Species & SpeciationSpecies & Speciation

Main Points for Class Meeting:Main Points for Class Meeting:1.1. How do new species arise?How do new species arise?

2.2. How do we organize species diversity?How do we organize species diversity?

3.3. How many species are there??How many species are there??

Review – Genetic Review – Genetic Variation & InheritanceVariation & Inheritance

Track a trait based on what we Track a trait based on what we learned in our last class session:learned in our last class session:

““Widow’s peak” is Widow’s peak” is dominantdominant No widow’s peak is No widow’s peak is recessiverecessive Example on board - Example on board -

What are some sources What are some sources of genetic variation?of genetic variation?

MutationMutation Sexual reproduction – the sorting & Sexual reproduction – the sorting &

recombination of genes from both recombination of genes from both parents leads to an almost endless parents leads to an almost endless set of different traitsset of different traits

Phenotypes & genotypes…Phenotypes & genotypes…

What happens when a What happens when a species species losesloses genetic genetic

diversity?diversity? Example: Example:

The Cheetah

What – again – makes a What – again – makes a species species distinct?distinct?

The Biological species concept:The Biological species concept:Species: Species:

A population whose members can A population whose members can interbreed to produce healthy, fertile interbreed to produce healthy, fertile offspring.offspring.

Via Via SpeciationSpeciation::

The keystone process in the formation The keystone process in the formation of diversity in higher taxa.of diversity in higher taxa.

1. How do new species 1. How do new species arise?arise?

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Two patterns of Two patterns of speciation:speciation:

1) Accumulation of 1) Accumulation of changes as one changes as one species is species is transformedtransformed into into another (= “another (= “verticalvertical changechange” – Wilson ” – Wilson ch. 5)ch. 5)

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Fig. 24.1a

Two patterns of Two patterns of speciation:speciation:

2) Branching 2) Branching evolution: the evolution: the budding of new budding of new species species fromfrom a a parent speciesparent species

Which type Which type increases diversity?increases diversity?

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Fig. 24.1b

For new species to arise, For new species to arise, gene flow gene flow between populations must be between populations must be interrupted.interrupted.

How might this occur? In your How might this occur? In your groups, discuss some possible groups, discuss some possible mechanisms.mechanisms.

1. How do new species 1. How do new species arise? arise? (cont’d)(cont’d)

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

AllopatricAllopatric speciationspeciationoccurs when occurs when geographic separation geographic separation of populations restricts of populations restricts

gene flow.gene flow.

Fig. 24.6

Geological processes: isolate Geological processes: isolate populations from each otherpopulations from each other

E.g.: Mountain ranges, glaciers, land E.g.: Mountain ranges, glaciers, land bridges, splintering of lakes…bridges, splintering of lakes…

OR, some individuals may colonize a OR, some individuals may colonize a new, geographically remote area and new, geographically remote area and become isolated from the parent become isolated from the parent population.population.

e.g. Galapagos Islandse.g. Galapagos IslandsCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

How significant a barrier must be to How significant a barrier must be to limit gene exchange depends on the limit gene exchange depends on the mobility of organisms.mobility of organisms.

A geological feature that is only a A geological feature that is only a minor hindrance to one species may minor hindrance to one species may be an impassible barrier to another.be an impassible barrier to another. The valley of the Grand Canyon is a The valley of the Grand Canyon is a

significant barrier for ground significant barrier for ground squirrels which have squirrels which have speciated on opposite speciated on opposite sides, but birds which sides, but birds which can move freely havecan move freely haveno barrier.no barrier.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 24.7

When populations come back in contact When populations come back in contact they may or may not interbreed and they may or may not interbreed and produce fertile offspring. produce fertile offspring.

Has speciation occurred in the 2 scenes Has speciation occurred in the 2 scenes below?below?

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 24.8

This is the area of biology called This is the area of biology called PhylogenyPhylogeny

We make “family trees”We make “family trees”

2. How do we organize 2. How do we organize species diversity?species diversity?

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

What is the taxonomic What is the taxonomic hierarchy used by hierarchy used by

biologists to organize biologists to organize diversity?diversity?

Mnemonic device for remembering Mnemonic device for remembering the levels of the hierarchy…?the levels of the hierarchy…?

3 Domains3 Domains

http://www.ucmp.berkeley.edu/alllife/threedomains.html

6 (+?) Kingdoms 6 (+?) Kingdoms

DOMAIN ARCHAEA

Assignment:Assignment:

Choose an organism you know or Choose an organism you know or have found (on campus, at your have found (on campus, at your home, somewhere you’ve visited)home, somewhere you’ve visited)

Figure out what it is, as closely as Figure out what it is, as closely as possible possible

Make a “Family Tree” for your Make a “Family Tree” for your organism – classify it according the organism – classify it according the taxonomic hierarchy, to the lowest taxonomic hierarchy, to the lowest level you can! level you can!

How many How many knownknown species are there? species are there? (approximately…) (Wilson ch.8)(approximately…) (Wilson ch.8)

What proportion of species have we What proportion of species have we probably described?probably described?

Why are we so uncertain about the Why are we so uncertain about the numbers of species on Earth? numbers of species on Earth?

3. How Many Species?

Examples of Examples of groups of groups of organisms that are organisms that are mostly unknownmostly unknown

Why is this the Why is this the case?case?

3. How Many Species?

SpeciesSpecies diversitydiversity can be can be measured measured at 3 scales, at 3 scales, for for comparison comparison of sites in of sites in different different areasareas

(3. How Many Species?)

Alpha (local) & gamma (regional) diversity, & beta diversity or turn-over between sites

http://www.redpath-museum.mcgill.ca/Qbp/2.About%20Biodiversity/definition.htm