Download Ecosystem Processes

Ecosystem Processes
Thinking Question:
• While browsing through the drinks
offered at a convenience store, you
notice a new soft drink advertised as a
“low-calorie energy drink.” Write out your
definition of “energy,” and then decide if
this drink label is accurate or a case of
false advertising.
Energy
• Energy is defined as the ability to do
work.
• Energy is NOT a material. Energy is a
phenomenon.
• Energy can be transformed (i.e.
mechanical to heat) and transferred, but
is not recycled.
Energy flows
• Energy for most ecosystems on earth
comes from the sun.
• Light energy is converted to chemical
energy by producers to power their own
metabolism.
• Energy is lost from the earth as heat.
Nutrients
• “Nutrient” in an ecological sense refers to
the inorganic materials taken in by
producers and converted into organic
molecules.
• Nutrients include carbon (as carbon
dioxide), nitrogen, phosphorous, oxygen,
and other building blocks of biological
molecules.
Nutrients Cycle
• Because nutrients ARE materials, they
cycle in the earth’s ecosystems. Carbon
from carbon dioxide may become carbon
in a sugar made by a plant.
• Decomposers break down organic
molecules and release inorganic
nutrients to the ecosystem.
Photosynthesis
• Energy is converted
and nutrients are
fixed by the process
of photosynthesis.
• Producers use the
sun’s energy to
convert inorganic
carbon dioxide into
organic molecules,
such as sugars.
Net Productivity
• Net primary productivity is the energy
that producers can make available to a
community at any one time.
• Net productivity determines how much
life an ecosystem supports.
• Productivity can be measured in calories
(units of energy) or biomass (amount of
organic material).
Biomass (g/m2)
Thinking question
discussion
• So what about that “low-calorie energy
drink?”
Energy Flows
Thinking Question:
• One reason that some people become
vegetarians is to reduce their impact on
the environment. List as many positive
ecological effects of vegetarianism as
you can think of. Then list as many
negative effects.
Food Chain Concept
• Chemical energy is passed through the
ecosystem as organisms consume other
organisms.
• Organisms occupy one or more trophic
levels (“feeding” levels) depending on
what they are eating.
Trophic Levels
• Producers: Use light energy to
manufacture organic molecules.
• Primary consumers: eat producers
• Secondary consumers: eat primary
consumers
• Tertiary consumers: eat secondary
consumers.
Food Webs
• A food web is a model of energy flow in a
community.
• Arrows indicate the direction in which
energy flows from one organism to the
next. (Note that this is NOT a cycle.)
• A single organism will be involved in
many food chains, and some will occupy
several trophic levels.
“Death Eaters”
• Decomposers: Bacteria and fungi, which
use external digestion to break organic
matter down into inorganic substances.
• Detritivores: Animals that feed on dead
plant material.
• Scavengers: Animals that feed on dead
animal flesh.
Energy Loss
• At each step in a food chain or food web,
energy is lost as heat. Each organism
takes in energy to meet its own needs,
so most of the energy taken in is
converted to motion and heat.
• 10% or less of the energy consumed will
be available to the next consumer.
Energy Pyramid
• Because 90% or more of consumed
energy is used by the organism, and only
a small amount can be passed on, the
entire system is inefficient.
• The higher an organism is on the food
chain, the greater amount of biomass is
required to support that organism.
Human Food Chain
• Humans are
omnivores, capable
of eating a wide
variety of foods.
• We can create a
human food chain
by looking at our
meat sources.
Grass-fed Food Chain
A cow can convert grass, which
we cannot eat, into meat, which
we can.
We obtain 8-10% of the
energy that a pasture-fed cow
consumes.
Industrial Food Chain
Corn, which could
be fed to humans, is
fed to feedlot cattle.
Because of
overproduction, corn
is cheap.
A cow’s digestive
system is not adapted to
eating corn. The cattle
are often sick, and much
of the energy is wasted.
Cheap burgers
come at a high
ecological cost.
The industrial food
chain is about 1/3
as efficient as the
grass food chain.
Thinking question
discussion
• What are possible positive and negative
effects of “going veggie?”
• How can your everyday food choices
have an impact on the environment?
Nutrients Cycle
Thinking Question:
• Global climate change has everyone’s
attention these days. One action that
some people take in response is to plant
trees. What does planting trees have to
do with alleviating global climate
change?
Material Cycles
• Material cycling follows the law of
conservation of matter.
• Elements used by living organisms are
taken up and used by producers, used
passed down the food chain by
consumers, and are released back to the
environment by decomposers.
Nitrogen Cycle
• The earth’s atmosphere is 78% nitrogen,
but in this form it cannot be used by
producers.
• Nitrogen-fixing bacteria convert nitrogen
gas into nitrogen compounds that plants
can absorb and use in making amino
acids to build proteins.
Nitrogen Cycle
Phosphorous Cycle
• Unlike other nutrients, phosphorous does
not exist as an atmospheric gas.
• Rock phosphates dissolve in rain as rock
weathers, carrying phosphates into
streams and soil.
• Phosphates settle out on the bottoms of
ponds, and may consolidate back into
phosphate-rich rock.
Phosphorous Cycle
Water Cycle
• Weather patterns form part of the water
cycle.
• Water remains chemically unchanged
during the water cycle. It is evaporated
as water vapor, condensed into rain
clouds, and finally falls as precipitation.
• Water may collect in rocks as
groundwater.
Water Cycle
Carbon Cycle
• Carbon forms the backbone of all organic
molecules.
• Carbon from the atmosphere is “fixed” by
producers, which manufacture organic
molecules using the sun’s energy.
• Breakdown of these molecules releases
carbon dioxide back to the atmosphere.
Carbon Cycle
Global “Warming”
• “Global Warming” — better termed
“Global Climate Change” — has been
strongly linked to levels of carbon dioxide
in the atmosphere.
• While natural events add carbon dioxide
to the atmosphere, humans activity also
contributes to carbon levels.
Fossil Fuels
• Fossil fuels are the remains of ancient
swamps. Plants fixed carbon as carbonrich organic compounds. Carbon
compounds accumulated in swamps
over hundreds of millions of years.
• In less than 200 years, humans have
burned nearly half of the world’s fossil
fuels.
Greenhouse Effect
Carbon and Temperature
Future Trends?
The outcome depends on what happens to the west
Antarctic ice shelf.
Current Effects
Thinking question
discussion
• What do trees have to do with global
climate change?
• In what other ways can people reduce
their carbon footprint?
Big, scary question:
• Is the “typical American lifestyle”
ecologically sustainable?