GEOGRAPHY 316: BIOGEOGRAPHY
B. Holzman, PhD
10/21/02

Evolution: Speciation and Extinction/
Novelty and Natural Selection

10/21/02 & 10/23/02
Note: On 10/21 we saw a video entitled Evolution: #80699 if you missed class  you may view the video at the Media Center (3rd Floor of the  Library)

Evolution
I.  The Theory
II. Population Growth
III.Variation:  heritability
     Non-heritable Variation
      Heritable Variation
IV. Patterns of Evolution
         Divergent Evolution
         Adaptive Radiation
     Convergent Evolution
     Coevolution
=============================================
I.   THEORY:  More offspring are produced than will survive. competition for survival will select for the fittest individuals.  The fittest individuals will survive to mate and reproduce and their offspring will carry those inherited traits in their genes

Chromosomes

Genes

Alleles

Mutation:  change in genotype

Genotype:  genetic constitution

Phenotype: the way the gene is expressed
==========================================
II. Barriers to Interbreeding

Isolating Mechanisms
1) courting rituals and mating behaviors

2) mating sites may differ

3) timing of mating
============================================
Natural selection:
Observation 1:  More young are born than survive to reproduce
Observation 2:  Variation exists among the members of a population
    Deduction 1:  Some of the variants are better suited to prevailing
    conditions and are more likely to survive to reproduce than other variants

Observation 3:  Some of this variation is heritable
    Deduction 2:  Because these attributes are to some degree heritable,
    favorable attributes will accumulate in the population over time.

========================================
Controversies:

1) continuous vs. punctuated
    Continuous
    Punctuated (S.J. Gould)

2) Is isolation necessary?
    Allopatric speciation
    Sympatric speciation

----------------------------------------------------------------------
III. Variation

Non-heritable variation:  differences arise from environment

ex. tree leaves (Sagebrush)
    Himalayan rabbit

Heritable Variation:  differences are passed through genotype

Geographic
Horned Larks (Eremophila alpestris) facial colors
Song Sparrow (Melospiza melodia) size and color

Polymorphism
Common flicker  (Colaptes auratus)
Yellow rumped warbler (Dendroica cornata)

IV.  Patterns of Evolution

Divergent Evolution and  Adaptive Radiation

Two conditions:
1) Species colonization of isolated habitat

2) Sudden evolutionary appearance of a novel morphological or physiological feature of an organism

Convergent Evolution
Evolutionary change causes unrelated species with very different evolutionary histories to acquire striking morphological, physiological and/or behavioral similarities.

Examples:
Jerboas and Kangaroo rats
Cacti and Euphorbs
Longclaws and Meadowlarks
Pocket Gophers and Tuco Tucos

CoEvolution
The interdependent evolution of two or more species

Examples:
Ants and acacias
Plants and pollinators
Predator and prey