Ecology (CQC&SCR&JBW) Flashcards

Question

what are examples of obligate anaerobes?

Answer 1

- clostridium tetani - methanogenic archaea

Answer 2

- E-coli - Saccharomyces

Answer 3

In photosynthesis energy from sunlight is used for fixing carbon dioxide and making the carbon compounds such as sugars and amino acids on which life is based.

Answer 4

- plants- mosses, ferns, conifers and flowering plants - eukaryotic algae- including seaweeds that grow on rocky shores and unicellular algae such as chlorella - cyanobacteria- (blue-green bacteria) and several other groups of bacteria, but many aren’t photosynthetic

Answer 5

Photosynthesis occurs in two of three domains of life (eukaryotes and bacteria). It does not occur in the other domain (archaea)

Answer 6

Animals obtain supplies of carbohydrates, amino acids and other carbon compounds by consuming food. They are heterotrophic because the carbon compounds come from other organisms. Molecules such as polysaccharides and proteins must be digested before they can be absorbed. Digestion in most animals happens internally , after the food has been ingested. This is holozoic nutrition- whole pieces of food are swallowed and then fully digested.

Answer 7

- ingestion- taking the food into the gut - digestion- breaking large food molecules into smaller molecules - absorption- transport of digested food across the plasma membrane of epidermis cells and thus into the blood and tissues of the body - assimilation- using digested foods to synthesise proteins and other macromolecules; this makes them part of the body’s tissues - egestion- voiding undigested material from the end of the gut

Answer 8

Some animals digest their food externally and so aren’t holozoic. Spiders for example inject digestive enzymes into their prey and suck out the liquids produced. They absorb the products of digestion in their gut and assimilate them

Answer 9

Some protists (unicellular eukaryotes) can obtain carbon compounds from other organisms or can make them themselves. Organisms that aren’t exclusively autotrophic or heterotrophic are mixotrophic.

Answer 10

Facultative mixotrophs can be entirely autotrophic, or use both modes. Euglena gracilis, for example has chloroplasts and carries out photosynthesis when there is sufficient light, but it can also feed on detritus or smaller organisms by endocytosis.

Answer 11

Obligate mixotrophs cannot grow unless they utilise both autotrophic and heterotrophic modes of nutrition. This may be because the food that they consume supplies them with a carbon compound that they cannot synthesise. In other cases, a protist that does not have its own chloroplasts obtains them by consuming algae. It uses the “klepto-chloroplasts” obtained this way for photosynthesis until they degrade and have to be replaced.

Answer 12

Saprotrophs feed on dead organic matter, but have cell walls so cannot take it in by endocytosis. Instead, they secrete organic matter around them and digest it externally. They secrete proteases to digest proteins into amino acids and other enzymes depending on the composition of the dead organic matter , for example cellulase to digest cellulose into glucose. If the small soluble products of digestion diffuse into the saprotrophs plasma membrane, they are absorbed and used. Many types of bacteria and fungi are saprotrophic.

Answer 13

There are three domains of life: archaea, bacteria and eukaryotes. The archaea are unicellular and have no nucleus, which is a similarity with bacteria. In other respects, archaea are closer to eukaryotes. Some types of archaea are adapted to extreme environments such as hot springs, salt lakes and soda lakes. Many are are difficult to culture in the laboratory, so they are less well researched than the other domains of life. Archaea are extremely diverse in their sources of energy for ATP production and carbon. 3 main types of archaea; photoheterotrophs, chemoheterotrophs and chemoautotrophs

Answer 14

Oxidation of carbon compounds obtained from other organisms

Answer 15

Obtained from other organisms- not photosynthesis

Answer 16

Absorption of light using pigments (not chlorophyll in archaea)

Answer 17

Obtained from using sunlight in photosynthetic reactions

Answer 18

Oxidation of inorganic chemicals e.g. Fe2+ ions oxidised to Fe3+ ions

Answer 19

Synthesised from carbon dioxide by anabolic reactions

Answer 20

The family Hominidae includes the genera that contain humans (Homo), orang-utans (Pongo), gorillas (Gorrila), and chimpanzees (Pan). Some members of the Hominidae have an exclusively herbivorous diet and others are omnivores as animal prey are sometimes eaten to supplement their plant-based diet. Living members of the Hominidae show a relationship between diet and dentition. The teeth of herbivores tend to be large and flat to grind down fibrous plant tissues. Omnivores tend to have a mix of different types of teeth to break down both meat and plants in their diet. Humans have flat molars in the back of their mouth to crush and grind food, and sharper canines and incisors than herbivores to tear tougher food, like meat.

Answer 21

Animals that feed only on plants are herbivores. They have structural features that adapt them to their diet. Insect mouthparts show great diversity but are all homologous-they have been derived by evolution from the same ancestral mouthparts.

Answer 22

- beetles and other insects that feed on leaves have jaw-like mouthparts with tough mandibles for biting off, chewing, and ingesting leaves - aphids and other insects that feed on phloem sap have sharp, tubular mouthparts for piercing leaves or stems to reach phloem sieve tubes - butterflies and other insects that feed on nectar have tubular mouthparts long enough to reach the nectary in flowers

Answer 23

- sharp spines - stings to cause pains - synthesis and storage of secondary metabolites that are toxic to herbivores. They may be stored in any part of a plant, particularly seeds, which are attractive to herbivores because of their high concentrations of protein and starch or oil. Primarily metabolites are substances that are part of the basic metabolic pathways of a cell. (In some cases, herbivores have responded to toxic compounds in plants by developing metabolic adaptations for detoxifying them. This has resulted in plant-herbivore specificity, with only a few species of herbivore adapted to feed on a particular plant.)

Answer 24

large pointed upper front teeth in vampire bats for piercing prey to suck blood

Answer 25

shells of limpets on rocky shores to protect soft parts of the molluscs body

Answer 26

Venom containing toxins produced by black mambas to paralyse and kill prey

Answer 27

In cinnabar moth larvae toxins are accumulated from ragwart plants eaten

Answer 28

Waving of a modified luminescent fin ray in anglerfish to lure prey

Answer 29

Swimming in tight groups (schooling) in blue-striped snappers and other fish

Answer 30

In ecosystems where light intensity is the limiting factor for photosynthesis, especially forests, plants compete for light. Plants use a variety of strategies in forests for obtaining light, so they show great diversity of form. - Trees have dominant leading shoot, allowing rapid growth in height up to the forest canopy so other trees do not cast shade - Lianas climb other trees using them for support, so they need less xylem tissue (wood) than free-standing trees - Epiphytes grow on the trunks and branches of trees so they receive higher light intensity than if they grew on the forest floor, but there is minimal soil for their roots - Strangler epiphytes climb up the trunks of trees, encircle them and outgrow the trees branches shading out its leaves. Eventually the tree dies leaving only the epiphyte. - Shade-tolerant shrubs and herbs absorb the small amounts of light that reach the forest floor

Answer 31

The range of conditions that an organism can survive and reproduce itself (range of tolerance) Each species tolerates a range of abiotic conditions and their adaptations do not allow them to survive outside this range. There are also biotic factors that a species needs. The fundamental niche of a species is the range of abiotic conditions tolerated together with the requirements for biotic factors. If a species was living without any competitors, it would occupy the entire fundamental niche. In natural ecosystems, there is competition and typically a species is excluded from parts of its fundamental niche by competitors. The actual extent of the potential range that a species occupies its realised niche.

Answer 32

Where the fundamental niches of two species overlap, one species is expected to exclude the other from that part of its range by competition. This was demonstrated experimentally with the flour beetles *Tribolium castaneum* and *Tribolium confusum*. These species both thrived when put individually into flour at varying combinations of temperature and humidity. However, when they were both introduced to the flour, T. castaneum was excluded by T. confusum in some combinations of temperature and humidity, but T. confusum was excluded by T. castaneum in other combinations. So they had different realised niches. If two species in an ecosystem have overlapping fundamental niches and one species outcompetes the other in all parts of the fundamental niche, the outcompeted species does not have a realised niche and will be competitively excluded from the whole ecosystem. According to ecological theory, every species must have a realised niche that differs from the realised niches of all other species if it is to survive in an ecosystem.

Answer 33

open systems where resources can enter or exit, including both chemical substances and energy

Answer 34

closed systems where energy can enter or exit, but chemical resources cannot be removed or replaced.

Answer 35

Organisms that use an external source of energy to make carbon compounds are producers. Energy fixed by producers in carbon compounds is available to other organisms, so sustains the whole ecosystem. The principle source of energy in most ecosystems is sunlight and the process used by producers to make carbon compounds is photosynthesis. There are ecosystems where little or no light penetrates, e.g. caves and oceans at depths greater than 200m. Some energy may pass to these ecosystems in dead organic matter transferred from other ecosystems, which can be digested by sapotrophs. Another source of energy is inorganic chemical reactions, which chemoautotrophs us. In sealed caves, this is the only energy source for an ecosystem.

Answer 36

A food chain is a sequence of organisms, each of which feeds on the previous organism. Producers are the first organisms in a typical food chain because they do not feed on another organism. Producers are the first organisms in a typical food chain because they do not need to feed on another organism; they use an external energy source instead to make all the carbon compounds they require from simple inorganic substances such as CO₂. The other organisms in a food chain are consumers. They obtain chemical energy from carbon compounds in the organisms on which they feed. Primary consumers feed on producers; secondary consumers feed on primary consumers; tertiary consumers feed on secondary consumers, and so on. The last organism in a food chain is not fed on. Chemical energy thus flows along a food chain from organism to organism. In any ecosystem, there are many specific food chains that provide organisms with a supply of energy. For example, in the Monte Desert (in South America), leaves of a shrub with the local name of tara (Senna arnottiana) are eaten by guanaco (Lama guanicoe). Pumas (Puma concolor) are predators of the guanaco. They are regarded as apex predators because nothing kills or eats them, though fleas and other parasites can obtain energy from them by feeding on their blood.

Answer 37

Feeding relationships within ecological communities tend to be complex and web-like. This is because many consumers feed on more than one species and are fed upon by more than one species. A food web is a model that summarizes all of the possible food chains in a energy and biomass. community. Arrows indicate the direction of transfer of When a food web is constructed, organisms at the same trophic level are often shown at the same level in the web. However, this is not always possible because some organisms feed at more than one trophic level.

Answer 38

Dead organic matter is generated by these processes - death of whole organisms - defecation (removal of faeces from the gut) - shedding of (leaves, skin cells, hairs, arthropod exoskeletons and other unwanted body parts) Dead organic matter contains chemical energy in carbon compounds. Some dead organic matter is eaten by animals such as earthworms and vultures, but large amounts are digested by saprotrophs. Dead organic matter supplies sapotrophs with amino acids, glucose and other carbon compounds, which are used for growth and also as a source of energy, which is released by cell respiration. Saprotrophic bacteria and fungi are decomposers because they break down insoluble macromolecules in dead organic matter into small, soluble molecules and ions. By doing this, they cause the gradual breakdown of solid structures. For example, a tree trunk on the forest floor will gradually soften and crumble away and fallen leaves dissapear. Without extracellular digestion carried out by decomposers, dead organic matter would build up year by year. Also ions such as ammonium would not be released into the abiotic environment, so other organisms that absorb them would lose their supply. Decomposers are the waste disposers and recyclers of ecosystems.

Answer 39

All organisms need a variety of carbon compounds Some organisms make all of these carbon compounds themselves, using carbon dioxide (CO₂) or hydrogen carbonate (HCO₃-) as a carbon source. Organisms that do this are called autotrophs, meaning self-feeding. A reduction reaction inside autotrophic cells converts the simple inorganic carbon sources into an initial carbon compound. This process is carbon fixation. The initial carbon compound produced by carbon fixation is then built up into a wide variety of other carbon compounds by anabolic reactions Carbon fixation and anabolic reactions in autotrophs require an external energy source. The two possible sources of external energy are inorganic chemical reactions and light.

Answer 40

Photoautotrophs use sunlight to make carbon compounds by photosynthesis. Chemoautotrophs use exothermic inorganic chemical reactions. A substrate in a reduced state, such as sulfur, hydrogen sulfide, iron, hydrogen or ammonia, is absorbed and then oxidised. Oxidation reactions release energy. Chemoautotrophs use energy from the oxidation reaction to synthesize carbon compounds such as sugars and amino acids. Two of the three domains of life contain chemoautotrophs: bacteria and archea. Iron oxidising bacteria are an example, such as *Acidithiobacillus ferroxodians*. Iron oxidising bacteria absorb Fe2+ ions from the environment and remove an electron from them. Because this is an oxidation reaction, the energy is excited. Fe2+ → Fe3+ + extra electron (excited) The excited electrons are accepted by chains of electron carriers in the plasma membrane of the iron-oxidising bacterium. Energy is released as the electrons flow along these chains. Some electrons flow to proton pumps and their energy is used to build a proton gradient that is then used for ATP production by chemiosmosis. Other excited electrons are passed to NAD, converting it to reduced NAD (NADH). NADH and ATP can be used to fix carbon dioxide and produce carbon compounds by reactions similar to those of photosynthesis.

Answer 41

Many organisms obtain carbon compounds from other organisms. These organisms are heterotrophic, which means they feed on others. They digest carbon compounds that were part of another organism and then use the products of digestion to build the large complex carbon compound they need. For example, guanacos digest proteins in the leaves of tara bushes, breaking them down into amino acids. Then they use these amino acids to synthesise the proteins they need. The process of absorbing carbon compounds and making them part of the body is called assimilation. Assimilation requires absorption of carbon compounds into cells, so the molecules must be small and soluble enough to pass across cell membranes. Proteins, polysaccharides, nucleic acids and other large compounds must be digested before they can be absorbed. Heterotrophs are sub-divided according to whether they digest food internally or externally. - Saprotrophs grow into or across the surface of food and secrete hydrolytic enzymes to digest the food externally. - Consumers ingest their food. - Multicellular consumers take food into their gut by swallowing it. Then they mix the food with enzymes from digestive glands. This is regarded as internal digestion although the food has not yet entered any cells. - Unicellular consumers such as Paramecium take the food into their cells by endocytosis, then digest it inside phagocytic vacuoles into their cytoplasm

Answer 42

All organisms require supplies of energy in the form of ATP in their cells. They use the energy for the following four processes. - anabolic reactions to synthesise molecules such as proteins, polysaccharides, triglycerides, and nucleic acids - active transport to generate concentration gradients - movement of vesicles and other structures inside cells; movement of whole organisms and of blood and other fluids in organisms due to muscle contraction - maintaining constant body temperature (birds and mammals) In both autotrophs and heterotrophs, ATP is produced by cell respiration. Carbon compounds such as carbohydrates and lipids are oxidised to release energy and this energy is used to phosphorylate ADP, producing ATP.

Answer 43

In any ecosystem, there are large energy losses between trophic levels. These losses vary and are not always 90%. There are three main forms of energy loss from food chains.

Answer 44

Some organisms are never consumed and instead they eventually die. Energy in dead organisms, or dead parts of organisms, passes to saprotrophs or detritus feeders, which aren’t part of food chains.

Answer 45

Not all substances in food are digested. For example, some animals cannot digest cellulose. Indigestible material is egested in faeces and the energy passes to saprotrophs.

Answer 46

Substrates are oxidised to carbon dioxide and water to release energy from them, which is used by the respiring organism. Carbon compounds that have been oxidised in respiration cannot pass to the next trophic level and the energy that they contained is lost from the food chain. Biomass is also lost between trophic levels so organisms in higher trophic levels do not need to eat a greater mass of food to gain enough energy

Answer 47

Energy transfers are never 100% efficient, so when energy is released by oxidising substrates in cell respiration, some of the energy is converted to heat. When the ATP is used within cells, more energy is converted to heat. Both autotrophs and heterotrophs generate heat this way. Ultimately all of the energy that enters food chains is transformed into heat and lost to the abiotic environment. For this reason, energy flows through food chains and cannot be recycled (unlike chemical elements).

Answer 48

Food chains are limited in length because so much energy is lost between each trophic level and the next. After only a few stages, not enough energy remains to support another trophic level. For this reason the number of trophic levels in an ecosystem is restricted to a maximum of four or five. Animals in higher trophic levels do not have to eat more food to gain enough energy. Their prey contains large amounts of energy per unit mass- there just is not much prey available. A condor for example is mainly a tertiary consumer and may need a territory of more than 10000km^2 to find enough to eat.

Answer 49

Production in ecosystems is the accumulation of carbon compounds in biomass. Both autotrophs and heterotrophs produce biomass by growth and reproduction. - primary production is mass of carbon compounds synthesized by CO2 and other simple substances by autotrophs (producers). The units of measurement are usually grams of carbon accumulated per square metre of ecosystem per year. - Gross primary production is the total biomass of carbon compounds made by plants - Net primary production is GPP minus the biomass lost due to respiration of the plant. It is the amount of biomass available to consumers

Answer 50

Animals and other heterotrophs obtain carbon compounds such as sugars and amino acids from organisms in a lower trophic level and use them in growth and reproduction. This results in an increase in biomass. Secondary production is accumulation of carbon compounds in biomass by consumers Carbon compounds are used as respiratory substrates by all organisms. Cell respiration results in a loss of carbon compounds and therefore biomass in every trophic level. These are the consequences for ecosystems: - secondary production is lower than primary production - net secondary production is lower than gross secondary production in every trophic level of consumers - secondary production declines with each successive trophic level from primary consumers onwards

Answer 51

- Photosynthesis- absorption of CO2 from air or water and its conversion to carbon compounds - Feeding- gaining carbon compounds from other organisms - Respiration- release to the atmosphere of CO2 produced by respiring cells In marine and aquatic ecosystems, the inorganic pool of carbon is dissolved CO2, and also hydrogen carbonate ions (HCO-) both of which can be absorbed by producers and used in photosynthesis.

Answer 52

Ecosystems are open systems because both matter and energy can enter and exit. Carbon enters and exits in the form of carbon dioxide, through photosynthesis and respiration. The rates of these processes for an ecosystem as a whole are not always equal. If photosynthesis exceeds respiration, there is net uptake of carbon. The ecosystem is acting as a carbon sink. This happens in growing forests and also in waterlogged habitats (bogs or swamps) where anaerobic respiration and acidic conditions prevent decomposition of dead organic matter by saprotrophs, so peat containing carbon accumulates If respiration exceeds photosynthesis, there is a net release. The ecosystem is acting as a carbon source. This happens if peatlands are drained and the peat decomposes. Fires in forests and other ecosystems cause release of CO2 by combustion of carbon compounds in living organisms and dead organic matter. The ecosystem therefore becomes a carbon source

Answer 53

Ecosystems can act as carbon sinks by accumulating biomass. Forests can store over 5,000 tonnes of biomass per hectare. Carbon atoms may remain sequestered in the wood of trees. Peat formed in wetland ecosystems can store carbon for thousands of years. Dead organic matter has been converted to coal, oil and natural gas at different times in the Earth’s history and the carbon in these sinks can remain sequestered for many millions of years. When carbon compounds burn in air, carbon dioxide is produced and released into the atmosphere. Fires are natural and frequent in some ecosystems, ignited by lightning strikes. In recent years, there have been increasingly frequent fires in areas of tundra located inside the arctic circle, combustion of peat, accumulated over thousands of years, has released large quantities of carbon dioxide. Most coal, oil and natural gas is deeply buried and so cannot burn due to a lack of oxygen. Humans have developed methods of extracting these materials and burning them as an energy source. Since the start of the Industrial revolution, the rate of extraction and combustion of fossil fuels has risen rapidly and huge quantities of carbon dioxide have been released into the atmosphere.

Answer 54

Since 1959, atmospheric carbon dioxide concentrations have been measured at Mauna Loa Observatory in Hawaii. Graphs of the results (Keeling Curve) show two trends: 1. Annual fluctuations Carbon dioxide concentration increases between October and May and then falls from May to October, due to global imbalances in rates of carbon dioxide fixation by photosynthesis and release due to respiration. There is relatively more photosynthesis during summer in the northern hemisphere, when plants over most of the Earth’s land surface are in their growth season, and relatively more respiration during the northern hemisphere winter. 2. Long-term trend The graph of carbon dioxide concentrations for one year shows that the increase is not completely reversed by the decrease, so the concentration at the end of the year is higher than it was at the start. This is also shown by the full Keeling curve, from 1959 onwards. This trend is largely due to burning of fossil fuels by humans, together with other anthropogenic factors such as deforestation.

Answer 55

The “greenhouse effect” keeps the earth much warmer than it would otherwise be. Greenhouse gases absorb long-wave thermal radiation. Without any greenhouse gases in the atmosphere, the average temperature on Earth would be below zero degrees celsius. The higher the concentrations of greenhouse gases, the warmer the Earth becomes.

Answer 56

Living organisms contain large amounts of C, H, O, N and P in their molecules. About 15 other elements have roles in living organisms. The quantities of each element are finite on Earth, but despite living organisms using them for three billion years, no element has run out. This is because all elements can be endlessly recycled. They are absorbed from the abiotic environment as inorganic ions or molecules, used within living organisms and then returned to the abiotic environment with the atomic structure unchanged. Autotrophs obtain all elements they need as inorganic nutrients from the abiotic environment, including C and N. Heterotrophs obtain these two elements and several others as part of the carbon compounds in their food. They obtain some other elements as inorganic nutrients from the abiotic environment, including Na+, K+ and Ca2+. Decomposers play a key role in recycling because as a consequence of their saprotrophic nutrition they digest carbon compounds and return elements from them to the abiotic environment. All elements needed by plants are in the first four periods of the periodic table.

Answer 57

1. short-wave radiation is emitted by the Sun 2. short-wave radiation can pass through the atmosphere 3. the earths surface is warmed by absorbing sunlight 4. long-wave radiation is emitted by the warmed earth 5. greenhouse gases absorb long-wave radiation emitted by the Earth, making the atmosphere warmer

Answer 58

Methane and carbon dioxide are the most significant greenhouse gases. Humans are increasing the amounts of both that are released into the atmosphere, resulting in anthropogenic climate change. *Carbon dioxide* is released by respiration and removed by photosynthesis. These natural processes would normally be in balance, but humans area causing the carbon dioxide concentration to increase *Methane* is naturally emitted by methanogenic organisms in marshes and other waterlogged habitats. It is gradually oxidised in the atmosphere so the atmospheric concentration would naturally remain stable.

Answer 59

- combustion of fossil fuels - burning or decomposition of biomass during deforestation - increases in frequency and severity of forest fires - drainage and decomposition or burning of peat

Answer 60

- anaerobic decomposition of organic matter in landfill sites - leaks during fossil fuel extraction and processing - digestive systems of ruminants (cattle and sheep) - bubbles of methane released from melting permafrost

Answer 61

- changes in prevailing wind direction - increased cloud cover - increased rainfall overall, but some areas are drier with longer and more severe droughts - increased average wind speeds with more frequent and intense cyclones, hurricanes and typhoons

Answer 62

Positive feedback is the amplification of a process by its end product. Global warming is amplified by positive feedback cycles, because an increase in the earths temperature causes increases in factors that cause warming. Proportion of sunlight that is reflected (albedo) - snow and ice are white so they reflect solar radiation back out into space. With global warming, snow and ice are melting and are being replaced by open ocean, rock, or vegetation, all of which are darker in colour so they tend to absorb solar radiation rather than reflect it, causing further warming. Atmospheric CO2 concentration - Decomposition of peat and other dead organic matter by saprotrophs speeds up as temperature rises. Cell respiration in saprotrophs releases carbon dioxide - Global warming causes the temperature of the oceans to rise, which reduces the solubility of carbon dioxide in the water. Carbon dioxide is therefore released from deep in the oceans into the atmosphere. This carbon dioxide then contributes to the greenhouse effect, whereas dissolved carbon dioxide in the oceans does not. - Increased temperatures lead to drier, more fire prone conditions, so forest fires are more frequent and severe. Carbon dioxide emissions from combustion are increased. Also there is less absorption of carbon dioxide by photosynthesis in the ecosystems that replace forest Atmospheric methane concentration - Permafrost is soil that remains frozen throughout the year. Any dead organic matter in permafrost (such as peat) remains undecomposed because saprotrophic bacteria and fungi are inactive. When global warming causes melting, frozen soils become waterlogged and anaerobic. This encourages methanogenic microbes to break down dead organic matter and release methane into the atmosphere.

Answer 63

Boreal forest (also known as taiga) covers huge areas of the northern hemisphere, with tundra further north and temperate forests to the south. Ecosystems can be carbon sources or sinks. Boreal forests are typically sinks because carbon is stored in the biomass of conifer trees and because dead wood, leaf litter and peat accumulate. It is in the cold conditions that it is digested by saprotrophs more slowly than it is produced. With climate change, summers in the boreal forest have become warmer and drier, resulting in widespread fires and huge carbon emissions of CO2 from combustion of the legacy carbon. As global temperatures continue to rise, a tipping point could be reached beyond which boreal forests as a whole change from being carbon sinks to carbon sources. Instead of helping to keep the earth cooler by removing carbon dioxide from the atmosphere, they would contribute to warming by releasing it instead and further hastening the loss of this biome.

Answer 64

The ocean is stratified. Warmer, less salty water is less dense and floats on top of denser, colder, saltier water. There is some mixing of the upper and lower layers, but transfers of heat and chemicals are restricted by the stratification. Atmospheric warming increases ocean stratification. This happens because the upper warmer water becomes less dense as it is heated and less saline as freshwater from melting ice flows into the ocean. As a result, there is less mixing. Rotation of the earth and prevailing winds cause currents that bring the colder, deeper water towards the coast in some parts of the oceans. This water is forced up to the surface, displacing warmer water. It causes an upwelling of mineral nutrients, increasing the growth of producers and therefore availability of food for consumers. Areas where upwelling occurs have very productive biological communities. If surface water becomes warmer, there tends to be less upwelling, reducing availability of mineral nutrients and therefore productivity. Areas of upwelling cover about 1% of the ocean surface but provide about 50% of the fish harvested for human consumption.

Answer 65

Ice floats on the surface of seawater, so it forms a solid surface. Sea ice moves, due to the wind and ocean currents, whereas landfast ice remains attached to a shore. The extent of landfast and sea ice is reducing due to global warming, with consequences for animals that use it as a habitat in both the Arctic and and Antarctic. Walruses use sea ice to rest between feeding sessions, shelter from rough seas and evade predators. They also use sea ice for breeding, giving birth and nursing their young. They can also use areas of coastal land for these purposes but they are limited in area and females prefer sea ice, so as to avoid the risk of their pups being trampled by the larger males. Sea ice also expands access to a broader range of feeding sites. Global warming is reducing sea ice so land-based walruses are having to make more feeding trips from coastal haul-outs to areas of high prey abundance that are far from shore. Walruses lose more heat in the water than when out of the water, so they expend more energy on these trips on thermoregulation. Emperor penguins breed on landfast ice in the Antarctic. It provides a relatively flat surface and the penguins are too large and unagile to climb over rocks or broken sea ice. To avoid predation, communal breeding sites are chosen at least 5km from the landfast ice edge; however, breeding success drops as distance from the ice edge increases beyond this, due to the difficulty of returning to the open ocean to feed. Climate change is making the extent of landfast ice very variable and unpredictable, making it difficult for emperor penguins to choose where they can successfully breed.

Answer 66

Continental climates are not influenced much by the oceans and tend to be hot in summer and very cold in winter. Temperate climates have intermediate temperatures throughout the year with nearby oceans making the summers cooler and the winters warmer. Plants and animal species that are adapted to temperate zones are therefore having to move their ranges towards the poles. Animal species may be able to achieve this by migration. Plant species are sessile, so range changes are due to deaths at the hotter end of the range nearer the equator and colonisation of cooler areas nearer the poles. On mountains, the climate becomes colder as altitude increases. There is therefore a series of altitudinal climate zones. Species adapted to the temperate zone on a mountain are having to move upslope as global warming shifts the zones upwards.

Answer 67

There is evidence that the ranges of temperate tree species in North america are shifting northwards. A large study of seed productionand seedling survival rates in tree species showed that many species are indeed shifting northwards, with the shift happening faster in western species. Another study suggested that conifers are moving north but trees that are flowering plants are tending to shift westwards.

Answer 68

There is evidence that temperate-zone montane bird species in New Guinea are shifting their range upslope. The upper altitude limit of the ranges of 20 species were measured in 1969 and again in 2013. The limit in all but four of the species had shifted upslope by up to 650 metres. In the other four species, the upper limit had not changed or had reduced a little

Answer 69

In addition to its contribution to global warming, emissions of carbon dioxide are affecting the oceans. Over 500 billion tonnes of carbon dioxide released by humans since the start of the industrial revolution have dissolved, reducing the pH of the Earths oceans. In the late 18th century, when there had been a little industrialisation, the average surface pH was 8.18, the average pH is now below 8.06 (this is 30% acidification). Marine animals that deposit calcium carbonate in their skeletons need to absorb carbonate ions from seawater. The concentration of these ions in seawater is low, because they aren’t very soluble. Dissolved carbon dioxide makes the carbonate concentration even lower as a result of two chemical reactions. Carbon dioxide reacts with water to form carbonic acid, which dissociates into hydrogen and hydrogencarbonate ions. Hydrogen ions react with dissolved carbonate ions, reducing their concentration. Reduced carbonate ion concentrations make it more difficult for reef-building corals to absorb carbonate and use it to calcify their skeletons. Also, if seawater ceases to be saturated with carbonate ions, calcium carbonate tends to dissolve, so existing skeletons of reef building corals are eroded. Hard corals live in a mutualistic in a mutualistic association with photosynthetic algae called zooxanthellae. The algae benefit by being kept safe from organisms that would feed on them and close to the ocean surface where they can access the sunlight penetrating the water. The corals get the benefit of carbohydrates and oxygen produced by the algae. When the ocean water surrounding corals becomes too warm, the zooxanthellae are ejected leading to a loss of colour, hence the term “coral bleaching”, which is happening more frequently leading to global warming. Coral species with calcium carbonate skeletons are collectively the keystones of the reef. Many other species depend on them and their loss due to ocean acidification, and warming would cause the collapse of reef ecosystems globally.

Answer 70

Carbon sequestration is capture and storage of carbon dioxide from the atmosphere. Two biological processes sequester carbon - accumulation of biomass, produced in ecosystems by photosynthesis, especially the long lasting wood of trees - accumulation of undecomposed or partially decomposed organic matter, especially peat in wetlands

Answer 71

Afforestation is planting trees in areas where they currently do not exist. This should only be done where forests are the natural ecosystems. There is ample opportunity for afforestation. For example, it is estimated that in the 8,000 years since the end of the last glaciation, the forests that grew in the upper Midwest of the US stored nearly a billion tonnes of carbon. This carbon was released into the atmosphere as forests were cleared, to extract timber and convert land to agriculture, over about 150 years. If such areas were reforested, large amounts of carbon could be sequestered. There is active scientific debate over whether non-native or native species offer the best approach to carbon sequestration. Native species have evolved to be adapted to the conditions in an area so they should grow rapidly, but climate change may result in non-native species being better adapted than the native species.

Answer 72

Restoration of wetlands: Peat is partially decayed organic matter that forms in waterlogged ecosystems in both temperate and boreal zones and also very rapidly in some tropical ecosystems. Peatlands are a huge carbon sink, but in many areas they have been drained to convert the land to plantation, forestry or agriculture. After the soils have dried out, saprotrophs can decompose the peat and may also be lost through the fire. It can be difficult to rewet former peatlands so that carbon sequestration restarts, but it can be done by blocking drains, restoring high water levels and re-establishing native species such as sphagnum moss

Answer 73

Living organisms are adapted to carry out stages of their life cycles at the most appropriate time of year. Photoperiod and temperature are used as cues by living organisms to determine when the appropriate time of year has arrived. There is much variation between species in how these cues are used. Photoperiod is the length of daylight during a 24-hour period. Each year it follows the same cycle of change with minimum and maximum daylength in the winter and summer solstices. Towards the poles there is greater variation in daylength through the year. Plants can measure the length of the night to an accuracy of five minutes and many species use it to time flowering. In most birds, the timing of migration and egg-laying are determined mainly by daylength. Temperature follows an annual cycle of warming and cooling in many parts of the world, though there is variation from year to year in how quickly temperatures rise in spring and drop in the autumn. Warm temperatures in spring advance the dates of egg laying in some bird species and bud-burst in many deciduous trees. Warm temperatures in the autumn delay leaf abscission (leaf-drop) in many trees. Phenology is studying the timing of seasonal events. Data obtained each year for as many years as possible can provide evidence of global warming and other climate changes. For example, the date of opening the first bud on a tree in Geneva has been recorded each year since 1810. It varies considerably from year to year, but there is a clear trend in the date becoming earlier.

Answer 74

Rangifer tarandus is native to tundra ecosystems in the Arctic. They are known as caribou in North America and reindeer in Europe. Their spring migration coincides with the emergence and growth of food plants such as the Arctic mouse-ear (Cerastium arcticum). This allows females secreting milk for their calves to obtain enough food. Evidence suggests that climate change has led to a mismatch between plant growth and caribou migration patterns so caribou and reindeer are less able to meet their nutritional needs.

Answer 75

Parus major (great tit) feeds its young on caterpillars. The dates of egg-laying and peak caterpillar biomass have been studied for over 50 years in a population of Parus major in the Netherlands. Caterpillar biomass now peaks much earlier in spring. The mean date of egg-laying has also become earlier, but not by as much.

Answer 76

Insects vary in how long their life cycle takes. Some species complete several cycles per year. Others take one or more years for a single cycle. In some species the time taken per cycle has become shorter due to global warming. An example is the spruce bark beetle, Dendroctonus rufipennis, which is native to forests in North America. Its larvae feed on the inner bark of older and weaker spruce trees and also deadwood and stumps. It takes between one and three years to complete a life cycle, but warmer temperatures have reduced the average time, increasing the potential population growth rate. The health of older spruce trees has declined due to reduced rainfall and droughts, together with warmer temperatures, so more trees are succumbing to beetle attacks. As a result, there have been major outbreaks in Alaska and other areas of boreal forest with hundreds of millions of spruce trees killed.

Answer 77

Global warming and other climate changes on earth are changing the adaptations that living organisms need to thrive. Many traits are now subject to directional selection. For example Strix aluco (tawny owl) varies in colour, with its feathers ranging from brown to pale grey. This is a heritable trait. A single gene has a dominant allele for brown and a recessive allele for pale grey feathers. The pale grey variant is better-camouflaged against snow. Winters have become milder in Finland, reducing snow cover. Between 1985 and 2010, the percentage of brown owls in the Finnish population of tawny owls more than doubled.

Answer 78

variety in the combinations of species living together in communities. This diversity is partly due to the very varied environments on Earth and the geographical ranges of organisms

Answer 79

The many different species on the evolutionary tree of life. These species have varied body plans, internal structure, life cycles and modes of nutrition

Answer 80

within species- variety in the gene pool of each species. There is variation between geographically separated populations and within populations

Answer 81

Animals/ plants are overharvested to the point it is very unsustainable, and they die off

Answer 82

- - Natural habitats have been destroyed leading to species extinctions. Agriculture is the main cause, with over 13 billion hectares of land now cultivated or used for rearing livestock. Natural habitats have also been destroyed to build towns and cities

Answer 83

when alien species are introduced to ecosystems, they can drive native species to extinction by predation, spreading of pests and diseases or competition for resources. Endemic species become extinct if they hybridise with alien species

Answer 84

chemical industries produce a vast range of substances that are used and then discarded in the environment. Burning of fossil fuels, agriculture, mining, oil extraction and pharmaceuticals are all major sources of pollutants

Answer 85

human activities are currently causing very rapid changes in temperature rainfall and other climatic variables. Species that fail to adapt quickly enough or cannot migrate face extinction.

Answer 86

1. Agriculture- the main cause of ecosystem loss. Most temperate forests and grasslands were cleared before the 1970s. Since then, much tropical forest has been lost 2. Urbanisation- building of homes, offices and factories, together with associated infrastructure of roads and railways. This has been inevitable given the rapid and continued rise in the human population; 3. Overexploitation of natural resources- such as gathering of fuel wood, hunting of animals for bushmeat and fishing. Loss of a single keystone species can threaten whole ecosystems 4. Mining and smelting- opencast mines destroy areas of natural ecosystem entirely. Smelting and disposal of waste from mining can cause pollution and more widespread damage. Much tropical rainforest has been lost due to mining 5. Water management- reservoirs created by building dams can flood natural ecosystems. Extraction of water for irrigation and for industrial or domestic use can greatly reduce river flows 6. Drying of wetlands- swamps and other wetlands are drained for conversion to agriculture. Wetlands are also destroyed by diverting the water that flowed into them for human use. 7. Leaching- washing of fertilisers into rivers and lakes causes eutrophication and algal blooms. Oligotrophic ecosystems in which organisms are adapted to low nutrient concentrations have been lost 8. Climate change- anthropogenic climate change is the most common cause of loss.

Answer 87

The EDGE of existence programme uses two criteria to identify animal species that are most deserving of conservation - **E**volutionary **D**istinct: does the species have few or no close relatives, so it is a member of a very small clade? - **G**lobally **E**ndangered: Is the species likely to become extinct because all remaining populations are threatened Species that fit both criteria (EDGE species) are listed and targeted for intense conservation efforts. Some species are the last members of a clade that has existed for tens or hundreds of millions of years and it would be tragic for them to become extinct as a result of human activities

Answer 88

A population is a group of individual organisms of the same species living in an area. Members of a population interact in various ways. They normally interbreed with each other and interbreeed less often or not at all with individuals in other populations. There are usually many non-breeding interactions between individuals in a population, such as competition for food or cooperation to avoid predation. The number of individuals in a population can be anything from a few up to billions. There may be one population of a species or many. Populations of a species are often separated by a geographical barrier, for example the sea that separates two islands.

Answer 89

1. capture as many individuals as possible in the area occupied by the animal population, using netting, trapping or careful searching 2. mark each captured individual, without making them more visible to predators 3. release all the marked individuals and allow them to settle back into their habitat 4. after a time period, recapture as many individuals as possible and count how many are marked and how many unmarked 5. calculate the population size using the lincoln index population size= ((number of individuals initially caught)(number of individuals recaptured))/ number of individuals recaptured that are marked

Answer 90

The number of different species in the area. If there are loads of different species, there is a high species richness

Answer 91

The relative abundance of different species in a given area. If the number of individuals of each species are similar, the evenness is high.

Answer 92

species richness+species evenness

Answer 93

Resources needed by populations, such as water and food, vary in abundance but are all limited. Resource limitation determines maximum population size. **Carrying capacity** is the maximum population size that an environment can support. If a resource becomes scarce, the members of a population will compete for it. If a population grows too large, some individuals will be unable to obtain enough of the resource. These individuals are likely to die, reducing the population size to the carrying capacity of the environment.

Answer 94

water space for breeding food or territory for obtaining food dissolved oxygen in water

Answer 95

water light soil nitrogen/phosphorus

Answer 96

Density-independent factors have the same effect whatever the population size. For example, in a population of plants that are not adapted to low temperatures, a frost kills all the plants, whether the population is large or small. Forest fires kill plants and animals. Density-independent factors cause populations to fluctuate.

Answer 97

Density-dependent factors have an increasing effect as a population becomes larger. They are the basis for negative feedback mechanisms because they reduce larger populations and allow smaller populations to increase. Density dependent factors tend to bring population size back to carrying capacity. - **competition** for limited resources such as water and food in animals and light in plants - **predation**- this becomes more intense if a population of prey becomes denser and therefore easier to find, and less intense if the prey becomes scarcer. There are similar interactions between plants and herbivores - **Infectious disease, parasitism and pest infestation**- these increase with population density because the transfer of pathogens, parasites and pests from host to host is easier if the hosts are closer together

Answer 98

natality- offspring produced and added to the population mortality- individuals die and are lost from the population immigration- individuals move into the area from elsewhere emigration- individuals move from the area to live elsewhere The overall change in the size of a population can be calculated using this equation: population change= (natality + immigration) - (mortality + emigration)

Answer 99

1. Exponential phase- if a population is established in an ideal unlimited environment, it follows an exponential growth pattern, with the population increasing more and more rapidly. This is because the natality rate is higher than the mortality rate. The resources needed by the population are abundant, and diseases and predators are rare. With abundant resources, immigration to the area is more likely than emigration 2. Transitional phase- population growth slows as the carrying capacity of the environment is reached- the maximum population size that can be supported by the environment. The natality rate starts to fall and/ or the mortality rate starts to rise. Natality is still higher than mortality, but by a decreasing amount 3. Plateau phase- Something has limited the population such as (shortage of food or other resources, more predators, more diseases or parasites) All of these factors limit population increase because they became more intense as the population rises and becomes more crowded. They either reduce the natality rate or increase the mortality rate. Emigration is now more likely than immigration. If the population is limited by a shortage of resources, it has reached the carrying capacity of the environment

Answer 100

- this is tested using any organism that proliferates under experimental conditions, provided there are no ethical concerns - a small number of organisms is given abundant resources and the numbers in the population are counted at regular intervals. There should be repeats so that reliability can be tested

Answer 101

All species depend on relationships with other species for their long term survival. A population of one species can never live in isolation. Instead, groups of populations live together. In ecology, a group of populations living together in an area and interacting with each other is known as a community. A typical consists of hundreds or even thousands of species, including all the plants, animals, fungi and bacteria, that live together in an ecosystem.

Answer 102

An intraspecific relationship is one that exists between individuals of the same species and usually also within the same population. Competition and cooperation are categories of intraspecific relationship. 1. Competition Members of a population have the same ecological niche so require the same resources. Unless a resource is abundant, there will be competition for it. Some individuals will be more successful and gain more of the resource, helping them to survive and reproduce. As a result, there is natural selection over the generations for traits that allow individuals to compete more effectively 2. Cooperation Individuals in a population may cooperate in a variety of ways. The extent of cooperation varies, with most in social animals. Cooperation relationships have strong advantages because all individuals benefit, whereas in competitive relationships all individuals tend to be harmed to some degree

Answer 103

Herbivory Primary consumers feed on producers. The producer may or may not be killed Predation One consumer species (the predator) kills and eats another consumer species (the prey) Interspecific competition Two or more species use the same resource, with the amount taken by one species reducing the amount available to the other species

Answer 104

Mutualism Two species live in close association, with both species benefiting from the association Pathogenicity One species (the pathogen) lives inside another species (the host) and causes a disease in the host Parasitism One species (the parasite) lives in or on another species (the host) and obtains food from them. The host is harmed and the parasite benefits

Answer 105

Mutualisms are close associations between species, where both species benefit. In many cases, the two species are from different taxonomic kingdoms so they have different capabilities and supply different services.

Answer 106

Species that occur naturally in an area are endemic. Species that were introduced by humans, deliberately or accidentally are alien. Density-dependent factors usually regulate the population size of endemic species. However, many alien species aren’t effectively regulated, because the pests or predators that would control them in their native habitat are absent in their new habitat. If an alien species increases in number and spreads rapidly, it is invasive.

Answer 107

Invasive species can have devastating impacts on communities. The competitive exclusion principle predicts that two species cannot occupy the same ecological niche indefinitely. Alien species compete for the resources with endemic species that have the same or overlapping ecological niches. To become invasive, an alien species must be successful in competition for resources with endemic species. As a result, the endemic species may occupy a smaller realised niche, causing a decline in population, or lose its niche entirely and become extinct in an area. This is currently a widespread phenomenon because humans transport high numbers of a species to new areas, where there are no limiting factors (or not enough) to control the populations of alien species

Answer 108

A range of approaches can be used to test for interspecific competition between species in a community that require the same resource 1. field manipulation can be used. e.g. one of two species can be removed from quadrats in grassland. There is evidence of interspecific competition if the other then increases in number/ biomass 2. laboratory experiments can be performed, under controlled conditions. Species can be grown together and apart to investigate whether they compete for resources 3. Tests for association between species can be carried out by random sampling

Answer 109

Predators kill and consume prey, but in many communities, the population of prey does not change much overall, because new prey individuals are born at about the same rate as they are lost due to predation. Similarly, the birth and death rates of the predator are approximately equal, so the predator population remains stable. Some communities do not show this dynamic equilibrium and instead there are cyclical oscillations in numbers of prey and predators, due to four types of density-dependent interaction: - A rise in prey numbers increases prey availability, so predator numbers rise - A rise in predator numbers increases predation, so prey numbers fall - a fall in prey decreases prey availability, so predator numbers fall - a fall in predator numbers decreases predation so prey numbers fall

Answer 110

- Top down control acts from a higher trophic level to a lower one. For example an increase in predator numbers will decrease the numbers of prey in lower trophic levels

Answer 111

- Bottom up control acts from a lower trophic level to a higher one. For example, a population of producers may be limited by the availability of mineral nutrients in the soil or water

Answer 112

Antibiotics and allelopathic agents are secondary metabolites. A secondary metabolite is a substance produced by a pathway that only exists in some taxonomic groups. Such substances are not essential for cell growth and instead have a wide range of other functions. Antibiotics and allelopathic agents are two functional groups of secondary metabolites. Both antibiotics and allelopathic agents are released into the environment, where they are toxic to other organisms and deter potential competitors. Antibiotics are secreted by microorganisms to kill, inhibit or prevent the growth of other species of microorganism. Allelopathic agents are secreted into the soil by plants to kill or deter the growth of neighbouring plants. This can result in bare areas of soil near the secreting plant, reducing competition for water or mineral ions.

Answer 113

Systems are sustainable if they can continue for an unlimited period of time. Ecosystems have the potential to be sustainable. This is demonstrated by examples that have existed for very long periods of time. The mechanisms that sustain ecosystems are fragile and easily disrupted , so ecosystems are not always stable. Even minor perturbations can cause change

Answer 114

- there must be a steady supply of energy, as it cannot be recycled. Sunlight is the energy source in most ecosystems. Very rarely this has been blocked by dust from volcanic activity, causing ecosystem collapse and mass extinctions - nutrient cycles should replenish abiotic reserves of all chemical elements needed by organisms. Any losses from the ecosystem should be balanced by gains - climatic variables, especially temperature and rainfall must remain within changes of tolerance of organisms in the ecosystem - individual species, especially keystone species, must have high genetic diversity, so there is variation for natural selection to work on. This allows adaptations in response to environmental change, so new conditions can be endured.

Answer 115

The amazon rainforest is so vast that it has major effects on climate. Evaporation of water from leaves (transpiration) has a cooling effect. Water vapour that has transpired from leaves condenses in the atmosphere above the forest, lowering air pressure and causing air flow (wind). The condensed water falls as rainfall, so it can be absorbed by trees and transpired again. Ecosystems show resilience, but this is not unlimited. Above a certain level of disturbance, a tipping point may be reached, beyond which positive feedback mechanisms cause rapid changes that are difficult or impossible to reverse. In the amazon rainforest there is disturbance due to deforestation. If a tipping point is reached, a positive feedback cycle will cause unstoppable changes. Even without further deforestation, all remaining parts of the amazon rainforest would then change to another ecosystem type, probably grassland. It is uncertain what area of the Amazon rainforest is needed to prevent tipping point being reached

Answer 116

(final amount-initial amount)/initial amount *100%

Answer 117

Ecosystems have the potential to be sustainable over long periods of time. As long as nutrients are recycled and there is a supply of energy, usually in the form of light, ecosystems have the potential to persist endlessly. This can be investigated using mesocosms. A mesocosm is a small experimental enclosure, set up for ecological research. Fenced-off enclosures in grassland or a forest model terrestrial mesocosms. Open tanks or sealed glass vessels model aquatic ecosystems. Sealed vessels allow entry and exit of matter to be controlled, with energy transfer happening freely. For sustainability, autotrophs and saprotrophs are essential components, but consumers and detritivores may not be essential. It is unethical to include large animals in mesocosms that cannot obtain enough food or oxygen.

Answer 118

A keystone species has a disproportionate effect on the structure of an ecological community. Species diversity decreases if a keystone species is lost and there may be a collapse of the entire ecosystem.

Answer 119

Before agriculture was developed, all foods and other resources needed by humans were harvested from natural ecosystems. This is sustainable if the rate of harvesting is lower than the rate of replacement . There is a long history of unsustainable harvesting and it has resulted in many species extinctions.

Answer 120

- Tillage is preparing soil for a crop. Soils are loosened by plowing, harrowing and other cultivations. Soil structure can become degraded and both wind and water can cause soil erosion at much faster rate than new soil is being generated. Tropical forests that are cleared for agriculture often have soils which quickly degrade and cannot sustain high yield agriculture for long - Nutrient depletion of soils is caused by removal of harvested crops and by leaching. Repeated applications of chemical fertiliser are required because of depletion. Phosphate and most other minerals are mined from non-renewable rock deposits. The manufacture of nitrogen fertiliser from fossil fuels requires energy - Cultivating large areas of single variety of crop plant (monoculture) and growing the same crop year after year encourages pests and weeds to become increasingly problematic. Intensive agriculture responds to this with applications of pesticide and herbicide. This can cause pollution problems. Resistance to an agrochemical tends to evolve in pests or weed if the chemical is repeatedly used. Manufacture of agrochemicals requires an energy source, which currently is supplied by fossil fuels - Mechanical tillage requires power, most of which comes from diesel oil used in tractors. Energy is also required for heating glasshouses and animal housing. The carbon footprint of agriculture is high. It makes a significant contribution to climate change.

Answer 121

When rainwater falls on terrestrial ecosystems, soluble nutrients such as phosphates and nitrates dissolve and are washed out of the soil as water drains through it (leaching). The nutrients enter river catchments and are eventually carried out to sea. Intensive crop production increases leaching, because of the use of artificial fertilisers. Intensive livestock production also increases the transfer of nutrients into river systems, especially if manure and urine aren’t stored correctly or are spread on land before rainfall. Intensive agriculture therefore tends to cause nutrient enrichment of ponds and lakes also flowing water in streams and rivers and in estuaries and shallow seas. Nutrient enrichment of aquatic and marine ecosystems is eutrophication. The water in some ecosystems is naturally eutrophic but agriculture has caused eutrophication of many lakes and rivers. 1. eutrophication due to leaching of mineral nutrients 2. excessive growth of algae and cyanobacteria due to to eutrophication 3. algae and cyanobacteria rise to seek light (algal bloom) but some are shaded out and die 4. decomposition of dead organisms causes a high biochemical and oxygen demand 5. water becomes anoxic due to high biochemical and oxygen demand resulting from decomposer respiration, so fish die

Answer 122

Plastic is accumulating because it is either non-degradable, or degrades very slowly Macroplastics are large visible items, such as fishing nets, ropes, drinks bottles and grocery bags. Marine wildlife such as seabirds and turtles can become entangled in nets and ropes and ingest plastic bags and other debris because they are mistaken for prey. Albatrosses confuse floating plastic bags with jellyfish or squid and give them to their chicks resulting in gut blockages and high mortality Microplastics are tiny granules of plastic, which are present in many products. They have been found in every marine ecosystem investigated Nanoplastics are less than 1 micrometer in diameter and can pass through cell plasma membranes and can accumulate in organs. They almost certainly have harmful effects, but they aren’t researched as of yet.

Answer 123

Bioaccumulation is an increase in concentration of a toxin in body tissues during an animals life. It is a particular problem with toxins that are fat soluble and therefore not easily excreted.

Answer 124

Biomagnification is an increase in concentration of a chemical substance at each successive trophic level in a food chain. Predators tend to accumulate higher concentrations of toxin than their prey. This is because the predator consumes large quantities of prey during its lifetime and biomass accumulates the toxins that they contain.

Answer 125

Natural ecosystems have been degraded by human actions and relatively little of the Earths surface remains as pristine natural habitat. Among the consequences are: - loss of biodiversity - rapid rates of species extinction - loss of ecosystem services e.g. carbon sequestration and climate regulation, flood protection, prevention of soil erosion and purification of air and water In many parts of the world, efforts are being made to encourage natural ecosystems to return. One approach to this is rewilding. The essential principle of rewilding is that there should be as little intervention by humans as possible because natural processes restore habitats more effectively than humans. A first step is to stop or reduce human activities such as agriculture, logging and other forms of resource harvesting. That may be all that is required for forests to recolonise abandoned farmland or for marine ecosystems to re-establish fishing exclusion zones. More commonly there is need for specific interventions to undo human actions: - spreading of seeds of plants that should be part of the ecosystem but no natural seed source is present - reintroduction of apex predators and other keystone species - re-establishment of connectivity where natural ecosystems have become fragmented - control of alien invasive species

Answer 126

Ecological successions are sequences of changes that progressively transform ecosystems. Species composition of the community and abiotic factors both change over time Consider an area of grassland that is being colonised by shrubs or trees. As the trees grow, light intensity at ground level diminishes and lower temperatures and higher humidity result. Leaf litter from the trees increases nutrient concentration, water infiltration and capacity for water retention of the soil. This means that plant species adapted to conditions in grassland will be lost from the community and others adapted to conditions in the forest will join it. There will also be changes in the animal species because of interdependency between specific species of animal and plants. Changes in an ecosystem often trigger other changes, so one ecosystem replaces another in a series. This is an ecological succession. A stable and persistent ecosystem then may develop that does not undergo further significant change. This is the climax community

Answer 127

Succession is either primary or secondary. Primary succession begins in environments where living organisms are largely or completely absent. On land, this could be bare rock or deposits of silt, sand or larger rock fragments, but not soil. Only organisms such as bacteria, lichens and mosses can colonise these inorganic substrata. Early colonisers generate small amounts of soil, allowing herbs with roots to start to colonise. As deeper soul develops, successively larger plants colonise. Animal populations change with plant populations, as do populations of decomposers. These are the general principles of primary succession: - species diversity increases as more species join the community than are eliminated - primary production increases as larger plants colonise and there is more photosynthesis per unit area - food webs become more complex - nutrient cycling increases as animals and plants generate more dead organic matter

Answer 128

Some ecosystems are characterised by cycles of change rather than stable climax. In cyclical succession, species replace each other over time repeatedly, even without the stimulus of large-scale disturbance. Cyclical succession also occurs when a community is changed by recurring events. E.g. repeated fire cycles leading to disturbance to an ecosystem

Answer 129

As succession proceeds, a stable climax community may develop that is not superseded. The type of climax community that develops depends on climate and other environmental conditions. Human influence can cause a deflected arrested succession, so a plagioclimax develops (an alternative stable community). Grazing by farm livestock and drainage of wetlands both result in a plagioclimax, instead of the climatic community. - grazing is the method of feeding farm livestock such as cattle and sheep. The livestock are kept at high stocking densities so grazing is more intense than in natural ecosystems. Grasses and many herbs can tolerate grazing, but tree and shrub seedlings are killed, so grassland persists as a plagioclimax where it would naturally be replaced by shrub and then forest - drainage of wetlands removes water from swamps and other waterlogged sites and increases soil aeration. Plants and animals adapted to wetlands migrate or die and saprotrophic fungi, which were inhibited by the lack if oxygen, can decompose any peat that had developed in the swamp. If the land is not cultivated, shrubs and trees may be able to colonise areas that were previously waterlogged.

Answer 130

r- strategists e.g. fish small body size large number of offspring no parental care very short gestation period large population shorter lifespan k-strategists e.g. humans large body size few offspring long term care to children large gestation period small population size longer lifespan.

Answer 131

resources in the environment that limit the growth, abundance and distribution of organisms/ populations in ecosystems