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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.
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 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 be
different.
• Both forests have 4
species of trees, but
the relative abundance
of species A is much
greater in forest 2.
• Ecologists would say
that forest 1 has a
greater degree of
diversity.
Biodiversity
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Species richness generally
declines along an equatorial-polar
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
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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.
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 could provide crops,
fibers and medicines for human use. 25% of
all prescriptions contained substances
derived from plants.
• 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 encompass 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 include:
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Identification of keystone species
Preservation of natural edges
Corridors
Establishment of protected areas
Captive breeding programs
Restoration ecology
Bioremediation
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
• Restoration ecology – seeks to reverse population declines by
applying ecological principles in an effort to return ecosystems
to their natural state.
• 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.
• 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
detoxify 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.
Ecotourism
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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