III. Ecosystem Def. - the combination of biotic and abiotic components through which energy flows and materials cycle (usually a self-contained unit, such as.
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III. Ecosystem Def. - the combination of biotic and abiotic components through which energy flows and materials cycle (usually a self-contained unit, such as a pond, swamp, meadow, or woods) A. Energy Flow 1. Ultimate source - SUN - 50% of suns energy reaches surface of earth - 0.1 % of that ends up in living organisms 2. Trophic levels (food chain or web) a. Producers (autotrophs) - first trophic level , primarily plants on the land and algae in the water (99% of all organic matter is at this level) Gross primary productivity (light energy converted) - Cost of metabolic activity (cell respiration by plant) Net primary productivity* (energy stored in chemical compounds) *when positive, there is an increase in biomass (total dry weight of all organisms being measured) b. Primary consumer (heterotrophs) (herbivores) c. Secondary consumer (carnivores), eat herbivores [There a four levels of consumer in most food chains] d. Detritovores - live on the refuse of the ecosystem, i.e. dead leaves, branches, carcasses, feces, etc. i. Scavengers - consumers of dead prey - vultures, jackals, crabs, earthworms ii. Decomposers - specialized organisms that get at the trapped chemical energy - fungi, bacteria 3. Efficiency of energy transfer a. In Cayuga Lake in New York 1000 calories of light yields 150 calories of algae, which yields 30 calories of smelt, which yields 6 calories of trout, which yields 1.2 calories of human b. Energy flow pyramid (“10% rule”) Food Web A given species may feed at more than one trophic level Decomposers (fungi + bacteria) complete the food web – use energy left in dead bodies Keystone Species Impact of Keystone species is greater than would be expected from relative abundance! Example: Pisaster starfish – predator of mussels Removal of starfish decreases biodiversity (dominated by mussels) Keystone species If they are removed, community structure is greatly affected. B. Biological magnification - increase in the concentration of toxins as those toxins move through the food chain (DDT, PCB’s) Bioaccumulation Energy Flow An ecosystem’s main decomposers are fungi and prokaryotes, which secrete enzymes that digest organic material and then absorb the breakdown products. Primary productivity NPP = GPP – Rs Net Primary Productivity = Gross Primary Productivity – Energy used for Respiration 6 CO2 + 6 H2O C6H12O6 + 6 O2 Primary Productivity expressed as biomass (weight) of vegetation added per unit are/unit time The amount of light that is converted to chemical energy by photosynthesis per unit time. Biomass Secondary Productivity 2/3 of ingested food is used as fuel for cellular respiration (inorganic waste and heat are byproducts) Only chemical energy stored as growth (33J) is available as food to secondary consumers Also, keep in mind, only a small fraction of producers is consumed. The amount of chemical energy in consumer’s food that is converted to their own new biomass during a given period of time. Pyramid of Net Productivity Average of 10% of energy transfers to next trophic level Carnivores – more efficient at converting food into biomass (meat is more digestible) BUT need more energy for C.R. and B.T. (endotherms) Only 1% of sun’s energy is converted into primary productivity Biomass Pyramid Pyramid of Numbers Explains why food webs usually include only 3-5 trophic levels not enough on the top level to support another level Implication: Fewer predators more susceptible to extinction + evolutionary consequences (e.g. genetic drift) C. Ecological succession- the succession of communities that follows the disturbing of and area (plowing, landslide, volcano, fire) Characteristics 1. Increase in total biomass 2. Gradual decrease in net productivity 3. Mature systems have a greater capacity to entrap and hold nutrients 4. Number of species increase 5. r-species early K-species late [Climax community = final stable stage] [Current thinking is that this model is simplistic and incomplete, that disturbances themselves drive succession throughout the process.] 1 10 2 20 5 Primary Succession Example: After glacier has retreated or new volcanic island Lichens (symbionts of fungus + algae) colonize first and cause development of soil Pioneers of soil builders Secrete acids that erode rock Small plants (grasses and mosses), shrubs, trees follow Succession Secondary Succession Example: Fire Grasses grow first, then trees and others Much faster than primary succession Climax Community Soil concentrations of nutrients show changes over time. Fig. 53.20 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Human Disturbances Logging & clearing farmland reduced and disconnected forests Agricultural development disrupted grasslands Overgrazing and agricultural disturbance current famine in Africa Problem: Early stages of succession, characterized by weedy and shrubby vegetation may persist for many years! D. Biogeochemical cycles - the cycling of chemicals through the biotic and abiotic portions of the ecosystem 1. Water cycle Hydrolytic Cycle Global Carbon Cycle Carbon Cycle, Greenhouse Effect CO2 in atmosphere What step of photosynthesis? Carbon Fixation Calvin Cycle (dark rxn) 3. Nitrogen cycle, Acid Rain Remember, N is important component of ___________________ Amino acids/proteins + ______________) Nucleic acids Nitrogen Cycle, 2 Artificial Fertilizer available N minute majority Rhizobium Eg Lichen 4. Phosphorus cycle, 2 Phosphorus Cycle P not in atmosphere, comes from rocks in form of PO4 3- Local cycling Through food web Excretion + Detritus Sedimentary Cycle: Sedimentation locks away PO4 3until uplifted in geological processes IV. Terrestrial Biomes (life zones) A. Def. - geographical areas distinguished by particular dominant plant types B. Characteristics 1. Not a place, but a class of plants 2. Determined by climate 3. Boundaries are indistinct 4. Convergent evolution common between similar biomes Terrestrial Biomes Tutorial Coral Reefs of the World Abyssal Zones 1. The mid-ocean ridge system with well known deep-water hydrothermal vent (ellipses) and cold seep (oblongs) regions. Vents: 1, Mid-Atlantic Ridge; 2, East Pacific Rise; 3, Galapagos Rift; 4, NE Pacific; 5 and 6, W Pacific back-arc spreading centres; 7, Central Indian Ridge. Cold seeps: 1, Gulf of Mexico; 2, NW Africa; 3, Laurentian Fan; 4, Barbados accretionary prism; 5, Monterey Bay; 6, Oregon subduction zone; 7, Sagami bay. V. Aquatic Biomes (life zones) A. Primary ecological subdivisions of organisms 1. Plankton - at mercy of currents, weak or nonswimmers (small or microscopic) a. Phytoplankton - primary producers, (cyanobacteria or diatoms) b. Zooplankton - protists and small animals (larval stages) 2. Benthos - bottom dwellers (sessile, walking, or burrowing) 3. Nekton - larger, strong swimmers (top of the food chains) B. Freshwater 1. Zones a. Littoral zone - near shoreline, richest in life b. Limnetic zone - open water, sparse life c. Profundal zone - deep. anaerobic, no light, detritovores, mineral rich 3. Types of lakes a. Oligotrophic - nutrient-poor, deep, sandy or rocky bottom, clear b. Eutrophic - nutrient-rich, phytoplankton very productive, shallow, murky Oligotrophic lake Eutrophication (lake aging) Eutrophic lake C. Marine life zones 1. Estuaries and salt marshes - where rivers (freshwater) meets saltwater of ocean - most fertile water in the world, breeding grounds for many fish, nutrients from rivers meets constant mixing of tides (plants) 2.Intertidal zone - between high and low tides, rich in life forms (barnacles, clams, crabs), tidal pools 3.Subtidal zone - sea stars, sea urchins, worms, crabs, flounder 4.Neritic zone - over continental shelf (nekton and most benthic organisms are here (food is here) [photosynthetic limit - 200 meters] 5. Pelagic zone – includes neritic and open ocean 6. Benthic zone - deep waters, mostly predators Ponds and Lakes Run off of water from terrestrial habitat accumulates in landlocked basin Warmer Colder/Denser Detritus sinks – Dead organic matter decomposed into minerals Decomposers use much O2 Lake Turnover H2O is most dense at 4oC sinks Warmer water in bottom, ice on top Surface cools, water sinks, mixing Ice melts water sinks, mixing O2 + nutrients Warm on top, thermocline, cold on bottom Oligotrophic and Eutrophic Lakes Classified according to production of organic matter Oligotrophic - Deep, shortage of nutrients limits phytoplankton growth clear water and O2 rich, not much life Eutrophic – shallow, nutrient rich, productive phytoplankton, murky waters O2 depletion Cultural Eutrophication Oligotrophic can become Eutrophic Runoff brings in large amounts of mineral nutrients and sediment This process is sped up with human activities called “cultural eutrophication”: - fertilizer run off - dumping of wastes Too much N and P overpopulation of algae and detritus depletion of O2 Streams and Rivers Headwaters – origin (spring or snowmelt) – clear, cold, clear Mouth – warmer, murkier, sediment picked up Fallen leaves organic compounds Erosion of rock inorganic compounds Current O2 mix no stationary plankton Producers - mainly attached algae, rooted plants, organic matter carried in run off Marine Zones Shallow zone where terrestrial habitat meets ocean’s water Beyond continental shelf From intertidal to edge of continental shelf Light supports photosynthesis Open waters of any depth seafloor No light penetration Estuaries Many marine invertebrates and fish use estuaries as breeding ground or migrate through them crucial feeding areas s.a. for waterfowl Many estuaries receive pollution Intertidal Zones Structural adaptations for attaching to rock Adaptations: Holdfast – rootlike, maintains position Blades – large surface area Floats – buoyancy Cellulose cell walls (and gels) – support against mechanical force of waves and prevent dessication Calcium carbonate – retard grazing Review: Adaptations of Seaweed? Coral Reefs Review: Corals Animalia Kingdom ___________ Phylum ____________ Cnidaria Radial Symmetry __________ Skeleton _______ CaCO3 Calcium carbonate Review: Dinoflagellates – components of phytoplankton Protista Kingdom ___________ Algae Type Single-celled ______________ Oceanic Pelagic Biome Pelagic Zone Benthos Deep sea vent communities -hot magam superheat water -Chemoautotrophic producers oxidize H2S (from H2O and SO4 2- ) -Giant tube dwelling worms shown here live symbiotically with chemoautotrophic bacteria What other domain thrives in extreme temperature conditions? Archaebacteria - Thermophiles Population Dispersion Clumped dispersion is when individuals aggregate in patches. -Resources concentrated in patches -Associated with mating or social behavior Population Dispersion Uniform dispersion is when individuals are evenly spaced. -Antagonistic interactions -Competition for resources (light, food) -Social interactions (territorial boundaries) Fig. 52.2b Population Dispersion In random dispersion, the position of each individual is independent of the others, NOT common in nature Overall, dispersion depends on resource distribution. Population Equations N/t = B-D Change in population size during time interval = Births during time interval – Deaths during time interval Can be rewritten as: N/t = rN OR dN/dt = rN where r = change in per capita birth and death rates(B-D) And N = population size If B = D then there is zero population growth (ZPG). If r > 0, population increasing If r <0, population decreasing Exponential population growth – under ideal conditions maximum growth rate for the population (rmax) dN/dt = rmaxN Exponential Growth Opportunisitc species often exhibit periods of exponential population growth – referred to as rselected species b/c their growth rates are close to rmax Logistic Growth Logistic Growth: dN/dt = rmaxN(K-N) K As N approaches K (carrying capacity), growth rate slows due to limited resources Logistic Growth Question: What factors determine K? Carrying capacities are determined by availability of: -Food resources -Nesting sites -Shelters -Refuges from predators -Accumulation of toxic wastes (yeast) Logistic model shows intraspecific competition – members of same species compete for limited resources r declines Population dynamics reflect a complex interaction of biotic and abiotic influences Why does logistic growth not necessarily apply to real populations? It is a model which provides a basis from which we can compare real populations. Population Cycles Other populations have regular boom-and-bust cycles. A good example involves the lynx and snowshoe hare that cycle on a ten year basis. What could be causing these cycles? Could be predation (density dependent) Hypothesis: The more hares, the lower the nutrient content of the plants they eat (Plants start to produce defensive chemicals) Human Population Growth What type of growth? -Human population has been growing exponentially for 3 centuries -Prediction of about 7.3-10.7 billion by 2050 -Overpopulation? -Hard to estimate Earth’s carrying capacity -Important to regulate population growth! Agriculture over hunting/gathering life style Age Structure Age structure – relative number of individuals of each age - can reveal population’s growth trends, and point to future social conditions Regulating Population Growth Voluntary contraception Government intervention Delayed reproduction Potential Future Problems??? Solutions??? Survivorship Curves Competitive Exclusion Principle Species grown in isolation Species grown in competition Exploitation competition depresses population sizes and can lead to extinction 2 Effects of Interspecific Competition 1.) Resource Partitioning 2.) Character Displacement Resource Partitioning Different species of lizards occupy different microhabitats. One may live on sunny surfaces, another on shady branches. This limits interspecific competition. Role of Natural Selection perch site specializations Character displacement -Allopatric populations of potential competitiors similar beaks, use same resources -Sympatric populations different beaks 2 species have adapted to eating different sizes of seeds to avoid competition example of resource partitioning Defenses against Predation Plant Defenses against herbivores include: toxic chemical compounds Animal Defenses against predators: Behavioral Defenses: fleeing, hiding, self-defense, noises Camouflage includes cryptic coloration, deceptive markings Defenses continued Mechanical defenses include spines Chemical defenses include odors and toxins Aposematic coloration – indicated by warning colors sometimes associated with other defenses (toxins) Defenses continued Mimicry – organisms resemble other species Batesian mimicry – harmless species mimics a harmful one Mullerian mimicry – 2 or more unpalatable species resemble each other predators learn more quickly Symbiosis Type of Relation -ship Description Examples Mutualism +/+ In this symbiosis both organisms benefit. Termite and gut protist Grouper cleaning Commensalism +/0 In this symbiosis, one organism benefits, the other is neither helped nor harmed. Robin and oak tree Remoras & pilot fish ParasiteHost +/- In this symbiosis, one organism benefits (parasite) and the other organism (host) is harmed usually gradually but not killed. Cat and flea Athlete’s foot fungus and human Isopod on Soldierfish PredatorPrey +/- In this symbiosis, one organism benefits (predator) and the other organism (prey) is harmed usually dying immediately as it is eaten. Cat and mouse Lion and gazelle Shark Breach Competitio n -/- While engaged in competition, both organisms are being harmed. Intraspecific competition occurs within the same species Interspecific competition occurs between different species Lion and lion Lion and hyena Hermit Crabs Identify the Symbiosis: Ancient Farmers of the Amazon Octopus Camouflage Ants and Butterflies Shark & Loggerhead Mimic Octopus, 2 Mimic Octopus, 2 Interspecific Interactions Parasitism Lamprey parasite feeds on a larger fish Tapeworms steal food of host, which is weakened. Mutualism Cleaner shrimp and fish: Shrimp gets bits of food, fish get their teeth cleaned Hummingbird & Flowering Plant: Hummingbird gets nectar, plant gets pollinated Commensalism Epiphytes grow on top of other trees: Epiphytes get sunlight, tree is unharmed. Barnacles on whales: Barnacle gets a ride through nutrient filled waters, whale is unaffected Resources Animation Quizzes