environmental science, 1e•includes all of the gaseous, liquid, and solid water on/near earth’s...

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Environmental Science, 1e SUSTAINING YOUR WORLD

G. TYLER MILLER | SCOTT E. SPOOLMAN

3Ecosystem

Dynamics


• Cover only 7% of the earth’s land surface, but

contain half of the world’s terrestrial plant and

animal species

• Human activities have destroyed or disturbed

more than half of Earth’s tropical rain forest.

– Impacts: biodiversity loss, accelerated

atmospheric warming, changing weather patterns

• How are your local ecosystems unique, and

what challenges do they face?

Case Study: Disappearing Tropical

Rain Forests


• Earth’s life-support system has four spherical

components that interact with each other

(geosphere, atmosphere, hydrosphere,

biosphere).

• Life is sustained by the cycling of nutrients

and energy between and through these

systems.

3.1 What Are Earth’s Major Spheres, and

How Do They Support Life?


Earth’s Four Life-Support Systems


• Composed of a hot core, a thick, mostly rocky

mantle, and a thin outer crust

• Gives planet the mass it needs to keep

atmosphere from escaping into space

• Contains nutrients, nonrenewable fossil fuels

(coal, oil, natural gas), mineral resources

Geosphere


• Envelope of gases surrounding Earth

– Shields planet from meteors, blocks most harmful

UV radiation

– Helps regulate Earth’s climates

– Five layers, from bottom to top:

• Troposphere (life, weather events)

• Stratosphere (ozone layer)

• Mesosphere

• Thermosphere

• Exosphere

Atmosphere


• Includes all of the gaseous, liquid, and solid

water on/near Earth’s surface

– Glaciers, lakes, rivers, aquifers, water vapor,

clouds, oceans

• Oceans contain about 96.5% of total water

supply, cover 71% of surface

• Less than 3% available as fresh water, most

of it frozen in ice caps, glaciers

Hydrosphere


• Very thin layer of air, water, soil, organisms

• Consists of the parts of the atmosphere,

hydrosphere, and geosphere where life exists

Biosphere


• Greenhouse effect

– Solar energy warms troposphere as it reflects

from Earth’s surface, interacts with CO2, CH4,

water vapor, other greenhouse gases

– Without it, Earth too cold to support life

• Air and water purification

– Living organisms (plants, animals,

microorganisms) absorb/filter pollutants from air,

water, soil

– Evaporation filters out water impurities

Earth’s Spheres Interact


• Ecology: organisms interact with each other

and with their nonliving environment

• Ecosystems are composed of energy,

chemicals, and organisms.

• Scientists classify matter into levels of

organization ranging from molecules to

galaxies.

– Ecologists study interactions within and among

several of these levels.

3.2 What Are the Major Components of an

Ecosystem?


Levels of the Organization of Matter in

Nature


• Biotic (living) and abiotic (nonliving)

components of the environment

– Biotic components: plants, animals, microbes, all

other organisms

• Trophic (feeding) level: depends on whether organism

makes food (producer) or finds food (consumer), and

what its feeding behavior is if it’s a consumer

– Abiotic components: water, air, rocks, nutrients,

thermal energy, sunlight

Ecosystems Have Several Important

Components


Living (Biotic) and Nonliving (Abiotic)

Components


• Producers (plants) use photosynthesis to

make nutrients.

– 6 CO2 + 6 H2O + light energy → C6H6 + 6 O2

• Consumers feed on other organisms or their

remains to obtain energy.

– Herbivores (plant eaters), carnivores (meat

eaters), or omnivores (eat both plants and meat)

– Primary (eat mostly green plans or algae),

secondary (eat primary consumers), or tertiary

(eat both primary/secondary consumers)

Producers and Consumers


• Decomposers: consumers that get their

nutrients by breaking down (decomposing)

nonliving organic matter (leaf litter, fallen

trees, dead animals)

• Detritivores: get nourishment by feeding on

detritus, or freshly dead organisms, before

they are fully decomposed

• Decomposers and detritivores are key to

nutrient cycling.

Decomposers and Detritivores


Decomposers and Detritivores Aid

Nutrient Cycling


The Main Components of an Ecosystem


• Release of chemical energy stored in glucose

and other organic compounds

• Aerobic respiration: uses oxygen and glucose,

opposite of photosynthesis

– C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy

• Anaerobic respiration (fermentation): carried

out in absence of oxygen

– By-products: methane, ethyl alcohol, acetic acid,

hydrogen sulfide

Cellular Respiration


• Energy flows through ecosystems via

movement between trophic levels through

food chains and food webs.

– The quality of energy available to organisms

decreases as each successive trophic level is

reached, because so much energy (heat) is lost

moving from one level to the next.

3.3 What Happens To Energy in an

Ecosystem?


• Food chains

– A sequence of organisms, each of which serves

as a nutritional source for the next

– About 90% energy lost at each link in food chain,

as organisms convert chemical energy from food

to energy needed to live and grow

• Food webs

– A complex network of interconnected food chains

Energy Flows Through Ecosystems in

Food Chains and Food Webs


Energy Flow in a Food Chain


Feeding Relationships in a Food Web


A Generalized Pyramid of Energy Flow


• Gross primary productivity (GPP)

– Rate at which an ecosystem’s producers convert

radiant energy into chemical energy

• Net primary productivity (NPP)

– Rate at which producers use photosynthesis to

produce and store chemical energy, minus the

rate at which they use energy for cellular

respiration

• A measure of the rate at which producers make

chemical energy potentially available to consumers

Primary Productivity


• Despite low NPP, oceans produce most of the

world’s biomass because of their vast size.

• Tropical rain forests have high NPP due to

their great variety and abundance of plants.

• Only plant matter represented by NPP is

available as nutrients for consumers.

– The planet’s NPP ultimately limits the number of

consumers that can survive.

Ecosystems Vary in Their Net Primary

Productivity (NPP)


• Elements and compounds that make up

nutrients move continually through air, water,

soil, rocks, and living organisms within

ecosystems via nutrient cycles.

3.4 What Happens To Matter in an

Ecosystem?


• Nutrient cycles, or biogeochemical cycles, are

driven directly or indirectly by incoming solar

radiation and Earth’s gravity.

– Nutrient cycles include the hydrologic (water),

carbon, nitrogen, and phosphorous cycles.

– Human activities are disrupting these cycles.

– Certain nutrients may accumulate in temporary

reservoirs, including the atmosphere, the oceans

and other bodies of water, underground deposits,

and living organisms.

Nutrients Cycle Within and Among

Ecosystems


• The hydrologic cycle collects, purifies, and

distributes Earth’s fixed supply of water.

• Incoming solar radiation causes evaporation

(conversion of liquid water to water vapor).

– Most water vapor rises into the atmosphere,

condenses in clouds

– 90% water vapor above land contributed by

transpiration (evaporation from plant surfaces)

• Gravity draws water back to Earth as

precipitation (rain, snow, sleet).

The Hydrologic Cycle—Evaporation and

Precipitation


• Most precipitation falling on land ecosystems

becomes surface runoff.

– Flows over land into streams, rivers, lakes,

wetlands, the ocean, where it can evaporate

• Some precipitation seeps into the soil.

– May evaporate or be used by plants, organisms

– May seep deeper into soil as groundwater that

collects in aquifers (underground layers of sand,

gravel, water-bearing rock)

The Hydrologic Cycle—Surface Runoff and

Groundwater


The Hydrologic Cycle


• By draining and filling in wetlands, which

disturbs natural flood control

• By withdrawing freshwater resources faster

than natural processes replenish it (aquifer

depletion, reduced river flow)

• By replacing forests/vegetation with urban

development—reducing infiltration and

increasing runoff

How Do Humans Alter the Water Cycle?


• Carbon dioxide gas, a key component of the

carbon cycle, significantly affects global

temperatures (due to the greenhouse effect).

• How does carbon cycle through the

biosphere?

– Photosynthesis by producers

– Aerobic respiration by producers, consumers, and

decomposers

– Marine sediments (Earth’s largest store of carbon)

The Carbon Cycle


The Global Carbon Cycle


• By adding large amounts of carbon dioxide to

the atmosphere

– Extracting and burning fossil fuels at a much

higher rate than they are naturally formed

• By clear-cutting forests faster than they re-

grow

– Destroys carbon-absorbing vegetation

How Do Humans Alter the Carbon Cycle?


• Atmospheric nitrogen cannot be absorbed

and used directly by organisms.

– Bacterial action makes nitrate ions available to

plants.

• Plant roots take up nitrate ions

• Animals eat plants, get nitrogen-containing compounds

• Organisms return nitrogen-rich organic compounds to

environment via waste, cast-off particles, dead remains

• Bacteria break down organic material, which eventually

releases nitrogen gas back to atmosphere

The Nitrogen Cycle


The Nitrogen Cycle


• By burning fossil fuels that add nitric oxide to

the atmosphere

– Nitric oxide can be converted to nitrogen dioxide

gas and nitric acid vapor, which fall as acid rain.

• By removing atmospheric nitrogen to make

fertilizer

– Excess nitrates in runoff from farm fields and

sewage discharge contaminate bodies of water

and cause excessive algal growth.

How Do Humans Alter the Nitrogen Cycle?


• Phosphorus cycles through soils, rocks, water

and plants, but not through the atmosphere.

– Water flows over rock, eroding inorganic

compounds containing phosphate ions

– Phosphate ions wash into soil, are absorbed by

producers

– Phosphate compounds transfer from producers to

consumers

– May wash into oceans, get trapped in marine

sediments for millions of years

The Phosphorus Cycle


The Phosphorus Cycle


• By mining phosphorus deposits to make

fertilizer

• By clearing tropical forests, which increases

erosion and reduces phosphorus in topsoil

• By adding large quantities of phosphate ions

to streams, lakes, and oceans as a result of

fertilizer runoff and topsoil erosion

– Excess phosphates stimulate algal growth

How Do Humans Alter the Phosphorus

Cycle?


• Scientists learn about ecosystems by:

– Using field and laboratory research

– Designing controlled experiments

– Developing mathematical and statistical models

3.5 How Do Scientists Study Ecosystems?


• Make direct observations and take samples,

measurements of ecosystems in the field

• Carry out controlled experiments

• Use satellites, aircraft, drones equipped with

cameras

• Use GIS software to collect/analyze data

• Use radio transmitters and GPS to track

organisms

Ecologists Study Ecosystems Directly


• Ecologists conduct research in laboratories.

– Use culture tubes, aquariums, greenhouses,

indoor/outdoor chambers with controlled variables

(light, temperature, etc.)

– Pros: allow for control of variables, study of

cause-and-effect relationships

– Cons: experiments may not reflect what actually

takes place in real ecosystem

• Mathematical modeling for large, complex

systems with many variables/large data sets

Ecologists Study Ecosystems Indirectly

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