Ecosystems

Chapter 15

Levels of ecological study• Remember how a population is defined?

• A community is

• An ecosystem is

An ecosystem then, has two parts

• Biotic and abiotic factors – biotic

– abiotic

Biomes• The largest of Earth’s ecosystems; they cover

huge geographic areas of land or water• Terrestrial biomes:

• Aquatic biomes:

Terrestrial biomes

Aquatic biomes

In an ecosystem,• Energy flows

– energy from the sun is captured & converted to chemical energy by photosynthesis

– captured energy is transformed again & again by living organisms as it passes through an ecosystem (as organisms eat one another)

– trophic structure is the pattern of feeding relationships consisting of several levels

Trophic levels• Producers: the plants

• Primary consumers: the herbivores

Trophic levels, cont.• Secondary consumers: the carnivores

• Tertiary consumers: the “top carnivores”

• The path of energy from producer to consumer is called a food chain

Food chains

• What do the arrows represent?

Food webs

• Food chains are a helpful tool for ecologists, but they are an oversimplification of an ecosystem’s trophic structure

• A food web, a network of interconnecting food chains, provides a more realistic view of trophic structure

Food webs

A simplified ( ! ) food web of the NW Atlantic

Missing from most food chain & food web diagrams. . .

• Detritivores: organisms that get their energy from detritus

• Decomposers: organisms that convert organic material to inorganic forms

Inefficiency of food chains• Energy flows through all the trophic levels,

but energy is lost as heat at each level – 5 lbs. of plants does not equal 5 lbs. of new body

weight– only about 10% of what an herbivore eats is

converted into its own tissue; same for carnivore consuming an herbivore, and so on

• 90% lost to fueling metabolic processes & as feces– this is called the 10% rule

10% rule limits length of food chain• How much plant biomass is

necessary to produce a single 1200 lb. cow?

• This is why there are not too many top carnivores; they require a huge geographic area to support themselves

• AND, this is why there are so many more plants than animals; it takes a whole lot of plants to support just a few animals

Biomagnification• When a chemical

becomes more & more concentrated in organisms at successively higher trophic levels

• Very low levels of toxins can be lethal over time

• Pollutant or chemicals share 2 characteristics

In an ecosystem,• Chemicals cycle

– chemicals just cycle around & around using the same pathway as energy– the food chain

– plants take up molecules from the air or soil which move into animals as consumed

– when plants & animals die, detritivores & decomposers return chemicals to the environment

– **chemicals cycle through both living and non-living components of the ecosystem

Carbon cycle• Carbon is necessary for plants to make sugar

(& feed the world!)• Primary reservoir is

• Most carbon released back to reservoir by

• Carbon also released into atmosphere from

Carbon cycle

Nitrogen cycle• Nitrogen is necessary for making proteins• Primary reservoir is

• Nitrogen returns to atmosphere when waste & dead bodies are broken down by other bacteria that convert it back to N2

Nitrogen cycle

Phosphorus cycle• Phosphorus is needed for every molecule of

ATP & DNA• Primary reservoir is• Plant growth is limited by phosphorus levels

in soil• Most fertilizers contain phosphorus &

nitrogen

Phosphorus cycle

The last word about ecosystems

• Keep this straight:

• energy FLOWS• chemicals CYCLE

Summary• Biomes are the largest ecosystems.• Ecosystems are all the living and non-living

elements in an area.• Energy flows through an ecosystem. Each

ecosystem has its own trophic structure.• Food chains & food webs illustrate trophic

structure and include producers, consumers, detritivores & decomposers at all levels.

• Chemicals cycle in an ecosystem through the trophic structure, going between the living and non-living components of the ecosystem.