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Sustainability
Important Definitions
Carrying capacity: the maximum population size that can be maintained over a period of time in a
particular habitat.
Competition: happens when resources like food or water are not present in adequate amounts to satisfy
needs of all the individuals who depend on those resources.
Intraspecific competition: competition between individuals of the same species.
Interspecific competition: competition between different species
Gause’s Competitive Exclusion principle: if two species occupy the same niche when interspecific
competition will result on one of the species being outcompeted and becoming extinct.
Succession: the gradual directional change in an ecosystem over time through a number of stages ending in
a stable climax community.
Primary succession: begins with totally bare ground that contains no pre-existing life
Secondary succession: takes place on ground that has already undergone succession – an area that has
previously been colonised.
Climax community: stable community that is established at the end of succession
Deflected succession: when human activity prevents natural succession form occurring
Plagioclimax: human activity stops succession before a climax community is reached.
Pioneer plants: species that colonise previously uncolonised land leading to ecological succession
Sustainable use: replacing or replanting whatever is removed form the environment so that harvesting can
continue year after year indefinitely while maintaining a stable ecosystem
Coppicing: cutting a tree trunk close to the ground to encourage new growth
Pollarding: cutting a tree trunk higher up to encourage new growth whilst ensuring new shoots are not
eaten by deer.
Conservation: maintenance of biodiversity, including genetic diversity between species, genetic diversity
within species and the maintenance of a variety of habitats and ecosystems
Preservation: usually involves protecting areas of land, as yet unused by humans, in their untouched form.
Population Growth
1. Lag phase:
Population
organisms are
adjusting to the
surrounding
conditions. This may
mean taking in water ,
cell expansion,
activating specific
genes and
synthesising specific
Time
enzymes. Organisms
are active but not
2. Log phase: the population size doubles
reproducing, so the
each generation because every individual
population remains
has enough space and enough nutrients to
fairly constant.
reproduce.
3. Stationary phase:
Competition means that
resources become
limiting factors on
growth. This is the
carrying capacity of the
habitat: birth rate
equals death rate.
4. Death phase: A large
population means that
there are lots of waste
products and increased
disease. The death rate
exceeds the birth rate
and population declines.
The carrying capacity of a habitat is the maximum population size that can be
maintained over a period of time in that place. The habitat cannot support a larger
population because of factors that limit the growth in population size. These are
limiting factors and may include availability of food, water, light or shelter.
If resources are in short supply, there will be
competition between organisms for that resource.
Intraspecific competition is competition between
individuals of the same species. Those individuals best
adapted to obtaining food will survive and reproduce , and
those that are less well adapted will die and fail to reproduce.
This type of competition can lead to directional selection:
the next generation will be better able to survive
because they have evolved due to natural selection.
Directional selection is a mode of
natural selection in which a single
phenotype is favoured. The
advantageous characteristic increases
in frequency .
Interspecific competition takes place between
different species. Interspecific competition can
affect both the population size of a species and
the distribution of a species in an ecosystem.
Competition will be more intense if the 2 species
have a similar niche – if they eat the same food
for example.
Predator-prey relationships
Predator-prey relations
undergo cyclic fluctuations.
The predator population
peaks after the prey
population peaks, but there
are never as many
predators as there are
prey.
 When there is a small predator population, there is less predation, so the prey
birth rate exceeds the death rate and the prey population increases.
 An increasing prey population means that more food is available to predators.
The predator population will begin to increase.
 As the predator population gets larger, more prey are eaten. The prey death
rate exceeds the birth rate so the prey population size decreases.
 With a reduced prey population, a large predator population cannot be sustained,
so the predators begin to die off and the population size decreases.
Succession
Succession is a natural directional change in a community of
organisms over a period of time. It involves a number of stages
called seres; one sere changes conditions to allow the next sere
to be established. These changes may include increasing the
depth of the soil or stabilising the soil. Succession leads to a
climax community – a stable population in which all the potential
niches have been filled.
We can prevent succession occurring – this is deflected
succession and leads to a plagioclimax. We do this by removing
trees, burning, grazing cattle, moving lawns, ploughing fields and
using herbicides and pesticides.
Sand Dune Succession…
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Primary succession begins with a
previously uncolonised area, with no
pre-existing life. Secondary
succession begins in an area that has
already undergone succession and has
previously been colonised.
Pioneer dune sere: Pioneer plants like sea rocket colonise the sand above the water mark. Pioneer plants often have
adaptations to allow them to survive in harsh conditions – like a high tolerance to salt or long roots.
Yellow dune sere: Wind blown sand builds up around the base of these plants forming a mini sand dune. As plants die
and decay, nutrients accumulate. The dune gets bigger and larger plants like sand couch grass colonise it. Sand couch
grass has long underground stems that helps to stabilise the sand.
With more stability and more nutrients, Marram grass starts to grow. Marram grass has an extensive vertical root
system that helps to stabilise the dune. The shoots trap sand as the dune gets larger.
The sand dune has built up humus and so other plants are able to colonise the dune. By the Grey dune sere, dunes
have continuous plant cover, anchoring the dune on one place.
Leguminous plants with nitrogen fixing bacteria in their root nodules convert nitrogen to nitrates and with more
nutrients available, an even more diverse range of species can grow.
The climax community is the woodland sere. The dominant species have excluded the competing species that are less
well adapted. The vegetation is in a stable balance with the climate and soils of the area.
Sustainable Management:
Timber production
“Whatever is removed from the environment is replaced or
replaced so that harvesting can continue year and year
indefinitely while maintaining a stable ecosystem.”
Coppicing is when a tree trunk is cut
close to the ground to encourage
new growth. Once cut, several new
shoots grow from the cut surface
and eventually mature into stems of
quite narrow diameter. These can
then be harvested and used for
fencing, firewood or furniture.
Pollarding is similar to coppicing but
involves cutting the tree higher up
to protect new shoots from deer.
Rotational coppicing involves
dividing a woodland into different
sections. One section is cut each
year, so that by the time we want to
coppice the first section again, the
new stems have grown and are ready
to be harvested.
A standard tree is a tree that is not cut
in rotational coppicing. They are left to
grow to full size, and eventually, they are
harvested when they are big enough to
provide large timber.
Rotational coppicing increases the
biodiversity of an area. Different
areas of woodland at different
points in the coppice cycle provide
different types of habitat, so
species diversity is maximised.
Clear felling is when all of the trees in an area are cut
down at once. This has many disadvantages: soil erosion
can occur, resulting in reduced soil mineral levels.
Habitats are destroyed on a large scale. Selective
cutting provides a more sustainable alternative: only the
largest and most valuable trees are removed so that
habitats are mostly unaffected.
The Galapagos Islands
Threats to Biodiversity:
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Population growth places huge demand on
water, energy and sanitation services. More
waste and pollution, increased building and
conversion of land for agriculture have caused
destruction of habitats.
Overfishing: fish species are harvested faster
than they can replenish themselves. Depletion
of sea cucumber populations has had a drastic
impact on under water ecology. Sharks species
around the islands have been depleted due to
hunting for shark fin.
Giant tortoises were taken from the island
because they could survive for a long time on
ships before being killed to eat. 200,000
tortoises were taken in less than half a
century.
Tourism is a rapidly growing industry and the
increase in numbers has meant more pollution
and more habitat destruction
Humans have introduced non-native species to
the islands that have an impact on existing
communities.
How are ecologists working to manage
and conserve the ecosystem?
 Quarantine system: searching any
arriving boats and tourists for
foreign species
 Use natural predators such as
ladybirds to wipe out insects that
were damaging native plant
species
 Culling of feral goats and pigs that
were damaging the tortoise
population
 Galapagos marine reserve
established ‘no take’ coastal zones
, where no extraction of resources
in allowed.
Exam-style questions
Explain, with reference to an example, what is meant by the term succession
 Succession is a natural directional change in species composition in a n area over a period
of time
 Succession involves a number of clearly defined stages called seres
 One sere changes the conditions to allow the next sere to be established
 Succession leads to a climax community, in which the species in the community are in
balance with the environmental conditions and all niches have been filled. The climax
community will be dominated by the largest and most well adapted species.
 Sand dunes are an example of where succession occurs. There are 4 seres in this
example: embryo dune, yellow dune, grey dune and woodland.
 Embryo dune is colonised by pioneer plants such as sea rocket that are tolerant to salt
water and unstable sand. Wind-blown sand builds up around the base of these plants. As
plants die and decay, nutrients accumulate.
 Yellow dune: With more nutrients, grasses like sea-couch grass and marram grass can
colonise. Their deep vertical root systems stabilise the sand and the taller grasses are
able to trap more sand. The sand dune and nutrients build up.
 Grey dune: other plants can now colonise the sand because the sand dune is fixed by
roots and has accumulated humus. Species such as hare’s foot clover and bird’s foot
trefoil are leguminous, meaning that the bacteria in their root nodules convert nitrogen
to organic nitrates.
 With more nitrates available, a diverse range of species can grow.
Exam-style questions
Using timber production as an example, explain how ecosystems can
be managed in a sustainable way
 Sustainable use involves replacing or replanting whatever is removed
from the environment so that harvesting can continue year after year
indefinitely
 Coppicing can be used: deciduous trees are cut close to the ground.
Once cut, several new shoots grow and mature into narrow stems that
can then be used for fencing, furniture or firewood.
 Pollarding involves cutting deciduous trees higher up to avoid deer
eating new shoots
 Rotational coppicing involves splitting a woodland area into sections.
One section is cut each year until each section has been cut and then
the cycle begins again.
 Standard trees are not cut when rotational coppicing is employed:
they are left to grow to their full size.
 Different stages of the coppice cycle provide different habitats for
organisms, encouraging biodiversity.
Exam-style questions
Discuss the reasons for conserving biodiversity
 Ethical reasons:
 Humans have a duty to preserve the natural world
 The biodiversity was here when we were born so we have no right to destroy it
 We are morally obliged to preserve biodiversity for future generations.
 Economic reasons:
 Money can be made from biodiversity from ecotourism
 Species of plants produce valuable products such as hardwoods and oils
 Natural environments are sources of potentially beneficial resources – many drugs
are discovered in natural plant species.
 Wild insect species are responsible for pollinating crop plants; without them
harvest would fail and farmers would go out of business
 Biological reasons:
 Whole food webs can collapse on the loss of just one species;
 Having lots of species means that there is a source of genetic diversity – each
species contains unique genes and alleles. In the future, we may need to use these
to genetically engineer plants that have useful properties like disease or drought
resistance
 Ecosystems recycle nutrients essential to human life – maintaining water quality,
protecting soil and breaking down waste products.
 Aesthetic reasons:
 A biodiverse ecosystem looks better to humans
 Make our lives more enriched and stimulating
Exam-style questions
Outline with examples the effects of human activities on the animal
and plant populations in the Galapagos
 Population growth places huge demand on water, energy and
sanitation services. More waste and pollution, increased building and
conversion of land for agriculture have caused destruction of
habitats.
 Overfishing: fish species are harvested faster than they can
replenish themselves. Depletion of sea cucumber populations has
had a drastic impact on under water ecology. Sharks species around
the islands have been depleted due to hunting for shark fin.
 Giant tortoises were taken from the island because they could
survive for a long time on ships before being killed to eat. 200,000
tortoises were taken in less than half a century.
 Tourism is a rapidly growing industry and the increase in numbers
has meant more pollution and more habitat destruction
 Humans have introduced non-native species to the islands that have
an impact on existing communities.