Ecology II:Ecology II:

EcosystemsEcosystemsTrophic Levels, Chains, Webs, Trophic Levels, Chains, Webs,

Pyramids, Primary Pyramids, Primary Productivity, Nutrient Cycles Productivity, Nutrient Cycles

EcosystemEcosystem

An association of organisms An association of organisms

and their physical environment, and their physical environment,

interconnected by ongoing interconnected by ongoing

flow of energy and a cycling of flow of energy and a cycling of

materialsmaterials

Modes of Nutrition

• Autotrophs– Capture sunlight or chemical energy

– Producers

• Heterotrophs– Extract energy from other organisms or

organic wastes

– Consumers, decomposers, detritivores

Simple Ecosystem

Modelenergy input from sun

nutrientcycling

PHOTOAUTOTROPHS(plants, other producers)

HETEROTROPHS(consumers, decomposers)

energy output (mainly heat)

Consumers Consumers

Herbivores Herbivores Carnivores Carnivores ParasitesParasites Omnivores Omnivores DecomposeDecompose

rsrs Detritivores Detritivores

SPRING

rodents, rabbits

fruits

insects

birds

SUMMER

rodents, rabbits

fruits

insects

birds

Seasonal variation in the diet of an omnivore (red fox)

Trophic Levels in Prairie

5th

4th

3rd

2nd

1st

Fourth-level consumers (heterotrophs):

Top carnivores, parasites, detritivores, decomposers

Third-level consumers (heterotrophs):Carnivores, parasites, detritivores, decomposers

Second-level consumers (heterotrophs):

Carnivores, parasites, detritivores, decomposers

First-level consumers (heterotrophs):

Herbivores, parasites, detritivores, decomposers

Primary producers (autotrophs):

Photoautotrophs, chemoautotrophs

Food Chain

• A straight line

sequence of who

eats whom

• Simple food chains

are rare in nature

MARSH HAWK

UPLAND SANDPIPER

GARTER SNAKE

CUTWORM

FoodWeb

Energy Losses

• Energy transfers are never 100

percent efficient

• Some energy is lost at each step

• Limits the number of trophic levels in

an ecosystem

Two Types of Food Webs

Producers (photosynthesizers)

Producers (photosynthesizers)

herbivores

carnivores

decomposers

decomposers

detritivores

ENERGY OUTPUT ENERGY OUTPUT

Grazing Food Web Detrital Food Web

Biological MagnificationBiological Magnification

A nondegradable or slowly A nondegradable or slowly

degradable substance becomes degradable substance becomes

more and more concentrated in the more and more concentrated in the

tissues of organisms at higher tissues of organisms at higher

trophic levelstrophic levels of a food web of a food web

DDT in Food Webs• Synthetic

pesticide banned in the United States since the 1970s

• Birds that were top carnivores accumulated DDT in their tissues

FUMIGATION of workers using DDT

Primary ProductivityPrimary Productivity

Gross primary productivityGross primary productivity is is

ecosystem’s total rate of photosynthesisecosystem’s total rate of photosynthesis

Net Net primary productivityprimary productivity is rate at which is rate at which

producers store energy in tissues in producers store energy in tissues in

excess of their aerobic respirationexcess of their aerobic respiration

Primary Productivity VariesPrimary Productivity Varies

Seasonal variationSeasonal variation

Variation by habitatVariation by habitat

The harsher the environment, The harsher the environment,

the slower plant growth, the slower plant growth, the the

lower the primary productivity lower the primary productivity

Silver Springs Study

• Aquatic ecosystem in Florida• Site of a long-term study of a grazing food web

5

decomposers, detritivores(bacteria, crayfish)

1.5

1.1

37

third-level carnivores(gar, large-mouth bass)

second-level consumers(fishes, invertebrates)

first-level consumers(herbivorous fishes,turtles, invertebrates)

809 primary producers (algae,eelgrass, rooted plants)

Biomass pyramid

Pyramid of Energy Flow

• Primary producers trapped about 1.2 percent of the solar energy that entered the ecosystem

• 6-16% passed on to next level

detritivores

21

383

3,368

20,810 kilocalories/square meter/year

top carnivores

carnivores

herbivores

producers

decomposers

Biogeochemical CycleBiogeochemical Cycle

The flow of a nutrient from the The flow of a nutrient from the

environment to living organisms and environment to living organisms and

back to the environmentback to the environment

Three CategoriesThree Categories

Hydrologic cycleHydrologic cycle

• WaterWater

Atmospheric cyclesAtmospheric cycles

• Nitrogen and carbonNitrogen and carbon

Sedimentary cycles Sedimentary cycles

• Phosphorus and sulfurPhosphorus and sulfur

Hydrologic Cycle

evaporation from ocean

425,000

precipitation into ocean 385,000

evaporation from land plants

(evapotranspiration) 71,000

precipitation onto land 111,000

wind driven water vapor40,000

surface and groundwater flow

40,000

Atmosphere

Oceans Land

Hubbard Brook Experiment• A watershed was experimentally

stripped of vegetation

• All surface water draining from

watershed was measured

• Removal of vegetation caused a six-fold

increase in the calcium & nitrate content

of the runoff water

Hubbard Brook ExperimentA classic study of deforestation effects

losses fromdisturbed watershed

time ofdeforestation

losses fromundisturbed watershed

Nitrogen Cycle

NO3-

IN SOIL

NITROGEN FIXATION

by industry for agriculture

FERTILIZERS

FOOD WEBS ON LAND

NH3-, NH4

+

IN SOIL

1. NITRIFICATION

loss by leaching

uptake by autotrophs

excretion, death,

decomposition

uptake by autotrophs

NITROGEN FIXATION

loss by leaching

AMMONIFICATION

2. NITRIFICATION

NITROGENOUS WASTES, REMAINS IN SOIL

GASEOUS NITROGEN (N2)

IN ATMOSPHERE

NO2-

IN SOIL

Carbon Cycle

photosynthesisTERRESTRIAL

ROCKS

volcanic action

weathering

diffusion

Bicarbonate, carbonate

Marine food webs

Marine Sediments

Atmosphere

TerrestrialRocks

Soil WaterPeat, Fossil

Fuels

Land Food Webs

Carbon (Carbon Dioxide) in Carbon (Carbon Dioxide) in AtmosphereAtmosphere

Carbon dioxide is added to Carbon dioxide is added to atmosphereatmosphereAerobic respiration, volcanic Aerobic respiration, volcanic

action, burning fossil fuels action, burning fossil fuels

Removed by photosynthesisRemoved by photosynthesis

Greenhouse Effect

• Greenhouse gases impede the escape

of heat from Earth’s surface

Carbon Dioxide IncreaseCarbon Dioxide Increase

►Carbon dioxide levels fluctuate seasonally Carbon dioxide levels fluctuate seasonally

►The average level is The average level is steadily steadily

increasingincreasing

►Burning of Burning of fossil fuels and deforestationfossil fuels and deforestation

are contributing to the increaseare contributing to the increase

Global Warming

• Long-term increase in the temperature

of Earth’s lower atmosphere

Other Greenhouse GasesOther Greenhouse Gases

CFCsCFCs - synthetic gases used in - synthetic gases used in

plastics and in refrigerationplastics and in refrigeration

MethaneMethane - produced by termites and - produced by termites and

bacteriabacteria

Nitrous oxideNitrous oxide - released by bacteria, - released by bacteria,

fertilizers, and animal wastesfertilizers, and animal wastes