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samba music
Rio de Janeiro, Brazil.
it was here
in nineteen ninety two
that a hundred and seventy two countries met
for the Earth Summit 2
the United Nations Convention
on the Environment
and Development
and it was here that
the official agenda
for biodiversity conservation
was opened for the first time
it's not that
people weren't conserving species
or setting up protected areas
but this was the first time that
international attention
was brought to the topic of biodiversity
it was here
that the official threefold definition
of biodiversity
as consisting of species diversity
habitat diversity
and genetic diversity
was first formulated
and now
twenty years on
the crisis in biodiversity
is even more severe that was then
and the feared sixth
mass extinction
seems very much
underway
in today's lesson
we look at
some of the factors
that lead to the loss of diversity
with four point two point one
we discuss the perceived vulnerability of tropical rainforests
and their relative value in
contributing to global biodiversity
four point two
point two
we also look at four point two point three
to discuss current estimates of the number of species
past
and present
and at the rate
of species extinction
and we describe in four point two point four
and we explain
the factors that make species more or less prone to extinction
and finally
with four point two point five we
outline the factors used
to determine
the Red List conservation status
of a species
in the four point five
billion years (of the planet's existence)
the fossil record
shows that there have been
five
major
periods
when most of the biodiversity on Earth
was eliminated
the causes of these extinctions are not
completely clear
but one thing seems fairly certain
is that
abiotic forces
in the environment
brought about
significant changes in the biotic component
that made it
very difficult for many species to survive
some of these events
include
massive
volcanic eruptions
widespread drought
though catastrophic
is also responsible
for significant
biodiversity loss
there is a powerful body of evidence to suggest that
and asteroid from space
impacted the Earth
sixty five million years ago
and ending
to age of the dinoosaurs
have occurred
bringing
mass species loss with the rise of humankind
massive habitat loss
continues habitats are fragmented
as human development occurs like this road
through a forest populations
become
isolated from each other
gene pools
which were once large
become smaller
and genetic diversity
and fitness
decline as a result
another human activity
agriculture
transforming biodiverse fields and forests
into
monoculture
the use of pesticides
another issue
that impact species
and leads to loss of biodiversity
genetic engineering
the science of modifying and manipulating genes
to create desirable traits
in crops and livestock
the danger of being that
genetically modified pollen
could make its way out into the wild
leading to
loss of diversity
this precious wild diversity
could contain genetic material
that guards against future
outbreaks of pests pollution
from industries in the use of fossil fuels
poaching
leading to this
ugly scene where the horn of a rhino is stripped
as trawlers drag a fine mesh net
across the ocean bottom
destroying the
abiotic environment
and catching unwanted species
catching shrimp that are too young
all of these are
a series of issues
that affect
the trawling industry
and fisheries
and have
a very significant impact
on marine ecosystems
the introduction of invasive species
like the cane toad-Bufo marinus
and its notorious introduction
into Australia in the nineteen thirties and forties
to control beetle pests
in sugar cane fields
the toad not only failed to control
the beetles
but it's poisonous
gland
threatened a lot of its new
predators
when it comes to the issue
of conservation
of biodiversity
one biome
stands above all others in commanding global attention and concern
that biome is the tropical rainforest
here we can see
the several layers of the forest clearly
the tall emergent later at the top
the biodiverse canopy
the understory
and of course
the floor of the forest
here you can see a good picture
of the thin soil
and the low amount of organic matter that settles on the force floor
due to high rates of productivity
the soil remains thin
and
this soil
can become very quickly eroded
if forests like these are cleared for agriculture
once cleared and the soil becomes exposed
and depleted of its nutrients
then it's very hard
for the rainforest to uncover
rainforest though might be very resistant to small changes
but once major clearing happens
it's very difficult
for the forest to recover
there are
a myriad of number of functions
that forests perform from regulating the amount of rainfall that happens
in all parts of the globe
to
providing
a place for
most of the biodiversity
on the planet it's been said that the rainforest is nature's pharmacy with
range of plant derivatives
providing medicines and cures and
economic opportunities
that are yet to be discovered
the rain forest
and in fact
any habitat
can be compared
to the stack of dominoes
with the inertia
referring to
how hard it is
to get the dominoes falling over in the case of the rain forest so
while they may be
hard to change
and have
high levels of inertia
once they are changed
and it's not that hard for modern machinery to
clear a rainforest
with large chunks
being cleared by the hour
once the forest is cleared
the capacity to recover
or it's resilience
is limited
and this presents
a serious cause for concern
because the rain forest
is the home
to a wide range
of diversity
it is because of the range of
human factors from
logging to genetic engineering
that scientists
believe that we are currently
in the midst of a sixth
mass extinction
the fossil record
which is
very clear here at the Grand Canyon
provides evidence of five mass extinctions in the past
extinctions
that may have been brought about by
ice ages
and asteroid strikes
and
other unexplained and not fully understood changes in climate
but today's sixth
mass extinction
stands apart from the previous five
because all of the previous extinctions
resulted from
abiotic factors like
drought and
volcanic eruptions or
asteroid strikes
something from
the earth's abiotic environment or from beyond today's six mass extinction
is coming from within the bowels of the
biota
or the living components of the environment
human beings
due to their activities
are impacting
not just
other living things
but also impacting
the abiotic environment
the rate
at which this is happening
this
sixth mass extinction
is also
much faster
than the five previous mass extinctions
which
by studying the stories in the rocks
we know
happened over
very long periods of time
today species loss
is happening at
an increasingly alarming rate
and this figure that I have here for
ten million species
just wild guesss really
because
the estimate for the number of species that we have living on earth
runs anywhere from five million to one hundred million
such is the level of uncertainty this is what makes the sixth mass extinction
different from the previous five
and it's what justifies
human concern
for the environment
because without the living environment
the life-support system of the planet
at least the system that supports life as we know it and our species
is under
severe threat and it is for this species centred
or anthropocentric reason
that biodiversity
and it's conservation
must occupy centre stage
as a global
environmental
issue
species come and species go
why is that
some species like
the american cockroach
Periplaneta americana
has been able to survive
over millions of years
why is it that biologists are
confident that
even if
a nuclear war happens.. a catastrophic event
that one species that's likely to survive
is the cockroach
some species
are clearly
less prone to extinction
than others
let's go into the Northern Range of Trinidad
way up into the mountains a thousand meters above sea level
where the clouds kiss the mountain tops
here
we will find
and ultra sensitive species
one whose range is limited
to just mere square kilometers of the planet earth
Phytotriades auratus
the golden tree frog
is endemic
to this tiny island in the Southern Caribbean only found
at the tops of the
two highest peaks on the island
its habitat
its survival is dependent upon a very delicate balance of moisture
pH
air quality
and it requires
bromeliads in the canopy
to lay its eggs and allow its tadpoles to develop
with such a high level of sensitivity and specificity
it is very unlikely
that this
highly endangered Golden Tree Frog
will survive much longer
and it is just one
of thousands
throughout the tropical rainforest biome
of the earth
many are still being discovered
many are still to be discovered
and indeed many that have never been discovered
have already because extinct
the International Union for the Conservation of Nature
classifies
the diversity of life
according to its Red List status
some species are
of very little concern others though
are critically endangered like the Golden Tree Frog
and if we were too
take these two extremes golden tree frog
and the american cockroach
and run them through this checklist
we can see why one is of
least concern
the pest which is the cockroach
and the other is
critically endangered species
sitting on the brink
of extinction
population size
the reduction in population size
not very significant in the case of the case of the frog because its population
was always
very small
the numbers of mature individuals
if you visit the the mountain tops
you would be lucky to find any individuals in your visit
the geographic range
is extremely limited
fragmentation or separation is not even an issue in this case because its range
his so narrow
habitat
is extremely sensitive to changes in the pH of rainfall
to pollutants that are in the air the area of occupancy
is extremely small
even within the actual area of the mountain top
the frog itself
is confined to the canopy
and the young are confined
to the aquatic environment
harbored within the bromelliads
obviously the probability of extinction
is extremely high in the case of the tree frog and
almost non-existent in the case
of the cockroach
so this list
is what determines
whether or not something
is classified as critically endangered
or not critically endangered think about some other creatures
and how they would fit into this list has been closed today and we
take-up discussion in the next lesson i would like you to
reflect
on the
importance of rain forests
reflect upon
our discussion from biomes this discussion
and to about constructing a argument
to support rainforest conservation an argument that can appeal to the
ecocentrics
and then an argument that can appeal to anthropocentrics and one that can
appeal to technocentrics
and we will continue this discussion in the next lesson
as we state the arguments
for preserving species and habitats in four point three
point one