The word species is Latin for “kind”.

What kind of animal is that?What species of animal is that?

>20,000 fish~8,700 birds~6,000 reptiles~4,500 mammals~2,500 amphibians

Species are based on inter-fertility, not physical similarity: Can things breed

together?

A species is a group of populations whose individuals have the potential to interbreed and produce fertile offspring. Populations of a species…

may be isolated from each other, or they may inter- grade with low densities in an intermediate region.are far more likely to breed with members of the same population than with mem-

bers of other populations.

Ex: the domesticated dog (Canis lupus familiaris) has become isolated from its parent species, the gray wolf (Canis lupus), but can still mate occasionally and produce fertile offspring.

A population is characterized by its genes.Genes can mutate, which produces variation within a species, one of the prerequisites

of Darwinian evolution.

As diploid beings,animals receiveone set of genes from each parent

Ex: AA, Aa, aaA & a are alleles, or versions of genes - eye color.

one gene

Evolution on the scale of populations, called micro-evolution, is defined as a change in the allele frequen-cies in a population’s gene pool over time.

Allele frequency is the probability that a particular allele is present within a population.Allele frequencies can change over time.Individuals are selected, but populations evolve.

The total accumulation of genes in a population at any one time is called the population's gene pool.

A population's gene pool is defined by its allele frequencies.It consists of all the alleles for every gene in every individual.

If there are two or more alleles for a gene, each contributes a relative frequency in the gene pool.

Ex: a wildflower population with two flower colors –red & white.

The R allele codes for a gene that makes a red pigment. The r allele makes a defect-ive protein.

Geographic barriers lead to speciation.Ex: Mountain ranges, glaciers, land bridges, or

splintering of lakes may divide one population into isolated groups.

Ex: the valley of the Grand Canyon is a significant barrier for ground squirrels and some plants but not to birds.

Geographic barriers lead to speciation.Some individuals may colonize new, geographically remote areas and become isolated from the parent population.

Ex: Mainland organisms colonized the

Galapagos Is.

then radiated into new

habitats.

Behavioral isolation prevents intermingling of populations and leads to speciation.

Some behaviors are cues to initiate specific responses.Without the proper cue, a female may not be receptive to the male.

Ex: courtship displays - ♀ fireflies flash back when ♂s give a species-specific rhythm.

Behaviors can also trace back to a com- mon ancestor!

Speciation – the formation of a new species by the splitting of an existing species.

Allopatric speciation: Geographic barriers lead to speciation. Mountain ranges, glaciers, land bridges, or splintering of lakes may divide one population into isolated groups.*

Speciation occurs in different geo- graphical areas. Isolated species must fail to inter-

breed if reunited.

* Outside the homeland

Allopatric speciationEx: a western salamander, Ensatina escholtzii:

Populations interbreed in the north, but barriers isolated groups, and new species formed in the south.

Sympatric speciation: New species can originate in the midst of the parent species (in the same geographical area). *

In plants, this results from accidents during cell division that produce extra sets of chromosomes: polyploidy. Or failure of meiotic disjunction

* Inside the homeland

The evolution of many diversely adapted species from a common ancestor is called an adaptive radiation.

Darwin’s finches – all originated from one in Ecuador.Hawaiian Archipelago:

Individuals were carried from distant continents to older is- lands. They changed. Later

they colonized the new islands as they rose from the sea. They changed again, and so on.(Florida keys are too close to the mainland for this to have happened here.)

Convergent evolution: the independent development of similarity between species as a result of their having similar ecological roles and selection pressures.

Birds and insects both can fly, but birds did not evolve from insects.

Flight may have devel- oped as a method of

escape from predators, independently in both cases.

Convergent evolution:The fish-like body of whales and dolphins (mammals)

A stream-lined shape aids movement through water.

Time ---------------------------->

Convergent evolution:Mimicry: animals can mimic one another to confuse predators; animals mimic their habitat as camouflage.

Divergent evolution: from a common ancestor a diversity of new species may arise over time.

Darwin’s finches diverged from an Ecuadorean species.

Divergent evolutionEquine

diversification

Divergent evolutionDinosaur diversification

Traditional evolutionary trees diagram the diversifi-cation of species as a gradual divergence over long spans of time.

They assume big changes occur as the accumulation of many small ones over time – the gradualism model.But in the fossil record, many species appear

suddenly, persist es-sentially unchanged, and then disappear.

This second model is called punctuated

equilibrium.

Phylogenetic trees

In the punctuated equilibrium model, the tempo of speciation is not constant.

Volcanic eruptions and meteor impacts (below) affect the pace of evolution.

When the environment changes rapidly, many creatures disappear, and others must change to adapt.And, while external morphology may appear unchanged for long periods, changes

in behavior, physiology,

or even internal anat-

omy may be changing quickly.

When 2 or more forms of a discrete character are represented in a population, the different forms are called morphs.

Ex: the white and red flowers of a flower population.Ex: eye color, hair color, and skin color in humans.

Polymorphism is when two or more forms of a physical character are represented in high enough frequencies to be readily noticeable.

A transient polymorphism is one that is changing in frequency over time.

Ex: Resistance to a disease – when the pathogen is present more people are resistant. The frequency of genes for resistance can decline when the pathogen disappears.

Industrial melanism – the peppered mothColors of the peppered moth in Great Britain form a range from speckled white to black.

During the Industrial Revolution trees became covered in black soot, and the speckled types were easy to spot and were eaten by birds.The dark type wasn’t seen

as easily; they reproduced and became common, and the speckled ones

became rare.Today, with less pollution,

the process has reversed.Gene frequencies change.