASS Individual impact of species Keystone redefined Keystone sp. Dominant sp. Ho hum Proportional biomass of species

Test with exclosure experiments CIi = [(tN-tD)/tN](1/pi) where tN is a quantitative measure of the trait in the intact community. tD is the trait after species i has been deleted. pi is proportional abundance of i prior to deletion. If species has effect directly proportional to abundance CI =1. Values much greater than 1 needed to indicate keystone species.

Once a Keystone, not always a keystone Keystones can be habitat specific. Pisaster is only a keystone on exposed intertidal habitats. Does not have the same role in sheltered communities on same headland. (Menge, Ec. Monogr. 1994). Keystone concept shows: Loss of some species of low abundance may have surprisingly dramatic effects:

Preservation of a species of concern may depend upon the distribution and abundance of other species with which the target has no recognized interaction; and conversely, Loss of a species, such as a top carnivore, may reverberate to affect members of the entire community in hard to predict ways.

Recently Viewed Presentations

  • Possessive Nouns - Suffolk City Public Schools

    Possessive Nouns - Suffolk City Public Schools

    Possessive Nouns Project LA Activity Jefferson County Schools Possessive nouns are used to show possession (owning, or having). The dog's collar is too large. The word "dog's" is the possessive noun. It tells you that the noun "collar" belongs to...
  • The Alamo - inetTeacher.com

    The Alamo - inetTeacher.com

    Texians reasoning: Alamos sits on an important road Travis and Bowie felt that they could hold the Alamo and felt safe there Alamo could slow down the Mexican army because it is in the middle of Texas The Siege of...
  • Intro to Mathematics Nathan Frey  Arithmetic Concepts Number

    Intro to Mathematics Nathan Frey Arithmetic Concepts Number

    Pyramids. Cylinder. Cones. Sphere. TEST 1 MATERIAL ENDS. Midpoint Formula. ... Term - part of algebraic expression separated by plus sign. Like terms - have the same variables with the same exponents. Properties. Commutative property - a property of addition...
  • WCL306: Evaluating Deployment Options for Diagnostic and ...

    WCL306: Evaluating Deployment Options for Diagnostic and ...

    Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of...
  • Nocturnal Chemistry observed from the R/V Atlantis Observations

    Nocturnal Chemistry observed from the R/V Atlantis Observations

    Nocturnal Chemistry observed from the R/V Atlantis Observations of NO3 and N2O5 Nick Wagner, Steven S. Brown, William P. Dubé, Brian M. Lerner, Eric J. Williams -
  • Context Clues - teachers.henrico.k12.va.us

    Context Clues - teachers.henrico.k12.va.us

    Antonym context clues are words around a difficult word that mean the opposite or nearly the opposite as the word.. EXAMPLE: Joe was . reluctant. to take the job of captain of the team. He was afraid that the time...
  • Applying Tungsten Inert Gas (TIG) Welding Techniques

    Applying Tungsten Inert Gas (TIG) Welding Techniques

    Lesson 8 Applying Tungsten Inert Gas (TIG) Welding Techniques Safety Procedures The danger of electrical shock is less with high frequency current than with current phasing at 60 cycles per second.
  • BATTLEMENT CREEK FIRE Fatalities & Injury July 17, 1976

    BATTLEMENT CREEK FIRE Fatalities & Injury July 17, 1976

    Tragically, only one of the four survived, and he suffered severe burns over most of his body…." "Figure 1 suggests that for this fire, the safety zone should have been large enough to separate firefighters from flames by 150 feet....