Opening ActivityAsk each student to choose twoanimals that live in the same community and interact. Prepare alist on the board or overhead withthree headings: Both Benefit, OneBenefits/One Suffers, One Benefits/One Not Affected. Ask students toplace the interaction of each animalpair into the appropriate category.
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IdentifyingMisconceptionsStudents do not often recognizethat, while an organism’s everydaybehavior is shaped by its encoun-ters with other organisms, thegenetic basis for its behavior doesnot change in that organism’s life-time. Traits in a population changeover time, as individuals with thegenes for those traits survive andreproduce more than individualswithout those traits.
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Answers1. In photosynthesis, light energy
and carbon dioxide are con-verted to oxygen and chemicalenergy which is stored in sug-ars (food). In cellular respira-tion, the chemical energystored in food is released asATP to do work. Oxygen isconverted to carbon dioxide inthis process.
2. A habitat is the place in whicha population lives. The manyspecies that live together in ahabitat are called a community.An ecosystem consists of acommunity and all the physicalaspects of its habitat.
3. Primary productivity, the rateat which food is producedthrough photosynthesis byautotrophs, determines theamount of energy available inan ecosystem. Energy flow isdecreased or increased in anecosystem based on primaryproductivity.
Quick Review
AnswersStudents will likely mention predator/preyrelationships. Students may also be familiarwith symbiotic relationships, such as the inter-action between flowers and their pollinators.
Reading Activity
Looking AheadQuick ReviewSection 1 How Organisms Interact in Communities
Evolution in CommunitiesSymbiotic Species
Section 2How Competition ShapesCommunities
Common Use of Scarce Resources and Competition
Competition and Limitations of Resource UseCompetition Without Division of Resources
Section 3Major Biological Communities
Climate’s Effect on Where Species LiveTerrestrial BiomesAquatic Communities
www.scilinks.orgNational Science Teachers Association sciLINKS Internet resources are located throughout this chapter.
Reading ActivityBefore you read this chapter, create a list of allthe ways that two species in an ecosystem caninteract. Then develop a list of all the differenttypes of communities or ecosystems you canthink of. Can any of the ecosystems be groupedinto larger systems (biomes)? Read the chapterto see how scientists have defined interactionsand biomes.
Harsh and unforgiving, the desert is home to plantsand animals equipped to thrive in the face of environ-mental challenges. No other terrestrial biome dis-plays a wider range of extreme conditions.
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Quick ReviewAnswer the following without referring to earlier sections of your book. 1. Compare the energy flow in photosynthesis
to the energy flow in cellular respiration. (Chapter 5, Section 1)
2. Differentiate between the terms habitat,community, and ecosystem. (Chapter 16, Section 1)
3. Analyze the relationship between primary productivity and energy flow in ecosystems.(Chapter 16, Section 2)
Did you have difficulty? For help, review the sections indicated.
OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. Section 1 describes typesof interactions among species. This section discusses how preda-tors and prey coevolve anddescribes symbiotic relationships.
Show the class a photograph of atapeworm. Point out adaptationsthat make it a successful parasite.(Hooks on the head enable the tape-worm to attach to the intestinal wallof its host. The tapeworm’s perme-able body wall allows absorption ofnutrients from the host. The bodyconsists of segments specialized forreproduction.) Tapeworms inhumans may grow as long as 6 m(20 ft). Ask students why it is notin the tapeworm’s best interest tokill its host. (Killing its host woulddestroy its home and food supply.)
IdentifyingPreconceptionsHave students read the paragraphentitled “Interactions AmongSpecies.” Ask students to thendescribe coevolution. Students mayhave difficulty understanding thatthe environment affects the survivalof traits after they appear in thepopulation. They often think thatthe change was the result of theenvironment acting on organismsto produce change. Provide exam-ples of coevolution. VerbalLS
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Section 1 How Organisms Interactin Communities
Evolution in CommunitiesWhat are the most important members of an ecosystem? When youtry to answer this question, you soon realize that you cannot view anecosystem’s inhabitants as single organisms, but only as members ofa web of interactions.
Interactions Among SpeciesSome interactions among species are the result of a long evolutionaryhistory in which many of the participants adjust to one another overtime. Thus, adaptations appeared in flowering plants that promotedefficient dispersal of their pollen by insects and other animals. In turn,adaptations appeared in pollinators that enabled them to obtain foodor other resources from the flowers they pollinate. Natural selectionhas often led to a close match between the characteristics of the flow-ers of a plant species and its pollinators, as you can see in Figure 1.Back-and-forth evolutionary adjustments between interactingmembers of a community are called .
Predators and Prey Coevolveis the act of one organism killing another for food.
Familiar examples of predation include lions eating zebras andsnakes eating mice. Less familiar, but no less important, examplesoccur among arthropods. Spiders are exclusively predators, as are centipedes.
In , one organismfeeds on and usually lives on orin another, typically larger,organism. Parasites do not usu-ally kill their prey (known as the“host”). Rather, they depend onthe host for food and a place tolive. The host often serves totransmit the parasite’s offspringto new hosts. Many parasites(such as lice) feed on the host’soutside surface. Among the exter-nal parasites that may have fedon you at some time are ticks,mosquitoes, and fleas. Morehighly specialized parasites likehookworms live entirely withinthe body of their host.
parasitism
Predation
coevolution
Objectives● Describe coevolution.
● Predict how coevolution canaffect interactions betweenspecies.
● Identify the distinguishingfeatures of symbiotic relationships.
AnswerCalamine lotion, Epsom salts,and bicarbonate of soda may allreduce the severity of a poisonivy rash.
Real Life
Predicting HowPredation WouldAffect a PlantSpeciesSkills AcquiredInterpreting results,applying information,predicting
Teacher’s NotesPoint out that a grazed Giliaplant has more stems than anungrazed plant.
Answers to Analysis1. The grazed plant would most
likely produce more seedsbecause it would have morestems and flowers.
2. Because grazing leads to denseregrowth and the productionof more flower heads, thegrazed plant would producemore offspring.
3. Dense regrowth and the pro-duction of more flower headsmay allow this plant to spreadin its environment and out-compete other plants.
4. If new stems were not pro-duced in response to grazing,the grazed plants would pro-duce few, if any, seeds. Overthe years, the plant mightbecome rare or extinct in areasof heavy grazing.
Using reference materials or the Internet,have students create a chart of plantsaround their home or school that are toxicto humans or pets. Included in this chartshould be names and photos or drawings ofthe plants, descriptions of how each plantaffects humans or their pets, and ways toresolve the reactions caused by plant inges-tion or contact.
• Gifted and Talented • Attention Deficit DisorderAs mentioned in the student text, virtually allplants contain defensive chemicals. Many ofthese defenses can be used to deter pests in aflower or vegetable garden. Some pest repel-lant plants and the pests they repel are:• mint, chives, onions and catnip, which repel
ants• basil, which repels mosquitoes• rosemary, wormwood, onions and chives,
which repel slugsHave students search the Internet for moreexamples of pest repellant plants.
REAL WORLDREAL WORLDCONNECTIONCONNECTION
Plant Defenses Against Herbivores As you might expect, animal prey species have ways to escape, avoid,or fight off predators. But predation is also a problem for plants,which live rooted in the ground. The most obvious way that plantsprotect themselves from herbivores is with thorns, spines, and prick-les. But it is even more common for a plant to contain chemicalcompounds that discourage herbivores. Virtually all plants containdefensive chemicals called . For some plants,secondary compounds are the primary means of defense.
As a rule, each group of plants makes its own special kind ofdefensive chemical. For example, the mustard plant family producesa characteristic group of chemicals known as mustard oils. Theseoils give pungent aromas and tastes to such plants as mustard, cab-bage, radish, and horseradish. The same tastes that we enjoy signalthe presence of chemicals that are toxic to many groups of insects.
How Herbivores Overcome Plant DefensesSurprisingly, certain herbivores are able to feed on plants that areprotected by particular defensive chemicals. For example, the larvaeof cabbage butterflies feed almost exclusively on plants of the mus-tard and caper families. Yet these plants produce mustard oils thatare toxic to many groups of insects. How do the butterfly larvaemanage to avoid the chemical defenses of the plants? Cabbage but-terflies have the ability to break down mustard oils and thus feed onmustards and capers without harm.
secondary compounds
Analysis
1. Identify the plant that is likely to produce more seeds?
2. Explain how grazing affects thisplant species.
3. Evaluate the significance to its envi-ronment of the plant’s regrowth pattern.
4. Hypothesize how this plant speciesmight be affected if individual plantsdid not produce new stems inresponse to grazing.
Predicting How PredationWould Affect a Plant Species Background
Grazing is the predation of plants by animals. Some plantspecies, such as Gilia, respond to grazing by growingnew stems. Consider a field in which a large number ofthese plants are growing and being eaten by herbivores.
Real LifeLeaflets three, let it be.Members of the genusToxicodendron,which includespoison ivy, pro-duce a defensivechemical calledurushiol (OO roo shee awl), whichcauses a severe, itchyrash in some people.Finding Information Do research to discovereffective treatments for therash caused by poison ivy.
ReteachingHave students make a chart to helpthem remember the different typesof species interactions—predation,parasitism, mutualism, and com-mensalism. Tell them to use thefour interactions as headings. Thenhave them place plus and minussigns in the row below to indicatewhether each of the two organismsis helped or harmed by the interac-tion above. For example, mutualismwould have a ! / ! because bothorganisms benefit. Visual
QuizTrue or False:1. Commensalism is a symbiotic
relationship in which both par-ticipating species benefit. (False.In a mutualism, both partners ben-efit. In commensalism, one partnerbenefits and the other is notaffected.)
2.A predator/prey relationship inwhich the predator does not killthe prey is called parasitism.(True)
3. Evolutionary change is the resultof the environment actingdirectly on organisms to producea change in an organism’s traits.(False. The environment affects thesurvival of traits after their appear-ance in the population.)
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Answers to Section Review1. In predator-prey coevolution, prey with certain
defensive traits (or “weapons”) survive preda-tion and reproduce. Predators with traits that allow them to catch prey, survive andreproduce. Thus, traits in predator and preypopulations change in response to each other,in an “arms race.”
2. Plants and pollinators have a mutualistic rela-tionship. Pollinators carry pollen to plants sothe plants are fertilized. Plants provide nectarand pollen to the pollinator as food.
3. No, the unaffected species neither gains norsuffers from the relationship, so there is noselective pressure for coevolution.
4. Native honeybees have been exposed toJapanese hornets for thousands of years, sotraits that protect the honeybees have becomeprevalent in the population. European honey-bees have only recently been exposed to theJapanese hornet and do not have the adapta-tions native honeybees do, so they cannotdefend themselves from the hornets.
5. A. Incorrect. Clown fish and sea anemoneshave a commensal relationship. B. Correct.Ants use aphid honeydew for food, and in turnprotect the aphids from insect predators.C. Incorrect. Zebra are prey for predator lions.D. Incorrect. Dogs are hosts to parasitic fleas.
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Explain why predator-prey coevolution can bedescribed as an “arms race.”
Critical Thinking Applying Information Isthe relationship between a plant and its pollinatormutualistic? Why or why not.
Critical Thinking Interpreting InteractionsIn a relationship that is an example of commen-salism, would the species that is neither helpednor harmed evolve in response to the otherspecies? Defend your answer.
Critical Thinking Illustrating PrinciplesIn Japan, native honeybees have an effectivedefense strategy against giant Japanese hornets.Imported European honeybees, however, areunable to defend themselves. Use this exampleto illustrate the results of natural selection inadaptation.
Which pair of organismshas a mutualistic relationship? A clown fish and C lion and zebra
sea anemoneB aphid and ant D flea and dog
Standardized Test PrepStandardized Test Prep
Section 1 Review
Symbiotic Species In (sim bie OH sis), two or more species live together in aclose, long-term association. Symbiotic relationships can be benefi-cial to both organisms or benefit one organism and leave the otherharmed or unaffected. Parasitism, mentioned earlier, is one type ofsymbiotic relationship that is detrimental to the host organism.While it is relatively easy to determine that an organism in a symbi-otic relationship is being helped, it can be difficult to determine thatan organism is neither harmed nor helped.
Mutualism is a symbiotic relationship in which both participating
species benefit. A well-known instance of mutualism involves antsand aphids, as shown in Figure 2. Aphids are small insects that usetheir piercing mouthparts to suck fluids from the sugar-conductingvessels of plants. They extract a certain amount of the sucrose andother nutrients from this fluid. However, much of the fluid—so-called honeydew—runs out in an altered form through their anus.Certain ants have taken advantage of this fact and “milk” the aphidsfor the honeydew, which they use as food. The ants, in turn, protectthe aphids against insect predators. Thus, both species benefit fromthe relationship.
Commensalism A third form of symbiosis is , a symbiotic relation-ship in which one species benefits and the other is neither harmednor helped. Among the best-known examples of commensalism arethe relationships between certain small tropical fishes and seaanemones, marine animals that have stinging tentacles. Thesefishes, such as the clown fish shown in Figure 3, have the ability tolive among and be protected by the tentacles of the sea anemones,even though these tentacles would quickly paralyze other fishes.
commensalism
Mutualism
symbiosis
Figure 2 Mutualism. Thesmall green insects on thisplant stem are aphids. They areprotected by their ant guards.
Figure 3 Commensalism.The clown fish can survive thestings of the sea anemone,which protects it from predators.
OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This section focuses oncompetition and how it affects pop-ulations comprising a community.
Tell students that a niche is verycomplex and includes all the waysan organism affects and is affectedby its environment. Then draw stu-dents’ attention to Figure 4. Thisfigure shows only three aspects ofthe jaguar’s niche. Have studentsmake a list of other aspects of thejaguar’s niche.
Discussion/QuestionAsk students to discuss why com-petition is usually most intensebetween closely related organisms.(Closely related organisms are likelyto be very similar and therefore arelikely to use resources in similarways.) VerbalLS
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How CompetitionShapes Communities
Objectives● Describe the role of compe-
tition in shaping the natureof communities.
● Distinguish betweenfundamental and realizedniches.
● Describe how competitionaffects an ecosystem.
● Summarize the importanceof biodiversity.
Common Use of Scarce Resourcesand Competition When two species use the same resource, they participate in a bio-logical interaction called . Resources for which speciescompete include food, nesting sites, living space, light, mineralnutrients, and water. Competition occurs for resources in short sup-ply. In Africa, for example, lions and hyenas compete for prey. Fiercerivalry between these species can lead to battles that cause injuriesto both sides. But most competitive interactions do not involvefighting. In fact, some competing species never encounter oneanother. They interact only by means of their effects on the abun-dance of resources.
To understand how competition influences the makeup of communities, you must focus on the day-to-day events within thecommunity. What do organisms eat? Where do they live? The func-tional role of a particular species in an ecosystem is called its (NICH). A niche is how an organism lives—the “job” it performswithin the ecosystem.
A niche may be described in terms of space utilization, food con-sumption, temperature range, requirements for moisture or mating,and other factors. A niche is not to be confused with a habitat, theplace where an organism lives. A habitat is a location; a niche is apattern of living. Figure 4 summarizes some aspects of the jaguar’sniche in the Central American rain forest.
A niche is often described in terms of how the organism affectsenergy flow within the ecosystem in which it lives. For example, theniche of a deer that eats a shrub is that of a herbivore. The niches ofsome organisms overlap. If the resources that these organisms shareare in short supply, it is likely that there will be competition betweenthe organisms.
Paired Reading Give the studentsself-stick notes, and have them mark areas of difficulty as theysilently read Section 2. Have stu-dents use a question mark to signifyan area that is unclear and a checkmark to indicate understanding.Remind students to study the cap-tions, diagrams, and illustrations as they read. After completing thesection, have students work with a partner to discuss what they did or did not understand. Havestudents write their remaining questions on the board for later discussion.
Interpersonal
Teaching TipWarblers Tell students that all fivewarbler species that MacArthurstudied belong to the same genus(Dendroica). Because closelyrelated species are often competi-tors, MacArthur was interested inhow these very similar speciescould coexist.
Interpreting Visuals Ecologistsuse the phrase “resource partition-ing” to describe the patterns ofresource use in a community. Havestudents examine Figure 5, and thendiscuss why resource partitioning isan appropriate description of thefeeding behavior of the five warblerspecies. (The warblers partition, ordivide up, the insect populations onwhich they feed by foraging in differ-ent parts of the tree.) VisualLS
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An analogy may help students understand thedifference between habitat and niche. Pointout that their houses or apartments and theplaces they frequent make up their habitats.What they do in their habitats—their patternsof living—are their niches. Ask students towrite short descriptions of their habitats andtheir niches. Have them also write aboutwhat would be different if they lived in otherhabitats (such as rural or urban habitats).
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TR E22 Warbler Foraging ZonesTR E21 Effects of Competition on Two
Species of Barnacles
Size of a Species’ NicheTo gain a better understanding of what a niche is, you can look moreclosely at a particular species. Imagine a Cape May warbler (a small,insect-eating songbird) flying in a forest and landing to search fordinner in a spruce tree. The niche of this bird is influenced by sev-eral variables. These variables include the temperature it prefers,the time of year it nests, what it likes to eat, and where on the tree itfinds its food. (The Cape May warbler spends its summers almostexclusively in the northeastern United States and Canada. It nests inmidsummer, eats small insects, and searches for food high onspruce trees at the tips of the branches.) The entire range ofresource opportunities an organism is potentially able to occupywithin an ecosystem is its .
Dividing Resources Among Species Now reconsider what the Cape May warbler is doing. It feeds mainlyat the very top of the spruce tree even though insects that the war-bler could eat are located all over the tree. In other words, Cape Maywarblers occupy only a portion of their fundamental niche. Why?
Closer study reveals that this surprising behavior is part of a largerpattern of niche restriction. In the late 1950s, the ecologist RobertMacArthur, while a graduate student at Yale University, carried out aclassic investigation of niche usage, summarized in Figure 5. He stud-ied the feeding habits of five warbler species—the Cape May warblerand four of its potential competitors. MacArthur found that all fivespecies fed on insects in the same spruce trees at the same time. AsFigure 5 shows, however, each species concentrated on a differentpart of the tree. Although all five species of warbler had very similarfundamental niches, they did not use the same resources. In effect,
fundamental niche
Cape May warbler Blackburnianwarbler
Black-throatedwarbler
Bay-breastedwarbler
Myrtle warbler
Each of these five warbler species feeds on insects in a different portion ofthe same tree, as indicated by the five colors shown below.
Teaching TipRealized Niches Point out that anorganism’s realized niche is a subsetof its fundamental niche. Thus, therealized niche can be smaller than(or the same size as) the fundamen-tal niche, but never larger.
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Predicting Changesin a RealizedNicheSkills Acquired Interpreting results,applying information,analyzing information,predicting outcomes
Teacher’s NotesExplain to students that thistype of graph is a convenientway to represent three vari-ables: height above the ground,prey length, and frequency ofselection of a combination ofprey length and feeding height.
Answers to Analysis1. Most selected prey are approx-
imately 3.5 to 4.5 mm. 2. Maximum feeding height is
nearly 11 m.3. Even though it is feeding at a
different time of day, Species Bmight reduce the prey availableto Species A, since it has thesame feeding preference.
4. Species C would reduce SpeciesA’s realized niche by competingwith Species A for large prey.Since Species A prefers smallerspecies, however, competitionfrom Species C would be minimal.
5. Accept any well-reasonedanswer. Sample answer: Itmight not affect how the graphlooks. However, since bothspecies have the same niche,one could be forced to extinc-tion in this area.
6. The lightest shade representsthe combination of feedingheight and prey length leastfrequently selected but stillexploited by Species A.
did you know?Bold Coyotes The coyote’s broad fundamentalniche has allowed it to thrive in areas of humanencroachment. For example, coyotes can surviveon a variety of animal and plant foods, includ-ing most of the food humans throw away. Thecoyote’s brazenness is a behavioral adaptationand therefore part of its niche as well. Its bold-ness pays off by allowing it access to areas thatcompetitors, such as bobcats, usually avoid.
Analysis
1. State the range of lengths ofSpecies A’s preferred prey.
2. Identify the maximum heightat which Species A feeds.
3. Critical ThinkingPredicting OutcomesSpecies B is introduced intoSpecies A’s feeding range.Species B has exactly the samefeeding preferences, but it huntsat a slightly different time ofday. How might this affectSpecies A?
4. Interpreting GraphicsSpecies C is now introducedinto Species A’s feeding range.Species C feeds at the sametime of day as Species A, but itprefers prey that are between10 and 13 mm long. Howmight this affect Species A?
Predicting Changes in a Realized NicheBackground
Two features of a niche that can be readily measured are the location where the species feeds and the size of its pre-ferred prey. The darkest shade in the center of the graphbelow indicates the prey size and feeding location most frequently selected by one bird species (called Species A).
Reading EffectivelyTo better understand therelationship between fundamental and realizedniches, draw two circles,one within the other. Labelthe larger circle “Funda-mental niche, entire tree.”Label the smaller circle“Realized niche.”
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they divided the range of resources among them, each taking a dif-ferent portion. A different color is used to represent the feeding areasof each of the five warbler species shown in Figure 5.
The part of its fundamental niche that a species occupies is calledits . Stated in these terms, the realized niche of theCape May warbler is only a small portion of its fundamental niche. How does this species of warbler benefit from hunting for food inonly a portion of the tree? MacArthur suggested that this feedingpattern reduces competition among the five species of warblers.Because each of the five warbler species uses a different set ofresources by occupying a different realized niche, the species arenot in competition with one another. MacArthur concluded that natural selection has favored a range of preferences and behaviorsamong the five species that “carve up” the available resources. Mostecologists agree with this conclusion.
realized niche
5. Critical ThinkingPredicting OutcomesHow would the introduction of a species with exactly the samefeeding habits as Species Aaffect the graph?
6. InterpretingGraphics What doesthe lightest shade at theedge of the contourlines represent?
Demonstration Competition between two speciescan result in one being eliminatedfrom the community. Show theclass photographs of a starling anda bluebird. Starlings were firstintroduced into Central Park inNew York City in 1890. Todaystarlings are found throughout thecontinental United States. In manyareas they have bested bluebirds fornesting sites, causing a drasticdecline in bluebirds. Make bluebirdhouse plans available to studentsand select an area to post them.Emphasize the importance of monitoring the houses to keep outnon-native competitors like starlings.
Group Activity Investigating Competition Dividestudents into groups of three. Tellstudents that each group is to inves-tigate an example of competition.Each group’s first task is to find anorganism to study. If the weather iswarm enough, have students explorethe school grounds or areas aroundtheir homes to select an organism.Next, have each group determine atleast one organism that competes forresources with the organism theyselected. Finally, ask groups togather information about the organ-isms they selected using the Internet,the library, or local experts. Withthis information, have them build astory about the interaction betweenthe organisms, focusing on how thisinteraction affects the organisms’resource use and realized niche.Encourage students to take photosof their “study” organisms or to findimages of them in magazines or onthe Internet. InterpersonalLS
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CareerCareerNaturalist Parks (local, state, and national) as well as school districts and private naturecenters, employ naturalists. Passionate about theworkings of living communities, naturalists edu-cate youths and adults about natural history,ecology, and environmental science in some ofthe most beautiful settings in the world. Strongcommunications skills and knowledge of ecol-ogy and natural history are required.
MISCONCEPTION ALERT
Environment Can Influence CompetitionBe sure students do not develop the miscon-ception that the same species of a competingpair will always eliminate the other species.Point out that it is possible to alter theenvironment so that the outcome is reversed.Thomas Park and his colleagues at theUniversity of Chicago conducted competitionexperiments on two species of flour beetles(Tribolium). The temperature and humidityat which the beetles were raised determinedwhich species was the superior competitor.
Competition and Limitations of Resource UseA very clear case of competition was shown by experiments carriedout in the early 1960s by Joseph Connell of the University ofCalifornia. Connell worked with two species of barnacles that growon the same rocks along the coast of Scotland. Barnacles are marineanimals that are related to crabs, lobsters, and shrimp. Young bar-nacles attach themselves to rocks and remain attached there for therest of their lives. As you can see in Figure 6, one species,Chthamalus stellatus, lives in shallow water, where it is oftenexposed to air by receding tides. A second species, Semibalanus bal-anoides, lives lower down on the rocks, where it is rarely exposed tothe atmosphere.
When Connell removed Semibalanus from the deeper zone,Chthamalus was easily able to occupy the vacant surfaces. Thisindicates that it was not intolerance of the deeper environment thatprevented Chthamalus from becoming established there. Chthamalus’sfundamental niche clearly includes the deeper zone. However, whenSemibalanus was reintroduced, it could always outcompeteChthamalus by crowding it off the rocks. In contrast, Semibalanuscould not survive when placed in the shallow-water habitats whereChthamalus normally occurs. Semibalanus apparently lacks the adap-tations that permit Chthamalus to survive long periods of exposure toair. Connell’s experiments show that Chthamalus occupies only a smallportion of its fundamental niche. The rest is unavailable because ofcompetition with Semibalanus. As MacArthur suggested, competitioncan limit how species use resources.
Fundamental niches
Fundamental niches
Realized niches
Realized niches
Chthamalus stellatus
Semibalanus balanoidesThe realized niche of Chthamalus is smaller than its fundamental niche becauseof competition from the faster-growing Semibalanus.
Figure 6 Effects of competition on two species of barnacles
The word niche is from the Latin word nidus,meaning “nest.” The placean organism occupies in its environment is part of its niche—its overallfunctional role.
Teaching Tip Competitive Exclusion Informstudents that the elimination of onecompeting species may be the resultof direct aggressive interactionsbetween the two species (interfer-ence competition) or the result ofthe one species using more of agiven resource (exploitative competition).
Paired Summarizing Pair stu-dents. Have each student readsilently about the competitionexperiments of Connell, Gause, and Paine. Then have one studentsummarize one of the experimentsout loud, without referring to thetext. The partner should listenwithout interrupting and be pre-pared to point out any inaccuraciesor omissions in the summary. Atthis point students can refer to the text. Have students switch roles for each of the three experiments.
Auditory
Interpreting Graphics Ask stu-dents to point out which graph inFigure 7 shows extinction and howit is shown. (The upper graph showsextinction. The population of P. cau-datum is shown reduced to zero after25 days.) Ask students why theplotting of the population of P.caudatum begins at day 6 on theupper graph, yet at day zero on thelower graph. (On the upper graph,the population of P. caudatum wasnot introduced into the culture tubeuntil the population of P. aurelia hadbeen growing for 6 days. At thispoint, both cultures had the samepopulation density. On the lowergraph, both populations were intro-duced into the culture tube at thebeginning of the experiment. Bothwere introduced at the same extremelylow population density.) VisualLS
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Using the information supplied in the text, have stu-dents analyze, review, and critique the scientificexplanations of MacArthur, Connell, Gause, Paine,and Tilman about competition. Have students identifyand describe the strengths and weaknesses of eachscientist’s hypothesis or theory. Ask students whetheror not these explanations are mutually exclusive oroverlap in any way.
Integrating Physics and Chemistry
MISCONCEPTION ALERT
Predation Can Increase Diversity Thenotion that the removal of a predator canreduce the diversity of an ecosystem mayseem counterintuitive to students. An example occurred in England when a viralepidemic wiped out the rabbit population.The grasses, once controlled by rabbits,grew out of control. At the same time, themany species of wildflowers that oncethrived in the chalky soils disappeared.
Competition Without Division of ResourcesIn nature, shortage is the rule, and species that use the sameresources are almost sure to compete with each other. Darwin notedthat competition should be most acute between very similar kinds oforganisms because they tend to use the same resources in the sameway. Can we assume, then, that when very similar species compete,one species will always become extinct locally? In a series of care-fully controlled laboratory experiments performed in the 1930s, theRussian biologist G. F. Gause looked into this question.
In his experiments, Gause grew two species of Paramecium in thesame culture tubes, where they had to compete for the same food(bacteria). Invariably, the smaller of the two species, which was moreresistant to bacterial waste products, drove the larger one to extinc-tion, as shown in the first graph in Figure 7. Gause hypothesized thatif two species are competing, the species that uses the resource moreefficiently will eventually eliminate the other. This elimination of acompeting species is referred to as .
When Can Competitors Coexist? Is competitive exclusion the inevitable outcome ofcompetition for limited resources, as Gause suggests?No. When it is possible for two species to avoid com-peting, they may coexist.
In a revealing experiment, Gause challengedParamecium caudatum—the defeated species in hisearlier experiments—with a third species, P. bursaria.These two species were also expected to compete forthe limited bacterial food supply. Gause thought onespecies would win out, as had happened in his previ-ous experiments.
But that’s not what happened. As shown in the sec-ond graph in Figure 7, both species survived in theculture tubes. Like MacArthur’s warblers, the twospecies of Paramecium divided the food resources.How did they do it? In the upper part of the culturetubes, where oxygen concentration and bacterialdensity were high, P. caudatum was dominant. It wasbetter able to feed on bacteria than was P. bursaria.But in the lower part of the tubes, the lower oxygenconcentration favored the growth of a differentpotential food—yeast. Paramecium bursaria was bet-ter able to eat the yeast, so it used this resource moreefficiently. The fundamental niche of each specieswas the whole culture tube, but the realized niche ofeach species was only a portion of the tube. Becausethe niches of the two species did not overlap toomuch, both species were able to survive.
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When two species competed for the same resource, one species drove the other to extinction.
When two species used differentresources, both were able to survive.
Effects of Competition
P. caudatum P. aureliaP. bursaria
Figure 7 Gause’s experiments. The outcome of competition depends on thedegree of similarity betweenthe fundamental niches of thecompeting species.
QuizTrue or False:1. An organism’s niche includes,
among other things, its diet andreproductive characteristics.(True. An organism’s niche is itspattern of living.)
2.The part of its realized niche thata species occupies is called itsfundamental niche. (False. Thepart of its fundamental niche thata species occupies is called its real-ized niche.)
3. One competing species eliminat-ing another is termed commen-salism. (False. It is termedcompetitive exclusion.)
AlternativeAssessment
Ecological VersusEconomic Competition
Have students write a short reportcontrasting competition betweenorganisms in a natural communitywith competition between busi-nesses in a human community.
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Answers to Section Review1. A habitat is where an organism lives. Its niche
is the role it plays within that habitat.2. Answers may vary. Connell concluded that
competition can limit how species use resources.Paine concluded that predation can promotebiodiversity.
3. Tilman showed that plots with the greatestspecies diversity displayed greater productivityand were more resilient to drought conditionsthan plots with lower diversity.
4. No, a realized niche can be smaller than, or thesame size as, a fundamental niche, but neverlarger. By definition, the fundamental niche isthe entire range of conditions an organism is
potentially able to occupy; the realized niche isa subset of that range.
5. The scientist may not be aware of competitiontaking place. Also, competition that is no longerapparent may have played a key role in the pastdevelopment of the ecosystem, even driving oneor more species out of the area or to extinction.
6. A. Incorrect. Space utilization refers to howorganisms use resources. B. Correct. C. Incorrect. Niche restriction refers to the part of a niche to which an organism is limited.D. Incorrect. Resource division implies thatcompeting species “carve up” availableresources and coexist.
370 Chapter 17 • Biological Communities
Distinguish between niche and habitat.
Describe the conclusions reached by Connelland Paine about how competition affects ecosystems.
Describe how Tilman’s experiments demon-strate the effects of biodiversity on productivityand stability.
Critical Thinking Applying InformationCan an organism’s realized niche be larger thanits fundamental niche? Justify your answer.
Critical Thinking Evaluating ConclusionsA scientist finds no evidence that species in acommunity are competing and concludes thatcompetition never played a role in the develop-ment of this community. Is this conclusion valid?Justify your answer.
When two species use thesame resource, one species may drive the other toextinction. This phenomenon is called A space utilization. C niche restriction.B competitive exclusion. D resource division.
Standardized Test PrepStandardized Test Prep
Section 2 Review
Predation and Competition Many studies of natural ecosystems have demonstrated that preda-tion reduces the effects of competition. A very clear example is provided by the studies of Robert Paine of the University ofWashington. Paine examined how sea stars affect the numbers andtypes of species within marine intertidal communities. Sea stars arefierce predators of marine animals such as clams and mussels.When sea stars were kept out of experimental plots, the number oftheir prey species fell from 15 to 8. The 7 eliminated species werecrowded out by the sea stars’ chief prey, mussels, shown in Figure 8.Mussels can outcompete other species for space on the rocks. Bypreying on mussels, sea stars keep the mussel populations too low todrive out other species.
Because predation can reduce competition, it can also promote, the variety of living organisms present in a community.
Biodiversity is a measure of both the number of different species ina community (species richness) and the relative numbers of each ofthe species (species diversity).
Biodiversity and Productivity A key investigation carried out in the early 1990s by David Tilmanof the University of Minnesota illustrates the relationship betweenbiodiversity and productivity. Tilman and some co-workers andstudents tended 207 experimental plots in a Minnesota prairie.Each plot contained a mix of up to 24 native prairie plant species.The biologists monitored the plots, measuring how much growthwas occurring. Tilman found that the greater the number ofspecies a plot had, the greater the amount of plant material pro-duced in that plot. Tilman’s experiments clearly demonstrated thatincreased species richness leads to greater productivity.
In addition to increased productivity, Tilman also found thatthe plots with greater numbers of species recovered more fullyfrom a major drought. Thus, the biologically diverse plots werealso more stable than the plots with fewer species.
biodiversity
Figure 8 Effect of removing sea stars. Whenthe sea star Pisaster wasremoved from an ecosystem,the diversity of its prey speciesdecreased. Mussels, the superior competitor, crowdedseven other prey species out of the ecosystem.
OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. The theme of Section 3 isbiomes—major biological commu-nities that occur over large areas ofland. This section first describes theseven major terrestrial biomes andthen discusses aquatic communities.
The kangaroo rat can survive thehot, dry climate of the deserts ofMexico and the southwesternUnited States without drinkingwater. Ask students to hypothesizehow the kangaroo rat obtains thewater it needs to survive. (The ratsurvives on the water in its food, sup-plemented with water it producesthrough cellular respiration. It alsoconserves water by spending the dayin a cool, humid burrow and excret-ing very concentrated urine.) Aftertaking attendance, discuss studenthypotheses. Logical
ActivityIn preparation for discussing bio-mes, have students work in pairs,using their prior knowledge, todevelop graphs of the year-roundtemperatures and precipitation inyour area. For the graphs, have stu-dents list the months of the year onthe X-axis and temperature or pre-cipitation on the Y-axis, dependingon the graph. After students maketheir graphs, compare graphsamong student pairs. Discuss anysimilarities or differences. Thenhave students research temperatureand precipitation data for the pastyear for your area using theInternet or the library, and havethem prepare new sets of graphs.Discuss how the real data comparewith students’ perceptions ofannual temperature and precipita-tion in your area. VisualLS
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• Reading Organizers• Reading Strategies
Planner CD-ROM
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TR BellringerTR E26 Elements of ClimateTR E27 Earth’s Biomes
• Directed Reading• Active Reading• Data Sheet for Quick Lab GENERAL
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Chapter Resource File
Climate’s Effect on Where Species Live If you traveled across the country by car you would notice dramaticchanges in the plants and animals outside your window. For example,the drought-tolerant cactuses in the deserts of Arizona do not live inthe wetlands of Florida. Why is this? The climate of any physical environment determines what organisms live there. refers tothe prevailing weather conditions in any given area.
Temperature and MoistureThe two most important elements of climate are temperature andmoisture. Figure 9 illustrates the different types of ecosystems thatoccur under particular temperature and moisture conditions.
Temperature Most organisms are adapted to live within a particularrange of temperatures and will not thrive if temperatures are colderor warmer. The growing season of plants, for example, is primarilyinfluenced by temperature.
Moisture All organisms require water. On land, water is sometimesscarce, so patterns of rainfall often determine an area’s life-forms.The moisture-holding ability of air increases when it is warmed anddecreases when it is cooled.
Climate
Major BiologicalCommunities
Section 3
Objectives● Recognize the role of
climate in determining thenature of a biological community.
● Describe how elevationand latitude affect the distribution of biomes.
● Summarize the key features of the Earth’smajor biomes.
● Compare features of plantsand animals found in differ-ent biomes.
● Compare and contrast the major freshwater andmarine habitats.
Key Terms
climatebiomelittoral zone limnetic zone profundal zone plankton
Figure 9 Elements of climate. Temperature andmoisture help determineecosystem distribution. Forexample, the asters and thesaxifrage shown are able toproduce flowers and seeds in the cold temperatures of the tundra.
DemonstrationShow the class photographs of thefive major biomes found in thelower 48 states and Alaska—desert,temperate grassland, temperate for-est (both deciduous and evergreen),tundra, and taiga. Ask studentswhat they can deduce about thephysical and biological characteris-tics of these biomes from examiningthe photos. Visual
Teaching TipRainfall Have students checklibrary or Internet resources
to identify areas in the world thatreceive the highest amounts of rain-fall. Have them write a report thatexplains the physical factorsresponsible for the heavy rainfallsin these areas. Interpersonal
Teaching TipLatitude and Longitude Using aglobe, remind students that longi-tude indicates east-west positionand that latitude indicates north-south position. Draw on the board a Graphic Organizer. Leadstudents to conclude that latitudeprofoundly affects climate, butlongitude is essentially irrelevant to climate.
Logical
Using the Figure Have students refer to Figure 10.Emphasize that a biome is acategory and not a place. Alsoemphasize that the boundaries ofbiomes are not as well defined as they are shown in this figure. VisualLS
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Graphic Organizer
Use this graphic organizer with Teaching Tip: Latitude and Longitudeon this page.
Tropical rain forest
Savanna
Desert
Temperate grassland
Temperate deciduous forest
Taiga
Tundra
Longitude
Latit
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Major Biological CommunitiesIf you were to tour the world and look at biological communities onland and in the oceans, you would soon learn a general rule of ecol-ogy: very similar communities occur in many different places thathave similar climates and geographies. A major biological commu-nity that occurs over a large area of land is called a .
A biome’s structure and appearance are similar throughout itsgeographic distribution. While there are different ways of classify-ing biomes, the classification system used here recognizes seven ofthe most widely occurring biomes: (1) tropical rain forest, (2) savanna, (3) taiga, (4) tundra, (5) desert, (6) temperate grass-land, and (7) temperate forest (deciduous and evergreen). Thesebiomes differ greatly from one another because they have devel-oped in regions with very different climates. The global distributionof these biomes is shown in Figure 10.
Many factors such as soil type and wind play important roles indetermining where biomes occur. Two key factors are particularlyimportant: temperature and precipitation. Figure 11 is based on thework of ecologist Robert Whittaker. The graph shows the relation-ship between temperature and humidity and the biological commu-nities that exist under different conditions. In general, temperatureand available moisture decrease as latitude (distance from the equa-tor) increases. They also decrease as elevation (height above sealevel) increases. As a result, mountains often show the samesequence of change in ecosystems that is found as one goes north orsouth from the equator.
biome
www.scilinks.orgTopic: BiomesKeyword: HX4023
60° N
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Equator
30° S
60° S
Tundra
Polar ice
Taiga
Mountain zones
Temperate forest
Tropical forest
Temperate grassland
Savanna
Desert or semidesert
Figure 10 Earth’s biomes.Seven major biomes covermost of the Earth’s land surface. Because mountainousareas do not belong to anyone biome, they are given their own designation.
Termite Mounds The savannas of Australiaand Africa are home to the world’s tallest non-human-built structures. These are termitemounds, which are built by Australian andAfrican termites. Termites live about 5 to 6 feetbeneath the mounds. Tunnels within themounds are used as ventilation systems for thetermite “living quarters” below. The largesttermite mounds are so tall that if the termitesthat built the mounds were the size of humans,then the mounds would be 180 stories tall!
Group Activity Biome Collages Place students ingroups of three. As students studyeach biome, have them collectimages of plants and animals thatare characteristic of that biome.After studying the biomes and col-lecting the images, have studentsdevelop a collage of each biome.Have the group present each collageto the class, explaining why theirimages are appropriate to eachbiome. Hang all the collages of eachtype of biome together on the walland label.
Visual
Teaching TipTropical Rain Forest CompetitionPoint out that the strongest compe-tition among trees in a rain forest isfor light. In the rain forest, about70 percent of all plant species aretrees. Their trunks are usually slen-der and tall. Their leaves are usu-ally large and dark
Activity Identifying Biomes Find imagesof the various biomes on theInternet or in magazines. As youproject each image onto a screen,ask students to identify the biome.Then ask students to justify theiranswers, supporting their identifi-cations with evidence. VisualLS
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Terrestrial BiomesTropical Rain Forests Tropical rain forestsreceive an average of as much as 450 cm (180 in.)of rain per year, with little difference in distribu-tion from season to season. The richest biome interms of number of species is the tropical rain-forest. Tropical rainforests may contain at leasthalf of the Earth’s species of terrestrial organ-isms—more than 2 million species. Tropical rainforests have a high primary productivity eventhough they exist mainly on quite infertile soils.Most of the nutrients are held within the plants;the soil itself contains few nutrients.
Savannas The world’s great dry grasslands,called savannas, are found in tropical areas thathave relatively low annual precipitation or pro-longed annual dry seasons. Annual rainfall isgenerally 90 to 150 cm (35 to 60 in.) in savannas.There is a wider fluctuation in temperature dur-ing the year than in the tropical rain forests, andthere is seasonal drought. These factors have ledto an open landscape with widely spaced trees.Many of the animals are active only during therainy season. Huge herds of grazing mammalsare found on the savannas of East Africa.
Tropical rain forest in Puerto Rico
Savanna in East Africa
Temperature and Moisture in Biomes
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Figure 11 Conditions inbiomes. Different biomes havecharacteristics of temperatureand humidity.
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StrategiesStrategiesINCLUSIONINCLUSION
Using index cards have students create post-cards to send to the class from a biome theyhave visited. Students should include adescription of the characteristics of thebiome, the kind of climate there, the kinds of animals there, and locations where thisbiome exists. On the postcard, studentsshould draw a picture of the biome. VisualLS
The Joshua Tree Show the class a photo-graph of a Joshua tree, a North Americandesert plant. This tree was named by earlyMormon colonists, who thought it resem-bled the biblical prophet Joshua wavingthem toward the Promised Land.
Many of today’s domesticated plants and ani-mals, including cattle, sheep, horses, wheat,barley, and oats, are descendants of the wildgrassland communities of Eurasia.
REAL WORLDREAL WORLDCONNECTIONCONNECTION
Procedure
1. Set up an MBL/CBL systemto collect and graph datafrom each temperature probeat 5-second intervals for 240data points. Calibrate theprobe using stored data.
2. Fill one test tube withwater. Fill another test
tube halfway with sand.
3. Place a temperature probe inthe sand, and suspendanother temperature probe atthe same depth in the water,
using one-holed stoppers tohold each temperature probein place.
4. Place both test tubes ina beaker of hot water.
Heat them to a temperature ofabout 70ºC. Caution: Hotwater can burn skin.
5. Using test-tube tongs, removethe test tubes and place themin the test-tube rack. Recordthe drop in temperature for20 minutes.
Analysis
1. Critical ThinkingAnalyzing Results Did thetwo test tubes cool at thesame rate? Offer an explana-tion for your observations.
2. Critical ThinkingPredicting OutcomesIn which biome—tropical rainforest or desert—would youexpect the air temperature todrop most rapidly? Explainyour answer.
Taiga Cold, wet climates promote the growth ofconiferous forests. A great ring of northern forestsof coniferous trees, primarily spruce and fir,extends across vast areas of Eurasia and NorthAmerica. This biome, one of the largest on Earth,is called by its Russian name, taiga (TIE guh).Winters in the taiga are long and cold, and most ofthe precipitation falls in the summer. Many largemammals, including herbivores such as elk,moose, and deer and carnivores such as wolves,bears, lynxes, and wolverines live in the taiga.
Tundra Between the taiga and the permanent icesurrounding the North Pole is the open, some-times boggy biome known as the tundra. Thisenormous biome covers one-fifth of the Earth’sland surface. Annual precipitation in the tundrais very low, usually less than 25 cm (10 in.), andwater is unavailable for most of the year becauseit is frozen. The permafrost, or permanent ice,usually exists within 1 m (about 3 ft) of the sur-face. Foxes, lemmings, owls, and caribou areamong the vertebrate inhabitants.
Taiga in Manitoba, Canada
Tundra in Denali National Park, Alaska
Investigating Factors ThatInfluence the Cooling of Earth’s Surface You can discover how the amount of water in an environ-ment affects the rate at which that environment cools.
Materials
MBL or CBL system with appropriate software, temperatureprobes, test tubes, beaker, hot plate, one-holed stoppers, water,sand, test-tube tongs, test-tube rack
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InvestigatingFactors ThatInfluence theCooling of Earth’sSurface
Teacher’s NotesPreparation tip: Be sure thateach lab station has therequired materials before thestart of class. Safety notes: Have studentswear safety goggles. Remindthem to handle the hot testtubes with tongs and to useextreme care. Remind them tobe careful of the hot plate at alltimes. Moisten the ends of theprobes to facilitate pushingthem through the stoppers.When test tubes are heated, thesand and water may not reach70˚C at the same time. Studentsmay remove each tube as itreaches 70˚C. Remind themthat they are interested inobserving the rate of cooling,and that the starting tempera-ture is not critical.
Answers to Analysis1. The sand should cool faster, as
water has a greater capacity tostore heat and therefore aslower cooling rate.
2. The desert temperature woulddrop more rapidly, due to thelack of water in the groundand the atmosphere.
did you know?Sunlight and Biomes Hours of sunlight perday range widely through the year in northernbiomes. The northernmost areas of taigareceive only 6 to 8 hours of sunlight during thewinter but nearly 19 hours during the summer.The extremes are even more exaggerated in thetundra, which receives less energy from the sunthan any other biome.
Just as temperature is one of the most importantelements of climate, it is also a critical factor thatinfluences solubility. The solubility of most solids riseswith increasing temperature. However, there areexceptions, such as cerium chloride, whose solubilitydecreases with increasing solvent temperature. Askstudents whether or not the solubility of gases goesup or down with increasing solvent temperature. Theymay be surprised to learn that increasing temperatureactually decreases the solvent’s ability to retain adissolved gas.
Integrating Physics and Chemistry
Terrestrial BiomesDeserts Typically, less than 25 cm (10 in.) of pre-cipitation falls annually in the world’s desertareas. The scarcity of water is the overriding fac-tor influencing most biological processes in thedesert. In desert regions, the vegetation is char-acteristically sparse. Deserts are most extensivein the interiors of continents. Less than 5 percentof North America is open desert. The amount ofwater that actually falls on a particular place in adesert can vary greatly, both during a given yearand between years.
Temperate Grasslands Moderate climates half-way between the equator and the poles promotethe growth of rich temperate grasslands calledprairies. Temperate grasslands once coveredmuch of the interior of North America. Suchgrasslands are often highly productive whenconverted to agriculture. The roots of grassescharacteristically penetrate far into the soil,which tends to be deep and fertile. Herds ofgrazing animals often populate temperategrasslands. In North America, huge herds ofbison once inhabited the prairies.
Temperate Deciduous Forests Relatively mildclimates and plentiful rain promote the growthof forests. Temperate deciduous forests (decidu-ous trees shed their leaves in the fall) grow inareas with relatively warm summers, cold win-ters, and annual precipitation that generallyranges from 75 to 250 cm (30 to 100 in.).Temperate deciduous forests cover much of theeastern United States and are home to deer,bears, beavers, raccoons, and other familiar ani-mals. The trees are hardwoods (oak, hickory, and beech).
Temperate Evergreen Forests In other temper-ate areas, drier weather and different soil conditions favor the growth of evergreens.Large portions of the southeastern and westernUnited States have temperate evergreenforests—extensive areas where pine forestspredominate over deciduous forests. Whereconditions are even drier, temperate forestsgive way to areas of dry shrubs, such as in thechaparral areas of coastal California and in theMediterranean.
Temperate grasslands in Kansas
Temperate evergreen forest in Washington
Temperate deciduous forest in Pennsylvania
Desert in Texas
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Teaching TipDeserts in the United StatesDesert covers less than 5 percent of North America. The NorthAmerican deserts are the Mojave,Sonoran, Great Basin, and Chihua-huan. Have students write a reportthat contrasts the animals, plants,geography, and climate of thesefour deserts.
Teaching TipDesert TemperaturesTemperatures in the desert undergodrastic changes over a 24-hourperiod. Daytime temperatures canbe 30˚C (54˚F) higher than night-time readings. These fluctuationsoccur due to the lack of heat-retaining moisture in the desert air.
Teaching TipNumbers Versus DiversityA deciduous forest usually has onlya few species of trees, but there arenumerous individuals of eachspecies. In contrast, a tropical rainforest usually has many species oftrees, but each species may be rep-resented by only a few individuals.
Teaching TipDeep-water Detritivores Infreshwater and marine communi-ties, there are no photosyntheticorganisms in the deep-water zone.Most of its inhabitants are detriti-vores, including scavenging fish,bacteria, and aquatic worms, whicheat the detritus (decaying material)that falls from above.
Teaching TipPhotosynthetic OrganismsWhen sunlight strikes the watersurface, red, orange, and yellowwavelengths of light are absorbed(converted into heat) first. Onlyblue and green can penetratedeeply. Thus, below a depth of afew meters, only those photosyn-thetic organisms capable of usingthese shorter wavelengths of lightcan survive.
Activity Viewing FreshwaterCommunities Have students col-lect water samples from a nearbypond or lake. Ask students to col-lect samples from various areas ofthe pond, collecting as much plantand animal life as they can see. Besure to have them collect surfacewater as well. In the classroom,place the pond samples in anaquarium for viewing. Have stu-dents make wet mounts of watersamples to see which phytoplank-ton (microscopic plants) andzooplankton (microscopic animals)live in the freshwater community inyour area. Have students choose anorganism in the community toresearch and report on to the class.
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Trends in LimnologyFollowing Fish Odors Limnology, which comesfrom a Greek word meaning lake or marsh, is thestudy of bodies of fresh water. One area of studyfor limnologists is the effect of fish odors on thebehavior of invertebrates such as the water flea,Daphnia hyalina. Limnologists have discoveredthat fish odors could trigger the daily migrationsof these tiny freshwater invertebrates. A chemicalnicknamed TMA (trimethylamine), which is acomponent of fish odor, appears to cue Daphniawhen predator fish are present. Daphnia respondby moving to areas where the fish are not swim-ming. Limnologists are currently researching suchaquatic chemical communication.
376 Chapter 17 • Biological Communities
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The physical link between rivers or streamsand their surrounding terrestrial communitiesis the stream bank, also called the riparianzone. Riparian zones often appear as ribbonsof vegetation around waterways. These areasprovide humans with many services, includingfiltering pollution and absorbing floodwaters.Riparian zones also provide vital habitat for abroad array of plant and animal species.
ENVIRONMENTAL SCIENCEENVIRONMENTAL SCIENCE
Aquatic CommunitiesAt a glance, you might at first think that freshwater and marine com-munities are separate from terrestrial biomes. Yet large amounts oforganic and inorganic material continuously enter both bodies offresh water and ocean habitats from communities on the land.
Freshwater Communities Freshwater habitats—lakes, ponds, streams, and rivers—are verylimited in area. Lakes cover only about 1.8 percent of the Earth’s sur-face, and rivers and streams cover about 0.3 percent. All freshwaterhabitats are strongly connected to terrestrial ones, with freshwatermarshes and wetlands constituting intermediate habitats. Manykinds of organisms are restricted to freshwater habitats, includingplants, fish, and a variety of arthropods, mollusks, and otherinvertebrates too small to be seen without a microscope.
Ponds and lakes have three zones in which organisms live, asillustrated in Figure 12. The is a shallow zone nearthe shore. Here, aquatic plants live along with various preda-tory insects, amphibians, and small fish. The refers to the area that is farther away from the shore but close tothe surface. It is inhabited by floating algae, zooplankton, andfish. The is a deep-water zone that is below thelimits of effective light penetration. Numerous bacteria andwormlike organisms that eat debris on the lake’s bottom live inthis zone. The breakdown of this debris releases large amountsof nutrients. Not all freshwater systems are deep enough toinclude a profundal zone.
profundal zone
limnetic zone
littoral zone
Organizing InformationMake a concept map thatdescribes the zones of apond or lake as described at right and in Figure 12. Foreach zone, include the plantand animal life found there.
Figure 12 Three lakezones. Each region, or zone, of a lake contains characteristic organisms.
EstuariesTeaching Strategies• Inform students that a
healthy estuary is third onlyto coral reefs and tropicalrain forests in biological pro-ductivity.The Chesapeake Bayhas received national atten-tion as an example of animperiled estuary. Over-fishingcombined with urban andagricultural pollution hasnearly destroyed one of themost productive ecosystemson the planet. The problem islarge scale: rivers and creeksfrom six different states flowinto the bay. Representativesof Maryland and the Districtof Columbia signed theAnacostia WatershedRestoration Agreement in1999, which includes goals ofrestoring the waterway andsurrounding land.
• Have students research anestuary, reporting on itshistorical significance, theseafood harvested, its currentenvironmental health, andefforts to preserve the ecosystem.
DiscussionAsk students why they thinkestuaries have been overhar-vested and polluted if they areso important to humans andwildlife. (Answers may vary.Students should be aware thatestuaries tend to be found inhighly populated areas and occurdownstream from agriculturalareas. Also, people tend to over-use public land or water becauseit is “free” for the taking.)
The National Oceanic and AtmosphericAdministration (NOAA) conducts researchand gathers data about the oceans, atmos-phere, space, and sun. One activity of NOAAis to guide the use of ocean and coastalresources and protect them. Since 1993,NOAA has maintained the world’s only per-manent undersea research laboratory. Located4 miles off the Florida coast, the “Aquarius”lab addresses scientific questions pertaining toocean environments and marine life.
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did you know?Wetlands and Avian Botulism The mostserious disease of wetland bird species is avianbotulism. It is estimated that millions of water-fowl die annually from this disease, which is aninternational concern.
Transparencies
TR E28 Three Lake Zones
WetlandsSwamps, such as the one shown in Figure 13, as well asmarshes, bogs, and other communities that are covered with alayer of water are called wetlands. Wetlands typically are cov-ered with a variety of water-tolerant plants, called hydrophytes(“water plants”). Marsh grasses and cattails are hydrophytes.Wetlands are dynamic communities that support a diversearray of invertebrates, birds, and other animals. Wetlands areamong the most productive ecosystems on Earth, exceededonly by coral reefs in diversity and concentration of species.They also play a key ecological role by providing water storagebasins that moderate flooding. Many wetlands are being dis-rupted by human development of what is sometimes perceivedas otherwise useless land, but government efforts are nowunderway to protect the remaining wetlands.
Estuaries
If you’ve ever eaten seafoodcaught in a saltwater marsh,
you’ve experienced one of thebenefits of estuaries. Estuariesare unique transition zonesbetween marine and freshwaterenvironments. Nutrients washedfrom nearby land stimulate thegrowth of plants and algae. As aresult, estuaries are among themost productive ecosystems onEarth. One hundred acres ofhealthy estuary can produce 4 to10 times as much organic matteras a cultivated cornfield of thesame size! The estuary’s plants,invertebrates, fishes, birds,mammals, and other animals arepart of a complex food web.
Where the River Meets the Sea In addition to serving as wildlifehabitats, estuaries filter sedimentand nutrients, purifying the waterthat drains off the land. Porous salt-marsh soils absorb floodwatersand protect coastal communitiesfrom erosion. Estuaries also
provide jobs for people in theseafood and recreation industries.
Estuaries in Peril Sadly, the public has longregarded estuaries as waste-lands. People have drained estu-aries to provide land for housingand agriculture. Pollutants andimproperly treated sewage havepoisoned some estuaries’ habi-tats. As a result, estuaries in theUnited States have greatlydecreased in size over the pastcentury. However, a variety of envi-ronmental organizations are nowworking to restore estuaries by
cleaning up pollutants and replant-ing native vegetation. For example,restoration efforts in Tampa Bay,Florida, improved sewage treat-ment facilities, enabling sea grassmeadows to return. When the seagrasses returned, so did the fishesand other animals that depend on them.
www.scilinks.orgTopic: EstuariesKeyword: HX4073
Figure 13 Forested wetlands.This swampy terrain is typical of theforested wetlands found in the south-eastern United States.
Teaching Tip Deep-sea Waters Humans firstreached the floor of the MarianaTrench in 1960. Two scientists usedthe bathyscaphe Trieste to descend11 km (7 mi) below the ocean’ssurface. It descended when waterwas pumped into air tanks at eitherend, and it ascended when waterwas pumped out. The Triesteobtained data about the conditionsat such depths, and its scientistsobserved many never-before-seendeep-water organisms.
ReteachingShow students pictures of various biomes. Ask them to identify each and to discuss itsphysical and biological character-istics, as well as where on theplanet such a biome might be found.
Visual
Quiz1. Why do mountains often show
the same sequence of ecosystemsthat is found as one goes northor south from the equator?(Temperature and precipitationdecrease as latitude or elevationincreases.)
2.Which biome is a transitionalarea between tropical rain forestand desert? (Savanna)
3. In a small pond or lake, which ofthe three life zones might not bepresent and why? (A small pondor lake might be shallow andtherefore not have a deep-waterprofundal zone.)
GENERAL
LS
CloseClose
Teach, continuedTeach, continued
Answers to Section Review1. The climate of a region determines what
species can live in that region. Only those welladapted to the conditions will prevail.
2. Savannas have low annual precipitation or pro-longed dry seasons, while tropical rain forestshave high rainfall year-round. Therefore, rainforest dwellers need little tolerance to lack ofwater, while savanna dwellers need high tolerance.
3. Photosynthesis cannot occur in deep waterbecause light is completely absorbed before itreaches these depths.
4. Ecuador has mountains, which create climateconditions different from those associated withlatitude alone.
5. A. Correct. Tropical rain forests have highannual precipitation with infertile soil, sincemost of the nutrients are held within theplants. B. Incorrect. Annual precipitation in the tundra is very low. C. Incorrect. The soil of temperate grasslands tends to be fertile. D. Incorrect. Savannas have low annual precip-itation or prolonged dry seasons.
378 Chapter 17 • Biological Communities
English Language Learners
Marine CommunitiesNearly three-fourths of the Earth’s surface is covered by ocean, which consists of three major kinds of marinecommunities.
Shallow Ocean Waters The zone of shallow water is smallin area, but compared with other parts of the ocean, it isinhabited by large numbers of species. The seashorebetween high and low tide, called the intertidal zone, ishome to many species of marine invertebrates. Coral reefcommunities, the world’s most diverse, occur in shallowtropical waters. The world’s great fisheries are located inthe coastal zones of cooler waters, where nutrients washedout from land support huge numbers of fishes.
Surface of the Open Sea Drifting freely in the upper watersof the ocean is a diverse community of , composedof bacteria, algae, fish larvae, and many small invertebrateanimals. Fishes, whales, and invertebrates such as jelly-fishes feed on plankton. And larger fishes and birds, in turn,feed on some of these animals. Photosynthetic plankton(algae such as diatoms and some bacteria) that form thebase of this food chain account for about 40 percent of allthe photosynthesis that takes place on Earth. Because lightpenetrates water only to the depth of about 100 m (328 ft),this rich community is confined to the ocean’s surface.
Ocean Depths In the deepest waters of the sea, the marinecommunity lives in total darkness, in deep cold, and undergreat pressure. Despite what seem like hostile conditions,the deep ocean supports a diverse community of bizarreinvertebrates and fishes. This includes great squids andangler fishes that attract prey with projections from theirhead that emit light. On the ocean floor, at an averagedepth of more than 3 km (1.9 mi), researchers have foundan unexpected abundance of species, a diversity that rivalsthe tropical rain forest.
plankton
Describe the relationship between climate andlocation of species.
Compare the tolerance to lack of water neededby plants and animals in savannas and tropicalrain forests.
Critical Thinking Analyzing InformationWhy can’t photosynthesis occur in the deepestparts of the ocean or in a deep lake?
Critical Thinking Forming ReasonedOpinions The equator passes across the country of Ecuador. But the climate there canrange from hot and humid to cool and dry. What might explain this?
In which biome would youmost likely find plants that are adapted to infertilesoils and fairly constant, plentiful precipitation? A tropical rain forest C temperate grasslandB tundra D savanna
Standardized Test PrepStandardized Test Prep
Section 3 Review
Diatoms from surface of the open sea
Anglerfish from ocean depths
Blue stripe snapper from shallow ocean watersBlue stripe snapper from shallow ocean waters
AlternativeAssessmentHave students imagine that a largeisland has suddenly appeared onthe surface of the planet. Have students work together to createclimate conditions for the islandbased on its location on the earth,then predict what biome(s) wouldbe found on the island in thefuture. Have them discuss some ofthe species they could expect tofind, and how those species mightinteract. InterpersonalLS
GENERAL
Answers to Concept MapThe following is one possible answer toPerformance Zone item 15.
Chapter 17 • Biological Communities 379
• Science Skills• Critical Thinking• Test Prep Pretest• Chapter Test GENERAL
Understanding Key Ideas1. a2. c3. The grass grows in sunlight and
recovers quickly from dry spellsand grazing. Energy from the sunis stored in its tissues and passedon to feeding zebra. Zebra areherbivores and live in herds,which offer some protection frompredators such as lions. Lionsfeed primarily on herbivores, cap-turing a portion of the grazedenergy. Lions hunt in smallgroups, which enables them tocapture large prey, such as zebra.
4. d5. b6. a7. Temperatures generally decrease
with increasing elevation (heightabove sea level) and latitude (dis-tance from the equator). In otherwords, increasing elevation andlatitude positively correlate withthe transition from tropical totemperate to arctic biomes.
8. Answers may vary.9. The flow of energy through
ecosystems ensures that biologi-cal communities have the samebasic structure. Ecosystems haveautotrophs, such as plants. Thereare heterotrophic herbivores,such as rabbit or deer and het-erotrophic carnivores, such asfoxes. An abundance of deadorganic matter provides fordecomposers, such as bacteria.
10. The answer to the concept map isfound at the bottom of the StudyZone page. Critical Thinking
11. The two could coexist if P. bursaria feeds onyeast at the bottom of the tube and P. aureliafeeds on bacteria at the top.
12. Native prey have often evolved defense mecha-nisms to protect them from native predators.These mechanisms may be ineffective againstintroduced predators.
13. Annual precipitation in deserts is less than 25cm, which is the same level as in the tundra.Additionally, water in the tundra is unavail-able for most of the year because it is frozen.
14. Students’ maps should realistically representyour state and its predominant communities.
380 Chapter 17 • Biological Communities
CHAPTER 17
Understanding Key Ideas1. In predator-prey coevolution, if the prey
gains a defense to stop predation, then thepredator may evolvea. in a way that enables it to overcome the
prey’s defense.b. so that it can parasitize the prey.c. secondary compounds.d. into a prey species.
2. The principle of competitive exclusion indi-cates thata. a niche can be shared by two species if
their niches are very similar.b. niche subdivision may occur.c. one species will eliminate a competing
species if their niches are very similar.d. competition ends in worldwide
elimination of a species.
3. Describe the niches of a lion, a zebra, andthe grass that grows on the African plain interms of how each species affects energyflow in the ecosystem.
4. Which abiotic factor is likely not a reason forthe desert biome’s low primary productivity?a. extreme temperaturesb. frequent floodingc. high predationd. availability of sunlight
5. When populations of similar speciesoccupy the same area at the same time,these populations oftena. share all their resources equally.b. divide their range of resources.c. compete for resources to the death.d. look in other areas for different
resources.
6. Which of the words sets below describes a vulture eating a dead rabbit?a. heterotroph, scavengerb. parasite, predatorc. herbivore, mutualismd. competitor, commensalisms
7. Describe how elevation and latitude affectthe distribution of biomes.
8. Why might digging a deepchannel in an estuary change the types ofliving things that thrive there?
9. How does the flow of energy through livingsystems help determine the components ofa biological community? (Hint: SeeChapter 5, Section 1.)
10. Concept Mapping Make a conceptmap that shows how the biomes can beclassified based on precipitation, tempera-ture, and geographical location. Try toinclude the following terms in your map:tropical rain forest, savanna, desert, temper-ate deciduous forest, temperate grassland,taiga, and tundra.
Critical Thinking11. Justifying Conclusions In Gause’s experi-
ments, Paramecium caudatum could coexistwith P. bursaria but not with P. aurelia.Predict what would happen if P. aurelia andP. bursaria were grown together, and justifyyour conclusions.
12. Justifying Conclusions Newly introducedpredators often prove devastating to nativeanimals. Explain why prey are often morevulnerable to introduced predators than tonative predators.
13. Analyzing Data Using the data presented inthis chapter, explain why many ecologistsrefer to the tundra as a frozen desert.
Alternative Assessment 14. Summarizing Information Work with a
small group of students to develop a mapthat shows the most prominent terrestrialand aquatic communities within your state,and for coastal states, those immediatelyoffshore as well. Be certain to include anylarge swamps or wetlands that connect ter-restrial and aquatic communities.
Understanding ConceptsDirections (1–4): For each question, write ona separate sheet of paper the letter of thecorrect answer.
1 Both a spruce tree and a hemlock treerequire nitrogen from the soil. What is theinteraction between these two species?A. competition C. mutualismB. commensalism D. succession
2 What term describes the ways in which anorganism interacts with its environment?F. ecosystem H. nicheG. habitat I. space
3 Which of the following is a transition zonebetween tropical rain forest and desert?A. savannaB. taigaC. temperate deciduous forestD. tundra
4 Why is the open ocean biome consideredonly slightly more productive than thedesert biome?F. Neither of these biomes receive very
much rain, which restricts productivity.G. Light penetrates only the top 100
meters of water in the open ocean,which restricts productivity.
H. The open ocean receives the sameamount of light, yet has significantlymore water than the desert.
I. Both lack large trees that block sun-light, but the open ocean lacks the soilneeded for plants to grow.
Directions (5): For the following question,write a short response.
5 Compare and contrast mutualism andcommensalism.
Reading SkillsDirections (6): Read the passage below.Then answer the question.
A keystone predator is one who regulatesthe populations of various competitors in an ecosystem. The Pisaster sea star is oneexample of a keystone predator. The sea starpreys on mussels who might otherwise outcompete other species that live in a marineintertidal community. Keystone predatorsreduce the occurrence of competitive exclusion of weak competitors.
6 How does a keystone predator promotebiodiversity?A. It reduces competition by decreasing
the populations of superior competitors.B. It reduces competition by decreasing
the populations of inferior competitors.C. It increases competition by increasing
the populations of superior competitors.D. It increases competition by decreasing
the populations of inferior competitors.
Interpreting GraphicsDirections (7): Base your answer to question7 on the graph below.
Comparative Productivity of Ecosystems
7 Where would you place a bar representingthe primary productivity of the temperategrassland biome, if it could be added tothis graph?F. between desert and open seasG. between open seas and savannaH. between savanna and estuaryI. between estuary and tropical rain forest
Desert Opensea
Savanna
Kind of biome
Incr
easi
ng
pri
mar
yp
rod
uct
ivit
y
Estuary Tropicalrain forest
TestIf you are unsure of the correct answer to a multiple-choice question, start by crossing out answers thatyou know are wrong. Reducing your choices in thisway may help you choose the correct answer.
381
Question 1 Answer A is the cor-rect choice. Answer B is incorrect;commensalism would involve oneof the organisms benefiting fromthe relationship. Answer C isincorrect because mutualismwould involve both organismsbenefiting from the relationship.Answer D is incorrect because suc-cession describes changes inecosystems.
Question 4 Answer G is the cor-rect choice. Answer F is incorrect;a lack of rain would not be a limi-tation for a large aquatic environ-ment. Answer H is incorrect; theabundance of water is not a limit-ing factor. Answer I is incorrect;the ocean has primary producersthat do not require soil.
Question 5 Both mutualism andcommensalism are symbiotic rela-tionships; however, they differ inwhether only one (commensalism)or both (mutualism) organismsbenefit.
Question 6 Answer A is the cor-rect choice. Answer B is incorrectbecause the inferior competitorswould die out due to competitiveexclusion. Answer C is incorrectbecause the superior competitorswould still out compete inferiorcompetitors. Answer D is incorrectbecause a decrease in the popula-tions of inferior competitors wouldnot lead to increased competition.
Question 7 Answer H is the cor-rect choice. Answer F is incorrectbecause the temperate grasslandbiome has high primary productiv-ity. Answer G is incorrect becausethe temperate grassland biome hasa higher primary productivity thanboth. Answer I is incorrect becausethe temperate grassland biome haslower primary productivity thanboth.
Answers1. A2. H3. A4. G5. Mutualism is a symbiotic relationship in which
both organisms benefit. Commensalism is asymbiotic relationship in which one organismbenefits and the other is unaffected.
Tips and TricksStudents should begin by observing the move-ment of brine shrimp through water. Tell studentsto allow the shrimp enough time to distributethemselves in response to environmental factors.This activity works well with groups of four stu-dents. When tubing is divided as directed, itallows for space taken up by stoppers and formsequal quarters. Students may count shrimp bylooking in the Petri dish or in the pipet. Studentsmight hold the pipet up to a light for better visi-bility. The Procedure section provides studentswith one method for randomly dividing brineshrimp into groups that can be experimentallymanipulated in the tubing or in the Petri dishes.
382 Chapter 17 • Biological Communities
Skills Practice Lab
Before You BeginDifferent organisms are adapted for life indifferent . For example, are small crustaceans that live in salt lakes.Given a choice, organisms select habitats thatprovide the conditions (e.g., temperature,light, pH, salinity) to which they are adapted.In this lab, you will investigate habitat selec-tion by brine shrimp and determine whichenvironmental conditions they prefer.
1. Write a definition for each boldface term inthe paragraph above.
2. Based on the objectives for this lab, write aquestion you would like to explore abouthabitat selection by brine shrimp.
ProcedurePART A: Making and Sampling
a Test Chamber1. Divide a piece of plastic tubing into
4 sections by making a mark at 12 cm, 22 cm, and 32 cm from one end. Label the sections 1, 2, 3, and 4.
2. Place a cork in one end of the tubing.Then transfer 50 mL of brine shrimp
culture to the tubing. Place a cork in theopen end of the tubing.
3. When you are ready to count shrimp,divide the tubing into four sections by plac-ing a screw clamp at each mark on the tub-ing. While someone holds the corks firmly inplace, first tighten the middle clamp andthen the outer clamps.
4. Starting at one end, pour the contents ofeach section into a test tube labeled withthe same number. After you empty a sec-tion, loosen the adjacent clamp and fill thenext test tube.
brine shrimphabitats
Skills Practice Lab
SKILLS• Using scientific methods
• Collecting, organizing, andgraphing data
OBJECTIVES• Observe the behavior of
brine shrimp.
• Assess the effect ofenvironmental variables on habitat selection bybrine shrimp.
MATERIALS• clear, flexible plastic tubing
• metric ruler
• marking pen
• corks to fit tubing
• brine shrimp culture
Observing How Brine Shrimp Select a Habitat
• screw clamps
• test tubes with stoppersand test-tube rack
• pipet
• Petri dish
• Detain™ or methylcellulose
• aluminum foil
• calculator
• fluorescent lamp orgrow light
• funnel
• graduated cylinder orbeaker
• hot-water bag
• ice bag
• pieces of screen
• tape
Brine shrimp
Magnification 20!
382
OBSERVING HOW BRINESHRIMP SELECT A HABITAT
Teacher’s Notes
Time Required Two labperiods of 40-50 minutes each
Answers to Analyze and Conclude1. Answers will vary.2. Answers will vary depending on the species of
Artemia used.3. The control was necessary to show that the
brine shrimp did not inherently prefer one part of the tube.
4. Many counts were taken to make allowancesfor variations in populations and to providedata for calculating an average.
5. Answers will vary. For example: How do brineshrimp react to water movement?
Answers to Do You Know?1. Fish are the main predators of brine shrimp.2. Answers will vary depending on the species of
animal chosen.
Answers to Before You Begin1. habitats—areas where organisms
live and to which they are adapted brine shrimp—small crustaceansthat live in salt lakes
2. Answers will vary. For example:Will brine shrimp prefer a warmhabitat or a cool habitat?
Sample ProcedurePerform steps 1–4 of part A. Recordthe number of shrimp and tempera-ture in each test tube, then calculatethe average number and temperature.This is the control sample. Thenmake a new test chamber using theprocedure outlined in part A steps 1and 2. Tape the tubing to the desktop and cover it with aluminum foil.Mark the foil to show the approxi-mate positions of sections 1 and 4.Carefully place a bag of very coldwater over section 1 and a bag ofvery warm water over section 4.After 10 minutes, quickly completesteps 4 and 5 of part A. Immediatelyread and record the temperature ofthe solution in the two test tubes.Then count the shrimp in each tube.Make a histogram plotting tempera-ture on the x-axis versus number ofshrimp on the y-axis versus. Include abar for the control sample.
Chapter 17 • Biological Communities 383
TREATMENT NO. OF SHRIMP
control even distribution . . . about 25warm water about 35room temperature about 17
Sample Data Table
5. Stopper one test tube, and invert it gentlyto distribute the shrimp. Use a pipet totransfer a 1 mL sample of shrimp cultureto a Petri dish. Add a few drops ofDetain™ to the sample. Count and recordthe number of live shrimp.
6. Repeat step 5 three more times for thesame test tube. Record the average num-ber of shrimp for this test tube.
7. Repeat steps 5 and 6 for each of theremaining test tubes.
PART B: Design an Experiment8. Work with the members of your lab group
to explore one of the questions written forstep 2 of Before You Begin. To explorethe question, design an experiment thatuses the materials listed for this lab.
9. Write a procedure for your group’s experi-ment. Make a list of all the safety precau-tions you will take. Have your teacherapprove your procedure and safety pre-cautions before you begin the experiment.
10. Set up and conduct your group’s experi-ment. Do not use water over 70°C, whichcan burn you. CAUTION: If you areworking with the hot-water bag, handleit carefully. If you are working with alamp, do not touch the bulb. Light bulbsget very hot and can burn your skin.
PART C: Cleanup and Disposal11. Dispose of broken glass in the desig-
nated waste container. Put brine
shrimp in the designated container. Donot pour chemicals down the drain or putlab materials in the trash unless yourteacher tells you to do so.
12. Clean up your work area and all labequipment. Return lab equipment to
its proper place. Wash your hands thor-oughly before you leave the lab and afteryou finish all work.
Analyze and Conclude1. Summarizing Results Make a bar
graph of your data. Plot the environmen-tal variable on the x-axis and the numberof shrimp on the y-axis.
2. Analyzing Results How did the shrimpreact to changes in the environment?
3. Analyzing Methods Why was a controlnecessary?
4. Analyzing Methods Why was it neces-sary to take many counts in each test tube(step 6 of Part A)?
5. Further Inquiry Write a new questionabout brine shrimp that could beexplored with another investigation.
You ChooseAs you design your experiment, decide the following:a. what question you will exploreb. what hypothesis you will testc. how to set up your controld. how to expose the brine shrimp to the con-
ditions you chosee. how long to expose the brine shrimp to the
environmental conditionsf. how you will set up your data table
Do You Know?Do research in the library or media centerto answer these questions:
1. What are some predators of brineshrimp?
2. What is the ideal habitat for one ofyour favorite animals?
Use the following Internet resources toexplore your own questions about habitatselection.
