Transcript Chapter 12

How Many
Species
Exist?
• Variety among
living species
is called
biodiversity
• There are
between 1.4
and 1.8 million
species
described by
scientists and
many more
have not been
discovered or
described
Bacteria and Archaea
• Unicellular: each cell is an
individual organism
• Prokaryotes (don’t have a
nucleus)
• Lack complex organelles
• Microscopic
• Also called microorganisms
or microbes
– Studied by microbiologists
• Incredibly ubiquitous,
chemically complex, and
diverse
Domain Bacteria
• Many of the
currently identified
bacterial species
are known because
they cause disease
in humans, other
animals, or crops
• Many other bacteria
do not cause
disease in humans
or other animals –
and some have
proven
tremendously useful
to science…
Domain Archaea
• Superficially similar
to bacteria, but are
fundamentally
different
• Many archaea are
well known for living
in extreme
environments
– High salt
– High sulfur
– High temperature
(source of Taq
polymerase)
Eukarya: Protista
• Protista are the
simplest eukaryotes
• Most protist are
single-celled, but
some are
multicellular
• The oldest fossil
record of eukaryotic
cells is 2 billion
years old – 1.5
billion later than the
first prokaryotic cell
Eukarya: Protista
• The appearance of
eukaryotes led to a
wide variety of
eukaryotic forms
• Protista have wide
diversity, although there
is no agreement on the
exact number of phyla
(next level of
classification) within the
kingdom
– Number ranges from 8 to
80
Protista
Fungi
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•
•
•
Heterotrophic
DNA sequence analysis
indicates that Fungi and
Animalia are more closely
related than either is to plants
Fungi are classified into phyla
according to their mode of
dispersal of spores
Convergent evolution has led to
the evolution of similar body
shapes and lifestyles (“fungal
forms”) among the different
phyla
• Hyphae are actually functional part of
most fungi
– Long thin strings that grow to cover a
food source
• Fungi feed by secreting molecules to
break down food and then absorb the
nutrients
• Yeast are single-celled fungi
• Yeasts can carry out
respiration, but can also
carry out fermentation in low
oxygen environments
– Fermentation produces
some ATP for the yeast, but
also produces alcohol,
which is toxic
• Mold is also considered
fungi
• Fast growing – can quickly
spoil food
• Also involved in cheese
making
• Have been used to produce
antibiotics – including
penicillin
– Discovered by Alexander
Fleming
Fungi
Eukarya: Plantae
• The kingdom Plantae
consists of multicellular
eukaryotes that can
make their own food by
photosynthesis
• Plants have been
present on land for over
400 million years and
have evolved to land
conditions with
increasing effectiveness
• The first land plants were
small and lacked means to
transport water from the
ground to their leaves
• Vascular tissue evolved for
transport of water and other
substances
– Allowed plants to reach
tree-size and to adapt to
drier land conditions
• Seeds, structures to protect
and provide food to young
plants evolved as well
• Just 140 million years ago,
the flower, a specialized
reproductive organ,
appeared
– Over 90% of known plant
species are flowering
plants
Naturally derived drugs from plants
Aspirin – from willow trees
Digitalis – from foxglove
Vincristine (cancer drug) – from
periwinkle
Morphine – from poppy
Caffeine – from coffee
Animalia
• Animals are defined as:
– Multicellular organisms
– Heterotrophic
– Have the ability to move
during at least one stage
of their life cycle
• Humans and all other
animals are almost identical
in terms of structure and
function of cells and
common organs
• There is much commonality
within the kingdom, but
significant diversity exists
within it as well
• Invertebrates, animals that don’t have backbones, make up
96% of animal species
• Most invertebrates are insects
• Invertebrates are of interest to biologists looking for new
chemicals to serve human needs (pain killing drugs)
Is the Population Too Large?
• There are 6.3 billion
people on Earth
• By 2050, there may be
between 10 and 12
billion people
• Growth is being fueled
by many factors:
– Declining infant mortality
– Increases in life
expectancy
– Improvements in
medicine
Population Growth
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Historians have used archeological evidence and written records to
estimate the size of the human population for the last 10,000 years
Gives a pattern of growth for the human population
This is an example of an exponential growth pattern – the quantity of
new offspring is an ever-growing number
– J-shaped growth curve
•
The larger the population, the faster it grows
– 77 million people added each year
– Three people every second
– Quarter of a million every day
The Demographic Transition
• Both birth rates and death rates were high
before the Industrial Revolution
• Many deaths due to infectious disease
• Many births, but most children did not survive:
high infant mortality
• At the same time, modern medicine has
lowered the death rate
• With high birth rates and lower death rates,
the population grows
The Demographic Transition
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•
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The period of time in a population
when birth rates are dropping
toward lowered death rates as the
demographic transition
The length of time that a human
population remains in transition
has a huge effect on the
population’s size
– The longer a population takes
to pass through the transition,
the higher their population
growth
Developed countries have passed
through demographic transition
and have low population growth
rates
Developing countries are still in
demographic transition – and still
have high growth rates
Infant mortality rates have
dropped drastically
Limits to Population Growth
• Even though populations can
theoretically grow exponentially, there
growth is limited by physical factors
Carrying Capacity and
Logistical Growth
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Carrying capacity – the
maximum population that can
be supported by a given
environment
Even though a population may
start out with exponential
growth, the growth rate tends to
slow down
The population growth graph of
this type is called an S-shaped
growth curve
The growth rate approaches
zero as the population size
reaches the carrying capacity
– There, birth rate = death
rate
– Population size is stable
Carrying Capacity and
Logistical Growth
• The growth rate slows
as it reaches the
carrying capacity
because of density
dependent factors
– Food supply
– Increased risk of
infectious diseases
– Increased risk due to
waste accumulation
Carrying Capacity and
Logistical Growth
• There are also density independent factors that
limit growth
– Severe weather, such as drought or very high or
low temperatures
Earth’s Carrying Capacity
for Humans
• If, and how rapidly, the
growth rate is declining
is a way of figuring out if
we are reaching Earth’s
carrying capacity
• The growth rate has
slowed
– From high of 2.1% in
1960 to 1.2% now
• The UN has offered
three projected tracks
for future growth to
2050
The amount of resources:
• The Net Primary
Production (NPP) is the
amount of food energy
available on the planet
– measured by plant
growth
• Estimates suggest that
we are only using 1/3 of
the total land NPP
– Suggests that the
carrying capacity is three
times the current
population (or 19 billion
people)
• But this human
population size would
consume all the
resources and leave
nothing for other
species
Signs That the Population Is
Near Carrying Capacity
• U.S. residents
comprise 5% of
Earth’s population,
but use 24% of its
energy
• U.S. residents
consume 815 billion
food calories every
day – 200 billion
more than are
necessary (this
could feed 80
million more people)
• 1 person U.S. uses as
many resources as:
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–
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2 Japanese
2 Spaniards
3 Italians
6 Mexicans
13 Chinese
31 Indians
128 Bangladeshians
301 Tanzanians
370 Ethiopians
13.3 The Future of the Human
Population
• Unlike other species,
the human population is
not completely at the
mercy of the
environment
• Through ingenuity
humans have the ability
to transform
environmental
conditions – at least the
hypothetical ability
A Possible Population Crash?
• A population crash is a steep decline
in number as death rates soar and birth
rates drop after a too large population
competes for too few resources
– Even if birth and growth rates continue to
grow for awhile
A Possible Population Crash?
• Some populations crash over and over again as a
result of a tendency to grow beyond carrying capacity
– “Booms” and “busts” continual indefinitely
• This is called a population cycle
A Possible Population Crash?
• Ecologists notice a lag between the time
humans reduce birth rates and when
the population size responds and call
this lag demographic momentum
• The demographic momentum can be
estimated by looking at a population
pyramid, a summary of numbers of
individuals at each age group
A Possible Population Crash?
• Stable population pyramids are actually shaped more
like a column
– The proportion that is young is not significantly larger than
the middle aged
• Populations with high demographic momentum have
a large proportion of young people
Avoiding Disaster
• Humans have one distinct advantage in that – unlike any other
known species – they can actively choose to limit birth rates
• Evidence of this is seen in the birth rates of countries
14.1 The Sixth Extinction
• The Endangered
Species Act (ESA) was
passed in 1973 to
protect and encourage
population growth of
threatened or
endangered species
– Ultimately, to avoid
species extinction – the
complete loss of a
species
– Threatened: Whooping
cranes, bald eagles,
peregrine falcons, gray
wolves, elephant seals
The Sixth
Extinction
•
Critics of the ESA:
– Unrealistic to try to save
all 10 million species
– Extinction is a natural
process
– Steps taken to stave off
extinctions can be
detrimental to humans
•The fossil record shows 5 mass
extinction events in Earth’s history
•A mass extinction is a species
loss that is global, affects large
numbers of species, and are
dramatic in impact
•50-90% of all living species
are lost
•Takes a few thousand to a
few hundred thousand years
•
Mass extinctions were probably
caused by global changes such as:
– Changes in sea levels
– Climate fluctuations
– Shifts in ocean and land forms
from continental drift
– Asteroid impact
•Normal extinctions occur when a
species lacks the ability to adapt to
environmental changes
When a species goes extinct, usually
a new species arises to fill the gap
Measuring Extinction Rates
• Malaysia: looked for evidence of 266 known species
of fish – only found 122
• Lake Victoria, Africa – 200 of 300 native fish species
haven’t been seen in years
• Oahu, Hawaii – half of the 41 native tree snail
species have not been found
• Tennessee River – 44 of 68 shallow-water mussel
species are missing
• Since 1600
– 113 (out of about 9000) identified bird species are
extinct
– 83 (out of about 4500) identified mammal species
are extinct
• Severe threats to species fall
into 4 categories:
– Loss or degradation of
habitat
– Introduction of nonnative
(exotic) species
– Over-harvesting
– Effects of pollution
• Habitat destruction is the
greatest threat
• Instead of completely
destroying a habitat, human
activity can often fragment a
habitat
– Subdividing one large
habitat into several
smaller sections (habitat
fragmentation)
Habitat Loss and
Food Chains
Habitat
Fragmentation
• Especially threatens large
predators, that require
large, intact hunting areas
• Energy flows in one
direction within an
ecological system along a
food chain
Energy flows from:
• Producers
(photosynthetic
organisms) 
• to primary consumers
that feed on them 
• to secondary consumers
(predators feeding on
primary consumers)
Habitat Fragmentation
• Each trophic level (level
of the food chain) only gets
about 10% of energy
available from previous
level
• The biomass (total
weight) of the low trophic
levels is larger than high
levels
• This is necessary to
support the chain as part
of the principle of the
trophic pyramid
• Habitat fragmentation
causes low levels of the
trophic pyramid to shrink,
so the higher levels also
shrink
Habitat Fragmentation
• Species that remain
in fragmented
habitats are
susceptible to
extinction because
they are very
isolated
•
• It is difficult to leave
the area and find a
more desirable
habitat
Asian elephants face almost certain
extinction in almost every place they exist
in the modern world. Only about 30,000
Asian elephants remain in the wild,
scattered across fragmented habitats in
13 Asian countries
Other Human Causes of Extinction:
Introduced Species
• Introduced species are
species that are brought in
by humans to an area they
have never been found
before
• This can be very dangerous
to existing species
Overexploitation
• Human also engage in
the overexploitation of
species
• Certain organisms are
highly prized and
therefore are
endangered
• Overexploitation can
occur in plants as well
as animals
15,000 of 50,000 medicinal plants are under threat of extinction
Pollution
• Pollution – the
release of poisons,
excess nutrients,
and other wastes
into the environment
–also threatens
biodiversity
• For instance, the
herbicide atrazine
can harm frogs and
salamanders
Disruption of Ecological Communities
• Most endangered species won’t affect survival of humans, but
the effect on the biological community can be disastrous
• A biological community consists of all the organisms of
different species living together in a particular area
• These organisms are connected by a food web – the complex
linkage among organisms within a community
Mutualism: How Bees Feed the World
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Bees are the primary pollinators
of flowering plants
Plant benefits by getting
fertilized
Bee benefits by getting pollen
and nectar for food
Wild bees pollinate at least 80%
of all agricultural crops in the
U.S.
But bees have suffered
dramatic declines in recent
years, dramatically threatening
humans in the process
– Threats to bees include
parasites, competition from
invading species, and
habitat destruction
Predation: How Songbirds May Save Forests
• Predator: a species that
survives by eating another
species
• Warblers collectively
remove tons of treedamaging insects from
forest trees every summer
• Warbler populations are
declining; this will affect the
growth rate of trees
– Warblers decline due to
habitat destruction and
increased attacks by
human-associated
predators (i.e. cats,
raccoons)
Keystone Species
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As seen in a food web, most organisms
have multiple connections
Some single species indirectly affect more
than one other species to the extent that –
if it is removed – the community collapses
(analogous to a keystone in an archway)
keystone species
Ex. grave wolves in Yellowstone National
Park
Their extermination within the park by the mid1920s and subsequent reintroduction in 2003
both had profound effects on organisms as
diverse as willow trees, elk, and beaver
Changed Ecosystems
• Ecosystem: all the organisms
in a given area along with
their non-biological
environment
• Energy flows through an
ecosystem
• Nutrients are recycled within
an ecosystem
• Nutrient cycling
– Nitrogen
– Carbon
– Other nutrients