Biodiversity Evolutionary Development “Paradox of the Plankton” Definition Margalef, Shannon-Wiener Diversity-index Oceanic Diversity Intermediate DisturbanceHypothesis How do we actually measure it?Textbook pp. 20-40, 457-464PHANEROZOIC MESOZOIC CENOZOICCarbon. Permian Triassic Jurassic Cretaceous TertiarySpecies diversity/abundance (relative scale)DinoflagellatesChlorophytesDiatomsCoccolithophoridsThe dominance by the big-3 is recentEnd-PermianextinctionEnd-Triassicextinction-In anenvironmentwhere nutrientsare suppliedregularlythe presence ofanutrientvacuoleprovidesan advantage.-In anenvironmentwhere nutrientsare suppliedless regularlythe presence ofanutrientvacuole doesnot providean advantage.time, days0 20 40 60 80 1000.080.120.160.200.240204060Synergistic interactions between environmentalvariables and impact on phytoplankton competitiontime, days0 20 40 60 80 1000.040.080.120.160204060Cells/ml * 106nutrient, mol/Lnutrient, mol/LCells/ml * 106ContinuouslightLight:Darkcycleirradiance-induced variation innutrient uptake can altercompetitive abilities of speciesand in changes in ambientnutrient concentration."If today is a typical day on planet Earth, we will lose 116 square"If today is a typical day on planet Earth, we will lose 116 squaremiles of rainforest, or about an acre a second. We will losemiles of rainforest, or about an acre a second. We will loseanother 72 square miles to encroaching deserts, as a result ofanother 72 square miles to encroaching deserts, as a result ofhuman mismanagement and overpopulation. We will lose 40 tohuman mismanagement and overpopulation. We will lose 40 to100 species, and no one knows whether the number is 40 or100 species, and no one knows whether the number is 40 or100. Today the human population will increase by 250,000. And100. Today the human population will increase by 250,000. Andtoday we will add 2,700 tons of chlorofluorocarbons to thetoday we will add 2,700 tons of chlorofluorocarbons to theatmosphere and 15 million tons of carbon. Tonight the Earth willatmosphere and 15 million tons of carbon. Tonight the Earth willbe a little hotter, its waters more acidic, and the fabric of lifebe a little hotter, its waters more acidic, and the fabric of lifemore threadbare."more threadbare." David Orr (1991) “What is Education For?”http://www.context.org/ICLIB/IC27/Orr.htm.DefiningBiodiversity 1992, International Convention onBiodiversity signed Agenda 21 Can refer to habitats; local or global speciescounts; or genetic variability within a species Diversity is always the product of evolution,but we also must take into account extinction(also a product of evolution)DeterminingDiversity Numerous ecological models(based on math), but none ofthese is based on a theoreticalrationale! Ramon Margalef (1951): R = (S -1) / logN R=Richness S= # of Species N= # of individuals(of all species)DeterminingDiversity Shannon-Wiener Index (H’) S=# of species N=total # of individuals pi=proportion of individuals of S(i) compared to N H’=Σ (pi • ln(pi)) – [(S-1)/2N] More complicated than Margalef’s index, butdoes essentially the same thing….Si=1Diversity Index:Margalef and H’ simply scalethe number of species tocalculate diversity, and doNOT take into account howclosely related the speciesare… the Diversity Indexincludes how similar thespecies are, and decreasesthe weighting of closelyrelated species….What CausesDiversity? The Time Hypothesis The Spatial Heterogeneity Hypothesis The Competition Hypothesis The Environmental Stability Hypothesis The Productivity Hypothesis The Predation HypothesisIntermediate Disturbance Hypothesis: too muchvariability is bad, but so is too much stability—maximizediversity at an intermediate level of disturbanceEvolutionary Trends In general, species richness increases with time In general, extinctions are constant Theory of Punctuated EquilibriumTerrestrial vs. Marine 11 Terrestrial vs. 28 Marine phyla 1900 copepod species vs. 1000xmore beetles 3500-4500 algal species, butapproximately 250,000 greenplants“He has an inordinate fondnessfor beetles…” J.B.S. Haldaner versus KstrategiesBased on the concept of ‘maximizing’ reproductiveefficiency by balancing offspring versus parenting r < ---------------------------------------------------------------> KRapid Growth Slow growthMultiple offspring Fewer offspringShort Life Long LifeSmall body size Large body sizeInvasive/Transient EstablishedGeneralists SpecialistMargalef’s MandalaRamon Margalef(1978) updated theidea of r-Kstrategies for theocean…said thatyou can definespecies successionbased on a “phasespace” defined byenergy (turbulence)and nutrientsHorizontal (East-West)GradientsOnshore-Offshore variability in species is dominated by the shelf-break,and then by the diversity of the shoreline habitatLatitudinalGradientsSampling Bias?For well studied organisms like corals and gastropods, it’sless clear that there is a strong latitudinal gradient….Vertical GradientsBenthic Diversityvs. DepthThere is a maximum indiversity at the shelf-breakdepth, declining inshoreand in deeper watersIntermediate DisturbanceHypothesis• Proposed by Connell in 1978• Basic concept is that too stable ecosystems havelow diversity (highly specialized organisms survive),while highly unstable ecosystems also have verylow diversity (only generalist “weed” species arepresent)• Maximum diversity should occur at “intermediatedisturbance”… this can be spatial, such as thecontinental shelf break, or temporal, such as theupwelling-relaxation cycle in the coastal oceanIntermediate DisturbanceHypothesisWhy Do We care AboutDiversity?Duffy and Stachowicz,Marine Ecology ProgressSeries 311: 179-189, 2006Published by AAASWorm et al., Science 314,787 -790 (2006)Why Do We care AboutDiversity?Why Do We care AboutDiversity?On giant filter feeders, Lionel Cavin, Science 327:968-969, 2010Why Do We care AboutDiversity?Climate, Critters, and Cetaceans: Cenozoic Driversof the Evolution of Modern Whales, Marx and Uhen,Science 327:993-996, 2010Summary• The oceans have not always had the sameorganisms—groups come and go depending on large-scaleforcing and evolutionary pressure• We DON’T KNOW what the natural rate of extinction is, butwe do know that there are, occasionally, mass extinctionsthat allow for rapid diversification afterwards•