I believe
that evolutionary change is generally gradual unless it is catalyzed by a super
natural event such as the meteor that caused the extinction of the dinosaurs or
a random beneficial mutation. Change is generally gradual because it is a stepwise
process that involves species evolving with small variations over millions of
years rather than large variations over a short amount of time. The factors
that might lead to slow change of flora would be environmental conditions such
as carbon dioxide levels or formations of mountain ranges. Millions of years
ago the atmospheric carbon dioxide levels were much higher than they are today
which is why broadleaf plants had lower stomata density and larger stomata when
compared with broadleaf plants today. As the atmosphere changed and carbon
dioxide became a less bountiful gas, the broadleaf plants slowly evolved to
have a higher stomata density and smaller stomata in order to be able to
compensate for the lower bioavailability of carbon dioxide. It can be verified
that this change was slow because we are still able to find broad leaf plant
fossils indicating that the change occurred over a long enough period to allow
the leaves to become fossilized. The formation of the Cascade mountain range
created a difficult barrier for rain clouds to pass over due to sheer weight so
that rain must be shed prior to passing over the mountain range. As a result,
this rain shadow effect lowers the amounts of water that will   be
available for plants which over millions of years caused the size of plants and
trees to decrease in order to ease survival with the amount of water they
received.   

 

 

            Spermophilus columbianus, lateralis and saturatus
all have similar tail lengths that account for roughly a third of their total body
length, small ears relative to their body sizes and sharp claws. Differences
amongst species include the shorter body lengths and claws that Spermophilus lateralis and saturatus possess
as well as their notable stripes running the length of their bodies’.  Conversely Spermophilus
columbianus has the longest body length of the three, long claws for
digging, a flat, fluffy tail and no stripes on its body. These squirrel species
likely had the same predators because they were all ground dwellers in a
similar area which could account for the shared similarities. The formation of
the Okanagan River likely lead to the homology between the three Spermophilus species. I hypothesize that
when the river formed, the species could no longer traverse the river and were
confined to the whichever side of the river they ended up on and this affected
the evolution of the claws amongst species. The Spermophilus saturatus ended up on the West side of the Okanagan
where it used its’ short claws to run from predators on the ground just like its’
relative Spermophilus lateralis which
ended up on the East side of the Okanagan.

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Spermophilus columbianus ended up in arid central Washington where it used
its’ longer claws to dig burrows that enable it to hide from predators in a
landscape that does not offer very much foliage cover.