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Ecosystems & Communities:Organisms and their Environments

Chapter 15

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Energy and chemicals flow within ecosystems

15.6 Energy flows from producers to consumers.

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First Stop: Primary Producers

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First Stop: Primary Producers• ecosystem: producers or consumers

• primary producers: plants, algae (some), bacteria • convert light energy from sun into chemical energy

through photosynthesis• chemical energy = food

• consumers eat or absorb their food• energy stored in chemical bonds of carbohydrate,

protein, and lipid molecules is captured and harnessed for consumers’ own movement, reproduction, and growth

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Second Stop: Primary Consumers – the Herbivores

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Third Stop: Secondary Consumers – the Carnivores

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Fourth Stop: Tertiary Consumers – the “Top” Carnivores

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Food Chain

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Food Web

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Food Web

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Food Chains & Food Webs• A change in one link in a food chain will affect the other

links. • The table on the next slide gives one example of a food

chain and the trophic levels represented in it:

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Food Chains & Food Webs

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GRASS

GRASSHOPPER

TOAD

SNAKE

HAWK

BACTERIA

IN GENERAL,

AUTOTROPHS (PRODUCERS)

HERBIVORES(PRIMARY

CONSUMERS)

CARNIVORES(2, 3, ETC.)

DECOMPOSERS

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Chain Reaction Game

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Energy Flows through a Food Web• Losses at every “step” in a food chain

• Inefficiency of energy transfers

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A grasshopper eats a plant. A mouse eats the grasshopper. A snake eats the mouse. A hawk could eat the snake or the mouse. In this food web, how would we categorize the hawk?

1. Producer2. Primary consumer3. Secondary consumer4. Tertiary consumer5. Quaternary consumer6. 4 and 5

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Summary 15.6• Energy from the sun passes through an ecosystem in

several steps. • First, it is converted to chemical energy in

photosynthesis. • Herbivores then consume the primary producers, the

herbivores are consumed by carnivores, and the carnivores, in turn, may be consumed by top carnivores.

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Summary 2, 15.6• Detritivores and decomposers extract energy from

organic waste and the remains of organisms that have died.

• At each step in a food chain, some usable energy is lost as heat.

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Energy and chemicals flow within ecosystems

15.7 Energy pyramids reveal the inefficiency of food chains.

Biomass• biomass: total weight of all living organisms in a given

area• only about 10% of the plants in an ecosystem is

converted into biomass• Food Energy Pyramid

• flow of energy through a food chain• trophic level: position that an organism occupies in a

food chain - what it eats, and what eats it• African savannas and grasslands sustain more species

of higher-order carnivores than any other terrestrial ecosystem

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Food Energy Pyramids• flow of energy through a food chain• trophic level: position that an organism occupies in a

food chain - what it eats, and what eats it

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You go out to eat at a fancy restaurant. You have a salad, salmon, and for dessert ice cream! Which part of the meal was the most energy efficient food for you to eat?

1. Salad* 2. Salmon3. Ice cream 4. 2 and 3

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Summary 15.7• Energy from the sun passes through an ecosystem in

several steps known as trophic levels. • Energy pyramids reveal that the biomass of primary

producers in an ecosystem tends to be far greater than the biomass of herbivores.

• The biomass transferred at each step along the food chain tends to be only about 10% of the biomass of the organisms being consumed, due to energy lost in cellular respiration.

• As a consequence of this inefficiency, food chains rarely exceed four levels.

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Energy and chemicals flow within ecosystems

15.8 Essential chemicals cycle through ecosystems.

Chemical Reservoirs• Each chemical is stored in a non-living part of the

environment.

• Organisms acquire the chemical from the reservoir, a non-living part of the environment.

• The chemical cycles through the food chain (biogeochemical cycles).

• Eventually, the chemical is returned to the reservoir.

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The Most Important Chemical Cycles

1) Carbon2) Nitrogen3) Phosphorus4) Sulfur

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Carbon Cycle Game

Fossil Fuels• created when large numbers of organisms die and are

buried in sediment lacking oxygen• In absence of oxygen, at high pressures, and after very

long periods of time, organic remains are ultimately transformed into coal, oil, and natural gas

• burning coal, oil, and natural gas releases large amounts of carbon dioxide• increases average CO2 concentration in the

atmosphere• current level of CO2 in the atmosphere is the highest it

has been in almost half a million years

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Global CO2 levels are rising in general, but they also exhibit a sharp rise and fall within each year – why?

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Why less CO2 in Summer in the Northern Hemisphere?• The plants consume CO2 in photosynthesis.• They photosynthesize more in the summer.• The Northern Hemisphere has more land plants because

it has more land.

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Fertilizers• Because it is necessary for the production of every plant

protein, and because all nitrogen must first be made usable by bacteria, plant growth is often limited by nitrogen levels in the soil.

• For this reason, most fertilizers contain nitrogen in a form usable by plants.

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Algal Blooms or Eutrophication• When too much fertilizer is released into the water in any

lake, algae and bacteria will grow unopposed.• These will use up all of the oxygen in the water and kill

other species.• Water will be fouled, slimy and unfit for recreation.

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Sulfur Cycle• component of protein • cycles in both a gas and sedimentary cycle• source : earth's crust• enters the atmosphere as  hydrogen sulfide (H2S)

during fossil fuel combustion, volcanic eruptions, gas exchange at ocean surfaces, decomposition

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Sulfur Cycle• H2S is immediately oxidized to sulfur dioxide (SO2) • SO2 + water vapor H2SO4 (falls to earth in rain)• Too much sulfuric acid (H2SO4) in the atmosphere

constitutes acid rain  • sulfur in soluble form is taken up by plant roots,

incorporated into amino acids such as cysteine• travels through food chain • eventually released through decomposition

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How is carbon recycled back to the atmosphere in the carbon cycle?

1. It is “fixed” by bacteria.2. It is a product of cellular respiration.3. Burning of fossil fuels.4. 2 and 3.5. All of the above.

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Why do commercial fertilizers usually contain usable forms of nitrogen and phosphorous?

1. These chemicals are not efficiently recycled in the soil.

2. Nitrogen and phosphorous need to be “fixed” by bacteria or the plant.

3. Nitrogen and phosphorous are found at high levels in the atmosphere but not in the soil.

4. Nitrogen and phosphorous only enter the soil through erosion.

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Summary 15.8• Chemicals essential to life—including carbon,

nitrogen, and phosphorus—cycle through ecosystems.

• They are usually captured from the atmosphere, soil, or water by growing organisms; passed from one trophic level to the next as organisms eat other organisms; and returned to the environment through respiration, decomposition, and erosion.

• These cycles can be disrupted as human activities increase or decrease the amounts of the chemicals used or released to the environment.

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Species interactions influence the structure of communities.

15.9 Interacting species evolve together.

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Natural Selection• Causes organisms to become better adapted to their

environment

• Does not distinguish between biotic and abiotic resources as selective forces

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Coevolution• two (or more) species reciprocally affect each

other’s evolution• likely to happen when different species have

close ecological interactions with one another including:• predator/prey• parasite/host• competitive species• mutualistic species

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Penicillin was first isolated from a fungus growing on a plate of bacteria. This is an example of an adaptation of the fungus to fight off the bacteria. This interaction could be described as:

1. coadaptation.2. coevolution.3. symbiosis.4. predation.

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Summary 15.9• In producing organisms better adapted to their

environment, natural selection does not distinguish between living and non-living (biotic and abiotic) things as selective forces.

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Species interactions influence the structure of communities.

15.10 Each species’ role in a community is defined by its niche.

More than just a place for living, a niche is a complete way of living

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More than just a place for living, a niche is a complete way of living• Full niche: the full range of environmental conditions

under which a species can live

• Real niche: where and how a species is actually living

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Summary 15.10• A population of organisms in a community fills a unique

niche, defined by how they use the resources in their environment.

• Organisms do not always completely fill their niche; competition with species that have overlapping niches can reduce their range.

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Species interactions influence the structure of communities.

15.11 Competition can be hard to see, but it still influences community structure.

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Why is competition hard to see in nature?

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Why is competition hard to see?• We see only the result after generations of competitors

have worked out how to live together.• The species are still in competition but the way they

compete is not readily visible. E.g. birds singing in the morning.

How can two very similar species avoid the consequences of competitive exclusion principle?

1. avoid predation 2. one species will become locally extinct 3. character displacement will occur 4. 2 and 3 5. all of the above

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Summary 15.11• Populations with completely overlapping niches cannot

coexist forever.

• Competition for resources occurs until one or both species evolve in ways that reduce the competition, through character displacement, or until one becomes extinct in that location.

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Species interactions influence the structure of communities.

15.12 Predation produces adaptation in both predators and their prey.

Predation• interaction between two species in which one species

eats the other• one of most important forces shaping composition and

abundance of species in a community

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Why do exotic species often flourish when released into novel habitats, even though natural selection has not adapted them to this new environment? E.g. Rabbits in Australia.

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Prey Adaptations for Reducing Predation• physical

• mechanical• chemical• warning coloration• camouflage mechanisms

• behavioral• passive and active behaviors

• hiding • escaping• alarm calling• fighting back

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1) Mechanical Defenses

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2) Chemical Defenses

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3) Warning Coloration

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4) Camouflage

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Predator adaptations for enhancing predation

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• toxic-avoidance methods • sensory perception

• faster running ability

• mimicry

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Why don’t predators become so efficient at capturing prey that they drive the prey to extinction?

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• predator adaptations are rarely so efficient that prey are driven to extinction

• “escape ability” in prey is stronger than selection for “capture ability” in predator

• cost of losing is much higher for prey

The gazelle can change direction very quickly while being chased by a cheetah (fastest land animal). The gazelle uses which method of defense listed below?

1. Mechanical defense2. Camouflage3. Behavioral4. Warning Coloration5. Chemical defense

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Summary 15.12• Predators and their prey are in an evolutionary arms

race.

• As physical and behavioral features evolve in prey species to reduce their predation risk, predators develop more effective and efficient methods of predation.

• The coevolutionary process can result in brightly colored organisms, alarm calling, and many types of mimicry.

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THANK YOU TO…• http://www.blueplanetbiomes.org• http://www.marietta.edu/~biol/biomes/biome_main.htm• http://www.ucmp.berkeley.edu/exhibits/biomes/• http://www.tburg.k12.ny.us/mcdonald/foodch1.htm• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/

FoodChains.html• http://ic.galegroup.com/ic/scic/ReferenceDetailsPage/

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