MACROEVOLUTION & SYSTEMATICS: CHAPTER 5
May 11, 2015
MACROEVOLUTION & SYSTEMATICS:CHAPTER 5
DEFINITIONS Microevolution: genetic change in a population from one generation to the next
Macroevolution: Processes through which new species arise
WHAT IS A SPECIES? Biological species concept: If
organisms from two populations are capable of breeding naturally and can produce fertile offspring, then they are classified in the same species.
Horse Donkey Mule
X =
SPECIATION The formation of new
species Gene flow keeps
populations similar to one another.
Reproductive Isolation: genetic isolation of populations that may cause them to become incapable of producing fertile offspring.
Gene flow is the glue that holds species together.
SPECIATION: A TWO STEP PROCESS1. Reproductive Isolation
Reduction of gene flow provides opportunity for speciation
Does not always lead to speciation
2. Genetic Divergence Other evolutionary forces
change population enough so that fertile interbreeding is no longer possible
ANAGENESIS: “STRAIGHT-LINE” EVOLUTION
Single species evolving into new species over time
CLADOGENESIS: “BRANCHING” EVOLUTION
Formation of one or more new species from another over time
3 TYPES OF SPECIATION
1. Allopatric speciation-speciation in organisms with no geographic overlap.
2. Parapatric speciation-speciation in organisms with partial geographic overlap.
3. Sympatric speciation-speciation in organisms with complete geographic overlap.
ALLOPATRIC SPECIATION
MODELS OF SPECIATION
PARAPATRIC SPECIATION
SYMPATRIC SPECIATION
Niche: the way of life of a species (How that species fits into the surrounding environment)
Niche partitioning: species evolve to occupy different niches and avoid competition Ex. occupying different
places in the habitat, feeding at different times, being active at different times of the year, etc.
Bees and moths use the same food resource
Bees diurnal, Moths nocturnal
☼ Can’t have two species occupying the same niche in the same area because this will lead to competition.
NICHE PARTITIONING
SPECIATION RATE
Rate of Speciation: depends on # of empty niches
Adaptive Radiation: Rapid diversification by a small # of species to fill many open niches
TEMPO OF EVOLUTION
Gradualism: Macroevolution is a relatively slow and gradual process.
Punctuated Equilibrium: Long intervals of time with little change (stasis) interspersed with short intervals of rapid evolutionary change.
THE BIRTH OF SPECIES
a) Gradualism
b) Gradualism with increase in rate of change
c) Punctuated Equilibrium =Staircase pattern
EXTINCTION The
disappearance of a group of organisms such as a species.
When a species cannot change fast enough to adapt to changes in its environment, it may become extinct.
NEARLY EVERYTHING THAT HAS EVER LIVED IS EXTINCT
PALEOSPECIES
Paleospecies: Identified in the fossil record based on physical similarities to and differences from other species
Assumption: physical similarity = genetic relatedness
CLASSIFICATION
Classification is used to order organisms into categories to show evolutionary relationships.
LINNAEAN SYSTEM OF CLASSIFICATION Hierarchical
classification Involves a number of
categories and subcategories reflecting evolutionary relationships Kingdom Phylum Class Order Family Genus Species
Carl Linnaeus
HOW CAN WE MAKE SENSE OF ALL OF THIS DIVERSITY?
PHYSICAL SIMILARITIES ARE ONLY USED TO CLASSIFY ORGANISMS IF THEY REFLECT EVOLUTIONARY RELATIONSHIPS
Analogous traits: Traits similar due to common function
Homologous traits: Traits similar due to common ancestry
NOT ALL HOMOLOGOUS TRAITS ARE EQUALLY USEFUL FOR
CLASSIFICATION Ancestral trait: Trait appearing early in the evolution of a lineage
Derived trait: Traits that are modified from the ancestral condition
USING DERIVED TRAITS TO BUILD PHYLOGENIES
Analogous Traits Ancestral TraitsDerived (Homologous) Traits
EVOLUTION OF THE COOTIEMOUTH
(PHYLOGENETIC TREE)
QUESTIONS1. What is a phylogeny? 2. What is the difference between
analogous and homologous traits?3. What is the difference between ancestral
and derived traits4. What is the difference between
microevolution and macroevolution?5. What is the biological species concept?7. What are allopatric, parapatric, and
sympatric speciation? 8. What is an adaptive radiation?9. How do you identify a paleospecies and
what are the problems with this method?
HAVE A NICE DAY!