Chapter 22: Ecosystems and the Biosphere

22-1 Energy Transfer

22-2 Ecosystem Recycling

22-3 Terrestrial Ecosystems

22-4 Aquatic Ecosystems

I. Energy Transfer

• Energy FLOWS from SUN AUTOTROPHS HETEROTROPHS; (e.g., ecosystem’s structure is HOW energy is TRANSFERRED).

22-1 Energy Transfer

II. Producers (2 Classes solar dependent AND independent)• Plants, bacteria, protists, transfer NRG into NUTRIENTS

(i.e., they “produce” food).

(1) Photosynthesis (sunlight-DEPENDENT producers)• Sunlight as NRG source, biochemical reactions lead to carbohydrates.

(2) Chemosynthesis (sunlight-INDEPENDENT producers)• PRODUCE carbohydrates through NRG released from CHEMICALS

(e.g., hydrogen sulfide).

(A) Measuring Productivity (How much NRG is available in an ecosystem?)• Differences in abiotic factors ALL influence PRODUCTIVITY.

(1) Gross Primary Productivity (GPP units: kcal/m2/y or g/m2/y)• RATE at which PRODUCERS in an ecosystem CAPTURE NRG.

(2) Net Primary Productivity (GPP units: kcal/m2/y or g/m2/y)• RATE at which captured NRG is USED to make BIOMASS.

(i.e., ONLY NRG in BIOMASS is available to other organisms)

(3) Biomass (the volume an organism takes up)• MATERIAL available in an ecosystem for FOOD

(i.e., producers ADD biomass ORGANIC COMPOUNDS)

III. Consumers (i.e., primary, secondary, tertiary, quaternary)• Different types based upon WHERE they obtain nourishment.

(i.e., NRG is obtained by consumption NOT production)

(1) Herbivores (predators—primary consumers)• Consume PRODUCERS for NRG.

(2) Carnivores (predators—secondary or tertiary consumers)• Consumer OTHER consumers for NRG.

(3) Omnivores (opportunistic predators—either primary or secondary)• Consume BOTH producers AND consumers for NRG.

(4) Detritivores (mostly non-predators)• Consume “GARBAGE” of an ecosystem

(i.e., dead organisms, fallen leaves and branches, and animal wastes).

(5) Decomposers (class of detritivores—RECYCLERS of an ecosystem)• Initiate DECAY by breaking down dead tissues into NUTRIENTS.

IV. Energy Flow• NUTRIENTS are metabolized and NRG is transferred.

(i.e., NRG flows through an ecosystem)

(1) Trophic Level (the NRG level)• An organism’s POSITION in the sequence of NRG transfers.

(A) Food Chains and Food Webs• Represent an organism’s POSITION in sequence of NRG flow.

(1) Food Chain (LINEAR NRG transfer)• Single pathway of feeding relationships among organisms in ecosystem.

(2) Food Web (INTERCONNECTED NRG transfer)

• Shows HOW food chains in an ecosystem are interconnected.

(B) Quantity of Energy Transfers• ONLY 10-15% of TOTAL NRG in a trophic level is PASSED on to the NEXT trophic 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).

I. Biogeochemical Cycle (Abiotic-Biotic-Abiotic)• UNLIKE NRG flow, WATER, C, N, Ca, and P can be RECYCLED.

(via biogeochemical cycles)

22-2 Ecosystem Recycling

(1) 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

II. The Water Cycle (evaporation-transpiration-precipitation)• WATER defines the PRODUCTIVITY of TERRESTRIAL ecosystems (i.e., Remember, CELLS are MADE of 70-90% water.)

(1) Ground Water (in addition to water vapor AND bodies of water)• In SOIL or UNDERGROUND inside POROUS rock, flows in RESERVOIRS.

(2) Transpiration (water VAPOR)

• ~ 90% returns to ATMOSPHERE via PLANTS during transpiration.

• Plants: Release H2O vapor through STOMATA in leaves (majority).• Animals: Release H2O during breathing (vapor), sweating, and excretion.

III. The Carbon Cycle • Photosynthesis (ABSORBS), Respiration (RELEASES), and Combustion of Fossil Fuels (RELEASES).

(2) 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

(A) Human Influence on the Carbon Cycle (~ 150 years)• [CO2] in our atmosphere has risen ~ 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).

Critical Thinking(3) 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.

IV. The Nitrogen Cycle (N needed to make Proteins and DNA, RNA)• N2 gas (78%) is in an UNUSABLE FORM to plants and animals BUT N-fixing bacteria exist.

(4) Explain why farmers often grow alfalfa, clover, or beans in a field after they have grown corn.

Critical Thinking

(1) Nitrogen Fixation (produces AMMONIA)

• Soil BACTERIA convert N2 gas into USABLE forms (i.e., ammonia, nitrates, and nitrites.)

(2) Nitrogen-Fixing Bacteria ( a MUTUALISM with LEGUME plants)

• Convert N2 gas into ammonia (NH3), then nitrite (NO2-), then nitrate

(NO3), 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 (BACK to the PRODUCERS)

• N found in DEAD organisms (proteins AND nucleic acids), as well as in URINE and FECES.

(1) Ammonification (DECOMPOSERS produces AMMONIA)• Carcasses AND wastes of organisms are BROKEN DOWN to release N as ammonia (NH3).

(2) Nitrification (ammonia nitrites) • Ammonia is oxidized (by bacteria) into NITRITES and NITRATES that are used by plants.

(3) Denitrification

• Anaerobic bacteria release N2 gas BACK into atmosphere, continuing the N-cycle.

http://www.tu-harburg.de/~wwvos/img/aqua-ani.gif

I. The Seven Major Biomes• LARGEST ecosystems of biosphere

(i.e., A BIOME holds SMALLER but RELATED ecosystems).

22-3 Terrestrial Ecosystems

NOTE: Biomes can exist in MORE than one location on Earth, AND tend to share ABIOITIC conditions (weather) AND inhabitants (species).

II. Tundra • COLD, treeless Belt across northern regions.

(2 month GROWING season, LOW precipitation—summer)

(1) Permafrost (prevents TREES from setting ROOTS)• FROZEN layer of nutrient-poor soil UNDER the surface,

(i.e., ONLY plants with SMALL root size can inhabit).

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.

IV. Temperate Deciduous Forests (often 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).

(5) Explain the benefits deciduous trees gain from shedding their leaves in the fall. Describe some possible disadvantages of shedding leaves.

Critical Thinking

V. Temperate Grasslands (a.k.a. Prairies, Steppes, Pampas, and Veldt)• LESS rainfall and RICH fertile soil; found in INTERIORS of continents. (supports GRAZERS, grasses actively grow BELOW soil).

VI. Deserts• Areas receive LITTLE rainfall with LOW PRODUCTIVITY adapted to DRY conditions (e.g., spines, waxy leaves, stomata at night).

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.

(1) Canopy• Continuous layer of TREETOPS that SHADES forest floor—jungle floor is relatively FREE of vegetation due to ABSENCE of sunlight.

(2) Epiphytes (adapted to the canopy, like VINES)• SMALL plants inhabit trunks AND branches of TALLER trees in order to reach available SUNLIGHT; (commensalistic OR parasitic?)

I. Ocean Zones (~ a 3% salt solution of seawater)• 70% of surface, depth: 2.3 miles AND, only 100-200 meters receive SUNLIGHT penetration (water absorbs sunlight).

22-4 Aquatic Ecosystems

(1) Photic Zone (permits photosynthesis, nutrient-RICH)

• UPPER regions of OCEANS with SUNLIGHT.

(2) Aphotic Zone (prevents photosynthesis, nutrient-POOR)

• LOWER regions of OCEANS with NO sunlight.

(3) Intertidal Zone (nutrient-richest)

• Susceptible to rises AND falls of SEA LEVEL due to TIDES.

(4) Neritic Zone (nutrient-rich)

• Extends from INTERTIDAL ZONE over CONTINENTAL SHELF.

(5) Oceanic Zone (average nutrients)

• BEYOND neritic zone (open sea) and is divided into PELAGIC and BENTHIC zones.

Ecologists Recognize THREE Zones Extending FROM the Beach

(6) Pelagic Zone

• TOP of OPEN OCEAN includes BOTH neritic and oceanic zones.

(7) Benthic Zone

• BOTTOM, or DEEPEST part of neritic and oceanic zones.

(NOTE: GEOTHERMAL VENTS give home to chemosynthetic bacteria and other predatory members, including clams, crabs, and worms)

(6) 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.

Critical Thinking

(A) The Intertidal Zone (crabs burrow, bivalves retreat, cling to rocks)• Species must ADAPT to withstand exposure to AIR (during low tide), DEHYDRATION, and forces of CRASHING waves.

(B) The Neritic Zone (habitat range of CORAL REEFS)• MOST productive, GREATEST species richness, and allows photosynthesis (nutrients from land AND from photosynthesis).

(1) Plankton (zooplankton and phytoplankton)• Communities DRIFT with ocean currents and provide a FOOD BASE for ecosystems.

(C) The Oceanic Zone

• LESS species richness than Neritic Zone due to LOWER nutrient levels.(1) Plankton• Sinks to APHOTIC zone with DEAD organisms.

(D) Estuaries (i.e., the “OCEAN’S NURSERIES” bays and salt marshes• 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).

(1) Eutrophic Lakes

• RICH in nutrients and VEGETATION, waters are MURKY and BRACKISH.

(2) Oligotrophic Lakes• Contain LITTLE nutrients AND much CLEARER water with a SANDY or ROCKY bottom.

(B) River and Streams (FLOWING body down a steep gradient)• Inhabitants adapted to WITHSTAND currents; the FASTER the water, the LESS nutrients in ecosystem.

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.

(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.

Assessing Prior Knowledge

• How do cellular respiration and photosynthesis relate to the recycling of carbon?

• Nutrient cycling in ecosystems often involves unique symbiotic relationships.

• How do you suppose atmospheric nitrogen is converted to a usable form for organisms?