envierment

Ecosystems: What Are They and How Do They Work?

How Does the Earth’s Life-Support System Work?

u Major components of the earth’s life-support system

u Atmosphere (air)

u Hydrosphere (water)

u Geosphere (rocks, minerals, and soil)

u Biosphere (living things)

Earth’s Life-Support System Has Four Major Components u Atmosphere

u Innermost layer is the troposphere

uContains the air we breathe

u Stratosphere: contains ozone layer

uFilters sun’s harmful UV radiation

u Hydrosphere

u All water vapor, liquid water, and ice

u Oceans contain 97% of the planet’s water

Earth’s Life-Support System Has Four Major Components

u Geosphere

u Upper portion of crust contains nutrients organisms need to live, grow, and reproduce

u Contains nonrenewable fossil fuels

u Biosphere

u Parts of atmosphere, hydrosphere, and geosphere where life is found

Three Factors Sustain the Earth’s Life

u One-way flow of high-quality energy from the sun that supports plant growth and warms troposphere (greenhouse effect)

Three Factors Sustain the Earth’s Life

 Cycling of nutrients through parts of the biosphere

 Gravity holds the earth’s atmosphere and enables movement and cycling of chemicals through air, water, soil, and organisms

What Are the Major Components of an Ecosystem?

u Ecologists study five levels of

matter

u Biosphere, ecosystems,

communities, populations,

and organisms

u Ecology assigns each organism to a feeding

level (trophic level)

u Organisms classified as producers or

consumers based on source of nutrients

Ecosystems Have Several Important Components

u During photosynthesis, plants generate energy and emit oxygen u CO2 + H2O + sunlight → glucose + oxygen

u Producers (autotrophs) make needed nutrients from their environment

u Consumers (heterotrophs) cannot produce the nutrients they need u Primary consumers (herbivores) eat plants

u Carnivores feed on flesh of other animals

u Secondary and tertiary (or higher) consumers

u Omnivores eat both plants and animals

Ecosystems Have Several Important Components

u Decomposers u Consumers that recycle dead plants and animals into chemical

nutrients like carbon and nitrogen that are released back into the soil, air and water

u Directly absorb nutrients through external chemical and biological processes

u Nutrients return to soil, water, and air for reuse u Bacteria, fungi and earthworms are big decomposers u Detritivores

uIngest and digest dead matter internally

Ecosystems Have Several Important Components

u Producers, consumers, and decomposers use chemical energy stored in glucose u In most cells, energy is

released by aerobic respiration

u Using oxygen to turn glucose back to carbon dioxide and water

Soil Is the Foundation of Life on Land

u Soil u Complex mixture of rock, particles, mineral nutrients, organic

matter, water, air, and living organisms

u Soil formation begins with weathering of rock u Various forms of plant and animal life begin living in the weathered

particles.

u Their waste and decaying bodies add organic matter and minerals to the slowly forming soil.

u Mature soils contain several layers (horizons)

u Differ in texture, composition, and thickness

Soil Is the Foundation of Life on Land

u Soil is a renewable resource u Renews very slowly u Formation of one inch of topsoil

can take hundreds to thousands of years

u Becomes nonrenewable if it is depleted faster than it can be replenished

u Protecting and renewing topsoil is key to sustainability

Soil Is the Foundation of Life on Land

What Happens to Energy in an Ecosystem?

u Energy flows through ecosystems in food chains and webs

u Food chain

u Movement of energy and nutrients from one trophic level to the next

u Food web

u Network of interconnected food chains

What Happens to Energy in an Ecosystem?

What Happens to Energy in an Ecosystem?

u Every use and transfer of energy involves energy loss as heat u Pyramid of energy flow

u 90% of energy lost with each transfer through metabolic heat: why food chains and webs rarely have more than 4 or 5 trophic levels

u Less chemical energy for higher trophic levels u About 2/3 of the world’s people survive by eating wheat,

rice, and corn at the first trophic level. u Biomass

u Total mass of organisms in a given trophic level

What Happens to Energy in an Ecosystem?

Some Ecosystems Produce Plant Matter Faster than Others Do u Gross primary productivity

(GPP) u Rate at which an ecosystem’s

producers (plants and phytoplankton) convert solar energy to stored chemical energy

u Measured in units such as kcal/m2/year

Some Ecosystems Produce Plant Matter Faster than Others Do

u Net primary productivity (NPP)

u Rate at which an ecosystem’s producers convert solar energy to chemical energy, minus the rate at which they use the stored energy for aerobic respiration

u The planet’s NPP ultimately limits the number of consumers (including humans) that can survive on the earth

Some Ecosystems Produce Plant Matter Faster than Others

What Happens to Matter in an Ecosystem?

u Matter in the form of nutrients cycles within and among ecosystems

u Cycles driven by incoming solar energy and gravity

u Can be altered by human activity

u Nutrient Cycles

u Water, carbon, nitrogen, and phosphorus

Water Cycle Sustains all Life

u The water cycle collects, purifies, and distributes the Earth’s fixed supply of water.

u Renews water quality. u The sun powers the water cycle. u Incoming solar energy causes

evaporation. u Gravity draws water back as

precipitation: u Surface runoff evaporates to complete the

cycle

u Some precipitation is stored underground as groundwater

u Some precipitation is converted to ice and stored in glaciers

Water Cycle Sustains all Life u Only 0.024% of the Earth’s freshwater supply is available to

humans and other species.

u The ways humans alter the water cycle:

u Withdrawing large amounts of freshwater from aquifers at rates faster than nature can replace it

u Clearing vegetation (agriculture, road building), which increases runoff

u Draining and filling wetlands for farming and urban development

Science Focus: Water’s Unique Properties

u Properties of water u Liquid over large temperature range

u Changes temperature slowly because it can store a large amount of heat

u Takes lots of energy to evaporate

u Can dissolve a variety of compounds (also can make it polluted)

u Filters out wavelengths of UV radiation and protects aquatic organisms

u Expands when it freezes

Carbon Cycles among Living and Nonliving Things

u Carbon is the basic building block of carbohydrates, fats, proteins, DNA, and other organic compounds.

u Photosynthesis from producers removes CO2 from the atmosphere and aerobic respiration by producers, consumers, and decomposers adds CO2 .

u Some CO2 dissolves in the ocean and is stored in marine sediments.

Human Disruption of the Carbon Cycle

u Humans have added large quantities of CO2 to the atmosphere

u Faster rate than natural processes can remove

u Levels have been increasing sharply since about 1960

u Carbon from fossil fuels are being burned back into atmosphere

u Result is the warming atmosphere and changing climate

u Clearing vegetation reduces ability to

remove excess CO2 from the atmosphere

Nitrogen Cycle: Bacteria in Action

u Nitrogen is a critical nutrient for all forms of life.

u Nitrogen gas makes up 78% of the volume of the atmosphere.

u Useful forms of nitrogen are created in the nitrogen cycle:

u Created by lightning and specialized bacteria in topsoil and bottom sediment of aquatic systems

u Used by plants to produce proteins, nucleic acids, and vitamins

u Bacteria converts nitrogen compounds back into nitrogen gas.

Nitrogen Cycle: Bacteria in Action

u Human alteration of the nitrogen cycle

u Burning gasoline and other fuels create nitric oxide, which can return as acid rain

u Removing large amounts of nitrogen from the atmosphere to make fertilizers

u Adding excess nitrates in aquatic ecosystems

u Human nitrogen inputs to the environment have risen sharply and are expected to continue rising

Nitrogen Cycle: Bacteria in Action

Phosphorous Cycles through Water, Rock, and Food Webs

u Phosphorus u Another nutrient that supports life u Cycles through water, the Earth’s crust, and living

organisms u Major reservoir is phosphate rocks u Cycles slowly u Does not cycle through the atmosphere because

few of the compounds exist as gas u Lack of phosphorus limits growth of producer

populations (plants)

Phosphorous Cycles through Water, Rock, and Food Webs

u Phosphorus

u Human activities and impacts

uClearing forests

uRemoving large amounts of phosphate from the Earth to make fertilizers

uErosion leaches phosphates into streams

Phosphorous Cycles through Water, Rock, and Food Webs