Miller Chap 5 - Evolution and Biodiversity: Origins, Niches,
Adaptation
Start with a story about Earth being "just right" for life "as we know it" in
terms of temperature (neither too hot nor too cold) and size (gravity right
for holding atmosphere)
Purpose of this chapter is to show how species have evolved and highlight
the roles they play
5-1 Life and its origins
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Some experiments suggest that inorganic compounds could have
produced organic molecules such as amino acids, simple sugars
Miller suggests a 2-stage sequence of evolution Fig 5-2:
 Chemical evolution of organic molecules leading to first protocell out of a "primordial soup" of inorganic compounds, electrical energy
(lightning) created amino acids, carbohydrates, nucleic acids, and
other organic compounds.
 Biological evolution thereafter - It is still a mystery as to how the
first single-celled organisms from these organic compounds
evolved to multicelled life of today.
Emergence of life
"we don't know the full story, but …" Fossil evidence suggests a record of
evolution shown in Fig 5-3
5-2 Biological Evolution and Adaptation
Evolution defined: "change in a population's genetic makeup through
successive generations".
Mechanism of evolution believed to be random genetic mutations that can
be inherited…those that are harmful tend to not be passed on throughout
the population. Those that are helpful do tend to be passed on throughout
the population.
Process of "natural selection" is this spread of helpful traits … they are
"naturally selected" through the process of procreation, and become more
and more common in successive generations, eventually becoming the
norm, not the exception.
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Interesting peppered moth story highlighting evolution and natural
selection Fig 5-4:
Light-colored moths were prevalent in pre-Industrial England, when
they blended in with light-colored lichen on trees and were protected
from predators.
Dark-colored moths became dominant after trees became darkened
with soot in post-Industrial England, and predators started eating all
the light-colored moths.
Moral of the story: dark-colored moths much better equipped to
survive, those are the ones whose traits become more widespread
throughout the population
Miller notes 3 common misconceptions about evolution:
1. "survival of the fittest" is a misnomer, because it suggests "tooth and
claw" competition. Reality is that this means that fittest species are
those that best work with their environment to survive.
2. "man evolved from the apes" - actually, the theory is that man and
apes separately evolved from some common ancestor, hundreds of
thousands, perhaps millions, of years ago.
3. "grand plan of species becoming more perfect" - no such plan, that we
know of, exists. Genetic mutations are random, and if they are of
benefit to a species' survival they will be passed on over time
throughout the population.
5-3 Ecological Niches and adaptation
Niche defined - a species' role in an ecosystem
"niche is a species' occupation, and a habitat is its address"
Miller distinguishes between a "fundamental" and a "realized"
niche…fundamental is what it could theoretically occupy, with no
competition. But there usually IS competition, so the realized niche is
different. Miller uses a corporate professional analogy…you COULD be a
CEO, but due to competition you are only a VP
Generalist vs Specialist - important distinctions of these types of species
(Fig 5-6)
Generalists:
-live in many diff areas
-eat diff foods
-tolerate wide range of envir conditions
examples: flies, cockroaches, mice, rats, deer, raccoons, catfish, humans
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Specialists:
-live in very limited habitat
-eat narrow range of food
-tolerate a narrow range of conditions
specialists tend to really dominate when conditions are right (Dinosaurs in
the Mesozoic), but they are more prone to extinction than generalists
because they don't like change…..
5-4 Speciation, extinction, biodiversity
Speciation - process of 2 species arising from one - example of arctic and
gray fox developing from common ancestor….(Fig 5-7)…each develops
certain characteristics that are well-suited to particular environment (cold
vs hot)
Mechanism first, the original population is split into 2 groups, and they become
geographically isolated
second, mutation operates independently in each of the populations, and
their gene pools become different through reproductive isolation. They
may look the same, but can no longer interbreed. This is what Darwin
observed with species in the Galapagos Is off S. America - they looked
almost identical to species on the mainland, but were different enough to
be unable to interbreed
Extinction When environmental conditions change, species can essentially go one
of 3 ways….
- they can either continue to evolve and survive in the new environment,
- move to a new environment in which they will prosper, or
- they can die off in large numbers and become extinct.
Most mass extinctions are thought to result from large-scale changes, like
plates drifting through different climates (Fig 5-8). Look carefully at India,
which migrated from the South Pole to the equator in the last 225 m.y.
Other causes include rapid climate change (warming or cooling) perhaps
associated with huge volcanic eruptions and dust clouds cutting off large
amounts of sunlight.
These changes kill off many species, but leave behind those that are able
to adapt to the new reality and continue to procreate. Mass extinctions
are not new - some big ones have occurred over last 500 million years Fig
5-9
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Biodiversity
Speciation - extinction = biodiversity
This simple equation says, the more species you get, and the less amount
of extinctions that happen, will result in the largest biodiversity.
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