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Honors Biology

Chapter 34Nature of Ecosystems

John ReganWendy Vermillion

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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34.1 The biotic components of ecosystems

• Populations of an ecosystem– Autotrophs- primary producers

• Require an energy source and inorganic nutrients to produce organic food molecules

• Manufacture organic nutrients for all organisms

• Green plants and algae-photosynthesis

• Bacteria-chemoautotrophs

– Heterotrophs- consumers• Consume organic nutrients

– Herbivores, carnivores, omnivores

• Decomposers- fungi, bacteria

– Break down decaying matter releasing nutrients

– Detritus- partially decomposed matter– Detritivore-eats detritus

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Biotic components

• Fig. 34.1

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The biotic components of ecosystems cont’d.

• Energy flow and chemical cycling– Energy enters ecosystem in the form of sunlight absorbed by

producers– Chemicals enter when producers absorb inorganic nutrients– Producers then make organic nutrients for themselves and all

other organisms in the ecosystem• Consumers (herbivores and omnivores) gain nutrients and energy

from eating producers

• Higher level consumers (carnivores) then gain nutrients and energy from eating herbivores and omnivores

– Some energy is released at each level to the environment in the form of heat and waste products

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Energy flow and chemical cycling

• Fig. 34.2

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Energy balances

• Fig. 34.3

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The biotic components of ecosystems cont’d.

• The following two slides illustrate food webs– Food webs illustrate the interrelationships between organisms in

the food chain– Identify the producers, primary consumers, and secondary

consumers

• Laws of thermodynamics– First law- energy is neither created nor destroyed

• Ecosystems depend on continual outside source of energy

– Second law- with every transformation, some energy is given off as heat

• The amount of available energy at each successive trophic level is less than the one below it

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Grazing food webs

• Fig. 34.4

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Detritis food web

• Fig. 34.5

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34.2 Energy flow

• Trophic levels– Trophic level is composed of all organisms that feed at a

particular link in the food chain• Primary producers- first trophic level• Primary consumers- second trophic level• Secondary consumers- third trophic level

• Ecological pyramids- diagrams of the community– Represent amount of available energy in each trophic level– Producers are at the base- the most available energy

• Energy is given off in less usable forms as producers are eaten by primary consumers, etc.

– Numbers, biomass, or energy– Biomass- the number of organisms at each level multiplied by

their weight

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Ecological pyramid

• Fig. 34.6

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34.3 Global biogeochemical cycles

• Biogeochemical cycles– Pathways involve both biotic and abiotic components

• Reservoir-source unavailable to producers

• Exchange pool-source from which organisms take chemicals

• Biotic community-chemicals move through community along food chains

– 2 main types of cycles• Gaseous cycle-drawn from and returns to the atmosphere

• Sedimentary cycle-element is drawn from soil by plant roots, eaten by consumers, returned to soil by decomposers

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Model for chemical cycling

• Fig. 34.7

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Global biogeochemical cycles cont’d.

• The water cycle– Freshwater evaporates from bodies of water– Precipitation over land enters ground, surface waters, aquifers– Eventually returns to oceans over time– Hydrologic cycle is illustrated on the following slide

• Note that size of arrow is proportional to rate of transfer

– Human impact• In arid southwest and southern Florida, water mining is occurring

– Aquifers are being drained faster than they can be naturally replenished

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The hydrologic cycle

• Fig. 34.8

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Global biogeochemical cycles cont’d.

• The phosphorus cycle– Phosphate enters soil as rocks undergo weathering process– Picked up by producers and cycles through consumers and

finally decomposers– Human impact

• Accelerated transfer rate due to phosphate mining, supplementation on farm fields, detergents

– Cultural eutrophication- over-enrichment» Can lead to increased algal bloom

» As algae die off, decomposers consume high levels of oxygen in the water

» Results in massive fish kills

– Phosphorus cycle is illustrated on the following slide

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The phosphorus cycle

• Fig. 34.9

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Global biogeochemical cycles cont’d.

• The nitrogen cycle– Nitrogen fixation-conversion of nitrogen gas N2 to ammonium NH4

+

by bacteria

– 78% of atmosphere is nitrogen gas, but unusable by plants

– Root nodules of legumes house nitrogen-fixing bacteria

– Nitrification-production of nitrates which plants can also use• Nitrogen gas converted to nitrate in atmosphere by lightning• Ammonium in soil converted to nitrate by nitrifying bacteria

– Nitrite bacteria ammonia →nitrite (NO2-)

– Nitrate bacteria nitrite → nitrate (NO3-)

– Denitrification-conversion of nitrate back to nitrogen gas by denitrifying bacteria

– Human activities- N2 from fertilizers increases transfer rates

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The nitrogen cycle

• Fig. 34.10

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Global biogeochemical cycles cont’d.

• The carbon cycle– Photosynthesis takes up carbon dioxide from the atmosphere– Cell respiration returns it to the atmosphere– Reservoirs of carbon

• Dead organisms- fossil fuels

• Forests

– Human activities• More carbon dioxide is being deposited in atmosphere than is being

removed

– Due to deforestation and burning of fossil fuels• Increased carbon dioxide in atmosphere contributes to global

warming

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The carbon cycle

• Fig. 34.11

Ozone

• O2 → O3

• Oxygen is converted into ozone in atmosphere by UV rays• Also by lightning and industry• Ozone in lower atmosphere –air pollutant• In stratosphere- blocks UV rays• UV rays cause sunburn, skin cancer, cataracts, slows growth of plants

• Ozone has been depleted

– 10% ↓ ozone, 26% ↑ cataracts, skin cancer

– Cause of ozone depletion- Chlorofluorocarbons (CFCs)

– CFCs banned 2000

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