How Ecosystems WorkChapter 3

“You could cover the whole world with asphalt, but sooner or later green grass would break through.”

Ilya Ehrenburg, Russian Writer

Section 3.1 Energy Flow in Ecosystems

Life depends on the sun• Organisms cannot survive without a supply of energy.

• Where does an organisms energy come from? Ultimately from the

SUN• Plants, algae and some kinds of bacteria capture solar energy and store

it as food through a process called PHOTOSYNTHESIS.

• The result is the production of sugar, an energy-rich food.

• Ex: When a rabbit eats a clover plant, the rabbit gets its energy from the food the clover made during photosynthesis. A coyote eats the rabbit, some of the energy transfers from the rabbit to the coyote.

• The clover is a producer (can make its own food;) the rabbit and coyote are consumers (also called heterotrophs or other feeders.) that get their energy by eating producers and other organisms.

An Exception to the Rule: Deep-Ocean Ecosystems

• In 1977, scientists discovered areas on the bottom of the ocean off the coast of Ecuador that had life without sunlight.

• Found were: communities of fish, worms, clams, mussels and barnacles living around cracks in the ocean floor.

• These communities exist in total darkness, where photosynthesis cannot occur.

• They found bacteria that made food from hydrogen sulfide, which is present in the hot water that escapes from the ocean floor.

• The bacteria are considered producers, and are making food without sunlight.

• Animals eat these bacteria, thus supporting this ecosystem.

What Eats What• Herbivores (plant-eaters) are consumers that eat only producers:

ex: rabbits, cows, sheep, deer, grasshoppers, etc.

• Carnivores (flesh-eaters) are consumers that eat only other consumers:

ex: lions, hawks

• Omnivores (eaters of all) are consumers that eat both producers and other consumers:

ex: humans, pigs, bears

• Decomposers are consumers that get their food by breaking down dead organisms, causing them to rot. Decomposers make it possible to return nutrients to the soil or water:

ex: bacteria, fungi

Respiration: Burning the Fuel• The food you ate contains a lot of energy.

• Your body gets energy out of the food by using oxygen you breathe to break down the food molecules.

• The process of breaking down food to yield energy is called cellular respiration.

C6H12O6 +6 O2 6 CO2 + 6 H2O + ENERGY

• During cellular respiration, sugar and oxygen combine to yield carbon dioxide, water, and most important, energy.

• A portion of the energy obtained through cellular respiration is used to carry out daily activities (walking, breathing, reading, thinking) and to make more body tissue, so you can grow (some stored as fat or sugar.)

• All living things use cellular respiration to get energy from food molecules.

Energy Transfer: Food Chains, Food Webs, and Trophic levels

• Each time one organism eats another organism, a transfer of energy occurs.

• We trace the paths that energy follows by studying food chains, food webs, and trophic levels.

• A food chain is a sequence in which energy is transferred from one organism to the next as each organism eats another.

ex: algae krill cod leopard seal killer whale• Ecosystems are more complicated than a simple food chain. There are

many species that feed off of more than one kind of food. This is called a food web and shows the feeding relationships in an ecosystem.

• Each step in the transfer of energy through an ecosystem is known as a trophic level.

Food Chains and Food Webs Food chain Food Web

Trophic levels• In this example, grass is at

the bottom of the trophic level and is the most prolific. Each time energy is transferred, less of it is available to the organisms at the next level.

• Why? Some energy is lost during the process of converting food to energy. The remaining energy is used to carry out life functions (making new cells, moving, breathing, etc.)

90% of the energy is lost at each level, only 10% passes on to the next level.

How energy loss affects an Ecosystem

• Decreased amount of energy at each level results in fewer organisms at the higher trophic levels.

ex: zebras and other herbivores outnumber lions on the African

savanna by about 1000 to 1.

• The loss of energy from trophic level to trophic level may place a limit on the number of trophic levels in an ecosystem. Therefore, ecosystems rarely have more than four or five trophic levels.

Section 3.2 The Cycling of Materials

• Materials in the ecosystem are used again and again; otherwise, they would be gone, and life could no longer exist.

• This section covers three different cycles that allow materials to be reused.

THE WATER CYCLE

THE CARBON CYCLE

THE NITROGEN CYCLE

• Water is essential to life.

• The sun provides the energy that drives the water cycle.

ex: Heat from the sun evaporates water from the Earth. As the water vapor cools in the atmosphere, it condenses, forms droplets in the clouds. When the clouds meet cold air, the water returns to Earth as precipitation (rain, sleet, snow.)

• Some of the water goes through the cycle again, other seeps into the ground or flows back to the ocean via rivers and streams.

The Water Cycle

WaterCycle

• Carbon is the essential component of the proteins, fats, and carbohydrates necessary for life.

• Carbon enters an ecosystems when producers take in CO2 from the atmosphere during photosynthesis.

• Consumers eat the producers, obtaining carbon.

• Consumers break down the food molecules during cellular respiration and release carbon back into the atmosphere as CO2.

• Photosynthetic organisms also release CO2 during cellular respiration.

The Carbon Cycle

Carbon Cycle

• Fossil fuels (coal, oil, natural gas) are essentially stored carbon.

• They are left over from the bodies of plants and animals that died millions of years ago and were trapped underground.

• When we burn fossil fuels, we release carbon into the atmosphere as CO2.

• Problem: We burn such large quantities of fossil fuels; we are increasing the CO2 levels in the atmosphere.

How Humans are affecting the Carbon Cycle

• All organisms need nitrogen to build proteins.

• There are vast quantities around us; nitrogen gas makes up 78% of the atmosphere.

• Nitrogen-fixing bacteria are the only organism that can use nitrogen gas directly from the atmosphere. All other organisms depend upon these bacteria for their nitrogen.

• These bacteria take nitrogen gas from the air and transform, or “fix,” it into a form that ecosystems can use.

• Nitrogen-fixing bacteria live within the roots of a few plants (beans, peas, clover, alder trees) and in the soil. They both release nitrogen into the soil.

• Animals obtain nitrogen through consumption of plants or other animals.

The Nitrogen Cycle

NitrogenCycle

• In the nitrogen cycle, nitrogen moves back and forth between the atmosphere and living things.

• Decomposers, such as fungi and bacteria, return nitrogen to the soil by breaking down dead organisms and waste products (urine, dung, leaves, and other plant parts.)

• After decomposers return the nitrogen to the soil, some nitrogen is converted into a usable form of nitrogen for plants and other bacteria transform a small amount into nitrogen gas, returning it back into the atmosphere, completing the nitrogen cycle.

• Once nitrogen enters an ecosystem, most of it stays within the ecosystem, cycling between organisms and the soil in an endless loop.

Closing the Nitrogen Cycle

• Scientists refer to ecological change as

Succession.• ex: As you walk through a forested area, you see many

different kinds of plants and animals. Your grandparents and great-grandparents may have walked through the same forested area and saw many of the same plants and animals; however, that area may not have always been a forest. It may have been a meadow or even a shallow lake.

Section 3.3 How Ecosystems Change

• Succession is a regular pattern of changes over time in the types of species in a community.

• May take hundreds or thousands of years.

• As each new community arises, the previous one dies.

ex: Tall pines trees shade the ground. Pine seedlings need

light but the taller trees block the sunlight. Maples

and oaks can grow in less light, so they replace the

pine trees.

• The community that eventually forms if the land is left undisturbed is called the climax community.

Succession

• In 1980, Mount St. Helens (Washington State) erupted, burning and flattening 18,000 hectares (about 44, 460 acres) of land.

• Today, if you were to visit, the forest has already begun to regenerate.

• Succession that occurs on a surface where an ecosystem has previously existed is call secondary succession.

Secondary Succession

• Succession that occurs on surfaces where no ecosystem existed before is called primary succession.

• Occurs on new islands created by volcanic eruptions and in areas exposed when a glacier retreats.

• Primary succession is much slower to progress than secondary succession because there is no soil. It takes several hundred to several thousand years to produce fertile soil naturally.

• After soil forms, seeds of small plants are able to germinate and grow.

Primary Succession