BSC 116 BSC 116
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This 9 page Class Notes was uploaded by Ashley Bartolomeo on Friday April 29, 2016. The Class Notes belongs to BSC 116 at University of Alabama - Tuscaloosa taught by Professor Harris in Spring 2016. Since its upload, it has received 13 views. For similar materials see Principles Biology II in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 04/29/16
Lecture 39 Ecosystems Overview Ecosystems: biotic + abiotic interactions o Flow of energy o Cycling of nutrients Human impacts on global ecosystem Ecosystems Are Different from Communities in that we Consider Abiotic Factors as well Ecosystem: sum of biotic and abiotic interactions in an area o Ranges from microhabitat to whole earth Two abiotic factors most interest us: o Flow of energy: energy (usually sunlight) transformed to chemical transformed to chemical energy by autotrophs, all eventually lost as heat o Cycling of nutrients: elements continually recycled; move between ecosystems Inputs: e.g., minerals from dust & rainwater, nitrogen from Nfixation Outputs: e.g., gases lost to atmosphere, water Generally, in/outputs small relative to amount recycled Both Energy & Nutrients Move Thru Trophic Levels Primary producers: autotrophs; e.g., plants o Also ecosystems based upon chemoautotrophs: e.g., hydrothermal vents Primary consumers: herbivores that producers Secondary consumers: carnivores that eat herbivores Tertiary consumers: carnivores that eat carnivores Detritivores/ decomposers: get energy from detritus (nonliving organic material) o Convert organic molecules into inorganic forms that producers can use o Important for recycling nutrients Production is Ultimately Limited by the Amount of Energy That Enters the System Primary production: amount of light energy converted to chemical energy in a given span of time There is a finite amount of energy available to ecosystems; all of it results from 1 production o Total sunlight to earth: 10^22 J = (1 N x m = 0.239 cal) Intensity varies with latitude o Minus the light that hits stuff that doesn’t photosynthesize o Minus light of wavelengths not absorbed by photopigments: ca. 99% (reflected, lost as heat) o What’s left available for 1 production: 150,000,000,000,000 kg organic matter per year Gross primary production (GPP): total 1 production for an ecosystem Net primary production (NPP): part stored as organic matter o NPP = GPP – respiration o This is the energy available to higher trophic levels o Expressed as either energy (J/m^2/yr) or biomass (g/m^2/yr) o NOTE: new biomass, not the same as standing crop Use light reflected back to satellites to measure how much is being absorbed by chlorophyll: chlorophyll = plant cells = net primary production o Terrestrial: highest in warm, humid, tropical areas o Oceans: not that productive The Transfer of Energy Among Levels is Inefficient Secondary production: new biomass added to consumers; amount of 1 production converted to consumer Most 1 is not eaten by herbivores (usually) Most of what they do eat no assimilated o E.g., feeding caterpillar: only 33 of 200 J eaten made into new tissue (2 production) Most lost as feces Rest used for respiration (used, rather than stored) o What’s eaten but not assimilated is lost as heat (even feces, by detritivores) % production efficiency = net 2 prod./assimilated 1 prod x 100% o Portion of assimilated 1 prod. (energy used by animal; growth + respiration) that is used for growth o Endotherms (birds, mammals) have low efficiency: 13% o Ecotherms (fish, inverts): 1040+% Trophic efficiency: % production transferred up to the next level o Whole trophic levels, not species o Considers the production that is not eaten by next level o About 90% of production at one level not transferred up o Only 0.1% primary production reaches 3 consumer: why food webs are so short o Can express pyramid of net production; measured in J Can also think of biomass pyramid of standing crop (not production) o Sometimes inverted in aquatic systems: 1 prod. By 1celled algae; rapid turnover Nutrients Are Limiting in Ecosystems Light ultimately limits 1 production: if plants had all the nutrients they needed, photosynthesis limited only by light Limiting nutrient: if adding a nutrient increases productivity, then it is limiting o i.e., production is limited by its availability o e.g., phytoplankton production off Long Island N limited but not P limited o Eutrophication: increased algal production due to pollination (sewage, fertilizer) Freshwater usually P limited Results in drop in oxygen N & P also limited in terrestrial environments o That’s why fertilizer works Different Nutrients Have Independent Biogeochemical Cycles Nutrient cycle thru ecosystems o Biogeochemical cycles: both abiotic and biotic o Inputs/outputs o Nutrients sometimes present but unavailable Nutrients can be available or unavailable, organic or inorganic o Transferred among “reservoirs” o Reservoir A: living animals (available, organic) o Reservoir B: fossils (unavailable, organic) o Reservoir C: air, water soil (available, inorganic) o Reservoir D: rock (unavailable, inorganic) The 4 most important nutrient cycles: H2O, C, N, P Decomposition critical for cycling o Detritivores break down organic molecules to inorganic so they can be used by 1 producers o Rates depend upon production in detritivores: faster in warm, humid Tropical forest: most nutrients in living things; 10% in soil Temperate forest: up to 50% in soil o No detritivores, no decomposition E.g., bottom of anoxic peat bog, no decomposition There Has Been a LongTerm Study of Nutrient Cycling at Hubbard Brook Hubbard Brook Experimental Forest (New Hampshire): forested mountainside with several separate valleys o Each valley has a similar ecosystem o Each valley has its own creek draining it: can compare nutrient outputs o Can modify them for experimental purposes E.g., cut down all the trees in the valley o Increases water flow 3040% o Increases nutrients lost by the ecosystem 4x more Ca lost 15x more K lost 60x more nitrate lost o Lesson: standing plants control outputs These kinds of long term, large area studies are needed to understand the natural functioning of ecosystems We have also conducted a lot of accidental experiments: changed the biotic and abiotic interactions in ecosystems, resulting in a change Humans Enrich the Nitrogen Cycle for Agriculture Farming removes N from soil o When land is first cleared, it has N in soil “Fertility” varies with preagriculture habitat Temperate grass land: lots of soil, lots of N that lasts decade Tropical forest: little soil, little N lasts a few years o Crops grown, removed: N is removed N ends up somewhere else: sewer o New N must be added to get same yield: fertilizer We’ve doubled the amount of N available to 1 production Excess (amount that exceeds critical load, no long limiting) runs off into rivers o Added to sewage and other N waste o E.g., extra N leads to algae blooms in Gulf of Mexico; excess 1 leads to )2 depletion: “dead zone” Can be mitigated by using less fertilizer, although it takes a long time to recover Lecture 40 Conservation Biology Overview Human population growth Human effects on populations, communities, and ecosystems Major treats to biodiversity o Habitat loss o Invasive species o Overexploitation o Global change There Are Multiple Threats to Biodiversity 1. Habitat loss and destruction: a. Biggest threat to biodiversity b. Caused 73% of known extinctions c. Fragmentation of habitats fragments populations 2. Introduced/ exotic species a. Increase in global travel led to increase in introduced species b. Non native species alter communities and ecosystems 3. Overexploitation a. Especially fisheries and large mammals b. Harvested at rates faster than they can reproduce 4. Global change a. Change in climate and atmospheric chemistry Global Human Population Size: positive growth but no longer exponential Annual percent increase in global human population size (no longer exponential) Human population growth and age structure varies by country depending on whether they are industrialized or developing o Demographic transition: switch from high birth and death rates to low birth and death rates in a given country, tends to accompany industrialization and improved living conditions Ecological Footprint Measures Human Impact Calculates how much land and water resources we consume to grow food, support lifestyles and assimilate waste; can also be measured as energy consumption Can be used to show changes in in impact through time and space The Goal of Conservation Biology is to Conserve Biodiversity, and Mitigate Negative Effects of Humans on Ecosystems Biodiversity = biological diversity Anthropogenic (human caused) ecosystem modification is causing increased extinction rates o Always some extinction, but more species going recently Why worry about conserving biodiversity? o We have an innate tie to nature: biophilia o We have an obligation to future generations o We are still discovering useful things we can get from species E.g., Malagasy rosy periwinkle has caner fighting substances E.g., the value of prokaryotes, like Thermus aquaticus, to biotechnology o Provide us with useful services: ecosystem services E.g., clean, detoxify waste, pollinate crops Provide services that would cost $$ o Those species that we rely on are in communities with other species Conservation Biologists Are Concerned with the Loss of Biodiversity at Multiple Levels Most often hear about extinction of species o USA Endangered Species Act, endangered species is “in danger of extinction throughout all of a significant portion of its range” o 12% (1200/10,000) birds endangered globally o 21% of the 5500 describes species of mammals are endangered o 730 endangered (200 extinct) plant species in US (of 20,000) o In US extinction of freshwater animals 5x greater than terrestrial Preservation of species genetic diversity o Within & among population variation: necessary for future adaption to changing environment o Loss of genetic diversity reduces adaptive potential of the species Community and ecosystem diversity: fates of species interconnected o Protect habitats, protect species Often More Efficient to Focus on Landscapes and Habitats than on Species Protecting species o Easy because here is something to point at o Hard because species sometimes not cute o Hard when jobs/money at stake Can protect areas instead: multiple species o Set aside to protect against fragmentation “Edges” change habitats, communities Lots of little not same as one big o Sometimes difficult to stop development, agriculture Can focus on biodiversity hot spots: smaller areas with lots of diversity o 1.5% of land on Earth has >30% of all plant & animal diversity o But, what’s a hot spot for one taxon, might not be for another Used to set aside land to keep it pristine o Based on old stability, “balanceofnature” thinking E.g., Yellowstone, old policy of putting out fires o Now, importance of disturbance to maintaining diversity Not only on land, marine reserves as well Occasionally, We Need to Step in when Ecosystems too far Gone Extremely damaged ecosystems may need repair before they can be restored o E.g., turning openpit mine to salt marsh takes bulldozers Bioremediation: using plants, fungi, prokaryotes, etc. to detoxify an area o In contaminated areas, plant plants that can take up the contaminants; then harvest the plants o Or with bacteris E.g., species used at Oak Ridge National Lab that converts soluble to insoluble uranium; can’t leak to ground water Biological augmentation: use organisms to add compounds to ecosystem o E.g., plant legumes to increase N in soils until native plants get established Sustainable Development is Good Planning If we want to preserve biodiversity, then development needs to be balances with sustainability o Long term instead of short term planning o E.g., not paying in the future vs. profit now Costa Rica has done both: protected its lands AND increased quality of life o Zoned reserves: have surround by “buffers” that separate Protected areas with areas set aside for regulated human populations, limited logging, etc. Buffers soften edge effects Protects 80% of native species Not perfect, but still good Since 1960: no loss of protected forest but lots of buffer forest gone Threatens to isolate parks o Since 1930s: infant mortality down, life expectancy up Requires long term planning o Think about ongoing sustainable development discussions… Lecture 41 Biodiversity & Conservation Overview Major threats to biodiversity o Habitat loss o Invasive species o Overexploitation o Global change Threats to Alabama’s biodiversity There Are Multiple Threats to Biodiversity 1. Habitat loss and destruction: a. Biggest threat to biodiversity b. Caused 73% of known extinctions c. Fragmentation of habitats fragments populations d. E.g., Mobile River: center of freshwater mollusk diversity; 40 species extinct 2. Introduced/ exotic species a. Increase in global travel led to increase in introduced species b. Non native species alter communities and ecosystems c. Some introduced by accident: stowaways i. E.g., brown tree snake Guam: 12 birds, 6 lizards extinct d. Some introduced on purpose i. E.g., kudzu introduced to stabilize sediments ii. E.g., various insects introduced as biological controls (predators, etc.) e. E.g., San Fransisco Bay establishes a new invasive species every 14 weeks, arrive via shipping 3. Overexploitation a. Especially fisheries and large mammals b. Harvested at rates faster than they can reproduce c. E.g., hunting of elephants, rhinos and whales 4. Global change a. Change in climate and atmospheric chemistry b. Climate change c. Acid rain Human Activities that Cause Habitat Degradation and Loss Agriculture – primary cause of ecosystem change Natural resource extraction (mining, logging, fishing) Urbanization and infrastructure development War and violent conflict Pollution Consequences of Pollution Besides Habitat Degradation: Toxins Accumulate in Top Predators Humans add lots of synthetic chemicals to ecosystems o E.g., pesticides like DDT, industrial chemicals like PCBs (polychlorinated biphenyls) o Not broken down by detritivores o Biological magnification: becomes more concentrated in higher trophic levels E.g., DDT (insecticide) used in USA from 1950s to 1970s o Accumulated in birds of prey, like bald eagles o Leads to weak egg shells o Still use DDT in Africa where malaria (spread by mosquitoes) a serious human health issue; tradeoffs Also release naturally occurring chemicals at unnatural levels o E.g., mercury from plastic manufacture, coal burning o Accumulates in predators, especially fishes Mitigated by regulating wastes, but may take decades to degrade Invasive Species Invasive species: an introduced species that establishes, expands its range, and has a substantial impact on native organisms & ecosystems Invasive Species Can Interact with Natives in Many Ways As competitors, predators and parasites Overexploitation Hunting Fishing Fisheries by catch Collecting for trade Can lead to a decrease in species abundance and ultimately extinction of the species Burning Fossil Fuels Creates Acid Rain Burning fossil fuels (oil, coal) releases S and N o Combines with water to make sulfuric and nitric acids o Leads to acid rain: pH < 5.2 o Lowers pH of water bodies in areas with weakly buffered water (less bicarbonate to neutralize it) Lower pH kills acidsensitive fishes o E.g., lake trout: keystone predators; drastically alters ecosystems Sources of pollution distant from the effects o E.g., 1960s factories Midwest killed lakes in eastern Canada Can be (has been) mitigated thru tougher regulations on emissions: still takes a long time to recover Chemicals we Release can also Alter Abiotic Factors CFCs (chlorofluorocarbons) used in refrigeration, air conditioners o Escape to atmosphere, Cl reacts with ozone (O3) 1725 km up o Ozone breaks down to O2 The layer of ozone in the atmosphere absorbs UV radiation o Less ozone means less UV protection Results in a large “hole” in the ozone, especially over Antarctica (and Australia, New Zealand, South America) o Less of an effect at middle latitudes Increased UV radiation leads to DNA damage in plants and animals o Predicted to result in increased skin cancers, lower crop & natural productivity Mitigated by banning the production of CFCs in 1987: has had measurable effect on ozone layer o Will take 50 years for Cl to cycle out Excess CO2 in Atmosphere from Burning of Fossil Fuels Associated with Increasing Global Temperatures Before the Industrial Revolution, [CO2] = 274 ppm o Now it is over 380 ppm o This is highly correlated with increased global temperatures CO2, CH4, H2O, etc. naturally warm the Earth Greenhouse Effect o Greenhouse gases have the same effect Solar heat retained The global warming trend on Earth has had greatest effect at high latitudes o Less polar ice means more absorption of heat (exacerbates warming) o Increase in the incidence of fires (exacerbates CO2 increase) o Predicted to lead to: Changes in precipitation patterns: aridification in some place, more water in others Increase in sea level from melting polar ice Extinctions as organisms can’t adapt to rapid change Can be mitigated by regulating CO2 emissions, but people fear change and expected economic impacts
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