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Biodiversity
Mass Extinctions
• There have been 5 mass
extinctions throughout
Earth’s history, the last one
believed to be about 65
million years ago when a
meteor collided with the
planet and wiped out the
dinosaurs.
• Scientists now believe that
a sixth mass extinction is
underway and that this
poses a major threat to
humans in the next century.
6th Mass Extinction
• Biologists are currently predicting that one
fifth (20%) of all living species could
disappear within the next 30 years.
• All of these losses can be attributed mainly
to human activities, especially the
destruction of plant and animal habitats.
• The explosion of human population,
especially in the post-Industrial Revolution
years of the past two centuries, coupled with
the unequal distribution and consumption of
wealth on the planet, is the underlying
cause of the sixth mass extinction.
What Is Biodiversity?
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Biodiversity - The variability among living
organisms on the earth, including the variability
within and between species and within and
between ecosystems.
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Biodiversity has 2 main components:
1) Species Richness – the total number of
different species within a community.
2) Relative Abundance – the actual number of
each type of species in a community.
Biodiversity
• Species richness may
be equal, but relative
abundance may affect
the degree of diversity.
• Both communities
have four species of
trees, but the relative
abundance of species
A is much greater in
community 2.
• Ecologists would say
that community 1 has a
greater degree of
diversity.
Biodiversity
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Species richness generally
declines along an equatorialpolar gradient. Tropical
habitats support a much larger
number of species than do
temperate or polar regions.
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Reasons:
1) solar energy
2) water availability
3) growing season
All three factors increase the
opportunity for speciation
events to occur.
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The same thing happens as
you increase in altitude on
land, or increase in depth in
the oceans.
Dominant and Keystone Species
• Dominant Species – those
species that have the
highest relative abundance.
• Keystone Species – those
species that exert a strong
control on community
structure due to their
ecological roles or niches.
• Where sea stars are
present, 15 to 20 species of
invertebrates and algae
occur. Where sea stars are
absent, less than 5 species
occur because the mussels
are unchecked.
• What is a possible
advantage to a keystone
species of being able to
feed mainly on those prey
species that are otherwise
dominant?
Three Levels Of Biodiversity
• Genetic Diversity – genetic variation
within and between populations due to
adaptations to local conditions.
• Species Diversity – the variety of
species within ecosystems.
• Ecosystem Diversity – the variety of
ecosystems in the biosphere.
The Biodiversity Crisis
• To date, scientists have described and formally
named about 1.5 million species of organisms.
• We can currently only estimate, but some biologists
believe the number of organisms that currently exist
is about 10 million.
• Insects, nematodes, fungi, protists and prokaryotes
head the list of organisms with great numbers of
undiscovered species.
• This means our efforts to understand the structure
and function of ecosystems on which our survival
depends will remain incomplete.
• Humans evolved in tune with ecosystems, and our
incomplete knowledge poses a huge risk to our
long term survival.
Why Should Humans Care?
Biodiversity is a crucial natural resource. Threatened species
provide medicinal, agricultural, ecological and economic
benefits to humans:
• About 40% of all prescriptions written today are composed
from the natural compounds from different plant and animal
species.
• Humans depend on about 20 species of plants, such as wheat
and corn, to provide about 90% of the world’s food. Wild
relatives of these common crops contain genetic material
essential for disease and drought resistance.
• Plant and animal species are the foundations of healthy
ecosystems that are vital to human survival.
• Various wild species contribute economically through such
activities as hunting, fishing, camping and tourism.
• Biodiversity represents the sum of all genomes on Earth. We
stand to lose the valuable genetic potential held in the genes
of species that become extinct.
Examples
• The Rosy Periwinkle
from Madagascar
contains alkaloids that
inhibit cancer cell
growth.
• Enzymes extracted
from bacteria that live
in hot springs allowed
scientists to develop
polymerase chain
reaction (PCR), a DNA
cloning technique.
Ecosystem Services
Ecosystem services - all the processes through which natural
ecosystems and the species they contain help sustain human
life on Earth. These include:
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Purification of air and water
Reduction of severity of draughts and floods
Generation and preservation of soil
Detoxification and decomposition of wastes
Pollination of crops and natural vegetation
Dispersal of seeds
Nutrient cycling
Control of pests by natural enemies
Protection from UV rays
Provision of aesthetic beauty
Biosphere II
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A $200 million experiment in
Arizona which attempted to
create a system of ecosystems
required to sustain human life.
The experiment was supposed
to house 8 humans in isolation
for 2 years.
The artificial biosphere failed
after 15 months and the
experiment had to be stopped.
O2 and CO2 concentrations
fluctuated wildly, most of the
vertebrate species became
extinct, all the pollinators died,
pest populations exploded and
trees toppled.
The experiment taught us that
no one yet knows how to
engineer a system that can
provide humans with all the life
support services that natural
ecosystems provide.
Causes
There are 3 major threats to biodiversity:
• Habitat destruction
• Introduced species
• Overexploitation
Habitat Destruction
Human alteration of habitat is the single greatest threat to diversity throughout the
biosphere. Habitat destruction is due to many factors. These include:
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Agriculture
Forestry
Urban sprawl
Mining
Pollution
Habitat Destruction
• The cumulative area of all tropical rainforests on Earth is
about the size of the continental U.S. We lose an area equal
to the size of West Virginia each year.
• Along with the oxygen production and air filtering capabilities,
we lose the genetic potential of any undiscovered species.
Habitat Destruction
• Open oceans are productive “pastures” of
phytoplankton which may help moderate the
greenhouse effect by consuming massive quantities
of CO2 for photosynthesis. The effects of pollution
on these expanses of open ocean is yet unknown.
Habitat Destruction
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In addition to habitat
destruction over large regions,
many natural landscapes have
been fragmented, broken up
into small patches.
In almost all cases, habitat
fragmentation leads to species
loss.
Example: Prairie covered most
of the mid-west when
Europeans first arrived, but
now occupies less than 0.1%
of its original area. The prairie
fragments lost 60-80% of their
original plant and animal
species.
Introduced Species
Introduced species – those that
humans move from the
species’ native locations to
new geographic regions. The
introductions can be intentional
or unintentional.
Introduced species rank
second behind habitat
destruction as a cause for loss
of biodiversity. Examples of
introduced species include:
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Nile Perch
Brown Tree Snake
Kudzu
Fire Ants
Starlings
Overexploitation
Overexploitation – the human harvesting of wild plants
or animals at rates exceeding the ability of those
populations to rebound.
Especially vulnerable are large species with low
reproductive rates such as elephants, whales,
rhinos and other animals considered valuable by
humans.
So What Can Be Done?
• Conservation efforts have to occur not only at the species and
population levels, but also at the community and ecosystem
levels. These conservation methods include:
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Identification of keystone species
Preservation of natural edges
Corridors
Establishment of protected areas and reserves
Captive breeding programs
Restoration ecology
Bioremediation and biological augmentation
Ecotourism
More intelligent use of renewable resources
Natural Edges and Corridors
• In contrast to the
abrupt edges created
by human activity,
natural edges are
gradual transitions that
have been found to be
important sites of
speciation events.
• Corridors are natural or
man-made strips of
suitable habitat that
connect otherwise
isolated patches.
Captive Breeding Programs
• In addition to educating the public about the plight of wildlife
and allowing people to see live animals up close, zoos are
important in the preservation of species through captive
breeding programs.
• Zoos keep genetic libraries of species and regularly exchange
animals to promote the genetic diversity.
Restoration Ecology
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Restoration ecology – seeks to reverse population declines by
applying ecological principles in an effort to return ecosystems to
their natural state.
Techniques such as bioremediation and biological augmentation can
help restore degraded ecosystems.
The basic assumption is that most environmental damage is
reversible. This assumption must be balanced by the realization that
ecosystems are not infinitely resilient to damage.
Biological communities can recover naturally from many types of
disturbances. The time frame for recovery is based more on the size
of the disturbance than the type of disturbance. The larger the
disturbed area, the longer the time frame for recovery.
Areas that have been abandoned such as rainforest after soil has
become unproductive and mining sites are prime targets.
The key to restoration ecology is understanding the specific
characteristics of succession for each type of disturbance and each
type of ecosystem.
Bioremediation
• Bioremediation – the use of living organisms
(usually prokaryotes, fungi or plants) to remove
toxins from polluted ecosystems.
• Some plants adapted to soils with heavy metals can
be used to re-establish sites degraded by mining.
The plants accumulate high concentrations of
metals such as zinc, lead and nickel. The plants are
then harvested to recover the metals.
• Certain strains of bacteria have been supplied with
growth stimulants and used to clean up oil spills on
beaches.
Biological Augmentation
Biological augmentation – the use of
organisms to add essential materials
to a degraded ecosystem.
• Example: Encouraging the growth of
plants that thrive in nutrient poor soil
often speeds up the rate of
successional changes that can lead to
the recovery of damaged sites.
Ecotourism
• Ecotourism - travel to
destinations where the
flora, fauna, and cultural
heritage are the primary
attractions.
• Examples include
photography safaris in
Africa and rainforest tours
in Central and South
America.
• Many countries are finding
that they can make more
money through tourism than
by exploitation of their
natural resources.
Ecotourism now comprises
a significant percentage of
their gross domestic
product.
“ We must consider our planet to be on loan
from our children rather than a gift from our
ancestors” – Chinese Proverb