¨       The flow of energy through an ecosystem is one of the most important factors that determines the system’s capacity to sustain life.

Producers

¨       Sunlight is the main energy source for life on Earth.

¨       In a few ecosystems, some organisms obtain energy from a source other than sunlight.

¨       The energy is stored in inorganic chemical compounds.

Ø       mineral water that flows underground or boils out of hot springs

Ø       undersea vents are loaded with chemical energy

¨       Autotrophs use energy from the environment to fuel the assembly of simple inorganic compounds into complex molecules.

v      plants, some algae, and certain bacteria are organisms that produce living tissues.

¨       Organisms that make their own food are also called producers.

Energy From the Sun

¨       The best-known autotrophs obtain energy through the process of photosynthesis.

¨       Photosynthesis is the process by which light energy is used to convert carbon dioxide and water into oxygen and energy-rich carbohydrates.

¨       Oxygen is added to—and carbon dioxide is removed from—the Earth’s atmosphere.

¨       On land, plants are the main autotrophs

¨       In freshwater and the upper layer of the ocean, algae are the main autotrophs.

¨       In tidal flats and salt marshes, cyanobacteria is the most common source.

Life Without Light

¨       Some autotrophs can produce food in the absence of light.

¨       These autotrophs rely on energy within the chemical bonds of inorganic molecules.

¨       Chemosynthesis is the use of chemical energy to produce carbohydrates.

¨       Several types of bacteria represent a large portion of living autotrophs.

Consumers

¨       Some organisms cannot make their food directly and must acquire it from other organisms.

¨       Heterotrophs are organisms that rely on other organisms for their energy and food supply.

v      animals, fungi and some bacteria fit into this group

¨       Heterotrophs are also called consumers.

¨       Types of heterotrophs are:

Ø       Herbivores obtain energy by eating plants.

Ex) cows, caterpillars, and deer

Ø       Carnivores eat animals.

Ex) snakes, dogs, and owls

Ø       Omnivores eat both plants and animals.

Ex) humans, bears, and crows

Ø       Detritivores food on plant and animal remains and other dead matter.

Ex) mites, earthworms, snails, and crabs

Ø       Decomposers break down organic matter

Ex) bacteria and fungi

Feeding Relationships

¨    Energy flows through an ecosystem in one direction, from the sun or inorganic compounds to autotrophs (producers) and then to various heterotrophs (consumers).

Food Chains

¨       The energy stored by producers can be passed through an ecosystem along a food chain.

¨       A food chain is a series of steps in which organisms transfer energy by eating and being eaten.

Ex) grassàgrazing antelopeàcoyote

      (producer)    (herbivore)                     (carnivore)

Ex) algaeàzooplanktonàsmall fishàsquidàshark

Food Webs

¨       A food web is a feeding relationship among various organisms in an ecosystem that form a network of complex interactions.

¨       A food web links all the food chains in an ecosystem together.

Trophic Levels

¨       A trophic level is each step in a food chain or food web.

¨       Producers make up the first trophic level.

¨       Consumers make up the second, third, or higher trophic levels.

¨       Each consumer depends on the trophic level below it for energy.

Ecological Pyramids

¨       The amount of energy or matter in an ecosystem can be represented by an ecological pyramid.

¨       An ecological pyramid is a diagram that shows the relative amounts of energy or matter contained within each trophic level in a food chain or food web.

Energy Pyramid

¨       There is no limit to the number of trophic levels but, only part of the energy that is stored in one trophic level is passed on to the next level.

¨       Only about 10 percent of the energy available within one trophic level is transferred to organisms at the next trophic level.

Ex) 100% producersà10% first-level consumersà1% second-level consumersà0.1% third-level consumers

¨       The more levels that exist between a producer and a top-level consumer, the less energy that remains from the original amount.

Biomass Pyramid

¨       Biomass is the total amount of living tissue within a given trophic level.

¨       Biomass is expressed in terms of grams of organic matter per unit area.

¨       A biomass pyramid represents the amount of potential food available for each trophic level.

Pyramid of Numbers

¨       A pyramid of numbers is based on the numbers of individual organisms at each trophic level.

¨       For some ecosystems, such as a meadow, the pyramid of numbers is the same as that of the energy and biomass pyramids.

¨       For others, such as a forest, there are fewer producers than there are consumers.

¨       A single tree has a large amount of energy and biomass, but it is only one organism.