Communities and Ecosystems. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Trophic structure is a key factor in community dynamics

Communities and EcosystemsCommunities and Ecosystems

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Trophic structure is a key factor in community dynamics

•Every community has a trophic structure

–A pattern of feeding relationships consisting of several different levels

–The sequence of food transfer from producer to consumer is called a food chain.

•Producers are autotrophs (“self feed”)

•Consumers are heterotrophs (“different feed”)


Food chains interconnect, forming food webs

• A food web

–A network of interconnecting food chains

–Arrows indicate direction of nutrient transfer

–Several 1° Consumers depend on same producer

–Some eat at multiple levels

Figure 37.10


Ecosystem ecology emphasizes the processes

energy flow and chemical cycling

Chemicalcycling

Energyflow

Lightenergy

Chemicalenergy

Chemical elements

Heatenergy

Figure 37.11

An ecosystemIncludes a community and the abiotic factors with which it interacts.

Transfer substances through trophic levels. But one flows out the other cycles within.


Each day Earth receives energy from the sun equivalent to 100 million atomic bombs…

Most is absorbed, scattered, and reflected by our atmosphere or by the Earths surface.

Only 1% of all the light energy the Earth receives is converted into chemical energy by primary producers through photosynthesis (the process of changing light into sugar and other foods/chemical energy).

However, on a global scale this is enough to produce170 billion tons of organic material per year.


The amount of living organic material in an ecosystem is its Biomass.

The amount of solar energy converted to chemical energy (organic material) by producers in a given area at a given time is called primary production.

Primary production


Primary production sets the energy budget for ecosystems

• Is the rate at which producers convert sunlight to chemical energy in organic matter (biomass)

Open ocean

Estuary

Algal beds and coral reefs

Tundra

Temperate grassland

Cultivated land

Boreal forest (taiga)

Savanna

Temperate deciduous forest

Tropical rain forest

0 500 1,000 1,500 2,000 2,500

Average net primary productivity (g/m2/yr)Figure 37.12

Desert and semidesert scrubContributes most to Earth’s total net production due to its size


Energy supply limits the length of food chains

• A pyramid of production

– Shows the flow of energy from producers to primary consumers and to higher trophic levels

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Producers

10 kcal

100 kcal

1,000 kcal

10,000 kcal

1,000,000 kcal of sunlight

Figure 37.13

Can’t eat all

Can’t digest all

2/3 digested used by cells

Rest to mass (growth)

Only this can be eaten by next

level.

1/1000 of the sun’s energy makes it this far

(1% of sun’s energy)


Only about 10% of the energy stored at each trophic level is available to the next level

• Only a tiny amount of the energy converted by primary producers flows through he food chain to the top consumer

• This is why top level consumers require so much territory…

– It takes a lot of vegetation to support trophic levels so many steps removed from photosynthetic production.

• Also why food chains are limited in size

– Limited by availability of energy


A production pyramid explains why meat is a luxury for humans

• A field of corn

– Can support many more human vegetarians than meat-eaters (less energy is wasted)

CONNECTION

Trophic level

Secondaryconsumers

Primaryconsumers

Producers

Humanvegetarians

Corn

Humanmeat-eaters

Cattle

Corn

Figure 37.14


Consumers

Producers

Nutrientsavailable

to producers

Abioticreservoir

Detritivores

3

2

1

4

Chemicals are recycled between organic matter (organisms) and abiotic reservoirs

Biogeochemical cycle

Figure 37.15

Soil

Decomposers


Water moves through the biosphere in a global cycle

Figure 37.16

Transportover land

Solar energy

Net movement ofwater vapor by wind

Runoff andgroundwater

Percolationthroughsoil

Precipitationover landEvaporation and

transpiration fromland

Precipitationover ocean Evaporation

from ocean

Solar heatdrives the global water cycle through

precipitation, evaporation, and transpiration


Human activity affects the global water cycle

1)Important source of atmospheric water is transpiration, so destruction of the rain forests will change amount of water in the atmosphere and can alter local and global weather patterns.

2) Pumping large amounts of ground water to the surface for irrigation can increase evaporation and deplete ground water supplies.


The carbon cycle relies on photosynthesis, respiration, and decomposition

Carbon compounds (organic) are consumed.

Respiration returns CO2 to the atmosphere.

Photosynthesis = Respiration

Burning fossil fuels is increasing CO2 levels and is causing global warming.


The nitrogen cycle relies heavily on bacteria

Figure 37.18

Nitrogen is a constituent of DNA and proteins…is essential for life.

Various bacteria in soil convert gaseous N2 to compounds that plants use:

ammonium (NH4+) and nitrate (NO3–)

Detritivores decompose organic matter and recycle nitrogen to plants.


Humans are altering the nitrogen cycle

1)Sewage treatment facilities often empty large amounts of nitrogen into rivers and streams

2) Fertilizer is routinely applied

• These nitrogen sources continue to fertilize when they enter lakes and streams causing algae blooms

• Nitrates enter ground water used as drinking water and can be toxic


The phosphorus cycle depends on rock weathering

Figure 37.19

Phosphorus is needed for nucleic acids (DNA), phospholipids (cell membranes), bones and ATP (energy)

It and other soil minerals are recycled locally.

Weathering is a slow process so phosphorus is limited.


In aquatic systems that have not been altered by humans the limited amount of phosphorus keeps algae to a minimum.

In areas affected by humans (sewage, fertilizers, pesticides) phosphate pollution leads to heavy algal growth.

Major algae blooms can kill aquatic organisms and be toxic to humans.

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Communities and Ecosystems. Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Trophic structure is a key factor in community dynamics