Ch 5 What do we know about ecosystems?

An ecosystem consists of all the organisms (biotic) in a community and the environment (abiotic) with which they interact. Ecosystems can be as small as the microorganisms living on your skin or as large as the entire biosphere.

Energy flows THROUGH ecosystems – open system

Nutrients cycle WITHIN ecosystems – closed system

HOW DO ECOSYSTEMS WORK?

• FOLLOW THE FLOW OF ENERGY THROUGH AN ECOSYSTEM

• FOLLOW THE CYCLING OF MATERIALS THROUGH AN ECOSYSTEM

• FOLLOW THE CHANGES IN AN ECOSYSTEM

The Earth’s Life-Support Systems

AtmosphereTroposphere -weather

Greenhouse gasesStratosphere

Lower portion (ozone) filters out harmful sun raysAllows life to exist on earth

Geosphere - LithosphereEarth’s crust

HydrosphereWater 3% is fresh

BiosphereLiving and dead

organisms

Solar Capital: Flow of Energy to and from the Earth

Greenhouse gasseswater vaporCO2MethaneOzone

Increases kinetic energy,Helps warm troposphere.Allows life to exist (as we know it) on earth.

As greenhouse gassesincrease, temperature oftroposphere increases.

Ecosystem Components

Abiotic factors• energy• mineral nutrients• CO2• O2

• H2OBiotic factors Range of tolerance for each species

ABIOTIC components:

•Solar energy provides practically all the energy for ecosystems.

•Inorganic substances, e.g., carbon, oxygen, sulfur, boron, tend to cycle through ecosystems.

•Organic compounds, such as proteins, carbohydrates, lipids, and other complex molecules, form a link between biotic and abiotic components of the system.

BIOTIC components:The biotic components of an ecosystem can be classified according to their mode of energy acquisition.

In this type of classification, there are:

Autotrophsand

Heterotrophs

Life Depends on the sun

Natural Capital: Sustaining Life of Earth

•One-way flow of energy from Sun

•Cycling of crucial elements

•Gravity

Three hundred trout are needed to support one man for a year. The trout, in turn, must consume 90,000 frogs, that must consume 27 million grasshoppers that live off of 1,000 tons of grass. -- G. Tyler Miller, Jr., American Chemist (1971)

Types of energy:

1. heat energy 2. chemical energy = energy

stored in molecular bonds

3. Light4. Mechanical5. Nuclear6. Electrical7. Magnetic8. gravitational

First Law of Thermodynamics

• Energy is neither created nor destroyed • Energy only changes form• You can’t get something for nothing

– Or “There is no such thing as a free lunch!”• ENERGY IN = ENERGY OUT• Energy flow is a one-directional process.• • sun---> heat (longer wavelengths)

Second Law of Thermodynamics• In every transformation, some

energy is converted to heat• You cannot break even in terms of

energy quality• You cannot break even in terms of energy

quality

SECOND LAW of THERMODYNAMICS

Transformations of energy always result in some loss or dissipation of energyorIn energy exchanges in a closed system, the potential energy of the final state will be less than that of the initial stateorEntropy tends to increase (entropy = amount of unavailable energy in a system)orSystems will tend to go from ordered states to disordered states (to maintain order, energy must be added to the system, to compensate for the loss of energy)

Internal combustion engines in cars are 25% efficient in converting chemical energy to kinetic energy; the rest is not used or is lost as heat.

My desk goes from a complex, ordered state to a simpler, disordered state

ENERGY FLOW IN ECOSYSTEMS• All organisms require energy, for growth, maintenance,

reproduction, locomotion, etc.

• Hence, for all organisms there must be:

A source of energy

A loss of usable energy

Life depends on the sun

• Energy in an ecosystem originally comes from the sun

• Energy enters an ecosystem when a plant/algae uses sunlight to make sugar in photosynthesis

Photosynthesis is the process of converting solar energy into chemical energy stored in foodCO2 + H20 ---> C6H12O6 + O2

•Light strikes leaf•Energy absorbed by chemical pigments•Absorbed energy drives chemical processes to convert CO2 into larger molecules

Energy absorbed in building larger molecules, released as they are broken down

How Photosynthesis Works

Absorption spectra of chlorophylls and carotenoids

Wavelengthreflected

In many plants production of chlorophyll ceases with cooler temperatures and decreasing light

other pigments become visible

CO2 must enter though stomatastomata (sing., stoma) are tiny holes on the undersides of leaves

CO2 enters and moisture is released

In hot, dry climates, this moisture loss is a problem

6 CO2 + 6 H20 SUNLIGHT

C6H12O6 + 6 O2

ENERGY RICH CARBOHYDRATES GLUCOSE

Organisms are classified by the source of their energy

PRODUCERS – organisms that make their own foodAlso known as AUTOTROPHS

Examples: plants, algae, some bacteria

CONSUMERS – get energy by eating other living thingsAlso known as HETEROTROPHS

TWO TYPES OF PRODUCERS AUTOTROPHS

Photosynthetic – algae, plants, some bacteria that use sun’s energy to synthesize organic compounds Chemosynthetic – bacteria that synthesize organic compounds from inorganic chemicals (hydrogen sulfide, ammonia) use energy in chemical bonds

Autotrophs (=self-nourishing) are called primary producers.

Photoautotrophs fix energy from the sun and store it in complex organic compounds(= green plants, algae, some bacteria)

simpleinorganiccompounds photoautotroph

s

complexorganic compounds

light

CO2 + H2O

chloroplasts GlucoseC6H12O6

Chemoautotrophs (chemosynthesizers) are bacteria that oxidize reduced inorganic substances (typically sulfur and ammonia compounds) and produce complex organic compounds.

reducedinorganiccompounds

oxygen

chemoautotrophs

complexorganic compounds

Other chemoautotrophs:

Nitrifying bacteria in the soil under our feet

When an animal eats a plant, energy is transferred from

the plant to the animal.l

Respiration is the process of releasing chemical energy stored in food to be used by living things.C6H12O6 + O2 ---> CO2 + H20

Heterotrophs (=other-nourishing) cannot produce their own food directly from sunlight+ inorganic compounds. They require energy previously stored in complex molecules.

complexorganic compounds

heterotrophssimpleinorganiccompounds

heat

glucose mitochondria

CO2 + H2O + ATP

TYPES OF CONSUMERS HETEROTROPHSHerbivore -

Carnivore -

Omnivore -

Scavenger -

Detrivore -

Decomposer -

Hummingbirds, moths, aphids, sap suckers …

Classes of HerbivoresBrowsers – woody materialGrazers – plant materialGranivores - seedsFrugivores – fruitOther: nectar & sap feeders

ENERGY TRANSFER• Follow energy transfer through an

ecosystem:– Food chain: follows path of energy– Food web: multiple food chains– Energy pyramids: shows loss of energy

as you move up trophic levels

– The arrow follows the flow of energy

Food chain• Plant rabbit snake

Arrows follow the flow of energy NOT who eats who __________________________________ NO:Plant rabbit snake

Food chain

Food chain

Problems

Too simplistic No detritivores

Chains too long

Rarely are things as simple as grass, rabbit, hawk, or indeed any simple linear sequence of organisms.

More typically, there are multiple interactions, so that we end up with a FOOD WEB.

Food Web• Multiple food chains• Rarely does 1 organism only eat 1 thing• Shows many possible feeding relationships that are possible in an ecosystem.• Arrows still follow the flow of energy from

producers through consumers to the top of the food web.

Energy Pyramids & Trophic levels• Trophic levels: feeding levels, each step of energy transfer

– 1st trophic level – producers– 2nd trophic level – primary consumers (herbivores)– 3rd trophic level – secondary consumers

(carnivores)– 4th trophic level – tertiary consumer (predator)

Trophic Level: Position in a food web determined by number of energy transfers from primary producers to current level:

Primary producers occupy first level. Autotrophic, energy from sun or chemicals.Primary consumers occupy second level.

herbivoresSecondary consumers occupy third level.

Omnivore or carnivoreTertiary consumers occupy fourth level.

Carnivore

ENERGY LOSS

• Each time energy is transferred, energy is lost (as heat)• Less energy is available for the next trophic

level• 90% of the energy in food used in respiration

to keep organism alive• 10% stored in body to be passed to next

energy level

ENERGY LOSS• Decreased loss of energy at each

trophic level affects the organization of an ecosystem:– Fewer organisms are found as you move

up the trophic levels– Loss of energy limits the number of

trophic levels in an ecosystem to no more than 4 or 5

5% of electricity is changed into useful light. 95% is lost as low-quality heat.

Primary productivity

Primary productivity is the rate of energy capture by producers.= the amount of new biomass of producers, per unit time and space

Gosz studied solar energy flow:15% reflected41% converted to heat42% absorbed during evapotranspiration2.2% fixed by plants as gross primary production1.2% used in plant respiration1% left for primary production

sun 30% reflected, 20% absorbed by atmosphere50% absorbed by ground, water or vegetation1% left for photosynthesis

Keystone species exert strong effects on their community structure, despite low biomass.

Exotic species have dramatic impacts on communities because they were outside the evolutionary experience of local prey populations.

Nile Perch (Lates nilotica) exotic fish predator in Lake Victoria.

Fish fauna dramatically reduced.

Christian observed native ants disperse 30% of shrubland seeds in fynbos of South Africa.

Seed-dispersing ants bury seeds in sites safe from predators and fire.

Argentine ants have displaced many native ant species that disperse large seeds.

Substantial reductions in seedling recruitment by plants producing large seeds.

Consumers

Producers

Decomposers

heat

heat

This pattern of energy flow among different organisms is the TROPHIC STRUCTURE of an ecosystem.

Biomass--the dry mass of organic material in the organism(s).(the mass of water is not usually included, since water content is variable and contains no usable energy)

Standing crop--the amount of biomass present at any point in time.

Gross primary production (GPP)= total amount of energy

captured

Net primary production (NPP)= GPP - respiration

Net primary production is thus the amount of energy stored by the producers and potentially available to consumers and decomposers.

Secondary productivity is the rate of production of new biomass by consumers, i.e., the rate at which consumers convert organic material into new biomass of consumers.

Note that secondary production simply involves the repackaging of energy previously captured by producers--no additional energy is introduced into the food chain.

And, since there are multiple levels of consumers and no new energy is being captured and introduced into the system, the modifiers gross and net are not very appropriate and are not usually used.

The standing crop, productivity, number of organisms, etc. of an ecosystem can be conveniently depicted using “pyramids”, where the size of each compartment represents the amount of the item in each trophic level of a food chain.

Note that the complexities of the interactions in a food web are not shown in a pyramid; but, pyramids are often useful conceptual devices--they give one a sense of the overall form of the trophic structure of an ecosystem.

producersherbivorescarnivores

A pyramid of numbers indicates the number of individuals in each trophic level. Since the size of individuals may vary widely and may not indicate the productivity of that individual, pyramids of numbers say little or nothing about the amount of energy moving through the ecosystem.

Mechanical defenses – spinesChemical defenses

Digestion disrupting chemicals – tannins, silica, oxalic acidToxins – alkaloids

More common in tropical speciesHow do animals respond?

DetoxifyExcreteChemical conversions – use as nutrient

How do plants respond to feeding pressures by herbivores?

CarnivoresPredators must catch and subdue prey - size selection.

Usually eliminate more conspicuous members of a population (less adaptive). act as selective agents for prey species.

Adaptations of Prey to being preyed uponPredator and prey species are engaged in a co-evolutionary race.Avoid being eaten – avoid starving/becoming extinctDefenses:

Run fastBe toxic – and make it knownPretend to be toxic

Predators learn to avoid

Consume nutritionally-rich prey.Cannot choose prey at will.

Prey Defenses:Aposomatic Coloring - Warning colors.Mullerian mimicry: Comimicry among several species of noxious organisms.Batesian mimicry: Harmless species mimic noxious species

Detritivores

Consume food rich in carbon and energy, but poor in nitrogen.

Dead leaves may have half nitrogen content of living leaves.

Fresh detritus may still have considerable chemical defenses present.

All other things being equal,more abundant prey yields larger energy return. Must consider energy expended during:

Search for preyHandling time

Tend to maximize rate of energy intake.What would a starving man do at an all you can eat buffet?

Slow-moving coastal plain stream choked with algal bloom caused by nitrogen and phosphorus from upstream farmland.

NUMBERS PYRAMID

BIOMASS PYRAMID

ENERGY PYRAMID