Objective 1:
History
of Darwinism
Lamarck
biography (optional)
The
Imaginary Lamarck: A Look at Bogus "History" in Schoolbooks
(optional)
Objective 3:
Evolution
is a Fact and a Theory (talkorigins.org)
Objective 4:
Polymorphisms and genetic variability (4a)
Variation
correlated with geography
Applied
to humans
Applied
to tree shrews
Ecological
rules (optional)
Objective 7:
Gene duplication
mechanisms
Objective 10:
Sexual
dimorphism (10c)
Size
Does Matter When Choosing a Mate.
Survival of the fittest females: Tiny animals evolve through
the ages without males' help (optional)
Objective 13:
Anagenesis vs. cladogenesis
Objective 14:
Divergent
evolution
Adaptive
radiation
Hawaii
- a natural laboratory for adaptive radiat ion
Objective 19:
Exaptation
Optional Supplementary Material:
Barcoding Life: A New
Approach to Defining Species.
What are hybrid zones?
Reduced hybrid fertility - check out a liger!
Where is speciation faster: tropics or temperate zones?
Darwin
Finch Die-off: Parasitic flies on the Galápagos Islands threaten
Darwin's famous finches.
|
Variation Correlated With Geography
The phenotypes of the individuals within a species often vary
in a systematic way across the range of species. Sometimes, all the individuals
in one part of the range will be the same but will be different from the individuals
in another part of the range. If these different types of individuals are distinctive
enough, each type may be recognized as a subspecies. Such differentiation within
a species is important because it may lead to speciation. This could occur
if the different groups within a species became isolated from each other for
a length of time sufficient to allow the evolution of intrinsic reproductive
isolating mechanisms. These are traits that would prevent the individuals of
one group from successfully reproducing with individuals of the other group
should they ever meet in the wild.
Geographic variation within a species can also be gradual. Such
variation is referred to as a cline. Clines often occur because of gradual
changes
in the
environment across the range of a species. Ecologists have noted a number of
general ways in which the characteristics of the individuals within a species
can vary because of climate. Here are three examples:
- Bergmann’s Rule: The members of a species of warm-blooded
animals (endotherms) tend to be larger in colder climates. Larger size decreases
the surface/volume ratio and so decreases the rate of heat loss.
- Allen’s
Rule: The extremities (ears, feet, tail) of endotherms tend
to be smaller in colder climates. What explanation can you give for this?
- Gloger’s
Rule: The members of a species living in arid regions tend to be lighter
in color than those living in more humid regions. Why do you
suppose
this is?
Zoogeographic variation in the Song Sparrow (Melospiza
melodia)
(click to enlarge, from The
Sibley Guide to Birds, David Allen
Sibley, 2000)
The diagram above shows a variety of song sparrow specimens
from different populations within the species’ North American range.
Although this species is migratory, birds
of
a given
subspecies
always return during the breeding season to the same general part of the
range inhabited by that subspecies. Originally, many of these subspecies
were considered full species until additional populations with morphologically
intermediate individuals were discovered. The image shows subspecies from:
the Aleutian islands in western Alaska, the humid Pacific Northwest, the
California Coast, The Northeastern U.S., and the arid Southwest. Which, if
any, of the zoogeographic
rules are in effect with song sparrow populations?
|
