Community Diversity - Montana State University

Community DiversityTopicsWhat is biodiversity and why is it important?What are the major drivers of species richness?Habitat heterogeneityDisturbanceSpecies energy theoryMetobolic energy theoryDynamic equilibrium hypothesis (interactions amongdisturbance and energy)Resource ratio theoryHow does biodiversity influence ecosystem function?Biodiversity and ecosystem function hypothesisIntegration of biodiversity theoryHow might the drivers of species richness and hence levels ofspecies richness differ among biomes?

Community Diversity DefinedBiodiversityMerriam-Webster - the existence of many different kinds of plants andanimals in an environment.Wikipedia - the degree of variation of life forms within a given species,ecosystem, biome, or an entire planet.U.S. Congress Office of Technology Assessment - the variety and variabilityamong living organisms and the ecological complexes in which they occur.Diversity can be defined as the number of different items and their relativefrequency. For biological diversity, these items are organized at manylevels, ranging from complete ecosystems to the chemical structures thatare the molecular basis of heredity. Thus, the term encompasses differentecosystems, species, genes, and their relative abundance."

Community Diversity DefinedSpecies richness -Species evenness -Species diversity -

Community Diversity DefinedSpecies richness - number of species present in the community (without regardfor their abundance).Species evenness - relativeabundance of the species thatare present.Species diversity - Considers both the number of species (richness) in thecommunity and their relative abundance (evenness or equability).Shannon-Wiener Diversity IndexWhere:H’ the value of the Shannon-Wiener diversity indexpi the proportion of the ith speciesloge the natural logarithms the number of species in the community

Community Diversity DefinedCommunityRichnessShannon’s indexAbundanceGuild – group of species that make their living in a similar wayRichnessShannon’s indexAbundanceIndividual speciesAbundance

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Rank-abundance curves for caddisfliesFigure 16.716-5Source: L. S. W. Terra

Community Diversity DefinedWhy do we care about biodiversity?

Factors Influencing Biodiversity

Factors Influencing BiodiversityProximate Factors AreaBirds on islandsEarthwormsacross Europe LatitudeBirds globallyGaston 2000Bats in Manu NP,Peru Elevation

Factors Influencing BiodiversityUltimate Factors Habitat heterogeneityDisturbanceSpecies energy theoryMetobolic energy theoryDynamic equilibrium hypothesis (interactions amongdisturbance and energy) Resource ratio theory

Factors Influencing BiodiversityHabitat HeterogeneitySpecies richness increases with vertical and horizontal habitatheterogeneity because habitat comprises niche axes for speciesand more niches can fit into areas with heterogeneous habitats.Verschuyl et al. 2008

Factors Influencing BiodiversityHabitat HeterogeneityGeomorphic variation also contributes to habitat heterogeneity

Factors Influencing BiodiversityDisturbanceSpecies richness is maximized at intermediate rates ofdisturbance because habitat is provided for both early and lateseral specialists.r-selected species –K-selected species -Intermediate DisturbanceHypothesis(Connell 1978)

Factors Influencing BiodiversityDisturbanceSpecies richness is maximized at intermediate rates ofdisturbance because habitat is provided for both early and lateseral specialists.r-selected species – In unstable or unpredictable environments, r-selection predominates asthe ability to reproduce quickly is crucial. There is little advantage in adaptations that permitsuccessful competition with other organisms, because the environment is likely to changeagain. Traits that are thought to be characteristic of r-selection include: high fecundity, smallbody size, early maturity onset, short generation time, and the ability to disperse offspringwidely.K-selected species - In stable or predictable environments, K-selection predominates as theability to compete successfully for limited resources is crucial and populations of K-selectedorganisms typically are very constant and close to the maximum that the environment canbear (unlike r-selected populations, where population sizes can change much more rapidly).Traits that are thought to be characteristic of K-selection include large body size, long lifeexpectancy, and the production of fewer offspring, which often require extensive parentalcare until they mature.

Factors Influencing BiodiversityDisturbanceSpecies richness is maximized at intermediate rates ofdisturbance because habitat is provided for both early and lateseral specialists.r-selected species –K-selected species -Intermediate DisturbanceHypothesis(Connell 1978)

Factors Influencing BiodiversitySpecies Energy TheoryAbundant food resources or warmer thermal conditions allow higher survival andreproduction of individuals within a population, and larger population sizes reduce thechance of species extinctions (Wright 1983).

Factors Influencing BiodiversitySpecies Energy TheoryWright, D. H. 1983. Species–energy theory, an extension of species-area theory. Oikos41: 496–506.A more general biogeographic theory of island species number is produced byreplacing area with a more direct measure of available energy in the models ofMac-Arthur and Wilson and Preston. This theory, species-energy theory,extends beyond species-area theory in that it applies to islands that differ intheir per-unit-area productivity due to differences in physical environment,such as climate

Factors Influencing BiodiversitySpecies Energy TheoryAngiosperm SpeciesAET – based on climate (temp,PPT, ET)Wright 1983

Factors Influencing BiodiversitySpecies Energy TheoryAfrican VertebrateRichnessNorth American GroupsNet primary productivityBalmford et al. 2001Currie 2002

Factors Influencing BiodiversitySpecies Energy TheoryBiodiversity is often strongly correlated with energy.EnergyHeat – e.g., temperature, potential evapotranspirationEcological productivity – e.g., NPPWhy?Abundant food resources or warmer thermal conditions allow higher survival andreproduction of individuals within a population, and larger population sizes reduce thechance of species extinctions (Wright 1983).“Measures of energy (heat, primary productivity) [and water balance] explainspatial variation in richness better than other variables in 82 of 85 cases”,Hawkins et al. 2003.

Factors Influencing BiodiversityEcosystem Energy

Factors Influencing BiodiversitySpecies Energy TheoryMore Individuals HypothesisAbundant food resources or warmer thermal conditionsallow higher survival and reproduction of individualswithin a population, and larger population sizes reducethe chance of species extinctionsCompetitive Exclusion HypothesisOne or a few canopy tree species dominate thecommunity and competitively exclude other plantspecies and plant diversity, structural complexity andfoods for consumers.

Species Richness for Landbirds across North AmericaHypothesisTypical PredictorsTemperature (mean annual)Kinetic energyTemperature (mean June)Potential evapotranspirationPrecipitation (mean annual)WaterPrecipitation (mean June)Evapotranspiration (annualsum)NDVI (mean annual or meanJune)Gross Primary Productivity(mean annual)USGS Breeding Bird Survey dataBBS native diurnal landbirdsPotentialEnergyGross Primary Productivity(June)Seasonality (June GPP/annualGPP)Richness aGPP – aGPP2 - %SCV PETInterannual variation in GPP%SCV: Interannual variation in GPPElevation rangeHabitatcomplexityAdj. R2 0.70Cover type variationPercent treeHansen et al. 2011. GlobalEcology and Biogeography

Carrying Capacity for Species Richness for Landbirds acrossNorth AmericaHansen et al. 2011.

Factors Influencing BiodiversitySpecies Energy TheoryUnresolved Issues: the form and magnitude of species energy relationship areknown to differ among groups of organisms and between scalesof observation; yet, we currently have no mechanism to explainhow or why PDR might qualitatively shift at different scales orlevels of biological organization. studies have tended to use a plethora of different variables torepresent diversity and productivity (climate, NPP, GPP,biomass ). Many studies have argued that these variables arenot interchangeable, nor do they even show the same qualitativerelationship to species diversity. Most studies are correlational and thus do not demonstratecausality. Large-scale experiments are difficult to impossible.

Factors Influencing BiodiversityExtinctions due toinability to recoverfrom disturbanceDisturbance RateSpecies RichnessLow ProductivityEcosystemSpecies RichnessSpecies RichnessInteractions Among FactorsDisturbance RateDynamic Equilibrium HypothesisHigh ProductivityEcosystemExtinctions due tocompetitiveexclusionDisturbance Rate

Factors Influencing BiodiversityExtinctions due toinability to recoverfrom disturbanceDisturbance RateSpecies RichnessLow ProductivityEcosystemSpecies RichnessSpecies RichnessInteractions Among FactorsDisturbance RateHIgh ProductivityEcosystemExtinctions due tocompetitiveexclusionDisturbance RateIncreased disturbanceincreases species richness.Increased disturbancereduces species richness.Dynamic Equilibrium Hypothesis

Factors Influencing BiodiversityLow EnergySystemsProulx and Mazumder (1998) - Meta analysis of 30 studies ofplant species richness in lake, stream, grassland, and forestgrazing systems.High Energy SystemsAll 19 comparisons from nonenriched or nutrient-poorecosystems exhibitedsignificantly lower speciesrichness under high grazingthan under low grazing.14 of 25 comparisons fromenriched or nutrient-richecosystems showedsignificantly higher speciesrichness under high grazingthan under low grazing.

community and their relative abundance (evenness or equability). Shannon-Wiener Diversity Index. Where: H’ the value of the Shannon-Wiener diversity index. p. i the proportion of the ith species. log e the natural logarithm. s the number of species in the community