Transcript APES Chapter 5 - Mrs. Reid's Webpage

APES CHAPTER 5
Evolution and Biodiversity: Origins, Niches, and
Adaptation
ORIGINS OF LIFE-2 PHASES:
Chemical evolution
Evolution of the
organic molecules,
biopolymers, and
systems of chemical
reactions needed to
from the first
protocells
 Lasted approx. 1
billion years

Biological evolution
Evolution of singlecelled organisms
(prokaryotes and then
eukaryotes) and then
multi-cellular
organisms
 Took approx. 3.7-3.8
billion years.

CHEMICAL EVOLUTION
4.6-4.7 billion years ago—cosmic dust cloud
condensed to from earth.
 4.4 billion years ago—atmosphere was formed—
contained NO oxygen.
 Energy available—lightening, heat from
volcanoes, and UV radiation.
 Stanley Miller and Harold Urey provided
experimental support the inorganic molecules
could combine to form simple organic molecules
under the conditions of the primitive Earth.
 Organic molecules may have formed membrane –
bound protocells.

BIOLOGICAL EVOLUTION
Protocells evolved into single-celled prokaryotes
 2.3-2.5 billion years ago, evolution of
photosynthetic prokaryotes started producing O2
 1.2 billion years ago the first eukaryotic cells
formed.
 400-500 million years: first plants on land, then
mammals, then man.

ORIGINS OF LIFE
Fig. 5-2 p. 96; Refer to Fig. 5-4 p. 98
HOW DO WE KNOW ORGANISMS LIVED IN
THE PAST?

Fossils

Relative dating—superposition and index fossils

Absolute dating—radioactive decay rate (half life)
EVOLUTION AND ADAPTION

Evolution—the change in a population’s genetic
makeup through successive generations.
Individuals do not evolve, only populations
evolve.
Microevolution—describes the small genetic
changes that occur in a population.
 Macroevolution—describes the long-term,
large-scale, evolutionary changes among groups
of species.

1. speciation (new species formed from ancestral species)
 2. species lost through extinction.

HOW MICROEVOLUTION WORKS

There must be a change in the Gene Pool (sum
total of all genes possessed by the individuals of a
population).

1. mutations—only changes in reproductive cells are
passed on to offspring
Random and unpredictable
 Most are harmful

NATURAL SELECTION

Three conditions necessary for evolution by
natural selection to occur.
1. natural variability
 2. heritable trait
 3. differential reproduction-greater chance for one
form to reproduce.


Three types of natural selection
1. directional
 2. stabilizing
 3. diversifying

Snail coloration
best adapted
to conditions
Average
New average
Natural
selection
Previous
average
Number of individuals
Number of individuals
Directional Natural Selection
Average shifts
Coloration of snails
Coloration of snails
Proportion of light-colored
snails in population increases
FIGURE 5-6 (1) PAGE 102
Light snails
eliminated
Dark snails
eliminated
Natural
selection
Number of individuals
Number of individuals
Stabilizing Natural Selection
Snails with
extreme
coloration are
eliminated
Coloration of snails
Average remains the same,
but the number of individuals with
intermediate coloration increases
FIGURE 5-6 (2) PAGE 102
Coloration of snails
Intermediate-colored snails
are selected against
Light
coloration
is favored
Dark
coloration
is favored
Natural
selection
Number of individuals
Number of individuals
Diversifying Natural Selection
Snails with light and dark
colors dominate
Coloration of snails
Number of individuals
with light and dark coloration
increases, and the number with
intermediate coloration decreases
FIGURE 5-6 (3) PAGE 102
Coloration of snails
COEVOLUTION

Interaction between species that results in
microevolution in each of their populations.
Ex: flowers and pollinators

predators and prey

HOW MACROEVOLUTION WORKS

Evolution that takes place over an extremely long
time involving groups of species.

Speciation—forming a new species

Geographic isolation  reproductive isolation speciation
MACROEVOLUTION

How do species become extinct?

When environmental conditions change, a species
may cease to exist if it cannot adapt.



Background extinction—disappearance of species’ at a low
gradual rate.
Mass extinction—abrupt rise in extinction rate above the
background level catastrophic and worldwide where large
numbers of species are eliminated.
We have had five major extinctions with the last being 65
million years ago (at the end of the mesozoic era). A sixth
mass extinction is currently happening and caused by
humans.
MACROEVOLUTION


Adaptive radiation—period of recovery, rapid
divergent evolution leading to speciation,
following mass extinctions.
There are two theories about how rapidly
macroevolution occurs:


1. gradualist model of evolution
2. punctuated equilibrium hypothesis—gradual
evolution interrupted periodically by rapid
speciation.
ECOLOGICAL NICHES AND ADAPTATION

Ecological Niche—the species’ way of life or role
in an ecosystem. Includes:
Range of tolerance
 Type of resources it uses
 How it interacts with components of the ecosystem


Fundamental niche—full potential range of physical,
chemical, and biological conditions under with an
organism could survive.

Realized niche—the actual part of the fundamental
niche occupied by the organism.


Species can have broad niches (generalists:
roaches, flies, coyotes, humans) while other have
narrow niches (specialists: spotted owls, giant
pandas)
Habitat—the physical location where a species
lives.
COMMON MISCONCEPTIONS
CONCERNING EVOLUTION
EVOLUTION MISCONCEPTIONS




Misconception: “Survival of the Fittest” means
survival of the strongest.
Truth: To biologists, Fitness is a measure of
reproductive success NOT strength.
Misconception: Evolution involves some grand
plan of nature in which organisms are becoming
more complex/perfect with time.
Truth: From a scientific standpoint, no plan or
goal exists in the evolutionary process.
Modern humans
(Homo sapiens)
appear about
2 seconds
before midnight
Age of
mammals
Age of reptiles
Insects and amphibians
invade the land
midnight
Origin of life
(3.6–3.8 billion
years ago)
Plants invade
the land
First fossil
record of
animals
Plants begin
invading
land
Recorded human
history begins
1/4 second
before midnight
noon
Evolution and expansion of life