APES CHAPTER 5Evolution and Biodiversity: Origins, Niches, and Adaptation

ORIGINS OF LIFE-2 PHASES:

Evolution of the organic molecules, biopolymers, and systems of chemical reactions needed to from the first protocells

Lasted approx. 1 billion years

Evolution of single-celled organisms (prokaryotes and then eukaryotes) and then multi-cellular organisms

Took approx. 3.7-3.8 billion years.

Chemical evolution Biological evolution

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. 98Fig. 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.

Fish Salamander Turtle Chick Hog Calf Rabbit Human

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.

MACROEVOLUTION

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

MICROEVOLUTION

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

DARWIN’S NATURAL SELECTION

Directional Natural Selection

Natural selection

Proportion of light-coloredsnails in population increases

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Snail colorationbest adaptedto conditions

Average

Coloration of snails

New average Previous average

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Coloration of snails

Average shifts

FIGURE 5-6 (1) PAGE 102

Coloration of snails

Snails withextreme

coloration areeliminated

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Stabilizing Natural Selection

Average remains the same,but the number of individuals withintermediate coloration increases

Natural selection

Coloration of snails

Light snailseliminated

Dark snailseliminated

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FIGURE 5-6 (2) PAGE 102

Number of individuals with light and dark coloration

increases, and the number with intermediate coloration decreases

Coloration of snails

Num

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of in

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Snails with light and darkcolors dominate

Diversifying Natural Selection

Coloration of snails

Num

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Light colorationis favored

Darkcolorationis favored

Intermediate-colored snails are selected against

Natural selection

FIGURE 5-6 (3) PAGE 102

COEVOLUTION

Interaction between species that results in microevolution in each of their populations. Ex: flowers and pollinators predators and prey

The parasites have often evolved eggs that closely mimic those of the host, and young with characteristics that encourage the hosts to feed them. In response, some hosts have developed the ability to discriminate between their own and parasitic eggs, and various methods of destroying the latter.

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.

GRADUALISM VS. PUNCTUATED EQUILIBRIUM

GRADUALISM

PUNCTUATED EQUILIBRIUM

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.

Plants begininvadingland

Evolution and expansion of life

First fossilrecord ofanimals

Plants invade the land

Age of reptiles

Age of mammals

Insects and amphibians invade the land

Modern humans(Homo sapiens)appear about2 secondsbefore midnight

Recorded humanhistory begins1/4 secondbefore midnight

Origin of life(3.6–3.8 billionyears ago)

noon

midnight