sign in sign up
<<
Home , Biogeochemical cycle

Final PDF to printer

CHAPTER 17 and Biogeochemical Cycles THE IS THE REALM OF . explores the biosphere and the systems that support organisms. Adequate water, energy, and nutrients are necessary to sustain life, and their availability is controlled by cli- mate and other aspects of . This chapter examines how organisms interact with each other and with their physical environment — . The provisions and constraints of the physical environment along with the entire of interacting organisms (, animals, and others) in an area is an . Biogeographers study eco- systems from a broad perspective that considers spatial and temporal variations of physical and chemical processes in the biosphere and how the biosphere impacts Earth’s systems, from local to global scales.

Costa Rica provides a wonderful example of ecology, ecosys- tems, and biogeography. Earlier in this textbook, we explored the region’s weather and climatic patterns, always an excellent place to start when considering the biogeography of a region. The large perspective view here (⊲) is a satellite image draped over the topography of the land.

Land, Water, and 17.00.a2 The backbone of the country is a line of volcanoes, such as Volcán Arenal (⊳), which has nearly continuous low-level eruptions of molten lava and ash. The volcanoes are formed by plate-tectonic activity (specifically subduc- tion) along the west coast. The eruptions of Arenal are sufficiently continuous that the volcano has become a major site for ecotourism. The volcano interacts with the moist air in this tropical place, so it is often partially obscured by clouds and volcanic steam.

How do interactions between the land and atmosphere affect life, including humans?

17.00.a1 17.00.a3 Eruptions of lava and ash flow down the mountain and bury anything on the surface (⊳). The initially barren lava flows are colonized by certain types of plants and animals that can establish themselves on such “new land,” and these are known as a pioneer commu- 17.00.a5 17.00.a6 nity. Once the pioneer community is Abundant tropical moisture sustains Tropical rains, combined with locally established, an entire succession of a dense growth of tropical rain forest, impermeable tropical soils, result in other types of life can colonize the and the rain forest releases some of plentiful runoff in streams. These area. Over time, weathering begins to

17.00.a4 this moisture during transpiration. In corridors of running water attract form soils (⊳), which in this volcanic addition, plants remove many animals, forming a small

terrain are mostly Andisols, and the dioxide (CO2) from the air to produce streambed ecosystem within the new land begins to blend into the carbon-rich wood, leaves, roots, and larger tropical ecosystem. landscape. other material. What are the main components of How do life and land interact chemi- How does carbon move from one an ecosystem, and what role does cally through the interface of soil? part of the environment to another? water play in a healthy ecosystem?

rey42432_ch17_534-563.indd 534 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 535

TOPICS IN THIS CHAPTER 1 7.1 How Is the Ecosystem Approach Useful 1 7. 9 What Is the Role of in Ecosystems? 552 in Understanding the Biosphere? 536 1 7.1 0 What Is the Role of in Ecosystems? 554 1 7. 2 What Types of Organisms Inhabit Ecosystems? 538 1 7.1 1 What Is the Role of in the Environment? 556 1 7. 3 What Interactions Occur in Ecosystems? 540 1 7.1 2 How Does a Lack of Harm Ecosystems? 558 1 7. 4 How Can Be Assessed? 542 1 7.1 3 CONNECTIONS: How Do 1 7. 5 How Does Through Ecosystems? 544 Impact U.S. Gulf Coast Ecosystems? 560 1 7. 6 How Do We Describe Ecosystem ? 546 1 7.1 4 INVESTIGATION: What Factors Influence 1 7.7 How Do Ecosystems React to ? 548 the Desert Ecosystems of Namibia in Southern Africa? 562 1 7. 8 What Is the Role of Carbon in Ecosystems? 550

Life 17.00.a8 17.00.a7 Various forms of life thrive in the tropical and mountain , including coatimundi (⊳), a mammal in the raccoon family, and colorful and interest- ing tropical birds, such as a toucan (⊲). The lush vegetation hosts other classes 17.00.a9 of animals, for example reptiles, including this eyelash snake, a venomous pit viper (⊲).

How do different types of animals interact, and what happens to their populations if they compete with one another or depend on one another? 17.00.a10 The rain forest is home to other small creatures, like this “poison- dart frog” (⊲), an amphibian, and The rain forest earns its name from the thick vegetation (the four countless types of insects, including photographs below) that forms a canopy and shades lower levels of ants that recycle vegetation and the ecosystem. Vines and other plants climb or drape on the trees, other materials that have fallen on trying to stay off the ground and gain better access to the light. Plants the ground (photograph on the grow brightly colored flowers to better attract insects that, in turn, bottom right). The number of pollinate the plants, a symbiotic relationship that helps the plants and species in an ecosystem is one the insects. measure of biodiversity. 17.00.a11 What does it mean for a relationship to be called symbiotic, and what What do we mean by biodiversity, other types of relationships exist between living organisms? and what can decrease biodiversity? 17.00.a14 17.00.a13 17.00.a12 17.00.a15 17.0

rey42432_ch17_534-563.indd 535 11/16/16 03:07 PM Final PDF to printer

536 17.1 How Is the Ecosystem Approach Useful in Understanding the Biosphere? IN AN ECOSYSTEM, organisms interact with individuals of the same species and with other types of organisms. The ecosystem is supported by various types of energy, matter, and processes, some that involve living organisms and others that involve nonliving components, like rocks, soil, and water. What Is Ecology? Ecology is the study of how organisms and populations of organisms interact with one another and the nonliving components of their environment. These interactions occur from the local to regional scale — the ecosystem. The intricate array of interactions within an ecosystem evolves in a way that promotes increasing efficiency in energy exchanges and nutrient cycling, because efficiency promotes survival. Ecologists study ecosystems, and biogeographers use ecological principles to explain the distribution of life — the realm of biogeography. Photographs below explore the Galápagos Islands (west of South America), one of the world’s truly unique and fragile ecosystems. 17.01.a1 17.01.a2 17.01.a3

Individual — Most living organisms exist as Population — Although many individuals spend Community — Not only do organisms interact individuals that can function somewhat significant time as solitary creatures, they are with others of their kind, but individuals from independently, at least for a while, such as this always part of a population of individuals of the different species interact, as part of a marine iguana, a type of lizard (reptile) that same species. The population can go up or community. Here, an ocean-dwelling seal started on land but forages in shallow waters. down as the ecosystem changes. sniffs a marine iguana. 17.01.a4 17.01.a5 17.01.a6

Biotic Components — Living plants and animals, Abiotic Components — Components of an Energy — All ecosystems require a source of along with materials such as digestive wastes, ecosystem not directly produced by living energy, in most cases ultimately derived from discarded parts, and decaying remains of organisms are abiotic components. These include the Sun. Insolation warms water and air, drives creatures, are the biotic components of an the air, rocks, soils, and water that provide a ocean currents, wind, and weather, and ecosystem. home for the plants and other organisms. provides energy for plant .

17.01.a7 17.01.a8 — Some species Ecological Niches — The live on land, such as this unique position of a species different species of iguana, in the ecosystem, especially whereas others live in the its role relative to the other water or air. The physical species, is called its environment in which a . How species , such as a would you characterize the rocky coast where it finds ecological niche of these its particular mix of food Galápagos fur seals? sources, is its habitat.

rey42432_ch17_534-563.indd 536 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 537 What Are the Structures and Functions of Ecosystems? All ecosystems consist of the storage and flow of matter and energy, and various interactions between an organism and other organisms. The components of an ecosystem can be categorized into structures and functions. Ecosystems also have a variety of spaces for a wide array of organisms to exist, both supporting and being supported by the ecosystem.

Ecosystem Structures 3. The biotic components include the 1. Ecosystem structures consist of the cow, the trees, the low bushes and biotic, abiotic, and energy components grass, and the roots of the plants. of the ecosystem. In most cases, these Other biotic components that are less are the tangible, observable aspects of visible, but certain to be present, an environment. Observe the ecosys- include insects, birds, burrowing tem structures shown in this diagram. animals, bacteria in the soil, fish, algae, and other organisms in the water. 2. In the site depicted here, the most obvious abiotic components are the 4. To understand this ecosystem, one land, water, and air. For the land, there of the first things we would want to do is the surface as well as the materials, is inventory the ecosystem structures. like soil and rocks, that are beneath the How many trees and cows are there, surface. Less obvious abiotic structures how thick is the soil, and what is the would include gases and small particles pH of the water? Biogeographers and in the air, the energy contained in ecologists do similar inventories and sunlight, nutrients in the soil, and quantitative measurements of structures chemicals dissolved in the water. 17.01.b1 in an ecosystem.

7. Other ecosystem processes involve Ecosystem Functions the atmosphere, such as changes in 5. Ecosystem functions are the dynamic the amount of sunlight from day to processes that occur in the environment night and season to season, the to support the ecosystem. This figure constant exchange of gases between shows a few of the processes that are the atmosphere and soil, water, and occurring in this scene. organisms (plants, animals, and microbes). Other processes include the 6. Some ecosystem functions occur on wind and evaporation, and at times or near the land surface. These include precipitation, which provides fresh the growth and other changes in the water to the system and causes the plants, including the sprouting of new processes of runoff and infiltration. plants, shedding of leaves, cycling (movement) of nutrients, the uptake and 8. A number of ecosystem functions release of water, and the eventual are also important but not so obvious. demise of organisms and return of their These include the capturing and components to the soil or other sites. converting of sunlight for photosynthesis (called fixation), of 17.01.b2 organisms, and chemical and physical weathering that slowly forms soil. The Aral Sea of Central Asia — A Dying Ecosystem Before You Leave n the 1960s, the USSR diverted flow in the Amu the sea, and the entire died. Toxic This Page Darya and Syr Darya Rivers to provide irrigation dust from the fertilizer and pesticides left behind as for agriculture, especially the Aral Sea evaporated has cotton.I Today, Uzbekistan is caused increasing instances Explain what ecology and an one of the leading exporters of of respiratory diseases and ecosystem are. cotton, but at what price? other ailments. This created Describe the difference When the streams were impacts on the land surface between habitat and niche. diverted, the Aral Sea, which that contributed to the Sketch and explain an example at the time was the world’s decline of terrestrial ecosys- that contrasts ecosystem fourth largest lake (left image), tems. The local temperature structures and ecosystem lost most of its inflow and has become more severe in functions. 17.1 became about one-tenth of its winter and summer, exacer- former surface area (right bating risks for drought and Discuss recent impacts on the image). The lack of inflow causing other severe human Aral Sea ecosystem. sharply increased salinity in impacts.

17.01.t1

rey42432_ch17_534-563.indd 537 11/16/16 03:07 PM Final PDF to printer

538 17.2 What Types of Organisms Inhabit Ecosystems? THE WORD “ECOSYSTEM” implies interdependencies and other interactions between different types of organisms and various other components in the environment. Together, the components and processes represent a complex and changing system. Most organisms are dependent on a particular setting, such as a fish needing water, but they are also dependent on other organisms, perhaps for nutrition, defense, or a place to live. There are some definite hierarchies that influence what happens in an ecosystem, and whether the ecosystem thrives or becomes threatened. How Do Organisms Depend on One Another for Food? Some organisms, most notably plants, extract what they need directly from the soil, water, air, and energy in the environment, but most other organisms are more interdependent, deriving their food from plants or from other organisms. In most ecosystems, there is a complex chain of interdependencies, called a .

Trophic Levels 3. If we consume the corn directly, we are a first-level , but if we 1. Organisms that acquire what feed corn to cattle and then drink the they need from the soil, water, cow’s milk, we are a second-level air, and energy of the environ- heterotroph. It takes large amounts of ment, without consuming other energy to grow corn — solar energy from organisms, are called . the Sun, energy to power the tractors, A plant, like the corn shown here harvesters, and trucks that get the corn (⊲), is a typical example of an from the field to the supermarket, and . Most plants absorb electrical energy to keep the corn nutrients and water from the soil refrigerated. If we eat as second- or and build their carbon-rich stems, higher-level , we require and

leaves, and roots from CO2 waste much more energy. At each stage extracted from the atmosphere. in this process, much energy is wasted, Other organisms may be involved generally as waste heat. A vegetarian 17.02.a1 in moving and processing diet would feed more people on the nutrients in the soil, but they are 2. Organisms that acquire their food from other organisms, same amount of farmland because this not consumed by the plants, such as from a plant, are heterotrophs. In the figure above, eliminates the intermediate trophic except in a few unusual cases. humans and cows are both heterotrophs. level(s) and associated waste of energy.

17.02.a2 TERTIARY Food Chains and Webs 6. Relationships between different types of organisms within an ecosys- tem are typically more complex than a single, linear . To rep- 4. One way to portray the depen- resent such complexities, we envision a network of links, forming a dence of one type of organism on food web (▼). The food web below incorporates the four types of another is to arrange them in the organisms from the food chain to the left, but adds other organisms order in which the consumption that are in the Great Horned Owl occurs, from bottom to top (⊳). The ecosystem. SECONDARYY CONSUMER autotrophs, represented by the three varieties of cactus, are at the base. 7. In this food They derive their nutrients from the web, an soil, water, and air, and their energy organism can from sunlight-driven photosynthesis. have several Coachwhip For this reason, autotrophs are also food sources Snake called primary producers. and be food for several PRIMARY CONSUMERCO 5. Grasshoppers eat parts of the organisms. A cacti, and so are first-level hetero- mouse can trophs. Snakes that eat the grass­ eat cactus or hoppers are second-level heterotrophs, grasshoppers, and owls that feed on the snakes are and be Grasshopper third-level heterotrophs. The sequenc- preyed upon ing of organisms from autotrophs to by owls or by PRIMARY PRODUCERSPR higher level heterotrophs is called a snakes, which food chain. One reason for this meta- are in turn Desert Vegetation phor is that the entire system (the preyed upon chain) can only be strong and survive by owls. if every link (organism) is present. 17.02.a3

rey42432_ch17_534-563.indd 538 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 539 , , , and 8. Different types of creatures prefer different kinds of foods. Some eat only plants, some eat only meat, some have diverse diets, and some find food in soils. Such food preferences control the position of that type of creature on a food chain or web.

17.02.a4 Africa 17.02.a5 Namibia 17.02.a6 Costa Rica 17.02.a7 Michigan

9. Carnivores exclusively or 10. Herbivores, like this elephant 11. Omnivores are creatures with 12. Detritivores eat , the mainly feed on animals. They (▲), eat plants. Grazing and brows- diverse diets that include plants, remains of decomposing (nonliving) include lions (▲) and similar pred- ing animals, like horses, goats, other creatures, and most any edi- plants and animals in the soil. ator cats, raptors, snakes and deer, and giraffes, are herbivores, ble things they find. These include Earthworms are the best known of other reptiles, and many insects. as are many birds (seed or fruit most bears, raccoons, coatimundi these, but others include milli- Carnivores that eat insects are eater), insects, and small mammals. (▲), some birds, small mammals, pedes, flies, and aquatic bottom also called . Some herbivores live in water. insects, fish, and humans. feeders, such as sea cucumbers.

Reproductive Strategies 17.02.a8 Kgalagadi Transfrontier Park, South Africa 17.02.a9 Sweden

13. We can group organisms based on their reproductive strategies. Some species, like humans, have few and infrequent offspring, in part to allow a longer period of protection and nurturing to increase their odds of survival. These are called K-selected species.

14. Other species have many offspring, resulting in a high reproduction rate, with the consequence that many of these offspring will not survive to adulthood. These are r-selected species. The letters K and r are derived from letters in an equation theorized to describe 15. K-selected species, such as these 16. r-selected species produce relatively populations. The r is lowercase, as it is in the equation. wildebeest (▲), have slow rates of frequent batches of numerous offspring, K- vs. r-selection is a continuum rather than two discrete reproduction and maturation, but have like lemmings (▲) and cockroaches. categories. strong and prolonged nurturing, with a Offspring mature faster but are less higher likelihood of survival into adulthood. supervised, and many do not survive.

Biomagnification and Food Chains s a chemical element or compound that replaced DDT are even more dangerous, and resurgence of malaria, which causes millions works its way up the food chain, it can the banning of DDT partially resulted in a of worldwide, mostly in tropical cli- become more concentrated, a process mates and in impoverished populations. calledA . Many toxins are biomag- nified with each step up the food chain. Higher- Fourth-Level Consumers level heterotrophs must consume many lower-level 13.8 ppm heterotrophs, which themselves consume many Before You Leave This Page autotrophs. Traces of heavy metals or other toxins taken up by the autotrophs may result in concentra- Third-Level Consumers 2.07 ppm Summarize the difference between tions high enough to cause illness or in their an autotroph and a heterotroph, predators or their predators’ predators. providing an example of each. DDT is a type of chlorinated hydrocarbon Second-Level Consumers 0.23 ppm used as a pesticide that has been banned in the Explain what a food chain or food U.S. since 1970. DDT is a substance that is bio- FirstFirst-Level-Level web shows, with some examples. magnified as it moves up the food chain, from ConsumerConsumerss 0.40 ppm Describe the differences between autotroph to higher level heterotrophs (▸). The what creatures generally eat and 17.2 banning of DDT has been linked to the comeback Producers two reproductive strategies. of the American bald eagle. There were trade- 0.04 ppm offs, however, because some of the pesticides Explain biomagnification. 17.02.t1

rey42432_ch17_534-563.indd 539 11/16/16 03:07 PM 17.3 The graph here ( here graph The time. versus individuals of number the plotting by tion popula a of reproduction rey42432_ch17_534-563.indd one. warm-adapted the of) expense the at (thrive out-compete will species cold-adapted the cools, region the of temperature the If tion. competi some is there so however, exists, overlap Some at times. area different same the in or areas different in are they because directly compete not do normally therefore They ranges. temperature different in best do species two the but niche, same the occupy (red) species warm-adapted and (blue) species cold-adapted a here, graph population the In ). same the consuming are (and niche ecological same the in are species two the if species, different from individuals will as resources, limited for compete 7. an is rate growth accelerating of type This offspring. more have offspring of offspring the as accelerates growth rates 4. Reproduction 540 with time, but at faster and faster faster and faster at but time, with increase to continues population The resources. unlimited of environment an in reproduction of impact the the original plant. original the of parts small from versions new grow cacti the contrast, In seeds. produce wildflowers These ways. different in reproduce animals and plants different and population, a sustain to required is 1. ihn pce ad ewe seis n involve and species between and species within both occur interactions These environment. their with and other each with ECOSYSTEMinteract AN IN ORGANISMS Some of these types of interactions result in benefits to all species involved, while others benefit the individual of one of survival. forindividual chances the other’s the benefit lowering others while involved,while species species all to benefits in result interactions of types these of Some

Reproduction Individuals within a species will species a within Individuals We can examine examine can We

— exponential growth curve. growth exponential

that is, the rate of population of rate the is, that What Interactions Occur Ecosystems? in

— ⊲

Some method of reproduction reproduction of method Some ) depicts depicts )

540

- 17.03.a1 Vulture Mtns.,AZ

POPULATION 17.03.a4 Growth Slow

POPULATION 17.03.a7 TEMPER- near its . In this graph ( graph this In capacity. carrying its near hovering off, level then and first at rapidly ecosystem its in increase will species a of population A capacity. carrying the called is population maximum theoretical This species. given a of individuals of number certain a support only can 5. does not decrease, but the rate of growth decreases. growth of rate the but decrease, not does AT IDEAL TIME Growth URE Rapid Cold-Adapted

In the real world, limitations dictate that an ecosystem ecosystem an that dictate limitations world, real the In Ve Species Growth ry Rapid

TEMPERATURE problem if resources are in short supply. short in are resources if problem a be also can species single a of members between Competition losers. and winners be to likely are there resources, sparse same the for compete dogs, wild and hyena as 2.

Competition Wa rm-Adapted Species Types of Interactions of Types reproduction, TEMPER- AT IDEAL TEMPERATURE OVERLAPPING URE

POPULATION — 17.03.a5 RANGE

If two or more species, such such species, more or two If Decreasing Growth CARRYING CAP Ra - tes TIME Growth Rates Increasing competition, ▲ Inflection position across space and a range of environmental conditions. environmental of range a and space across position for compete will species All species. preexisting the of or both one out-compete may it habitat, its of range the broaden to able is species new the If niche. ecological vacant newly the to occupy in move or arise may green, in shown species, third A species. two the between (areas) temperatures the in up opened has niche AC ) the population the ) Po

POPULATION ITY int TEMPER- 17.03.a2 Namibia AT IDEAL Cold-Adapted URE Species

TEMPERATURE , Species V 17.03.a6 Niche POPULATION New acant in CARRYING CAP var a on prey lions These disappears. or scarce is source food that if problematic becomes survival food, of kind one only on relies true also is opposite The strategy. good a never is creature other some 3.

OVERLAP Wa iety of first-order heterotrophs like antelope. like heterotrophs first-order of ­iety Predators and Prey and Predators NO decreases rapidly, or “crashes.” or rapidly, decreases population the and food, their all eat animals grazing when as such exceeded, is capacity carrying the when case a represent also can curve of kind This above. curve the in as pattern population a in resulting period, time short relatively Population TIME r Species m-Adapted Growth and , decomposition TEMPER- AT IDEAL 17.03.a8 Population URE AC Decline ITY overlap or compete at at compete or overlap not may they ranges, temperature ideal their in apart farther move species however, an ecological ecological an however, here, graph the of case the In time. same the at areas same the of any all 8.

— — If over time the two two the time over If

Being a food source for for source food a Being they do not inhabit inhabit not do they population growth ( growth population of cycle bust” or “boom a experience animals and plants of and dying in a a in dying and blooming, sprouting, mostly curve, of kind this exhibit flowers wild spring Many 6.

Many populations Many

— . 11/16/16 03:07 PM Final PDFtoprinter

if an animal animal an if survival survival ­ 17.03.a3 ­ ⊳ ). ). like wolves. like predators, keystone of removal the often is ecosystems on impact human harmful A expand. to populations other causes removal Their numbers. small their despite ecosystem the on effect strong a have they because interest great of are and chain food the of top the at are generally jaguars, and otters ecosystem. an in chain food and health the assess to low) very generally are (which ratios predator/prey study can We prey). (their heterotrophs level lower- than ecosystem the in numerous less be always will Higher-levelpredatorsshortage. of times in suffice may prey rey42432_ch17_534-563.indd anemone. the eat would that fish other away drives turn, in fish, The predators. off ward that tentacles stinging anemone’s the in refuge finds above clownfish The interaction. the from benefit 15. Symbiosis 10. of benefit to the species involved. species the to benefit of called species interaction some life-long other), close, the a on have impact detrimental a has involved species the of one only which (in 14.

Most predators have certain prey they prefer, but other but prefer, they prey certain have predators Most Unlike competition (in which both species have detrimental impacts on each other) or predation or other) each on impacts detrimental have species both which (in competition Unlike 17.03.a9 SecretaryBird,Namibia

—

Both species Both

17.03.a14 Indonesia 541

17.03.a12 CostaRica Keystone predators Keystone Predation tem relatively stable. relatively tem ecosys the keeps feedback negative This fall. also will population predator the low, too falls population prey’s the If stability. ecosystem’s the to contributing thereby capacity, carrying its exceeding from population prey’s their keep they species, other consume 9.

As heterotrophs ( heterotrophs As from the chameleon’s presence. chameleon’s the from return in little gains plant the but plant the from protection gains chameleon This interaction. the by unaffected largely is other the and benefits species 16.

Commensalism . There are three types, depending on the degree the on depending types, three are There symbiosis. Decomposition shoreline ( shoreline the along kelp instance for environments, marine in occurs also Decomposition material. complex more by followed in a tropical setting ( setting tropical a in as higher, are content moisture and temperature when faster is decomposition of rate The decomposition. for agents main the are fungi and Bacteria nutrients. inorganic into materials by and vores by organisms dead of consumption through occurs 13.

The final dissipation of usable energy in an ecosystem an in energy usable of dissipation final The , such as such , ⊳ ⊲ ) ). ).

— 17.03.a15 Namibia

One One , the breakdown of organic of breakdown the decomposition, - ⊳ ). Reactions break down glucose first, glucose down break Reactions ). heterotroph-autotroph) relationships ( relationships heterotroph-autotroph) 11. on a single species for predation. predation. for species single a on exclusively almost relies predator the when occur usually times lag minimal with relationships Such “bee-eaters.” of population the in increase an by and bees of number the in increase an by accompanied immediately almost is wildflowers in increase an above, graph the In predator). (i.e., consumer the of population the in increase resulting a and prey) (i.e., consumed the of population the in increase an between times lag short very display POPULATION the plant’s leaves and tomatoes. and leaves plant’s the decimate can which hornworm, tomato a by eaten being is plant tomato a above, photograph the In interaction. the from harmed is other the while benefit 17.

Some predator-prey (and predator-prey Some Wildflowers

Parasitism NORMAL L NORMAL L OW OW

— TIME Bee Eater -LEVEL POPULATIONS-LEVEL POPULATIONS

One species may may species One Bees Ecosystems andBiogeochemicalCycles detriti- 17.03.a16

17.03.a10 ▲ ) Before You Leave ThisPage

about 1/4 of a year. a of 1/4 about is case this in lag The lag. observed the in resulting young, new bear to predator the for months take may it but prey, of increased the of advantage take to increases population predator The summer. of onset the with increases rapidly but winter, the in sparse relatively is green) (in species prey the above, example the In again. increase to begin and decrease, increase, to prey the for required time the of 1/4 commonly increase in prey ( prey in increase an behind lags usually population 12. Explain the processes of processes the Explain two of populations how Explain different the explain and Sketch ecosystems. in symbiosis of types different three the and decomposition predation. and consumption, competition, of effects the under time, over change can ecosystem an in species ecosystem. an in growth population of patterns

POPULATION WIN

The increase of a predator predator a of increase The Prey

SUMMER 1/4 CYCLE

TIME ▲ 17.03.a13 Point Lobos, CA ). The lag is is lag The ). ONE CYCLE

WINTER Predator Final PDFtoprinter 11/16/16 03:07 PM

17.03.a11

SUM 541 17.3 17.4 month to month. to month and day to day from consistent relatively is that tropics, the like environment, an in best thrive they so and environment their of capacity carrying the near subsist dominant in tropical regions ( regions tropical in dominant more be to tend species) (K-selected rates reproduction low have and long-lived are that species example, For spatially. Asia. Southeast and Africa, America, South of forests rain tropical the in specifically tropics, the in is amphibians the called is present species of number The population). the (i.e., species that in individuals of number the indicates bar the of height the and species, different a represents bar color Each ecosystems. hypothetical simple, two in exist that species different of populations the number of individuals of any single species. species. single any of individuals of number the reduces tropics the in competition intense but ecosystems, polar than diverse more far are ecosystems Tropical richness. and populations both limit environment the of variability temperature and harshness environments, alpine or polar In disruptions. climatic major without exist can species many so year, the throughout similar are conditions atmospheric and length day areas, tropical In factor. abiotic limiting most rey42432_ch17_534-563.indd 5. 2. 1. 1. ecosystem. an in species those of lations the within pool gene the in variety unusual an is commonly,however,Most to refersspecies. there diversity if or species of number large a includes it if diverse considered AREA AN IN LIFE VARIETYOF THE 542

This map shows that the richest areas for for areas richest the that shows map This show graphs two These With regard to biodiversity, climate is the the is climate biodiversity, to regard With The types of organisms also differ differ also organisms of types The richness. richness of amphibian species around the world. Similar maps exist for mammals, birds, reptiles, and other creatures. other and reptiles, birds, mammals, for exist maps Similar world. the around species the showsamphibian below of map richness The geographically.varies ecosystems of biodiversity world, our of attributes other most with As population surveys are examined for two measures of biodiversity: of these measures of two results for examinedThe are whole. surveys a population as population a to extrapolating involvessur then inventory and population subpopulation a generallyor but area individual, representative each a veyingcount to possible is it cases, few a In site. field working bya commonly in ecosystem, an in individuals of number the of inventories complete biogeographers and Ecologists How Biodiversity Can Be Assessed? How DoesBiodiversityVary Geographically? What AreSomeSimpleIndicatorsofBiodiversity?

542

⊲ ). They They ). species to three. to species seven of score a by graph), (right B Ecosystem in than A Ecosystem in 2.

POPULATION The richness is greater greater is richness The

Ecosystem A

SPECIES

° 0 6° 90° 60° 30° 0° POPULATION biodiversity in tropical areas than in single-layered ecosystems, such as grasslands. as such ecosystems, single-layered in than areas tropical in and biodiversity richness higher the to contribute also canopies, tree multi-layered as such environment, 3.

is its is All other factors being equal, a more complicated vertical structure and variety of the physical physical the of variety and structure vertical complicated more a equal, being factors other All 17.04.a1

K-Selected , which can be expressed in various ways. An ecosystem can be can ecosystem An ways.various in expressed be can which diversity, LATITUDE present have a more more a have present species the but species, populations. same the about have distri even 3. biodiversity POPULATION Ecosystem B has fewer fewer has B Ecosystem

r-Selected

Ecosystem B

SPECIES bution ­ 17.04.b2

—

— 17.04.a2

they all all they

the number of species and the evenness of the popu the of evenness the and species of number the and richness at high latitudes. high at resources limited more the to response in partly feeders, opportunistic more generally are heterotrophs r-selected spring. the in blooming and growing rapidly behavior, reproduction of type this display weeds Most survival. species for reproduction rapid necessitates precipitation, and daylight, of hours of number temperature, as measures such in environment, ever-changing the because regions, alpine and polar in live to tend species) (r-selected rates 6.

Species that are short-lived and have high reproduction reproduction high have and short-lived are that Species Shannon Index indicates a diverse ecosystem. diverse a indicates Index Shannon the of value high A equitability. and richness the called diversity ecosystem of measure a calculate then and populations the inventory ecologists and Biogeographers biodiversity. to related be not may or may which present, species all of population total the account into takes variables these of neither that Notice biodiversity. of components two are equitability and Richness distribution. uneven more a has which A, ecosystem in that than greater is B ecosystem of equitability The ecosystem. the of species in an ecosystem is known as the as known is ecosystem an in species 4.

The evenness of the populations of different different of populations the of evenness The equitability. (S), which incorporates both both incorporates which (S), Index Shannon 17.04.b1 upslope in mountains. in upslope and poleward decrease to tends biodiversity equator, the to closer richness overwhelming the of because but latitude, increasing with increases here) shown (not equitability ecosystems, 4.

In some types of of types some In 11/16/16 03:07 PM Final PDFtoprinter equitability - -

Final PDF to printer

Ecosystems and Biogeochemical Cycles 543 Why Is Biodiversity Important and How Is It Threatened? Lack of, or loss of, biodiversity is a major concern in many parts of the world. Degradation of ecosystems results in loss of species and a loss of individuals of some species but not others — loss of diversity. It is difficult to gauge what such losses represent, in part because we do not yet understand the role of many species in their ecosystems or the potential uses of these species, such as for medicine. Importance of Biodiversity 1. Human Health and Medicinal Uses — Some species have properties that are used to treat ailments and disease. Aloe vera (⊳) is a succulent used to treat burns and other skin discomforts. Aloe vera is thought to be extinct in the wild, but it persists because it is widely cultivated. Maintaining biodiversity in plant, bird, and mosquito populations protects us against emerging diseases, such as West Nile virus.

2. Aesthetic and Spiritual — Many places, such as this temperate rain forest (⊲), owe their special aesthetics to a delicate balance between the environment and the living organisms 17.04.c1 that inhabit these special places — that is, the ecology. Disturbing one component could have positive or negative feedbacks, inducing unanticipated consequences. 17.04.c2 Forks, WA

3. Food Security — Genetic diversity in agricultural lands (⊳), like different kinds of corn, ensures variety in food supply and flexibility for future breeding stocks — an “insurance policy” against the impacts of a new plant disease, or climate variability or change.

4. Environmental Ethics — Animals and plants belong in their natural habitats, and humans should try to keep these ecosystems as undisturbed as possible. This goal conflicts to some degree with the goal of ecotourism, especially in fragile places like the penguin colonies and biologically rich offshore waters of Antarctica (⊲). 17.04.c3 Eastern Colorado

5. Buffers Against Extreme Events — The “checks and balances” in diverse ecosystems 17.04.c4 Antarctica protect the ecosystem, for example, against the effects of storms (⊳), and allows the ecosystem to continue to provide structures and functions, many of which help people.

6. Ecotourism — Loss of wild animals threatens the ecotourism industry of ecologically threatened places, such as tropical rain forests and coral reefs around the world, the habitat of the mountain gorillas of central Africa, the lemurs and other unusual wildlife of Madagascar, and the fragile island ecosystem of the Galápagos (⊲).

17.04.c5 Pemaquid Point, ME Threats to Biodiversity 17.04.c6 Galápagos 7. Biodiversity is threatened by many human activities, including clear-cutting of forests for farms and timber (⊳), especially when this occurs in species-rich tropical rain forests. Densely planted “energy crops” are grown in tropical ecosystems to provide biofuels as a way out of poverty, but at a cost to biodiversity. Equally harmful is the growth of communities and the building of roads into previously pristine ecosystems.

8. Another threat to biodiversity is contamination (⊲). Government contractors released millions of gallons of toxic mine waters down the Animas River of Colorado, threatening ecosystems downstream in this river and in the San Juan River and Colorado River, into 17.04.c7 Eastern Mississippi which the Animas River flows.

17.04.c8 Animas River, CO Protecting Biodiversity here are no easy answers to pro- In some regions, species have been tecting global biodiversity, but sev- reintroduced to areas that were once their Before You Leave This Page eral solutions, in combination with habitats, but from which they have disap- Tone another, may offer the best hope. peared. This usually involves harvesting a Explain the components of biodiversity. Wildlife and nature preserves have been select number of plants and animals from Sketch or describe how and why biodiversity successful in protecting delicate ecosys- an ecosystem where they are thriving and varies across latitudes and altitudes, tems from too much human intrusion. safely transporting them to their new including the difference in spatial distribution Some of these preserves are the result of locale. This acts as an insurance policy if between K-selected and r-selected species. 17.4 governments and legislation, but others some calamity strikes the place from are created with private funds, completely where the organisms were harvested. Gene Summarize the importance of biodiversity, outside of any government. Both and seed banks provide “insurance” for the how it is threatened, and ways to protect it. approaches work if done thoughtfully. long-term survival of species.

rey42432_ch17_534-563.indd 543 11/16/16 03:07 PM Final PDF to printer

544 17.5 How Does Energy Flow Through Ecosystems? ENERGY IS AS FUNDAMENTAL to all ecosystems as it is to the rest of the universe. Unlike nutrients and water, energy is not recycled; instead it flows through or is stored by systems. Energy can be converted from one form to another in the way that electromagnetic energy from the Sun causes moisture to evaporate and rise, gaining latent heat and potential energy, but energy is neither created nor destroyed, only converted from one form to another. How Do Energy and Chemical Substances Flow Through Ecosystems?

5. As processes occur in ecosystems, heat, chemicals, nutrients, and water Inputs and Outputs are the output. In other words, these can be released from the living matter 1. Any system, including an ecosystem, through waste heat, respiration, has inputs and outputs of energy and transpiration of water from leaves, matter, accompanied by storage or decomposition, or waste products. processing of energy and matter within Strong ecosystems are generally the system. Inputs to an ecosystem more efficient than weaker ecosys- consist of energy and materials such as tems, but no ecosystem can be 100% nutrients, soils, and water. Some of efficient. Some energy and matter are these materials are stored in the living 17.05.a1 always wasted. tissue of organisms. 4. Processes in the ecosystem that 2. If inputs of energy and matter come 3. Energy and matter can be stored in the ecosystem, as magnify the flow of energy or matter from outside the system, we refer to resource reservoirs, for later use. Energy and matter also flow through the ecosystem are positive this as an open system. A plant is an through the ecosystem as producers, or autotrophs, use the feedbacks. Negative feedbacks open system, receiving energy from the energy and matter for sustaining life. Heterotrophs consume reduce the flow, maintaining them Sun, water and nutrients from the soil, the autotrophs or materials produced by autotrophs, acquiring within an acceptable range. and exchanging gases with the air. energy and matter in a less direct manner.

Flow of Energy Through an Ecosystem 6. The figure below illustrates the efficiency of energy transfers, expressed as percent- ages, at each step from Sun to producers to consumers, up the food chain. The waste heat is represented by purple arrows escaping from each step in the energy transfer up the food chain or food web. Examine the figure and then read on.

Fusion Reactions PRODUCERS PRIMARY PRODUCERS SECONDARY CONSUMERS TERTIARY CONSUMERS (Autotrophs) (Heterotrophs) (Heterotrophs) (Heterotrophs)

Photosynthetic Herbivores Carnivores Usually a Radiant Organisms “top” Energy 50% 50% 50% 50% Radiant Chemical Chemical and Chemical and Chemical and Energy 1% USED BY Energy 10% Mechanical Energy 10% Mechanical Energy 10% Mechanical Energy AUTOTROPHS CONSUMED CONSUMED CONSUMED BY HETEROTROPHS BY HETEROTROPHS BY HETEROTROPHS

40% DECOMPOSED 40% DECOMPOSED 40% DECOMPOSED 50% DECOMPOSED Energy Loss Through 17.05.a2 Respiration and Waste Heat Detritivores (consumers that feed at all levels) recycle matter, but not energy, throughout the biosphere.

7. The First Law of Thermodynamics states that energy 8. The Second Law of Thermodynamics states that when energy transfer occurs, can be neither created nor destroyed, but merely trans- some will be changed into less useful energy (waste heat) — energy can never be ferred from one form to another. In ecosystems, organisms transferred with 100% efficiency. Within ecosystems, energy is transferred from one cannot generate their own energy but instead they must organism to another as moves through the system. As shown in this acquire it from other sources. The fusion reactions on the figure, only about 10% of the energy is transferred from one level to the next, with Sun’s surface release solar radiation (insolation) that the rest being waste, either physical waste that is decomposed or waste heat that provides energy for the vast majority of autotrophs on escapes into the environment. With so much waste along the way, only 1% of the Earth. Likewise, heterotrophs rely on the energy acquired energy, or less, used by autotrophs reaches the higher-level heterotrophs at the by autotrophs or by other heterotrophs. top of the food chain or food web.

rey42432_ch17_534-563.indd 544 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 545 How Does Photosynthesis Work? The amount of energy flowing through an ecosystem depends on the amount captured, or “fixed,” by autotrophs. This is accomplished mostly by photosynthesis within plants and algae. The resultant energy is transferred to higher trophic levels through consumption of autotrophs by heterotrophs. 1. Plant cells and some algae have specialized organelles called , which capture insola- Insolation + 6CO + 6H O C H O + 6O tion and produce sugar during photosynthesis, as represented by a simplified (⊲): 2 2 6 12 6 2

2. There are two components of photosynthe- 5. C plants tend to thrive in 17.05.b1 4 sis. The first, the light reaction, occurs when hotter and drier environ- chlorophyll in the chloroplasts “fixes” insola- ments because the C4 tion, exciting electrons. The energy released pathway reduces water loss by the electrons is used to make molecules of through pores on the plant’s ATP (adenosine triphosphate) and a phosphate leaf (called stomates). compound called NADPH. The ATP transfers Agriculture in such environ- energy among the cells and is recycled over ments sometimes involves C4 and over, in slightly differing forms, releasing crops, such as sorghum and O in the process. 2 sugarcane. Many plants can 3. The second component, the “Calvin cycle” expand their habitats by carrying on C photosynthesis phase of photosynthesis, occurs even in the 3 absence of sunlight, as long as ATP and in some parts of the leaf and C in others. Still others NADPH remain available. ATP and NADPH fix 4 CO from the air to create organic molecules (known as CAM plants) may 2 conduct C photosynthesis at (sugars) that are energy to the plant. 4 some times and C3 at others, in an effort to enhance their 4. Most green plants create 3-carbon-based molecules in photosynthesis. These are known as C3 plants. However, in the 1960s, it was discovered that some plants can form a 4-carbon molecule instead of 3-carbon chance of survival.

molecules. These are called C4 plants.

17.05.b2 17.05.b3 6. This graph (⊳) plots the rate of 7. This graph (⊳) compares the rate of

C4 photosynthesis as a function of the photosynthesis as a function of leaf amount of incoming radiation (light) for C temperature for C and C plants. Both C 3 C4 3 4 SYNTHESIS SYNTHESIS 3 and C plants. At low levels of radiation types of plants have a peak tempera- 4 C (not much light), the rate of photosynthe- 3 ture for production (where they are sis increases at about the same rate for most efficient), but that rate is higher

both types of plants as light increases. at higher leaf temperatures in C4

However, at higher light intensities, plants than in C3 plants. What habitat RATE OF PH OTO RATE RATE OF PH OTO RATE increased energy is available to power would a C4 plant most likely occupy? RADIANT INTENSITY LEAF TEMPERATURE the C4 plants relative to the C3 plants. Warm conditions favor C4 plants.

Other Energy Sources in Ecosystems lthough photosynthesis is by far the then becomes the fundamental power source for something, in this case for extreme conditions. most important mechanism for fixing the autotrophs in the ecosystem. Amazingly It is an antonym to the suffix “phobe,” which the energy that supports ecosystems, it productive and diverse ecosystems have been refers to an aversion to something. isA not the only mechanism. In places where sun- discovered at hydrothermal vents on the deep light is unavailable, such as the deep ocean floor ocean floor. These rely on energy from the oxi- and within Earth’s subsurface, dation of hydrogen sulfides in organisms must rely on an alter- and support native energy source. Chemosyn- eerie life forms, such as tube thesis is a process by which worms. It has been proposed Before You Leave This Page inorganic compounds, such as that any life discovered on or diatomic other planets may rely on che- Sketch and describe how energy and hydrogen, make energy available mosynthesis to convert energy chemical substances flow through for the synthesis of organic mol- to usable forms. Organisms ecosystems in the context of the First ecules when combined with oxy- that live in these extreme envi- and Second Laws of Thermodynamics. oxidation gen (in the process of ). ronments, for example scald- Describe how photosynthesis works,

In chemosynthesis, carbon is ing hydrothermal vents at the 17.5 explaining the differences between C3 extracted (usually from carbon very high pressures of the and C species. dioxide or methane) and converted deep seafloor, are called 4 into organic materials. Energy extremophiles. The suffix Briefly describe chemosynthesis. released in chemosynthesis “phile” means an affinity for 17.05.t1

rey42432_ch17_534-563.indd 545 11/16/16 03:07 PM Final PDF to printer

546 17.6 How Do We Describe Ecosystem Productivity? ENERGY DRIVES ALL BIOTIC PROCESSES and is therefore vital for the health of an ecosystem. Energy input, in the form of insolation, is measured in watts per square meter or in calories. Autotrophs convert this energy into organic molecules, but efficiency cannot be 100%. In examining the flow of energy and matter up through the food chain, we begin by quantifying the energy initially fixed by the autotrophs.

What Is Primary Productivity? To compare the relative productivity of ecosystems, we calculate a variable known as the net primary productivity (NPP). This is the total amount of energy fixed for photosynthesis, which is the gross primary productivity, minus the energy wasted or used for plant respiration and maintaining existing tissue. Net primary productivity represents the plant growth rate and is expressed in grams of carbon in new growth (or ) per m2 of surface area per year (g/m2/yr). The map below shows the average annual distribution of NPP on land, as estimated from satellite data of vegetation greenness and solar radiation absorption. Observe this map and try to explain the larger patterns.

17.06.a1 1. On land, differences in 2. The lowest NPP is NPP can be estimated at high latitudes. This using a factor called the is mostly due to the Normalized Difference limited and inconsis- Vegetation Index (NDVI). tent amounts of inso- The index and associated lation and the low NPP show the amount of humidity of cold air. trees, shrubbery, grasses, Most deserts also and other plants. On this have low NPP. map, darker greens indi- cate higher NPP, whereas 3. The highest NPP is brown and white indicate in tropical rain forests, much lower NPP. Gray such as those in mari- indicates essentially no time Southeast Asia, NPP, as in the ice- central Africa, and the covered land and some Amazon basin of sand-covered deserts. South America.

4. Land and sea have such different characteristics that we use 6. The highest chlorophyll 7. In the open ocean, some of different measures of NPP for each. In the oceans, we can use concentrations, which indicate a the highest chlorophyll concen- satellites to measure the concentration of chlorophyll, which is a high abundance of phytoplankton trations are in the mid- and measure of NPP. Chlorophyll is produced mostly by phytoplank- and high amounts of productivity, high-latitude oceans, such as ton, which are microscopic photosynthesizing organisms, whose are along the edges of the conti- between Europe and North name is derived from the Greek words for “wandering plant.” nents and in shallow seas, such as America, adjacent to the Arctic For the oceans, red and orange indicate the highest chlorophyll the Baltic Sea in northern Europe. Ocean, and east of Japan. (NPP), purple and blue indicate the lowest NPP, 8. Much of the ocean and yellow and green rep- is relatively unproduc- resent intermediate tive (blue and purple), particularly in areas values. beneath the subtropi- cal highs. Values are 5. Observe the patterns only slightly higher on this map and identify along the equator. which settings in the ocean generally have the 9. Locally high pro- highest and lowest NPP. ductivity occurs in Try to explain these pat- areas where upwelling terns, using such factors brings nutrients into as latitude, proximity to shallow-enough levels land, ocean currents, and for photosynthesis. areas of upwelling (all One obvious area of presented elsewhere in upwelling is along the 17.06.a2 this book). west coast of Africa.

rey42432_ch17_534-563.indd 546 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 547 What Factors Control Primary Productivity? The primary productivity of an area depends on many factors, some that operate at global or regional scales and others that result from local conditions. We present a few factors below, but there are many more than are presented here. Global and Regional Influences 1. These globes present three 17.06.b1 17.06.b2 17.06.b3 important factors in productivity (from left to right): (1) a measure of the length of the growing season, called growing degree days, which conveys the number of days that were warm enough for plant growth; (2) the average amount of precipitation, and (3) the soil conditions, here expressed as soil pH, where red is acidic and purple is alkaline. Compare these three maps with the map that shows NPP on land (on the left page). What patterns do you observe?

2. Using just these three examples, you can gauge how productivity includes complex 3. Light-use efficiency is the energy fixed interactions between many factors that vary spatially, requiring a geographic approach. during photosynthesis as a percentage of total available energy in insolation. It is measured as the ratio of calories of har- Local Influences vested vegetation to total solar energy The figure below illustrates some of the local factors that affect NPP. intercepted. Even in the most productive 7. Shading by ecosystems, less than 10% of the available 4. Intensity of insolation higher trees limits insolation is converted successfully (▼). Note depends on Sun angle the amount of in the table below how inefficient is the use and cloud cover. Low Sun sunlight for plants of sunlight, particularly in the central and angles and more clouds closer to the northern parts of North America. mean less insolation and ground, affecting therefore less NPP. their growth. 5. Air and surface June – September Light-Use temperatures can trig- 8. Other factors Efficiency (%) ger germination, cause include wind, the Cornfield near Champaign, Illinois 2.2 plants to lose too much steepness of water, and wilt. They slopes, which Tall-grass prairie near Manhattan, Kansas 1.7 also influence leaf size. 17.06.b4 influences water Mid-latitude forest near Athol, 1.8 6. Soil is required by most plants, and plants grow better retention and soil formation, and Massachusetts if there is a good supply of soil nutrients and moisture. the abundance of plant eaters. Boreal forest in north-central Manitoba, 1.0 Canada 9. We can calculate the ratio of energy demand by the human population (Human Appropria- tion of NPP or HANPP) to total NPP. When the ratio, expressed as a percentage, exceeds 100%, the local ecosystem cannot support its human population. Such areas are shown here in orange and purple. How are such populations sustained? 17.06.b5 Before You Leave This Page

Explain the concept of net primary productivity. Describe the spatial variations of NPP, both globally and locally, and explain why those variations exist. Identify the relationship between 17.6 human population and capacity of the local to support those populations.

rey42432_ch17_534-563.indd 547 11/16/16 03:07 PM Final PDF to printer

548 17.7 How Do Ecosystems React to Disturbance? DISTURBANCES SUCH AS FIRE, storms, or human interference are common to most ecosystems. Following the disturbance, an ecosystem may remain largely unaffected, try to rebound from the disturbance, or start over. As an ecosystem recovers from a disturbance or tries to colonize new land, a succession of organisms may populate the area. While it is tempting to think of disturbance as endangering or destabilizing an ecosystem, disturbances can promote the stability of some ecosystems. How Does Disturbance Affect Ecosystem Stability? Ecosystem stability refers to the degree of fluctuation in population of species over time. Buffering mechanisms help species avoid stress and thrive. For example, animals may hibernate during times of the year when food is scarce, or plants may go dormant in the winter or evolve to tolerate a wider range of conditions. When these buffering mechanisms allow populations of all species within the ecosystem to stabilize, the ecosystem is said to be in balance, or stable.

17.07.a1 1. This graph shows how the populations of three 3. The middle curve shows a species whose species, in three different ecosystems, change over Stable, High Population population varies widely with time, including time. The top curve represents the population of an some abrupt increases and decreases. This abundant species. The number of individuals varies ecosystem is unstable and vulnerable to a only slightly over time, so the ecosystem, as measured population crash due to some event or change by this species, is stable. This species and its Unstable in conditions. This generally occurs in ecosys- ecosystem can withstand environmental stresses Population tems that are considered to be less mature.

without experiencing drastic changes in populations. POPULATION Stable, Low Population 4. Some ecologists argue that energy constraints 2. The bottom curve depicts a species with fewer prohibit the stabilization of ecosystems, such as individuals. The population of this species is also stable. when there is not enough energy to withstand TIME the addition of a new predator species.

17.07.a2 17.07.a3 LETHAL LIMIT LETHAL LIMIT LETHAL LIMIT LETHAL LIMIT LETHAL LIMIT 5. Organisms generally 7. Some species have LETHAL LIMIT OPTIMAL OPTIMAL RANGE have a limited range of RANGE wider optimal ranges and conditions (⊲), such as stress zones than others STRESS STRESS temperature and mois- (⊲). An organism that can ZONE ZONE ture, in which they can STRESS STRESS tolerate a wide range of STRESS STRESS survive. The levels at ZONE ZONE conditions for a given ZONE ZONE POPULATION which these conditions POPULATION “Eury” Species abiotic factor (e.g., “Eury” Species “Steno” become too high or low temperature) is described OPTIMAL Species for that organism to with the prefix of “eury-” RANGE survive are known as before a root word that ENVIRONMENTAL VARIABLE ENVIRONMENTAL VARIABLE the lethal limits. (Temperature, Moisture, Salinity, Etc.) refers to the factor, as in (Temperature, Moisture, Salinity, Etc.) euryhaline for a creature 6. Within the lethal limits exists an optimal range of conditions that can tolerate a wide 8. In contrast, some species can only tolerate under which the organism tends to thrive, resulting in a relatively range of salinities. On a narrow range of conditions for a given large population. If conditions fall outside the optimal range but the curve to the right, a environmental factor, as represented by the inside the lethal limits (the “stress zone”), the organism can “eury” species would be black curve (▲). They are given a prefix of survive but does not prosper, so the population will be low expressed by a broad “steno,” as in a stenohaline species that cannot under these conditions. curve of tolerances, tolerate changes in salinity or stenothermal for represented by the a species with a narrow range of tolerable green curve. temperatures. Inertia and Resilience 11. Over the last 200 years, many 9. There are two other important components of scientists have viewed the natural world ecosystem stability. One is the ability of an in the context of uniformitarianism — the ecosystem to resist change after a stress is concept that the natural world has applied — inertia. If an ecosystem is relatively evolved in the past by processes and stable, it may not respond or may respond slowly rates similar to those we observe today. to an imposed change, like a decrease in rainfall At the opposite end from uniformitarian- at the start of a drought. It has inertia. ism is catastrophism, which emphasizes the importance of sudden events in 10. The other is resilience, the rate at which an creating change. The eruption of Mount ecosystem recovers following stress. For example, St. Helens was a perfect example of an the area around Mount St. Helens was devastated abrupt catastrophe to the ecosystem, by a volcanic eruption in 1980. Since that time, the but the recovery of the ecosystem is vegetation has recovered quite rapidly (⊲). an example of uniformitarianism. 17.07.a4 Mount St. Helens, WA

rey42432_ch17_534-563.indd 548 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 549 What Is the Process of Succession? Disturbances tend to cause great fluctuations in populations, as stresses affect species in different ways. The ecosystem typically responds with a predictable change in species composition, called succession. If the successional process begins with the formation of new land or with so much disturbance that little life is able to survive the disturbance (as in glaciations), the recovery process is a primary succession and begins with a pioneer community. Secondary succession occurs when soil is present in the landscape from the outset, as occurs in an area affected by a forest fire — the vegetation is destroyed but the soil is largely unaffected. Succession can lead to a stable community.

1. This figure shows the stages of 3. With time, K-selected 4. The final stable community, called a , develops recovery in a primary succession species, such as tree species, and includes an intricate food web and efficient nutrient cycling, with with early stages on the left and become possible and begin to the diversity and productivity determined by the abundance or lack of later ones on the right. The dominate the ecosystem. necessary abiotic factors, specifically sunlight, water, and nutrients. underlying graph shows a typical sequence of 5. The concept of patch species replacement as dynamics refers to the idea that the ecosystem evolves. subareas within an ecosystem may be influenced by different 2. A pioneer processes and are at different community successional stages at the contains mostly same time. Over time, a climax r-selected community may be disturbed species, and then reestablish a new including mosses climax community. and lichens.

17.07.b1 6. Biodiversity increases in the early successional stages, but eventually it 8. Before the establishment of a climax community, more decreases as nutrient cycling becomes more efficient and competition energy is fixed by autotrophs than is consumed by respiration weeds out less robust species. Different species have differing abilities to in the ecosystem. deal with disturbance, even in the same ecosystem. 9. At the time when the climax Gross Primary community is established, the 7. The resulting distribution of species (⊳) Productivity total energy fixed (gross primary after this steady-state “endpoint” is productivity) will nearly balance achieved (some time after the ecosystem energy expended in respiration. was disturbed) represents the climax community. K-selected species become CLIMAX 10. After the climax community is increasingly favored, and r-selected Respiration established, nearly all of the SHANNON INDEX

species are at an increasing disadvantage AMOUNT OF ENERGY energy available is used in CLIMAX at greater times after the disturbance. respiration to break down food. 17.07.b2 TIME 17.07.b3 TIME

How Does Disturbance Affect Biogeochemical Cycles? An important aspect of how ecosystems become established, evolve, and die is the concept of a biogeo­chemical cycle. A is a way to conceptualize chemical connections between various components of an ecosystem — land, groundwater and surface water, oceans, ice, air, and organisms.

This figure illustrates the main aspects of a biogeochemical cycle. Arrows indicate how some , for example carbon, flows between various compo- nents of an ecosystem (a flux), including between the soils, biota, atmosphere, and oceans. Typically, the amounts of that chemical substance are listed next to each arrow to convey the magnitude of the flux and how some change in the ecosystem could affect the ecological balance. Ecosystems store and cycle nutrients, so any changes Before You Leave This Page in that ecosystem will be felt in the biogeochemical cycles Explain the concept of ecosystem involving them. This, in turn, can stability. affect other ecosystems. The following pages have biogeo- Give examples of primary and

chemical cycles for carbon, secondary succession resulting from 17.7 nitrogen, phosphorus, and sulfur, a disturbance of the land. but others exist for many other chemical elements and Describe a biogeochemical cycle. compounds. 17.07.c1

rey42432_ch17_534-563.indd 549 11/16/16 03:07 PM Final PDF to printer

550 17.8 What Is the Role of Carbon in Ecosystems? OF THE 92 STABLE ELEMENTS, only 17 are essential for all plants, and a few more are vital for animals. The nutrients formed by these elements must be recycled continuously through all of the “spheres” of the Earth to sustain life — forming biogeochemical cycles. Despite its very minute abundance on Earth, carbon (C) is the element that forms the building block for life. Organic molecules contain the carbon-hydrogen bond and include carbohydrates, lipids, proteins, and nucleic acids, all found in the many life-forms in ecosystems. What Processes Are Involved in Carbon Storage and Cycling? 17.08.a1 1. This figure depicts the 5. The C emitted by human global as a activities (red arrows) to the series of arrows that show atmosphere, while small, the direction in which car- causes imbalance in the sys- bon moves between com- tem. Of this anthropogenic

ponents of the environment.­ CO2, some is cycled back to The number with each the surface by enhanced arrow indicates how much photosynthesis by plants, carbon moves along that some remains in the atmo- pathway (the flux), and sphere, and some goes into numbers next to the main the ocean. storage sites (stores) of carbon (e.g., oceans) indi- 4. The C going into and cate how much carbon is out of the oceans would in that reservoir. In both balance naturally, but two cases, the amounts are in units of the extra units pro- gigatons (1015 gm or a duced by people are quadrillion grams). Some absorbed by the ocean, of these values are not causing acidification. Over known precisely, so they long timescales, this extra are educated guesses. carbon is cycled to the ocean floor as sediments.

2. Over time, Earth’s atmospheric CO2 was moved to the lithosphere as carbonate 3. Notice that the exchange of carbon between two res- rocks formed over geologic time in a cycle so slow that it is considered to be in ervoirs is essentially balanced. For example, 120 gigatons “storage” rather than in a cycle. So the amount stored in the lithosphere is much goes from the atmosphere to land in the form of gross greater than that stored in the atmosphere. When considering the flux of carbon, we primary production (photosynthesis) and almost the same mostly focus on the amount in fossil fuels, not the entire lithosphere. amount goes from the land to the atmosphere.

How Do Humans Impact and Become Impacted by the Carbon Cycle? The production of greenhouse gases through fossil fuel combustion is the most obvious way that humans impact the C cycle, but deforestation and other land-use changes also add carbon to the atmosphere. Aside from and its

associated impacts, elevated atmospheric CO2 also increases weathering and decay rates by forming carbonic acid.

17.08.b1 17.08.b2 Central British Columbia, Canada 17.08.b3 Washington 17.08.b4

1. Fossil fuel combustion for 2. Most of the other 5% comes 3. Deforestation reduces the 4. Crops remove C from the industrial, transportation, and from cement production, which amount of plants, which in turn atmosphere, but the problem is domestic uses amounts to about grinds up and processes carbon- reduces the amount of carbon that that they are usually only sea- 95% of the C that people emit to ate rocks (limestone and marble), is extracted from the atmosphere. sonal. They often replace forests the atmosphere. releasing C as a by-product. Changes in the rate of deforesta- that would have removed much tion can affect the carbon balance. more atmospheric carbon.

rey42432_ch17_534-563.indd 550 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 551 How Does the Carbon Cycle Regulate Earth’s Long-Term Temperature? The massive quantities of stored C may change on timescales of millions of years through feedbacks tied to the global water

and rock cycles. As atmospheric CO2 concentration changes, so does the global climate.

1. Falling rain or snow moves CO2 from the atmosphere to the lithosphere 7. By this process, some of the stored carbon gradually moves after it reacts with the precipitation to form a weak acid called carbonic back to the atmosphere, which then slowly intensifies the acid (H2CO3). This loss of CO2, a greenhouse gas, can cool the atmosphere. greenhouse effect and warms the Earth again. 17.08.c1

2. If the acidic 6. CO2 dissolved in magma precipitation falls on rises with the magma toward land, the H2CO3 the surface. As the magma causes increased nears the surface, the reduced rates of chemical pressures allow the CO2 to weathering. This escape, either as a slow type of chemical outgassing or in a quick weathering release during an explosive (hydrolysis) volcanic eruption. In either releases ions of case, the CO2 goes back calcium and other into the atmosphere. elements into surface waters and groundwater. 5. Some of the oceanic 3. Overland flow and streams move the sediments are taken to ions to the ocean. and shell- depth and heated, liberat- building organisms, as they grow, convert ing CO2 from the hot rock. the calcium ions to calcium carbonate 4. Plate tectonics moves limestone and its carbonates very Some CO2 rises toward the (CaCO3). When they die, the CaCO3 falls to slowly over millions of years to subduction zones. Most of the surface, mostly in dissolved the ocean floor to become limestone, chalk, sediment is plastered against the overriding plate, effectively magma. or other types of seafloor sediments. taking the enclosed carbon out of the cycle for a while.

8. How effective the system is — and whether it leads to 9. Periods in geologic history with abundant mountain building may offer more warming or cooling overall — is affected by several factors. If opportunity for chemical weathering, which stores extra carbon in the lithosphere. most limestone and other carbonate-bearing rocks end up This would limit atmospheric CO2 and keep Earth cool, but these natural changes being scraped off the subducting plate, then this carbon is are extremely slow. In the last 50 million years, the buildup of the Himalaya, due to removed from the system by the combined action of the plate tectonics, is linked to a global temperature drop that has occurred since very (rivers, groundwater, and oceans), biosphere warm time periods between 50 and 120 million years ago. During that time, global ( and shell builders), and lithosphere. temperature and sea level were much higher than today.

How May the Carbon Cycle Be Impacted at Shorter Timescales?  There are various schemes considered to affect the Process 2: Ocean Fertilization — Scattering iron on the ocean surface may promote carbon cycle, especially because of concerns about the phytoplankton growth, which would increase the efficiency of Step 3 above. Would this climatic effects of CO2. Three are most discussed. be a logical and safe means of removing atmospheric CO2 to combat global warming? 17.08.d1 Bushveld, South Africa Why or why not? Process 1: Carbonation — Process 3: Invigorated Vegetation — Higher Before You Leave Ultramafic igneous temperatures may increase the rate of carbon rocks (those with uptake by plants under longer growing seasons This Page very high magne- with more favorable conditions for photosynthe- sium and iron, and sis. The increased rates of decay in a warmer Sketch, label, and explain low silica content), world may liberate the carbon cycle, like the ones nutrients from identifying the main carbon shown here, dead organisms reservoirs and fluxes,

absorb atmospheric CO2 efficiently during mineral quickly to allow mentioning some possible formation. Humans may be able to accelerate this for increased human impacts. slow natural process either by heating the rock or by carbon fixation by Sketch and explain how injecting it with water rich in CO2. In the U.S., plants. Would this ultramafic rocks are most common along the West be a possible CO2 regulates global 17.8

Coast and near the Appalachian Mountains, near strategy for Cambodia Angkor Wat, 17.08.d2 temperatures. major population centers. Might this spatial distribu- decreasing the Describe some possible ways tion, which resulted from a complex sequence of amount of CO in 2 to decrease atmospheric CO . geologic events unrelated to humans, be helpful? the atmosphere? 2

rey42432_ch17_534-563.indd 551 11/16/16 03:07 PM Final PDF to printer

552 17.9 What Is the Role of Nitrogen in Ecosystems?

NITROGEN (N) IS ANOTHER ESSENTIAL NUTRIENT. The largest available stores for diatomic nitrogen (N2) are the atmosphere and hydrosphere, rather than the biosphere or lithosphere. Thus, the , like the carbon cycle, is primarily a gaseous cycle. The nitrogen cycle differs from the carbon cycle in that it is involved in neither photosyn- thesis nor respiration. For humans, we inhale and exhale nitrogen without really using it in this form. Yet nitrogen is essential for life because it is fundamental to cell and is in amino acids and nucleic acids (DNA and RNA). Nitrogen is also the limiting nutrient in many ecosystems. A limiting nutrient prevents ecosystem health even if all other biotic and abiotic components are adequate. What Forms of Nitrogen Are Found in the Environment?

Nitrogen occurs in many forms in the biosphere; these are summarized in the table below. Atmospheric N2 is inert and is not useful to plants and animals. Nitrogen is the essential nutrient in the shortest supply in many ecosystems, so it is the resource that limits growth at cellular to global scales. Most fertilizers therefore include nitrogen.

Form of Nitrogen Properties and Uses

N Nitrogen chemical element, common component of Earth and other planetary

N2 Nitrogen gas 78% of atmospheric mass; necessary for biological processes, but unusable by plants

NO Nitric oxide by-product of combustion; oxidizes readily to form NO2

NOX NO2 Nitrogen dioxide brown, pungent odor, toxic gas; prevents growth of some bacteria in large concentrations

NO3 Nitrate natural rocks; explosives; fertilizers when combined with positive ions such as potassium, sodium, and calcium

N2O Nitrous oxide greenhouse gas; anesthetic (laughing gas)

NH3 Ammonia pungent odor; cleaning products; pharmaceuticals; fertilizers; neutralizes acids including in the kidneys

- HNO3 Nitric acid highly corrosive; fertilizers; rocket fuel, forms from NO2 reacting with hydroxide (OH )

How Does the Global Nitrogen Cycle Operate? 5. The Haber-Bosch indus- 17.09.b1 This figure depicts the trial process extracts nitrogen 1. Molecular Nitrogen N2 nitrogen cycle as a series (3.9 x 109) from the atmosphere and of arrows showing the Haber-Bosch Biological Nitrogen combines it with hydrogen (100˜290) Fixation gas to produce ammonia fluxes of nitrogen in all of Fixation Fossil Fuel (80)(80) Nitrogen and other nitrogen com- its forms between various Combustion (20˜25) Oxides Lightning (13) pounds that each of us uses, reservoirs (stores). As with ATMOSPHERE the carbon cycle, the num- in one way or another, every ber with each arrow indi- day (e.g. fertilized crops). Denitrification BIOTA cates how much nitrogen (43˜390)(43˜390) ˝4,100˙˝4,100˙ 4. Note that there is little moves along that pathway Agriculture (40)(40) direct exchange of nitrogen (the flux), and numbers between the atmosphere next to the main storage FRESH WATER and oceans, in part because sites (stores) of nitrogen Nitrogen-Fixing Bacteria Ammonia NH ˝30˜300˙˝30˜300˙ BIOTA ˝0.5˙ the two reservoirs are (e.g., atmosphere) indicate 3 Fertilizers Biological essentially in equilibrium. Fertilizers Uptake Decay and Wastes how much nitrogen is in (40)(40) Uptake Nitrogen does enter the Sewage (30˜300) (0˜3) that reservoir. The amounts oceans, but does so mostly 12 SOILS are in megatons (10 gm), Runo˛ and through the flow of streams, ˝95,000˙˝95,000˙ OCEAN ˝2,000˙ three orders of magnitude Erosion (40) including those that are (1,000 times) less than in Nitrates Nitrobacter Nitrites (16˜19)(16˜19) NO and Ammonia NO3 NO2 N2O NH3 draining agricultural areas the equivalent diagram for where nitrogen-based fertil- Nitrosomonas carbon. izers are used.

2. The N cycle consists of natural and anthropogenic components, 3. Nitrogen moves from the atmosphere to the land mostly through and some stores (reservoirs) between which nitrogen is exchanged. plants and nitrogen-fixing bacteria. Nitrogen going the other direction is The largest reservoir is the atmosphere, with almost 4 billion mega- released into the atmosphere by the denitrification process, where

tons. Recall that nitrogen gas (N2) makes up 78% of the atmosphere. microbes convert other forms of nitrogen into nitrogen gas, and by com- The next largest reservoir is in soils, followed by the ocean. bustion of fossil fuels.

rey42432_ch17_534-563.indd 552 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 553

How Does Nitrogen Act as a Water Pollutant?

Since about 1990, humans have been creating more NOx than have natural processes. The accumulation of NOx in the

environment has been an increasing problem. However, NOx is needed to supply the world’s population with food. This

creates the dilemma of how to produce more food while minimizing the addition of NOx to the lithosphere and hydrosphere. Most of the “extra” nitrogen ends up as water pollution.

1. Humans add nitrogen to the environment in various ways, 2.0 17.09.c1 2. This graph shows the both directly and indirectly. Production of fertilizer converts annual flow, or flux, of Nitrate-N Entering the Gulf atmospheric N2 to other forms (almost as much as natural nitrogen entering the Gulf biological processes) through the Haber-Bosch process. 1.5 of Mexico through the Runoff from fertilized agricultural areas adds nitrogen to Mississippi River and its aquatic systems (where it is not needed as much as on 1.0 tributaries. Observe the land). This causes too much aquatic plant growth, which overall increase in uses up oxygen and nutrients and encourages population nitrogen as a function of explosions among second-degree heterotrophs, stressing FLUX, NITRATE 0.5 time, as well as the yearly and destabilizing ecosystems with low inertia. We also add ups and downs related to nitrogen to the environment through fossil-fuel combustion, IN MILLIONS OF METRIC TONS 0 short-term climatic and 1960 1970 1980 1990 2000 2010 animal feedlots, and sewage. economic factors.

How Does Nitrogen Act as an Air Pollutant?  Humans also release nitrogen to the atmosphere. Atmospheric NOx (nitric oxide [NO], NO2, and NO3) is such a widespread concern that it appears on the U.S. Environmental Protection Agency’s list of criteria pollutants (pollutants of most concern). 17.09.d1 17.09.d2 3. NOx reacts with ammonia

(NH3 ) in the formation and intensification of particulate matter, which is linked to haze, decreasing visibility, and respiratory

ailments. NOx also combines with water to

form HNO3, a very strong acid

1. Atmospheric NOx is monitored by satellite and other 2. NOx is a major pollutant that is and a compo- methods in the U.S. and other parts of the world (▲). As monitored by the EPA in the U.S. nent, along with sulfuric acid, of acid rain. you can observe from these maps, high concentrations Greater effort to limit NOx production The chemical reaction that results in of NOx are mostly associated with industrial areas. NOx at the state level has been under- ­nitrogen-related acid rain is summarized in is released primarily by power plants and automobiles, taken, with wide disparity in the the chemical reaction below: and it contributes to the danger posed by other degree of success at controlling it. pollutants, including tropospheric ozone, tiny aerosols known as particulate matter, and acid rain. NOx + H2O HNO3

4. Nitrous oxide (N2O) is a greenhouse gas. An increase in N2O in the atmosphere has potential environmental and human impacts, including melting of glaciers, rising sea levels, and stressing of ecosystems. Before You Leave This Page 17.09.d3 5. Tropospheric ozone (O ) is 6. The unstable 3 Describe the forms of nitrogen that a product of NO (⊲). Unlike Sunlight O bonds with O to 2 2 are circulated throughout the stratospheric ozone that protects O form O3, which itself is NO + 2 biosphere and explain how us from harmful ultraviolet radiation, 2 a pollutant near the O they occur. tropospheric O3 has undesirable ground. NOx reacts with impacts, including causing respira- sunlight and volatile Sketch and describe the nitrogen 17.9 O3 tory issues. One way that it is NO organic compounds cycle, including human influences. produced is when sunlight triggers (VOC) to produce + O the breakdown of NO (photodis- O ground-level ozone, an Explain the role of NOx in pollution. 2 NO 2 sociation) into NO and O. or air pollutant. Hydrocarbon NO2

rey42432_ch17_534-563.indd 553 11/16/16 03:07 PM Final PDF to printer

554 17.10 What Is the Role of Phosphorus in Ecosystems? PHOSPHORUS (P) IS AN ESSENTIAL NUTRIENT for every living plant and animal cell, but in nature it occurs as -2 inorganic phosphate (PO4 ). Unlike carbon and nitrogen, the occurs largely in the lithosphere, so it is termed a sedimentary biogeochemical cycle. As little as 1% of the phosphorus in the crust is available to plants. To be economically feasible to mine, a rock must contain at least 8% phosphate.

How Does the Phosphorus Cycle Operate?

17.10.a1 1. This schematic depicts 5. Notice the small storages the global phosphorus of phosphorus in the cycle. Storages are atmosphere and the very shown in metric tons of small fluxes in and out of phosphorus, and fluxes the atmosphere, unlike the are in metric tons per C and N cycles. year, with red arrows depicting the fluxes 4. Locally significant primarily caused by phosphate deposits occur human activity. Note how at sites with large popula- much smaller the fluxes tions of birds and bats. are for phosphorus These deposits represent (metric tons) compared the accumulation of excre- to those of nitrogen and ment (called guano) from carbon (megatons or these airborne creatures. If gigatons), but the large enough, these reservoir represented deposits can be mined as a by ocean-floor source of phosphate, as sediments is substantial. occurs along the western coast of South America. 2. Various parts of the phosphorus (P) cycle occur on different timescales, as 3. The deep replenishment of phosphorus via the rock occurred with the carbon cycle. The part that occurs near Earth’s surface is the cycle requires millions of years, but it contains by far the relatively fast part of the cycle. Some plants, like dandelions, have roots that are most phosphorus, with an estimated one billion metric exceptionally adept at attracting nutrients (like P) that have leached downward tons. Finding an economically feasible way to retrieve below the root zone. When these “hyperaccumulator” plants die or are consumed, such phosphorus would solve the problem of availability. the P is available for other organisms.

Where Are Major Phosphate Deposits Located? 17.10.b3 17.10.b1 Florida 1. Phosphate is a general term for rocks and chemical substances 50% that have phosphorus. Plants generally use the phosphate ions 30% in building ATP, DNA, and proteins. Phosphate occurs in recent 20% marine deposits in Florida (⊳) and elsewhere. Teeth of various 10% creatures contain a phosphate mineral, so accumulations of these AFRICA materials can occur when these organisms die, and they repre- sent an important resource of phosphate.

Equator

Phosphate occurs 2. SOUTH in many parts of the AMERICA world (⊲). In addition to guano and recent marine layers, phosphate occurs in 3. Atmospheric transport of phosphorus can enrich older sedimentary water thousands of miles from the point of origin. units, including some The map above shows the percentage of insolation important ones in that is scattered and absorbed by dust particles, Idaho and adjacent some of which contain phosphorus. In this region, parts of Wyoming the trade winds carry phosphorus all the way from and Utah. Africa to the coast of South America. 17.10.b2

rey42432_ch17_534-563.indd 554 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 555 What Role Does Phosphorus Play in Biological Processes? Phosphorus is one of the most important elements for life. It is essential to the cell structure of many creatures and plants, and it occurs in teeth. Here, we highlight a few important and interesting aspects of the role of phosphorus in .

17.10.c1 1. Part of the value of phos- TA 3. When phosphorus is added to ATP T A phorus (P) is its highly reactive or removed from proteins, various nature, which allows it to bond G C types of cellular functions are A P P P C G with many other atoms and T A regulated to optimal levels for the G C molecules in forming essential P health of the organism. compounds (⊲). For example, P T A phosphorus forms part of G C TA Deoxyribonucleic adenosine triphosphate (ATP), 4. T A acid (DNA) contains which stores the energy G C Sugar- the genetic code of acquired in the “light reaction” Energy CG Energy Phosphate every cell (⊳). Without phase of photosynthesis. This From Food For Cells TA G C Backbone phosphorus, DNA, same substance is involved in A P P the building block of food consumption in humans most life, would not and other creatures. ADP have its characteristic 2. ATP also releases that energy during cellular respiration in the Calvin cycle phase of double helix struc- photosynthesis, liberating it as fuel for other biological processes. At that point, ATP ture, or even exist, becomes adenosine diphosphate (ADP) or the even lower-energy adenosine monophos- for that matter. phate (AMP). When additional phosphorus is present, AMP can become ADP or ATP, 17.10.c2 increasing the amount of energy available to the organism.

What Happens When Too Much Phosphorus Is Added Locally? Local overabundance of phosphorus can be a problem in some aquatic ecosystems. If phosphates have been added to a water body, the water can undergo the process of , which is the response of an aquatic ecosystem to the addition of a foreign substance or the addition of too much of a substance that is normally present but not in such high concentrations. Water bodies with low nutrient concentrations and low net primary productivity (NPP) are termed oligotro- phic, while those with high nutrient concentrations and higher NPP are eutrophic.

The figure below illustrates the processes that occur in a water body in which phosphorus has been added, causing eutrophication. Typically, succession in aquatic ecosystems causes eutrophication as a natural process over time. Humans, however, have accelerated the eutrophication process by adding P and N primarily through runoff from fertilized fields and golf courses, leaky septic systems, and municipal sewage systems. This can have serious consequences, produc- ing algal blooms that then reduce the 17.10.d1 amount of oxygen upon which other organisms depend.

Before You Leave This Page

Sketch and explain the phosphorus cycle, identifying the major reservoirs and explaining the major fluxes. Summarize the types of deposits in which phosphate occurs. Summarize the role of phosphorus in the biosphere, identifying biotic components where it occurs and what its role is. 17.10 Explain the process of eutrophication and why it can be harmful to aquatic ecosystems.

rey42432_ch17_534-563.indd 555 11/16/16 03:07 PM Final PDF to printer

556 17.11 What Is the Role of Sulfur in the Environment? SULFUR IS ANOTHER ESSENTIAL NUTRIENT for life. Sulfur (S) is necessary for plant growth, especially for legumes like peas and beans, which return N to the soil as they grow. S is present in the molecules that protect plants and animals from bacterial infections. S is also used as the energy source in chemosynthesis to make food for deep-ocean organisms and for bacteria in oxygen-poor environments. The S cycle is not very well understood, largely because of the 2- complicated chemical changes involving different forms of S, such as sulfur dioxide (SO2), sulfate ions (SO4 ), and

hydrogen sulfide (H2S). How Does the Global Operate? The sulfur cycle looks similar to the phosphorus cycle in that it is almost entirely sedimentary, involving only minor interaction with the atmosphere. Again, the red arrow indicates the flow linked to the human-produced (anthropogenic) part of the cycle. 17.11.a1 1. This figure depicts 5. Although the effects of the global sulfur cycle, acid precipitation are most identifying the reser- obvious outside the oceans, voirs of sulfur and the such as damage to land fluxes of sulfur between plants, most acid rain actually those reservoirs. The falls into the oceans, causing numbers indicate the damage to aquatic animals. size of the reservoir or the size of the flux in 4. Some sulfur goes from the 1012 moles. The largest ocean to atmosphere, and reservoirs are in the sulfur also goes from the lithosphere, including atmosphere to the ocean and sediments in the ocean. to the land, in the form of Large amounts of sulfur precipitation. In the atmo-

also occur in sedimen- sphere, sulfur oxides (SOx) tary rocks that were react with water to form sulfu-

deposited in the ocean ric acid (H2SO4), which but are now on land becomes incorporated into and in rocks that have the precipitation, causing acid been affected by hot rain (or more generally acid (hydrothermal) waters. precipitation).

2. As sulfur shifts between reservoirs, it moves from the land to the 3. Sulfur is relatively mobile in water, so it enters streams and ground- atmosphere from burning and petroleum, both of which contain water when sulfur-bearing rocks are weathered. Streams then carry this variable amounts of sulfur. Sulfur is also released from volcanoes, and sulfur to the ocean. When sediment accumulates on the seafloor, it an increased release of sulfur may indicate that a volcanic eruption is incorporates significant amounts of sulfur, essentially removing it from imminent. Sulfur can be picked up by wind. circulation through the system for a while.

Sulfur in the Land and Water

17.11.a2 Kidd Creek Mine, Ontario, Canada 17.11.a3 Silverton, CO 17.11.a4 Silverton, CO 6. Sulfur occurs naturally in rocks, including 7. Sulfide are not stable when exposed 8. The reddish rocks in the center photo- these (▲) that are almost all sulfide minerals. to atmospheric oxygen in the process of graph (to the left) drain into local streams, They are exposed underground in a copper weathering. As a result, they convert to red and causing the water and sediments to be acidic mine with a rock hammer for scale. orange oxide and sulfate minerals. and stained orange by the sulfur and iron.

rey42432_ch17_534-563.indd 556 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 557 What Impacts Do Humans Have on the Sulfur Cycle? The human impact on the S cycle is miniscule on a global scale, but it can be significant at the regional and local scales.

About half of the atmospheric emissions come from humans, but much more than half is released in industrial areas. SOx

emissions, especially SO2, are dangerous because they destroy plant hormones, stunt plant growth, reduce plant reproduction rates, and cause respiratory illnesses in humans.

1. The burning of coal (⊳), especially coal that is high in sulfur, is AREAS IN NON-ATTAINMENT FOR SO2 EMISSIONS the prime human source of atmospheric S. The sulfur falls back Lewis and Clark, MT toward the surface in acid precipitation, like acid rain. The term Yellowstone (MT) acid deposition is also used because dust can be coated with Oneida (WI) acid and then fall to the surface. Later, when moisture comes in contact with this acidified dust, anything in contact with it, Tooele (UT) Salt Lake (UT) Warren including raindrops, will become acidified. (PA)

2. Only a few counties in the U.S. (⊲) are in noncompliance with

the clean-air standard for SO2, such as areas that have smelters Pinal (AZ) 17.11.b2 (furnaces in which to heat rocks) that process sulfur-rich rocks. St. Bernard (LA) Areas in yellow on this map exceeded 1971 EPA standards, whereas those in red exceeded tougher standards established (June 13, 2016) by the EPA in 2010. By 1971 EPA Standards By 2010 EPA Standards 17.11.b1 Fruitland, NM

Spatial and Temporal Variations in Human-Generated Sulfur 17.11.b3 5. The impacts of acid precipitation and acid deposition are most pronounced where bedrock compositions cannot buffer the acid deposition and where rainfall is orographically concentrated, for example in the Adirondack Mountains of upstate New York and the Appalachian Mountains. The good news is that there has been an improvement in the U.S. over the last 30 years (▼). 17.11.b4

30 National Standard (Health-Based) 90% of sites have concentrations 3. These two maps (▲) depict the amount of sulfur emitted in the 4. The decrease in emis- below this line. continental U.S., averaged over two different three-year periods. sions between the first and 20 10% of sites have concentrations Examine the left map and consider what might be causing the second maps is due largely below this line. Average observed patterns. The largest emissions are in the eastern half to natural gas replacing 10 of the country, around the industrial centers, including at coal- coal-fired power plants in ANNUAL MEAN AMBIENT ANNUAL 2 fired power plants. the generation of electricity. ˜PPB° CONCENTRATION SO 0 1980 1985 1990 1995 2000 2005 2010 17.11.b5 6. This unusual-looking map, called a carto- gram, shows the size of each country in proportion to the amount of sulfur it Before You Leave releases into the This Page atmosphere. Note that the industrialized countries, which look Sketch and explain the main like big balloons, are reservoirs and fluxes responsible for most involved in the sulfur cycle. of the SO2 emissions. Explain the role of humans in the sulfur cycle.

7. Emissions elsewhere in the world are extremely variable. They are decreasing in many locations, 17.11 Describe the spatial and such as in European Union countries, where emissions have fallen by 76% from 1990 to 2009. Emissions are increasing in the developing world, such as in China, which has been building temporal trends in sulfur coal-fired power plants at the rate of several per week! Scientists have tracked the increased dioxide emissions. emissions from China all the way across the Pacific and into the Pacific Northwest.

rey42432_ch17_534-563.indd 557 11/16/16 03:07 PM Final PDF to printer

558 17.12 How Does a Lack of Oxygen Harm Ecosystems?

ORGANISMS IN TERRESTRIAL AND AQUATIC ECOSYSTEMS depend on available oxygen (O2). Oxygen is the second most abundant atmospheric constituent, so it is in constant contact with the upper surfaces of the land and water bodies. As a result, it can become incorporated into soils and surface waters. Aquatic ecosystems are particularly susceptible to having

too little O2 to accommodate their resident organisms. What determines dissolved O2 content, what causes O2 shortages, and

what are the impacts of having too little O2 available in an ecosystem?

Where Is Dissolved Oxygen Most Available in a ? Cold water can absorb more dissolved gas than warm water, because molecules are more energetic at high temperatures and

so gas can more easily escape into the atmosphere. All other factors being equal, more O2 is available to organisms in

colder water, including bacteria that decompose organic matter. On a hot afternoon, the amount of O2 needed by the biological oxygen demand bacteria — the (BOD) — is highest. This occurs precisely when dissolved O2 concentrations are lowest, as described below for a typical lake. 17.12.a1 1. Near the top of the lake where 5. Dumping waste hot water from

sunlight is available, more O2 is factories into rivers flowing into generated from photosynthesis the lake decreases its ability to than is used by respiration or hold dissolved oxygen. Also, fermentation. The upper zone in as temperature increases, the which this occurs is called the metabolic rate of organisms limnetic (or photic) zone. increases, accelerating the need

for more O2. If O2 concentrations 2. Near the bottom of the lake, fall low enough, fish and other little or no photosynthesis is aquatic organisms can suffocate.

occurring, so more O2 is used by respiration or fermentation 4. As temperature increases, the than is released by photo­ metabolic rate for organisms synthesis. This is the profundal increases, accelerating the need for

(or aphotic) zone. more O2. So, a lake ecosystem is most sensitive to organic pollution 3. The level where the production of O2 through photosynthesis is balanced by the use of O2 by respiration near the end of summer, after or fermentation is the compensation point. The compensation point (or level) moves downward during the months of intense photosynthesis, daytime, when photosynthesis is most active, and upward all through the night. It also varies from season to and just before dawn, when the season. limnetic zone is the thinnest.

How Does Oxygen Availability Affect the Health of a Lake? hypoxia If O2 is lacking in aquatic ecosystems — a condition known as — the amount and type of circulation within the lake determine the severity of the problem. This circulation is affected by the depth of the thermocline, the boundary between the sun-warmed upper waters and the cold bottom waters. Little circulation occurs across the thermocline.

In extratropical climates, the compensation point is usually above But at some point in winter, the lake “turns over” suddenly, as the upper the thermocline in summer. This allows lake circulation to move to layer becomes chilled by cold air masses. The increased density of this

the surface any hypoxic water below the compensation point but chilled surface layer, which is rich in O2, causes it to flow downward, above the thermocline. This setting restricts circulation to the upper below the thermocline, and to trade places with the now-warmer, less

part of the lake, making this scenario the more serious case for the dense waters below it. Some water with a net O2 surplus below the input of organic pollutants. thermocline will be diffused to the area with a deficit, minimizing the 17.12.b1 problem. 17.12.b2 Above the thermocline, no water has

an O2 deficit. As a result, this is the less serious case for the input of organic pollutants.

rey42432_ch17_534-563.indd 558 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 559 How Can Nutrient Inputs Affect Oxygen Availability? One of the world’s most severe hypoxic zones is in the northern Gulf of Mexico, near where the Mississippi River, the largest river in North America, empties into the Gulf. The Mississippi River drains huge areas of the country, from the eastern side of the Rocky Mountains to the Appalachian Mountains on the east. The region between the two mountain ranges includes the agricultural areas of the Great Plains and Ohio River and Mississippi River valleys. Water draining off agricultural fields in these areas can end up in the Mississippi, and ultimately in the Gulf.

17.12.c4 1. This map of atmospheric nitrogen deposi- 8 tion reflects the heavy agricultural practices in Sources of Nitrates the Mississippi River Basin. Fertilizers and 6 manure (in addition to fossil-fuel combustion) greatly increase nitrogen emissions, which are 4 EN INPUTS

redeposited to the ground by wind and rain, OG adding even more nitrogen to the soil. 2 Fertilizer

NITROGEN INPUTS Legumes and Pasture

(millions of metric tons) Animal Manure 0 2. Runoff from the Mississippi River drainage 1960 1970 198021990 000 2010 system carries nutrient-rich agricultural fertilizers and manure into the Mississippi 2.0 17.12.c3 River and out to the Gulf of Mexico. ) Nitrate Entering 17.12.c1 ns o the Gulf of Mexico 1.5 3. From there, the prevailing longshore current brings the Mississippi’s waters 1.0 westward along the Louisiana coast. The

nitrates and other chemicals in the water FLUX NITRATE 0.5 promote growth that uses up oxygen causing (millions of metric tons) Hypoxic 0 a linear hypoxic zone offshore of Louisiana 1960 1970 1980 1990 2000 2010 and southeastern Texas. The hypoxic zone Zone 17.12.c2 acts as a barrier — called a “dead zone” — to the migration of many marine species that 4. The nitrate loading into the Gulf is increasing over time, with wetter years over the Mississippi use the adjacent coastal swamps and River basin producing larger hypoxic zones than drier years. The Chesapeake Bay area experi- marshes as nurseries, preventing individuals ences similar problems with hypoxia. The graph on the top right shows that fertilizer usage in from reaching the open Gulf after maturation. the drainage basin of the Mississippi has increased, exacerbating the hypoxia problem.

How Do Storms Cause Fish Kills in Coastal Ecosystems?

1. Hurricanes or 3. After the storm passes, water is pulled back out to sea and the other severe coastal hydrogen sulfide and tannic acid accumulate in locations where storms can force salt organic matter is left behind. If the debris is floating, it can water inland, killing cut off surface water from receiving atmospheric O2. freshwater fish, Thus, the ecosystem cannot break down the addi- particularly those that tional organic matter into nutrients because too little are more stenohaline O2 is available. The positive feedback continues as

(unable to survive more fish die, using more of the scarce O2. changes in salinity). The decay of these organisms uses more Before You Leave This Page dissolved O2, further stressing the remaining Explain the trend in dissolved O and fish in the area. As 17.12.d1 2 BOD by season and time of day. stressed fish and other aquatic organisms die, a 17.12.d2 Sketch the seasonal position of the positive feedback occurs, 2. When a storm blows leaves, thermocline and the compensation as detritivores (decom- branches, and other organic point in a lake, explaining how they posers) use even more debris into aquatic ecosystems, influence the oxygen content and the O to break down dead hydrogen sulfide (H S) and 2 2 response to organic nutrient loadings. organisms, causing more tannic acid are produced as organisms to die (⊲), and by-products of the decomposi- Explain the origin of the hypoxia so on. This process tion process. The heavy concen- problem in the Gulf of Mexico. 17.12 continues until the inflow tration of these by-products of other O -rich water prohibits the growth of phyto- Explain how storms can compound 2 problems related to hypoxia. can restore O2 levels. plankton that would be able to help restore depleted O2 levels.

rey42432_ch17_534-563.indd 559 11/16/16 03:07 PM Final PDF to printer

CONNECTIONS 17.13 How Do Invasive Species Impact U.S. Gulf Coast Ecosystems? WHEN A NEW OR “EXOTIC” SPECIES is introduced in an ecosystem, either intentionally or accidentally, it often dies off quickly in its new surroundings because it does not have an ecological niche that will permit its survival. Spe- cies that survive and become a part of the ecosystem are called non-native species. A non-native species is referred to as an invasive species if it disrupts the ecosystem by developing a broad geographical range and occupying a biological niche. As an invasive species invades habitats, it can negatively impact or even eliminate one or more native species. In some cases, invasive species remain uncontrolled by predators, because they are not a familiar prey to the predator. Invasive species are most common in ecosystems where the biotic and abiotic factors are not particularly limiting and where species from other regions enter and leave an area easily. The U.S. Gulf of Mexico Coast is one location where invasive species have been particularly troublesome.

What Are Some Terrestrial Invasive Species and Their Impacts on the Gulf Coast? Invasive species have been introduced on land and in local waters of the region. Three invasive land species— the coypu (nutria), Burmese python, and kudzu — represent mammals, reptiles, and plants, respectively.

17.13.a1 17.13.a4 Lynchburg, VA 1. Beaver-like mammals called coypu, locally known as nutria, were introduced to the area from Brazil accidentally through the Port of New Orleans in the 1930s. Burrowing by the nutria has caused tremendous structural problems for levees in southern Louisiana. Hunting them is encouraged by governments. After nutria eat marsh vegetation, they leave a barren landscape.

17.13.a2 2. Burmese pythons were likely introduced into the Florida Everglades by pet owners, and also as pet stores were destroyed in 1992 by Hurricane Andrew. They ingest 3. Kudzu is a vine in the pea family that is native to east Asia. It has small alligators, deer, and nearly any many uses, including animal fodder, erosion control, and medicines. other native species. In 2012, Since its introduction to the U.S. in 1876, however, its very rapid rate of researchers caught one that was over growth in the Gulf states has caused it to out-compete native vegetation 5 m (17.5 ft) in length. Fortunately, as for sunlight. Expensive and potentially harmful herbicides are used to the map below shows, the Burmese control kudzu’s spread. Kudzu has been reported in the counties shown python has not been able to migrate below. It has also been introduced to other tropical and subtropical beyond Florida, so far. areas, such as Pacific islands and northeastern Australia.

17.13.a3 17.13.a5

BURMESE KUDZU PYTHON

560

rey42432_ch17_534-563.indd 560 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 561

What Are Some Aquatic Invasive Species and Their Impacts on the Gulf Coast? Other invasive species were introduced into waters of the region, mostly in lakes and streams. These include non-native plants, such as water hyacinth, and various species of fish, including the silver carp and blue tilapia. All three of these species, and others not described here, have caused extensive damage to the ecosystems by displacing native plants and animals.

17.13.b1 17.13.b3 17.13.b5

1. The water hyacinth, a floating plant with 3. Species of carp were brought to catfish 5. Tilapia, a type of fish originating in Africa, lavender flowers, has spread from its native ponds in the Gulf states to clean up algae was introduced into Florida waters in the South America to the southern U.S. and buildup. Flooding moved them into larger 1960s purposely, as a sport fish. In a way beyond, probably since it was introduced at rivers, including the Mississippi, where they similar to the silver carp, their effects on the World’s Industrial and Cotton Centennial can be as large as 100 pounds. Silver carp existing native fish were very harmful. A map Exposition in New Orleans in 1884–1885. It have disrupted the food chain significantly. showing the extent of their range is shown has since spread to nearly all tropical and They are considered a delicacy in some below. They have spread across many parts subtropical areas of the world. It is also Asian cuisines, so people fish for these of the Gulf Coast. Separate introductions present in waterways of California. Asian carp in the middle of America. occurred elsewhere.

17.13.b2 WATER HYACINTH 17.13.b4 SILVER CARP 17.13.b6 TILAPIA June 2016 June 2016 June 2016

2. The water hyacinth is notorious for clogging 4. The map above shows that carp have 6. The examples shown on these pages are navigation waterways and damaging boats. It spread far beyond the Gulf states. This just a few of the numerous invasive species also prevents photosynthesis in phytoplankton, invasive species worked its way up the that plague just one region. As globalization resulting in the depletion of aquatic oxygen Mississippi River and into its tributaries, “shrinks our world,” careful control of the and interfering with the food chain. Its rapid including the Ohio, Missouri, and Platte rivers. spread of exotics will become even more reproduction results in abrupt fish kills. As a result, it has reached Colorado and the important. Are any of these invasive species a Great Lakes. problem where you live, or does your area have others?

The Law of Unintended Consequences lthough it is not a law in the way the etc.). But they did not consider all the possible Second Law of Thermodynamics is, side effects — the unintended consequences. It Before You Leave This Page the “Law of Unintended Conse- is nearly impossible to know how the introduc- Aquences” is something that we should always tion of an exotic species will interact with eco- Give several examples of terrestrial 17.13 consider, especially in matters of ecosystems. systems, which as we’ve seen from this chapter and aquatic invasive species in the When well-meaning people introduced these are very complex, with a tremendous number of U.S. Gulf Coast, describing the non-native species into the Gulf Coast region, physical, chemical, and biological connections. harmful effects of these species. they thought it was for the good (to clear algae,

rey42432_ch17_534-563.indd 561 11/16/16 03:07 PM Final PDF to printer

INVESTIGATION 17.14 What Factors Influence the Desert Ecosystems of Namibia in Southern Africa? IN EXAMINING AN ECOSYSTEM, we would like some measure of its diversity, productivity, and what the inter- relationships are between different species. In this exercise, you will examine some ecosystems of Namibia, a country along the west coast of southern Africa. Namibia features a suite of interesting landscapes, animals, and plants. You will construct a food web, identify what factors are most likely to limit or disrupt the productivity of the ecosystems, and contrast your findings with the ecosystems of Costa Rica, as presented in the opening pages of this chapter.

Goals of This Exercise: • Make observations and inferences about ecosystems in Namibia based on maps and on photographs and descriptions of landscapes and organisms. • Construct a simple food web of selected plants and animals, identifying animals that are probably competing for the same limited resources. • Identify factors that are likely to be limiting the productivity of the ecosystems, and what changes to the environment could cause a disruption. • Contrast the overall ecosystems, limiting resource factors, and potential threats to biodiversity in Namibia versus those in Costa Rica.

Procedures Follow the steps below, entering your answers for each step in the appropriate place on the worksheet or online. 1. Examine the regional map of Namibia (below left) to note its general location. Next, observe the satellite image (below right), noting the different regions. Read the descriptions that accompany the three photographs of three main regions. 2. Observe the 12 photographs of different organisms in Namibia, and read the associated descriptions. For additional insight, examine other photographs of Namibia earlier in this chapter and elsewhere in this book (consult the index in the back of the book). 3. Construct a plausible food web of the 12 organisms shown on the next page, and identify those that appear to compete for the same resource. Also indicate any predator-prey relationships. 4. Make a list of what environmental factors are likely to be limiting the productivity of ecosystems in Namibia, explain your reasons, and propose how each organism would respond if a drastic change caused a disruption in one resource. 5. Observe the photographs and read the text in the opening two pages of this chapter, which describe some aspects of the ecosystems of Costa Rica. Compare the overall ecosystems, their limits, and possible threats to ecosystems in each country.

Regional Setting of Namibia These three photographs show Satellite Image of Most of Namibia three regions of Namibia. The 17.14.a2 one below shows huge sand dunes of the coastal desert. The one to the upper right is of Etosha, a world-famous ecosystem centered around water holes next to a large, often dry lake. The photograph on the lower right shows the interior, which has grasslands, savanna, and nearly barren, 17.14.a4 rocky mountains. 17.14.a5 17.14.a3

17.14.a1 562

rey42432_ch17_534-563.indd 562 11/16/16 03:07 PM Final PDF to printer

Ecosystems and Biogeochemical Cycles 563

17.14.a6 17.14.a7 17.14.a8

1. Oryx: that grazes on grass and 2. Agama Lizard: Reptile and that 3. Namibian Giraffe: Herbivore; uses its long browses on shoots of trees; can live in drier forages mostly on insects, with some grass neck to browse on trees and tall shrubs that conditions than similar large herbivores. and berries; can withstand high temperatures. shorter grazers cannot reach. 17.14.a9 17.14.a10 17.14.a11

4. Southern Yellow-billed Hornbill: Omnivore 5. Rhinoceros: Herbivore that mostly grazes on 6. Lion: Carnivore that attacks and feeds that grazes on small mammals, snakes, eggs, grass and can go without water for several days; upon mostly large grazing mammals, except insects, and berries. no natural predators, except humans. fully grown rhinos, elephants, and giraffes. 17.14.a12 17.14.a13 17.14.a14

7. Stone Grasshopper: Well-camouflaged 8. Snake: Reptile and carnivore that feeds on 9. Mountain Zebra: Herbivore preferring to insect that lives in rocky ground; herbivore lizards, small mammals, insects, eggs, and graze on grass, but will consume small bushes grazing mostly on grasses and leaves. other small creatures. if necessary; a threatened species.

17.14.a15 17.14.a16 17.14.a17 17.14

10. African Elephant: Herbivore that grazes on 11. Meerkat: Small mammal of the mongoose 12. Goats: Human-introduced omnivore that trees, shrubs, and herbs; world’s largest living family and primarily an , but will eat browses on various plants, especially weeds land animal; adults have no natural predators. lizards, snakes, spiders, eggs, and plants. and shrubbery, but will sample various items.

rey42432_ch17_534-563.indd 563 11/16/16 03:07 PM