Chapter 36: Ecosystems and the Biosphere. Feeding relationships Energy flow in Ecosystems Recycling in Ecosystems Human impact on Chemical Cycles

Transcription

1 Chapter 36: Ecosystems and the Biosphere Feeding relationships Energy flow in Ecosystems Recycling in Ecosystems Human impact on Chemical Cycles Energy Transfer I. Energy Transfer Energy FLOWS from SUN AUTOTROPHS HETEROTROPHS; (e.g., ecosystem s structure is HOW energy is TRANSFERRED. 1

2 II. Producers (TWO Classes solar dependent AND independent) PLANTS, photosynthetic and chemosynthetic BACTERIA and PROTISTS, transfer NRG to nutrients. (1) Photosynthesis (sunlight-dependent producers) Sunlight as NRG source, biochemical reactions lead to the synthesis of carbohydrates. 2

3 (2) Chemosynthesis (sunlight-independent producers) Synthesize carbohydrates through the energy released from inorganic molecules (hydrogen sulfide). (A) Measuring Productivity Variations in SUNLIGHT/TEMPERATURE, PRECIPITATION, and NUTRIENT AVAILABILITY influence PRODUCTIVITY of ecosystems. 3

4 (3) Biomass MATERIAL available in an ecosystem for FOOD (i.e., producers ADD biomass to an ecosystem via synthesizing ORGANIC COMPOUNDS) 4

5 Net Primary Productivity (GPP units: kcal/m 2 /y or g/m 2 /y) Rate at which captured NRG is used to produce BIOMASS (i.e., ONLY NRG stored in BIOMASS is available to other organisms in the ecosystem) III. Consumers (i.e., primary, secondary, tertiary, quaternary) Classified based upon type of nutrition attainment (i.e., NRG is obtained by consuming organic molecules found in OR made by other organisms) 5

6 (1) Herbivores (predators primary consumers) Consume producers, either photosynthetic or chemosynthetic. (2) Carnivores (predators secondary or tertiary consumers) Consume OTHER consumers for NRG. (3) Omnivores (opportunistic predators either primary or secondary) Consume either producers OR consumers for NRG. 6

7 (4) Detritivores (mostly non-predators) Consume the GARBAGE of the ecosystem (i.e., recently dead organisms, fallen leaves and branches, and animal wastes). (5) Decomposers (a class of detritivores the RECYCLERS) Initiate DECAY by breaking down the COMPOUNDS in dead tissues and wastes into simpler NUTRIENTS. 7

8 IV. Energy Flow WHEN one consumes another, NUTRIENTS are metabolized and energy is transferred. (i.e., NRG flows through an ecosystem) (1) Trophic Level (the energy level) An organism s POSITION in the sequence of NRG transfers based upon their ROLE in the ecosystem. (A) Food Chains and Food Webs Represent an organism s POSITION in the sequence of NRG flow. 8

9 (1) Food Chain (LINEAR NRG transfer) Single pathway of feeding relationships among organisms in an ecosystem. (2) Food Web (INTERCONNECTED NRG transfer) Used to display HOW food chains among all organisms in an ecosystem are interrelated. 9

10 (B) Quantity of Energy Transfers ~ 10-15% of the TOTAL NRG in ONE trophic level is passed on to the organism in the NEXT level. Ex: Consider what happens when a DEER eats 1,000 kcal of LEAVES (biomass) from a TREE. About 350 kcal are LOST by the deer through urine and feces. Another 480 kcal are LOST as metabolic heat (the deer is an endotherm) Therefore, ONLY about 170 kcal are actually STORED as BIOMASS that can be consumed for NRG at the NEXT trophic level ABOVE. (C) Short Food Chains LOW rate of NRG transfer between trophic levels EXPLAINS why some ecosystems RARELY contain more than a FEW TROPHIC levels. Ex: If you go on an African Safari, you would see about 1,000 zebras, gazelles, wildebeest, and other herbivores for EVERY lion or leopard you see, and there are FAR MORE grasses, trees, and shrubs than there are herbivores. (i.e., the HIGHER trophic levels contain LESS energy and, as a consequence, HIGHER LEVELS can support FEWER individuals). 10

11 22-2 Ecosystem Recycling I. Biogeochemical Cycle (Abiotic-Biotic-Abiotic) While NRG flows THROUGH an ecosystem, WATER, C, N, Ca, and P are RECYCLED (via biogeochemical cycles). 11

12 II. The Water Cycle (evaporation-transpiration-precipitation) WATER defines the PRODUCTIVITY of terrestrial ecosystems (i.e., CELLS are made of between 70-90% water.) 12

13 (1) Ground Water (in addition to water vapor and bodies of water) In the SOIL or in underground formations of POROUS rock, moving between RESERVOIRS. (2) Transpiration (water VAPOR) ~ 90% returns to the ATMOSPHERE via PLANTS during transpiration. Plants: Release H 2 O vapor through STOMATA in leaves (majority). Animals: Release H 2 O during breathing (vapor), sweating, and excretion. 13

14 III. The Carbon Cycle Photosynthesis (ABSORBS), cellular respiration (RELEASES), and combustion (RELEASES) of fossil fuels FORM the basis of the C cycle. 14

15 (A) Human Influence on the Carbon Cycle (~ 150 years) [CO 2 ] in atmosphere has risen nearly 30% (human activity, increasing Greenhouse Effect Global Warming) Burning of fossil fuels (coal, oil, and natural gas) Burning of vegetation (combustion) in tropical rain forests for cattle farming (double-negative). IV. The Nitrogen Cycle (N needed for protein and DNA synthesis) N 2 gas (78%) is in an UNUSABLE FORM to plants and animals N-fixing bacteria assist plant productivity assist consumers. 15

16 (1) Nitrogen Fixation (produces AMMONIA) Soil BACTERIA convert N 2 gas to a USABLE forms (i.e., ammonia, nitrates, and nitrites.) (2) Nitrogen-Fixing Bacteria ( a MUTUALISM with LEGUME plants) Convert N 2 gas into ammonia (NH 3 ), then nitrite (NO 2- ), then nitrate (NO 3 ), which plants can ABSORB. NOTE: Bacteria inhabit the NODULES (bumps in the ROOTS) of plants belonging to the legume family (beans, peas, clovers, and alfalfa) (A) Recycling Nitrogen (to the PRODUCERS) N contained in the BODIES of dead organisms (proteins & nucleic acids), as well as in urine and feces of animals. 16

17 (1) Ammonification (DECOMPOSERS produces AMMONIA) Carcasses and wastes of organisms are BROKEN DOWN to release the N as ammonia (NH 3 ). (2) Nitrification (ammonia nitrites) Ammonia is oxidized (by bacteria of dung and carcasses) into NITRITES and NITRATES that can be used by more types of plants. 17

18 (3) Denitrification Anaerobic bacteria BREAK DOWN nitrates and nitrites to release N 2 gas BACK into the atmosphere, continuing the cycle. 18

19 22-3 Terrestrial Ecosystems I. The Seven Major Biomes LARGEST ecosystems of the biosphere (i.e., each biome contains a number of SMALLER but RELATED ecosystems). NOTE: Biomes can exist in MORE than one location on Earth, but tend to share ABIOITIC conditions (weather) AND inhabitants (species). 19

20 II. Tundra COLD, treeless biome forming a belt across northern North America, Europe, and Asia (2 month GROWING season, LOW precipitation summer) (1) Permafrost (prevents TREES from setting ROOTS) A permanently FROZEN layer of nutrient-poor soil under the surface, (i.e., ONLY plants can inhabit the area are SMALL root size). III. Taiga (long, cold winters, NOT as long as the tundra) A FORESTED biome evergreen trees, SHORT growing season, LOW precipitation, poorer SOIL than temperate forests. NOTE: Hibernation is used for many species between 6-8 months a year. 20

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22 IV. Temperate Deciduous Forests (often get converted into FARMLAND) Seasons with trees that LOSE leaves and include an IDEAL habitat for AGRICULTURE (e.g., long growing season, precipitation, nutrient-rich soil). V. Temperate Grasslands (a.k.a. Prairies, Steppes, Pampas, and Veldt) LESS rainfall and RICH fertile soil; usually found in the interiors of continents. (supports GRAZERS, grasses actively grow BELOW soil). 22

23 VI. Deserts Areas that receive LITTLE rainfall and supports LOW PRODUCTIVITY that has adapted to dry conditions (spines, waxy leaves, stomata at night). 23

24 VII. Savannas (largely in Africa, parts of S. America, Australia) Rainfall > deserts BUT < rainforests Distinct WET and DRY seasons (leaves LOST in dry season, back in wet season & grasses die during dry). VIII. Tropical Rainforests (20% of ALL species in the biosphere) STABLE, year-round GROWING season, abundant RAINFALL, greatest species RICHNESS and MOST productive of all biomes. 24

25 (1) Canopy Continuous layer of TREETOPS that SHADES the forest floor the jungle floor is relatively FREE of vegetation due to absence of sunlight. (2) Epiphytes (adapted to the canopy, like VINES) SMALL plants inhabit the trunks and branches of TALLER trees in order to reach available SUNLIGHT; (commensalistic or parasitic?) 25

26 22-4 Aquatic Ecosystems I. Ocean Zones (~ a 3% salt solution of seawater) ~ 70% of surface, avg depth of 2.3 miles and since water absorbs light, only ~ FEW hundred meters receive SUNLIGHT penetration (photic zone). 26

27 (1) Photic Zone (permits photosynthesis, nutrient-rich) UPPER regions of the oceans with SUNLIGHT penetration. (2) Aphotic Zone (prevents photosynthesis, nutrient-poor) LOWER regions of the oceans with NO sunlight penetration. 27

28 Ecologists Recognize Three Zones Extending FROM the Beach (3) Intertidal Zone (nutrient-richest) Susceptible to rises and falls of SEA LEVEL due to TIDE fluctuations. (4) Neritic Zone (nutrient-rich) Extends from the INTERTIDAL ZONE over the CONTINENTAL SHELF. (5) Oceanic Zone (average nutrients) Extends BEYOND the neritic zone (the open sea) and is vertically divided into the PELAGIC and BENTHIC zones. 28

29 (6) Pelagic Zone The TOP zone of the OPEN OCEAN which is compromised of BOTH neritic and oceanic zones. (7) Benthic Zone The SMALLER zone of the ocean BOTTOM, or the deepest part of the neritic and oceanic zone (NOTE: GEOTHERMAL VENTS give home to chemosynthetic bacteria and other predatory members, including clams, crabs, and worms) 29

30 (A) The Intertidal Zone (crabs burrow, bivalves retreat, cling to rocks) Species must ADAPT to withstand exposure to AIR (during low tide), DEHYDRATION, and the forces of CRASHING waves. (B) The Neritic Zone (habitat range of CORAL REEFS) MOST productive zone, GREATEST species richness, and PERMITS photosynthesis (nutrients from land AND from photosynthesis). (1) Plankton (zooplankton and phytoplankton) Communities of small organisms that DRIFT with ocean currents, and provide a FOOD BASE for numerous marine ecosystems. (C) The Oceanic Zone LESS species richness than Neritic Zone due to LOWER nutrient levels. (1) Plankton Sinks to the APHOTIC zone with dead organisms to provide nutrition. 30

31 (D) Estuaries (i.e., the OCEAN S NURSERIES bays and salt marshes Ecosystems where FRESHWATER rivers and streams flow INTO the OCEAN. NOTE: Abundance of sunlight & minerals (river runoff), BUT adaptations to variations in temperature and salinity are NECESSARY for inhabitation. II. Freshwater Zones LOW levels of dissolved SALTS (0.005% vs. 2-3% of marine) (i.e., freshwater lakes, ponds, streams, and rivers). (A) Lakes and Ponds (TWO classes exist) Classified as freshwater based upon ABIOTIC conditions (nutrients). 31

32 (1) Eutrophic Lakes RICH in organic matter and VEGETATION, waters are murky and brackish. (2) Oligotrophic Lakes Contain LITTLE organic matter and have much CLEARER water with a sandy or rocky bottom. 32

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34 (B) River and Streams (FLOWING body down a steep gradient) Inhabitants adapt to WITHSTAND currents; the FASTER the water, generally, the LESS nutrients the ecosystem contains. Critical Thinking (1) Thinning of the ozone layer by release of CFCs may lead to reduced population of photosynthetic plankton in the ocean. Explain how this phenomenon may affect the carbon cycle. 34

35 Critical Thinking (2) Nitrogen, water, and carbon are recycled and reused within an ecosystem, BUT energy is not. Explain as to why energy cannot be recycled? Critical Thinking (3) Explain why farmers often grow alfalfa, clover, or beans in a field after they have grown corn. Critical Thinking (4) This rare species of squid has several adaptations for living in deep water. Explain what you believe may be some of the selective pressures that exist at great depths. 35

36 Critical Thinking (5) Explain TWO ways that the burning of vegetation affects carbon dioxide levels in the atmosphere. How do you think the removal of vegetation affects oxygen levels in the atmosphere? Critical Thinking (6) Explain the benefits deciduous trees gain from shedding their leaves in the fall. Describe some possible disadvantages of shedding leaves. Extra Slides AND Answers for Critical Thinking Questions (1) Photosynthetic plankton in the ocean account for about 50 percent of the photosynthesis on Earth. If their population is reduced, carbon dioxide levels will likely rise, intensifying the greenhouse effect. (2) At each trophic level, energy is dissipated as heat, a form of energy organisms cannot use. Thus, energy is continually lost to the ecosystem. (3) These plants contain nitrogen-fixing bacteria in their roots. The bacteria release any excess nitrogen they fix into the soil. (4) The selective pressures at great depths include cold temperatures, absence of light, scarcity of prey, slippery prey that is hard to see, and extremely high pressure. (5) The burning of vegetation contributes carbon dioxide to the atmosphere though the process of combustion. Also, the removal of vegetation by burning (or other methods) eliminates the plants that absorb carbon dioxide and produce oxygen during photosynthesis. 36

37 (6) Transpiration cannot occur if the leaves are absent. Deciduous trees conserve water by shedding their leaves. The energy and materials that went into growing and maintaining the leaves are lost to the tree when they are shed. In addition, sugars cannot be synthesized. Revisiting Interdependence of Organisms Energy relationships within a food web are intricate. Nutrient cycling in ecosystems often involves unique symbiotic relationships. Assessing Prior Knowledge How do cellular respiration and photosynthesis relate to the recycling of carbon? How do you suppose atmospheric nitrogen is converted to a usable form for organisms? 37