Chapter 22:
Descent with Modification: A Darwinian View of Life
A.
The Historical Context for Evolutionary
Theory
·
Introduction
-
Biology came of age on November 24, 1859, the
day Charles Darwin published On the Origin of Species by Means of Natural
Selection.
-
Focus on the great diversity of organisms –
origins, relationships, similarities and differences, their geographic
distribution, and their adaptations to surrounding environments
-
Darwin made two points:
1.
species today descended from ancestral
species
2.
mechanism for evolution termed natural selection.
-
Populations of organisms can change over the
generations if individuals having certain heritable traits leave more offspring
that other individuals.
-
Result is evolutionary
adaptation: a prevalence of inherited characteristics that enhance
organism’s survival and reproduction in specific environments.
-
Genetic composition of the population had
changed over time. (evolution)
·
Western culture resisted evolutionary views
of life
·
The Scale of Nature and Natural Theology
1.
Plato and Aristotle held opinions that
opposed any concept of evolution.
-
Species permanent, perfect and do not evolve
2.
Judeo-Christian culture
-
Species were individually designed and
nonevolving
·
Carolus Linnaeus
-
Specialized in taxonomy: branch of biology concerned with naming and classifying
the diverse forms of life.
-
Binomial system of classification: genus –
species
·
Cuvier, fossils and catastrophism
-
Study of fossils also layed the groundword
for Darwin’s ideas.
1.
Fossils
-
relics or impressions of organisms from the
past preserved in rock. Shows that a succession of organisms has populated
earth throughout time
·
Paleontology
-
Study of fossils
-
Developed by Georges Cuvier
-
Cuvier found out that extinction had been a
common occurrence in the history of life. Advocated catastrophism.
·
Theories of geologic gradualism helped clear
the path for evolutionary biologists
-
James Hutton: possibility to explain
landforms by looking at the current mechanisms operating at the world
-
Hutton and Gradualism
1.
Gradualism
-
Profound changes is the cumulative product of
slow but continuous process
-
Charles Lyle and Uniformitarianism
1.
Uniformitarianism
-
Geologic processes have not changed
throughout the Earth’s history.
-
Led Darwin to believe two things
1.
Earth must be very old
2.
slow and subtle processes persisting over a
long period of time can add up to substantial changed
·
Lamarck placed fossils in an evolutionary
context
-
Erasmus Darwin: Life evolved as environments
changed
-
Jean Baptiste Lamarck
1.
Use and disuse
-
Useful part stronger and bigger, not useful
part deteriorated
2.
inheritance of acquired characteristics
-
modifications can be passed to offspring
B.
The Darwinian Revolution
·
Charlers Darwin
-
Born in Shrewsbury, W. England
-
University of Edinburgh to study medicine
-
Christ College in Cambridge University to
become a clergy
-
Under Rev. John Henslow
-
Capt. Robert FitzRoy
·
Field research helped Darwin frame his view
of life: The Voyage of the Beagle
-
HMS Beagle in Dec. 1831
-
Mission of the voyage was to chart
poorly known stretches of the South
American coastline
-
Endemic species in the Galapagos island
-
Collected finches from Galapagos, although
similar seemed to be of different species
-
Read Lyell’s Principles of Geology, led him to believe
1.
earth very old,
2.
constantly changing
3.
life on earth has also evolved
·
Darwin’s focus on Adaptation
-
New species arise from gradual accumulation
of adaptations to a different environment
-
Finches and their beaks which are adapted to
specific foods in their environments
-
Was already a famous naturalist, visits from
Lyell, Henslow
-
1858, Darwin received a letter from Alfred
Wallace a British naturalist working in the East Indies with a manuscript of
natural selection similar to Darwin’s
-
July 1 1858, presented Wallace paper with
excerpts from Darwin to the London Linnaean Society
-
A year later, Darwin finished the Origin of Species
-
Biological diversity is a product of
evolution
·
The Origin of Species developed two main
points: the occurrence of evolution and natural selection as its mechanism
1.
Descent with Modification
-
All organisms related through descent from
some unknown ancestor from the remote past
-
Descendants spilled over and adapted to the
various environments
-
Asian and African elephant
-
Most branches of evolution are dead ends, 99%
of all species that have ever lived are extinct
-
Linnaeus helped Darwin by his idea of “groups
subordinate to groups”
-
Linnaean scheme reflected the brainching
history of the tree of life, organisms at different taxonomic levels related
through descent from common ancestors
2.
Natural selection and adaptation
-
Ernst Mayr dissected the logic of Darwin’s
theory of natural selection
-
E. Mayr, The Growth of Biological Thought: Diversity, Evolution, and
Inheritance. (Cambridge, MA: Harvard University Press, 1982)
-
Observations (1-3):
a.
All species had a great potential fertility
that population size will increase exponentially if all that were born
reproduced successfully (completed one life cycle)
b.
Populations tend to be stable in size except
for seasonal fluctuations
c.
Environmental resources are limited
-
Inferences (1)
a.
Production of more offspring for survival,
only a fraction of offspring survives each generation
-
Observations (4-5):
a.
Individuals in a population vary, no two are
the same
b.
Much of the variation is heritable
-
Inference (2-3):
a.
Survival is not random, depends in part on
the hereditary constitution of the individuals
b.
Unequal ability to survive and reproduce will
lead to gradual change in population, favorable characteristics accumulating
over the generations
-
Summary of Darwin’s ideas:
a.
Natural selection is differential success in
reproduction
b.
Natural selection occurs through an
interaction between environment and the variability inherent among individual
organisms
c.
Product of natural selection is the
adaptation of populations of organisms to their environment
-
Elaborations
a.
Idea of overpopulation
-
After reading Thomas Mathus’ essay on human
population (1798)
® Much of
human suffering – disease, famine, wars – was the consequence of the potential
for the human population to increase faster than the food supplies and other
resources
b.
Increasing frequency of favored traits in a
population is evolution
-
Artificial selection of Darwin, selective
breeding
-
Darwin incorporated gradualism into
evolutionary theory: minute changes operating in varying contexts over vast
spans of time could account for the entire diversity of life.
-
Summarize two main features of the Darwinian
view of life:
1.
diverse forms of life have arisen by discent
with modification from ancestral species
2.
the mechanism of modification has been
natural selection working over enormous tracts of time.
·
Some subtleties of Natural Selection
1.
Importance of populations in evolution
-
A group of interbreeding individuals
belonging to a particular species and sharing a common geographic area
-
Smallest unit that can evolve, individuals do
not evolve
-
Evolution measured only in changes in a
population over a succession of generations.
2.
natural selection can only amplify or
diminish only heritable variations
-
no evidence that characteristics acquired
during a lifetime can be inherited
3.
specifics of natural selection are
situational
-
environmental factors vary from place to
place from time to time.
·
Examples of natural selection provide
evidence for evolution
1.
natural selection in action: the evolution of
insecticide-resistant insects
-
insects that survive the first wave of
insecticide attack have genes that enable them to resist the chemical attack
-
offspring inherit genes for pesticide
resistance
-
insecticide does not create resistance
individuals but selects for resistant insects that are already present in the
population
2.
the evolution of drug-resistant HIV
-
3TC
·
Other evidence of evolution pervades biology
1.
Homology
-
Novel features are altered versions of
ancestral features
-
Similarity in characteristics resulting from
common ancestry is known as homology
a.
Anatomical Homologies
-
Forelimbs of all mammals
-
Taking on different functions in each
species, the basic structures were modified
-
Comparative anatomy (comparison of body
structures between species) confirms that evolution is a remodeling process
b.
Vestigial organs
-
Structures of little importance to the
organism
-
Remnants of structures important to ancestors
c.
Embryological Homologies
-
Pharyngeal pouches in all vertebrate embryos
d.
Molecular homologies
-
All species of life use the same basic
genetic machinery of DNA and RNA, genetic code is essentially universal
e.
Homologies and the Tree of Life
-
Homologies mirror the taxonomic hierarchy of
the tree of life.
2.
Biogeography
-
Geographic distribution of species suggested
evolution to Darwin
-
Species more related to other species living
in the same areas, than similar species on a different area
a.
Sugar glider and flying squirrel : converget
evolution
-
Endemic: found no where else in the world
a.
Fruit flies Drosophila in Hawaii
3.
The Fossil Record
-
Prokaryotes precede all eukaryotes
-
Fishes then amphibians, then reptiles then
mammals and birds
-
Evolutionary transitions leave signs in the
fossil record
-
Darwinian view of life supported by
evolutionary patterns of homology that match patters in space (biogeography)
and time (fossil record)
·
What is theoretical about the Darwinian view
of life?
-
Darwin gave biology a sound scientific basis
-
“There is grandeur in this view of life.
-
Basilosaurus ancient
what linking past and present.
Chapter 23:
The Evolution of Populations
A.
Introduction
-
Evolution on the smallest scale or
microevolution, can be defined as a change in the allele frequencies of a
population.
-
Liguus fascitus
marine
snail
B.
Population Genetics
·
Darwin not gain acceptance that natural
selection be the mechanism for evolution
·
The modern evolutionary synthesis integrated
Darwinian selection and Mendelian Inheritance
-
Quantitative characters are influenced by
multiple genetic loci
-
An important turning point for evolutionary
theory is the birth of population genetics
1.
Population Genetics
-
Emphasis on the extensive genetic variation
within populations and the importance of quantitative characters
-
Darwinism and Mendelism reconciled; genetic
basis of variation and natural selection worked out.
1.
Modern Synthesis
-
A comprehensive theory of evolution in the
1940s.
-
Integrates paleontology, taxonomy,
biogeography, population genetics
-
Theodosius Dobzhansky and Sewall Wright,
Ernst Mayr, George Gaylord Simpson, G. Ledyard Stebbins
-
Emphasis on the importance of populations as
the units of evolution, central role of natural selection as the mechanism for
evolution, the idea of gradualism.
·
A populations’ gene pool is defined by its
allele frequencies
1.
Population
-
A localized group of individuals belonging to
the same species
2.
Species
-
A groups of populations whose individuals
have the potential to interbreed and produce fertile offspring in nature.
3.
Gene pool
-
The total aggregate of genes in a population
at one time
-
Consists of all alleles at all gene loci in
all individuals of the population
·
The Hardy-Weinberg theorem describes a
nonevolving population
-
Gene pool for a nonevolving population
-
Theorem states that the frequencies of
alleles and genotyps in a population’s gene pool remain constant over the
generations unless acted upon by agents other than Mendelian segregation and
recombination of alleles.
-
* check notes on this
C.
Causes of Microevolution
·
Microevolution is a generation-to-generation
change in a population’s allele frequencies
-
if frequencies of alleles or genotypes
deviate from values predicted by the Hardy Weinberg equation, it is because the
population is evolving
-
new definition of evolution
1.
Evolution
-
Is a generation-to-generation change in the a
population’s frequencies of alleles.
-
Referred to as microevolution due to its
small scale
2.
Microevolution
-
Occurring even if the frequencies of alleles
are changing for only a single genetic locus.
·
The two main causes of microevolution are
genetic drift and natural selection
-
Natural selection always has a positive
effect, only on that adapts populations to its environment
1.
Genetic Drift
-
Smaller the sample the greater the chance of
deviation from an idealized result (sampling error)
-
A change in population’s allele frequencies
due to chance is called genetic drift.
a.
The bottleneck effect
-
Genetic drift due to a drastic reduction in
population size
-
Reduces overall genetic variability in a
population, some alleles are likely to be lost from the gene pool
b.
The founder effect
-
Genetic drift likely whenever few individuals
from a larger population colonize an isolated island or lake, or some other new
habitat
-
The smaller the sample size, the less
representative of the population they left
-
Genetic drift in a new colony is known as
founder effect
-
Probably accounts for high frequency of
certain inherited disorders in humans
2.
Natural Selection
-
Differential success in reproduction
-
Results to disproportion
-
Only one to adapt the population to its
environment
-
Maintains and accumulates favorable genotypes
in a population
3.
Gene Flow
-
Genetic exchange due to the migration of
fertile individuals or gametes between populations
-
Tends to reduce difference between
populations
4.
Mutation
-
A change in an organism’s DNA
-
Alters the gene poopl of a population by substituting one allele for another
D.
Genetic Variation, the substrate for natural
selection
·
Genetic variation occurs within and between
populations
-
Occurs in all sexually reproducing
individuals
-
Not all variations are heritable
-
Only the genetic component of variation can
have evolutionary consequences as a result of natural selection because it is
the only component that transcends generations
·
Variations within populations
-
Both quantitative and discrete characters
contribute to variation within a population
-
Quantitative variation usually indicates
polygenic inheritance
-
Discrete characters are an either-or basis,
determined by a single gene locus
·
Polymorphism
-
When two or more distinct morphs are each
represented in high frequencies to be readily noticeable
-
Occurs only with discrete characters
·
Measuring genetic variation
-
Measure both at the level of whole genes
(gene diversity) and at the molecular level of DNA (nucleotide diversity)
·
Variations Between Populations
1.
geographic variation
-
differences in gene pools between populations
or subgroups of populations
2.
cline
-
graded change in some trait along a
geographic axis
E.
Mutation and sexual recombination gamete
genetic variation
-
Two random processes that create variation in
the gene pool o f a population
·
Mutation
-
new alleles originate only by mutation
-
Only mutations that occur in cell lines that
produce gametes can be passed along to offspring
-
A mutation that alters a protein is often
harmful than beneficial
·
Sexual recombination
-
Genetic differences from the unique
recombinations of existing alleles each individual receives from the gene pool
F.
Diploidy and balanced polymorphism preserve
variation
·
Diploidy
-
Recessive alleles in heterozygotes
-
The rarer the recessive allele the greater
the degreeof protection from natural selection
·
Balanced polymorphism
-
Ability of natural selection to maintain
stable frequencies of two or more phenotypic forms in a population
1.
Heterozygote advantage
2.
frequency dependent selection
-
survival and production of one morph declines
when it becomes too common in the population
·
Neutral Variation
-
No selective advantage
G.
A Closer Look at Natural Selection as the
Mechanism of Adaptive Evolution
·
Evolutionary fitness is the relative
contribution an individual makes to the gene pool of the next generation
1.
Darwinian fitness
-
Is the contribution an individual makes to
the gene pool of the next generation relative to the contribution of other
individuals
2.
relative fitness
-
the contribution of a genotype to the next
generation compared to the contribution of alternative genotypes for the same
locus
-
survival alone does not guarantee
reproductive success
-
relative fitness is zero for a sterile plant
even if it outlives others
·
The effect of selection on a varying
characteristic can be directional, diversifying or stabilizing
-
Natural selection can affect the frequency of
a heritable traits in a population is three different ways:
1.
Directional selection
-
Common during environmental change and
migration
-
Peter and Rosemary Grant – finches in the
Galapagos
2.
Diversifying selection
-
Occurs when environmental conditions are
varied in a way that favors individuals on both extremes of a phenotypic range
over intermediate phenotypes
3.
Stabilizing selection
-
Act against extreme phenotypes and favors
that more common intermediate variants
·
Natural selection maintains sexual
reproduction
-
The advantage of sex is that the process of
meiosis and fertilization generate the genetic variation upon which natural
selection can act as the agent of adaptation
·
Sexual selection may lead to pronounced
secondary difference between sexes
1.
Sexual dimorphism
-
Distinction in appearance
2.
Intrasexual selection
-
Direct competition among individuals of the
same sex for mates of the opposite sex
3.
Intersexual selection
-
Also called the mate choice; individual’s of
one sex are choosy in selective their mates from individuals of the other sex.
H.
Natural Selection cannot fashion perfect
organisms
·
Four reasons why natural selection cannot
produce perfection
1.
evolution is limited by historical
constraints
-
do not create from scratch
2.
adaptations are often compromises
3.
not all evolution is adaptive
-
affected by chance
4.
Selection can only edit existing variations
-
new alleles do not arise on demand
-
natural selection operates on a “better than
basis”
Chapter 24:
The Origin of Species
A.
Introduction
·
Macroevolution
-
The origin of new taxonomic groups
·
Speciation
-
The origin of new species
-
The key process because any genus, family, or
higher taxon originates with a new species that is novel enough to be the
inaugural member of the higher taxon.
-
2 patterns of speciation:
1.
Anagenesis
-
Phyletic evolution,
-
The accumulation of changes associatied with
the transformation of one species into another
2.
Cladogenesis
-
Branching evolution
-
The budding of one or more new species from a
parent species that continues to exist.
-
Only one to promote biological diversity by
increasing the number of species.
B.
What is a species?
·
Species
-
Comparing morphology, differences in body
functions, biochemistry, behavior and genetic make-up.
·
The biological species concept emphasizes
reproductive isolation
-
Ernst Mayr, 1942 : biological
species concept
1.
Biological species concept
-
Defines a species as a population or group of
populations whose members have the potential to interbreed with one another in
nature to produce viable, fertile offspring, but who cannot produce viable,
fertile offspring with members of other species.
-
United by being reproductively compatible
-
Reproductive isolation with each species
isolated by factors that prevent interbreeding, blocking genetic mixing with
other species.
-
Emphasis on separateness of different species
due to reproductive barriers
·
Prezygotic and postzygotic barriers isolate
gene pools of biological species
1.
Prezygotic barriers
a.
Prezygotic barriers
-
Impede mating between species or hinder the
fertilization of ova if members of different species attempt to mate
b.
Habitat isolation
-
Two species that live in different habitats
within the same ara may encounter each other rarely.
® Thamnophis garter
snakes
c.
Behavioral isolation
-
Elaborate courtship rituals of particular
species
d.
Temporal isolation
-
Two species that breed during different times
of the day, different seasons, or different years cannot mix their gametes
e.
Mechanical isolation
-
Anatomically incompatible
-
Male and female copulatory organs may not fit
together
f.
Gametic isolation
-
Even if gametes of different species meet,
they rarely fuse together to form a zygote
2.
Postzygotic barriers
a.
Postzygotic barriers
-
Prevent the hybrid zygote from developing
into a viable fertile adult
b.
Reduce hybrid viability
-
Genetic incompatibility between the two
species may abourt development of the hybrid at some embryonic stage.
® Rana
c.
Reduced Hybrid Fertility
-
Hybrids are completely or largely sterile
-
Prevents gene flow
® Mules:
cross between horse and donkey
d.
Hybrid breakdown
-
First generation hybrids are viable and
fertile, but second generation mate, their offspring are feeble and sterile
·
The biological species concept has some major
limitations
-
Does not work as a criterion for
distinguishing species in nature.
-
No utility for life-forms that are asexual
·
Biologists have proposed several alternative
concepts of species
1.
Ecological species concept
-
Defines species in terms of its ecological
niche, the set of environmental resources a species use
-
Accommodates asexual species
2.
pluralistic species concept
-
the factors that are most important for the
cohesion of individuals as a species vary
-
non is useful in actually identifying various
species in nature, hence taxonomists depend mainly on morphological
characteristics
1.
Morphological species concept
-
Does not explain why species exist
-
Characterizes each species in terms of a
unique set of structural features
2.
genealogical species concept
-
defines a species as a set of organisms with
a unique genetic history
-
define species in terms of unique genetic
markers
C.
Modes of Speciation
-
Two main modes based on how gene flow among
populations is initially interrupted
1.
Allopatric speciation
-
Speciation takes place in populations with
geographically separate ranges
-
Separation in space
2.
sympatric speciation
-
speciation takes place in geographically
overlapping populations
·
Allopatric speciation: Geographic barriers
can lead to the origin of species
-
Conditions for allopatric speciation
1.
can occur if individuals colonize a new
geographically remote area and become isolated from the parent population
2.
likelihood increases when population is small
and isolated
3.
if cannot interbreed when come into contact,
speciation has occurred
·
Ring species: allopatric speciation in
progress?
-
Ensatina eschscholtzii
north
American salamander
·
Adaptive Radiation on Island Chains
-
Evolution of many diversely adapted species
from a common ancestor
·
How do reproductive barriers evolve?
-
Two things to consider
1.
geographic isolation does not qualify as
reproductive isolation in the biological sense
2.
speciation is not due to some drive to erect
reproductive barriers around a population.
·
Example of evolution of Prezygotic barrier
-
Dianne Dodd of Yale University
-
Reproductive barriers evolve in allopatric
populations as the result of the population’s adaptive divergence in different
environments
-
Experimented with fruit flies, Drosophila pseudoobscura
exhibite mate choice
·
Example of evolution of postzygotic barrier
-
Robert Vickery of the University of Utah
-
Interbreeding of monkey flower Mimulus glabratus
-
Proportion of fertile offspring decreased
upon mating species from more distant populations
-
Exhibited hybrid breakdown
·
Summary of allopatric speciation
-
New species forms while geographically
isolated from its ancestor
D.
Sympatric speciation: A new species can
originate in the geographic midst of the parent species
·
Polyploid speciation in Plants
-
Polyploidy: cell division that results in an
extra set of chromosome, a mutant condition
-
Autopolyploid: an individual that has more
than 2 chromosomes sets all derived from a single species.
-
Allopolyploid: contribution of two different
species to a polyploidy hybrid
·
Sympatric speciation in Animals
1.
Lake Victoria in East Africa
-
home to 200 species of closely related fish
belonging to the cichlid family.
a.
Pundamililia pundamilia vs Pundamilia nyererei (rigid
mating preferences of females)
-
can result when some subset of the population
become reproductively isolated because of a switch to a habitat, food source,
or other resource notused by the parent population (wasps)
·
Summary of sympatric speciation
-
Requires the emergence of some type of
reproductive barrier that isolates the gene pool of a subset of a population
without geographic separation from the parent population
E.
Punctuated equilibrium model has stimulated
research on the tempo speciation
·
Punctuated equilibrium
-
Incorporates ideas about the tempo of
speciation in their explanations of what we see in the fossil record
-
Species diverge in spurts of relatively rapid
change instead of slowly and gradually
F.
From Speciation to Macroevolution
·
Microevolution
-
A change over the generations in a
population’s allele frequencies, mainly by genetic drift and natural selection
·
Speciation
-
Occurs when a population’s genetic divergence
from its ancestral population results in reproductive isolation
·
Macroevolution
-
Cumulative change during millions of
speciation over vast tracts of time
-
Level of change evident over the time scale
of the fossil record
·
Most evolutionary novelties are modified
versions of older structures
-
Complex structures evolved in increments from
much simpler versions that had the same basic function
1.
Exaptation
-
Structures that evolves in one context but
become co-opted for another function
a.
Honeycomb bones of birds
·
“Evo-devo” genes that control development
play a major role in evolution
1.
Evo-devo
-
the interface between evolutionary biology
and the study of how organisms develop
-
how slight genetic divergences can become
magnified into major morphological difference between species
2.
allometric growth
-
proportioning that helps give a body its
specific form
3.
heterochrony
-
evolution of morphology that arises by a
modification in allometric growth
-
evolutionary change in the rate or timing of
developmental events
a.
salamander feet
4.
paedomorphosis
-
retention of juvenile structures in an
ancestral species
-
macroevolution can also occur from changes in
genes that control the placement and spatial organization of body parts
1.
homeotic genes
a.
Hox genes
-
Provide positional information in an embryo
·
An evolutionary trend does not mean that
evolution is goal oriented
-
Horse descended from smaller ancestor Hyracotherium modern horses are larger genus Equus
1.
species selection
-
analogous to the production of a trend within
a population by natural selection
Chapter
25: Phylogeny and Systematics
A.
Introduction
·
Phylogeny
-
The evolutionary history of a species or
group of related species
·
Systematics
-
The study of biological diversity in an
evolutionary context
B.
Fossil record and geologic time
·
Fossil record
-
Ordered array in which fossils appear within
layers of sedimentary rocks that make the passing of geologic time
·
Sedimentary rocks are the richest source of
fossil
·
Paleontologists use a variety of methods to
date fossils
-
Fossils are reliable only if we can determine
their ages
1.
Relative Dating
a.
Index fossils
-
Similar fossils belonging to same strata
® Shells of
sea animals
b.
Geologic time scale
-
Consistent sequence of historical periods
-
Geologic time scale grouped into 4 eras:
a.
Precambrian
b.
Paleozoic
c.
Mesozoic “age of reptiles”
-
dinosaurs
d.
Cenozoic
® Each era
represents a distinct age in the history of earth and its life
® Boundaries
between the eras correspond to times of mass extinctions when many forms of
life disappeared and were replaced by diversification of the survivors
® Eras
divided more into epochs
® Geologic
eras not equal in duration.
2.
Absolute dating
-
Age is given in years
a.
Radiometric dating
-
The measurement of certain radioactive
isotopes in fossils or rocks is the method used to determine the age of rocks
and fossils on the scale of absolute time
® Carbon 14
b.
Half-life
-
Each radioactive isotope has fixed rate of
decay
-
The number of years it takes for 50% of the
original sample to decay is unaffected by temperature, pressure etc
-
Carbon 14 has a half life of 5,730 years
-
Uranium-238 half life of 4.5 billion years
·
The fossil record is a substantial but
incomplete chronicle of evolutionary history
-
A substantial fraction of species that have
lived probably left no fossils, most fossils that are formed have been
destroyed, and only a fraction of the existing fossils have been discovered
·
Phylogeny has a biogeographic basis in
continental drift
-
Formation of Pangaea
-
Pangaea broke up during the Mesozoic era
-
Continental drift
1.
explains much about the current distribution
of organisms
·
The history of life is punctuated by mass
extinctions
-
Mass extinctions followed by diversification
of certain taxonomic groups that escaped extinction
-
A species may become extinct when:
1.
habitat destroyed or changed
2.
evolutionary change in one species has and
impact on other species, making other susceptible to extinction
-
extinction is inevitable in a changing world
-
most distinct mas extinction
1.
Permian mass extinction
-
250 million years ago
-
defines the boundary between Paleozoic and
Mesozoic eras
-
claimed 90% of the species of marine animals
-
time continents merged to form the Pangaea
-
massive volcanism
-
oxygen deficits in oceans
2.
Cretaceous mass extinction
-
65 million years ago
-
boundary between Mesozoic and Cenozoic eras
-
doomed more than half the marine species and
exterminated many families of terrestrial plants and animals including
dinosaurs
-
volcanic eruptions contributed to cooling
-
but what is favored is the impact hypothesis
a.
impact hypothesis
-
collision of an asteroid or large comet with
earth.
-
Cloud blocked sunlight disturbed climate
-
Has two parts: collision occurred and event
caused the cretaceous mass extinctions
® Chicxulub
crater
-
Impact caused the earth to darken for years
and reduction of photosynthesis lasted long enough for food chains to collapse
-
Caused a firestorm
Chapter 50:
An introduction to ecology and the biosphere
A.
The Scope of Ecology
·
Ecology
-
The scientific study of interactions between
organisms and their environments.
·
Abiotic components
-
Non-living chemical and physical factors such
as temperature, light, waters and nutrients.
·
Biotic components
-
Living. All the organisms that are part of
the individual’s environment.
·
Charles Darwin
-
Laid the groundwork for ecology.
-
Events that occur in the framework of ecological time translate into effects
over the longer scale of evolutionary
time.
·
Organismal ecology
-
Is concerned with the morphological,
physiological and behavioral ways in which individual organisms meet the
challenges posed by their biotic and abiotic environements.
·
Population
-
Is a group of individuals of the same species
living in a particular geographic area.
·
Population ecology
-
Concentrates mailing on factors that affect
how many individuals of a particular species live in an area.
·
Community
-
Consists of all organisms of all the species
that inhabit a particular area
·
Community ecology
-
Deals with the whole array of interacting
species in a community.
-
Focus on the ways in which interactions such
as predation, competition, and disease affect community structure and
organization.
·
Ecosystem
-
Consists of all the abiotic factors in
addition to the entire community of species that exist in a certain area.
·
Ecosystem ecology
-
Emphasis on energy flow and cycling of
chemicals among the various biotic and abiotic components.
·
Landscape ecology
-
Deals with arrays of ecosystems and how they
are arranges in a geographic region.
·
Landscape
/ seascape
-
Consists of several different ecosystems
linked by exchanges of energy, materials and organisms.
-
Focuses on the ways in which interactions
among populations, communities and ecosystems are affected by the combination
of different ecosystems.
·
Biosphere
-
Is the global ecosystem.
B.
Ecology provides a scientific context for
evaluating environmental issues
·
Rachel Carson’s Silent Spring (1962)
-
Pesticide use and its effect on nontarget
organisms causing population decline.
·
Precautionary principle
-
An ounce of protection is worth a pound of
cure.
C.
Factors affecting the distribution of
organisms
-
Distribution of animals associated with
patterns of continental drift that followed the break-up of Pangaea
·
Biogeography
-
Is the study of the past and the present
distribution of individual species.
·
Flowchart of factors limiting geographic
distribution
1.
Dispersal
-
Is a critical process for understanding both
geographic isolation in evolution and the broad patters of current geographic
distributions
a.
Species transplants
-
Able to determine success only after one life
cycle is complete.
-
2 possible outcomes:
® transplant
successful: distribution limited because the area is inaccessible, time has
been too short to reach the area, failure of species to recognize the area as a
suitable living space
® transplant
unsuccessful: distribution limited either by other species or by physical and
chemical factors.
2.
Behavior
-
Habitat selection
3.
Biotic factors (other species)
-
Predators, parasitism, competition, disease
4.
Abiotic factors
a.
Chemical factors: water oxygen, salinity, pH,
soil nutrients, etc.
b.
Physical factors: temperature, light, soil
structure, fire, moisture, etc.
D.
Problems with Introduced Species
·
African
Honeybee
-
Example of unpredicted and undesirable
consequences.
-
Apis mellifera scutellata
-
Very aggressive subspecies of honeybee
brought to Brazil in 1956 to produce more honey than the standard Italian
honeybee (Apis mellifera
ligustica)
-
Escaped by accident and been spreading
throughout the Americas.
-
Since aggressive may drive out established
colonies of Italian honeybees and threaten the honey industry.
·
Zebra
Mussel
-
1988, Dreissena polymorpha native to the freshwater Caspian
Sea of Asia.
-
Discovered in Lake St. Clarie near Detroit.
-
1985, a ship carried larvae of the mussel in
its ballast water from a freshwater port in Europe to the Great Lakes, where it
was emptied.
-
A pest. Reproduces rapidly and forms dense
clusters several layers thick on hard surfaces.
-
Efficient suspension feeders, alter the
native communities of organisms in the process.
-
Depress populations of zooplankton
-
Crowd out native mollusk species by
colonizing all hard surfaces, including the shells of freshwater clams.
-
May result to extinction of native species
·
The Tens Rule
-
A rough generalization for the success of
introduced species which makes the statistical prediction that an average of
one out of ten introduced species become established and one out of ten
established species become common enough to become pests.
E.
Behavior and habitat selection contribute to
the distribution of organisms
-
Distribution of species may be limited by the
behavior of individuals in selecting habitat.
-
Insects have a very sterotypes oviposition
(egg-depositing) behavior, restrict their local distribution to certain host
plants. ex. European corn borer.
-
Anopheline mosquitoes are
important carriers of disease.
-
Evolution does not produce perfect organisms
for every suitable habitat.
-
Not all evolved behaviors remains adaptive
due to human intervention and environmental changes.
·
Biotic factors affect the distribution of
organisms
-
Negative interactions with other species,
predation, competition and disease.
-
Absence of other species in which the
transplanted species depends on.
1.
sea urchins and kelp (predation)
-
where sea urchins that graze on kelp are
common, kelp cannot be established.
-
Local distribution of kelp limited by sea
urchins.
F.
Abiotic factors affect the distribution of
organisms
1.
Temperature
-
Effect on biological processes and the
inability of most organisms to regulate body temperature precisely.
2.
Water
-
Essential to life, water balance
3.
Sunlight
-
Provides energy that drives nearly all
ecosystems
-
Meter of water selectively absorbs 45% of the
red light and about 2% if the blue light passing through it.
4.
Wind
-
Wind-chill factor
5.
Rock and soil
-
Physical structure, pH and mineral
composition of rocks and soil limit the distribution of plants and animals that
feed upon them.
G.
Water and Temperature are the major climatic
factors determining the distribution of organisms
-
Four abiotic factors – temperature, water,
light and wind – are the major components of climate.
·
Climate
-
The prevailing weather condition at a
locality.
·
Climate and Biomes
1.
Biomes
-
Are major types of ecosystems that occupy
broad geographic regions.
-
Temperature and rainfall
·
Global climate patterns
-
Earth’s global climate patterns are largely
determined by the input of solar energy and the planet’s movement in space.
-
Earth tilted 23.5 degrees relative to its
plane of orbit
-
More sunlight on the areas near the equator,
the tropics and experience least
seasonal variation.
·
Local and Seasonal Effects on Climate
-
Proximity to water
-
Mountains effect on solar radiation, rainfall
and local temperature.
·
Microclimate
-
Climate variation at a fine scale
-
Trees in forests, moderate climate below
·
Long term climate change
-
Climatic warming (global warming) will have
profound effects on the biosphere
-
American beech (Fagus grandifolia)
H.
Aquatic and terrestrial biomes
·
Aquatic biomes occupy the largest part of the
biosphere
-
Distinguish between freshwater biomes and
marine biomes on the basis of physical and chemical differences.
-
Marine (3% salt concentration) freshwater
(less than 1%)
·
Vertical stratification of aquatic biomes
-
Light absorbed by water and microorganisms in
it, intensity decreases with depth
1.
Photic zone
-
Where there is sufficient light
2.
Aphotic zone
-
Little light penetrates
3.
Thermocline
-
A narrow stratum of rapid temperature change;
separates a more uniformly warm upper layer from a more uniformly cold deeper
waters.
4.
Benthic zone
-
The bottom of all aquatic biomes, the
substrate.
-
Made up of sand and organic and inorganic
sediments (ooze)
-
Occupied by communities of organism called benthos which have a major source of food called detritus.
·
Freshwater biomes
-
2 general categories:
1.
standing bodies of water (lakes and ponds)
2.
moving bodies of water (rivers and streams)
-
in most lakes organisms are distributed
depending on the distance from the shore.
1.
Littoral zone
-
Rooted and floating aquatic plants flourish;
shallow well lit waters close to shore.
2.
limnetic zone
-
well lit waters farther from the shore,
occupied by a variety of phytoplankton consisting of algae and cyanobacteria
3.
Profundal zone
-
Where remains of organisms in limnetic zone
sink into; aphotic.
-
Lakes often classified according to their
production of organic matter.
1.
Oligotrophic
-
Deep and nutrient poor with sparse and
unproductive phytoplankton in limnetic zone.
2.
Eutrophic
-
Shallower, high nutrient content,
phytoplankton are very productive and waters are often murky.
3.
Mesotrophic
-
Moderate amount of nutrients and
phytoplankton productivity.
-
Cultural eutrophication
-
at headwaters of streams, the water is often
cold and clear, little sediment, few mineral content
-
nutrient content of flowing water biomes is
largely determined by the terrain and vegetation through which water flows.
·
Wetlands
-
An area covered with water that supports
aquatic plants
-
Favor growth of specially adapted plants
called hydrophytes, which can grow in
water or in soil that is periodically anaerobic due to the presence of water.
-
Different types of wetlands, ranging from
marshes to swamps to bogs.
-
Among the richest of biomes
-
Provide water storage basins that reduce the
intensity of flooding, improve water quality by filtering pollutants
·
Estuaries
-
Area where a freshwater stream or river
merges with the ocean.
-
Often bordered by extensive coastal wetlands
called mudflats and salt marshes.
-
One of the most biologically productive
biomes
-
Breeding ground for many marine organisms.
·
Zonation in marine communities
-
Marine communities are distributed according
to depth of water, degree of light penetration, distance from shore, and open water
versus bottom.
-
Intertidal zone: zone where land meets water,
beyond it is the neritic zone, the shallow region over the continental shelves.
-
Oceanic zone: past continental shelves, very
great depths.
-
Pelagic
zone: open water
of any depth, bottom is the seafloor or the benthic zone.
·
Intertidal zones
-
Is alternately submerged and exposed by the
twice-daily cycle of tides.
-
Affected much by humans and pollution
·
Coral reefs
-
In warm tropical waters in the neritic zone
-
Currents and waves constantly renew nutrient
supplies to the reefs and sunlight penetrates to the ocean floor, allowing
photosynthesis.
-
Dominated by the structure of the coral
itself.
-
Dinoflagellate algae live on their tissues;
such affect corals rate of calcium carbonate deposition. Reef formation depends
on this symbiotic relationship.
-
Susceptible to pollution.
-
High water temperatures cause corals to
“bleach” – to expel their symbiotic dinoflagellates and die.
-
Global warming could destroy coral reefs.
-
Crown of thorns sea star
·
The oceanic pelagic biome
-
Far from shore, constantly mixed by ocean
currents.
-
Nutrient concentrations generally lower than
in coastal areas
·
Benthos
-
Nutrients reach bottom through “raining down”
in the form of detritus
-
Neritic benthic communities are extremely productive.
Composition of species varies with distance from the shore, water depth, and
composition of the bottom.
1.
Abyssal
zone
-
very deep benthic communities, organisms are
adapted to continuous cold, high water pressure and near or total absence of
light, and low nutrient concentrations.
2.
deep-sea hydrothermal vents
-
midoceanic ridges.
-
Dark hot, oxygen deficient environment,
chemoautotrophic prokaryotes.
I.
The geographic distribution of terrestrial
biomes is based mainly on regional variations in climate
-
Latitudinal patterns of climate over the
earth’s surface, there are latitudinal patterns of biome distribution.
-
Terrestrial biomes often named for major
physical or climatic features and for their predominant vegetation.
-
Also characterized by microorganisms, fungi,
and animals adapted to that particular environment.
-
Vertical stratification in forest: canopy,
low-tree stratum, shrub, ground layer of herbaceous plants, the forest floor
(litter layer) and finally the root layer.
-
Arctic tundra, has a permanently frozen
stratum called permafrost.
-
Vertical stratification of a biome’s
vegetation provides different habitats for animals.
1.
ecotone
-
area of intergradation of one terrestrial
biome to another.
-
Biomes are dynamic and natural disturbance
rather than stability tends to be the rule.
·
Tropical forest
-
Pronounced vertical stratification, little
light
-
Many of the trees are covered with epiphytes
(plants that grow on other plants instead of soil)
-
Rainfall is the prime determinant of the
vegetation growing in the area.
·
Savanna
-
Large herbivores (giraffe) and their
predators
-
Grasses and scattered trees are the dominant
plants
-
Fire an important abiotic component
-
Regular seasons of water drought
·
Desert
-
Sparse rainfall (less than 30 cm per year)
main determinant
-
Water conservation adaptations by both plants
and animals
·
Chaparral
-
Dense, spiny evergreen shrubs dominant
vegetation
-
Bush fires
·
Temperate grassland
-
Key to persistence of grasslands is seasonal
drought, occasional fires and grazing by large mammals, all of which prevent
establishment of woody shrubs and trees.
-
Prairie
·
Temperate deciduous forest
-
Dense stands of deciduous trees where there
is sufficient moisture to support these trees.
-
More open than rain forests, has distinct
vertical layers
-
Drop leaves during winter and animals undergo
hibernation and bird migrate to
warmer climates
·
Coniferous forest / taiga
-
Dominated by conifers
-
Temperate rain forests
-
Warm moist air from the Pacific supports
these unique communities
-
Receive heavy snowfall during winter
·
Tundra
-
Permafrost (permanently frozen subsoil)
bitterly cold temperatures and high winds are responsible for the absence of
trees and other tall plants
-
Receives very little annual rainfall, water
cannot penetrate the permafrost and accumulates in pools on the shallow
topsoil.
J.
The spatial scale of distributions
·
Different factors may determine the
distribution of a species on different scales
·
Most species have small geographic ranges
Chapter 52:
Population Ecology
A.
Introduction
·
Population ecology
-
Concerned with measuring changes in
population size and composition and with identifying the ecological causes of
these flunctuations
B.
Characteristics of populations
·
Population
-
A group of individuals of a single species
that simultaneously occupy the same general area
-
Rely on the same resources
-
Are influenced by similar environmental
factors
-
High likelihood of breeding with and
interacting with one another
·
Two important characteristics of any
population are density and the spacing of individuals
1.
population size
-
no of individuals it includes
-
two important characteristics of any
population is its density and its dispersion
1.
Population density
-
Number of individuals per unit area or volume
2.
dispersion
-
pattern of spacing among individuals within
the geographic boundaries of the population
·
Patterns of dispersion
-
Not all areas provide equally suitable
habitat giving rise to patchiness
-
Forms of dispersion
1.
clumped
-
most common
-
individuals aggregated in patches
-
also associated with mating behavior
a.
“safety in numbers”
2.
uniform
-
evenly spaced
-
may result from direct interactions between
individuals in a population
-
not as common
3.
random
-
unpredictable dispersion
-
occurs in the absence of strong attractions
or repulsions among individuals of a population
-
position of each individual is independent of
others
C.
The logistic model of population growth
incorporates the concept of carrying capacity
-
Populations subsist in a finite amount of
available resources
-
Ultimately there is no limit to the number of
individuals that can occupy a habitat
·
Carrying capacity
-
Maximum population size that a particular
environment can support at a particular time with no degradation of habitat.
-
Not fixed, varies over space and time with
the abundance of limiting resources
-
Energy limitation is one of the most
significant determinants of carrying capacity
-
Crowding and resource limitation can have a
profound effect on the population growth rate
1.
if organisms cannot obtain sufficient
resources to reproduce, birth rate will decline
2.
if cannot find enough energy to maintain
themselves, per capita death rate increases
D.
The logistic population growth model and life
histories
-
Life history traits that natural selection
favors may vary with population density and environmental conditions
·
K-selection
-
Selection for life history traits that are
sensitive to population density
-
Density-dependent selection
-
Tends to maximize population size
-
Operates in populations living at densities
near the limit imposed by their resources
·
r-selection
-
selection for life histories that maximize
reproductive success in uncrowded environments c
-
density independent selection
-
tends to maximize r, the rate of increase
-
occurs in variable environements in which
population densities flunctuate well below carrying capacity
E.
Population Limiting Factors
·
Terms:
1.
Density dependent
-
Death rate rises as population density rises
-
Birth rate falls with rising density
-
Example of negative feedback
2.
Density independent
-
Birth rate or death rate does not change with
population density
-
No feedback to slow down population growth
·
Negative feedback prevents unlimited
population growth
-
Resource limitation is crowded populations
can stop population growth by reducing reproduction
-
Increasing population density intensifies
intraspecific competition for declining nutrients, resulting in lower birth
rate
-
Territoriality: the defense of a well bound
physical space may set a limit on density
-
Population density also influences the health
and thus the survival of organisms
-
Predation may also be an important cause of
density dependent mortality
-
Accumulation of toxic waste is another
component that can contribute to density-dependent regulation of population
size
-
Impact of disease
Chapter 53:
Community Ecology
A.
What is a community?
·
Community
-
Is any assemblage of populations in an area
or habitat
·
Species richness
-
The number of species that they can contain
·
Relative abundance
-
Differ in kinds of species
B.
Interspecific interactions and community
structure
·
Interspecific interactions
-
Relationships between species of a community
·
Populations may be linked by competition, predation
mutualism and commensalisms
1.
Competition
-
Interspecific competition for resources can
occur when the resources are in short supply
-
Competition for two species that need the
same resource
-
Result may be a reduction in density of one
or both species, or the elimination of one or both.
a.
The competitive exclusion principle
-
G. F. Gause (Russian ecologist) 1934
-
Paramecium Aurelia and paramecium caudatum
-
Even a slight advantage will eventually lead
to local elimination of the inferior competitor
b.
The ecological niche
-
The sum total of a species use of the biotic
and abiotic resources in its environment
-
Two species cannot coexist in a community if
their niches are identical
2.
Predation
-
Includes herbivory and parasitism
3.
Mutualism
-
Mutual symbiosis
-
An interspecific interaction that benefits
both species
-
Requires coevolution of adaptations in both
participating species
4.
Commensalism
-
And interaction between species that benefits
only one of the species involved in the interaction.
C.
Trophic structure is a key factor in community
dynamics
·
Trophic structure
-
The dynamics and structure of a community
depend to a large extent on the feeding relationships between organisms
·
Food chain
-
Transfer of food energy from its source in
plants (primary producers) through herbivores (primary consumers) to carnivores
(secondary and tertiary consumers) and eventually to decomposers
-
Charles Elton: food chains are not isolated,
hooked together into food webs
·
Food webs
-
What transforms food chains into food webs?
1.
a species may weave into the web at more than
one trophic level
·
What limits the length of a food chain?
-
Two hypotheses as to why food chains are
relatively short
1.
energetic hypothesis
-
length is limited by inefficiency of energy
transfer along the chain
2.
dynamic stability hypothesis
-
long food chains are less stable than short
chains.
-
Fluctuations at lower trophic levels are
magnified at higher levels potentially causing extinction of top predators
D.
Dominant species and keystone species exert
strong control on community structure
·
Dominant species
-
Are species in the community that have the
highest abundance or highest biomass.
-
Exert powerful control over the occurrence
and distribution of other species.
a.
American chestnut
E.
Ecological succession is the sequence of
community changes after disturbance
·
Ecological succession
-
Transition in species composition over
ecological time
·
Primary succession
-
If it begins in a virtually lifeless area
where soil has not yet formed
·
Secondary succession
-
Occurs when an existing community has been
cleared by some disturbance that leaves the soil intact
Chapter 54:
Ecosystems
A.
Introduction
·
Ecosystem
-
Consists of all the organisms living in a
community as wells as all the abiotic factors with which they interact.
-
Involves two processes
1.
energy flow
2.
energy cycling
B.
The ecosystem approach to ecology
-
Trophic levels bases on main source of
nutrition and energy
·
Trophic relationships determine the routes of
energy flow and chemical cycling in an ecosystem
1.
primary producers
-
trophic level that support all others
-
autotrophs
2.
heterotrophs
-
organisms above the trophic level of the
primary producers
-
directly or indirectly depend on the
photosynthetic output of primary producers
3.
primary consumers
-
herbivores that eat primary producers
4.
secondary consumers
-
carnivores that eat herbivores
5.
tertiary consumers
-
carnivores that eat other carnivores
6.
Detritivores or decomposers
-
Consumers that get their energy from
detritus, the nonliving organic material.
-
Play a central role in material cycling
·
Decomposition connects all trophic levels
-
Organic material that makes up the living
organisms in an ecosystem gets recycled
C.
The efficiency of energy transfer between
trophic levels is usually less than 20%
·
Trophic efficiency
-
is the percentage of production transferred
from one trophic level to the next.
-
80-95% of the energy available at one trophic
level never transfers to the next
·
Pyramids of production
-
Represents the multiplicative loss of energy
from a food chain
-
Trophic levels are stacked in blocks with
primary producers forming the foundation
-
Size of each block is proportional to the
production of each trophic level
·
Pyramids of biomass
-
Represents one ecological consequence of low
trophic efficiencies
-
Each tier represents the standing crop (the
total dry weight of all organisms) in a trophic level
-
Most pyramids narrow because energy transfers
in trophic levels are so inefficient
1.
turnover time
-
have small standing crop biomass compared to
their production
a.
phytoplankton
·
Pyramids of numbers
-
Multiplicative loss of energy from food
chains severely limits the overall biomass of top-level carnivores that any
ecosystem can support
-
Pyramid numbers: the size of each block is
proportional to the number of individual organisms present in each trophic
level
D.
Herbivores consume a small percentage of
vegetation: the green world hypothesis
·
Green world hypothesis
-
Herbivores consume relatively little biomass
because they are held in check by a variety of factors including predation,
parasites and disease
1.
plants have defenses against herbivores
2.
nutrients, not energy supply, usually limit
herbivores
3.
abiotic factors limit herbivores
4.
intraspecific competition can limit herbivore
numbers
5.
interspecific interactions check herbivore
densities
E.
The cycling of chemical elements in
ecosystems
-
Chemical elements are available only in
limited amounts
-
Biochemical cycles: because nutrient circuits
involve both biotic and abiotic components of ecosystems
·
Biological and geologic processes move
nutrients between organix and inorganic compartments
-
Two general categories of biochemical cycles
·
A general model of chemical cycling
-
Nutrients accumulate in four reservoirs which
have two characteristics:
1.
whether it contains organic or inorganic
materials
2.
whether or not materials are directly
available for use by organisms
-
compartments or organic materials:
1.
living organisms and detritus
2.
fossilized deposits
-
coal, oil, peat
-
nutrients not assimilated directly
-
inorganic compartments:
1.
available for use by organisms
-
matter (elements and compounds)
2.
not available
-
tied up in rocks become available only after
erosion and weathering
-
water cycle not fit in so well, more of a
physical process than a chemical one.
·
The Nitrogen Cycle
-
80% nitrogen, most in nitrogen gas form which is unavailable to plants
-
enters ecosystem via two pathways:
1.
atmospheric deposition
-
NH4+ and NO3- two forms of nitrogen available
to plants are added to soil by being dissolved in rain
2.
nitrogen fixation
-
convert N2 to mineral that can be used to
synthesize nitrogenous organic compounds such as amino acids.
-
Rhizobium
at root nodules of legumes
-
Cyanobacteria
-
Returned to atmosphere through atmospheric
deposition
a.
Nitrification
-
Oxidation of ammonium to nitrite and then to
nitrate
b.
Denitrification
c.
Ammonification
-
Decomposition of organic nitrogen back to
ammonium
·
*ack tamad na, check diagrams na lang
F.
Human activities may be causing climate
change by increasing carbon dioxide concentration in the atmosphere
·
Greenhouse effect
·
Global warming
Chapter 55:
Conservation
A.
Introduction
-
Conservation biology is a goal-orriented
science that seeks to counter the biodiversity crisis, the current rapid
decrease in the Earth’s great variety of life
B.
The biodiversity crisis
-
Extinction is a natural phenomenon that has
been occurring almost since life first evolved
-
High rate of species extinction caused by an
escalating rate of ecosystem degradation by a single species – Homo sapiens
·
The three levels of biodiversity are genetic
diversity, species diversity and ecosystem diversity
1.
Lost of genetic diversity
-
First level of biodiversity is genetic
variation
-
Genetic variation between and within
populations
-
Detrimental effects to other species and to
humans
2.
Loss of species diversity
-
Second level of biodiversity is a variety of
species in an ecosystem or throughout the entire biosphere what we call species
richness
a.
Endangered species
-
One that is in danger of extinction
throughout all or a significant portion of its range
b.
Threatened species
-
Those that are likely to become endangered in
the foreseeable future throughout all or a significant potion of their range.
-
Concerns of conservations biologists
regarding species loss
a.
International Union for Conservation of
Nature and Natural Resources, 13% of the 9040 known bird species in the world
are threatened. 1,183 species
b.
Center for Plant Conservation 20,000 known
plant species in the US, 200 have become extinct, 730 are endangered
c.
20% of freshwater fishes in the world have
become extinct or are endangered.
-
One of the largest extinction events was the
loss of 200 of 300 species of cichlids in Lake Victoria, East Indies, have been
lost due to the introduction of the exotic predator the Nile perch.
d.
123 freshwater vertebrate and invertebrate
species have become extinct in N.America, hundreds are threatened.
e.
Harvard biologist, Edward O. Wilson and the
Hundred Heartbeat Club, where species that belong are those that have a number
of 100 individuals
f.
Half of all plant and animal species will be
gone by the end of this century
-
Global extinction: loss for all its locales
3.
Loss of Ecosystem Diversity
-
Variety of the biosphere’s ecosystems is the
third level of biological diversity
-
Each ecosystem have an important impact on
the biosphere
·
Biodiversity at all three levels is vital to
human welfare
-
E.O. Wilson: biophilia (our sense of
connection to nature and other forms of life)
·
Benefits of species diversity and genetic
diversity
-
Biodiversity is a crucial natural resource
-
Loss of species means the loss of genes
·
Ecosystem services
-
Benefits that individual species provide to
humans are often substantial
-
Humans are dependent on ecosystems and on
interactions with other species
-
We are also at risk
1.
Ecosystem services
-
Encompass all the processes through which
natural ecosystems and the species they contain help sustain human life on
Earth.
a.
Purification of air and water
b.
Reduction of the severity of droughts and
floods
c.
Generation and preservation of fertile soils
d.
Detoxification and decomposition of wastes
e.
Pollination of crops and natural vegetation
f.
Dispersal of seeds
g.
Nutrient cycling
h.
Control many agricultural pests by natural
enemies
i.
Protection of coastal shores from erosion
j.
Protection from ultraviolent rays
k.
Moderation of weather extremes
l.
Provision of aesthetic beauty
-
Human life would cease without these services
C.
The four major threats to biodiversity are
habitat destruction, introduced species, overexploitation and food chain
disruptions
·
Habitat Destruction
-
Habitat fragmentation leads to species loss
1.
Habitat reduction and fragmentation in the
Wisconsin forest
·
Introduced species
-
Contributed to about 40% of extinctions
1.
Introduced species
-
Are those that humans move from the species
native locations to a new geographic regions
-
Some cases intentional
a.
European red foxes
-
Introduced to Australia
b.
Nile perch to Lake Victoria
-
Accidentally
a.
Brown tree snake
-
12 species of birds and 6 lizard species have
become extinct in Guam
-
introduced species that gain a foothold
usually disrupt their adopted community often preying on native species or
outcompeting native species for resources
-
good intentions
a.
Kudzu (from
Japan)
-
to prevent soil erosion
-
took over vast expanses of Southern landscape
b.
purple loosestrife
-
claiming 200,000 wetlands per year
-
crowding out native plants and the animals
that feed on the native flora
c.
European starling
-
120 european starlings in Central Park in
1890
-
population increased to 100 million in less
than a century, displacing many of the native songbird species in the US and
Canada
d.
fire ants
-
eliminated 2/3 of native species of ants in
Texas
e.
Argentine ant
-
Decimating populations of native ants in
California
f.
Caurlerpa
-
California lagoon
-
Displacing many of the algae there
-
50,000 introduced species in the United
States alone with the cost to the economy of over $130 billion in damage and
control efforts not including the priceless loss of native species
·
Overexploitation
-
Humans harvesting of wild plants or animals
at rates exceeding the ability of populations of those species to rebound
-
Overhunting and overfishing of animals
-
Elephants, whales, rhinoceroses
a.
Great auk (Pinguinis impernnis)
-
Islands in Atlantic Ocean
-
Extinct because of demand for feathers, meat
and eggs
b.
Decline of African
elephant
-
Take 10-11 years to reach sexual maturity
-
Fertile female has a single calf every 3 – 9
years
-
6% growth rate per year
-
illegal hunting for ivory is the major cause,
poaching
c.
North American Blue Fin Tuna
-
Sushi and sashimi
-
$100 per pound
-
reduced to 20% of its natural size in 1980
·
Disruption of food chains
-
Extinction of one species can doom its
predators
-
Host-specific parasites can become instinct
if their host become extinct
1.
Forest eagle of New
Zealand extinct upon the extinction of Moas, flightless
birds.
2.
black footed ferret on the
Great Plains of N. America parralled decline of its main prey, prairie dogs.
D.
Conservation at the population and species
levels
-
Two main approaches:
1.
small-population approach
2.
declining-population approach
·
According to the small population approach, a
population’s small size can draw it into an extinction vortex
-
A species is designated as endangered when
its populations are very small
-
This approach studies the processes that can
cause very small populations to finally become extinct
1.
Extinction vortex
-
A downward spiral unique to small populations
-
A small population is prone to positive
feedback loops of inbreeding and genetic drift that draw the population down
the vortex toward smaller population size until no individuals exist
-
Key factor is the loss of genetic variation
on which a population depends for adaptive evolution
a.
Lousewort Pedicularis
-
low genetic variability
-
low genetic variability does not necessarily
lead to permanently small populations
·
How small is too small for a population?
-
Depends on type of organism
1.
Minimum viable population size
-
Minimum population size where rare species
will be able to sustain their numbers and survive
2.
Population viability analysis
-
Objective of analysis is to be able to make a
reasonable prediction of a population’s chances for survival over a particular
time
3.
Effective population size
-
Based on breeding potential of the population
·
The declining population approach is a
proactive conservation strategy for detecting, diagnosing and halting population
declines
-
Focus on threatened and endangered
populations even if they are far greater than minimum viable size
-
Emphasis on environmental factors that cause
a population to decline
1.
Steps in the Diagnosis and treatment of
declining populations
a.
Confirm that the species is presently in
decline or that it was formerly more widely distributed or more abundant
b.
Study the species’ natural history to
determine its environmental requirements
c.
Determine all the possible causes of the
decline
d.
List the predictions of each hypothesis for
the decline
e.
Test the most likely hypothesis first
f.
Apply the results of this diagnosis to the
management of threatened species
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