Ecosystems Notes PDF

Bio20 Ecosystems Notes Bushell Ecology Relationships between biotic and abiotic aspects of an environment. Ecosystem Ecology – how larger-scale organisms interact with one another in their environment to...

Bio20 Ecosystems Notes Bushell Ecology Relationships between biotic and abiotic aspects of an environment. Ecosystem Ecology – how larger-scale organisms interact with one another in their environment to cycle energy and matter. In ecosystems & communities, equilibrium is dynamic. o Fluctuations are normal but factors usually stay within a range that supports the success and survival of living things. Ecologists decide what ‘scale’ they are interested in studying. Biosphere – living part of earth as a whole o Hydrosphere, lithosphere, atmosphere Biomes – regions of earth that have characteristics temperatures, level of precipitation & biotic communities o Aquatic & terrestrial Ecosystem – smaller region with a somewhat defined group of biotic and abiotic factors. Community – a group of interacting populations of organisms. Population – a group of organisms of the same species in the same place at the same time. Organism – one individual member of a species Ecosystem Terminology Organisms play different roles in their communities & ecosystems. o Role is typically defined by diet o Niche – role an organism plays & the habitat it occupies ‘Diet’ Types Autotrophs – make their own nutrients. o Support all other organisms in the community o Photoautotrophs – make food through photosynthesis o Chemoautotrophs – use heat & inorganic molecules to make food through chemosynthesis Heterotrophs – must consume other organisms to meet their needs Trophic Levels The suffix ‘troph’ means ‘feeder’ Trophic level refers to an organism’s position in their food chain/web. o Based on what they feed on or who feeds on them Producer – autotrophs o typically form the base of the food chain/web Consumer – heterotroph o Primary consumer – eat the autotrophs. Herbivores. o Secondary consumer – eat primary consumers. Carnivores. o Tertiary consumer – eat secondary consumers, may be apex predators. o Quaternary consumer – may exist, but only in ecosystems with lots of energy. Apex predators. 1 Bio20 Ecosystems Notes Bushell Detritivores – eat dead or decaying material. o Critical for waste recycling in ecosystems o E.g., cockroaches or millipedes Decomposers – similar to detritivores but break down material outside their bodies. o e.g., fungi secrete enzymes onto material then absorb small molecules Omnivores – feed on two or more trophic levels. o Can eat both animals and plants Ecological Models What are models? Demonstrations of how we believe systems to work Ecologists use models to track the flow of matter & energy from the abiotic environment, through the organisms in a system. Models are simplified versions of the natural world Food chains Simplest ecological model Illustrates one organism at each trophic level, starting with producers Arrows indicate the flow of matter & energy Removing one organism in the chain will have an affect on the others Food chain length is limited because of the second law of thermodynamics: o some energy is wasted at every transfer from one trophic level to the next. o This energy is ‘lost’ through chemical bonds in waste products, & some is used by the organism going about its business (looking for resources, escaping predators) Food chains are useful, and you need to be able to interpret them, but some ecosystem elements are missing in food chains. What are these missing elements?! Food webs Include a larger number of organisms More accurate because they illustrate more relationships but harder to interpret/ work with 2 Bio20 Ecosystems Notes Bushell Applications Tracking how energy & matter are transferred in an ecosystem allows us to identify the consequences of changes made to the environment. Biomagnification – when environmental toxins become concentrated the higher up you go in a food chain. Not to be confused with bioaccumulation (the buildup of a contaminant in one individual over time) Feeding the planet As global populations continue to rise, feeding the world will become more challenging. As countries become more industrialized, the trend is toward including more meat in the diet. In terms of energy efficiency, more people could be fed on a plant-based diet…. Or…eat insects?! Ecological Pyramids Used to show the relative amounts of material/energy at each trophic level. Dimensions of each part of the pyramid are proportional to the amount of material/energy at that level. 3 types (numbers, biomass, energy) Pyramid of Numbers Number (n) of all the organisms at each trophic level (each may include multiple species). May be inverted or spindle-shaped because of the how the food chain is built and the size of the base organism. o One single large producer can support an entire food chain. o Numerous parasites (tertiary consumers) can live on a single host. 3 Bio20 Ecosystems Notes Bushell Pyramid of Biomass Shows the dry mass of materials present in each trophic level. May be inverted o Common in aquatic environments where producers & primary consumers are small. Pyramid of Energy Shows the amount of chemical energy present at each trophic level, typically in kJ or kcal. Always an upright pyramid because they illustrate the limit there is on energy transfer from one level to the next. 10% Rule Only 10% of the energy in one trophic level makes it to the next. You should be able to calculate how much energy from one level is transferred to the next. o (energy in 1st level) x 0.10 = energy in next level Where does the energy go?! Used by organisms within the level to do the things they need to do to survive o Find food, water, shelter, run from predators, mate… Lost from organisms in the form of chemical bonds o CO2 they breathe out, urine, feces Radiated out in the form of heat from mammals Ecological Feedback & Trophic Cascades Feedback Our bodies have numerous feedback and regulatory systems to keep us healthy and to maintain equilibrium. 4 Bio20 Ecosystems Notes Bushell Ecological feedback A healthy feedback system in ecology is when populations remain at the size that the environment can support (carrying capacity). Healthy feedback systems maintain moisture, energy & nutrient levels that fluctuate, but still support the community. There is biodiversity in healthy ecosystems & as many trophic levels as can be supported. Trophic cascades Occur when an organism is removed from an ecosystem Like a series of falling dominoes Example: wolves from Yellowstone o the wolves are a keystone species – animal at the top of the food chain that stabilizes everything below. Example: otters from the north pacific o When otters were removed, there was no predator to keep sea urchins in check. o As sea-urchin populations exploded, they ate all the kelp. o Kelp forests are a critical habitat for many ocean species. Ecosystem engineers Animals that modify the habitat in such a way that supports other organisms in the ecosystem. Beavers – turn rivers into rich wetlands that provide habitat for other organisms. These wetlands also filter water & enrich soil. Elephants – prevent trees in grasslands from taking over. Create channels for water in the rainy season. Trophic cascades can cause major problems in disturbed ecosystems BUT they also point to the most effective solutions. By restoring & protecting keystone species or ecosystem engineers, ecosystems can recover. Nutrient Cycling in Terrestrial Ecosystems Terrestrial ecosystems Founded on the productivity of primary producers. Energy transfer in the system comes from the amount of light energy photoautotrophs can convert into organic matter. Matter, energy and nutrients are passed up the chain as consumers eat the producers. o Nutrients in the soil are absorbed by plants and then assimilated by consumers. Soil Literal foundation of terrestrial ecosystems. Contains the substrate for rooting. Storage reservoir for nutrients plants need. Composition of soil Litter: top layer o Made of organic matter like dead leaves, grasses & feces 5 Bio20 Ecosystems Notes Bushell o Decomposers & detritivores occupy this layer, breaking down materials & making them more accessible to plants Topsoil: small rocks with partially decomposed organic matter known as humus o Typically, dark & rich in nutrients Subsoil: contains more rock and less organic matter Bedrock: solid rock that marks the end of the soil layer. o Often impermeable – water can sit above this layer in a reservoir Soil quality can influence diversity of the plant community & productivity of an ecosystem Plant community then dictates diversity of the animal community o Providing organic molecules that heterotrophs feed on o Creating micro-habitats that animals can specialize in More diverse plant communities = more niches available in the ecosystem Forest structure Nutrient cycles Nutrients move through ecosystems via absorption in the producers to the consumption & assimilation in consumers but also through abiotic processes. Some nutrients have large reservoirs (storage) in the biosphere. Abiotic processes like the hydrologic cycle can help move some of these nutrients around. The hydrologic cycle Precipitation – rain or snow Condensation – formation of clouds 6 Bio20 Ecosystems Notes Bushell Evaporation – L → G Transpiration – evaporation from stomata Percolation – moves through soil Leaching – water dissolves nutrients Watershed – land area that supplies water for a river/ body of water Water table – level of ground water under soil Runoff/ overland flow – when soil is saturated & water flows over top & into bodies of water Nitrogen cycle N is one of the most critical nutrients for plant growth o Essential component of chlorophyll o Required for making amino acids and proteins Largest reservoir is N2 gas in the atmosphere but cannot be used by organisms in this form o Plants can absorb nitrates (NO3-), ammonia (NH3), ammonium (NH4+), & sometimes nitrites (NO2-). Plants & animals can also assimilate organic forms of nitrogen, like amino acids Atmospheric nitrogen gas must be fixed into bio-available forms Terminology Nitrogen Fixation – converting N2 gas into biologically available nitrogen. o Lightning can provide the energy to bind N to the O in the atmosphere o Nitrifying bacteria can also fix N Nitrification – forming nitrates from other nitrogen sources (pretty much the same thing as nitrogen fixation) Nitrifying bacteria – can covert inorganic nitrogen into nitrates through an aerobic reaction. Often found in soil or on nodules on the roots of some plants. Denitrification – anaerobic. o The middle step of this process is forming nitrites from nitrates. The end of this process is the formation of N2 gas which is no longer available. o Part of the process but not directly beneficial to living organisms. Ammonification – formation of ammonia from other nitrogen sources like urine or feces or decomposing organic matter (proteins). 7 Bio20 Ecosystems Notes Bushell Phosphorous cycle No P is stored in the atmosphere, main reservoir is in sedimentary rock P is biologically available in the form of phosphate (PO43=). o Phosphate is found in cell membranes, nucleic acids, and in calcium phosphate (in bones & shells) There are 2 interacting cycles that move phosphorous: o Short cycle – moves P around in a food chain o Long cycle – involves geologic activity Animal waste (i.e., bird & bat feces) is a rich source of P o Can easily be absorbed and assimilated by plants and then animals Another source of P is from the broken-down shells of marine animals. When this phosphorous is sunk out of the ecosystem it is referred to as sedimentation When sediments are compacted, the P becomes stored long-term in rock formations o Only large-scale tectonic activity can push the rock up in a process called uplift or upwelling and expose it. When rock is exposed, erosion or lichen can release the stored P so that it can be absorbed by plants. o This process is called weathering ▪ Lichens complete this process by secreting enzymes onto the surface of rock to liberate nutrients Law of the minimum Describes the concept that the nutrient that is in the least supply is the one that provides the limitation Phosphorous is the most limiting nutrient in aquatic environments meaning it will restrict overall productivity and growth. Example: if a phytoplankton requires 10 C, 6 N & 4 P but 30 C, 18 N & 5 P are available, only ONE phytoplankton can be produced o There is enough C & N for three phytoplankton, but only enough P for one 8 Bio20 Ecosystems Notes Bushell Eutrophication P is a common component of fertilizer and was a common component of detergents. Contamination of water bodies with P often leads to a process called eutrophication. Aquatic Ecosystems Physical Factors Affecting Aquatic Ecosystems Depth – determines the amount of light that will reach the soil. o Deeper bodies of water will have aphotic (lightless) zones. ▪ Aphotic zones cannot rely on photosynthetic organisms in their food chain. o Shallow waters are photic zones, they can be highly productive given the amount of light. Turbidity – a measure of clarity. o dirt, silt, phytoplankton, & algae can call make the water turbid o Turbid areas are likely to have cellular respiration (decomposition) outpace photosynthesis. o Measured using a secchi disk. 9 Bio20 Ecosystems Notes Bushell Soil – regions that have light and soil are going to support more organisms. Aquatic plants can root into the soil and obtain nutrients o These plants provide a greater diversity of habitats Benthic zone – soil region in the aphotic zone o Benthos – organisms that live in this zone Littoral zone – where light reaches the soil (photic zone) Where there is only open water is the limnetic zone (photic) or the profundal zone (aphotic). Motion – flow rate, rapids & ripples stir up the water o may make choppy water difficult for organisms to live in but also increases the amount of dissolved gases. Temperature – cooler waters contain more dissolved gases & are more nutrient rich and productive. o Warmer waters are more hospitable & favor reactions in organisms’ bodies, but nutrients become depleted easily. Density – water is most dense at 4oC o Because of this, bodies of water become stratified (layered) as different regions will have different temperatures, and therefore, different densities. o Water at 0oC (ice) is also less dense than the less cool water, so it floats ▪ Life can be supported underneath winter ice Lakes in Temperate Zones Stratified because of differences in temperature and density. Layers are separated by a region of steep temperature change known as the thermocline. o Summer: water lies above the thermocline in the epilimnion ▪ nutrients are locked at the bottom of lakes in the hypolimnion 10 Bio20 Ecosystems Notes Bushell Mixis or turnover occurs in the fall & spring which pushes nutrients up and around o provides nutrients to limnetic organisms & oxygen to benthic organisms Chemical Factors in Aquatic Ecosystems N & P from fertilizers can runoff into aquatic ecosystems & result in eutrophication. o As organisms die, their bodies settle & decompose at the bottom of the lake reducing the depth of the lake. o Shallower lakes are more productive, which leads to more decomposing matter. o Over time, lakes become shallow, murky, anaerobic & less diverse. Deep lakes are called oligotrophic & have oxygen rich waters but fewer phytoplankton & algae. Eutrophication over time is natural but excess fertilization runoff can lead to algal blooms which block out sunlight, limit productivity & reduce the amount of oxygen available. pH – influenced by geologic surroundings, runoff, plant life & pollutants such as sulfur compounds. o Narrow range can support life o Low pH can be damaging to tissues Dissolved Oxygen – amount of oxygen available to organisms for cellular respiration. o Influenced by motion of water, temperature & amount of producers Biological Oxygen Demand – amount of oxygen required by organisms. o Higher when there is lots of decomposing material because decomposers use up oxygen fast and reduce the amount available for others Estrogen (mimics): compounds like bisphenol-A act as estrogens & can feminize aquatic species due to persistent exposure, especially during development. o from birth control pills – contaminate waterways (any medications can) ▪ These compounds are small and difficult to remove so often remain in water even after it has been treated Biological Indicators of Health Coliform Bacteria – water contaminated with coliforms means there is a relatively large amount of feces in the water because this bacteria reside in the digestive systems of animals (humans too). o Indicative of larger water contamination problems Aquatic Invertebrates o Pollution tolerant o Pollution intolerant 11 Bio20 Ecosystems Notes Bushell Amphibian Indicators (frogs, salamanders, etc.) o Complete gas exchange through their skin so they are very susceptible to changes in the chemical environment o Life stage includes aquatic & terrestrial forms – if quality of either declines, amphibians will be affected o Eat different foods at the larval stage than adult stage so will be influenced by materials at different points in a food chain o External development – exposed to contaminants in the water o Rely on moisture – many habitats are drying up and warming up and this also makes them more prone to fungal infections 12