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Ecosystems
Objectives
5.1.9 – State that light is the initial energy source for almost all communities.
5.1.3 – Distinguish between producers, consumers, detritivores, and saprotrophs.
5.1.4 – Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms).
5.1.5 – Describe what is meant by a food web 5.1.8 – Construct a food web containing up to 10
organisms, using appropriate information.
CommunitiesCommunity: a group of populations living and inter-acting with each other in the same area
Everglades community Coral Reef community
Community relationshipsEcosystems are energy machines and matter processors.
Sunlight provides theenergy that powers
almost all life on Earth.
A few communities(ex: in geothermal
ecosystems) arepowered by heat
or chemicals.
Food chains Producers capture the sun’s energy and convert it to chemical energy in the form of
complex organic mol- ecules such as lipids,
carbohydrates, and proteins.
Consumers must get their energy by eating it.
Food chainsConsumers are named ac- cording to what they eat.
Herbivores (plant-eaters)eat the producers; primary consumers.Carnivores (meat-eaters) eat the herbivores or
other carnivores; secondary consumers.
Omnivores eat both plants and animals.
Food chainsConsumers are named ac- cording to what they eat.
Detritivores consume decaying organic matter.
Ex: earthworms, vultures, termites
Saprotrophs (decomposers) absorb complex, soluble
organic nutrients from decaying organisms
and convert them to simple inorganic chemicals
Ex: bacteria, fungi.
Food chainsThe transfer of food energy from photo- synthetic organisms through herbivores and carnivores is
called the food chain.A food chain can
usually have as many as 4 or 5 links, called trophic levels.
(trophic = food)
Food chains Trophic levels
4th
3rd
2nd
1st
Coniferous forest food chains
Food chains
Arctic food chain (near right)
Woodland food chain (far right)
Food chains
Food chains
Food chains are hooked together into food webs.
Food webs show all trophic (feed-
ing) interactions within some community.(Roman numerals refer to the trophic
levels.)
Arrows points toward the eaters.
Deciduous forest food web
Food chains
Food chains
Arctic food web
Ecosystems
Objectives5.1.6 - Define trophic levels
5.1.2 – Distinguish between an autotroph and a heterotroph.
5.1.7 - Deduce the trophic level of organisms in a food chain and a food web.
5.1.10 – Explain the energy flow in a food chain.
5.1.11 – State that energy transformations are never100% efficient.
5.1.12 – Explain the reasons for the shape of pyramids of energy.
Trophic levelsTrophic levels: the feeding relationships within com-
munities, which show the route of energy flow.
Producers are always on level 1.
Herbivores are always on level 2.
Trophic levels
4th
3rd
2nd
1st
Trophic levelsTrophic relationships create routes of energy flow and
chemical cycling. Ecosystems are energy machines and matter processors.
Autotrophs are the primary producers - often
photosynthetic (plants, algae);
use light energy to make
organic compounds. →
Trophic levelsTrophic relationships create routes of energy flow and
chemical cycling. Heterotrophs are consumers.
Animals are at levels above primary producers and de-
pend on their output. →
Detritivores: eat decaying material
Herbivores
Carnivore
Dust mite
Trophic levelsTrophic relationships create routes of energy flow and
chemical cycling. Saprotrophs are decomposers.
Bacteria and fungi absorb complex soluble organic nutrients from
decaying organisms and convert them to simple inorganic chem- icals.
Trophic levelsSo which trophic level is represented by …
the grass?the lion?the zebra?
1st 2nd 3rd
Trophic levelsAnd which trophic level
is represented by …the seal?the plankton?the algae?the polar bear?the arctic cod?
Trophic levels
1st
2nd
3rd
4th
5th
Trophic levelsAnd which trophic level is represented by …
the squirrel?the pine tree?the moose?the wolf?the songbird?
It is hard to categorize anomnivore.
Energy flow in a food chainRemember: in an ecosystem,
energy flows from the sunthrough producers andconsumers. Where doesit end up ultimately?
The laws of thermodynamics
say that energy cannot be destroyed.
Energy doesn’t recycle; it dissipates (disperses).
Energy flow in a food chainWhat happens to all the energy that is in grass when it
is eaten by a cow?
Energy flow in a food chainWhat happens to all the energy that is in a wildebeest
when it is killed and eaten by a lion?
the muscle?the skin?the bones?the body heat?
Energy flow in a food chainEnergy transformations are never 100% efficient.
Approx. 90% of the energy is lost at each level.
Only 1% of the sun’s energy is captured by plants.
Energy flow in a food chainThe mouse doesn’t eat
the grass’s roots.The owl can’t digest the
snake’s skin and bone.Energy is wasted by
a consumer whenparts are uneaten.
Digestible parts of themouse represent a small portion of the calories that a mouse consumed itself.
Pyramids of energyEnergy is less at each
trophic level.The result is an energy pyramid.
The pyramid can represent 1 food chain …
… or the entire ecosystem.
Pyramids of biomassEnergy is less at each
trophic level.Energy produces biomass.
Biomass decreases at each level as well,
in the same proportion: a loss of 90% at each level.
Pyramids of numbers
With less energy at each level, thereare also fewer crea-tures, especially ifmore than 1 speciesmust share a level.
Energy transformationsSo what is wrong with this picture?
Eating the cow is wasteful of the plant’s resources.
Eat plants instead.
Energy transformationsWhere does the energy
that a cow consumes as grass ultimately go?
MovementMetabolism
ChemistryBreathingMaking body mass
ReproductionHomeostasisHeatConsumers
Energy transformationsWhat part of that cow’s lifetime production of energy do
we get?
Meat
Hide
And a few other things.
Energy transformationsDecay organisms recycle the remains.
Nutrient Cycles
Objectives 5.1.10 – Review: Explain the energy flow in a food
chain. 5.1.11 – Review: Energy transformations are never
100% efficient. 5.1.13 – Explain that energy enters and leaves
ecosystems, but nutrients must be recycled.
5.1.14 – State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.
5.2.1 –-- Draw and label a diagram of the carbon cycle to show the processes involved.
5.2.2 – Analyze the changes in concentration of atmospheric CO2 (with acid rain) using historical records.
5.2.3 – Explain the relationship between rises in concentrations of atmospheric CO2, methane, and oxides of nitrogen and the enhanced greenhouse effect.
Energy flow in a food chain Remember: in an eco-
system, energy flowsfrom the sun throughproducers and con-sumers. Where doesit end up ultimately?
The laws of thermo- dynamics say that energy cannot be destroyed.
Energy doesn’t recycle; it dissipates (disperses).
Energy flow in a food chain Example: a caterpillar’s metabolism
J = joule, a measure of energy
Pyramids of energy
Nutrient recyclingEnergy enters and leaves ecosystems, but nutrients must be recycled.
In terrestrial ecosystems, temperature, moisture, and nutrients limit primary production.
Consider diversity in rainforest vs. tundra.
On a local scale, mineral nutrients in the soil can play key roles in limiting
biomass production.Practical applications in agriculture.
Farmers fertilize.
Nutrient recyclingBiogeochemical processes move nutrients between organic and inorganic compartments.
Know theprocessesin black.
Nutrient recyclingThe water cycle: know definitions of the four processes.
Transpiration: Water passes from soil through roots then out leaves to the atmosphere.Evaporation:
from liquid to gas.
Condensation: (precipitation)
from gas to liquid.
Runoff: from land to river,
lake, ocean.
Nutrient recyclingThe nitrogen cycle: based upon bacterial action.
Remember: Rhizobium bacteria take nitrogen gas and convert it to ammonia fertilizer for legumes like beans & peas (nitrogen
fixation is a form of mutualism).
Other bacteria convert nitrogen
compounds in soil back to nitro-gen gas for the atmosphere. Air
is 78% nitrogen.
Nutrient recyclingThe nitrogen cycle
The air is 78% N2 gas, but only nitrogen-fixing bacteria like Rhizobium species can turn it into ammonia (NH3), which feeds plants.Animals eat plants. All life makes proteins with nitrogen that decay back to the soil, where more bacteria convert them into N2 gas again.
Nutrient recyclingThe nitrogen cycle
Bacteria like Rhizobium and fungi like mychorrizae have a mutualistic
symbiosis with plants providing them with nitrogen compounds.
Plants provide food such as glucose.
of legumes,like pea & bean
Nutrient recyclingThe carbon cycle
CO2 is converted to carbohydrates during photosynthesis.Consumers cycle C up a food chain; ultimately respire CO2.
Nutrient recyclingThe carbon cycle
C is tied up 100s of yrs in trees & millions of yrs in coal.Burning fossil fuels (coal, oil, & natural gas) releases CO2.
Nutrient recyclingSaprotrophic bacteria & fungi (decomposers) recycle nutrients.
Acid precipitationFossil fuel combustion produces acid precipitation.
Burning fossil fuels releases sulfur and nitrogen oxides that react with water in the atmosphere to produce sulfuric and nitric acids → fall to earth as acid precipitation.
Also CO2 + H2O →H2CO3 (carbonic acid)
CO2
CO2
Acid leachesminerals intolakes
Acid precipitationFossil fuel combustion produces acid precipitation.
The acids can kill plants and aquatic organisms.Severe in NE US where soil has less buffering capacity.
alkaline soils (as in S. Florida) are not much affected.
Fish eggs die, and mycorrhizal fungi associated with plant roots die as a result of acidity.
Northeastern forest
Acid precipitationFossil fuel combustion produces acid precipitation.
The acids also damage limestone and marble.
Marble statue in Italy (1908 & 1968)
Acid precipitationFossil fuel combustion produces acid precipitation.
Contributions to CO2 emissions since the Industrial Revolution
Highest CO2 levels in red
Acid precipitationBurning sulfur-rich coal produces most of the acid rain.
Levels of acid rain have been dropping since the 1990s.
pH tests lowest (more acid) in the red areas.
Most recent data
Greenhouse effectAs a result of burning fossil fuels, atmospheric CO2 has risen.
Atmospheric CO2 traps heat like the glass of a greenhouse.
Light passes through the atmosphere and heats the land. Heats rises, but much of it cannot escape to space due to excessive CO2.
Greenhouse effectAs a result of burning fossil fuels, atmospheric CO2 has risen.
Some scientists warn that atmospheric levels of CO2 are directly related to an increase in Earth’s temperature.
Greenhouse effectAs a result of burning fossil fuels, atmospheric CO2 has risen.
It was 316 ppm in 1958, and is 370 ppm today.
Global warmingJustification for strong action in response to the threats posed by the enhanced greenhouse effect.
Sea level rise endangers coastal cities and nations.
Sea level rise of 3 feet Sea level rise of 25 feet
The sea could rise over 100 feet if all the polar ice melts.
Global warmingMethane is another greenhouse gas pro-
duced by living and decaying organisms.
Precautionary principleThreat of global warming requires action now to preserve the environment as we have come to know it.
Anticipate harmAct to prevent or minimize such harm.
even when all the scientific evidence is not available
Actions required:Reduce greenhouse gases
Alternatives to fossil fuelsScrub out the CO2, SO2, etc.
Reduce deforestationPlant trees to absorb CO2
Reduce industrializationReduce over-population
Human overgrowth…is the root of the problem.
But there is some good news.
