Biodiversity in Plants What influences species richness? Tropics vs ...

Regional Pool & Local Species Richness!%.%+"9'*"K%+.'05'-0+%'+%4,0."9'$*%7,%$'+%$#9/$',.'-0+%'907"9'$*%7,%$C'D,99'A0#'4%/'-0+%'907"9'$*%7,%$'"$'A0#'%F09F%'-0+%'+%4,0."9'$*%7,%$L'Regional Pool & Local Species Richness!%.%+"9'*"K%+.'05'-0+%'+%4,0."9'$*%7,%$'+%$#9/$',.'-0+%'907"9'$*%7,%$C'D,99'A0#'4%/'-0+%'907"9'$*%7,%$'"$'A0#'%F09F%'-0+%'+%4,0."9'$*%7,%$L'Tropics vs. TemperateDisturbance and environ heterogeneity•! More ecological niches•! Intermediate Disturbance•! Herbivore and Pathogen•! Random ecological drift•! Number of species covary with habitat heterogeneity•! Disturbance results in a mosaic of habitats

Connel’s Intermediate Disturbance HypothesisConnel’s Intermediate Disturbance Hypothesis•!Moderate levels of disturbance results in a mosaic of habitat patches whichallow coexistence of many species•! Applies to coral’s too•! Intermediate habitatsshow greatest diversityM**9,%E'/0'J+0*,7$C',$'E,$/#+G".7%',$'4+%"/%+L'Connel’s Intermediate Disturbance HypothesisPest-Herbivore Pressure Hypothesis•!Contrary Results. No pattern with gaps/disturbances and species richesacross time (Hubbell et al. 1999, Barro Colorado Island, Panama)•!Pest/parasites attack most common, dominant species = opens upopportunities for rarer, less “attractive” species to persist

Pest-HerbivorePressure Hypothesis-! Thinningincreased survival-! Removal ofpathogensincreased survivalBut is this differentbetween tropics andtemperate?Not known….Hubbell’s Random Ecological Drift-! Past 50 to 60 years, explanations of diversity have been focusedon niches-! What if diversity is simply random processes.-! Hubbel’s model:1. Pest pressure and recruitment limitations reduces interspecificcompetition (self limitation). Most tropical trees are thuscompetitively similar2. Instead of thinking of a community as populations with verydifferent niches and abilities, populations are functionallyequivalent (equal/similar per capita vital rates)3. Individuals of all species have equal probability of filling ingaps left by dead trees4. If there is no speciation and no migration, drift will result in asingle species dominatingHubbell’s Random Ecological DriftSo far…ecological (proximate) processes.What about longer time scales?How does history influence a region’s orlocal areas’ species diversity?Can neutral theory/random ecologicaldrift explain forest diversity?1.! Geography2.! Phylogenetic history

Age of mammalsDynamic Earth: Continental DriftAffects position on earthAffects isolationAge of reptilesAnimals with hard shellsCambrian ExplosionMicrobes, early on mostly anaeorobicDynamic Earth: IsolationVicariance event: splitting of populations due to creation of physicalbarrier (vs. dispersal)Convergence Across RegionsLand masses isolated millions of years ago have unique biotae.g., Wallace’s six major zoogeographic regionsEutherianMammals of Nand S AmericaMarsupialMammals ofAustralasia

Dynamic Earth: ClimateLong-term changes in climate will affect species distribution…At equilibrium?Dynamic Earth: ClimateDynamic Earth: Putting it TogetherComparing species richness across three regions with differentevolutionary history and geography•!Similar climates in Asia,Europe and NA havedifferent number ofregional speciesDynamic Earth: Putting it TogetherComparing species richness across three regions with differentevolutionary history and geography•!Similar climates in Asia,Europe and NA havedifferent number ofregional speciesNumber of GeneraDifferences can be due to evolutionary affiliation with tropical generaWhy?Asia – many species come from tropical genera; connected to tropical AsiaNA – even with isthmus of Panama, tropics are separated by desertEur – tropical Africa is separatedAlso, differences are ancient….Why?Asia – higher rate of species productionEur – Extinction during ice age so fewer species now

Thursday ….Conclude with “Why is Tropics More Diverse?”&Evolutionary Perspective of Species Richness