OBJECTIVES: 1) EXPLAIN WHY DEFINING SPECIES IS DIFFICULT 2) IDENTIFY CAUSES OF SPECIATION 3) DESCRIBE MACROEVOLUTIONARY PROCESSES/PATTERNS SPECIATION & MACROEVOLUTION

Are these spiders the same species?

What is a species?? Different species concepts…  Biological species concept  Phylogenetic species concept  Ecological species concept

Biological Species Concept 1 or more populations whose members interbreed and produce fertile offspring Reproductively isolated from other species Has own gene pool

Problems with Biological Species… Asexual Reproduction.. Hybrids…

Speciation Event that splits lineage and produces 2 or more species Speciation can be difficult to identify…

Ring species (ex. Ensatina)  All of these salamanders can interbreed with their immediate neighbors except E. eschsholtzii and E. klauberi  Where did speciation occur?

ISOLATION + SELECTIVE PRESSURE What causes speciation?

GEOGRAPHIC REPRODUCTIVE Types of Isolation

Geographic Isolation…  Event causes populations to separate  Gene flow ceases

 Over time, the 2 populations experience different selective pressures  Physical changes  Food/Habitat preferences  Courtship

Species do not need to be completely separated  Broad geographic range  Reduced gene flow  Hybrid zones  May or may not = speciation

Reproductive Isolation Prezygotic barriers – prevent fertilization  Temporal  Habitat  Behavioral

 Mechanical  Gametic

Postzygotic barriers  Hybrid inviability  Hybrid sterility  Hybrid breakdown

Types of Speciation: Allopatric Results from geographic isolation  Natural selection  Genetic drift Most common Sympatric Same location  Change in ploidy  Ecological change More common in plants

Rate of change 2 models try to explain fossil record Gradualism  Proposed by Darwin  Evolution is a continuous process  Change is slow and steady  Series of transitional forms  Millions of years  Difficult to observe in fossil record

Punctuated equilibrium  Proposed by Gould and Eldridge (1970s)  Fossil record may not be as incomplete as we believe  Long periods with little change are interrupted by short bursts of rapid speciation (tied to speciation event)  Macromutation  Skip transitional forms  Thousands of years

Macroevolution Large-scale Evolution  Species level + Zooms out on tree of life

Patterns in Macroevolution

Stasis Lineage remains stable/little change for long period of time What can this tell us?

Speciation Phylogenetic tree can reveal history, frequency of speciation in a clade

Extinction Opens ecological niches Surviving species rapidly diversify

Adaptive Radiation Evolutionary diversification of many species from one/few ancestral species in short amount of time Divergent Adaptive zones – new ecological opportunities