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LAMC Bio 3 Lecture Notes: Chapters 13 & 34 – Darwinian
Evolution and Biodiversity
Reading
Assignment: Chapter 13 and 34
Learning
Outcomes:
By the end of this lecture you should be able to:
- identify the names of the people who influenced
Darwin
, and explain their ideas
- list the observations and inferences that
Darwin
made regarding his views of evolution
- explain the process that can cause evolution to occur
- explain the conditions necessary for evolution to occur through natural
selection
- identify the main characteristics of each of the aquatic
and terrestrial biomes
- explain the reasons behind the variation in species number estimates
-
identify the different levels of biodiversity
I. Darwinian Evolution
Before Charles Darwin (1809-1882) –
creationist view prevailed (natural theology: philosophy dedicated to
discovering the Creator’s plan by studying nature)
The Earth was thought to be about 6000 years old, based on Biblical inference.
All species are non-changing entities, created by God.
People/Ideas/Events that influenced
Darwin
:
Carolus Linnaeus (1707-1778) – specialized in
taxonomy (binomial nomenclature). Clustering
similar organisms together – he did not suggest that similar organisms had
shared ancestry.
Georges Cuvier (1769-1832) – studied
paleontology (fossils). Realized the relationship between strata location (and
the fossils contained in them) and the relative age of those fossils.
He thought that extinction was local and caused by catastrophic events (catastrophism).
James Hutton (1726-1797) – studied
geology. Proposed the idea that
geological changes occur gradually and slowly over time, rather than due to the
result of catastrophic events (gradualism).
Charles Lyell (1797-1875) – studied
geology. Incorporated Hutton’s
gradualism into the idea of uniformitarianism – the geological
processes that have shaped the Earth have not changed over time.
à
The conclusion based on this information: the Earth is much older than 6000
years and slow, subtle processes can add up to substantial change.
Thomas Malthus – published “Essays on
the Principles of Population.” Proposed
that human suffering is the inescapable consequence of the potential for the
human population to increase faster than food supplies and other resources.
Jean Babtiste Lamarck – published his
theory of evolution the year
Darwin
was born.
Studied fossils and reached the conclusion that they represented lines of common
descent.
Proposed the idea that evolution occurs through evolution of acquired
characteristics.
- if an organism uses a particular body part during its lifetime, it will become
better developed.
- these changes acquired during the lifetime of the organism will get passed
onto its offspring.
Darwin
published the Origin of Species. Two
main points of this book were:
1. Evolution does occur and this is what leads to diversity of species
2. Natural Selection is the mechanism by which evolution occurs.
His classification of organisms fell into the taxonomic scheme that Linnaeus had
already developed.
Darwin’s Theory of Natural Selection:
Observation 1: All species have the
potential to overproduce offspring.
Observation 2: Population sizes tend to remain stable.
Observation 3: Environmental resources are limited.
Inference 1: Overproduction of offspring must lead to a struggle for
existence such that only a fraction of the offspring that are produced actually
survive.
Observation 4: Individuals in a population vary in their characteristics
and abilities.
Observation 5: A lot of this variation is heritable.
Inference 2: Survival is not random, but based on the heritable
difference that individuals possess. Individuals
that are best adapted to their environment are likely to leave more offspring.
Inference 3: This unequal ability to survive and reproduce will lead to a
change in a population, with more favorable characteristics accumulating over
the generations.
Natural Selection: unequal ability of
individuals to survive and reproduce.
Artificial Selection: similar
mechanism, but humans choose which individuals reproduce. Ex. Dogs, crops.
c. Gene Flow (migration) – the
characteristics of a population changes when there is mixing of individuals from
different populations having different characteristics.
d. Mutation: a change in the organism’s
DNA.
III. Requirements for Evolution to occur through
Natural Selection:
a. There is variation in the phenotype –
natural selection acts on physical differences.
b. Fitness of the organism is related to its
phenotype – if the physical difference doesn’t affect an individual’s
reproductive success, it won’t cause a change in the population.
c. The phenotypic variation is heritable –
if the variation is not heritable, it won’t get passed on to the next
generation, even if it is a beneficial characteristic.
IV.
Biomes:
1.
Aquatic Biomes: occupy the largest part of the planet;
cover ~ 75% of the earth’s surface
- marine biomes have ~ 3% salt concentration; freshwater biomes have less
than 1% salt concentration
a) Lakes: some lakes are deep, nutrient-poor
and do not contain much life, whereas others are shallower and have more
nutrients.
b) Streams and rivers: bodies of water
moving continuously in one direction
c) Estuaries: areas where freshwater and
saltwater meet; crucial feeding areas for water birds
d) Intertidal zones: are submerged and
exposed by the cycle of tides
e) Coral reefs: dominated by coral; include
a diverse community of animals
f) Pelagic zone: includes most of the
ocean’s water; water constantly mixed by ocean currents; contains plankton,
fish and mammals
2.
Terrestrial Biomes:
a) Tropical Rainforest: areas with high
annual rainfall and high average temperatures; have vertical stratification in
vegetation and large plant and animal diversity but the soil is nutrient poor
b) Savanna (tropical grassland): grasses and
scattered trees are the predominant vegetation
- contains large herbivores but the dominant herbivores are insects
c) Desert: receives very little rainfall;
some deserts are cold, others are hot (depending on latitude); characterized by
large daily fluctuations in temperature; plants and animals adapted to storing
water and tolerating/escaping extreme heat
d) Chaparral (Mediterranean-type
vegetation): characterized by mild, rainy winters and long hot, dry summers
- plants are adapted to and dependent on periodic fires, seeds contain food
reserves and germinate quickly after a fire, using the nutrients in the soil
released by fire
e) Temperate grassland: characterized by
seasonal drought, occasional fires, and grazing by large mammals that prevent
establishment of woody vegetation; soil is rich in nutrients and very fertile;
most grasslands in the
US
have been converted to agricultural land
f)
Temperate
Deciduous
Forest
: receives less rainfall than rainforest and occur along the midlatitudes;
characterized by trees and shrubs that drop their leaves before winter; many
animal species either hibernate or migrate during the winter
g)
Coniferous
Forest
: dominated by cone-bearing, evergreen trees; winters characterized by snowfall;
conical shape of conifers prevents snow accumulation
h) Tundra: characterized by permafrost
(permanently frozen subsoil), cold temperatures and high winds; lack trees and
tall plants
V
1.5 million species named so far; 30-80
million species estimated to exist
Variation in species # estimates due to: small species hard to see (e.g.
bacteria); rare species hard to find; inaccessible habitats (e.g. deep ocean);
species identification takes time
There are three levels of biodiversity:
1. Genetic diversity: Fewer individuals à
reduced genetic diversity à
less adaptable populations à
greater risk of extinction
2. Species diversity: Endangered species: in danger of extinction throughout
all or a large part of its range
3. Ecosystem diversity: How many different types of ecosystems are there? (the
aquatic and terrestrial biomes)
Ecosystem services: services that are provided for free by ecosystems
- purification of groundwater
- microorganisms recycle nutrients
- winds circulate air and stabilize temperatures
- vegetation prevents soil erosion
- plants and animals recycle O2 and CO2
Ecosystem services are numerous and difficult and expensive to recreate.
Example: Biosphere II in
Arizona
Plants and Human Welfare:
1. Agriculture is based almost entirely on
angiosperms
2. Plants have important medicinal properties
3. Plant diversity is a non-renewable resource
Biotechnology and Agriculture
1. Transgenic technology (genetically modified crops): inserting DNA from
other organisms into crop plants to:
- increase food production / yield / nutritional benefits, improve pest
resistance & decrease pesticide application
2. Problems with transgenic crops:
- increased resistance of pests, unknown consequences of mixing transgenic and
traditional varieties of plants, increased cost of using patented, transgenic
crops for farmers
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