Transcript Natural Selection

Geography 210: Physical Geography and
Environmental Issues
Biodiversity
Biogeography
The Creation by Michelangelo
Natural Selection
• Organisms that have
characteristics better suited to the
environments they are in survive
better, as do their offspring, given
that the parents’ traits are
inherited.
– Taller giraffes, faster cats,
smarter hunters, can get more
food, survive
– Pests become resistant to
pesticides
Idealized relation of an island’s size, distance from the mainland,
and number of species.
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The main bio-geographic realms for animals are
based on genetic factors.
In each biogeographic realm, certain families or orders are dominant.
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The major vegetation realms are also based on
genetic factors.
© 2003 John Wiley and Sons Publishers
Ocean Floor Spreading
Plate Tectonics
Continents in motion
Divergent Evolution
Ostrich – Africa
Rhea – South America
evolution from a common ancestor
Evolution of Life on Earth
• Past history from fossils and other
stratigraphic deposits
• Earliest beginnings: microorganisms
• Early evolution was slow
• 2 B y b p for 1st organisms.
– Bacteria
• 2-0.4 B y b p – the age of plants
• 0.5 B y b p – first critters, mussels,
trilobites
• 0.2 B y b p – proto human
Symbiosis
“living together”
Fig 7.8 The
stomach of a
reindeer
illustrates
complex
symbiotic
relationships.
© 2003 John Wiley and Sons Publishers
Succession
Change in the relative abundance of a species over an area or a distance
is referred to as an ecological gradient.
© 2003 John Wiley and Sons Publishers
Biogeographer, Dr. Keith H. Topps, Nipissing University, Ontario, Species
Replacement at an Alpine Treeline, Top of the World Highway, Yukon, Canada
All organisms are adapted to the
environment in which they live
Support: Fossils
Support: Fossils
•Earliest fossils were
prokaryotes
•Appeared in fossil
record about 3.5
billion years ago
Chronological Appearance of Vertebrates
Support: Fossils
Fossils link past and present
Whales have
forelegs in the
form of flippers,
however, they
also have
vestigial hind-leg
and foot bones
that do not extend
from their body
Support: Fossils
Basilosaurus is
an extinct
whale that had
hind-legs
These also are
vestigial legs
as the ancient
whale was an
aquatic animal
Other Support: Comparative Anatomy
• Comparative Anatomy: comparison of
body structures in different species
• Anatomical similarities among many
species give signs of common descent
Other Support: Molecular Biology
Artificial Selection
German shepherd
Yorkshire terrier
English springer
spaniel
Hundreds to
thousands of years
of breeding
(artificial selection)
Ancestral dog
Mini-dachshund
Golden retriever
Natural Selection
African wild
dog
Coyote
Fox
Thousands to
millions of years
of natural selection
Ancestral canine
Wolf
Jackal
Natural Selection in Action
Chromosome
with gene
conferring
resistance
to insecticide
Insecticide
application
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
Microevolution
Chromosome
with gene
conferring
resistance
to insecticide
Insecticide
application
Gene pool changes
as most alleles
that do not confer
insecticide resistance
are removed
Survivor
Causes of Microevolution
• Bottleneck
effect:
genetic drift
that results
from event
that
drastically
reduces
population
size
Causes of Microevolution
•Founder effect: random change in gene pool that occurs
in a small colony of a population
•A type of genetic drift
•Over time, random changes in allele frequencies will
continue until population is large enough that genetic
drift is minimal
Variation is extensive in populations
2 morphs of California King Snake