Chapter 16: The Origin of Species

Species: Groups of interbreeding natural populations that are Chapter 16: Origin of Species Species: Groups of interbreeding natural populations that are reproductively isolated from other groups Biological-species Concept What about asexually reproducing species? Speciation: Process by which new species form (Ernst Mayer - 1930s) Require: 1) Isolation of populations (restricted gene flow…) 2) Genetic divergence (evolve genetic differences…) Unable to produce vigorous, fertile offspring

Mechanisms of Speciation: Chapter 16: Origin of Species Mechanisms of Speciation: 1) Allopatric Speciation: Populations are geographically separated from one another Impassible Barrier Forms (e.g. mountains, river, ocean) Gene Flow

Mechanisms of Speciation: Chapter 16: Origin of Species Mechanisms of Speciation: Major Mechanism of speciation among animals 1) Allopatric Speciation: Populations are geographically separated from one another Impassible Barrier Forms (e.g. mountains, river, ocean) Time Passes Gene Flow Species 1

Allopatric Speciation: Chapter 16: Origin of Species Allopatric Speciation: (Figure 16.2)

Mechanisms of Speciation: Chapter 16: Origin of Species Mechanisms of Speciation: 2) Sympatric Speciation: Populations share the same geographic area Gene Flow

Mechanisms of Speciation: Chapter 16: Origin of Species Mechanisms of Speciation: Polyploidy is a common mechanism of speciation among plants 2) Sympatric Speciation: Populations share the same geographic area Why is gene flow reduced? A) Ecological Isolation: Gene Flow Two distinct habituate types in the same geographic area leads to habitat specialization Time Passes B) Chromosome Aberrations: Changes in chromosome #s can cause reproductive isolation Polyploidy: Acquisition of multiple copies of each chromosome

Sympatric Speciation: Chapter 16: Origin of Species Sympatric Speciation: (Figure 16.2)

Speciation “Produces” Evolutionary Trees: Chapter 16: Origin of Species Lines that reach the top represent extant species Speciation “Produces” Evolutionary Trees: Lines that don’t reach the top represent extinct species Vertical slopes represent slow changes in form Forks represent speciation events Horizontal slopes represent rapid changes in form Each line represents a species

+ = Species: Groups of interbreeding natural populations that are Chapter 16: Origin of Species Species: Groups of interbreeding natural populations that are reproductively isolated from other groups Isolating Mechanisms: Structural and / or behavioral modifications that prevent interbreeding Table 16.1 Adaptive Value: Prevent “wasting” of reproductive effort by producing unfit / sterile offspring + =

Mechanisms of Reproductive Isolation: Chapter 16: Origin of Species Mechanisms of Reproductive Isolation: 1) Premating Isolating Mechanisms: Incompatibilities that prevent mating events A) Geographical Isolation: The separation of two species by a physical barrier B) Ecological Isolation: The separation of two species occupying separate niches

Mechanisms of Reproductive Isolation: Chapter 16: Origin of Species Mechanisms of Reproductive Isolation: 1) Premating Isolating Mechanisms: Incompatibilities that prevent mating events C) Temporal Isolation: The separation of two species due to different breeding seasons Pond Spring Autumn D) Behavioral Isolation: The separation of two species due to different courtship rituals croak… croak... clack… clack...

Mechanisms of Reproductive Isolation: Chapter 16: Origin of Species Mechanisms of Reproductive Isolation: 1) Premating Isolating Mechanisms: Incompatibilities that prevent mating events E) Mechanical Incompatibility: The separation of two species due to differences in reproductive structures Tailed Frog Tree Frog

+ Mechanisms of Reproductive Isolation: Chapter 16: Origin of Species Mechanisms of Reproductive Isolation: 2) Postmating Isolating Mechanisms: Incompatibilities that prevent production of vigorous, fertile offspring A) Gamete Incompatibility: Sperm from one species are unable to fertilize eggs from another species B) Hybrid Inviability: Hybrid offspring survive poorly + C) Hybrid Infertility: Hybrid offspring unable to reproduce

Extinction: The death of all members of a species Chapter 16: Origin of Species Extinction: The death of all members of a species 99.9% of all species ever existing are extinct (fossil record) Cause of Extinction = Environmental Change Species Vulnerable to Extinction Display... 1) Localized Distribution (susceptible to localized catastrophes) 2) Overspecialization (susceptible to minute changes)

Environmental Changes Driving Species to Extinction: Chapter 16: Origin of Species Environmental Changes Driving Species to Extinction: 1) Competition With Other Species: Competitors evolve superior adaptations that allow them to out-compete a species 2) Introduction of Parasites / Predators: Predators / Parasites prey upon naïve species 3) Habitat Change / Destruction: Single greatest cause of extinctions