Transcript What is Evolution and how has it led to the current

What is Evolution and how has it led to the
current diversity of organisms on the Earth?
How It All Began!
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It is impossible for life to have
evolved with oxygen
No oxygen in atmosphere (CO2,
CH4, CO, N2 & H2O)
Cyanobacteria photosynthesis
Anaerobic prokaryotes->
photosynthetic prokaryotes>aerobic prokaryotes->
eukaryotes-> multicellualr
organisms
What is Evolution and Natural Selection?
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Evolution: Cumulative
genetic changes over time
in a population
 Natural Selection:
Hypothesis proposed by
Charles Darwin in 1859;
The process in which
better adapted individuals
are more likely to survive
and reproduce, increasing
their proportion in the
population (Survival of the
Fittest)
How Does Natural Selection Work?
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Overproduction: Each species produces more
offspring than will survive.
Variation: Each individual exhibits a unique
combination of traits.
Limited Resources: There is only so much food,
water, light, growing space.
Differential Reproductive Success: Those
individuals with the most favorable combination of
traits are more likely to survive, reproduce and
pass their traits to the next generation.
Types of Natural Selection
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Directional Selection: Favors one extreme
phenotype (antibiotics killing bacteria)
Stabilizing Selection: Favors average
phenotype (birth weight)
Disruptive Selection: Favors both extremes
(bill size in the finches)
Which of these selections favors diversity?
Life is a Genetic Dice Game
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A population’s ability to adapt is limited by its gene pool
(genetic composition) and how fast it can reproduce.
Microevolution: small genetic changes that a population
within a species undergoes (peppered moth in England)
Macroevolution: Long term, large scale changes through
which new species form from ancestral species and
other species are lost through extinction.
Coevolution: Two different species interact over a long
time, changes in gene pool of one species can lead to
changes in the gene pool of the other.
How does the gene pool change?
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Individuals do not evolve! Populations do.
Sexual Selection: Females select males with better resources
Mutation: Occurs constantly (random)
Migration: Tends to eliminate genetic differences in populations by
equalizing allele frequencies: But causes increased diversity in
small populations (animal swapping in zoos)
Genetic Drift: Change in allele frequency due to random chance
(more pronounced in small populations)
 Bottlenecking: event in which a significant percentage of a
population or species is killed or otherwise prevented from
reproducing, and the population is reduced by 50% or more,
often by several orders of magnitude (cheetahs: lots of
inbreeding & loss of allele frequencies)
What Limits Adaptation?
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Reproductive Strategies:
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K-selected species: large body size, long life spans, slow
development, late reproduction, low reproductive rate,
parental care (elephants, whales)
R-selected species: small body size, early maturity, short
life span, large broods, little or no parental care (insects,
weeds, mice)
Many species posses a combination as well as traits that
are neither
Which strategy has a better chance of surviving a large
disturbance? Why?
What is the probability of survivorship?
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Type I survivorship curves : are for species that have a
high survival rate of the young, live out most of their
expected life span and die in old age. (Humans)
Type II survivorship curves : are for species that have a
relatively constant death rate throughout their life span.
Death could be due to hunting or diseases. (coral,
squirrels, honey bees and many reptiles)
Type III survivorship curves : are found in species that
have many young, most of which die very early in their
life. (Plants, oysters and sea urchins)
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Which type of survivorship curve does the cheetah have?
What does parental care have to do with the shape of these
curves?
SURVIVAL HANGS IN THE BALANCE!
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When facing a new powerful selective
pressure, such as climate change or a new
species invading the ecosystem, species
have three alternatives:
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Adaptation
Migration
Extinction
What is biodiversity and how do we determine it?
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ECOSYSTEM #1
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55 SPECIES OF TREES
1 OR 2 INDIVIDUALS
OF 54 OF THOSE
SPECIES
200 INDIVIDUALS OF A
SINGLE SPECIES
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ECOSYSTEM #2
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40 SPECIES OF TREES
50 INDIVIDUALS OF
EACH SPECIES
WHICH ECOSYSTEM IS MORE DIVERSE?
SHANNON-WEINER BIODIVERSITY
INDEX
H’ = AMOUNT OF DIVERSITY
pi = REPRESENTS THE PROPORTION OF EACH
SPECIES TO THE TOTAL
ln pi = NATURAL LOG OF pi
SIMSPSON INDEX
n = the total number of organisms of a particular species
N = the total number of organisms of all species
The value of D ranges between 0 and 1
With this index, 0 represents infinite diversity and 1, no diversity.
Simpson's Index of Diversity 1 – D
Simpson's Reciprocal Index 1 / D
How do new species evolve?
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Reproductive Isolation: Original population
must separate into smaller populations that
do not interbreed
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Geographical: Mountains/rivers/cities
Spatial: Distance (maple trees in NJ & Maine)
Temporal: Timing of reproductive events
Morphological: chihuahua & great dane
Physiological: Chemical signals in plants to allow
pollen in
Separated Populations must be Exposed to
Different Selective Pressures!
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Geographic Isolation:
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Due to glaciation in North America fox population
was separated
In the Arctic, selective pressure favored heavier
fur, shorter tail, legs, ears and nose and white fur
all of which would be harmful in warmer climates
Therefore speciation occurred: arctic fox/gray fox
How are Species Interconnected?
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Symbiosis: Individuals of one species live
in or on another species.
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Mutualism: Both species benefit (Nitrogen fixing
bacteria live in nodules in the roots of legumes)
Commensalism: One species benefits without
harming the other (barnacles on whales)
Parasitism: One organism obtains nourishment
(parasite) from another (host). Parasites may
weaken its host but rarely kills (tapeworms).
Predator – Prey Relationships
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Predator chases and the prey avoids
Countless Strategies
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Camouflage & Mimicry
Being Big (elephant)
Groups (odds of being caught is less)
Fast, hide
Plants: spines, thorns, tough leaves, toxic
What’s all this Competition About?
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Competition: Interaction among organisms that vie for
the same resources such as food or living space
Interspecific Competition: Competition between different
species (hyenas and lions)
How can interspecific competition be
avoided?
Eating at different times
Resource partitioning
Character displacement
More Competition!
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Intraspecific Competition: Competition among
individuals within a population (two male lions)
The competitive exclusion principle: (Gause's
Law) states that two species that compete for the
exact same resources cannot stably coexist.
Competition can lead to character displacement.
If this occurs long enough you get speciation
(different beak sizes eat different types of food)
Why is Biodiversity So Important?
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1.8 million species identified so far
99% of all species that ever lived are now
extinct
25% of all mammals are at risk of becoming
extinct in the wild in near future
Highest risk are apes & mammals
What roles do various species play?
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Niche: The role of a
species in the community
or way of life
Keystone species: Have
a larger effect on the
types and abundance of
other species in the
community
(otters, bats, sea stars)
Going, Going, Gone!
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Indicator species:
Species that serve as
early warnings of
damage or danger to a
community.
Why are amphibians
(frogs) indicator species?
Life in both water/land
Thin absorbent skin
Feedback Loops
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Positive Feedback: change increases condition
already present
Negative Feedback: change decreases condition
already present
All Species Are Important!
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Ecological Value: Each species plays a role to
increase resilience (ability of ecosystem to
bounce back after a disturbance)
Economic Value: 7 yr old lion in Kenya is worth
$515, 000 in tourist attraction
Medical & Scientific Value: 25% of all medicine
derived from plants (Taxol)
Intrinsic Value: Regardless of usefulness all
species morally have value (aesthetic)
How do ecosystems respond to
change?
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Primary Succession: Establishing life on lifeless ground
(bare rock)
Secondary Succession: Life building on life. Life emerges
again after a disturbance.
Aquatic Succession: Water to land
How Do Species Replace One
Another?
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Facilitation: One set of species makes an area
suitable for another (mosses and lichens build
up soil on rocky areas for grasses and herbs to
grow)
Inhibition: Early species hinder the growth of
other species (release toxic chemicals, walnut
trees)
Tolerance: Late successional plants are
unaffected by plants at earlier stages.
Biodiversity on an Island
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Theory of Island Biogeography (MacArthur & Wilson)
states that two factors affect biodiversity on an island,
immigration & extinction.
Two features of islands affect immigration and
extinction, size & distance from nearest mainland
What size island would have more biodiversity? Why?
Which distance would have more biodiversity? Why?