MARS 345031 October, 2013Marine BiodiversityBiodiversity hotspots proposed by Conservation InternationalGuest SpeakersTuesday, Nov 5: Dr. Mary Ann MoranSocial Behavior and SymbiosisThursday Nov 7: Dr. Mary Ann MoranMigration and NavigationTuesday Nov 12: Dr. Patricia YagerClimate Change in Polar RegionsQuantifying BiodiversitySpecies diversity has 2 components:RichnessEvennessNumber of different speciesDistribution of individuals among speciesExample: two communities each with 50 individualsDivided among five speciesCommunity A: 10, 10, 10, 10, 10Community B: 46, 1, 1, 1, 1Same Richness, Different EvennessCommunity – interacting organismsAssemblage – collection of organismsSide bar:How is Diversity Expressed?1. Diversity Index: a mathematical calculationExamples: Simpson index DS= 1/ni/N)2)Shannon Index, H’H’ = -ni/N * ln ni/N)ni= importance value for each speciesN = total importancetotal # individuals# individuals in species iCommunity A: 10, 10, 10, 10, 10Community B: 46, 1, 1, 1, 1H’ = 1.6H’ = 0.4How is Diversity Expressed?2. Diversity Curves: a graphical representationBenthic invertebratesfrom Buzzards BayTwo islands from theGreat Barrier Reef(Valiela 1995)Species-AreaCurveRarefactionCurvesampledsampledHow is Diversity Expressed?2. Diversity Curves: a graphical representationA practical limitation is deciding what is included in the “community”Usually determined by the technical limitations of identificationBiases the assessment(Valiela 1995)sampledsampledAccumulation curves n = number sampled•Michigan plants (n = 1,783)•Costa Rican birds (n = 5,007)•Human oral bacteria (n = 264)•Costa Rican moths (n = 4,538) •East Amazonian soil bacteria (n = 98)Hughes et al. (2001) Appl Environ Microbiol. 67: 4399–4406. doi: 10.1128/AEM.67.10.4399-4406.2001Curvature tells how well the population has been sampledExcellent discussionNormalized sampling effortTropical moths (n = 4,538)(100’s of km of forest) Temperate soil bacteria (n = 137)(a few g of soil)396173Most abundant class(omitted from graph)Our ability to sample bacterial diversity in a few grams of some soils may be similar to our ability to sample moth diversity in a few hundred square kilometers of tropical forest. The flip-side: most species are rareWhat is a species? Is the definition the same for all species?How does this affect “biodiversity”?A Central Problem of Field Biology(marine or otherwise):How do we estimate true richness or diversity from that sampled?How do we correct for undiscovered species?Parametric Richness EstimatorsBased on an assumption about the underlying structure of the population being sampled, the shape of the species-abundance curve:PoissonLog-NormalOtherRegression-based estimateProblem: do we know that the distribution model we are using is correct ?•Makes no assumptions about the underlying distribution•Adapted from mark-release-recapture (MRR) statistics for estimating the size of animal populations•Considers the proportion of species that have been observed before (“recaptured”) to those that are observed only once. •In a very diverse community, the probability that a species will be observed more than once will be low, and most species will only be represented by one individual in a sample. •In a depauperate community, the probability that a species will be observed more than once will be higher, and many species will be observed multiple times in a sample.Non-parametric estimatorsChao1 estimator for species richnessS*1= Sobs+ (a2/2b) whereSobs is the number of species observeda is the number of species observed just onceb is the number of species observed just twice•The Chao1 and Abundance-based Coverage Estimators (ACE)•Use an MRR-like ratio to estimate richness by adding a correction factor to the observed number of species•Particularly useful for data sets skewed toward the low-abundance classes (very rich populations).Two Commonly-Used FormsChao1 estimator for species richnessS*1= Sobs+ (a2/2b) whereSobs is the number of species observeda is the number of species observed just onceb is the number of species observed just twiceThe ACE incorporates data from all species with fewer than 10 individuals, rather than just singletons and doubletons. ACE estimates species richness as: Abundance-based Coverage EstimatorSACE= Sabund+ (Srare/CACE) + (F1/CACE) 2ACESrare= Number of rare species (each with 10 or fewer individuals) when all samples are pooledSabund= Number of abundant species (each with more than 10 individuals) when all samples are pooledCACE= Sample abundance coverage estimator = 1 – (Fi/Srare)Fi= Number of species that have exactly i individuals when all samples are pooled (F1is the frequency of singletons, F2the frequency of doubletons, etc.)ACE= Estimated coefficient of variation of the Fifor rare speciesWhat Factors Determine Diversity?Littorina snails graze rockyNew England shores andeat macroalgae1. PredationLocal Factors(Valiela 1995)•Most competitive (= most abundant) are preferentiallypreyed on; relaxes competition•Too intense: few species survive•Intermediate predation intensity promotes diversity?Shannon IndexSpecies Richness# Snails per m2Chondrus:Unpalatable dominantEnteromorpha:Competitive dominantWhat Factors Determine Diversity?Local Factors(Valiela 1995)2. Disturbance•Many different ecological states occur sequentially•Relaxes competition•Too intense: few can handle•Intermediate disturbance promotes diversity?Storm disturbanceSpecies RichnessAustralian coral reefsA variant of this is used to explain plankton diversity –Hutchinson paperWhat Factors Determine Diversity?Local Factors3. Resource Availability•Limited critical resource results in fewer species•Dominated by a few specialists -“Competitive Exclusion”Global survey of coral reefs(Bellwood and Hughes 2001)Most important factor: suitable habitat within 600 kmPercent of diversity differences explainedWhat Factors Determine Diversity?Diversity goes upwith distance from sewage outfallBaltic Sea sewage outfallLocal Factors(Valiela 1995)4. Pollution, Deleterious Substance - Stress•Natural (e.g., hydrogen sulfide, salinity variation)•Anthropogenic (e.g., PCBs)•High concentrations: lowest diversityShannon IndexWhat Factors Determine Diversity?Local Factors5. Immigration and Invasion•Imigration: natural expansion of species’ range•Invasion: human-aided transport of speciesInvasion occurs by:Ship travel: