Chapter 2: Principles of Ecology - Wikispaces studying nature for thou-sands of years. ... MiniLab 2-1MiniLab 2-1 Experimenting the world. ... by observing organisms in the field

EcologyEcologyA tropical rain forest ecosystem consists ofinteractions among organisms, andbetween organisms and their environment.For example, rain forest plants are adaptedto use the ample water and sunlight in theproduction of nutrients. The plants usethese nutrients for their own growth anddevelopment, and, in turn, the nutrientsthat make up the plants may then be passedto animals that feed on them. Scarletmacaws eat seeds and fruits from rain forest trees, but they also eat clay soil thathelps to detoxify many of the poisonousplants that they eat.

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UNIT CONTENTSUNIT CONTENTS

Principles of Ecology

Communities and Biomes

Population Biology

Biological Diversity andConservation

Unit 2Unit 2

EcologyBIODIGESTBIODIGEST

UNIT PROJECTUNIT PROJECT

Use the Glencoe Science Web site for more project

activities that are connected to this unit.science.glencoe.com

BIOLOGY

http://science.glencoe.com

36 PRINCIPLES OF ECOLOGY

Principles of Ecology

What You’ll Learn■ You will describe ecology and

the work of ecologists.■ You will identify important

aspects of an organism’s environment.

■ You will trace the flow ofenergy and nutrients in theliving and nonliving worlds.

Why It’s ImportantTo understand life, you need to know how organisms meettheir needs in their naturalenvironments. To reduce theimpact of an expanding humanpopulation on the naturalworld, it is important to under-stand how living things dependon their environments.

As you look through Chapter 2,pick out one or two new vocab-ulary words from the text.While reading the chapter, tryto see how charts or diagramsdemonstrate the vocabularywords’ meanings.

To find out more about ecol-ogy, visit the Glencoe ScienceWeb site.science.glencoe.com

READING BIOLOGYREADING BIOLOGY

2ChapterChapter

You might think mosquitoesare pests, but for trout andother animals, mosquitoesand their larvae are a majorfood source.

BIOLOGY


Section

What Is Ecology?Do you know anyone who likes to

observe nature? Perhaps it is a personwho knows the names of many ani-mals, plants, or rocks. People haveenjoyed studying nature for thou-sands of years. Birdwatchers knowthe names and behaviors of the birdsin their area. Some people carefullyrecord observations of rainfall andtemperature. Others make it a hobbyto study plants; they keep log bookswith records of when plants pro-duced leaves, flowers, and fruit, asshown in Figure 2.1. Some peoplewho are interested in nature record

observations, discuss their results,and note how patterns change fromyear to year.

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s shown in the photographs, people can impact plant andanimal communities in both

positive and negative ways. Learninghow ecological principles explain interaction between organisms andtheir environment can help you understand environmental issuesand form your own opin-ions about them. Inthis section, you willlearn some of thehistory and thefocus of ecology.

SECTION PREVIEW

ObjectivesDistinguish betweenthe biotic and abioticfactors in the environ-ment.Compare the differentlevels of biological organization and livingrelationships importantin ecology.Explain the differencebetween a niche and a habitat.

Vocabularyecologybiosphereabiotic factorbiotic factorpopulation communityecosystem habitatnichesymbiosis commensalismmutualism parasitism

2.1 Organisms and Their Environment

Animals wander into citiesin search of food (above).A wildlife rehabilitatorreleases an owl (inset).

Figure 2.1 An amateur naturestudy log book fromthe 17th century.

A

Ecology definedThe branch of biology that devel-

oped from natural history is calledecology. Ecology is the scientificstudy of interactions among organ-isms and their environments.Ecological study reveals relationshipsamong living and nonliving parts of

MiniLab 2-1MiniLab 2-1 Experimenting

the world. Ecology combines infor-mation and techniques from manyscientific fields, including mathemat-ics, chemistry, physics, geology, andother branches of biology.

You have learned that scientificresearch includes both descriptiveand quantitative methods. Most ecol-ogists use both types of research.They obtain descriptive informationby observing organisms in the fieldand laboratory. They obtain quanti-tative data by making measurementsand carrying out carefully controlledexperiments. Using these methods,ecologists learn a great deal aboutrelationships, such as what organismsa coyote eats, how day length influ-ences the behavior of migratingbirds, how tiny shrimp help rid oceanfishes of parasites, or how acid rainthreatens some of Earth’s forests.

Aspects of Ecological Study

As far as we know, life exists onlyon Earth. Living things can be foundin the air, on land, and in both fresh-and salt water. The biosphere (BI uhsfihr) is the portion of Earth thatsupports life. It extends from high inthe atmosphere to the bottom of theoceans. This life-supporting layermay seem extensive to us, but if youcould shrink Earth to the size of anapple, the biosphere would be thin-ner than the apple’s peel.

Although it is thin, the biosphereis very diverse and supports a widerange of organisms. The climate,soils, plants, and animals in a desertare very different from those in atropical rain forest. Living things areaffected by both the physical envi-ronment and by other living things.Ecologists study these interactionsamong different organisms and theirenvironments.


Salt Tolerance of Seeds Salinity, or the amount of salt dis-solved in water, is an abiotic factor. Might salt water affect howcertain seeds sprout or germinate? Experiment to find out.

Procedure! Soak 20 seeds in freshwater and 20 seeds in salt water

overnight.@ The next day, wrap the seeds in two different moist

paper towels. Slide the towels into separate self-sealingplastic bags.

# Label the bags “fresh” and “salt.”$ Examine all seeds two days later. Count the number of

seeds in each treatment that show signs of root growth orsprouting, which is called germination. Record your data.CAUTION: Be sure to wash your hands after handlingseeds.

Analysis1. Did the germination rates differ between treatments? If

yes, how?2. What abiotic factor was tested in this experiment? What

biotic factor was influenced?3. Might all seeds respond to salt in a similar manner? How

could you find out?

Salt marshFreshwater pond

The nonliving environment:Abiotic factors

Ecology includes the study of fea-tures of the environment that are notliving because these features are animportant part of an organism’s life.For example, a complete study of theecology of moles would include anexamination of the types of soil inwhich these animals dig their tunnels.Similarly, a thorough investigation ofthe life cycle of trout would need toinclude whether these fish lay theireggs on rocky or sandy stream bot-toms. The nonliving parts of an organ-ism’s environment are the abiotic factors (ay bi AHT ihk). Examples ofabiotic factors include air currents,temperature, moisture, light, and soil.

Abiotic factors have obvious effectson living things and often determinewhich species survive in a particularenvironment. For example, lack ofrainfall can cause drought in a grass-land, as shown in Figure 2.2. Canyou think of changes in a grasslandthat might result from a drought?Grasses would grow more slowly,wildflowers would produce fewerseeds, and the animals that dependon plants for food would find itharder to survive. Examine otherways that abiotic factors affect livingthings in the MiniLab and Problem-Solving Lab shown on these pages.

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Figure 2.2 Droughts are common ingrasslands. As the grasses dryout, they turn yellow andappear to be dead, but newshoots grow in the low-lyingareas soon after it rains.Some animal species areadapted to living in grass-lands by their ability to bur-row underground and sleepthrough the dry periods.

How does an abiotic factor affect food production?Green plants carry out the process of photosynthesis. Glucose,a sugar, is one of the products produced during this process.Thus, glucose production can be used as a means for judgingthe rate at which the process of photosynthesis is occurring.

AnalysisExamine the following graph of a plant called salt bush

(Atriplex). It shows how this plant’s glucose production isinfluenced by temperature.

Thinking Critically1. Name the abiotic factor influencing photosynthesis and

describe the influence of this factor on photosynthesis.2. Name the biotic factor being influenced.3. Based on the graph, describe the type of ecosystem this

plant might live in. Explain your answer.4. Does the graph tell you how the rate of photosynthesis

might vary for plants other than salt bushes? Explain youranswer.

5. Hypothesize why the formation of glucose drops quicklyafter reaching 30°C.

Problem-Solving Lab 2-1Problem-Solving Lab 2-1 Interpreting Data

Food

pro

duct

ion

(mg

of g

luco

se f

orm

ed/h

r)

Temperature °C10 20 30 40 50

5

10

15

Food Production in Salt Bush

The living environment: Biotic factors

Look at the goldfish in Figure 2.3.Now consider its relationships withother organisms. It may depend onother living things for food, or it may be food for other life. Thegoldfish needs members of the samespecies to reproduce. To meet itsneeds, the goldfish may competewith organisms of the same or differ-ent species.

A key consideration of ecology isthat living organisms affect otherorganisms. All the living organismsthat inhabit an environment arecalled biotic factors (by AHT ihk).Ecologists investigate how biotic fac-tors affect different species. To helpthem understand the interactions ofthe biotic and abiotic parts of theworld, ecologists have organized theliving world into levels.

Levels of Organizationin Ecology

The study of an individual organ-ism, such as a male deer, known as abuck, might reveal what food items itprefers, how often it eats, and howfar it roams to search for food orshelter. Although it spends a largepart of its time alone, it does interactwith other individuals of its species.For example, it periodically goes insearch of a mate, which may requirebattling with other bucks.

All organisms depend on othersfor food, shelter, reproduction, orprotection. So you can see that thestudy of an individual would provideonly part of the story of its life cycle.To get a more complete picturerequires studying its relationshipswith other organisms.

Ecologists study interactionsamong organisms at several different


CAREERS IN BIOLOGY

Science Reporter

Does science fascinate you? Can you explain complex

ideas and issues in a clear andinteresting way? If so, youshould consider a career as ascience reporter.

Skills for the JobAs a science reporter, you

are a writer first and a scientistsecond. A degree in journalismand/or a scientific field is usually neces-sary, but curiosity and good writing skills are also essential.You might work for newspapers, national magazines, medicalor scientific publications, television networks, or Internetnews services. You could work as a full-time employee or afreelance writer. You must read constantly to stay up-to-date.Many science reporters attend scientific conventions andevents to find news of interest to the public. Then they care-fully and accurately translate what’s new so nonscientists canunderstand it.

Figure 2.3 How might other living things affect this goldfish?

BIOLOGY For more careers in relatedfields, be sure to check theGlencoe Science Web site.science.glencoe.com


levels, as shown in Figure 2.4. Theystudy individual organisms, interac-tions among organisms of the samespecies, and interactions among

organisms of different species.Ecologists also study how abiotic fac-tors affect groups of interactingspecies.

2.1 ORGANISMS AND THEIR ENVIRONMENT 41

Figure 2.4 Ecology deals with severallevels of biological organi-zation, including organ-isms, populations, commu-nities, ecosystems, biomes,and the biosphere.

Organism

Communities

Populations

Ecosystems

Biosphere

Interactions within populationsThe marsh marigolds shown in

Figure 2.5 form a population. Apopulation is a group of organisms ofone species that interbreed and livein the same place at the same time.

Members of the same populationmay compete with each other forfood, water, or other resources. Com-petition occurs only if resources arein short supply. How organisms in apopulation share the resources oftheir environment determines howfar apart organisms live and howlarge the populations become.

Some species have adaptations thatreduce competition within a popula-

tion. An example is the life cycle of afrog, shown in Figure 2.6. The juve-nile stage of the frog, called the tad-pole, not only looks very differentfrom the adult but also has com-pletely different food requirements.Many species of insects, includingdragonflies and moths, also producejuveniles that differ from the adult inbody form and food requirements.

Individuals interact within communities

No species lives independently ofother species. Just as a population ismade up of individuals, a communityis made up of several populations. Acommunity is a collection of inter-acting populations. An example of acommunity is shown in Figure 2.7.

A change in one population in acommunity will cause changes in theother populations. Some of thesechanges can be minor, such as when asmall increase in the number of indi-viduals of one population causes asmall decrease in the size of anotherpopulation.

For example, if the population ofmouse-eating hawks increasesslightly, the population of mice will,as a result, decrease slightly. Otherchanges might be more extreme, aswhen the size of one population


Figure 2.5 These marshmarigolds representa population oforganisms. Whatcharacteristics areshared by this groupof flowers that makethem a population?

Figure 2.6 Adult frogs and theiryoung have differentfood requirements.This limits competitionfor food resources forthe species.

Eggs that adult frogs lay in thewater hatch into tadpoles. Tadpoleshave gills, live in water, and eatalgae and small aquatic creatures.

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Adult frogs live both on land andin the water. They breathe airand eat insects such as dragon-flies, grasshoppers, and beetles.

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grows so large it begins affecting thefood supply for another species in thecommunity.

Interactions among living things and abiotic factors form ecosystems

In a healthy forest community,interactions among populations mightinclude birds eating insects, squirrelseating nuts from trees, mushroomsgrowing from decaying leaves or bark,and raccoons fishing in a stream. Inaddition to population interactions,ecologists also study interactionsamong populations and their physicalsurroundings in ecosystems. Anecosystem is made up of the interac-tions among the populations in a com-munity and the community’s physicalsurroundings, or abiotic factors.

There are three major kinds ofecosystems. Terrestrial ecosystemsare those located on land. Examples

include forests, meadows, and desertscrub. Aquatic ecosystems occur inboth fresh- and saltwater. Freshwaterecosystems include ponds, lakes, andstreams. Saltwater ecosystems, alsocalled marine ecosystems, make upapproximately 75 percent of Earth’ssurface. Figure 2.8 shows a marineand a freshwater ecosystem.

Figure 2.7 Beech and maple treesdominate this forestcommunity; therefore,it is called a beech-maple forest. Beech-maple forests arefound in the easternUnited States, Europe,and northeast China.

Figure 2.8 There may be hundreds of populations interacting in apond or tide pool. How do you think the abiotic factorsin these environments affect the biotic factors?

Dragonflies live near moist meadows and ponds. They feed on small insects theycatch while flying. Dragonflies lay their eggsin the pond or on pond plants.

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Organisms living in tide pools must survivedramatic changes in abiotic factors. Whenthe tide is high, ocean waves replenish thewater in the pool. When the tide is low,water in the pool evaporates.

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Organisms inEcosystems

A prairie dog living in a grasslandmakes its home in burrows it digsunderground. Some species of birdsmake their homes in the trees of abeech-maple forest. In these forests,they find food, avoid enemies, andreproduce. The grassland and beech-maple forests are examples of habi-tats. A habitat (HAB uh tat) is theplace where an organism lives out itslife. Organisms of different speciesuse a variety of strategies to live andreproduce in their habitats. Habitatscan change, and even disappear, froman area. Examples of how habitats

change due to both natural andhuman causes are presented in Biologyand Society at the end of this chapter.

Niche Although several species may share

a habitat, the food, shelter, and otheressential resources of that habitat areoften used in different ways. Forexample, if you turn over a log likethe one shown in Figure 2.9, youwill find millipedes, centipedes,insects, and worms living there. Atfirst, it looks like this community ofanimals is competing for foodbecause they all live in the same habi-tat. But close inspection reveals thateach feeds in different ways, on


Figure 2.9 This series of photographs showshow a habitat can be seen as a col-lection of several niches. As you cansee, each species uses the availableresources in a different way.

A worm obtains nourishmentfrom the organic material it eatsas it burrows through the soil.

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A centipede is a predatorthat captures and eatsbeetles and other animals.

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different materials, and at differenttimes. These differences lead toreduced competition.

Each species is unique in satisfyingall its needs; each species occupies aniche. A niche (nich) is the role andposition a species has in its environ-ment—how it meets its needs forfood and shelter, how it survives, andhow it reproduces. A species’ nicheincludes all its interactions with thebiotic and abiotic parts of its habitat.It is an advantage for a species tooccupy a niche different from thoseof other species. Life may be harsh inthe polar regions, but the polar bear,with its thick coat, flourishes there.Nectar may be deep in the flower,

inaccessible to most species, but thehummingbird, with its long beak,gets it. Unique strategies and struc-tures are important to a species’niche and important for reducingcompetition with other species.

Living relationshipsSome species enhance their

chances of survival by forming rela-tionships with other species.Biologists once assumed that allorganisms living in the same environ-ment are in a continuous battle forsurvival. Some interactions are harm-ful to one species, yet beneficial toanother. Predators are animals suchas lions and insect-eating birds that


A millipede eats decayingleaves near the log.

CC

These ants eat dead insects.DD

kill and eat other animals. The ani-mals that predators eat are calledprey. Predator-prey relationshipssuch as the one between lions andwildebeests involve a fight for sur-vival. Use the BioLab at the end ofthis chapter to more closely examinea predator-prey relationship. Butthere are other relationships amongorganisms that help maintain survivalin many species. The relationship in

which there is a close and permanentassociation among organisms of dif-ferent species is called symbiosis(sihm by OH sus). Symbiosis meansliving together.

There are several kinds of symbio-sis. A symbiotic relationship betweenthe peregrine falcon and red-breastedgoose has evolved in the cold arcticregion of Siberia in Russia, as shownin Figure 2.10. Normally, the pere-grine falcon preys upon the red-breasted goose, but the falcon huntsaway from its nesting area. Duringthe nesting season, the falcon fiercelydefends its territory from predators.The geese take advantage of this,choosing nesting areas close to thoseof the falcons, and are thereby pro-tected from predators. The geesebenefit from the relationship, and thefalcon is neither benefited norharmed. This is called a commensalrelationship. Commensalism (kuhMEN suh lihz um) is a symbiotic rela-tionship in which one species benefitsand the other species is neitherharmed nor benefited.

Commensal relationships alsooccur among plant species. Spanishmoss, a kind of flowering plant thatgrows on the branch of a tree, isshown in Figure 2.11. Orchids,ferns, mosses, and other plants some-times grow on the branches of largerplants. The larger plants are notharmed, but the smaller plants bene-fit from the additional habitat.

Sometimes, two species of organ-isms benefit from living in close asso-ciation. A symbiotic relationship inwhich both species benefit is calledmutualism (MYEW chuh lihz um).Ants and acacia trees living in the sub-tropical regions of the world illustratemutualism, as shown in Figure 2.12.The ants protect the tree by attackingany animal that tries to feed on it.The tree provides nectar and a home

Figure 2.11Spanish moss growson and hangs fromthe limbs of trees butdoes not obtain anynutrients or cause anyharm to the trees.

Figure 2.10Red-breasted geese (a) and peregrine falcons (b) both nest in the Siberian arcticin the spring. They share a symbiotic relationship.

a

b

for the ants. In an experiment, ecolo-gists removed the ants from some aca-cia trees. Results showed that thetrees with ants grew faster and sur-vived longer than trees without ants.

Sometimes, one organism harmsanother. Have you ever owned a dogor cat that was attacked by ticks orfleas? Ticks and fleas, shown inFigure 2.13, are examples of para-sites. A symbiotic relationship inwhich one organism derives benefitat the expense of the other is calledparasitism (PER uh suh tihz um).Parasites have evolved in such a waythat they harm, but usually do notkill, the host. If the host dies, theparasite also will die unless it canquickly find another host. Some par-asites, such as tapeworms and round-worms, live inside other organisms.


Section AssessmentSection AssessmentUnderstanding Main Ideas 1. List several different biotic and abiotic factors

in an ecosystem.2. Compare and contrast populations and

communities.3. Give examples that would demonstrate the dif-

ferences between the terms niche and habitat.4. A leaf-eating caterpillar turns into a nectar-

eating butterfly. How is this feeding behavior an advantage for this species?

Thinking Critically5. Clownfish are small, tropical marine fish

usually found swimming among the stinging tentacles of sea anemones. What type of symbi-otic relationship do these animals have if theclownfish are protected by the sea anemone, but the anemone does not benefit from theclownfish?

6. Designing an Experiment Design an experi-ment to test the hypothesis that clownfish andsea anemones have a mutualistic relationship.For more help, refer to Practicing ScientificMethods in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

Figure 2.13Ticks cause harm to the animals they liveon when they obtainnutrients from theirhost animal. This relationship is calledparasitism.

Figure 2.12These ants and acacia trees both benefit from living in closeassociation. This mutualistic relationship is so strong that innature the trees and ants are never found apart.

OriginWORDWORD

ecology From the Greekwords oikos, mean-ing “homestead,”and logos, meaning“the study of.”Ecology is the studyof how organismsinteract with their environments.

Section


How Organisms Obtain Energy

A roadrunner sprints, a cactusflowers, an aphid reproduces. Energydrives all these events. One of themost important characteristics of aspecies’ niche is how the speciesobtains its energy. Ecologists tracethe flow of energy through commu-nities to discover nutritional relation-ships. The ultimate source of theenergy is the sun, which supplies theenergy that fuels life.

The producers: AutotrophsPlants use the sun’s energy to man-

ufacture food in a process called pho-tosynthesis. Organisms that useenergy from the sun or energy stored

in chemical compounds to manufac-ture their own nutrients are calledautotrophs (AWT uh trohfs). Thegrass in Figure 2.14 is an autotroph.Although plants are the most familiarterrestrial autotrophs, some unicellu-lar organisms also make their ownnutrients. Most other organismsdepend on autotrophs for nutrientsand energy.

The consumers: HeterotrophsA deer nibbles the leaves of a

clover plant, a bison munches grass,an owl swallows a mouse. The deer,buffalo, and owl are incapable of pro-ducing their own food. They obtainnutrients by eating other organisms.Organisms that cannot make theirown food and must feed on other

What eats what? The orioleeats the grasshopper. Thegrasshopper eats the grass.

Organisms, such as the oriole,grasshopper, and grass, need nutri-tion for growth, repair, and energy.How they satisfy their nutritionalneeds is an importantpart of their niche,and an importantfocus of ecology.

SECTION PREVIEW

ObjectivesCompare how organisms satisfy theirnutritional needs.Trace the path ofenergy and matter in an ecosystem.Analyze how nutrientsare cycled in the abioticand biotic parts of thebiosphere.

Vocabularyautotrophheterotrophscavengerdecomposerfood chaintrophic levelfood web

2.2 Nutrition and EnergyFlow

OriginWORDWORD

autotroph From the Greekwords auto, meaning“self,” and trophe,meaning “nourish-ment.” Autotrophsare self-nourishing;they make their own food.

heterotroph From the Greekwords hetero, mean-ing “other,” and trophe, meaning“nourishment.”Heterotrophs consume otherorganisms for theirnutrition.

Orioles (above) andgrasshoppers (inset)form part of a foodchain.

organisms are called heterotrophs(HET uh ruh trohfs). Heterotrophsinclude organisms that feed only onautotrophs, organisms that feed onlyon other heterotrophs, and organ-isms that feed on both autotrophsand heterotrophs.

Some heterotrophs, such as graz-ing, seed-eating, and algae-eatinganimals, feed directly on autotrophs.The wildebeests in Figure 2.14depend on plants for their food. Aheterotroph that feeds only on plantsis called a herbivore. Herbivoresinclude rabbits, grasshoppers,beavers, squirrels, bees, elephants,and fruit-eating bats.

Some heterotrophs eat other het-erotrophs. Animals such as lions thatkill and eat only other animals arecalled carnivores. Some animals donot kill for food; instead, they eatanimals that have already died.Scavengers such as black vulturesfeed on carrion and refuse, and play abeneficial role in the ecosystem.Imagine for a moment what the envi-ronment would be like if there wereno vultures to devour animals killed

on the African plains, no buzzards toclean up dead animals along roads,and no ants and beetles to removedead insects and small animals fromsidewalks and basements.

Humans are an example of a thirdtype of heterotroph. The teenagersin Figure 2.15 are eating a variety offoods that include both animal andplant materials. They are omnivores.Raccoons, opossums, and bears areother examples of omnivores.

Figure 2.14 Many kinds of organisms live in the savanna of EastAfrica. Identify theautotrophs and theheterotrophs.

Figure 2.15 People are omnivores because they eatboth autotrophs and heterotrophs.

OriginWORDWORD

herbivore From the Latinwords herba, mean-ing “grass,” andvorare, meaning “todevour.” Herbivoresfeed on grass andother plants.

carnivore From the Latinwords caro, meaning“flesh,” and vorare,meaning “todevour.” Carnivoreseat animals.

omnivore From the Latinwords omnis, mean-ing “all,” and vorare,meaning “todevour.” Omnivoreseat both plants andanimals.

Some organisms, such as fungi,break down and absorb nutrientsfrom dead organisms. These organ-isms are called decomposers.Decomposers break down the com-plex compounds of dead and decay-ing plants and animals into simplermolecules that can be more easilyabsorbed by the decomposers, and byother organisms. Some protozoans,many bacteria, and most fungi carryout this essential process of decom-position.

Matter and Energy Flow in Ecosystems

When you pick an apple from atree and eat it, you are consumingcarbon, nitrogen, and other elementsthe tree has used to produce the fruit.That apple also contains energy fromthe sunlight trapped by the tree’sleaves while the apple was growingand ripening.

Matter and energy flow throughorganisms in ecosystems. You havealready learned that feeding relation-ships and symbiotic relationshipsdescribe ways in which organismsinteract. Ecologists study these inter-actions to make models that trace theflow of matter and energy throughecosystems.

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Figure 2.16 In order for a wetland ecosystem to function, itsorganisms must depend on each other for a supplyof energy. Follow the steps in the wetland foodchain shown here.

First-order heterotrophs, or herbi-vores, compose the second trophiclevel of a food chain. For example,in this wetland, small fishes andcrustaceans feed on algae.

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The first trophic level in all foodchains is made up of photosyntheticautotrophs—the producers. In thiswetland community, grasses, mangrove and cypress trees, and aquatic phytoplankton are autotrophs.

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Food chains: Pathways for matter and energy

The wetlands community picturedin Figure 2.16 illustrates examples offood chains. A food chain is a simplemodel that scientists use to show howmatter and energy move through anecosystem. Nutrients and energyproceed from autotrophs to het-erotrophs and, eventually, to decom-posers.

A food chain is typically drawn usingarrows to indicate the direction inwhich energy is transferred from oneorganism to the next. One food chainin Figure 2.16 could be shown as

algae ➜ fish ➜ heron

Food chains can consist of threelinks, or steps, but most have no

more than five links. This is becausethe amount of energy remaining inthe fifth link is only a small portionof what was available at the first link.A portion of the energy is lost as heatat each link. It makes sense, then,that typical food chains are three orfour links long.

2.2 NUTRITION AND ENERGY FLOW 51

Second-order heterotrophs, which are carni-vores, make up the third trophic level. Theyfeed on first-order heterotrophs. The heronis a carnivorous bird that feeds on fishes,frogs, and other small animals of the wet-land habitat.

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Third-order heterotrophs, carnivoresthat feed on second-order heterotrophs,make up the fourth trophic level. An alli-gator eating a shorebird is one exampleof a third-order heterotroph. Bacteriaand fungi decompose all the links of thefood chain when organisms die.

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How can you organize trophic level information?Diagrams or charts may help to summarize information orconcepts in a more logical and simpler manner. This is thecase with information that shows relationships amongtrophic levels.

AnalysisCopy the diagram above. It will show, when completed

correctly, the various relationships in a food chain.

Thinking Critically1. Each box represents a trophic level. Write the name for

each trophic level in the proper box. Use these choices: 1storder heterotroph, autotroph; 3rd order heterotroph; 2ndorder heterotroph.

2. Each bracket identifies one or more traits of the trophiclevels. Use the following labels to identify them in theirproper order: herbivore, autotroph, carnivore, het-erotroph, producer.

3. What is being represented by the small arrows connectingtrophic levels?

Problem-Solving Lab 2-2Problem-Solving Lab 2-2 Applying Concepts

Trophic levels represent links in the chain

Each organism in a food chain rep-resents a feeding step, or trophiclevel (TROHF ihk), in the passage ofenergy and materials. Examine howenergy flows through trophic levelsin the Problem-Solving Lab shownhere. A food chain represents onlyone possible route for the transfer ofmatter and energy in an ecosystem.Many other routes may exist. As

Figure 2.16 indicates, many differentspecies occupy each trophic level in awetlands ecosystem. In addition,many different kinds of organisms eata variety of foods, so a single speciesmay feed at several trophic levels.For example, the great blue heroneats largemouth black bass, but it alsoeats minnows, bluegills, and frogs.The alligator may feed on the heron,fish, or even a deer that comes tooclose. Can you think of other possi-ble food chains in this ecosystem?

Food websSimple food chains are easy to

study, but they cannot indicate thecomplex relationships that existamong organisms that feed on morethan one species. Ecologists who areparticularly interested in energy flowin an ecosystem set up experimentswith as many organisms in the com-munity as they can. The model theycreate, a food web, expresses all thepossible feeding relationships at eachtrophic level in a community. A foodweb is a more realistic model than afood chain because most organismsdepend on more than one otherspecies for food. Notice how the foodweb of the forest ecosystem shown inFigure 2.17 represents a network ofinterconnected food chains. In anactual ecosystem, many more plantsand animals would be involved in thefood web.

Energy and trophic levels:Ecological pyramids

How can you show how energy isused in an ecosystem? Ecologists usefood chains and food webs to modelthe distribution of matter and energy within an ecosystem. Theyalso use another kind of model, called an ecological pyramid. An eco-logical pyramid shows how energyflows through an ecosystem. The


base of the ecological pyramid repre-sents the autotrophs, or first trophiclevel. Higher trophic levels are lay-ered on top of one another. Examineeach type of ecological pyramid inFigures 2.18, 2.19 and 2.20. Eachpyramid gives different information

about an ecosystem. Observe thateach pyramid summarizes interac-tions of matter and energy at eachtrophic level. Notice that the initialsource of energy for all three of theseecological pyramids is energy fromthe sun.


Figure 2.17 A forest communityfood web includesmany organisms ateach trophic level.Arrows indicate theflow of materials andenergy.

Red tail hawk

Grizzly bear

Marmot

Grouse

Chipmunk

Seeds

Berries

Grasses

Insects

Deer

The pyramid of energy shown inFigure 2.18 illustrates that energydecreases at each succeeding trophiclevel. The total energy transfer fromone trophic level to the next is onlyabout ten percent because organismsfail to capture and eat all the foodavailable at the trophic level belowthem. When an organism consumesfood, it uses some of the energy inthe food for metabolism, some forbuilding body tissues, and some isgiven off as waste. When the organ-ism is eaten, the energy that was usedto build body tissue is available asenergy to be used by the organismthat consumed it. The energy lost ateach successive trophic level entersthe environment as heat.

Ecologists construct a pyramid ofnumbers based on the populationsizes of organisms in each trophiclevel. The pyramid of numbers inFigure 2.19 shows that populationsizes decrease at each higher trophiclevel. This is not always true. Forexample, one tree can be food for 50000 insects. In this case, the pyramidwould be inverted.

A pyramid of biomass, such as theone shown in Figure 2.20, expressesthe weight of living material at eachtrophic level. Ecologists calculate thebiomass at each trophic level by find-ing the average weight of eachspecies at that trophic level and mul-tiplying by the estimated number oforganisms in each population.


Figure 2.19Pyramid of numbers Each barin the pyramid repre-sents population sizewithin a trophic level.Notice that popula-tion size decreases asthe trophic levelincreases.

Figure 2.18 Pyramid ofenergy Each bar inthe pyramid repre-sents energy avail-able within a trophiclevel. Notice thatenergy decreases asthe trophic levelincreases.

Hawks 1

Grasshoppers260

Partridges25

Grass3000

Producers

Herbivores

Carnivores

Top carnivores

Cycles in NatureFood chains, food webs, and eco-

logical pyramids all show how energymoves in only one direction throughthe trophic levels of an ecosystem.Ecological pyramids also show howenergy is lost from one trophic levelto the next. This energy is lost to theenvironment as heat generated by the body processes of organisms.Sunlight is the primary source of allthis energy, so energy is always beingreplenished.

Matter, in the form of nutrients,also moves through the organisms ateach trophic level. But matter cannotbe replenished like the energy fromsunlight. The atoms of carbon, nitro-gen, and other elements that make upthe bodies of organisms alive todayare the same atoms that have been onEarth since life began. Matter is con-stantly recycled.

The water cycleLife on Earth depends on water.

Even before there was life on Earth,water cycled through stages, asshown in Figure 2.21. Have you everleft a glass of water out and a fewdays later observed there was lesswater in the glass? This is the resultof evaporation. Just as the water

55

Figure 2.21 In the water cycle,water is constantlymoving betweenthe atmosphereand Earth.

Figure 2.20Pyramid of biomass Each barin the pyramid repre-sents the amount ofbiomass within atrophic level. Noticethat biomassdecreases as thetrophic levelincreases.

Second orderconsumers

Herbivores

Producers

Evaporation

Runoff

Oceans

Groundwater

Lakes

Evaporation

Transpiration

Precipitation

Detecting Carbon DioxideCarbon dioxide is given offduring respiration. When car-bon dioxide is dissolved inwater, an acid is formed.Certain chemicals called indi-cators can be used to detectacids. One indicator, calledbromothymol blue, willchange from its normal bluecolor to green or yellow if an acid is present.

Procedure! Half fill a test tube with bromothymol blue solution.@ Add a quarter of an effervescent antacid tablet to the

tube and note any color change. # Half fill a test tube with bromothymol blue solution.

Using a straw, exhale into the bromothymol blue at least30 times. CAUTION: Do not inhale the bromothymol blue.Record any color change in the test tube.

Analysis1. Describe the color change that occurs when carbon

dioxide is added to bromothymol blue.2. What was the chemical composition of the bubbles seen

in the tube with the antacid tablet?3. Does exhaled air contain carbon dioxide? Explain.

MiniLab 2-2MiniLab 2-2 Observing and Inferring

evaporated from the glass, waterevaporates from lakes and oceans andbecomes water vapor in the air.

Have you ever noticed the drops ofwater that form on a cold can ofsoda? The water vapor in the air con-denses on the surface of the canbecause the can is colder than thesurrounding air. Just as water vaporcondenses on cans, it also condenseson dust in the air and forms clouds.Further condensation makes smalldrops that build in size until they fallfrom the clouds as precipitation inthe form of rain, ice, or snow. Thewater falls on Earth and accumulatesin oceans and lakes where evapora-tion continues.

Plants and animals need water tolive. Plants pull water from theground and lose water from theirleaves through transpiration. Thisputs water vapor into the air. Animalsbreathe out water vapor in everybreath; when they urinate, water isreturned to the environment. Naturalprocesses constantly recycle waterthroughout the environment.

The carbon cycleAll life on Earth is based on carbon

molecules. Atoms of carbon form theframework for proteins, carbohy-drates, fats, and other important mol-ecules. More than any other element,carbon is the molecule of life.

The carbon cycle starts with theautotrophs. During photosynthesis,energy from the sun is used to con-vert carbon dioxide gas into energy-rich carbon molecules. Autotrophsuse these molecules for growth andenergy. Heterotrophs, which feedeither directly or indirectly on theautotrophs, also use the carbon mole-cules for growth and energy. Whenthe autotrophs and heterotrophs usethe carbon molecules for energy, car-bon dioxide is released and returnedto the atmosphere. Learn how todetect the presence of carbon dioxidein the MiniLab shown here. The car-bon cycle is described in the InsideStory on the next page.

The nitrogen cycleIf you add nitrogen fertilizer to a

lawn, houseplants, or garden, youmay see that it makes them greener,bushier, and taller. Even though theair is 78 percent nitrogen, plantsseem to do better when they receivenitrogen fertilizer. This is becauseplants cannot use the nitrogen in theair. They use nitrogen in the soil thathas been converted into more usableforms.


57

The Carbon Cycle

From proteins to sugars, carbon is the building block of the molecules of life. Linked carbon atoms form the frame

for molecules produced by plants and other living things.Organisms use these carbon molecules for growth and energy.

Critical Thinking How is carbon released from the bodies oforganisms? Forests use carbon dioxide.

INSIDESSTORTORYY

INSIDE

Atmosphere Carbondioxide gas is one form ofcarbon in the air.

11

PhotosynthesisAutotrophs use car-bon dioxide in photo-synthesis. In photo-synthesis, the sun’senergy is used to make high-energy carbon molecules.

22Wastes Auto-trophs and hetero-trophs break downthe high-energycarbon moleculesfor energy. Carbondioxide is releasedas a waste.

33

Organisms use high-energy carbonmolecules for growth. A large amountof the world’s carbon is contained inliving things.

44

Fuel Over millions of years, the remains of deadorganisms are converted into fossil fuels, such as coal,gas, and oil. These fuels contain carbon molecules.

66

Pollution Combustionof fossil fuels and woodreleases carbon dioxide.

77Carbon dioxide

Soil When organisms die and decay, the carbon molecules inthem enter the soil.Microorganisms breakdown the molecules,releasing carbon dioxide.

55

As Figure 2.22 shows, lightningand certain bacteria convert thenitrogen in the air into these moreusable forms. Chemical fertilizersalso give plants nitrogen in a formthey can use.

Plants use the nitrogen to makeimportant molecules such as pro-teins. Herbivores eat plants and con-vert nitrogen-containing plant pro-teins into nitrogen-containing animalproteins. After you eat your food,you convert the proteins in your foodinto human proteins. Urine, an ani-mal waste, contains excess nitrogen.When an animal urinates, nitrogenreturns to the water or soil. Whenorganisms die, their nitrogen mole-cules return to the soil. Plants reusethese nitrogen molecules. Bacteria

also act on these molecules and putnitrogen back into the air.

The phosphorus cycle Materials other than water, carbon,

and nitrogen cycle through ecosys-tems. Substances such as sulfur, cal-cium, and phosphorus, as well as oth-ers, must also cycle through anecosystem. One essential element,phosphorus, cycles in two ways.

All organisms require phosphorusfor growth and development. Plantsobtain phosphorus from the soil.Animals get phosphorus by eatingplants, as shown in Figure 2.23.When these animals die, theydecompose and the phosphorus isreturned to the soil to be used again.This is the short-term phosphorus

58

Figure 2.22In the nitrogen cycle,nitrogen is convertedfrom a gas to com-pounds important for life and back to a gas.

Nitrogen inatmosphere

Storm cloudsand lightning

Animal wastesDeath

Amino acidsynthesis

Decay bacteria

Nitrates

Infiltration ofground water

Ammonia,ammonium, andnitrate fertilizers

Runoff

Bacteria in soiland root nodules


Figure 2.23In the phosphorus cycle, phosphorusmoves between the living and non-living parts of the environment.

Section AssessmentSection Assessment

Understanding Main Ideas1. What is the difference between an autotroph

and a heterotroph?2. Why do autotrophs always occupy the lowest

level of ecological pyramids?3. Give two examples of how nitrogen cycles

from the abiotic portion of the environment into living things and back.

4. Describe a food chain that was not presented in this section.

Thinking Critically5. The country of Avorare has many starving

people. Should you encourage the people togrow crops such as vegetables, wheat, and corn,or is it better to encourage them to use the landto raise cattle for beef?

6. Designing an Experiment Suppose there is a fertilizer called GrowFast. It contains extra nitrogen and phosphorus. Design an experiment to see if GrowFast increases thegrowth rate of plants. For more help, refer to the Practicing Scientific Methods in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

cycle. Phosphorus also has a long-term cycle, where phosphates washedinto the sea are incorporated intorock as insoluble compounds.Millions of years later, as the envi-

ronment changes, the rock contain-ing phosphorus is exposed. As therock erodes and disintegrates, thephosphorus again becomes part ofthe local ecological system.

Death

Limestone

Phosphorusin soil

Phosphorus incorporatedinto limestone

Long-term phosphorus cycleShort-term phosphorus cycle

Ocean

Phosphates washedinto ocean


How can one populationaffect another?

W hy don’t prey populations disappear when predators are present?Prey organisms have evolved a variety of defenses to avoid being

eaten. For example, some caterpillars are distasteful to birds, and somefishes confuse predators by appearing to have eyes at both ends of theirbodies. Just as prey have evolved defenses to avoid predators, predators have evolved mechanisms to overcome those defenses.

Even single-celled protists such as Paramecium have predators. Didinium is another unicellular protist that attacks and devours Paramecium larger than itself. Do populations of Paramecium change when a population of Didinium is present? In this investigation, you will use various methods to determine how both of these species interact.

YOUR OWNDESIGN

YOUR OWNDESIGN

■ Use appropriate variables, con-stants, and controls in experimentaldesign.

Possible Materialsmicroscopemicroscope slidescoverslipsculture of Didiniumculture of Parameciumbeakers or jarseyedropperssterile pond water

Safety PrecautionsTake care when using electrical

equipment. Always use goggles in thelab. Handle slides and coverslipscarefully. Dispose of broken glass in acontainer provided by your teacher.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

ProblemHow does a population of

Paramecium react to a population ofDidinium?

HypothesesHave your group agree on an

hypothesis to be tested. Record yourhypothesis.

ObjectivesIn this BioLab, you will:■ Design an experiment to establish

the relationships betweenParamecium and Didinium.

Didinium

Paramecium

PLAN THE EXPERIMENTPLAN THE EXPERIMENT

1. Review the discussion of feed-ing relationships in this chapter.

2. Decide which materials youwill use in your investigation.Record your list.

3. Be sure that your experimentalplan contains a control, tests asingle variable such as popula-tion size, and allows for thecollection of quantitative data.

4. Prepare a list of numbereddirections. Explain how youwill use each of your materials.

Check the PlanDiscuss the following points

with other group members todecide final procedures. Make anyneeded changes to your plan.1. What will you measure to

determine the effect of theDidinium on Paramecium? Ifyou count Paramecia, will youcount all you can see in thefield of vision of the micro-


1. Analyzing Data What differ-ences did you observe among theexperimental groups? Were thesedifferences due to the presence ofDidinium? Explain.

2. Drawing Conclusions Did theParamecium die out in any cul-ture? Why or why not?

3. Checking Your Hypothesis Wasyour hypothesis supported byyour data? If not, suggest a newhypothesis.

4. Thinking Critically List severalways that your methods may have

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

scope at a certain power? Willyou have multiple trials? If so,how many?

2. What single factor will youvary? For example, will you putno Didinium in one culture ofParamecium and 5 mL ofDidinium culture in anotherculture of Paramecium?

3. How long will you observe thepopulations?

4. How will you estimate thechanges in the populations ofParamecium and Didinium dur-ing the experiment?

5. Your teacher must approveyour plan before you proceed.

6. Carry out your experiment.7. Make a data table that has

Date, Number of Paramecium,and Number of Didiniumacross the top. Place the dataobtained for each culture inrows. Design and complete agraph of your data.

affected the outcome of theexperiment.

Going FurtherGoing Further

Project Based on this lab experience, designanother experiment that would help youanswer any questions that arose from yourwork. What factors might you allow to vary ifyou kept the number of Didinium constant?

To find out more about population biology, visit

the Glencoe Science Web site.science.glencoe.com

A Didinium capturesa Paramecium.

BIOLOGY


This subtropical region receives between 100and 165 cm (40-65 inches) of rain each year,

but only during the rainy season, which lastsfrom May to October. The heavy rainfall causesshallow Lake Okeechobee to overflow. A wide,thin sheet of water spreads out from the lake,creating an extensive marshy area.

Early in the twentieth century, the slow-mov-ing river that flows out of Lake Okeechobee was80 km (50 miles) wide in some places, and only15-90 cm (six inches to three feet) deep. Thiswetland teemed with fishes, amphibians, andother animals that fed millions of wading birds.Healthy populations of crocodiles, alligators, andother large animals also lived here. During thedry season, from December to April, water levelsin the marshes gradually dropped. Fishes andother water dwellers moved into deeper poolsthat held water all year long.

Changing the Everglades Water from LakeOkeechobee is no longer allowed to flood thecountryside. Instead, it is diverted into channelsto create dry land for agriculture and homes, and

stored behind levees to supply water for cities. Asa result, half the acreage of the original Evergladeshas been drained. Habitats have disappeared.

Different ViewpointsEverglades National Park was established to

preserve a portion of the Everglades. But the landthat forms the park is an island surrounded byfarms and towns and cut off from the waters ofLake Okeechobee. Human needs determine howmuch water comes into the park. When reservesare low, water is held back for people to use,depriving Everglades habitats of the moisture theyneed. If floods threaten, large amounts of waterare released quickly. These sudden flows destroythe nests of wading birds and other animals.

Restoring the Everglades In 1993, Floridadeveloped a restoration plan for rescuing theEverglades. The goals of the plan are to restore,as much as possible, the natural flow of unpol-luted water through the area, recover nativehabitats and species, and create a sustainableecosystem that permits both humans and nativespecies to flourish.

The Florida Everglades—An Ecosystem at RiskThe Florida Everglades ecosystem covers the southern portion of theFlorida peninsula. As with any wetlands, water is the critical factorthat defines the ecology of the area.

INVESTIGATING THE ISSUEINVESTIGATING THE ISSUEATLANTICOCEAN

LakeOkeechobee

EvergladesNational Park

Florida

Big CypressNational Parks

Analyzing the Issue When EvergladesNational Park was established, scientists andgovernment officials believed a portion of theEverglades ecosystem could be preserved bydrawing boundaries around it and declaring it off limits to development. Why did thisapproach fail to preserve the Everglades?

To find out more about the Everglades, visit the

Glencoe Science Web site. science.glencoe.com

The map (above) shows the loca-tion of the Everglades (inset).

BIOLOGY


Chapter 2 AssessmentChapter 2 Assessment

SUMMARYSUMMARY

Section 2.1

Section 2.2

Main Ideas■ Natural history, the observation of how organ-

isms live out their lives in nature, led to thedevelopment of the science of ecology—thestudy of the interactions of organisms with oneanother and with their environments.

■ Ecologists classify and study the biological levelsof organization from the individual up to theecosystem. Ecologists study the abiotic and bioticfactors that are a part of an organism’s habitat.They investigate the strategies an organism usesto exist in its niche. An aspect of its niche mayinvolve symbiosis with other organisms.

Vocabularyabiotic factor (p. 39)biosphere (p. 38)biotic factor (p. 40)commensalism (p. 46)community (p. 42)ecology (p. 38)ecosystem (p. 43)habitat (p. 44)mutualism (p. 46)niche (p. 45)parasitism (p. 47)population (p. 42)symbiosis (p. 46)

■ Autotrophs, such as plants, make nutrients thatcan be used by the plants and by heterotrophs.Heterotrophs include herbivores, carnivores,omnivores, and decomposers.

■ Food chains are simple models that show oneway that materials move from autotrophs toheterotrophs and eventually to decomposers.

■ Food webs represent many interconnected foodchains and illustrate possible ways materials aretransferred within an ecosystem. Energy fromthe sun fuels life in the ecosystems. Althoughthe sun adds new energy, the materials of life,such as carbon and nitrogen, do not increase.These materials are used and reused as theycycle through the ecosystem.

Vocabularyautotroph (p. 48)decomposer (p. 50)food chain (p. 51)food web (p. 52)heterotroph (p. 49)scavenger (p. 49)trophic level (p. 52)

Nutrition andEnergy Flow

CHAPTER 2 ASSESSMENT 63

1. Which of the following would be abiotic fac-tors for a polar bear?a. extreme cold, floating iceb. eating only live preyc. large body sized. paws with thick hair

2. Organisms that use the sun’s energy to makefood are called ________.a. herbivores c. autotrophsb. animals d. heterotrophs

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS3. In the food web below, which of the organ-

isms, X, Y, or Z, is a herbivore?a. Z c. both X and Yb. Y d. X

Organisms and TheirEnvironment

Grass

X Grasshopper

Y Z


4. Which organism is a carnivore?a. human c. lionb. rabbit d. opossum

5. Biotic factors in a wetland community mightinclude ________.a. water c. temperatureb. crayfishes d. soil type

6. Which of the following would decrease theamount of carbon dioxide in the air?a. a maple tree growingb. a dog runningc. a person driving a car to workd. a forest burning

7. As energy flows through an ecosystem,energy ________ at each trophic level.a. remains the sameb. increasesc. decreases then increasesd. decreases

8. An elk eats grass. A grizzly bear eats the elk.This is an example of a ________.a. pyramid of numbersb. commensal relationshipc. food webd. food chain

9. Which of the following is true concerning theflow of energy and matter in an ecosystem?a. Both energy and matter are recycled and

used again.b. Matter is recycled and used again, energy

is lost.c. Energy is recycled and used again, matter

is lost.d. Neither energy nor matter are recycled

and used again.

10. Cowbirds get their namebecause they follow cows and eat the insects disturbed by the walk-ing cows. Cowbirdshave an unusual methodfor reproducing. Thebrown-headed cowbird goesto the nest of a different birdspecies, such as the red-wing blackbird. Thecowbird rolls one of the blackbird’s eggs outof the nest and lays its own egg in place. Theblackbird protects the cowbird egg and feedsthe chick when it hatches. This descriptionbest describes part of the cowbird’s ________.a. community c. nicheb. habitat d. tropic level

11. For the cowbird description in question 10,the symbiotic relationship between the cowand the cowbird is ________. The associationbetween the cowbird and the blackbird is a(n)________ relationship.

12. The presence of predators, prey, and para-sites are examples of ________ factors in anorganism’s habitat.

13. A close and permanent relationship betweentwo organisms is called ________. If bothorganisms benefit it is ________.

14. A group of organisms of the same species living in the same area is called a(n) ________.When the group includes different species, it is called a ________.

15. A(n) ________ eats both plants and animals.A(n) ________ eats only plants.

16. A(n) ________ chain is a model of how matterand energy pass through organisms. Eachorganism is at a different ________ level.

17. ________ is a branch of biology that studiesthe interactions of organisms and their envi-ronment.

18. An ecological pyramid that shows the amountof energy for different trophic levels is calleda(n) ________. If it shows how many organ-isms are at each tropic level, it is called a(n)________.

64 CHAPTER 2 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

Quiet ZoneIt’s best to study in an environment similar to theone in which you’ll be tested. Blaring stereos,video game machines, chatty friends, and beepersare NOT allowed in the classroom during testtime. So why get used to them?


CHAPTER 2 ASSESSMENT 65

19. Plants absorb ________ from the air, and withthe sun’s light energy they make high-energycarbon molecules.

20. Lightning and bacteria act to move and con-vert ________ from the air into compounds inthe soil that can be readily used by plants.

21. Explain how pesticides sprayed on the waterin a wetland ecosystem could affect a differ-ent ecosystem.

22. Sloths are slow-moving herbivores that havealgae growing in their fur. Caterpillars of cer-tain kinds of moths eat the algae. Birds eat themoths. Using this example, draw a food chainand describe one symbiotic relationship.

23. Sequencing Place the following organismsin correct order in a food chain: mouse,hawk, wheat, snake.

24. Sequencing Describe one example of feed-ing relationships that cycle matter through anecosystem.

25. Concept Mapping Complete the conceptmap by using the following vocabulary terms:autotrophs, decomposers, food webs, heterotrophs.

THINKING CRITICALLYTHINKING CRITICALLY

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

The graph below compares the growth ratesof two organisms when grown together andwhen grown separately.

Interpreting Data Use the graph and infor-mation to answer the following questions.1. When grown separately, approximately

how long after the extinction ofOrganism 2 did it take the population ofOrganism 1 to reach its highest point?a. 3 days c. 3 weeksb. 1 week d. 5 weeks

2. When the organisms were growntogether, what was the approximate rateof growth between weeks 2 and 6?a. 75 per week c. 50 per weekb. 100 per month d. 25 per day

3. Observing and Inferring From thedata, it is clear that the associationbetween the organisms is ________.a. commensalism c. mutualism b. parasitism d. socialism

4. Hypothesizing Describe one possiblebenefit that Organism 2 gets from itsassociation with Organism 1. Explain a possible reason why the associationlowers the population of Organism 1.

Num

ber

pres

ent

in h

undr

eds

Time in weeks

Organism #1 and #2

grown together

Organism #1 alone

Organism #2 alone

1 2 3 4 5 6 7

1

2

3

4

5

Growth Rates of Two Organisms

For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web site.science.glencoe.com

CD-ROM

show interactions between

2.

1.

such as

3.

4.


Documents

Chapter 2: Principles of Ecology - Wikispaces studying nature for thou-sands of years. ... MiniLab 2-1MiniLab 2-1 Experimenting the world. ... by observing organisms in the field