IB Biology/Option G - Ecology and Conservation

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Return to IB Biology Originally obtained from [1] and edited by Robert Wiblin.

Ecology of Species[edit]

Ecology is the scientific study of the interrelations between the living organisms and their environment including both the abiotic and biotic factors with emphasis on the interspecific and intraspecific relations between them.

Outline the factors that affect the distribution of plant species including temperature, water, light, soil pH, salinity, and mineral nutrients.

  • High temperature denatures enzymes and retards growth of plants; the rate of transpiration (loss of :water) is also increased. Low temperatures decrease enzyme activity and freezing temperatures inactivate enzymes. Most plants live in moderate temperature zones.
  • Water is needed for enzyme activity, transport, photosynthesis, support, and many other things. There is a low diversity of plants in deserts and polar regions.
  • Light is important for photosynthesis and flowering. Dark areas have small numbers of plants.
  • Soil pH is important for absorption of nutrients. If soil is acidic, desertification can occur; the use of limestone can neutralise the soil.
  • Salinity has an affect on the absorption through osmosis. High salinity causes plants to lose water through osmosis. Halophytes live in high salinity.
  • Mineral nutrients are needed for many vital functions. Nitrogen is needed to manufacture proteins, enzymes, nucleotides, vitamins, and other compounds. Phosphorous is used in the formation of phospholipid and other structures.

Explain the factors that affect the distribution of animal species including temperature, water, breeding sites, food supply and territory.

  • Temperatures affect the concentration of animals. Only especially adapted organisms can live in extreme temperatures.
  • Water is needed for vital functions, so only animals that can conserve water are found in deserts.
  • Breeding sites are needed for growth and protection of young. Some need specific areas to breed. High animal diversity is found in areas with varied topographical nature.
  • Food supply is important for survival since animals are heterotrophs. High animal diversity is once again found in the rain forest.
  • Some animals are territorial and need large areas for feeding, mating, and protecting their young. Some are territorial during breeding season and occupy areas to prevents others from approaching them. There is high animal distribution where there is room to occupy territory and defend against other members of the species.

Deduce the significance of the difference between two sets of data using calculated values for t and the appropriate tables.

  • The t-test can be used to measure whether there is a significant difference between the means of two populations. For example if you measure the weight of rabbits on two islands the t-test formula will work out whether there is a significant difference based on the difference between the means and the degree of variation among them. A table of critical t values is used to determine the probability that the difference is simply random chance.

Explain what is meant by the niche concept, including an organism's spatial habitat, its feeding activities and its interactions with other organisms.

  • A niche is all the characteristics, biotic and abiotic, specific to a species. It includes the habitat, nutrition, and relationships. For example, the place that the species sleeps, lives, breeds, its food source and relationship with other species.

Explain the principle of competitive exclusion.

  • First proposed by Lokta and Volterra, competitive exclusion takes place when two species need the same resources, and will therefore compete until one species is removed. In any situation where two species are very similar and are vying for the same food source or breeding ground, one would be somewhat more capable of controlling the resources or reproducing rapidly. The other is run out of existence. Experiments with bacteria populations in the lab of Russian ecologist G.F. Gause demonstrated that this concept was accurate in practice. This principle was termed competitive exclusion.
  • No two species can live in the same niche, because there is competition for the resources of the land and only one species will survive.

Ecology of Communities[edit]

Explain the following interactions between species, giving two examples of each: competition, herbivory, predation, parasitism, and mutualism.

  • Competition is when two species need the same resource such as a breeding site or food. Usually one of the species will out-compete the other. The Douglas Fir and Western Hemlock are trees that compete in the USA.
  • Herbivory is the relation between an animal and a plant. Different animals feed on different plants. Deer feed on tree leaves, rabbit feed on grass, giraffes on trees.
  • Predation is the relation between the predator, which is usually bigger, and the prey, which is usually smaller. An example would be a fox and a rabbit, or bonitos on anchovies.
  • Parasitism is the relation between the host and the parasite. The parasite causes harm to the host to get food and other resources. Examples of parasites are the malaria protist and tapeworm in humans.
  • Mutualism is where two members of different species benefit and neither suffers. Examples include rumen bacteria/protazoa that digest cellulose in the digestive systems of cows, providing the cow with an energy source and the bacteria with a stable habitat. Lichens and Chlorella/Chlorohydra, an algae, also exhibit such a relation. The lichen provide an means of attaching to the surface, and the algae photosynthesize to produce a source of sugars and nutrients.

Define gross production, net production, and biomass.

  • Gross production is the total amount of organic matter produced per unit area per unit time by a trophic level in an ecosystem.
  • Net production of an ecosystem is gross production less the material expended by the plants in respiration.
  • Both of these are measured in kJ per squared meter per year.
  • Biomass is the dry mass of organic matter in organisms of an ecosystem.

Calculate values for gross production and biomass from given data.

  • Gross Production - Respiration = Net Production

Discuss the difficulties of classifying organisms into trophic levels.

  • It is difficult due to the fact that some organisms can be secondary, tertiary, and may be quaternary consumers at the same time, such as humans. It is difficult to place them on a certain level of the food pyramid.
  • For this reason, an alternate method of classification - the food web - has been developed. The food web displays relationships not as a simple hierarchy but rather a complex network, with the various feeding relationships between species existing as connections and the animals themselves existing as the hubs.

Explain the small biomass and low numbers of organisms in higher trophic levels.

  • There is a decreasing biomass of organisms in the higher trophic levels because energy is lost between levels in the form of heat (respiration), waste, and dead material. Around 10-20% of the energy proceeds on to the next trophic level.

Construct a pyramid of energy given appropriate information.

  • The lowest bar of the pyramid of energy represents gross primary productivity, the next bar is the energy ingested as food by primary consumers, and so on. The arrows demonstrate the direction of energy flow. The units are energy per unit area per unit time.

Describe ecological succession using one example

  • Ecological succession is the gradual change in the composition of a community with time in an ecosystem. If succession occurs in a lifeless area it is primary succession. It can start after things such as volcanoes, fire or flood.
  • The process is usually goes: lichen, moss, ferns, flowerings plants, conifers.
  • For example on the Volcan Osorno in south Chile after ash covers the ground: mosses spread over the ash. Small herbs and ferns arrive and through the activity of their roots, soil formation starts to occur. Shrubs and bushes grow and replace these. Then flowering trees grow, then conifers, and other larger trees producing a forest.

Explain the effects of living organisms on the abiotic environment with reference to the changes occurring during ecological succession to climax communities

  • Living organisms can help with soil development, as a plant grows, their roots grow deeper down and break rock into small particles, helping soil formation. Plants enrich the soil with minerals as they die and decompose. The plant roots hold the soil particles together, preventing soil erosion and retain nutrients. The water that evaporates from many plant leaves condenses and comes down in the form of rain. The presence of organic materials in the soil and the presence of roots and root hair help in the retention of water and slows down drainage.

Biodiversity and Conservation[edit]

Discuss reasons for the conservation of biodiversity using rainforests as an example. Reasons should include ethical, ecological, economic, and aesthetic arguments.

  • Biodiversity is highest in the tropical rainforests.
  • Ethical reasons for conserving biodiversity are that all species have a right to live on this planet. Many People have a cultural connection to the biological world. Future humans have a right to enjoy a healthy planet as we do today.
  • Ecological reasons are that species live with great interaction and dependence on each other. If one species dies out, a food chain is disrupted, therefore disrupting all of the other species as well. Species are adapted to particular conditions while other species may take a long time to adapt themselves. They help to dramatically reduce carbon dioxide levels.
  • Aesthetic reasons are that the tropical rain forest is one of the most beautiful attractions on this planet. There is variety everywhere in the rainforest. Many artists have been inspired by the diversity of life around them.
  • Economic reasons include that the rainforest is a source of materials important to human life. They regulate the weather and recycle nutrients and detoxify water. Medicinal substances can be taken from a variety of plants in the rain forest, new crop plants may be uncovered and ecotourism offers a new source of funds for the many impoverished nations these forests exist in.

Outline the factors that caused the extinction of one named animal and one named plant species.

  • The Arizona Jaguar became extinct due to an increased demand for its fur. As the human population increased in the areas inhabited by the jaguar, the hunting and shooting increased and the last of this rare animal was shot in 1905 in New Mexico.
  • The Fluffy groundsel is a kind of herbal plant with clusters of yellow flowers. It became extinct because of farming, building, road construction and other sorts of human impact in the American South West.

Outline the use of the Simpson diversity index.

  • The Simpson diversity index is a measure of species diversity
  • D = (N(N-1))/(summation of n(n-1)). D is the diversity index, N is the total number of organisms of all species found, n is the number of individuals of a particular species.
  • A high value of D suggests a stable and ancient ecosystem and a low D value could suggest pollution, recent succession or agricultural management.
  • The index is determined by counting organisms on randomly chosen parts of an area. Monitoring over time shows changes in an ecosystem.

Explain the use of biotic indices and indicator species in monitoring environmental change.

  • Indicator species are highly sensitive to environmental changes and their populations increase or decrease significantly depending on changes in the environment. They are good indicators of change. Frog populations are very vulnerable to pollution and other forms of change, while sludge worms are good indicators of low oxygen concentration in waterways.
  • Biotic indices are calculated via the number of tolerant and intolerant species at a time. The numbers of these organisms in the indicator species populations can be monitored over time directly so they are easy to keep track of.

Outline the damage caused to marine ecosystems by the over-exploitation of fish.

  • If the population of fish is fished excessively and the number of adult fish fall below a critical level, spawning fails which can lead to fish population crashes and destroy the fishing industry.
  • This occurred in Peru to anchoveta fishers in 1973 when the haul plummeted to nothing.

Discuss the international measures that would promote the conservation of fish.

  • International measures are necessary because many fish move through the oceans of multiple countries. Fish stocks in the ocean have fallen very significantly over the last 50 years due to excessive fishing. Enforcement is very difficult for any rules.
  • International measures that could be taken are monitoring of stocks and of reproduction rates, quotas for catches of species with low stocks, moratoria on catching endangered species, minimum net sizes, so that immature fish are not caught, and banning of drift nets, which catch many different species of fish indiscriminately.
  • The ICES is a name example of an international agency that advises limits on catching fish.

Discuss the advantages of in situ conservation of endangered species (terrestrial and aquatic nature reserves).

  • These are places where the animal is found in its own natural habitat and is not allowed to be disturbed by humans and their activities.
  • This keeps the animals out of danger zones and allows them to live and reproduce naturally in its own environment. Most animals typically survive at a much greater rate using in situ conservation, and preserving their habitat allows other species to live there also, thus preserving other animals and biodiversity. Greater genetic variety is also ensured.
  • However, sometimes numbers reach such low levels that the animals cannot be left unprotected in the wild or a habitat is being destroyed and this will not be stopped.

Outline the management of nature reserves.

  • A nature reserve is maintained by controlling alien species. Those that are not originally supposed to be in the area are removed.
  • They restore degraded areas where human impact has destroyed the ecosystem by methods such as reforestation and species reintroduction.
  • They promote the recovery of threatened species through feeding, for example.
  • They also control the exploitation by humans. Logging is controlled along with land clearing. If trees are cut down, more are planted.

Outline the use of ex situ conservation measures including captive breeding of animals, botanic gardens, and seed banks.

  • For captive breeding, animals kept in zoos or parks are allowed to reproduce in order to give them a chance to increase in number, with the possibility of eventually reintroducing some of the offspring into the wild. Unfortunately many do not reproduce. Elephants are an example.
  • Botanic gardens are sites where many plant species are planted in controlled environments to maintain their species. The Botanic Gardens of Kew has a massive collection of 50,000 species.
  • Seed banks are where seeds are kept in cold and dry storage, since they stay in good condition for hundred of years.

Discuss the role of international agencies and conservation measures including CITES and WWF.

  • CITES is an agreement that aims to control and regulate cross-border trade in endangered wildlife and wildlife products and so reduce poaching. Elephant poaching for example has been reduced through its listing on the agreement.
  • WWF is an independent organisation that attempts to save biodiversity and wildlife through political lobbying and monitoring projects. They try to keep areas from being cut down by buying areas of land and establishing them as nature reserves.

AHL The Nitrogen Cycle[edit]

State that all chemical elements occurring in organisms are part of biogeochemical cycles and that these cycles involve water, land and the atmosphere.

Explain that all biogeochemical cycles summarize the movement of elements through the biological components of ecosystems (food chains) to form complex organic molecules, and subsequently simpler inorganic forms which can be used again.

  • All chemical elements occurring in organisms are part of biogeochemical cycles and these cycles involve water, land and the atmosphere.
  • The simple inorganic forms are absorbed and converted into complex organic forms but then broken down again into simple forms and released into the environment for reabsorption.

Explain that chemoautotrophs can oxidise inorganic substances as a direct energy source to synthesize ATP.

State that chemoautotrophy is found only among bacteria.

  • Only bacteria can make their food through chemoautotrophy. They perform reactions using inorganic substances such as nitrates, ammonia and sulphur. The oxidisation of these substances results in energy. The energy is then used to fix carbon dioxide into glucose as in the Calvin cycle.

Draw a diagram of a nitrogen cycle. See Nitrogen cycle

  • Gaseous nitrogen is converted into biomass nitrate for plants and bacteria through the process of nitrogen fixation. Other bacteria also release nitrogen back into the air. When plants and animals die, proteins are broken down - deamination occurs, ammonia is formed, oxidation occurs producing nitrite, more oxidation occurs producing nitrate, then it can follow this path through another plant again or continue through bacteria in the soil. Ammonia is also formed by nitrogen gas through lighting and the Haber process (produces fertilizer).
  • This nitrogen cycle is not the only one present in an ecosystem that returns complex molecules to simple and simple to complex over and over again. The vast majority of other organic substances, such as potassium are also recycled in this manner, thus allowing ecosystems to survive without a constant influx of new organisms or nutrients.

Outline the roles of Rhizobium, Azobacter, Nitrosomonous, Nitrobacter and Pseudomonas dentrificans in the nitrogen cycle.

  • Rhizobium Azobacter are nitrogen fixing bacteria that can create nitrate from nitrogen gas. Nitosomonous oxidises ammonia to form nitrite. Nitrobacter oxidizes nitrite to form nitrate. Pseudomonas is a dentrifying bacteria that creates free nitrogen in the air from nitrate. The first four of these take inorganic nitrogen compounds found in the soil and transform them into a substance that can be used by plants and the last returns them to the atmosphere, away from plants.

Describe the conditions that favour dentrification and nitrification.

  • A harmful type of bacteria are denitrifying bacteria. They converts nitrate into free nitrogen gas. This decreases soil fertility and plant growth. These kind of bacteria are usually only found in water-logged soils. Water logging results in poor aeration and deficiency of oxygen in the soil.
  • Nitrification occurs in ploughed soil because then the oxygen gets into the soil and makes it unfavourable for dentrifying bacteria.

Discuss the action taken by farmers/gardeners to increase the nitrogen fertility of the soil including fertilizers, ploughing /digging and crop rotation (use of legumes).

  • Farmers plough the soil to make air space between the soil particles. The oxygen makes it an unfavourable condition for dentrifying bacteria and encourage the growth of nitrogen fixing bacteria.
  • Fertilizers are another option used to ensure proper nitrogen levels in the soil: processed from inorganic nitrogen, they provide a guaranteed heavy source of nitrogen compounds to plants. However, they have a tendency to leach out of the soil rapidly, and can often harm to the surrounding environment.
  • The final method, crop rotation, involves rotating crop planting between the crop the farmer wishes to grow and some kind of legume crop. Legumes form symbiotic relationships with nitrogen-fixing bacteria, allowing these bacteria to produce their own source of nitrates from inorganic or atmospheric nitrogen. Under favourable conditions, these plants can produce enough excess nitrogen that it renews the soil's store of nitrates capable of being used by plants next year. The following year, non-legume crops are planted on the field the legumes previously grown on.

AHL Impacts of Humans on Ecosystems[edit]

Describe the role of atmospheric ozone in absorbing ultra violet (UV) radiation.

  • Ozone exists in the upper atmosphere and is formed from oxygen. It absorbs UV light from the sun, breaking down and converting the UV energy into heat. This results in the conversion of UV light energy into heat energy. The ozone layer is continually formed and destroyed and protects the Earth from most dangerous UV radiation.

Outline the effects of UV radiation on living tissues and biological productivity.

  • UV radiation can kill phytoplankton, the sea-going organisms that account for a significant portion of net photosynthesis that occurs in the biosphere. This affects the whole oceanic food web.
  • The radiation retards the growth of terrestrial plants by slowing their rate of photosynthesis, usually a result of radiative damage and subsequent mutations in plant leaves. High levels of UV light can also kill symbiotic bacteria that fixes nitrogen in the root nodules of legumes.
  • Increases in UV exposure will increase rates of skin cancer, sunburn and eye cataracts in animals

Outline the chemical effect of chlorine on the ozone layer.

  • Chlorine (broken away from CFC molecules by UV light) reacts with ozone and breaks down into oxygen. One chlorine can break down thousands of ozone molecules. This leads to depletion of the ozone layer and the passage of UV light through the ozone hole.

Discuss methods of reducing the manufacture and release of ozone depleting substances including recycling refrigerants, reducing production of gas-blown plastics and using CFC-free propellants.

  • In 1987, after research had shown that CFCs were depleting the ozone layer, the Montreal protocol was created which set deadlines for the replacement of CFCs with non-ozone depleting substances.
  • Two of the largest sources of ozone-depleting substances come from the production of recycling refrigerants, gas blown plastics and the use of (CFCs) for propellants in spray cans, hairspray, etc. These chemicals have largely been removed and most corporations now recycle the refrigerants used rather than produce entirely new ones.
  • Nitrogen oxides also deplete the ozone layer and can be reduced through reduced use of fossil fuels, less polluting combustion engines and cleaner plane engines.
  • Ozone levels should start returning to normal around 2010 and be normal again by 2050 due to these measures.

Outline the consequences of releasing raw sewage and nitrate fertiliser into rivers.

  • Water polluted nitrate fertilisers will become rich in nutrients. The algae absorb large amounts of nitrates and this results in quick growth and reproduction of these algae and so the ecosystem becomes overpopulated with algae (algal blooms). This blocks the sun from reaching the photosynthetic plants at deeper levels and blocks the entry of carbon dioxide and oxygen from the atmosphere. The algae exceed their carrying capacity, the nutrients run out and they start to die quickly, encouraging the growth of the bacteria which digest them and increase the biochemical oxygen demand. They consume a large amount of oxygen and this results in deoxygenation of the water and aerobic organisms die. Finally, anaerobic bacteria develop producing poisonous hydrogenous compounds like H2S. By now most aquatic life has died.
  • When raw sewage is released bacteria grow first, deoxygenate the water and release the phosphates and nitrates used by algae. These grow and reoxygenate the water, after which they are eaten. At this time aquatic life may recover.
  • Raw sewage can also release pathogens into the bathing and drinking water supplies, causing the risk of human and animal infection when this water is used.

Outline the origin, formation and biological consequences of acid precipitation on plants and animals.

  • Acid precipitation occurs primarily because of the presence in the atmosphere of sulphur oxides and nitrogen oxides that react with water in the air to form acids like sulphuric acid and nitric acid. Sulphur and nitrogen oxides come from the combustion of fossil fuels and industries.
  • The acidic rain helps release aluminium ions from soil into waterways. Aluminium is acidic too and toxic to fish. Both lower the pH of lakes and contaminate freshwater habitats. It affects fish, amphibians and aquatic invertebrates the most, due to the destruction of their freshwater lake and river environment.
  • Calcium, magnesium and potassium ions are leached out of the soil, reducing fertility and plant growth.

State that biomass can be used as a source of fuels such as methane and ethanol.

  • Biomass, like wood, is already burnt for fuel. Biomass can also be used as a source of fuels such as methane and ethanol.

Explain the principles involved in the generation of methane from biomass, including the conditions needed, organisms involved and the basic chemical reactions that occur.

  • Any organic rubbish, such as remains of food, are placed in a sealed container. Methanogenic bacteria such as methanobacillus and methanococcus are added. The container must be sealed to ensure anaerobic conditions. Bacteria decompose organic material in the rubbish to organic acids and alcohol. Bacteria use these as a source of hydrogen. The hydrogen is used to reduce carbon dioxide into methane. The methane is then burnt as a source of energy. The digested material is rich in nutrients and used as fertiliser.