Ecosystems: What Are They and How Do They Work?

THE NATURE OF ECOLOGY

• Ecology is a study of connections in nature.– How organisms

interact with one another and with their nonliving environment.

Figure 3-2Figure 3-2

Populations, Communities, and Ecosystems

• Members of a species interact in groups called populations.

• Populations of different species living and interacting in an area form a community.

• A community interacting with its physical environment of matter and energy is an ecosystem.

Populations

• A population is a group of interacting individuals of the same species occupying a specific area.– The space an

individual or population normally occupies is its habitat.

Genetic Diversity

– In most natural populations individuals vary slightly in their genetic makeup.

ECOSYSTEM COMPONENTSLife exists on land systems called biomes and in

freshwater and ocean aquatic life zones.

100–125 cm (40–50 in.)

Coastal mountain

ranges

SierraNevada

Mountains

GreatAmerican

Desert

Coastal chaparraland scrub

Coniferous forest

Desert Coniferous forest Prairie grassland

Deciduous forest

1,500 m (5,000 ft.)3,000 m (10,000 ft.)

4,600 m (15,000 ft.)

Average annual precipitation

MississippiRiver Valley

AppalachianMountains

GreatPlains

RockyMountains

below 25 cm (0–10 in.)25–50 cm (10–20 in.)50–75 cm (20–30 in.)75–100 cm (30–40 in.)

Nonliving and Living Components of Ecosystems

Ecosystems consist of nonliving (abiotic) and living (biotic) components.

Fig. 3-10, p. 57

SunOxygen (O2)

Carbon dioxide (CO2)

Secondary consumer(fox)

Soil decomposers

Primaryconsumer

(rabbit)

PrecipitationFalling leaves

and twigs

Producer

Producers

Water

Factors That Limit Population Growth

Availability of matter and energy resources can limit the number of organisms in a population.

Producers: Basic Source of All Food

Producers: Basic Source of All Food

• Chemosynthesis:– Some organisms such

as deep ocean bacteria draw energy from hydrothermal vents and produce carbohydrates from hydrogen sulfide (H2S) gas .

Consumers: Eating and Recycling to Survive

• Consumers (heterotrophs) get their food by eating or breaking down all or parts of other organisms or their remains.– Herbivores

• Primary consumers that eat producers

– Carnivores• Primary consumers eat primary consumers• Third and higher level consumers: carnivores that eat

carnivores.

– Omnivores• Feed on both plant and animals.

Decomposers and Detritivores

– Decomposers: Recycle nutrients in ecosystems.– Detritivores: Insects or other scavengers that feed

on wastes or dead bodies.

Aerobic and Anaerobic Respiration: Getting Energy

for Survival• Organisms break down carbohydrates and other

organic compounds in their cells to obtain the energy they need.

• This is usually done through aerobic respiration.– The opposite of photosynthesis

Aerobic and Anaerobic Respiration: Getting Energy for Survival

• Anaerobic respiration or fermentation:– Some decomposers get energy by

breaking down glucose (or other organic compounds) in the absence of oxygen.

– The end products vary based on the chemical reaction:

• Methane gas• Ethyl alcohol• Acetic acid• Hydrogen sulfide

Two Secrets of Survival: Energy Flow and Matter Recycle

An ecosystem survives by a

combination of energy flow and matter recycling.

Biodiversity Loss and Species Extinction: Remember HIPPO

• H for habitat destruction and degradation

• I for invasive species

• P for pollution

• P for human population growth

• O for overexploitation

Why Should We Care About Biodiversity?

• Biodiversity provides us with:– Natural Resources (food water, wood, energy,

and medicines)– Natural Services (air and water purification, soil

fertility, waste disposal, pest control)– Aesthetic pleasure

Energy Flow in Ecosystems

• Food chains and food webs show how eaters, the eaten, and the decomposed are connected to one another

• Ecologists assign each organism in an ecosystem to a trophic level

• There is a decrease in the amount of energy available to each succeeding organism in a food chain or food web

-The percentage of usable energy transferred as biomass from one trophic level to the next is called ecological efficiency

-Ecological efficiency ranges from 2% - 40%

The pyramid of energy flow illustrates energy loss for a simple food

chain assuming a 90% energy loss at each

transfer

Energy flow pyramids explain why Earth can support more people if

they eat at lower trophic levels

Number of individuals

“weight” of biological material

Energy content

Ecological Pyramids

Pyramid of Numbers• Illustrates the number of organisms at each

trophic level– Usually, organisms at the base of the pyramid

are more numerous• Fewer organisms occupy Fewer organisms occupy

each successive leveleach successive level

o Do not indicate the Do not indicate the biomass of the biomass of the organisms at each level organisms at each level or the amount of energy or the amount of energy transferred between transferred between levelslevels

Pyramid of Biomass• Illustrates the total biomass at each

successive trophic level– Biomass: measure of the total amt of living

material• Biomass indicates the Biomass indicates the

amount of fixed energy at amount of fixed energy at a given timea given time

o Illustrates a progressive Illustrates a progressive reduction in biomass reduction in biomass through trophic levelsthrough trophic levels

Pyramid of Energy• Illustrates how much energy is present at

each trophic level and how much is transferred to the next level– Most energy dissipates between trophic levels

o Explains why there Explains why there are so few trophic are so few trophic levelslevels• Energy levels get too Energy levels get too

low to support lifelow to support life

Productivity of Producers: The Rate Is Crucial

• Gross primary production (GPP) – Rate at which an

ecosystem’s producers convert solar energy into chemical energy as biomass.

Net Primary Production (NPP)

• NPP = GPP – R– Rate at which

producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R).

• What are nature’s three most productive and three least productive systems?

MATTER CYCLING IN ECOSYSTEMS

• Nutrient Cycles: Global Recycling– Global Cycles recycle nutrients through the

earth’s air, land, water, and living organisms.– Nutrients are the elements and compounds that

organisms need to live, grow, and reproduce.– Biogeochemical cycles move these substances

through air, water, soil, rock and living organisms.

The Water Cycle

Effects of Human Activities on Water Cycle

• We alter the water cycle by:– Withdrawing large amounts of freshwater.– Clearing vegetation and eroding soils.– Polluting surface and underground water.– Contributing to climate change.

The Carbon Cycle:Part of Nature’s Thermostat

Effects of Human Activities on Carbon Cycle

• We alter the carbon cycle by adding excess CO2 to the atmosphere through:– Burning fossil fuels.– Clearing vegetation

faster than it is replaced.

The Nitrogen Cycle: Bacteria in Action

Effects of Human Activities on the Nitrogen Cycle

• We alter the nitrogen cycle by:– Adding gases that contribute to acid rain.– Adding nitrous oxide to the atmosphere through

farming practices which can warm the atmosphere and deplete ozone.

– Contaminating ground water from nitrate ions in inorganic fertilizers.

– Releasing nitrogen into the troposphere through deforestation.

Effects of Human Activities on the Nitrogen Cycle

• Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined.

The Phosphorous Cycle

Effects of Human Activities on the Phosphorous Cycle

• We remove large amounts of phosphate from the earth to make fertilizer.

• We reduce phosphorous in tropical soils by clearing forests.

• We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers.

The Sulfur Cycle

Effects of Human Activities on the Sulfur Cycle

• We add sulfur dioxide to the atmosphere by:– Burning coal and oil– Refining sulfur containing petroleum.– Convert sulfur-containing metallic ores into free

metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.

HOW DO ECOLOGISTS LEARN ABOUT ECOSYSTEMS?

• Ecologist go into ecosystems to observe, but also use remote sensors on aircraft and satellites to collect data and analyze geographic data in large databases.– Geographic Information Systems– Remote Sensing

• Ecologists also use controlled indoor and outdoor chambers to study ecosystems

Geographic Information Systems (GIS)

• A GIS organizes, stores, and analyzes complex data collected over broad geographic areas.

• Allows the simultaneous overlay of many layers of data.

The End