Transcript ESR173U7LecA

ESR 173 Unit 7 Lecture
• Biodiversity
• Evolution
• Species Interactions
Biodiversity
• Degree of variation of life-forms in a given
habitat or ecosystem
• Measure of the health of the ecosystem
– Biodiversity-stability hypothesis: greater
biodiversity means greater resilience to
disturbance
• Varies geographically; some areas very
rich in diversity and other areas much less
so
Plants
Animals
Fungi
Protists
Bacteria
Archaea
1.7-1.9 million named
and identified (to
science) different
unique kinds of livings
organisms
The Theory of
Biological Evolution
• Charles Darwin’s theory of evolution by means of natural
selection explains the unity and diversity of life as
“descent with modification”
– Parents pass traits to their offspring (heredity)
– Individuals within a population vary in those traits (variation)
– Some individuals have traits that are better adapted to particular
circumstances and conditions than other (fitness)
– Those more fit have greater reproductive success than those with
less fit, increasing the proportion of “fit” genes in the population
through each successive generation
– Heritable traits + variation + environment = differential
reproduction
• All living organisms are related to one another in a
common tree of descent
Charles Darwin
Primary Characteristics of
Natural Selection
1. Inheritance of traits from one generation to the
next and some variation in these traits—that is,
genetic variability
2. Environmental variability acts on the genetic
variation within the population favoring some
traits over others
3. Differential reproduction that varies with the
environment … those individuals with more
favorable traits leave more offspring on
average increasing the fitness of the
population to the environment
Natural Selection based on
3 Observations and 2 Inferences
• Observation #1: For any species,
population sizes would increase
exponentially if all individuals that are born
reproduced successfully
• Observation #2: Populations tend to be
stable in size, except for seasonal
fluctuations
• Observation #3: Resources are limited
• Inference #1: Production of more
individuals than the environment can
support leads to a struggle for existence
among individuals of a population, with only
a fraction of their offspring surviving
– More offspring are born than survive to
reproduce in natural populations
• Observation #4: Members of a population
vary extensively in their characteristics; no
two individuals are exactly alike
Variation In Snails
Variation In Human Height
Variation in Human Height
Variation In Human Skin Color
• Observation #5: Much of this variation is
heritable (passed from parent to offspring
through reproduction); in other words,
many of the traits an individual has are
due to their inherited genetic makeup
• Inference #2: Survival depends in part on
inherited traits; individuals whose inherited
traits give them a high probability of
surviving and reproducing are likely to
leave more offspring than other individuals
• Inference #3: This unequal ability of
individuals to survive and reproduce will
lead to a gradual change (in genotype and
phenotype frequencies) in a population,
with favorable characteristics
accumulating over generations
Summary of Natural Selection
• Natural selection is differential success in
reproduction from interaction between individuals
that vary in heritable traits and their environment
• Natural selection produces an increase over time
in adaptation of organisms to their environment
• If an environment changes over time, different
traits are favored resulting in a change in the
frequency of the newly favored traits
– Salt n’ pepper moth and industrial pollution
– Blue eyes and UV-b radiation
– Frizzle feather gene in chickens and temperature
Natural Selection
Geographic Isolation and
the Origin of New Species
A single population is divided
into two due to a geographic
barrier to reproduction and
over time, due to differences
in the environment selecting
for different traits becomes 2
different species.
Spotted Owl Species Have Genetic
and Physical Differences
Genetic Diversity
• Genetic variation within a population depends
on genetic diversity
• Genetic diversity is the degree of difference
between the genes of individuals in a
population
• Without genetic variation, a population cannot
adapt to changes in the environment and so
is at a greater risk of extinction
• Genetic variation is a result of mutations
occurring in the replication of DNA
Habitat Diversity
Variation in the type of environments organisms can live in. More habitat
diversity allows for greater species diversity.
Habitat Diversity Affects Species Diversity
Habitat Diversity
Species Diversity
• Species richness: the total number of different unique
kinds of organisms (species) living in a habitat or
ecosystem
• Species evenness: the relative percentage each
species makes up of the total community
• Species dominance: a single species has a very large
population relative to all of the other species populations
• Two communities, each with the same species richness
have unequal species diversity if one has greater or
lesser species evenness (has species dominance)
Is Richness important?
•
How does species richness affect the entire living system
– Experiments link total system productivity to richness (probably because
resources include lots of different things [sunlight, different minerals] and the
entire spectrum of resources are more efficiently used by a group of species,
each most efficient with a particular resource)
– There may be a link between richness (diversity) and the stability of ecosystems
– Rich, diverse systems may be less susceptible to invasion by foreign species･
diversity may reduce the total amount of unused resources, preventing a new
species from gaining a foothold
– Diverse communities may be less susceptible to changes brought about through
disease
– Rich communities have lower average species density, so many species may be
below their threshold density of susceptibility, preventing disease from
establishing itself
•
Importance to us
– Many individual species provide benefits to us, and the argument is that we do
not know what is out there, but we do know that losing a species is the loss of
potential human benefit
– aesthetic considerations (not to be discounted in the face of short-term economic
benefit)
– ecosystems provide many services (fresh water, cleaning the air, etc.), and there
may be a link between the diversity of an ecosystem and its ability to provide
those systems (here, more diversity means better services)
Species Diversity
Stabilizing selection
• is a form of selection in which both
extremes form an array of phenotypes are
eliminated
– the result is an increase in the frequency of
the already common intermediate phenotype
– for example, human birthweight is under
stabilizing selection
Forms of selection found in nature
Disruptive selection
• is a form of selection in which the two
extremes in an array of phenotypes
become more common in the population
– selection acts to eliminate the intermediate
phenotypes
– for example, beak size in African blackbellied
seedcracker finches is under disruptive
selection because the available seeds are
only large or small
Forms of selection found in nature
Directional selection
• is a form of selection that occurs when
selection acts to eliminate one extreme
from an array of phenotypes
– for example, the enzyme lactate
dehydrogenase has a cold-adapted form that
is more common in northern latitudes
Forms of selection found in nature
Three kinds of natural selection
Symbiosis
• Living together
• A relationship in which ones organism (the
symbiont) lives on or in another organism (the
host)
• Parasitism: the symbiont benefits (+) and the
host is harmed (-)
• Mutualism: both the symbiont and the host
benefit (++)
• Commensalism: the symbiont benefits (+) and
the host is neither benefited nor harmed (0)
Parasitism: + -
Mutualism:
++
Mutualism: + +
Commensalism: + 0