Environmental stress model of community organization

Relative importanceEnvironmental stresscompetitionpredationstress alleviationassociationaldefensesBruno, Stachowicz & Bertness (2003)Environmental stress modeldiversity ofbasal species

Overall richness / diversityBruno, Stachowicz & Bertness (2003)Trends in Ecology and Evolution 18: 119-125Scrosati & Heaven (2007)Marine Ecology Progress Series 342: 1-14Richness of secondary space holders (sessile and mobile associated species)Richness of primary space holders

Vertical gradientDesiccation - TemperatureIrradiance - Osmotic potentialHorizontal gradientWave exposure - Ice scourTest of ESM on the NW Atlantic coast

Nova ScotiaNew England- Gulf of St. Lawrence coast- Atlantic coastNova Scotia

MethodsEnvironmental stress gradientsVertical gradient (3 levels)High - Mid - Low intertidalUpper limit determined using barnaclesHorizontal gradient (2-3 levels)Gulf (wave + ice): Sheltered - ExposedAtlantic (wave): Sheltered - Intermediate - Exposeddynamometers(wave exposure)cages(ice scour)

Richness Sr of speciesDiversity (Simpson's index) 1 - D = 1 - (pi) Evenness (Simpson's index) E = (D * S)-1MethodsRichness, Diversity & Evenness Summer Abundance of all seaweeds and invertebrates (% cover) 25 cm x 25 cm quadrats (n = 20 per Elevation x Exposure combination)

38 seaweeds - 29 invertebratesResults

Gulf of St. LawrenceAtlantic2 = 41 %2 = 39 %Means SEElevationResults - Richness across ElevationElevation

Wave - Ice ExposureWave Exposure2 = 10 %2 = 12 %Results - Richness across ExposureGulf of St. LawrenceAtlanticMeans SE

Test of ESM on the NE Atlantic coast

Helgoland's elevation gradient(wave-sheltered shores)Test of ESM on the NE Atlantic coast (Helgoland Island)

Overall richness and diversity (Helgoland Island)Zwerschke, Bollen, Molis & Scrosati (2013)Helgoland Marine Research 67: 663-674

Environmental stress model (ESM)Menge & Sutherland (1987, American Naturalist 130: 730-757)RICHNESSPredation HypothesisIntermediate Disturbance HypothesisSESSILE SPECIES(PRIMARY SPACE HOLDERS)

***********