Chapter 28 Energy Flow and Nutrient Cycling in Ecosystems.

Chapter 28Energy Flow and Nutrient Cycling in

Ecosystems

http://www.mediaresource.org/instruct.htm

How Do Nutrients and Energy Move Through Ecosystems?

• All ecosystems consist of two components– Biotic - living organisms in a given area—bacteria,

fungi, protists, plants, and animals– Abiotic - all nonliving physical or chemical aspects

of the environment, such as the climate, light, temperature, availability of water, and minerals in the soil


• Nutrients are atoms and molecules that organisms obtain from their environment– The same nutrients have been sustaining life on

Earth for about 3.5 billion years– Your body includes oxygen, carbon, hydrogen, and

nitrogen atoms that were once part of a dinosaur or a wooly mammoth

– Nutrients are transported around the Earth, but they never leave Earth


• Energy, in contrast, takes a one-way journey through ecosystems– Solar energy is captured by photosynthetic

bacteria, algae, and plants, and then flows from organism to organism

– Eventually, all of life’s energy is converted to heat that is given off to the environment and cannot be used to drive the chemical reactions of living organisms

– Life requires a continuous input of energy

Figure 28-1 Energy flow, nutrient cycling, and feeding relationships in ecosystems

energy fromsunlight producers

primaryconsumers

nutrients

detritivores anddecomposers

higher-levelconsumers

solar energyheat energy

energy stored inchemical bondsnutrients

How Does Energy Flow Through Ecosystems?

• Much of the energy reaching Earth from the sun is reflected back into space by the atmosphere, clouds, and the Earth’s surface

• Some is absorbed by the Earth to warm the planet• Less than 0.03% of the energy reaching Earth from

the sun is captured by photosynthetic organisms, and supports life on Earth


• Energy enters ecosystems through photosynthesis – Plants, algae, and photosynthetic bacteria acquire

nutrients such as carbon, nitrogen, oxygen, and phosphorus from the abiotic portions of ecosystems

– Photosynthesizers bring energy and nutrients into ecosystems


• Energy is passed from one trophic level to the next – Each category of organisms is called a trophic level

• Producers (or autotrophs) photosynthesizing organisms• Consumers (or heterotrophs) cannot photosynthesize

– They acquire energy and nutrients from molecules in the bodies of other organisms


• Energy is passed from one trophic level to the next (continued) – There are several levels of consumers

• Primary consumers (herbivores) feed directly and exclusively on producers

• Carnivores act as secondary consumers when they prey on herbivores

• Some carnivores eat other carnivores and are called tertiary consumers


• Net primary production is a measure of the energy stored in producers – The amount of life that a particular ecosystem can support is

determined by the energy captured by the producers in that ecosystem

– Biomass, or dry biological material, is usually a good measure of the energy stored in organisms’ bodies

openocean(125)

continentalshelf (140)

tundra(140)

coniferousforest (800)

temperatedeciduousforest (1,200)

desert (90)

grassland (600)

estuary(1,500)

tropical rainforest (2,200)


• The net primary production of an ecosystem is influenced by many factors

• The amount of sunlight• The availability of water and nutrients• The temperature

• An ecosystem’s contribution to Earth’s total production is determined by the ecosystem’s productivity and by the portion of Earth that the ecosystem covers


• Food chains and food webs describe the feeding relationships within communities – A food chain is a linear feeding relationship with

just one representative at each trophic leveltertiary consumer

(fourth trophic level)

secondary consumer(third trophic level)

primary consumer(second trophic level)

producer(first trophic level)

A simple terrestrial food chain

Figure 28-3b A simple marine food chain

phytoplankton zooplankton

producer(first trophic level)

primary consumer(second trophic level)

secondary consumer(third trophic level)

tertiary consumer(fourth trophic level)

quaternary consumer(fifth trophic level)

A simple marine food chain


• Food chains and food webs describe the feeding relationships within communities (continued) – Animals in natural communities often do not fit

neatly into the categories of primary, secondary, and tertiary consumers depicted in simple food chains

– A food web shows many interconnected food chains, and actual feeding relationships in a community

– Some animals, such as raccoons, bears, rats, and humans, are omnivores (“everything eaters”) and act as primary, secondary, and tertiary consumers

Figure 28-4 A simplified grassland food web


• Detritivores and decomposers release nutrients for reuse– Among the most important strands in a food web are

the detritivores and decomposers• Detritivores (“debris eaters”) are an army of mostly small

and often unnoticed organisms– Nematode worms and Earthworms– Vultures– Millipedes– Dung beetles– Slugs


• Detritivores and decomposers release nutrients for reuse (continued) – Decomposers are primarily fungi and bacteria

• They feed on the same material as detritivores• They do not ingest chunks of organic matter• They secrete digestive enzymes outside their bodies, where

the enzymes break down nearby organic material• Decomposers absorb some of the resulting nutrient

molecules but leave the rest


• Detritivores and decomposers are absolutely essential to life on Earth– Without detritivores and decomposers, ecosystems

would gradually be buried by accumulated wastes and dead bodies, whose nutrients would be unavailable to enrich the soil and water


• Energy transfer through trophic levels is inefficient – Second Law of Thermodynamics– Inefficiency is a rule in living systems

• Waste is heat produced by all biochemical reactions that keep cells alive

• Only a fraction of the energy captured by producers of the first trophic level can be used by organisms in the second trophic level


• Energy transfer through trophic levels is inefficient (continued)– The average net energy transfer between trophic

levels is roughly 10% efficient and is known as the “10% law”

• An energy pyramid illustrates the energy relationships between trophic levels—widest at the base, and progressively narrowing in higher trophic levels

• A biomass pyramid for a community has the same general shape

Figure 28-5 An energy pyramid for a grassland ecosystem

tertiaryconsumer(1 calorie)

secondaryconsumer(10 calories)

primaryconsumer(100 calories)

producers(1,000 calories)


• Energy transfer through trophic levels is inefficient (continued)– The most abundant organisms are plants– The most abundant animals are herbivores– Carnivores are relatively scarce because there is

far less energy available to support them– Energy losses within and between trophic levels

mean that long-lived animals at higher trophic levels eat many times their body weight in food


• Energy transfer through trophic levels is inefficient (continued)– If the food contains certain types of toxic

substances, they may be stored and become more concentrated

– This biological magnification can lead to harmful and even fatal effects

• Mercury in fish

How Do Nutrients Cycle Within and Among Ecosystems?

• Nutrient cycles, also called biogeochemical cycles, describe the pathways that nutrients follow as they move from their major sources in the abiotic parts of ecosystems, called reservoirs, through living communities and back again


• The hydrologic cycle has its major reservoir in the oceans – The water cycle, or hydrologic cycle, is the

pathway that water takes as it travels from its major reservoir—the oceans—through the atmosphere, to reservoirs in freshwater lakes, rivers, and groundwater, and then back again to the oceans


• The hydrologic cycle– The hydrologic cycle would continue even if life on

Earth disappeared because the biotic portion of ecosystems plays a small role in the hydrologic cycle

– The hydrologic cycle is crucial for terrestrial communities because it continually restores the fresh water needed for land-based life

– The oceans cover 70% of the Earth’s surface and contain more than 97% of Earth’s water

– Solar energy evaporates water, and it comes back to Earth as precipitation

reservoirs

Figure 28-6 The hydrologic cycle

reservoirsprocessesprocesses

precipitationover land

water vapor inthe atmosphere

evaporationfrom the landand from the

leaves of plants

lakes and rivers

evaporation fromlakes and rivers

runofffrom rivers

and land

evaporationfrom the

ocean

water inthe ocean

precipitationover the ocean

extraction foragriculture

groundwater,includingaquifers

seepage through soilinto groundwater


• The carbon cycle has major reservoirs in the atmosphere and oceans – Carbon atoms form the framework of all organic

molecules – The carbon cycle is the pathway that carbon takes

from its major short-term reservoirs in the atmosphere and oceans, through producers and into the bodies of consumers, detritivores, and decomposers, and then back again to its reservoirs

Figure 28-7 The carbon cycle

reservoirsprocessestrophic levels

CO2 dissolvedin the ocean

CO2 in theatmosphere

burningfossil fuels

respiration fire

consumersproducers

photosynthesis

fossil fuels(coal, oil, natural gas)

detritivoresand decomposers

decomposition


• The carbon cycle – The complementary processes of uptake by

photosynthesis and release by cellular respiration continually recycle carbon from the abiotic to the biotic portions of an ecosystem and back again


• The carbon cycle – Much of Earth’s carbon is bound up in limestone

rock, formed from calcium carbonate (CaCO3) deposited on the ocean floor in the shells of prehistoric phytoplankton

• This cycling requires millions of years

– Fossil fuels, which include coal, oil, and natural gas, are additional long-term reservoirs for carbon


• The nitrogen cycle has its major reservoir in the atmosphere – Nitrogen is a crucial component of proteins, many

vitamins, nucleotides (such as ATP), and nucleic acids (such as DNA)

– The nitrogen cycle is the pathway taken by nitrogen from its primary reservoir—nitrogen gas (N2) in the atmosphere—to much smaller reservoirs of ammonia and nitrate in soil and water, through producers, consumers, detritivores and decomposers, and back to its reservoirs


• The nitrogen cycle– While nitrogen gas (N2) makes up 78% of the

atmosphere, this form of nitrogen cannot be utilized by plants

• Plants utilize nitrate (NO3) or ammonia (NH3) as their

nitrogen source

– N2 is converted to ammonia by specific bacteria during a process called nitrogen fixation

Figure 28-8 The nitrogen cycle


burningfossil fuels

N2 in theatmosphere

lightning

application ofmanufactured fertilizer

producersconsumers

decomposition

ammonia andnitrates in water

denitrifyingbacteria

detritivoresand decomposers

uptake byproducers

ammoniaand nitrates

in soil

nitrogen-fixingbacteria in soil

and legume roots


• The nitrogen cycle– People significantly manipulate the nitrogen cycle,

both deliberately and unintentionally• Plant legumes to fertilize fields• About 150 million tons of nitrogen-based fertilizer are

applied to farms each year• The heat produced by burning fossil fuels combines

atmospheric N2 and O2, generating nitrogen oxides that form nitrates

– Human activities now dominate the nitrogen cycle


• The phosphorus cycle has its major reservoir in rock, bound to oxygen as phosphate – Phosphorus is found in biological molecules such as

nucleic acids and the phospholipids of cell membranes– It also forms a major component of vertebrate teeth

and bones– The phosphorus cycle is the pathway taken by

phosphorus from its primary reservoir in rocks to much smaller reservoirs in soil and water, producers, consumers, detritivores and decomposers and back

Figure 28-9 The phosphorus cycle

phosphatein rock


geologicaluplift

application ofmanufactured

fertilizer

runofffrom rivers

runoff fromfertilized

fields

phosphatein water

uptake byproducers

producers

consumers

detritivores anddecomposers

decomposition phosphatein soil

phosphatein sediment

formation ofphosphate-containing

rock

Review

1. Why is energy flow not cyclical like nutrients?2. Name the trophic levels in a community.3. Why are detritivores and decomposers

essential to ecosystem function?4. What are the four major nutrient cycles?

What Happens When Humans Disrupt Nutrient Cycles?

• As the human population grew and technology increased, people began to act more independently of natural ecosystem processes– The Industrial Revolution resulted in a tremendous

increase in our reliance on energy stored in fossil fuels for heat, light, transportation, industry, and agriculture


• Overloading the nitrogen and phosphorus cycles damages aquatic ecosystems – Fertilizers are applied to farm fields– Water dissolves and carries away some of the

phosphate and nitrogen-based fertilizer– Overstimulating the growth of phytoplankton in the

ocean “bloom”


• Overloading the nitrogen and phosphorus cycles damages aquatic ecosystems (continued) – The phytoplankton die, and their bodies sink into

deeper water and provide food for decomposer bacteria

– The decomposers use up most of the available oxygen, and other aquatic organisms, such as invertebrates and fish, die, creating “dead zones” in many waters (Gulf of Mexico)


• Overloading the sulfur and nitrogen cycles causes acid deposition – Burning of sulfur-containing fossil fuels, primarily

coal, accounts for about 75% of all sulfur dioxide emissions worldwide

– Days later and often hundreds of miles from the source, these acids fall to Earth in rain or snow


• Interfering with the carbon cycle is warming Earth’s climate– Natural process called the greenhouse effect,

which keeps our atmosphere relatively warm and allows life on Earth as we know it

– For Earth’s temperature to remain constant, the total amount of energy entering and leaving Earth’s atmosphere must be equal

Figure 28-13 The greenhouse effect

volcanoesforestfires

power plantsand factories

homes and otherbuildings

agriculturalactivities

Heat isradiated back intothe atmosphere

Some atmospheric heat isretained by greenhouse gases

Most heat is radiatedinto space

Sunlight energyenters the atmosphere

Some energyis reflected backinto space

Most sunlight strikesEarth’s surface and isconverted into heat

vehicleemissions

Sun


• Interfering with the carbon cycle is warming Earth’s climate (continued)– If atmospheric concentrations of greenhouse gases

increase, more heat is retained than is radiated into space, causing Earth to warm

– Greenhouse gases are increasing because people burn fossil fuels, releasing CO2

– Other important greenhouse gases include methane (CH4), released by agricultural activities and burning fossil fuels


• Burning fossil fuels is causing climate change– Climate scientists predict that the warming

atmosphere will cause more severe storms, including stronger hurricanes

– Greater amounts of rain or snow will fall in single storms

– More frequent and more prolonged droughts will occur

– Increased CO2 makes the oceans more acidic

Chapter 28 Energy Flow and Nutrient Cycling in Ecosystems.

Documents

Transcript of Chapter 28 Energy Flow and Nutrient Cycling in Ecosystems.