This document discusses ecosystems and energy flow between organisms. It begins by defining producers (autotrophs) which get energy from the sun through photosynthesis. Consumers (heterotrophs) depend on producers for nutrients and include herbivores, carnivores, scavengers, and decomposers. Energy and matter are transferred between trophic levels in food chains and food webs. Ecological pyramids illustrate how biomass, numbers, and energy decrease at higher trophic levels due to energy lost as heat. Cycles of water, carbon, nitrogen, and phosphorus allow these essential elements to be reused in ecosystems.

1. Section ObjectivesSection Objectives
• Trace the path of energy and matter in an
ecosystem.
• Compare how organisms satisfy their
nutritional needs.

2. The producers: Autotrophs
 The ultimate source of the energy for life isThe ultimate source of the energy for life is
thethe sunsun..
 Plants use thePlants use the
sun’s energy tosun’s energy to
manufacturemanufacture
food in afood in a
process calledprocess called
photosynthesis.photosynthesis.

3. The producers: Autotrophs
 Other organisms in the biosphere depend onOther organisms in the biosphere depend on
autotrophs for nutrients and energy. Theseautotrophs for nutrients and energy. These
dependent organisms are calleddependent organisms are called consumers.consumers.
 An organism that uses light energy or energyAn organism that uses light energy or energy
stored in chemical compounds to makestored in chemical compounds to make
energy-rich compounds is a producer, orenergy-rich compounds is a producer, or
autotrophautotroph..

4. The consumers: Heterotrophs
 An organism that cannot make its own foodAn organism that cannot make its own food
and feeds on other organisms is called aand feeds on other organisms is called a
heterotroph.heterotroph.

5. The consumers: Heterotrophs
 A heterotrophA heterotroph
that feeds only onthat feeds only on
plants is anplants is an
herbivore.herbivore.

6. The consumers: Heterotrophs
 SomeSome
heterotrophs eatheterotrophs eat
otherother
heterotrophs.heterotrophs.
Animals such asAnimals such as
lions that killlions that kill
and eat onlyand eat only
other animalsother animals
areare carnivorescarnivores..

7. The consumers: Heterotrophs
 ScavengersScavengers eat animals that have already died.eat animals that have already died.

8. The consumers: Heterotrophs
 DecomposersDecomposers
break down thebreak down the
complexcomplex
compounds ofcompounds of
dead anddead and
decaying plantsdecaying plants
and animals intoand animals into
simplersimpler
molecules thatmolecules that
can be morecan be more
easily absorbedeasily absorbed
•Bacteria and fungi, are
decomposers.

9. Flow of Matter and Energy in Ecosystems
Autotrophs
First-order
heterotrophs
Third-order
heterotrophs Second-order
heterotrophs
Decomposers

10. Food chains: Pathways for matter
and energy
 In aIn a food chainfood chain, nutrients and energy move, nutrients and energy move
from autotrophs to heterotrophs and,from autotrophs to heterotrophs and,
eventually, to decomposers.eventually, to decomposers.

11. Food chains: Pathways for matter
and energy
 A food chain is drawn using arrows to indicateA food chain is drawn using arrows to indicate
the direction in which energy is transferredthe direction in which energy is transferred
from one organism to the next.from one organism to the next.
berries → mice → black bear

12. Food chains: Pathways for matter
and energy
 A portion of the energy is given offA portion of the energy is given off as heatas heat atat
each transfer.each transfer.

13.  Each organism in a food chain represents aEach organism in a food chain represents a
feeding step, orfeeding step, or trophic level,trophic level, in the passage ofin the passage of
energy and materials.energy and materials.

14. Food webs
 AA food webfood web, shows all the possible feeding, shows all the possible feeding
relationships at each trophic level in arelationships at each trophic level in a
community.community.

15. Food
webs
Chihuahuan raven Honey mesquite
(pods eaten by beetles)
Pronghorn
antelope
Gambel
quail
Jackrabbit
Desert
tortoise
Prickly
pear cactus
Long-tail
weasel
Coyote
(top carnivore)
Roadrunner
Kangaroo rat
(seed eater)
ants
Texas horned
lizard
Red spotted
toad Mexican
whiptail lizard
Mojave
rattlesnake

16. Energy and trophic levels: Ecological
pyramids
 TheThe basebase of the ecological pyramid representsof the ecological pyramid represents
the autotrophs, or first trophic level. Higherthe autotrophs, or first trophic level. Higher
trophic levels are layered on top of onetrophic levels are layered on top of one
another.another.

17. Energy and trophic levels: Ecological
pyramids
 The pyramid ofThe pyramid of
energy illustratesenergy illustrates
that the amountthat the amount
of availableof available
energyenergy
decreases atdecreases at
each succeedingeach succeeding
trophic level.trophic level.
Pyramid of Energy
Heat
Heat
Heat
Heat
0.1% Consumers
1% Consumers
10% Consumers
100%
Producers
Parasites, scavengers, and
decomposers feed at each
level.

18. Energy and trophic levels: Ecological
pyramids
 The total energy transfer from one trophicThe total energy transfer from one trophic
level to the next is only aboutlevel to the next is only about ten percentten percent
because organisms fail to capture and eat allbecause organisms fail to capture and eat all
the food energy available and some of thethe food energy available and some of the
energy enters the environment as heat, butenergy enters the environment as heat, but
the total amount of energy remains the same.the total amount of energy remains the same.

19. Energy and trophic levels: Ecological
pyramids
 A pyramid ofA pyramid of
numbers showsnumbers shows
that populationthat population
sizes decreasesizes decrease
at each higherat each higher
trophic level.trophic level.
Pyramid of Numbers
Fox (1)
Birds (25)
Grasshoppers (250)
Grasses (3000)

20. Energy and trophic levels: Ecological
pyramids
 BiomassBiomass is the totalis the total
weight of livingweight of living
matter at eachmatter at each
trophic level. Atrophic level. A
pyramid of biomasspyramid of biomass
represents the totalrepresents the total
weight of livingweight of living
material available atmaterial available at
each trophic level.each trophic level.
Pyramid of Biomass
1 kilogram of
human tissue
10 kilograms
of beef
100 kilograms
of grain

21. Cycles in Nature
 Matter is cycledMatter is cycled and isand is not replenishednot replenished likelike
the energy from sunlight. There is a finitethe energy from sunlight. There is a finite
amount of matter.amount of matter.

22. The water cycle
 Water is constantly moving between theWater is constantly moving between the
atmosphere and Earth.atmosphere and Earth.
Precipitation
Evaporation
Runoff
Groundwater
Transpiration
Evaporation
Condensation
Oceans

23. The carbon cycle
 Carbon is the building block of the moleculesCarbon is the building block of the molecules
of life (like proteins and sugars).of life (like proteins and sugars).
 Organisms use these carbon molecules forOrganisms use these carbon molecules for
growth and energy.growth and energy.

24. The nitrogen cycle
 Nitrogen is converted from a gas toNitrogen is converted from a gas to
compounds important for life and then back tocompounds important for life and then back to
a gas.a gas.

25. The phosphorus cycle
 In the phosphorus cycle, phosphorus movesIn the phosphorus cycle, phosphorus moves
between the living and nonliving parts of thebetween the living and nonliving parts of the
environment.environment.