Ecosystems transfer energy from producers to consumers in food chains and webs. Only about 10-40% of energy is transferred between trophic levels with the rest lost as heat. This inefficiency means organisms at higher trophic levels require more resources. Humans have appropriated over 40% of primary production and 11% of land for agriculture, diminishing ecosystem services. Ecosystem management aims to balance human uses with sustainability.
3. Trophic Levels
• trophic level: feeding level
• food chains: describe where the
energy and nutrients go as they move
from one organism to another
• energy moving “up” the food chain
• seldom isolated entities
• food web: interconnected food chains
4. Trophic
Categories
• autotroph: produce their own food
• heterotroph: must consume their
food
• consumers: eat living prey
• decomposers: break
down dead organic matter
5.
6. Producers
• primary production:
photosynthesis and growth of producers
• most are green plants
• chlorophyll: green pigment involved in
photosynthesis
• chemosynthesis: using
inorganic chemicals to form organic
matter
7. Consumers
• consumers: eat living stuff
• primary consumers: animals that feed
directly on producers
• secondary consumers: animals that feed
on primary consumers
• carnivores: secondary and higher-order
consumers
• omnivores: eat both plants and animals
8. Decomposers
• decomposers: eat dead stuff
• detritus: dead stuff (leaves, grasses, plant
material, fecal wastes, dead bodies) eaten
by decomposers
• scavengers, detritus feeders, chemical
decomposers
• fermentation: modified cell respiration
that occurs in the absence of oxygen
• anaerobic: without oxygen
12. Energy Flow
• photosynthesis captures only
2% of incoming solar energy
• 120 Gigatons = terrestrial net
production
• standing-crop biomass:
actual biomass of primary
producers at any given time
13. Fate of Food
• 60-90% of food is burned for
energy
• remaining 10-40% converted
to body tissues
• cellulose: cell wall material
that is not digested
14. Energy Flow
• Only a fraction is passed on...
1. much of the preceding
trophic level is biomass that
is not consumed
2. much of what is consumed
is used as energy to fuel the
heterotroph’s cells and
tissues
3. some of what is consumed
is undigested and passes
through the organism as
waste
15. • Inefficiency means two things...
1. individuals at higher levels in the biomass pyramid
represent a greater amount of the Sun’s energy for the
same amount of body tissue
i takes a longer time to produce a top-order
consumer
ii top-order consumer also
requires more water and
other resources
2. Some materials are difficult
to get rid of and remain in
the bodies of predators at
higher rates than in their
prey
17. Aquatic Systems
• energy transfer is often more efficient • takes less energy to support
your body weight in water than on land or air
• food chains can be longer
18.
19. Aquatic Systems
• The biomass pyramid in aquatic
systems often does not resemble the
biomass
pyramid on terrestrial ecosystems •
phytoplankton is often ephemeral
20. Human Values and
Ecosystem Sustainability
Human Values: Energy
Flow
• almost 11% of Earth’s land has been converted from forest/ grassland
to agriculture
21. • Benefits of forests: 3.3 billion cubic meters of wood
• 15% of the world’s energy consumption is
derived from plant material
• 40% of primary production on land
appropriated for human needs - yet we
only represent 5% of the biomass
22. Human Values: Cycles
• burning of fossil fuels has increased CO2 in the atmosphere, where, by
the mid-21st century, it will have doubled since the beginning of the
industrial revolution
23.
24. Value of Ecosystems
• incremental value: the economic value placed on changes in the
quantity or quality of various types of services may influence human
welfare
• Total value of ecosystems to humans was $41 trillion in
2004....close to the $55 trillion calculated for the gross world
economic product in 2004
25.
26. Value of Ecosystems
• ecosystem capital stock: the ecosystems
and the populations in them, including the
lakes and wetlands) • must be given
adequate weight in public-policy decisions
involving changes to that stock
• annual loss of $250 billion through habitat
conversion alone!
27. Restoration
• Potential for restoration rests
on...
1. Abiotic factors must have remained
unaltered, or, if not, can at least be
returned to their original state
2. viable populations of the species
formerly inhabiting the ecosystem
must still exist
3. ecosystem must not have been
upset by the introduction of one or
more nonnative species that cannot
be eliminated and that may preclude the survival of reintroduced
species
28. Restoration
• Why restore ecosystems?
1. aesthetic reasons
2. for the benefit of human use
3. benefit of the species and ecosystems themselves
29. The Future
• agriculture will likely require at
least 15% more land in the
future
• must use these resources
sustainably
30. Managing Ecosystems
• virtually no ecosystem can
escape human impact •
objectives can be to maximize
profit OR maintain the forest as
a sustainable and diverse
ecosystem that yields multiple
products and services
31. Managing Ecosystems
• ecosystem management:
comprises several main principles
• looks at ecosystems on both
small and large scales
• looks at the human element of
these ecosystems
32. US Forest Service
• responsible for managing 192
million acres of national forests •
believes the policy of sustainability
should be the guiding star for
stewardship of the national forests
and grasslands
33. Human Effects: Summary
• everyone in the world depends on nature
• humans have made
unprecedented changes to
ecosystems:
• weakened nature’s ability to deliver
other key services such as the
purification of air/water, protection
from disasters, provision of
medicines
• edge of a massive wave of species extinctions
• pressures on ecosystems will increase globally
