Download No Slide Title

Ecosystems
The Rise of Life on Earth
Ecosystems
• Classification of Organisms
– All organisms are classified base on
their cell structure:
• Eukaryotes
• Prokaryotes
Ecosystems
• Classification of Organisms
– Eukaryotic Cells
• Cell membrane
• Nucleus
– Nuclear membrane
– DNA
Ecosystems
• Classification of Organisms
– Prokaryotic Cells
• Bacteria
• Cell membrane
• No distinct nucleus
Ecosystems
• Classification of Organisms
– Taxonomic Classification classification based on common
characteristics
Ecosystems
• The Rise of Life on Earth
– Requirements
• Restricted temperature range
• Liquid water
Ecosystems
• The Rise of Life on Earth
– Reasons for these conditions
•
•
•
•
•
Earth’s distance from Sun
Earth spins on tilted axis
Earth’s size
Internal heat engine
Protective ozone layer
Ecosystems
• The Rise of Life on Earth
– The rise of life on Earth is intimately
linked to the physical and chemical
evolution of the Earth
Ecosystems
• The Rise of Life on Earth
– Two phases of development
• Chemical evolution of organic molecules
• Biological evolution of organisms
Evolution of the Earth and Its Life forms
Ecosystems
• The Rise of Life on Earth
– Chemical Evolution
• Formation of oceans
• Formation of primitive atmosphere
• Formation of organic compounds necessary
for life
Ecosystems
• The Rise of Life on Earth
– Chemical Evolution
• Formation of oceans
– Volcanic “degassing” triggered start of
hydrologic cycle
Ecosystems
• The Rise of Life on Earth
– Chemical Evolution
• Formation of primitive atmosphere
–
–
–
–
–
–
CO2
N2
H 2O
Methane (CH4)
Hydrogen sulfide (H2S)
Hydrogen chloride (HCl)
Ecosystems
• The Rise of Life on Earth
– Chemical Evolution
• Formation of organic compounds
– Electrical discharges (lightning)
– UV radiation
– Geothermal energy
Ecosystems
• The Rise of Life on Earth
– Chemical Evolution
• Possible sites of formation of organic
compounds
– Atmosphere
– Space
– Mid-ocean hydrothermal vents
Ecosystems
• The Rise of Life on Earth
– Chemical Evolution
• Organic compounds probably collected in
warm, shallow waters
– Millions of years of chemical reactions gave rise
to protocells capable of growing and dividing
Ecosystems
• The Rise of Life on Earth
– Biological Evolution
• Protocells evolved into prokaryotic
anaearobic cells
• Anaerobic cells underwent billions of years
of evolution into a diversity of prokaryotic
cells
Ecosystems
• The Rise of Life on Earth
– Biological Evolution
• No life on primitive Earth
– No protective ozone layer to protect DNA
– No evidence of fossils
Ecosystems
• The Rise of Life on Earth
– Biological Evolution
• The Oxygen Revolution
– Photosynthetic algae in oceans
– Evolution of ozone layer
– Rise of life on land ~ 400 million years ago
Ecosystems
• Population Responses to Stress
– Evolution
– Adaptation
– Natural Selection
Ecosystems
• Population Responses to Stress
– Biological Evolution - a change in a
population’s genetic makeup through
successive generations
– Theory of Biological Evolution - all lifeforms developed from earlier liofe-forms
Ecosystems
• Population Responses to Stress
– Evidence of Earth’s life history
• Fossils - mineralized of petrified remains of
skeletons, bones, teeth, seeds, or
impressions of these features
• Paleontology - the study of fossilized
organisms
Ecosystems
• Population Responses to Stress
– Evidence of Earth’s life history
• Fossil record is incomplete
– Fossil record represents only 1% of species
believed to have existed in the past
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Gene - segments of DNA molecules found
in chromosomes; coded units of
information about specific traits that are
passed from parents to offspring during
reproduction
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Gene Pool - the sum total of all genes found
in individuals of a population of a particular
species
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Members of a population generally have the
same number and kinds of genes
• Allelle - slightly different molecular forms
found in a particular gene
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Different combinations of alleles are
inherited so that different members of a
population have genetic diversity
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Mutation - random change in the structure
or number of DNA molecules in a cell
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Causes of mutations
–
–
–
–
Radioactivity
X-rays
Chemicals (mutagens)
Random mistakes during DNA replication
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Types of mutations
– Harmful
– Beneficial
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Beneficial Mutation - a mutation that results
in new genetic traits that give their bearer
and its offspring better chances for survival
– Adaptive Trait - a genetically-controlled trait that
helps an organism survive and reproduce under
a given set of environmental conditions
• Development of coloration that allows prey to
hide from predators
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Differential Reproduction - a phenomenon in
which individuals with adaptive genetic
traits produce more living offspring than do
inviduals without such traits
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Natural Selection - the process by which a
particular beneficial gene (or set of genes)
is reproduced more than other genes in
succeeding populations.
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• The end result of natural selection is a
population that contains a greater
proportion of organisms better adapted to
certain environmental conditions
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Limits to Adaptation
– A change in environmental conditions can only
lead to the adaptation for traits already present in
the gene pool
Ecosystems
• Population Responses to Stress
– The Theory of Biological Evolution
• Limits to Adaptation
– Even if an adaptive trait is present in a
population, the population’s ability to actually
adapt to a change in environmental conditions
can be limited by its reproductive capacity
• Reproductive lag time
• Example: r-strategists vs K-strategists
Ecosystems
• Population Responses to Stress
– Evolution of Species (Speciation)
• Two components of speciations
– Geographic Isolation
– Reproductive Isolation
Ecosystems
• Population Responses to Stress
– Evolution of Species (Speciation)
• Two components of speciation
– Geographic Isolation - separation of populations
of a species for a long time into areas with
different environmental conditions
• Separation due to physical barriers
• Separation due to natural disasters
• Separation by wind and oceanic currents
Ecosystems
• Population Responses to Stress
– Evolution of Species (Speciation)
• Two components of speciation
– Reproductive Isolation - long-term geographic
separation of members of a particular sexually
reproducing species
Ecosystems
• Population Responses to Stress
– Evolution of Species (Speciation)
• Two components of speciation
– Reproductive Isolation
• Occurs when mutations and natural selection
operate independently between to
geographically isolated populations
• Results in divergence (divergent evolution)
and speciation
Ecosystems
• Population Responses to Stress
– Extinctions
• Causes
– Continental drift
– Climate change
• Gradual
• Catastrophic
Ecosystems
• Population Responses to Stress
– Extinctions
• Types
– Background Extinctions
• Caused by changes in local conditions
– Mass Extinctions
• Abrupt rise in extinction rate above
background levels
Ecosystems
• Population Responses to Stress
– Extinctions
• Mass extinctions are followed by periods of
recovery called adaptive radiations in which
new species fill new or vacated niches
• Extinction of dinosaurs allowed for the
radiation of mammals
Ecosystems
• Community and Ecological
Responses to Stress
– Ecological Succession - the process in
which communities of plant and animal
species in a particular area are replaced
over time by a series of different and
often more complex communities
Ecosystems
• Community and Ecological
Responses to Stress
– Types of succession
• Primary Succession - sequential
development of communities in a bare area
that has never been occupied by a
community of organisms
– Pioneer Species - first plants to colonize a
lifeless area; typically r-strategists
Ecosystems
• Community and Ecological
Responses to Stress
– Types of succession
• Secondary Succession - sequential
development of communities in an area in
which the natural vegetation has been
removed or destroyed but the soil is not
destroyed
Ecosystems
• Human Impacts on Ecosystems
– Simplification of natural ecosystems
– Enhancing populations of pest species
– Elimination of predators
– Introduction of exotic species
– Overuse of potentially renewable
resources
– Interference with biogeochemical cycles