Unit 3: Sustainability and Interdependence. Sub-topic 3.7 Mass extinction and biodiversity. Sub-topic 3.8 Threats to biodiversity

Transcription

1 Unit 3: Sustainability and Interdependence Sub-topic 3.7 Mass extinction and biodiversity Sub-topic 3.8 Threats to biodiversity

2 3.7 Mass extinction and measuring biodiversity By the end of this sub-topic you should be able to: understand that fossil evidence indicates that there have been several mass extinction events in the past; know that following each mass extinction event, biodiversity has been regained slowly due to speciation of survivors; understand the difficulties in estimating past and current species extinction rates; know that the extinction of megafauna is correlated with the spread of humans; understand that the rate of ecosystem degradation caused by humans is causing the rate of species extinction to be much higher than the natural background rate; understand that measurable components of biodiversity include: genetic diversity, species diversity, ecosystem diversity, know that genetic diversity comprises the genetic variation represented by the number and frequency of all the alleles in a population; know that species diversity comprises the number of different species in an ecosystem (species richness) and the relative abundance of each species; understand the effects of isolation and area on the species diversity of habitat islands. 3.8 Threats to biodiversity By the end of this sub-topic you should be able to: describe exploitation and recovery of populations and the impact on their genetic diversity; know that small populations may lose the genetic variation necessary to enable evolutionary responses to environmental change (the bottleneck effect); understand habitat loss, habitat fragments and their impact on species richness. understand that habitat fragments suffer from degradation at their edges and this may further reduce their size; species adapted to the habitat edges (edge species) may invade the habitat at the expense of interior species. explain how to remedy widespread habitat fragmentation, isolated fragments can be linked with habitat corridors allowing species to feed, mate and recolonise habitats after local extinctions. Page 1 of 18

3 3.8 Threats to biodiversity (cont.) By the end of this sub-topic you should be able to: understand that introduced, naturalised and invasive species impact on indigenous populations. know that introduced (non-native) species are those that humans have moved either intentionally or accidentally to new geographic locations. know that naturalised species are those that become established within wild communities; know that invasive species are naturalised species that spread rapidly and eliminate native species. know that invasive species may well be free of the predators, parasites, pathogens and competitors that limit their population in their native habitat. know that invasive species may prey on native species, out-compete them for resources or hybridise with them. understand the effect of climate change and its impact on biodiversity. Page 2 of 18

4 N5 Prior Learning Sub-topic (3.2) Energy in ecosystems competition can occur when organisms struggle for the same or similar resources that are in short supply. interspecific competition occurs when organisms of different species require similar resources in an ecosystem. intraspecific competition occurs when organisms of the same species require the same resources in an ecosystem. intraspecific competition is more intense than interspecific competition. Sub-topic (3.4) Adaptation, natural selection and the evolution of species a species is a group of organisms that can freely interbreed to produce fertile offspring. living organisms can evolve and adapt to changing environmental conditions. variation exists within a population. variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions. living organisms often produce more offspring than the environment can support. natural selection (survival of the fittest) occurs and only those best suited to the environment survive. those individuals best suited for survival will live long enough to breed and pass on their favourable genes to their offspring. having the most desirable genes confers a selective advantage. the process of new species evolving is called speciation. speciation can occur when some individuals in a population becomes isolated by an isolation barrier. isolation barriers can be categorised into three groups: geographical ecological reproductive due to differing selection pressures, natural selection favours some individuals over others. Page 3 of 18

5 Mass Extinction and Biodiversity Extinction Extinction is the process in which groups of organisms die out. If over an extended period of time the birth rate of a species is less than the death rate, then extinction will eventually occur. Extinction is a natural phenomenon predicted by Darwin in his theory of evolution. A species can become extinct if it is not able to adapt to changes in its environment, or compete effectively with other organisms. Ever since life evolved on Earth, new species better suited to the environment have appeared and older, less successful species have died out. It is thought that over 99% of all the species that have ever lived have become extinct. Mass Extinction Events Mass extinctions are periodic rises in the extinction rate above the background level. They are events which are not caused by changes in habitat or competition between organisms but are closely related global climate change. During an ice age, for example, sea levels drop and vast areas of frozen land appear. As a result, many animals native to warm, sheltered marine waters and estuaries perish. Fossil evidence indicates that there have been several mass extinction events. Five main extinction events have been identified as shown in the graph below. When the environment changes, previously successful species may find themselves at a selective disadvantage and become extinct. Previously less successful species may then find themselves more suited to the new environment e.g. mammals began to dominate when a major event (perhaps global warming) caused the demise of the dinosaurs. Page 4 of 18

6 Regaining of Biodiversity Following a mass extinction, biodiversity has been regained by adaptive radiation of the survivors. New niches become available for the surviving species groups to exploit. Through natural selection mammals became adapted to the different ecological niches available e.g. jungle, dessert, grassland, icy regions, ocean. This success was promoted by them being endotherms, producing milk and giving parental care to their young. Extinction Rate Extinction Rate = number or percentage of species that become extinct in a given area per unit time. The extinction rate is usually calculated from the presence or absence of birds and mammals. This calculation is only an estimate. Estimating extinction rate is difficult and approximate. List the reasons why scientists have difficulty in measuring actual extinction rates: Page 5 of 18

7 Holocene Extinction The Holocene is the name given to the last 11,700 years of the Earth's history the time since the end of the last major glacial epoch, or "Ice Age." The Holocene extinction event is happening now and is largely due to the result of destructive human activity rather than nature phenomena. It remains to be seen whether humans will be the first ever biological cause of a mass extinction event of a similar scale to those in the past. Extinction caused by Humans Humanity has greatly influenced the Holocene environment; while all organisms influence their environments to some degree, few have ever changed the globe as much, or as fast, as our species is doing. The vast majority of scientists agree that human activity is responsible for "global warming," an observed increase in mean global temperatures that is still going on. Habitat destruction, pollution, and other factors are causing an ongoing mass extinction of plant and animal species; according to some projections, 20% of all plant and animal species on Earth will be extinct within the next 25 years. What is biodiversity? Measuring Biodiversity Biodiversity measurements are important as they provide data which is useful in monitoring; Page 6 of 18

8 Biodiversity has three main measurable components: genetic diversity species diversity ecosystem diversity Complete the following by giving a description of each. Genetic diversity If a population loses some of its genetic diversity (e.g. due to human activity) then the species may not be able to adapt to future environmental conditions. Species diversity A community with a dominant species has a lower species diversity than a community with the same species richness but no particularly dominant species. Ecosystem diversity Species Diversity Index Investigation into the species diversity of a local area may involve the use of a species diversity index. This is a mathematical measure of species diversity in a community. These biodiversity indices can be used to compare habitats e.g. polluted or unpolluted; invasive species. Page 7 of 18

9 The Effect of Isolation on Species Diversity Island biogeography is the study of factors that affect the distribution and diversity of species on islands. In a biographical context an island can refer to: A true island is a land mass surrounded by water. A habitat island an area surrounded by an unlike ecosystem that cannot be colonised by the enclosed area species e.g. an oasis in a desert, cold mountain top surrounded by warmer lowland or a forest pocket surrounded by farmland. The more isolated the habitat island the lower the diversity found amongst its species. Also the smaller the habitat island s surface area the lower the species diversity. There are two factors which must be taken into account when quantifying the species diversity of an ecosystem; Species richness, which is the number of species groups present in the ecosystem Relative abundance of each species i.e. the proportion of each species in the ecosystem. Complete the question below: The following table shows data from two communities from two different ecosystems. By comparing the species richness and relative abundance at each site give one similarity and difference between the two areas. Species Relative Abundance (%) Community P Community Q A B C D E F Actions to maintain biodiversity must be taken at local, national and global levels. Now complete: Testing your knowledge Torrance text book p323 Q1-4 Page 8 of 18

10 Threats to Biodiversity There are many threats to Biodiversity, both globally and locally. These can be can be remembered as HIPPO factors. HIPPO Factor Example of species affected Habitat loss and fragmentation Invasive species Population increase Pollution and climate change Over harvesting Over-Exploitation and Habitat Loss Humans exploit many natural resources, including plant and animal species; for food, medicines, raw materials and space. Over-exploitation is the consumption of resources at a greater rate than they can be replaced e.g. removal of more of a species than can be replaced by reproduction. Make notes on the following: Briefly describe the over-exploitation and recovery of cod in the North Sea. Why was there a need for a moratorium on whaling? Give the reason for the Caribbean monk seal extinction. Page 9 of 18

11 The Bottleneck Effect A bottleneck event is an evolutionary event in which a significant percentage of a population or species is wiped out or otherwise prevented from reproducing e.g. natural disaster such as a fire, flood or earthquake or from over exploitation. If the surviving population is very small in number the population may have lost much of its genetic diversity. Genetic diversity is needed to be able to adapt to future environmental change such as climate change or a loss of available resources. Such a population is said to have suffered from the bottleneck effect as a result of the disaster. If the members of the surviving population are so genetically similar, reproduction will be equivalent to inbreeding, with further loss in of variability and poorer rates of reproductive success the population could become extinct or may slowly recover and survive. Give an example of a species with naturally low genetic diversity that remains viable: Page 10 of 18

12 Habitat Loss by Fragmentation Habitat fragmentation is the process by which habitat loss results in the division of large, continuous habitats into smaller, more isolated areas. Habitat fragmentation can be caused by: geological processes that slowly alter the layout of the physical environment e.g. river formation human activity e.g. forest clearance for; agriculture, housing or motorways. Habitat fragmentation caused by humans happens rapidly and often leaves tiny islands which are isolated from one another. Degradation at the edges of the fragment may lead to further reduction in its size therefore an increased loss of habitat. Normally fragments have limited resources and are therefore only able to support a lower species richness than that of the original habitat. Also, smaller fragments can only support small populations which are more vulnerable to extinction than larger populations as they have less genetic diversity. Therefore, the resulting habitat fragments typically have; smaller total surface areas than the original habitat lower species richness than a large area of the same habitat. Page 11 of 18

13 Edge to Interior Ratio Fragmentation itself and the ongoing degradation at the edge of the fragments results in an increase in the ratio of the total length of the fragment s edge to the total surface area of its interior. As a result edge species adapted to life at the habitat edges may increase in number and invade the habitat at the interior resulting in increased competition for resources with species already there. Habitat Corridors A possible solution to this problem is to link isolated fragments with habitat corridors. Habitat corridors are pathways of natural habitat linking otherwise disconnected fragments e.g. hedgerows linking forest fragments; motorway underpasses for wildlife. The benefit of this is that they attract species and act as safe passages for species to move between neighbouring habitats. However, a possible negative side effect of habitat corridors is that they allow the spread of disease. In China, habitat corridors have been established to link small, adjacent populations of giant pandas. In Russia and India habitat corridors have been set up for Tigers with varying degrees of success. The Siberian Tiger have increased in number but are genetically similar. Habitat corridors between fragments allow members of a species to feed, mate and recolonise habitats after local extinctions. Page 12 of 18

14 From the list below, select the advantages and disadvantages of habitat corridors and fill them in the appropriate column in the table; List: Allow invasive species to spread between fragments Allow movement of organisms that are vulnerable to predation Facilitates spread of disease between fragments Immigrants from neighbouring populations can recolonise Lessens threat of extinction of endangered species Some species may not use them Advantages of habitat corridors Disadvantages of habitat corridors Introduced, Naturalised and Invasive species: Over the years many non-native species have been introduced to the UK. Most of these species have become naturalised but some have become invasive and have a negative impact on the local native communities and the economy. Give the definition of each of the following terms shown in bold. Introduced species: Page 13 of 18

15 Naturalised species: Invasive species: Summary of the Development of an Invasive Species Foreign species introduced into a new geographical location. These become introduced species and establish themselves in the new location. They then become naturalised species in the location. Some naturalised species spread rapidly and outcompete native species. These naturalised species then become invasive species. Hedgehogs released into garden in South Uist in 1974 to control snails and slugs. No predators, pesticides or busy roads so hedgehogs multiplied and discovered ideal food source - eggs of ground-nesting birds. 20 years later, hedgehog population was over 5000 and numbers of internationally important wading birds had fallen dramatically. Project set up in Uist to trap and remove hedgehogs but hedgehogs are now established throughout the islands. Invasive Species Success An invasive species is often successful because it may: lack predators (that would keep their numbers in check) lack parasites and pathogens lack competitors (in its adopted community) may prey on native species outcompete the native species for resources hybridise with related native species Therefore, it is free to undergo a population explosion. Page 14 of 18

16 Invasive species have an impact on: Impact of an Invasive Species biodiversity of native wildlife e.g. Rhododendron will out compete most native plants and is causing destruction of habitats across the British Isles. Red squirrels facing extinction by its more competitive American rival the Grey. economy e.g. Japanese knotweed roots damage foundations of building and car parks and the cost is high each year to try to eradicate it. health e.g. Giant hogweed was introduced as a garden plant it has poisonous sap and causes severe burns and blistering to the skin irritation Climate Change and Biodiversity Climate change is a natural part of the history of the planet. The Earth is warm enough for life because of the greenhouse effect : heat energy form the sun strikes the Earth and is the reflected from its surface; carbon dioxide and methane gas ( greenhouse gases ) in the atmosphere trap some of this reflected heat energy, keeping the planet warm. Page 15 of 18

17 Anthropogenic Climate Change This is caused by human activities. The increasing human population has led to increased demand for food and other resources. This in turn has led to activities such as: Deforestation removing trees which would have converted the CO2 back to oxygen Burning of fossil fuels contributing larger volumes of CO2 to the atmosphere. Some forms of large scale agriculture These have all contributed to climate change. Effect of Climate Change on Biodiversity Changes in climate and weather patterns have a great effect on biodiversity. A temperature rise of just 2 C can cause a global shift in climate. Some regions will become warmer; some will become drier while others become wetter: e.g. reduced rainfall in the tropics will have a major effect on the biodiversity of the rainforests, while Alpine flora may not survive increasing temperatures at high altitude. Effects include: change in the distribution and abundance of species; change in timing of seasonal events e.g. migration; changes in composition of plant and animal communities; habitat loss; increase in sea temperatures. The overall trend is a loss of biodiversity. Modelling Climate Change Scientist use computer models to predict the impact of future climate change on biodiversity of species. These can be used to predict temperatures, rainfall and extreme weather events. Modelling is not always accurate and can only make predictions about future events and their impact. The real challenge is in finding ways to reduce the levels of greenhouse gases on a global scale. Now complete: Testing your Knowledge Torrance text book p332 Q1-5 Page 16 of 18

18 Mass Extinction, Regaining Biodiversity and Measuring Biodiversity I can State that fossil evidence indicates that there have been several mass extinction in the past. Describe how biodiversity has been slowly regained following each mass extinction due to speciation of survivors. Outline the difficulties in estimating past and current species extinction rates. Highlight that the escalating rate of ecosystem degradation caused by humans is causing the rate of species extinction to be much higher than the natural background rate. State that the measurable components of biodiversity include genetic diversity, species diversity and ecosystem diversity. State that genetic diversity can be measured by the number and frequency of alleles in a population. State that genetic diversity includes the genetic variation represented by the number and frequency of all the alleles in a population. State that species diversity includes the number of different species in an ecosystem (the species richness) and the proportion of each species in the ecosystem (the relative abundance). The effects of degree of isolation and area of habitat islands on their species diversity. Outline the effects of isolation and area of habitat islands on their species diversity. State that ecosystem diversity refers to the number of distinct ecosystems within a defined area. Threats to Biodiversity I can Define the term exploitation. Describe how it is possible for populations to recover from exploitation and the impact this would have on genetic diversity. Explain the bottleneck effect in relation to evolutionary responses brought about by environmental change, particularly in small populations. Define habitat loss and habitat fragmentation. Outline the impact of habitat fragmentation on species richness with reference to degradation at the edges of the habitat fragments. Describe how to remedy widespread habitat fragmentation using habitat corridors. Define introduced (non-native) species as those that humans have moved either intentionally or accidentally to new geographic locations. Define naturalised species as those that become established within wild communities. Define invasive species as groups of naturalised species that have spread rapidly and eliminated native species. Discuss their advantages over other species to include lack of predators, parasites, pathogens and competitors that would normally limit their population in their native habitat. With reference to climate change, analyse its impact on biodiversity Page 17 of 18