Unit 7 – Ecology and Evolution

Unit 7 – Ecology and Evolution Topic 5 – Ecology and Evolution

5.1 – Communities & Ecosystems • 5.1.1 Definitions. • 5.1.2 Autotrophs and heterotrophs. • 5.1.3 Consumers, detritivores and saprophytes. • 5.1.4 Food chains. • 5.1.5 Food webs. • 5.1.6Trophic level. • 5.1.7 Determining trophic levels in food chains and food webs. • 5.1.8 Constructing a food web. • 5.1.9 Light and food chains. • 5.1.10 Energy flow in a food chain. • 5.1.11 Efficiency of energy transformations. • 5.1.12 Shape of energy pyramids. • 5.1.13 Energy and matter in ecosystems. • 5.1.14 Decomposers.

5.1.1 Define species, habitat, population, community, ecosystem and ecology • Species: A group of organisms that can interbreed and produce fertile, viable offspring • Habitat: The environment in which a species normally lives or the location of a living organism • Population: A group of organisms of the same species who live in the same area at the same time • Community: A group of populations living and interacting with each other in an area • Ecosystem: A community and its abiotic environment • Ecology: The study of relationships between living organisms and between organisms and their environment

5.1.2 Distinguish between autotroph and heterotroph • Autotroph: An organism that synthesises its organic molecules from simple inorgance substances (e.g. CO2 and nitrates) - autotrophs are producers • Heterotroph: An organism that obtains organic molecules from other organisms - heterotrophs are consumers

5.1.3 Distinguish between consumers, detritivores and saprotrophs • Consumer: An organism that ingests other organic matter that is living or recently killed • Detritivore: An organism that ingests non-living organic matter • Saprotroph: An organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion

5.1.4 Decribe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms) • A food chain shows the linear feeding relationships between species in a community • The arrows represent the transfer of energy and matter as one organism is eaten by another (arrows point in the direction of energy flow) • The first organism in the sequence is the producer, followed by consumers (1°, 2°, 3°, etc.)

Examples of food chains

5.1.5 Describe what is meant by a food web • A food web is a diagram that shows how food chains are linked together into more complex feeding relationships within a community • There can be more than one producer in a food web, and consumers can occupy multiple positions (trophic levels)

5.1.6 Define trophic level • An organism's trophic level refers to the position it occupies in a food chain • Producers always occupy the first trophic level, while saprotrophs would generally occupy the ultimate trophic level of a given food chain or food web • The trophic levels in a community are:

5.1.7 Deduce the trophic levels of organisms in a food web and food chain • The trophic level of an organism can be determined by counting the number of feeding relationships preceding it and adding one (producer always first) • Trophic Level = Number of arrows (in sequence) before organism + 1 • In food webs, a single organism may occupy multiple trophic levels

5.1.8 Construct a food web containing up to 10 organisms, using appropriate information • Hint: When constructing a food web, always try to position an organism relative to its highesttrophic level (to keep all arrows pointing in same direction)

Food web (trophic levels in red)

5.1.9 State that light is the initial energy source for almost all communities • All green plants, and some bacteria, are photo-autotrophic - they use light as a source of energy for synthesising organic molecules • This makes light the initial source of energy for almost all communities • Some bacteria are chemo-autotrophic and use energy derived from chemical processes (e.g. nitrogen-fixating bacteria)

5.1.10 Explain the energy flow in a food chain • Energy enters most communities as light, where it is absorbed by autotrophs (e.g. plants) and converted into chemical energy via photosynthesis • Energy then gets passed to the primary consumer (herbivore) when they eat the plant, and then gets passed to successive consumers (carnivores) as they are eaten in turn • Only ~10% of energy is passed from one trophic level to the next, the rest is lost • Because ~90% of energy is lost between trophic levels, the number of trophic levels are limited as energy flow is reduced at higher levels

Summary of Energy Flow in a Food Chain

5.1.11 State that energy transformations are never 100% efficient • When energy transformations take place in living organisms the process is never 100% efficient • Typically, energy transformations in living things are ~10% efficient, with about 90% of the energy lost between trophic levels • This energy may be lost as heat, be used up during cellular respiration, be excreted in faeces or remain unconsumed as the uneaten part of food

5.1.12 Explain the reason for the shape of pyramids of energy • A pyramid of energy is a graphical representation of the amount of energy of each tropic level in a food chain • They are expressed in units of energy per area per time (e.g. kJ m2 year -1) • Pyramids of energy will never appear inverted as some of the energy stored in one source is always lost when transferred to the next source • This is an application of the second law of thermodynamics • Each level of the pyramid of energy should be approximately one tenth the size of the level preceding it, as energy transformations are ~10% efficient

Pyramid of energy

5.1.13 Explain that energy enters and leaves ecosystems, but nutrients must be recycled • The movement of energy and matter through ecosystems are related because both occur by the transfer of substances through feeding relationships • However, energy cannot be recycled and an ecosystem must be powered by a continuous influx of new energy from an external source (e.g the sun) • Nutrients refer to material required by an organism, and are constantly being recycled within an ecosystem as food (either living or dead) • The autotrophic activities of the producers (e.g. plants) produce organic materials from inorganic sources, which are then fed on by the consumers • When heterotrophic organisms die, these inorganic nutrients are returned to the soil to be reused by the plants (as fertilizer) • Thus energy flows through ecosystems, while nutrients cycle within them

5.1.14 State that saprotrophic bacteria and fungi (decomposers) recycle nutrients • In order for organisms to grow and reproduce, they need a supply of the elements of which they are made • The saprotrophic activity of decomposers (certain bacteria and fungi), free inorganic materials from the dead bodies and waste products of organisms, ensuring a continual supply of raw materials for the producers (which can then be ingested by consumers) • Thus saprotrophic bacteria and fungi play a vital role in recycling nutrients within an ecosystem

5.2 – Greenhouse effect • 5.2.1 Carbon cycle • 5.2.2 Historical records of atmospheric gases. • 5.2.3 Atmospheric gases and the enhanced greenhouse effect. • 5.2.4 The precautionary principle. • 5.2.5. The precautionary principle and the greenhouse effect. • 5.2.6 Greenhouse effect and the arctic ecosystem.

5.2.1 Draw and label a diagram of the carbon cycle to show the processes involved • here are four main 'pools' of carbon in the environment: • • Atmosphere • Biosphere • Sediments • Ocean • There are a number of processes by which carbon can be cycled between these pools: • Photosynthesis: Atmospheric carbon dioxide is removed and fixed as organic compounds (e.g. sugars) • Feeding: In which organic carbon is moved from one trophic level to the next in a food chain • Respiration: All organisms (including plants) metabolize organic compounds for energy, releasing carbon dioxide as a by-product • Fossilization: In which carbon from partially decomposed dead organisms becomes trapped in sediment as coal, oil and gas (fossil fuels) • Combustion: During the burning of fossil fuels and biomass • In oceans, carbon can be reversibly trapped and stored as limestone (storage happens more readily at low temperatures)

The Carbon Cycle

5.2.2 Analyze the changes in concentration of atmospheric carbon dioxide using historical records • Recent Trends: • Atmospheric carbon dioxide concentrations have been measured at the Mauna Loa atmospheric observatory in Hawaii from 1958 and has since been measured at a number of different locations globally • The data shows that there is an annual cycle in CO2 concentrations which may be attributable to seasonal factors, but when data from the two hemispheres is incorporated, it suggests that atmospheric CO2 levels have risen steadily in the past 30 years

Long Term Estimates: • Carbon dioxide concentration changes over a long period of time have been determined by a variety of sources, including analysing the gases trapped in ice (and thus providing a historical snapshot of atmospheric concentrations) • Data taken from the Vostok ice core in Antarctica shows that fluctuating cycles of CO2 concentrations over thousands of years appear to correlate with global warm ages and ice ages • It is compelling to note that CO2 levels appear to be currently higher than at any time in the last 400,000 years

Recent and Long-term Changes in Carbon Dioxide Concentration Mauna Loa CO2 Data (last 50 years)

Vostok Ice Core Data - CO2vs Temperature (last 400,000 years)

5.2.3 Explain the relationship between the rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect • The greenhouse effect is a natural process whereby the earth's atmosphere behaves like a greenhouse to create the moderate temperatures to which life on earth has adapted (without the greenhouse effect, temperatures would drop significantly every night)

The incoming radiation from the sun is short-wave ultraviolet and visible radiation • Some of this radiation is reflected by the earth's surface back into space as long-wave infrared radiation • Greenhouse gases absorb this infrared radiation and re-reflect it back to the earth as heat, resulting in increased temperatures (the greenhouse effect)

The Greenhouse Effect

The enhanced greenhouse effect refers to the suggested link between the increase in greenhouse gas emissions by man and changes in global temperatures and climate conditions • The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4) and oxides of nitrogen (e.g. NO2) • While these gases occur naturally, man is increasing greenhouse gas emissions via a number of processes, including: • • Deforestation (less trees) • Industrialisation (more combustion) • Increased farming / agriculture (more methane) • With increases in greenhous gas emission, it is thought that the atmospheric temperature may increase and threaten the viability of certain ecosystems, although this link is still being debated

5.2.4 Outline the precautionary principle • The precautionary principle states that when a human-induced activity raises a significant threat of harm to the environment or human health, then precautionary measures should be taken even if there is no scientific consensus regarding cause and effect • Because the global climate is a complex phenomena with many emergent properties, and is based on time frames well beyond human lifespans, it is arguably impossible to provide appropriate scientific evidence for enhanced global warming before consequences escalate to potentially dire levels • According to the precautionary principle, the onus falls on those contributing to the enhanced greenhouse effect to either reduce their input or demonstrate their actions do not cause harm - this makes it the responsibility of governments, industries, communities and even the individual • The precautionary principle is the reverse of previous historical practices whereby the burden of proof was on the individual advocating action

5.2.5 Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect • Arguments for Action • Risks of inaction are potentially severe, including increased frequency of severe weather conditions (e.g. droughts, floods) and rising sea levels • Higher temperatures will increase the spread of vector-borne diseases • Loss of habitat will result in the extinction of some species, resulting in a loss of biodiversity • Changes in global temperature may affect food production, resulting in famine in certain regions • The effects of increased temperatures (e.g. rising sea levels) could destroy certain industries which countries rely on, leading to poverty • All of these consequences could place a far greater economic burden on countries than if action were taken now • These factors would increase competition for available resources, potentially leading to increased international tensions

Arguments for Inaction • Cutting greenhouse emissions may delay economic growth in developing countries, increasing poverty in these regions • Very difficult to police - what level of action would be considered sufficient on a global scale in the current absence of scientific consensus? • Boycotting trade with non-compliant countries could negatively effect economies and create international tensions • No guarantee that human intervention will be sufficient to alter global climate patterns • Money and industrial practices that may be used to develop future technologies may be lost due to restrictions imposed by carbon reduction schemes • Carbon reduction schemes will likely result in significant job losses from key industries, retraining workers will require significant time and money

5.2.6 Outline the consequences of a global temperature rise on arctic ecosystems • Increases in global temperature pose a credible threat to arctic ecosystems, including: • Changes in arctic conditions (reduced permafrost, diminished sea ice cover, loss of tundra to coniferous forests) • Rising sea levels • Expansion of temperate species increasing competition with native species (e.g. red fox vs arctic fox) • Decomposition of detritus previously trapped in ice will significantly increase greenhouse gas levels (potentially exacerbating temperature changes) • Increased spread of pest species and pathogens (threatening local wildlife) • Behavioural changes in native species (e.g. hibernation patterns of polar bears, migration of birds and fish, seasonal blooms of oceanic algae) • Loss of habitat (e.g. early spring rains may wash away seal dens) • Extinction and resultant loss of biodiversity as food chains are disrupted

5.3 - Populations • 5.3.1 Factors affecting population size. • 5.3.2 Population growth curve. • 5.3.3 Phases of the population growth curve. • 5.3.4 Factors limiting population growth.

5.3.1 Outline how population size is affected by natality, immigration, mortality and emigration • The change in population size over a given period of time can be summarised by the following equation: Population Size = ( N + I ) - ( M + E )

Natality: Increases to population size through reproduction (i.e. births) • Immigration: Increases to population size from external populations • Mortality: Decreases to population size as a result of death (e.g. predation, senescence) • Emigration: Decreases to population size as a result of loss to external populations

5.3.2 Draw and label a graph showing the sigmoid (S-shaped) population growth curve

5.3.3 Explain reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases • Initially, population growth may be slow, as there is a shortage of reproducing individuals which may be widely dispersed • As numbers increase and reproduction gets underway, three stages of population growth are seen: • Exponential Growth Phase • There is a rapid increase in population size / growth as the natality rate exceeds the mortality rate • This is because there is abundant resources (e.g. food, shelter and water) and limited environmental resistance (disease and predation uncommon)

Transitional Phase • As the population continues to grow, eventually competition increases as availability of resources are reduced • Natality starts to fall and mortality starts to rise, leading to a slower rate of population increase • Plateau Phase • Eventually the increasing mortality rate equals the natality rate and population size becomes constant • The population has reached the carrying capacity (K) of the environment • Limited resources, predation and disease all contribute to keeping the population size balanced • While the population size at this point may not be static, it will oscillate around the carrying capacity to remain relatively even (no net growth)

5.3.4 List three factors that sets limits to population increase • Every species has limits to the environmental conditions it can endure and must remain within appropriate levels for population growth to occur • Some of these factors are density-dependent, while others are unrelated to the density of the population • Factors affecting population growth:

5.4 - Evolution • 5.4.1 Definition. • 5.4.2 Evidence of evolution. • 5.4.3 Population size and evolution. • 5.4.4 Population size and survival. • 5.4.5 Variation in a species. • 5.4.6 Sexual reproduction and variation • 5.4.7 Natural selection • 5.4.8 Examples of evolution.

5.4.1 Define evolution • Evolution is the cumulative change in the heritable characteristics of a population

5.4.2 Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures • Something provides evidence for evolution when it demonstrates a change in characteristics from an ancestral form • The Fossil Record • A fossil is the preserved remains or traces of any organism from the remote past • Fossil evidence may be either: • Direct (body fossils): Bones, teeth, shells, leaves, etc. • Indirect (trace fossils): Footprints, tooth marks, tracks, burrows, etc.

The totality of fossils (both discovered and undiscovered) is known as the fossil record • The fossil record reveals that, over time, changes have occurred in features of organisms living on the planet (evolution) • Moreover, different kinds of organisms do not occur randomly but are found in rocks of particular ages in a consistent order (law of fossil succession) • This suggests that changes to an ancestral species was likely responsible for the appearance of subsequent species (speciation via evolution) • Furthermore, the occurrence of transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken within a single genus • While fossils may provide clues regarding evolutionary processes and ancestral relationships, it is important to realise that the fossil record is incomplete • Fossilization requires a unusual combination of specific circumstances to occur, meaning there are many gaps in the fossil record • Only the hard parts of an organism are preserved and often only fragments of fossilized remains are discovered

Selective Breeding • Selective breeding of domesticated animals is an example of artificial selection, which occurs when man directly intervenes in the breeding of animals to produce desired traits in offspring • As a result of many generations of selective breeding, domesticated breeds can show significant variation compared to the wild counterparts, demonstrating evolutionary changes in a much shorter time frame than might have occurred naturally • Examples of selective breeding include: • Breeding horses for speed (race horses) versus strength and endurance (draft horses) • Breeding dogs for herding (sheepdogs), hunting (beagles) or racing (greyhounds) • Breeding cattle for increased meat production or milk • Breeding zebras in an attempt to retrieve the coloration gene from the extinct Quagga

Homologous Structures • Comparative anatomy of groups of animals or plants shows certain structural features are basically similar, implying a common ancestry • Homologous structures are those that are similar in shape in different types of organisms despite being used in different ways • An example is the pentadactyl limb structure in vertebrates, whereby many animals show a common bone composition, despite the limb being used for different forms of locomotion (e.g. whale fin for swimming, bat wing for flying, human hand for manipulating tools, horse hoof for galloping, etc.) • This illustrates adaptive radiation (divergent evolution) as a similar basic plan has been adapted to suit various environmental niches • The more similar the homologous structures between two species are, the more closely related they are likely to be

5.4.3 State that populations tend to produce more offspring than the environment can support • The Malthusian dilemma states that populations tend to multiply geometrically, while food sources multiply arithmetically • Hence populations tend to produce more offspring than the environment can support

Unit 7 – Ecology and Evolution