Ecosystems and the Biosphere
Energy transfer
 All organisms need energy to carry out essential functions – growth, movement, maintenance,
repair, and reproduction
 In ecosystems, energy flows from sun to autotrophs to organisms that eat autotrophs to
organisms that feed on other organisms.
 Amount of energy ecosystem receives and the amount. transferred from organism to organism
have an effect on the ecosystem’s structure.
Energy Flow
 Whenever one organism eats another, molecules are metabolized and energy is transferred.
 Energy flows through an ecosystem from producer to consumer
 Trophic level indicates the organism’s level of nourishment, or position in the sequence of
energy transfer illustration
o First level – all producers
o Second level – herbivores
o Third level – predators of herbivoresFood chain – single
pathway of feeding relationship that results in energy
transfer (pic to right
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http://www.sugar.ca/english/images/tradealliances/food_chain.jpg)
Grass (primary producer) to mouse to snake to hawk
Feeding relationships in ecosystems are usually too complex to be represented by a single
food chain.
Many consumers eat more than one type of food and many organisms may feed on the same
organisms.
 food webs are models of complex feeding networks
within ecosystems; series of food chains interwoven
(blue pic to left)
http://www.absc.usgs.gov/research/seabird_foragefish/marinehabitat/images/Food_Web3.gif)
Energy Pyramid – distribution of energy and matter in an ecosystem (pic to right
http://www.mesa.edu.au/friends/seashores/images/energy_pyramid.gif)
 Shows the distribution of energy in a food chain
 Energy flows upwards from producers to consumers
 Energy is lost as head between each tier of the pyramid;
average of 10% of energy is passesd from one level to
the next level
Other types of pyramids
 Biomass pyramid shows the total mass or organisms at
each tropic level
o Less biomass at higher tropic levels than
lower
levels
 Pyramid of numbers shows the actual number of
organisms present in each trophic level (pic to right
http://www.earthforce.org/files/1284_image2_Energy_Pyramid_for_Galvbay.jpg)
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Organisms that belong to the lowest trophic level
are more abundant th an organisms in the highest
level
Example – in Africa you will see about 1000 zebras,
gazelles, or other herbivores for every lion or
leopard and there are a lot more grasses, trees and
shrubs than there are herbivores