Key Area 7 (b) : Biodiversity Unit 3: Sustainability and Interdependence

Key Area 7 (b) : Biodiversity

Unit 3: Sustainability and Interdependence

Ecosystem degradation

CfE Higher BiologySustainability

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• Increasing human activities have escalated the rate of destruction of the many ecosystems that exist.

• Activities such as:– Deforestation– Damming– Farming– Industrial pollution– Over hunting

• Due to these activities the level of species extinction is running at a higher level than the natural or background rate.

Endangered species


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• Due to these human activities such as habitat destruction and over hunting, there are several ‘high profile’ animals threatened with extinction or are endangered.

• These are:– Pandas– Whales– Gorillas– Snow leopard

Megafauna


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• The megafauna are considered to be the first victims of human caused extinction.

• Megafauna were giant animals such as:– Four tusked elephants– Wombats as big as hippos– Armadillos as big as cars– Giant sloth

• These animals existed and flourished for millions of years.

• However, fossil records show that as humans moved into new territories the megafauna living there disappeared.

Biodiversity


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• There are 3 main levels of biodiversity:– Genetic diversity– Species diversity – Ecosystem diversity

• What is genetic diversity?– This results from the number and frequency of all the alleles

of the genes in a population.– It is the genetic variation within a population and the

variation between populations associated with adaptations to local conditions.

• Why is it important to maintain genetic diversity?– It is the raw material for evolution or change or for entering

new environments or niches. It allows the species to respond to changing conditions.

Biodiversity


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• What is species diversity?– The variety of species in an ecosystem or

across the biosphere.

• This can be quantified as:• Species richness

– The number of different species in an ecosystem

• Relative abundance or species evenness– The proportion of each species in an

ecosystem

Biodiversity


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• How could a dominant species reduce species diversity but not species richness?

• The dominant species will have a much higher relative abundance so even if there are other species present they will be in small proportions.

Biodiversity


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e.g. Relative abundance %

Species Community P Community Q

A 50 20

B 10 15

C 10 15

D 10 20

E 10 15

F 10 15

These two communities share the same species richness.They both have species A,B,C,D,E and F.They differ in the relative abundance of each species though.Community P is dominated by species A and therefore has a lower species diversity than community Q.Community Q is not dominated by one species.

Biodiversity


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• The following graph shows the effect of grazing on species diversity. Explain the curve:

Grazing intensity

Speci

es

div

ers

ity

At low levels of grazing, a small number of aggressive competitors are taking over.As grazing increases these are held in check, allowing other species to increase.As grazing increases further, less species are able to tolerate the grazing.

Measuring species diversity


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• When carrying out a practical investigation into the species diversity of a local area, a species diversity index can be used.

• These use mathematical calculations.• Different diversity indices assign different

weightings to species richness and abundances.

• The one that is used depends on the circumstances.

• There are two that are widely used:– Shannon index– Simpson’s index

Measuring species diversity


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• Collect the Simpson’s Index example sheet and work out the Simpsons Index for the communities provided.

Benefits of species and genetic diversity


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• What are the benefits of species and genetic diversity?

• Threatened species could provide medicines, food, fibres.

• Products from aspirin to antibiotics were derived originally from natural products.

• If wild populations of plants are lost then genetic resources are also lost.

Benefits of species and genetic diversity


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• e.g. in the 1970’s it was discovered that the rosy periwinkle which grows on Madagascar, contains alkaloids that inhibit cancer cell growth. From this treatments for two forms of cancer were developed. 5 other species of periwinkles live on Madagascar, one of which is near extinction. Losing these species could mean the loss of medicinal benefits.

Ecosystem diversity


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• What is ecosystem diversity?–Ecosystem diversity refers to the

variety of ecosystems in a given place. Within a broader landscape there is a mosaic of interconnected ecosystems.

–Ecosystems vary in size. A large patch of forest or a small pond can each be described as an ecosystem.

Ecosystem diversity


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• Because of the many interactions between populations of different species in an ecosystem, the local extinction of one species can have a negative impact on other species in the ecosystem.e.g. bats called flying foxes are important pollinators and seed dispersers in the Pacific Islands. However, as they are increasingly hunted for food there are concerns that decreasing numbers of these foxes will harm the plants on these islands where about 4/5ths of the tree species depend on these animals for pollination and seed dispersal.

Ecosystem diversity benefits


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• The natural ecosystems of the earth and all their natural processes help sustain human life.

• Such as:– Purify air/water– Detoxify/decompose wastes– Reduce impact of extreme weather/flooding– organisms in ecosystems pollinate crops/control

pests– Create and preserve soils– Services are provided for free.

• So if the functioning of ecosystems is impaired then the planets ability to perform these critical processes for survival is reduced.

Central database


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• Currently there is a huge gap in the information surrounding organisms.

• Estimates of the total number of species on earth therefore vary.

• A huge source of genetic variation and potential has barely been touched.

• A central database with profiles on every known species is needed.

• Many databases already exist but one which is centralised would be ideal.

• This however, would need extensive country cooperation and funding.

Island Biogeography


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• Islands provide excellent opportunities for studying the biogeographic factors that affect the species diversity of communities.

• This is due to their isolation and their limited size.

• By islands we mean not only oceanic islands but also habitat islands on land, such as lakes, mountain peaks separated by lowlands or habitat fragments.

• These habitat islands are any patch surrounded by an environment/habitat not suitable for the ‘island’ species.

Island Biogeography


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• The more isolated the habitat island, the lower the extent of the diversity found among its species.

• The smaller the habitat island’s surface then the lower the level of its species diversity.

• What would happen to species diversity if habitat islands remain isolated for a long time:

• e.g. Madagasgar– Adaptive radiation and or natural selection can

lead to the formation of groups that are different from others.

Island Biogeography


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• What impact does the size of habitat islands have on species diversity and why?

• Generally the smaller the island the less the species diversity because a complex food web cannot be built.

• Territorial and wide ranging animals will be also be affected by the size.

• As will the richness of resources.

Threats to Biodiversity


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• There are 5 main threats to biodiversity:–Habitat loss/destruction–Introduced /invasive species–Overexploitation/harvesting–Population change–Global change/pollution

Habitat Destruction

Invasive Species

Population (human) Increase

Pollution Over-Harvesting

Scottish wildcat

…

Red Squirrel

…

Red-backed Shrike

…

Slender stonewort

…

Right whales

…

Ecosystem Diversity = the number of distinct ecosystems within a defined area.Threats to BiodiversityOften summed up as the HIPPO factors – give example(s) of species affected.

Habitat Loss/Destruction


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• This is the single greatest threat to biodiversity.

• Habitat loss has been brought about by factors such as:– Agriculture– Urban development– Forestry– Mining – Pollution



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• When habitat loss occurs if there is no alternative habitat available then a species will be unable to move.

• This can lead to extinction.• The IUCN (International Union for

Conservation of Nature) implicates habitat loss as being responsible for 73% of species that have become extinct/endangered/vulnerable or rare.



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• Habitat loss and fragmentation can occur over immense regions.

• Approximately 98% of the tropical dry forests of Central America and Mexico have been cut down.

• Tropical rain forest clearing in Veracruz, Mexico has resulted in the loss of 90% of the original forest, leaving relatively small isolated patches of forest.



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• Habitat loss is major threat to aquatic biodiversity.

• About 70% of coral reefs, which are the most species rich aquatic communities, have been damaged by human activities.

• Freshwater habitats are being damaged by dams, reservoirs, river bed modifications.

Habitat Fragmentation


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• Apart from the obvious damage caused by habitat loss, habitat fragmentation can also cause problems.

• Fragmentation of a habitat results in the formation of several fragments.

• The surface area of these fragments tends to be smaller than that of the original habitat.

• A further decrease in habitat size can occur due to degradation of the edges of these fragments.


Link habitat size to relative abundance of interior and edge speciesSmaller fragments mean an increase in the length of edge to total surface area of interior ratioHow does this effect edge degradationMore edges, more degradation



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• The boundaries or edges between ecosystems are defining features.

• An edge will have its own set of physical conditions that differ from those on either side of it.

• Some organisms thrive in edge communities gaining resources from both adjacent areas.

• Ecosystems with degraded edges often have reduced biodiversity however.



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• In a area of edge degradation, an edge adapted species may thrive due to the increase in edge area.

• As the number of this species increase however, they may move into and invade the fragment interior.

• This edge species may then compete with any interior species living there and possibly displace them.

• This would result in a loss of biodiversity.• Small fragments do not favour interior habitat

species.

CfE Higher Biology

Habitat Corridors


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• In fragmented habitats, the presence of a movement corridor can be extremely important.

• This movement corridor can be a narrow strip or small clumps of habitat that connect isolated patches.

• They can be man made bridge or tunnels.

• Their purpose is to conserve biodiversity.

Habitat Corridors


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• They do this by allowing species to meet and mate, feed or recolonize areas.

• They also allow species to migrate seasonally between different habitats.

• One disadvantage to these corridors is that they can allow the spread of disease to occur throughout a vulnerable genetically limited species.

• It is not yet clear whether these corridors do actually increase biodiversity.

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Introduced/Invasive Species


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• Introduced species are those that humans have moved intentionally or accidently from the species native location to new geographic regions.

• Human travel by ship and airplane has accelerated this movement of species.

• These moved species are then free from predators, parasites and pathogens that would normally limit their populations in their native habitats.

• This means that they can spread rapidly through a new region.



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• Introduced species can become naturalised in their new environment.

• They can however then become invasive and disrupt their new community

• They either prey on the native organisms of that ecosystem or outcompete these native organisms for resources.

• They can then undergo a population explosion.



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• e.g. giant hogweed was introduced as a garden plant but is very invasive. It has poisonous sap that burns and blisters the skin.

• e.g. the zebra mussel arrived from the Caspian Sea and is thriving due to cleanliness of our water supplies. Their larvae spread very easily and invading mussels kill British native mussels. They also block water pipes.



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• e.g. North American signal crayfish were introduced to Britain in the 1970’s . They are very destructive causing river bank erosion and collapse. They prey on young fish and eggs. Carries crayfish plague which is deadly to our native crayfish.

• e.g. Japanese knotweed was originally introduced as a garden plant. It is able to grow through hard structures like concrete and is now widespread throughout the country. It is very difficult to get rid of once established.

Overexploitation/harvesting


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• This refers to the removal or harvesting of wild organisms at rates exceeding the ability of their populations to reproduce.

• Species with restricted habitats, i.e. small islands, are particularly vulnerable to overexploitation.

• An example of this was the great auk, a large flightless seabird found on islands in the North Atlantic Ocean. By the 1840s it had been hunted to extinction.



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• Also susceptible to overexploitation are large organisms with low reproductive rates such as elephants, whales and rhinoceroses.

• These animals decline is a classic example of overhunting by man.

• International bans now exist on the sale of products from these animals but their effectiveness is debatable.



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• Overfishing is another example of overexploitation where stocks of fish have been reduced significantly to unsustainable levels.

• Bans on fishing and fixed quota catches have been introduced to allow fish stocks to recover.

• Where these have been adhered to recovery has been seen to an extent.

Population Bottleneck


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• A sudden change in the environment, such as fire or flood, can drastically reduce the size of a population.

• A severe drop in the size of a population by these changes can cause the bottleneck effect.

• This means that the population has passed through a ‘bottleneck’ that reduces its size.

• Not only has the population size decreased but so has the gene pool due to loss of alleles present in the original population.



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• The resulting population has a low level of genetic diversity, which means that there may be few genetic characteristics in the population.

• Reduced genetic variation means that the population may not be able to adapt to new selection pressures such as climatic change or a shift in available resources.



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• e.g. bottleneck example: Northern elephant seals have a reduced genetic variation probably because of a population bottleneck humans inflicted upon them in the 1890s.

• Hunting reduced their population size to about 20 individuals at the end of the 19th century.

• Their population has bounced back to over 30000 but their genes still contain the marks of this bottleneck.

• They have much less genetic variation than a population of Southern elephant seals that was not so intensely hunted.

Global change/pollution


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• Human activities release a variety of gaseous waste products.

• It was originally thought that the atmosphere would be able to absorb these materials indefinitely.

• It is now known that these additions can cause fundamental changes to the atmosphere and its interactions.

• Because of these changes there is evidence that many species are moving their range in response to a shift in climate.



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• e.g. warmer spring temperatures may cause birds to begin their seasonal migration or nesting earlier; bears may emerge from hibernation earlier.

• What problems could there be for these animals?

• For birds there may be issues with migration routes not being clear or bad weather occurring. Food may not be available and they may starve.

• For bears they may emerge before their regular food sources are available, they may starve or wander into urban areas.



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• e.g. the red fox is extending its range in the artic tundra due to the warming temperatures. It is now preying on the artic fox and competing with it for habitat and food.

• As the tundra’s climate warms, it is predicted that it will be replaced by forest which is an unsuitable habitat for the artic fox.

Climate Modelling


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• Climate change models are computer simulations and mathematical representations of the interactions between the atmosphere, oceans, land surface, ice and the sun.

• Scientists use these to help them understand the behaviour of the climate system and how it may respond to changes.

Climate Modelling


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• These models however have limitations.–They require vast quantities of information which may based on speculation.

–They require vast amounts of computing power.

Documents

Key Area 7 (b) : Biodiversity Unit 3: Sustainability and Interdependence