Ecology Part 1Ecology Part 1Chapter 2 – Chapter 2 – Principles of Principles of

EcologyEcology

Ecosystems and Ecosystems and the Biospherethe Biosphere

Energy TransferEnergy Transfer• Autotrophs – organisms that can Autotrophs – organisms that can

makemake their own food their own food• Because Because autotrophsautotrophs capture energy capture energy

and use it to make and use it to make organicorganic molecules, they are called molecules, they are called producersproducers..

• Most are Most are photosyntheticphotosynthetic• Chemosynthetic organisms do not use Chemosynthetic organisms do not use

sunlightsunlight as an energy source. They as an energy source. They use use inorganicinorganic molecules to produce molecules to produce carbohydratescarbohydrates..

• In terrestrial ecosystems, In terrestrial ecosystems, plantsplants are the are the major major producersproducers..

• In In aquaticaquatic ecosystems, photosynthetic ecosystems, photosynthetic protistsprotists and and bacteriabacteria are the major are the major producers.producers.

• Gross primary productivityGross primary productivity is the rate is the rate at which producers capture energy.at which producers capture energy.

• Organic material in an ecosystem is Organic material in an ecosystem is known as known as biomassbiomass..

• Producers Producers addadd biomass to an ecosystem biomass to an ecosystem by by makingmaking organic molecules. organic molecules.

• Net primary productivityNet primary productivity is the rate is the rate at which biomass accumulatesat which biomass accumulates• Usually expressed in units of Usually expressed in units of energy per energy per

year year (kcal/m(kcal/m22/yr) or in units of mass per /yr) or in units of mass per unit area per year (g/munit area per year (g/m22/yr)/yr)

• Equals the gross primary productivity Equals the gross primary productivity minusminus the rate of the rate of respirationrespiration in in producers.producers.

• In terrestrial ecosystems, productivity In terrestrial ecosystems, productivity is determined by is determined by lightlight, , temperaturetemperature, , and and precipitationprecipitation..

• In aquatic ecosystems, productivity is In aquatic ecosystems, productivity is determined by determined by lightlight and the and the availability of availability of nutrientsnutrients..

ConsumersConsumers• Organisms that cannot manufacture their Organisms that cannot manufacture their

own food are called own food are called heterotrophsheterotrophs• Heterotrophs obtain energy by Heterotrophs obtain energy by consumingconsuming

organic molecules made by other organisms. organic molecules made by other organisms. They are know as They are know as consumersconsumers..

• HerbivoresHerbivores eat producers eat producers• CarnivoresCarnivores eat other consumers eat other consumers• OmnivoresOmnivores eat both producers and eat both producers and

consumersconsumers• DetritivoresDetritivores are consumers that feed on are consumers that feed on

dead and decaying matter.dead and decaying matter.• DecomposersDecomposers are a type of are a type of detritivoredetritivore. They . They

cause decay by breaking down complex cause decay by breaking down complex molecules in dead tissue into simpler molecules molecules in dead tissue into simpler molecules that can be that can be recycledrecycled..

Energy FlowEnergy Flow• In an ecosystem, energy flows in In an ecosystem, energy flows in oneone

direction only, from direction only, from producersproducers to to consumersconsumers..

• An organism’s An organism’s trophic leveltrophic level shows the shows the organism’s position in the sequence of organism’s position in the sequence of energy transfersenergy transfers

• All All producersproducers belong to the belong to the firstfirst trophic level.trophic level.

• HerbivoresHerbivores belong to the belong to the secondsecond trophic leveltrophic level

• PredatorsPredators of herbivores belong to the of herbivores belong to the thirdthird trophic level. trophic level.

• Most ecosystems contain only Most ecosystems contain only threethree or or fourfour trophic levels. trophic levels.

• A A food chainfood chain is a single pathway of is a single pathway of feedingfeeding relationships in an relationships in an ecosystem that results in ecosystem that results in energy energy transfertransfer..

• Most food chains Most food chains interlinkinterlink..• A A food webfood web shows the interrelated shows the interrelated

food chains in an ecosystem.food chains in an ecosystem.

Quantity of Energy Quantity of Energy TransferTransfer

• Roughly Roughly 10% 10% of the total energy in one of the total energy in one trophic level is trophic level is availableavailable to the to the organisms in the next levelorganisms in the next level• The rest of the energy is used for The rest of the energy is used for

metabolismmetabolism and is lost as and is lost as heatheat..

• Since the rate of energy transfer between Since the rate of energy transfer between trophic levels is so trophic levels is so lowlow, ecosystems , ecosystems rarely contain more than a few trophic rarely contain more than a few trophic levels.levels.

• It takes many It takes many moremore producers to support producers to support first, second, and third order first, second, and third order consumersconsumers..

• If the first trophic level contained 50,000 If the first trophic level contained 50,000 kcal of energy, how much would be kcal of energy, how much would be available to the:available to the:• First-order consumers?First-order consumers?• Second-order consumers?Second-order consumers?• Third-order consumers?Third-order consumers?

Ecosystem RecyclingEcosystem Recycling• Remember, Remember, energyenergy flows through an flows through an

ecosystem (one direction only)ecosystem (one direction only)• Water and minerals like Water and minerals like carboncarbon, ,

nitrogen, calcium, and phosphorus are nitrogen, calcium, and phosphorus are recycledrecycled and and reusedreused..

• Biogeochemical cycles move substances Biogeochemical cycles move substances from the from the abioticabiotic (non-living) part of the (non-living) part of the environment, into living things, and back environment, into living things, and back again.again.

• We will look at the water cycle, carbon We will look at the water cycle, carbon cycle, and nitrogen cycle.cycle, and nitrogen cycle.

The Water CycleThe Water Cycle

The Carbon CycleThe Carbon Cycle

The Nitrogen CycleThe Nitrogen Cycle

The Nitrogen CycleThe Nitrogen Cycle• Nitrogen gas, NNitrogen gas, N22, is readily available in , is readily available in

the the atmosphereatmosphere..• Most plants can use nitrogen only in the Most plants can use nitrogen only in the

form of form of nitratenitrate..• The process of converting nitrogen gas The process of converting nitrogen gas

into nitrate is called into nitrate is called nitrogen fixationnitrogen fixation..• Nitrogen-fixing Nitrogen-fixing bacteriabacteria convert convert

nitrogen gas into nitrogen gas into ammoniaammonia, then , then nitritenitrite, and then , and then nitratenitrate, which plants , which plants can use.can use.

• Nitrogen-fixing bacteria live in the Nitrogen-fixing bacteria live in the soilsoil and in and in the the rootsroots of some kinds of plants, like of some kinds of plants, like beansbeans, peas, , peas, cloverclover, and alfalfa (a , and alfalfa (a mutualistic relationship)mutualistic relationship)

• Decaying organisms release nitrogen as Decaying organisms release nitrogen as ammonia in a process called ammonia in a process called ammonificationammonification

• Bacteria in the soil take up Bacteria in the soil take up ammoniaammonia and and oxidize it into nitrates and nitrites in a oxidize it into nitrates and nitrites in a process called process called nitrificationnitrification..

• Plants use nitrates to form Plants use nitrates to form amino acidsamino acids..• Nitrogen is returned to the atmosphere Nitrogen is returned to the atmosphere

through through denitrification, denitrification, which occurs when which occurs when anaerobicanaerobic bacteria break down nitrates and bacteria break down nitrates and release nitrogen release nitrogen gasgas back into the back into the atmosphere.atmosphere.

• Plants can Plants can absorbabsorb nitrates from the nitrates from the soil, but animals cannot.soil, but animals cannot.

• How can animals get nitrogen?How can animals get nitrogen?• Animals get nitrogen the same way Animals get nitrogen the same way

they get energy – by they get energy – by eatingeating plants plants and other organisms and then and other organisms and then digestingdigesting the proteins and amino the proteins and amino acids to get acids to get nitrogennitrogen..

The Phosphorus CycleThe Phosphorus Cycle

Phosphorus CyclePhosphorus Cycle• Unlike carbon, oxygen, and nitrogen, Unlike carbon, oxygen, and nitrogen,

phosphorus does not enter the phosphorus does not enter the atmosphereatmosphere..

• Phosphorus remains mostly on land in Phosphorus remains mostly on land in rockrock and and soilsoil minerals, and in minerals, and in ocean ocean sedimentssediments..

• Phosphorus exists in the form of Phosphorus exists in the form of inorganic phosphateinorganic phosphate

• As the rocks and sediments gradually As the rocks and sediments gradually wear down, wear down, phosphatephosphate is released. is released.

Any Questions ???Any Questions ???