Ecosystems

Chapter 15

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

– a group of organisms of the same species living in a specific area

• A community is all the populations living in a certain area that are able to potentially interact with each other– or more simply, all the living things in an area

• An ecosystem is composed of all the living organisms in a community, and all the non-living factors they interact with in the environment

An ecosystem then, has two parts• Biotic and abiotic factors

– biotic factors refer to all the living things in an environment (a community)

– abiotic factors are all the non-living components; the physical environment or the organism’s habitat

• made up of chemicalrecourses (carbon, nitrogen & phosphorus)

• and physical conditions (temperature, salinity, humidity & energy sources)

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

geographic areas of land or water• Terrestrial biomes’ characteristics determined

primarily by temperature and rainfall– this leads to primary vegetation in the area, which

determines the type of animals• Aquatic biomes’ characteristics based on salinity,

water movement & depth

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

• two kinds of organisms; producers & consumers

Trophic levels• Producers: the plants

– convert light energy from the sun into chemical energy through photosynthesis

• this “chemical energy” = food!

• Primary consumers: the herbivores– the animals that eat plants– animal breaks chemical bonds (of food),

releasing energy to fuel growth, reproduction & movement

Trophic levels, cont.• Secondary consumers: the carnivores

– eat herbivores– energy stored in herbivore is released to fuel growth,

reproduction & movement of carnivore• Tertiary consumers: the “top carnivores”

– as with each prior step, top carnivores break down foods to fuel their own needs

– several steps removed from the initial capture of solar energy by the plant

• The path of energy from producer to consumer is called a food chain– rarely have a 5th level

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– many organisms are omnivores and can occupy

more than one position in the food chain• 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 (dead material produced at all trophic levels like animal waste & leaf litter)– ex: vultures, earthworms, dung

beetles • Decomposers: organisms that

convert organic material to inorganic forms– ex: fungus, bacteria

• Both groups release many important chemical components that can eventually be recycled & used by the primary producers

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?– Approx. 12,000 lbs. of grain – BUT, that 1200 lb. cow will only add 120

lbs. of biomass to the carnivore that eats it & only 12 lbs. to the top carnivore

• 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

• Generally, it occurs at the same rate as energy moving through the trophic levels; about 10% per level

• Very low levels of toxins can be lethal over time

• Pollutant or chemicals share 2 characteristics– fat soluble – do not readily degrade

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

• each chemical is stored in a non-living part of the environment, called a reservoir

• organisms acquire chemicals from reservoir then cycles through the food chain

Carbon cycle• Carbon is necessary for plants to make sugar

(& feed the world!)• Primary reservoir is atmosphere, CO2

• Secondary reservoir is the ocean; organisms use dissolved carbon to build shells

• Most carbon released back to reservoirs by metabolic processes of organisms

• Carbon also released into atmosphere from burning of fossil fuels

Carbon cycle

Nitrogen cycle• Nitrogen is necessary for making proteins• Primary reservoir is the atmosphere in the form of

N2– unusable form for most organisms– must be metabolized by bacteria in soil to be converted

into useable form; the bacterial “fix” the nitrogen, so called nitrogen-fixing bacteria

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

• Plant growth is limited by nitrogen levels in soil

Nitrogen cycle

Phosphorus cycle• Phosphorus is needed for every molecule of

ATP & DNA• Primary reservoir is soil (leached from rocks)• 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