Speciation and Extinction Biogeography October 29 - Nov 2

Speciation and Extinction  Defining a species Morphological definition Morphological definition Biological definition Biological definition Subspecies Subspecies  Mechanisms of Speciation Genetic drift Genetic drift Natural selection Natural selection Gene flow Gene flow  Types of Speciation Allopatric speciation Allopatric speciation Sympatric speciation Sympatric speciation  Other Issues Convergent evolution Parallel evolution Coevolution Punctuated equilibrium  Extinction Probability of extinction Recent extinctions Fossil extinctions

Defining a Species  Morphologically Species are morphologically distinct Species are morphologically distinct  Biologically Reproductively isolated (geologically or biol) Reproductively isolated (geologically or biol)  Subspecies Populations that are morphologically (and therefore presumably) genetically distinct Populations that are morphologically (and therefore presumably) genetically distinct

Mechanisms of Speciation  Genetic Drift Changes in genetic characteristics of population due to pure chance Changes in genetic characteristics of population due to pure chance Founder Effect Founder Effect  Natural Selection Change in population (genetic/morphological) resulting from expression of genetic characteristics by individuals in population that enhances their survival Change in population (genetic/morphological) resulting from expression of genetic characteristics by individuals in population that enhances their survival  Gene Flow Change in genetics of population due to introduction of genetic materials from outside the population Change in genetics of population due to introduction of genetic materials from outside the population

Types of Speciation  Allopatric Speciation occurs when pops are geographically isolated so gene flow b/w pops cannot occur occurs when pops are geographically isolated so gene flow b/w pops cannot occur Vicariance eventsVicariance events Disperal/Founder eventsDisperal/Founder events PeripatricPeripatric Peripheral populations are Peripheral populations are geog. isolated from main geog. isolated from main population and thus genetic population and thus genetic divergence is accelerated divergence is accelerated (form of Adaptive Radiation)

Types of Speciation  Sympatric Speciation Speciation occurring within spatially contiguous populations Speciation occurring within spatially contiguous populations ParapatricParapatric evolutionary divergence (speciation) in populations that occupy different habitat in the same geographic area (sympatric form of adaptive radiation) evolutionary divergence (speciation) in populations that occupy different habitat in the same geographic area (sympatric form of adaptive radiation) Chromosomal changesChromosomal changes Polyploidy in plants Polyploidy in plants

Other Issues  Convergent Evolution Unrelated species separated geographically evolve similar traits Unrelated species separated geographically evolve similar traits

Other Issues  Parallel Evolution Descendants of an ancestor now isolated evolve in a similar fashion Descendants of an ancestor now isolated evolve in a similar fashion

Other Issues  Coevolution Mutualistic associations Mutualistic associations  Punctuated Equilibrium Long periods with no change followed by severe environmental changes Long periods with no change followed by severe environmental changes As compared to phyletic gradualism As compared to phyletic gradualism

Extinction  “ The ultimate fate of every species is extinction.” Brown and Lomolino 2000  RED QUEEN HYPOTHESIS “A species must continually evolve in order to keep pace with an environment that is perpetually changing, because all other species are evolving, altering the availability of resources and the nature of biotic interactions.” Van Valen 1973 “A species must continually evolve in order to keep pace with an environment that is perpetually changing, because all other species are evolving, altering the availability of resources and the nature of biotic interactions.” Van Valen 1973

The Probability of Extinction  Taxon level individuals individuals subspecies subspecies species species more inclusive taxon levels more inclusive taxon levels trophic cascades trophic cascades

The Probability of Extinction  Ecological Groups Large body size Large body size Upper trophic levels Upper trophic levels Highly specialized Highly specialized Specifc habitats Specifc habitats

The Probability of Extinction  Population Size Birth rates Birth rates Death rates Death rates Carrying capacity Carrying capacity  Small populations Intrinsic demographic events Intrinsic demographic events Extrinsic ecological events Extrinsic ecological events  MVP = Minimum Viable Population

The Probability of Extinction (Quammen 1996: Song of the Dodo, p. 295)

Recent Extinctions  Passenger Pigeon  Barro Colorado Island  Gray Whale

Fossil Extinctions  Mass extinctions Permian-Triassic (225 mybp) Permian-Triassic (225 mybp) Pleistocene megafauna (10-12K ybp) Pleistocene megafauna (10-12K ybp) Overkill hypothesisOverkill hypothesis Climate hypothesisClimate hypothesis Cretaceous-Tertiary (65 mybp) Cretaceous-Tertiary (65 mybp)

Millenium Ecosystem Assessment 2005