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TOPIC 2: Ecosystems 2.1 Structure NOTES Biotic: Living organisms in a system. Abiotic: The chemical and physical factors in an ecosystem. Distinguish between biotic and abiotic (physical) components of an ecosystem. Define the term trophic level. Each of several hierarchical levels in an ecosystem, comprising organisms that share the same function in the food chain and the same nutritional relationship to the primary sources of energy. Identify and explain trophic levels in food chains and food webs, selected from the local environment. *Trophic level: Position of an organism within a food chain. Explain the principles of pyramids of numbers, pyramids of biomass and pyramids of productivity, and construct such pyramids from given data. 1st trophic level (producers): Produce their own food from simple inorganic processes (support energy requirements for all other trophic levels). 2nd trophic level (primary consumer/herbivore): Feed on producers to obtain energy. 3rd trophic level (secondary consumer/carnivore): Feed on lower level consumers or producers to obtain energy. 4th trophic level (tertiary consumer/carnivore): Feed on lower level consumers to obtain energy. *Pyramids are graphical models of the quantitative differences that exist between the trophic levels of a single ecosystem. 1. 2. CASE STUDIES/EXAMPLES Biotic examples: plants, animals, fungi, microbes. Abiotic examples: Temperature, moisture, salinity, soil type, light, air. First example: Producer example: plants which capture the sun’s energy and convert it to glucose. Primary consumer example: grasshopper Secondary consumer example: rat Tertiary consumer: snake Second example: 1. Pyramid of numbers example: Pyramids of numbers: shows the number of organisms at each trophic level in a food chain. The length of each bar gives a measure of the relative numbers. Advantages: This is a simple easy method of giving an overview and is good at comparing changes in population numbers with time or season. Disadvantages: All organisms are included regardless of their size, also they do not allow for juveniles or immature forms. Numbers can be too great to represent accurately. Pyramids of biomass: Contains the biomass (mass of each individual × number of individuals) at each trophic level. Biomass is the quantity of (dry) organic matter in an organism, a population, a particular trophic level or an ecosystem. The units of a pyramid of biomass are units of mass per unit area (often grams per square meter/g m-2 or volume of water (g m-3) or sometimes as energy 1 content (joules, J). 2. Pyramid of biomass example: Advantages: Overcomes the problems of pyramids of number. Disadvantages: Only uses samples from populations, so it is impossible to measure biomass exactly. Also the time of the year that biomass is measured affects the result. 3. Pyramids of productivity: Contains the flow of energy through each trophic level. It shows the energy being generated and available as food to the next trophic level during a fixed period of time. Advantages: Show the actual energy transferred and allows for rate of production. Allows comparison of ecosystems based on relative energy flows. Disadvantages: It is very difficult and complex to collect energy data as the rate of biomass production over time is required. Discuss how the pyramid structure affects the functioning of an ecosystem. Because energy is lost through food chains, carnivores are at risk from disturbance. Disturbance at the lowest level (producers) directly affects the existence of species at consumer level and ultimately the top carnivores. Define the terms species, population, community, niche and habitat with reference to local examples. Species: A group of organisms that interbreed and produce fertile offspring. Population: A group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding. Community: A group of populations living and interacting with each other in a common habitat. Niche: When species share a habitat and the resources in it. An organism’s ecological niche depends not only on where it lives but on what it does. Habitat: The environment in which a species normally lives. 3. Pyramid of productivity example: Species example: 2 Population example: Community example: Niche example: Habitat example: Competition: A common demand by 2 or more organisms upon limited Examples of intraspecific competition: In a 3 Describe and explain population interactions using examples of named species. 2.2 Measuring Physical Components of the System List the significant abiotic (physical) factors of an ecosystem. Describe and evaluate methods for measuring at least three abiotic factors within an ecosystem. supply of a resource i.e. food, water, light, space, mates, nesting sites. May be intraspecific where the competition is between members of the same species or interspecific where the competition for a resource is between individuals of different species. Predation: The interaction of two organisms where the predator (which has a higher trophic level) feeds on the prey (lower trophic level). Herbivory: An animal (herbivore) eating a green plant. Parasitism: The relationship between two species in which one species (the parasite) lives in or on another (the host), gaining its food from it. Mutualism: A relation between two or more species in which both or all benefit and none suffer. seagull colony on an oceanic outcrop, as the population grows, so does the pressure for good nesting sites. (As the population grows so does the competition between individuals for the same resources.) Examples of interspecific competition: Competition for a resource like water between amphibians, reptiles and mammals in an ecosystem. Examples of predation: Lions eating zebras. Examples of herbivory: Herbivores include animals such as elephants, cattle, rabbits, insects. Examples of parasitism: Vampire bats or intestinal worms. Examples of mutualism: Lichens are an example of mutualism. It benefits from obtaining sugars from the photosynthetic alga. The alga or bacterium benefits from minerals and water lichens absorb and pass on to it. PH, Temperature, Light intensity, Salinity, Turbidity, Dissolved oxygen. PH - PH meter Temperature - Thermometer (C degrees) Dissolved oxygen - Oxygen meter (PPM) Light intensity - Light meter (LUX) Salinity - Salinity meter (ppt) Marine—salinity, dissolved oxygen, wave action 4 Freshwater—turbidity, temperature, dissolved oxygen Terrestrial—temperature, wind speed, particle size, slope, soil moisture, drainage, mineral content. 2.3 Measuring Biotic Components of the System Construct simple keys and use published keys for the identification of organisms. Describe and evaluate methods for estimating abundance of organisms. Keys called dichotomous keys are used to identify species, the key is written so that the identification is done in steps. At each step two options are given based on different possible characteristics of the organism you are looking at. You go through all the steps until the name of the species is discovered. Example of a dichotomous key: Simpson’s diversity index: This method allows for an estimate of the total population size of an animal in a study area. This method includes collecting a sample from the population, then marking them, releasing them back into the wild and then re-sampling a time later and counting how many marked individuals you found in the second capture. Also known as capture-markrelease-recapture. The formula for calculating is as follows: Where: D = diversity index N = total number of organisms of all species found n = number of individuals of a particular species n = number of individuals of a particular species Describe and evaluate Biomass is a measurement of the mass of living material at a trophic level or 5 methods for estimating the biomass of trophic levels in a community. within an ecosystem. Define the term biodiversity. Biodiversity is a measure of the relative abundance of different living organisms within an ecosystem. Apply Simpson’s diversity index and outline its significance. A numerical measure of species diversity that is derived from both the number of species (variety) and their proportional abundance. 2.4 Biomes Since all organisms are made of roughly the same organic molecules in similar proportions, a measure of their dry weight is a rough measure of the energy they contain. Therefore, material brought into the lab must be dried completely before measuring its mass. Normally, this is accomplished by placing the material in a warm drying oven and allowing it to dry completely over a day or two before weighing it. Biome: A collection of ecosystems sharing similar climatic conditions. Define the term biome. Explain the distribution, structure, and relative productivity of tropical rainforests, deserts, tundra, and any one other biome. Examples of biomes: tundra, tropical rainforest, desert. Tropical rainforest: High productivity High precipitation (2500 mm yr¹) throughout the year High isolation High temperature (26 ℃) Good nutrient cycling/ high right of decomposure Highest NP Tundra: 6 Low productivity Low insolation (days are shorter) Low precipitation (50 mm yr¹) Low temperature Poor nutrient cycling (because its locked in the permafrost therefore it has a low rate of decomposure) For 1-2 months the productivity is very high because the sun is up for almost the whole day. Desert: Very low productivity Low precipitation (Under 250 mm yr¹) High insolation (but all water is evaporated or absorbed by the ground) Hot days & Cold nights Low nutrient cycle Species adapted to survive Grassland: Wide diversity, but low levels of productivity Enough precipitation to prevent deserts forming, but not enough to support forests Nutrient cycle is sufficient Insolation, precipitation and evaporation rates are balanced Grass can grow under the surface even in cold periods, waiting to emerge until the ground warms. 2.5 Function Explain the role of produces, consumers, and decomposers in the ecosystem. Producers: organisms that make their own organic material from simple inorganic substances. For most of the biosphere the main producers are photosynthetic plants and algae that synthesis glucose from carbon dioxide and water. The glucose produced is used both as an energy source and combines with other molecules from the soil to build biomass. It is this biomass that provides the total theoretical energy available to all non photosynthesizing organisms in the ecosystem. Consumers: organisms that obtain organic molecules by eating or digesting Producers example: Consumers example: 7 other organisms. These are the herbivores and carnivores of the ecosystem. By eating other organisms they gain both food as an energy supply and nutrient molecules from within the biomass ingested. Decomposers: the waste managers of any ecosystem. They are the final link in a food web breaking down dead organic matter from producers and consumers and ultimately returning energy to the atmosphere in respiration and inorganic molecules back to the soil during decomposition. Decomposers example: Describe photosynthesis and respiration in terms of inputs, outputs, and energy transformations. 1. Photosynthesis (CO2 + H2O --> C6H12O6 + O2) Inputs: carbon dioxide and water Outputs: Glucose and oxygen Producers transform light energy (from the sun) into chemical energy 2. Respiration (C6H12O6 + O2 --> CO2 + H2O + Heat) Inputs: Glucose and oxygen Outputs: Carbon dioxide and water Transformations: chemical energy turns into heat Describe and explain the 8 transfer and transformation of energy as it flows through an ecosystem. Almost all ecosystems are driven by energy from the sun (solar radiation) Describe and explain the transfer and transformation of materials as they cycle within an ecosystem. Define the terms gross productivity, net productivity, primary productivity, and secondary productivity. Define the terms and calculate the values of both gross primary productivity (GPP) and net primary productivity (NPP) from given data. Gross productivity (GP): The total gain in energy or biomass per unit area per unit time, which could be through photosynthesis in primary producers or absorption in consumers. Net productivity (NP): The gain in energy or biomass per unit area per unit time remaining after allowing for respiratory losses (R). Primary productivity: The gain by producers in energy or biomass per unit area per unit time (can refer to either net or gross productivity). Secondary productivity: The biomass gained by heterotrophic organisms, through feeding and absorption, measured in units of mass or energy per unit area per unit time. Gross primary productivity (GPP): The total gain in energy or biomass per unit area per unit time fixed by photosynthesis in green plants. Net primary productivity (NPP): The gain by producers in energy or biomass per unit area per unit time remaining after allowing for respiratory losses (R). 9 Define the terms and calculate the values of both gross secondary productivity (GSP) and net secondary productivity (NSP) from given data. 2.6 Changes Explain the concepts of limiting factors and carrying capacity in the context of population growth. Gross secondary productivity (GSP): The total gain by consumers in energy or biomass per unit area per unit time through absorption. Net secondary productivity (NSP): The gain by consumers in energy or biomass per unit area per unit time remaining after allowing for respiratory losses (R). Carrying capacity is the maximum number of organisms that an area or ecosystem can sustainably support. It is dependent on the resource allocation of an ecosystem and the extent of the competition for those resources. Limiting factors are factors that limit the distribution or numbers of a particular population. Population limiting factors: Example: In a seagull colony space for breeding sites may be the limiting factor that regulates how large the population can grow and so the Carrying capacity of that habitat would be set by the availability of suitable nest sites. 10 Describe and explain “S” and “J” population growth curves. S curves are associated with exponential growth but above certain size the growth rate slows down gradually, finally transforming into a population of constant size. Numbers stabilize at the carrying capacity of the environment. S curve example: J curves show a rapid increase and a boom pattern. At first population grows exponentially and then it suddenly collapses. Collapse is called dieback. Often in this type of curve population exceeds the carrying capacity before it collapses. This is called overshoot. J curve example: 11 Describe the role of density-dependent and density-independent factors, and internal and external factors, in the regulation of populations. Describe the principles associated with survivorship curves including, K- and rstrategists. Describe the concept and processes of succession in a named habitat. Explain the changes in energy flow, gross and net productivity, diversity, and mineral cycling in different stages of succession. 2.7 Measuring Changes in the System Describe and evaluate methods for measuring changes in abiotic and biotic components of an ecosystem along an environmental gradient. 12 Describe and evaluate methods for measuring change in the abiotic and biotic components of an ecosystem due to a specific human activity. Describe and evaluate the use of environmental impact assessments (EPAs). 13