Chapter 5: How Ecosystems Work 5-1 Energy Flow in Ecosystems Today’s Objectives: Demonstrate an understanding of Ch. 4. Describe how energy is transferred from the sun to producers and then to consumers. Describe one way in which consumers depend on producers. List 2 types of consumers. Explain how energy transfer in a food web is more complex than energy transfer in a food chain. Explain why an energy pyramid is a representation of trophic levels.

Life Depends on the Sun Nearly all energy in an ecosystem ultimately comes from the sun. Photosynthesis: plants use sunlight to make sugar (carbohydrates) CO2 + H2O + Sun  C6H12O6 + O2 Carbon dioxide + water + solar energy  glucose (sugar) + oxygen Carbohydrates: energy-rich molecules used by organisms. Chemosynthesis (an exception) Some deep-ocean bacteria can use hydrogen sulfide to make their own food without sunlight So, how do we burn this fuel??? Cellular Respiration – breaking down food to yield energy C6H12O6 + O2  CO2 + H2O + Energy

What Eats What in an Ecosystem Energy Source Examples Producer a.k.a. autotroph Makes its own food through photosynthesis or chemosynthesis Plants, algae, some bacteria Consumer heterotroph Gets energy be eating producers or other consumers Animals (mice, starfish, elephants, turtles, humans, ants), fungi, some protists and bacteria

Types of Consumers in an Ecosystem Energy Source Examples Herbivore Producers (plants) Cows, sheep, deer, grasshoppers Carnivore Other consumers (“meat”)` Lions, hawks, snakes, spiders, sharks, alligators, whales Omnivore Both producers & consumers (“meat & veggies”) Bears, pigs, gorillas, rats, raccoons, cockroaches, some insects, humans (most) Decomposer Breaks down dead organisms in an ecosystem and returns nutrients to soil, water, and air Fungi and bacteria

Energy Transfer Through Ecosystems Primary Productivity: amt. of organic material that the photosynthetic organisms of an ecosystem produce - Determines the energy budget (amount of available energy) of an ecosystem!

Trophic Level = Energy Level 1st T.L. = producers (plants, algae, bacteria) 2nd T.L. = primary consumers (herbivores- eat the producers) 3rd T.L. = secondary consumers eat herbivores (carnivores & omnivores) 4th T.L. = tertiary / top consumers (carnivores that consume other carnivores)

Food Chain: linear path of energy transfer through the trophic levels of an ecosystem ex. PlantRatSnakeEagle

Food Web: network of feeding relationships in an ecosystem Food Web: network of feeding relationships in an ecosystem *organisms usually feed at several trophic levels

Energy Transfers Between Tropic Levels are Very Inefficient Biomass: dry weight of living tissue used to determine the amount of energy present in trophic levels 10% Rule: On average, only 10% (90% less) of the energy or biomass in any trophic level will be incorporated into the next level.

Pyramid of Energy/Biomass: block diagram that portrays the flow of energy through an ecosystem.

Energy Loss Limits the Number of Tropic Levels in an Ecosystem Most terrestrial (land) ecosystems involve only 3 or, rarely, 4 trophic levels Too much energy is lost (mostly as HEAT) at each level to allow more levels!

Food Web & Pyramid Cut & Paste Groups of 2 Create - 1 Pyramid, 1 Web *arrows go from food source to food consumer* Label all – Autotroph, heterotroph, consumer, producer, decomposer, herbivore, carnivore, omnivore

5-2 The Cycling of Materials Biogeochemical Cycles: Materials Cycle (recycled/reused) Between Organisms and the Nonliving Environment Water, Carbon, Nitrogen, and Phosphorous are essential for life – each is recycled.

The Water Cycle It’s driven by the sun condensation: gas to liquid precipitation: water falls to the earth’s surface Runoff groundwater transpiration: “Plant Sweat” water evaporating from the leaves of plants respiration: organisms give off water vapor evaporation: liquid to gas How humans affect the water cycle: When forests are cut down, the water cycle is disrupted and less moisture is returned to the atmosphere.

The Carbon Cycle Linked to the flow of energy. Atmospheric CO2 (carbon dioxide) Carbon taken in by plants (enters the living portion of the carbon cycle) through photosynthesis. Heterotrophic Nutrition (animals eat plants) Organisms release CO2 through cellular respiration. Fossil Fuels (coal, oil, natural gas) – stored carbon left over from bodies of plants and animals that died millions of years ago Combustion – burn fossil fuels – releases CO2 back into the atmosphere Decomposition – carbon from carbohydrates in organisms (converted into fats, oils, etc.) is released into the soil or air after an organism dies – some can form deposits of fossil fuels carbonates - hard parts of bones & shells – don’t break down easily carbon sinks (carbon reservoirs {store more carbon than they release}) – over millions of years carbonate deposits produce huge formations of limestone rocks (one of the largest carbon sinks on Earth) - the ocean is also a carbon sink

How humans affect the carbon cycle: Burning fossil fuels releases CO2 into the atmosphere (cars, factories, power plants, forest fires, etc.). The amount of CO2 is steadily increasing and contributes to global warming (an overall increase in the temperature of the Earth). Deforestation (cutting down/burning forests) adds CO2 to the atmosphere as forests are burned (mainly to create agricultural land), and by destroying trees that take CO2 out of the atmosphere by photosynthesis.

The Nitrogen Cycle

The Nitrogen Cycle Nitrogen – needed by organisms (DNA, amino acids / proteins…) 1. Nitrogen Gas (N2) - 79% of air, BUT not usable by plants Part I: Nitrogen Fixation – making nitrogen gas (N2) into nitrogen that plants can use (ammonia, nitrates) 2. N2—lightning nitrates (dissolved in rain) 3. N2—heat/pressurefertilizer 9. N2—bacteriaammonia Part II: Food Web 4, 5. Absorption of nitrogen by Plants – make amino acids / protein 6. Nutrition - Animals eat plants – nitrogen moves through food web 7. DECAY excretions/dead stuff—bacteriaammonia Part III: 8. Denitrification Nitrates—bacterianitrogen gas

How humans affect the nitrogen cycle: 1. Fertilizers and the Nitrogen & Phosphorous Cycle Fertilizers – contain nitrogen & phosphorous More nitrogen and phosphorous = faster/bigger plant growth Excessive amounts of fertilizer runoff land and enter terrestrial and aquatic ecosystems / nearby water ways Causes Algal Bloom: rapid and over abundant growth of algae – dense, visible patches near the surface of the water Algal blooms and plants and animals that break down algae can deplete nutrients (like oxygen) from aquatic ecosystems Fish and other aquatic organisms need oxygen to survive 2. Acid Precipitation Burning fuel releases nitric oxide (a harmful gas) into the atmosphere Nitric oxide + water vapor  nitric acid Acid Precipitation = nitric acid dissolved in rain / snow

5-3 How Ecosystems Change Ecological Succession: replacement of one kind of community by another over time ex. lichengrassbushespineoak

Primary Succession: nothing has grown there before (rocks, cliffs, sand dunes, new volcanic islands) Secondary Succession: there has been previous growth – disturbed by humans (abandoned fields, forest clearings) , animals, or natural processes (storms, floods, earthquakes, volcanoes Fire & Secondary Succession: natural fires (caused by lightning) are a necessary part of succession (some species of trees release seed during fires, removes brush and deadwood that would otherwise fuel even bigger fires) Old-field Succession: when farmland is abandoned Pioneer grasses & weedsperennial grassesshrubspine foresthardwood forest

Secondary Succession 12 years after the eruption of Mt. St. Helens

Pioneer Organisms / Pioneer Species = 1st organisms – 1st organisms to colonize a newly available area Commonly bacteria or lichens (can live w/out soil and help break down rock surfaces into soil) Lichens: fungus & algae together Climax Community: when succession ends - among the most stable of ecosystems, remaining relatively unchanged for long periods of time

Pioneer Organisms Lichen Plants growing through cracks in a parking lot.