APES Ch 3.pdf

Tropical Rain Forests Are Disappearing dioxide (CO,), a gas that contributes to T r o p i c a l r a i n f o r e s t s are found destruction and degradation of these...

Tropical Rain Forests Are Disappearing dioxide (CO,), a gas that contributes to T r o p i c a l r a i n f o r e s t s are found destruction and degradation of these atmospheric warming and climate change centers of biodiversity is increasing. Ecol- near the earth?s equator and contain an Third, large-scale loss of tropical rain amazing variety of life. These lush forests ogists warn that without protection, forests can change regional weather and most of these forests will be gone or are warm year round and have high climate patterns. Sometimes such severely degraded by the end of this humidity because it rains almost daily. changes can prevent the tegrowth of ratn Rain forests cover only 2% of the earth's century. forests in cleared or degraded areas. land but contain up to half of the world?s Why should we care that tropical rain forests are disappearing? Scientists give When this ecological tipping point is known terrestrial plant and animal spe- three reasons. First, clearing these forests reached, tropical rain forests in such areas cies. These properties make rain forests reduces the earth's vital biodiversity by become less diverse tropical grasslands. natural laboratories in which to study destroying the habitats for many of the In this chapter, you will learn how tropi- ecosystems?communities of organisms earth?s species. Second, destroying these cal rain forests and other ecosystems work, that interact with one another and with forests contributes to atmospheric warming how human activities are affecting them, the physical environment of matter and and speeds up climate change, which you and how w e can help sustain them. @ energy in which they live. To date, at least half of the earth?s will learn about in Chapter 20. How does this occur? Eliminating large areas of trees rain forests have been destroyed or degraded by humans cutting down faster than they can grow back decreases r e the ability of the forests to remove some of How does the concept of Tragedy of the trees, growing crops, grazing cattle, and the human-generated emissions of carbon Commons apply to tropical deforestation? building settlements (Figure 3.1). The F I G U R E 3.1 N a t u r a l capital degradation: Satellite image of the loss of tropical rain forest, cleared for farming, cattle grazing, and settlements, near the Bolivian city of Santa Cruz between June 1975 (left) and May 2003 (right). This is the latest available view of the area, but forest deg- radation has continued since 2003. 6 6 @ CHAPTER 3 ECOSYSTEMS: WHAT ARE THEY AND HOW DO THEY WORK?  3.1 H O W DOES T H E EARTH'S t h e a i r w e b r e a t h e. It is 7 8 % n i t r o g e n (N2) a n d 2 1 % o x y - g e n ( O , ). T h e r e m a i n i n g 1 % of a i r is m o s t l y w a t e r v a p o r , LIFE-SUPPORT SYSTEM W O R K ? carbon dioxide, and methane. T h e n e x t l a y e r o f t h e a t m o s p h e r e is t h e s t r a t o s p h e r e. CONCEPT 3.1A The f o u r m a jo r c o m p o n e n t s of t h e earth's It r e a c h e s 17 t o 5 0 k i l o m e t e r s ( 1 1 - 3 1 miles) above the life-support system are t h e a t m o s p h e r e (air), t h e hydrosphere earth?s s u r f a c e , T h e l a y e r o f t h e s t r a t o s p h e r e closest t o t h e (water), the geosphere (rock, soil, a n d sediment), a n d t h e bio- earth?s s u r f a c e c o n t a i n s e n o u g h o z o n e ( O ; ) gas t o f i l t e r o u t sphere (living things). a b o u t 9 5 % o f t h e sun?s h a r m f u l u l t r a v i o l e t ( U V ) r a d i a t i o n. CONCEPT 3.1B Life is sustained by t h e f l o w o f energy f r o m T h i s global s u n s c r e e n allows life t o exist o n t h e surface o f the sun t h r o u g h t h e biosphere, the cycling of nutrients within the planet. t h e biosphere, a n d gravity. T h e h y d r o s p h e r e i n c l u d e s all o f t h e w a t e r o n o r n e a r t h e earth?s s u r f a c e. It is f o u n d as w a t e r vapor i n t h e a t m o - s p h e r e , as l i q u i d w a t e r o n t h e s u r f a c e a n d underground, a n d as i c e ? p o l a r ice, i c e b e r g s , glaciers, a n d ice i n f r o z e n Earth's Life-Support System Has Four s o i l - l a y e r s c a l l e d permafrost. S a l t y o c e a n s t h a t c o v e r a b o u t Major Components 71% of t h e earth?s s u r f a c e c o n t a i n 9 7 % o f t h e planet?s T h e earth?s l i f e - s u p p o r t s y s t e m c o n s i s t s o f f o u r m a i n s y s - water and support almost half of the w o r l d ? s species. t e m s ( F i g u r e 3. 2 ) t h a t i n t e r a c t w i t h o n e a n o t h e r. T h e y are A b o u t 2. 5 % o f t h e earth?s w a t e r is f r e s h w a t e r a n d t h r e e - t h e a t m o s p h e r e (air), t h e h y d r o s p h e r e ( w a t e r ) , t h e geo- f o u r t h s o f t h a t is ice. s p h e r e ( r o c k , soil, a n d s e d i m e n t ) , a n d t h e b i o s p h e r e ( l i v - T h e g e o s p h e r e c o n t a i n s t h e earth?s r o c k s , m i n e r a l s , ing things) (Concept 3.1A). a n d soil. I t c o n s i s t s o f an i n t e n s e l y h o t core, a t h i c k m a n t l e T h e a t m o s p h e r e is a s p h e r i c a l mass o f a i r s u r r o u n d i n g o f v e r y h o t r o c k , a n d a t h i n o u t e r crust o f r o c k a n d soil. T h e t h e earth?s s u r f a c e. Its i n n e r m o s t l a y e r , t h e t r o p o s p h e r e , crust?s u p p e r p o r t i o n c o n t a i n s s o i l c h e m i c a l s o r n u t r i e n t s e x t e n d s a b o u t 17 k i l o m e t e r s (11 m i l e s ) a b o v e sea l e v e l at t h a t o r g a n i s m s n e e d t o l i v e , g r o w , a n d r e p r o d u c e. It a l s o the e q u a t o r and about 7 kilometers (4 miles) above the c o n t a i n s n o n r e n e w a b l e fossil f u e l s ? c o a l , o i l , a n d n a t u r a l earth?s N o r t h a n d S o u t h Poles. T h e t r o p o s p h e r e c o n t a i n s g a s ? a n d m i n e r a l s t h a t w e e x t r a c t a n d use. T h e b i o s p h e r e consists o f t h e parts o f t h e a t m o s p h e r e , hydrosphere, a n d g e o s p h e r e w h e r e l i f e is f o u n d. If y o u c o m p a r e t h e e a r t h w i t h a n a p p l e , t h e b i o s p h e r e w o u l d be as t h i c k as t h e apple?s s k i n. Biosphere (lving organisms) T h r e e F a c t o r s S u s t a i n t h e Earth?s L i f e Life on the earth depends on three i n t e r c o n n e c t e d factors ( C o n c e p t 3.1B): 1. O n e - w a y flow of h i g h - q u a l i t y energy f r o m the sun. T h e sun?s e n e r g y s u p p o r t s p l a n t g r o w t h , w h i c h p r o - vides e n e r g y f o r plants a n d a n i m a l s , i n k e e p i n g w i t h the solar e n e r g y p r i n c i p l e o f s u s t a i n a b i l i t y. eae & _ - - ? Geosphere As solar e n e r g y interacts w i t h c a r b o n d i o x i d e (crust, mantle, core) (CQ3), w a t e r v a p o r , a n d s e v e r a l o t h e r gases i n t h e t r o - posphere, it w a r m s t h e t r o p o s p h e r e ? a process k n o w n as t h e g r e e n h o u s e e f f e c t ( F i g u r e 3.3). W i t h o u t t h i s n a t u r a l process, t h e e a r t h w o u l d b e t o o c o l d to s u p - ? > Atmosphere port m o s t o f t h e f o r m s o f life w e f i n d h e r e today. {air) 2. Cycling of nutrients t h r o u g h parts of the biosphere. N u t r i e n t s are chemicals that organisms need to survive. Because the earth does n o t get significant inputs of m a t t e r from space, its fixed supply o f ? Hydrosphere nutrients must be recycled to support life. This is i n (water) keeping w i t h the chemical cycling p r i n c i p l e o f sustainability. 3. Gravity allows the planet to hold on to its atmosphere FIGURE 3. 2 Natural capital: The earth consists of a land sphere (geosphere), an air sphere (atmosphere), a water sphere and enables the m o v e m e n t and cycling o f chemicals (hydrosphere), and a life sphere (biosphere) (Concept 3.1A). t h r o u g h air, water, soil, a n d organisms. 67  a GLa F I G U R E 3. 3 Greenhouse Earth. High-quality solar energy flows from the sun to the earth. It is __ degraded to lower-quality energy (mostly heat) as it interacts with the earth?s air, water, soil, and life h?s atmosphere retain enough of f o r m s , a n d e v e n t u a l l y r e t u r n s t o space. Certain gases in t h e e a r ! t h e sun?s i n c o m i n g e n e r g y as h e a t to w a r m t h e p l a n e t in w h a t is k n o w n as t h e g r e e n h o u s ee f f e c t. m a t t e r ? t h e biosphere, ecosystems, communities, populations, C H E C K P O I N T F O R U N D E R S T A N D I N G 3.1 and o r g a n i s m s ? w h i c h are s h o w n and d e f i n e d i n Figure 3.4. The biosphere and its ecosystems are made u p of living 1. Define t h e natural greenhouse effect. Explain h o w it affects (biotic) and n o n l i v i n g (abiotic) c o m p o n e n t s (Figure 3.5). t h e c u r r e n t life f o u n d on t h e earth. N o n l i v i n g c o m p o n e n t s i n c l u d e water, air, n u t r i e n t s , rocks,. Explain h o w gravity plays a significant role in sustaining life 3 heat, a n d solar energy. L i v i n g c o m p o n e n t s i n c l u d e plants, ie i on earth, | animals, and microbes. Ecologists assign each organism i n a n ecosystem to afeed- ing level, or t r o p h i c l e v e l , based o n its source of nutrients. Organisins are classified as producers a n d consumers.P r o d u c - 3.2 W H A T ARE THE M A J O R ers (also called a u t o t r o p h s ) are organisms, such as green C O M P O N E N T S OF A N plants, that m a k e the nutrients they need f r o m compounds and energy obtained f r o m their e n v i r o n m e n t (Concept 3.2A). ECOSYSTEM? In the process k n o w n as p h o t o s y n t h e s i s , plants capture solar energy t h a t falls o n their leaves. T h e y use i t to combine CONCEPT 3. 2 A Some organisms produce the nutrients carbon dioxide and w a t e r a n d f o r m carbohydrates such as they need, others get the nutrients they need by consuming glucose (CsH20¢), to store chemical energy t h a t plants need other organisms, and some recycle nutrients back to produc- and emit oxygen (O;) gas i n t o the atmosphere. This oxygen ers by decomposing t h e wastes and remains of other keeps us and most other animal species alive. The following organisms. chemical reaction summarizes t h e overall process: C O N C E P T 3. 2 B Soil is a renewable resource that provides nutrients that support terrestrial plants and helps purify water carbon dioxide + water + solar e n e r g y > glucose +o x y g e n and control the earth?s climate. 6 CO, + 6 H , 0 + solar energy > C.H)20,+ 602 A b o u t 2.8 b i l l i o n years ago, p r o d u c e r organisms called cyanobacteria, m o s t of t h e m floating on the surface o f the Ecosystems Have Several ocean, started c a r r y i n g o u t photosynthesis, w h i c h added Important Components o x y g e n to the atmosphere. A f t e r several h u n d r e d m i l l i o n years, o x y g e n levels reached about 21 % ? h i g h e n o u g h to Scientists classify m a t t e r into levels of organization ranging keep o x y g e n - b r e a t h i n g animals alive. f r o m a t o m s t o galaxies. Ecologists study five levels of 68 ] CHAPTER 3. ECOSYSTEMS: WHAT ARE THEY AND HOW DO THEY WORK?  Parts of t h e e a r t h ' s arr,. [ o x y g e n ((02) 07)] e Biosphere w a t e r , a n d soil w h e r e hfe 1s f o u n d A community of different species i n t e r a c t i n g w i t h o n e Carbon dioxide (C : Ecosystem another a n d w i t h their ia * h n o n l i v i n g e n v i r o n m e n t of matter and energy 4 : P o p u l a t i o n s of d i f f e r e n t species living in a p a r t i c u l a r Community place, a n d p o t e n t i a l l y : A i n t e r a c t i n g w i t h each o t h e r Secondary consumer A group of individuals of the (fox) Population same species living ina particular place Organism ? A n individual living being The fundamental structural and functional unit of I f e F I G U R E 3. 5 Key living (biotic) a n d n o n l i v i n g (abiotic) c o m p o - Chemical combination of t w o nents o f an ecosystem in a field. Molecule or more atoms of the same or Water different elements Smallest unit of a chemical. (H) Atom element that exhibits its Fes Hydrogen Oxygen chemical properties F I G U R E 3. 4 Ecology focuses on t h e t o p five of these levels o f t h e o r g a n i z a t i o n o f m a t t e r in n a t u r e. iN: LEARNING FROM NATURE Scientists hope to m a k e a molecular-sized solar cell by mimick- ing h o w a leaf uses photosynthesis to capture solar energy. These artificial leaf f i l m s m i g h t be used to coat t h e roofs, w i n - FIGURE 3. 6 This lioness (a carnivore) is feeding on a freshly dows, o r walls o f a b u i l d i n g and provide electricity for most killed zebra (an herbivore) in Kenya, Africa. homes a n d other buildings. feeding on o t h e r organisms (producers o r o t h e r c o n s u m - ers) o r o n t h e i r wastes a n d r e m a i n s. Today, m o s t producers o n land are trees and other There are several types of consumers. P r i m a r y c o n - green plants. In f r e s h w a t e r and ocean ecosystems, algae s u m e r s , o r h e r b i v o r e s ( p l a n t eaters), are animals that eat and aquatic plants g r o w i n g near shorelines are the m a j o r m o s t l y green plants. Examples are caterpillars, giraffes, and producers. I n the o p e n w a t e r of the oceans, floating and z o o p l a n k t o n (tiny sea animals t h a t feed o n p h y t o p l a n k - d r i f t i n g microscopic organisms k n o w n as phytoplankton are ton). C a r n i v o r e s (meat eaters) are animals t h a t feed on the d o m i n a n t producers. t h e flesh of o t h e r animals. Some carnivores, i n c l u d i n g spi- Some producer bacteria live i n dark and extremely hot ders, lions (Figure 3.6), and most small fishes, a r e s e c o n d - water around fissures on the ocean floor. Their source of energy a r y c o n s u m e r s t h a t feed o n the flesh o f herbivores. O t h e r is heat from the earth?s interior, or geothermal energy. They are carnivores such as tigers, h a w k s , a n d k i l l e r whales (orcas) an exception to the solar energy principle of sustainability. are t e r t i a r y (or higher-level) c o n s u m e r s that feed o n the The o t h e r organisms i n an ecosystem are c o n s u m e r s flesh of herbivores a n d o t h e r carmivores. Some of these (also called h e t e r o t r o p h s ) t h a t c a n n o t produce the n u t r i - relationships are s h o w n i n Figure 3.5. O m n i v o r e s such as ents t h e y n e e d (Concept 3.2A). T h e y get t h e i r n u t r i e n t s by pigs, rats, and h u m a n s eat b o t h plants a n d animals. 69  CONSIDER THIS,.. ? - glucose + oxygen > carbon dioxide + water + energy THINKING A B O U T W h a t You Eat CoHy20, + 602 7 6 COz + 6 H , 0 + energy W h e n you ate y o u r m o s t r e c e n t meal, w e r e carnivore, or an omnivore? ? y o u n herbvore, ° To summarize, ecosystems and the biosphere a r e sus- enw tained by the one-way energy f l o w f r o m the sun a n d the nutrient cycling of k e y m a t e r i a l s ? i n k e e p i n g w i t h t w o of the s c i e n t i f i c p r i n c i p l e s o f s u s t a i n a b i l i t y ( F i g u r e 3.8). r e l e a s i n g n e e r s a r ec o n s u m e r s t h a t getn o u r i s h m e n t by a n d a n i m a l s. T h e s e nutrie: is r e t u r nt o ves o i l , 5 o t e a s S o i l Is t h e F o u n d a t i o n o f L i f e a i r f o r reuse b y p r o d u c e r s ?co r e t u r n t o t h e soil, water, a n d o n Land ers a r e b a c t e r i a a n d f u n g i O t h e r eon O s. ff e e d e r s , o rd e t r i t i v o r e s f e e d o ?the w a n e s o f d e a uet Terrestrial life depends o n soil, o n e o f t h e most i m p o r t a n t. n t h e wastes o r d e a d bod- c o m p o n e n t s of the earth?s natural capital. The m i n e r a l s ies ( d e t r i t u s ) o f o t h e r o r g a n i s m s. E x a m p l e s a r e e a r t h - that m a k e u p y o u r muscles, bones, and m o s t o t h e r parts of w o r m s , soil i n s e c t s , h y e n a s , a n d v u l t u r e s. D e t r i t i v o r e s a n d d e c o m p o s e r s can t r a n s f o r m af a l l e n y o u r b o d y c o m e almost e n t i r e l y f r o m soil. Soil also sup- plies most of t h e n u t r i e n t s needed f o r p l a n t g r o w t h and t r e e t r u n k i n t o s i m p l e i n o r g a n i c m o l e c u l e s t h a t plants can purifies water. T h r o u g h aerobic respiration, organisms liv- a b s o r b as n u t r i e n t s ( F i g u r e 3.7). I n n a t u r a l ecosystems, t h e i n g i n soil r e m o v e some of t h e carbon d i o x i d e i n t h e a t m o - w a s t e s a n d d e a d b o d i e s o f o r g a n i s m s a r e resources f o r sphere a n d store it as organic c a r b o n c o m p o u n d s , thereby o t h e r o r g a n i s m s i n k e e p i n g w i t h t h e c h e m i c a l cycling h e l p i n g to c o n t r o l t h e earth?s climate. p r i n c i p l e o f s u s t a i n a b i l i t y. W i t h o u t decomposers and de- Soil is m u c h m o r e t h a n t h e d i r t that w e w a s h o f f o u r t r i t i v o r e s , m a n y o f w h i c h a r e m i c r o s c o p i c o r g a n i s m s (Sci- h a n d s and clothes. S o i l is a c o m p l e x m i x t u r e of rock e n c e Focus 3.1), t h e planet's land surfaces w o u l d be buried i n pieces a n d particles, m i n e r a l n u t r i e n t s , decaying organic p l a n t a n d a n i m a l wastes, dead a n i m a l bodies, a n d garbage. matter, water, air, a n d l i v i n g organisms t h a t s u p p o r t plant P r o d u c e r s , c o n s u m e r s , a n d d e c o m p o s e r s use t h e Say life, w h i c h supports a n i m a l life (Concept 3.2B). Life o n c h e m i c a l e n e r g y stored in glucose and o t h e r organic land depends o n r o u g h l y 15 centimeters ( 6 inches) of c o m p o u n d s t o f u e l t h e i r l i f e processes. I n m o s t cells, t h i s t o p s o i l ? t h e earth?s l i v i n g skin. e n e r g y is r e l e a s e d b y a e r o b i c r e s p i r a t i o n , w h i c h uses Soil is a renewable resource b u t it is r e n e w e d very o x y g e n to c o n v e r t g l u c o s e ( o r o t h e r o r g a n i c n u t r i e n t m o l - s l o w l y a n d becomes a n o n r e n e w a b l e resource i f w e deplete e c u l e s ) b a c k i n t o c a r b o n d i o x i d e a n d w a t e r. The o v e r a l l i t faster t h a n nature can replenish it. T h e f o r m a t i o n of just c h e m i c a l r e a c t i o n f o r t h e a e r o b i c r e s p i r a t i o n is s h o w n i n 2.5 centimeters (1 inch) of topsoil can take h u n d r e d s to the following equation: Detritus feeders Decomposers F I G U R E 3. 7 Various detriti- vores and decomposers (mostly fungi and bacteria) can ?feed on" or digest parts of a log and eventually convert its com- plex organic chemicals into sim- pler inorganic nutrients that can be taken up by producers. Carpenter rmite and ant galleries Te Bark beetle carpenter engraving ant work, Ory rot Long-horned fungus beetle holes - Wood Mushroom aes reduced p = to powder Powder broken d o w n by Time progression ? ) decomposers into plant nutnents in soil OW DO THEY WORK? 70 ] CHAPTER 3 ECOSYSTEMS: W H A T ARE THEY AND H  Usable energy available FIGURE 3.10 Generalized at each trophic level pyramid o f energy f l o w showing (in kilocalories) Tertiary t h e decrease in usable chemical consumers 10 e n e r g y available at each (human) succeeding t r o p h i c level in a f o o d chain o r f o o d w e b. This model assumes that w i t h each transfer f r o m o n e t r o p h i c level Secondary to another, there 1s a 9 0 % loss consumers of usable e n e r g y to t h e (perch) at, e n v i r o n m e n t in t h e f o r m o f l o w - Decomposers cHeat® ones a d quality heat. (Calories a n d joules are used t o measure energy Primary 1 kilocalorre = 1,000 calories = consumers 4 , 1 8 4 joules.) C r i t i c a l (zooplankton) t h i n k i n g : W h y 1s a vegetarian diet more energy efficient than @ meat-based diet? Producers (phytoplankton) organisms in each trophic l e v e l ? a s illus- * Humans trated by this hypothetical example: 1,000 4 2, kilograms (2,200 pounds) of producers might p r o v i d e 100 kilograms (220 pounds) Blue w h a l e ? , of food for herbivores, w h i c h might pro- T = vide 10 kilograms (22 pounds) of food f o r carnivores, w h i c h might supply a top car- nivore w i t h 1 kilogram (2.2 pounds) of food. Crabeater In natural ecosystems, most consumers seal feed on more t h a n one type of organism, a n d most organisms are eaten o r decom- posed by more t h a n o n e type of consumer. Because of this, organisms i n most ecosys- tems f o r m a complex n e t w o r k o f intercon- nected food chains called a f o o d w e b. Adelie Food chains and food w e b s s h o w h o w penguin producers, consumers, a n d decomposers are connected to o n e a n o t h e r as energy flows t h r o u g h t r o p h i c levels i n an ecosys- tem, Figure 3.11 shows an aquatic food web and Figure 3.12 s h o w s a terrestrial food web. FIGURE 3. 1 1 A greatly simplified aquatic Herbivorous food web found in the southern hemisphere. zooplankton The shaded middle area shows a simple food chain that is part of these complex interacting feeding relationships. Many more participants in the web, including an array of decomposer and detritus feeder organisms, are not shown here.  FIGURE 3.12 G r e a t l y s i m p i t f i e d terres- trial f o o d w e b f o u n d i n a t e m p e r a t e desert e c o s y s t e m The s h a d e d m i d d l e area s h o w s a s i m p l e f o o d c h a i n t h a t ts p a r t o f t h e s e c o m - plex interacting f e e d i n g relationships M a n y m o r e p a r t i c i p a n t s in t h e w e b , including an a r r a y o f d e c o m p o s e r a n d d e t r i t u s f e e d e O r g a n i s m s , are n o t s h o w n h e r e C r i t i - c a l t h i n k i n g : Can y o u imagine a f o o d w e b of w h i c h y o u are a Part? Try d r a w i n g a s i m p l e d i a g r a m o f it Gila woodpecker Palhd-winged grasshopper _GONSIDERTHIS... ?... - d u c t i v i t y ( N P P ) is the rate at w h i c h producers use , LEARNING FROM NATURE photosynthesis to produce and store c h e m i c a l energy mi- nus the rate at w h i c h they use some of this stored chemical T h e r e is no w a s t e in n a t u r e because t h e wastes o r remains of | o n e o r g a n i s m p r o v i d e f o o d f o r another. Scientists and eng!- energy t h r o u g h aerobic respiration. NPP measures how ; neers s t u d y f o o d w e b s t o learn h o w t o reduce or eliminate fast producers can m a k e the chemical energy that is stored ; f o o d w a s t e a n d the o t h e r wastes w e produce. in their tissues and that is p o t e n t i a l l y available to other organisms (consumers) i n an ecosystem. T s Gross p r i m a r y p r o d u c t i v i t y is s i m i l a r t o t h e r a t e a t w h i c h y o u m a k e money, or the n u m b e r of dollars y o u earn per S o m e Ecosystems P r o d u c e Plant M a t t e r year. N e t p r i m a r y p r o d u c t i v i t y is s i m i l a r t o t h e a m o u n t of F a s t e r T h a n O t h e r s Do m o n e y earned p e r year that you c a n spend after subtract- i n g y o u r e x p e n s e s s u c h as t h e costs o f transportation, G r o s s p r i m a r y p r o d u c t i v i t y ( G P P ) is t h e rate at w h i c h clothes, food, a n d supplies. a n ecosystem?s p r o d u c e r s (such as p l a n t s and p h y t o p l a n k - Terrestrial ecosystems and aquatic life zones differ in t o n ) c o n v e r t solar e n e r g y i n t o c h e m i c a l e n e r g y stored i n their NPP as illustrated in Figure 3.13. Despite its low NPP. c o m p o u n d s f o u n d i n t h e i r tissues. To s t a ya l i v e , grow, a n d the open ocean produces more of the earth?s biomass per r e p r o d u c e , p r o d u c e r s m u s t use some of t h e i r stored c h e m - year than any other ecosystem o r life zone. This happens ical e n e r g y f o r t h e i r o w n respiration. N e t p r i m a r y p r o - STEMS: W H A T ARE THEY A N D H O W D O THEY WORK? 74 CHAPTER 3 ECOSY:  What happens to energy in a food chain? e h E c o l o g i c a l e f f i c i e n c y is t h e p e r c e n t a g e o f into the environment as heat (seeFigure Explain why many hectares of grass are re- energy t r a n s f e r r e d f r o m o n e t r o p h i c level t o 3.10). quired to support a single hawk. Include in t h e next in an ecosystem. Energy t r a n s f e r While most of the energy at each trophic your discussion how the second law of ther- can d i f f e r slightly f r o m level t o level, b u t on level will be converted into waste heat that modynamics applies. average t h e p e r c e n t a g e o f e n e r g y trans- results from metabolism, some energy will be ferred is a p p r o x i m a t e l y 10 p e r c e n t , as P o s s i b l e R e s p o n s e : M a n y hectares o f grass contained in detritus or metabolic waste (indi- s h o w n in Figure 3. 1 0. Ecologists r e f e r t o this are required to s u p p o r t a single h a w k gestible biomass, feces, dead organisms that as t h e t e n p e r c e n t r u l e. because w h e n h i g h - q u a l i t y chemical e n e r g y were not food for other organisms) that can if only 10 percent of the energy is trans- is t r a n s f e r r e d f r o m o n e t r o p h i c level in a be used as an energy source for decomposers ferred from trophic level to trophic level, f o o d chain t o a n o t h e r r o u g h l y 9 0 % o f this and detritus feeders. As these detritivores where does the rest of the energy go? Most e n e r g y is d e g r a d e d t o l o w - q u a l i t y energy consume the detritus, they too will generate of it ends up as low-quality heat in the envi- t h a t is lost as h e a t t o t h e e n v i r o n m e n t , as waste heat through their own metabolism and ronment because of the second law of required b y t h e s e c o n d l a w o f within their own food chain (see Figure 3.9). thermodynamics. According to this law, when thermodynamics. high-quality energy is transferred by chemical FRQ A p p l i c a t i o n reactions in the cells of organisms from one Question: Consider a simple grassland trophic level to another, roughly 90% of it is food chain: degraded to lower quality energy that flows grass = mouse =» snake = hawk because oceans c o v e r 7 1 % of the earth?s surface a n d con- Study) or burned to make w a y for crops or for grazing cattle, tain h u g e n u m b e r s of p h y t o p l a n k t o n and other producers. they suffer a sharp drop in net primary productivity. They also Tropical rain forests have a high net primary productivity lose much of their diverse array of plant and animal species. because they have a large n u m b e r and variety of producer trees O n l y the plant matter represented by NPP is available and other plants. W h e n these forests are cleared (Core Case as nutrients for consumers. Thus, the planet?s NPP ultimately T e r r e s t r i a l Ecosystems Swamps and marshes Tropical rain forest Temperate forest Northern coniferous forest (taiga) Savanna Agricultural land Woodland and shrubland Temperate grassland Tundra (arctic and alpine) Desert scrub Extreme desert A q u a t i c Ecosystems Estuaries Lakes and streams Continental shelf Open ocean 800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600 A v e r a g e n e t p r i m a r y p r o d u c t i v i t y (kcal/m?/yr) FIGURE 3. 1 3 Estimated annual average net primary productivity in major life zones and ecosystems expressed as kilocalo- ties of energy produced per square meter per year (kcal/m2/yr). Q u e s t i o n : W h a t are the three most productive and the three least productive systems? 75  l i m i t s t h e n u m b e r o f consumers ( i n c l u d i n g h u m a n s ) t h a t can s u r - es, wetlands. and oceans, fromw h i c h it can rivers, lak vive o n t h e earth. T h i s is a n i m p o r t a n t l e s s o n f r o m n a t u r e. to repeat the cycle, Some precipitation seeps into evaporate { soils and is used by plants, and some the upper layers © C H E C K P O I N T FOR U N D E R S T A N D I N G 3.3 evaporates from the soilsb a c k i n thea l m o s p h e r e. o m e recipitation also sinks through soil into ? erg o u n ay- ers of rock, sand, and gravel called aquifers. Thisw a t e r 1. Explain why there are rarely more than four levels in a tro- phic pyramid. j stored underground is called g r o u n d w a t e r. Some precipi. e e e e d tation is converted to ice that is stored inglaciers. Because w a t e r is good at dissolving m a n y different 3.4 W H A T HAPPENS T O MATTER compounds, ft can easily be p o l l u t e d. H o w e v e r , n a t u r a l processes i n the w a t e r cycle can p u r i f y w a t e r ? a n i m p o r - IN A N ECOSYSTEM? tant and free ecosystem service. Only about 0.024% of the earth?s hugew a t e r supply is C O N C E P T 3. 4 Matter, in the form of nutrients, cycles within available to humans and other species asl i q u i d freshwater in a n d among ecosystems and the biosphere, and human activi- accessible groundwater deposits and in lakes, rivers, and ties are altering these chemical cycles. streams. The rest of the planet's water is too salty, is too deep underground to extract at affordable prices, o r is stored as ice. Humans alter the w a t e r cycle i n three m a j o r ways (see N u t r i e n t s Cycle W i t h i n the red arrows and boxes i n Figure 3.14). First, sometimes a n d A m o n g Ecosystems w e w i t h d r a w freshwater f r o m rivers, lakes, a n d aquifers at rates faster t h a n natural processes can replace it. As a re- T h e e l e m e n t s a n d c o m p o u n d s t h a t m a k e up n u t r i - ~ sult, some aquifers are being depleted a n d s o m e rivers n o ents m o v e c o n t i n u a l l y t h r o u g h air, water, soil, rock, i g a n d l i v i n g o r g a n i s m s w i t h i n ecosystems, i n cycles tonger f l o w to the ocean. called n u t r i e n t c y c l e s , o r biogeochemical cycles (life-earth- c h e m i c a l cycles). T h e y represent t h e chemical cycling eee eelel p r i n c i p l e o f s u s t a i n a b i l i t y i n action. These cycles are 0. 0 2 4 = : d r i v e n d i r e c t l y o r i n d i r e c t l y by i n c o m i n g solar energy and 2 Re ny b y t h e earth?s g r a v i t y a n d i n c l u d e t h e h y d r o l o g i c (water), e s s carbon, n i t r o g e n , a n d p h o s p h o r u s cycles. H u m a n activities am n e are a l t e r i n g these i m p o r t a n t c o m p o n e n t s of the earth?s n a t u r a l capital (see F i g u r e 1.3, p. 7) (Concept 3.4). Second, w e clear vegetation f r o m land f o r agriculture, mining, road building, and o t h e r activities, a n d cover much CONSIDER THIS... of the land w i t h buildings, concrete, a n d asphalt. This in- CONNECTIONS Nutrient Cycles and Life creases water r u n o f f and reduces i n f i l t r a t i o n that w o u l d N u t r i e n t cycles c o n n e c t past, present, and future forms o f life. n o r m a l l y recharge g r o u n d w a t e r supplies. Some o f t h e c a r b o n a t o m s in your skin may once have been p a r t o f an o a k leaf, a dinosaur?s skin, o r a layer o f limestone Third, w e drain and f i l l wetlands f o r f a r m i n g a n d urban tock. Your g r a n d m o t h e r , George W a s h i n g t o n , or a h u n t e r - development. Left undisturbed, w e t l a n d s p r o v i d e the eco- g a t h e r e r w h o lived 2 5 , 0 0 0 years a g o may have inhaled some of system service of flood control. T h e y act like sponges to t h e n i t r o g e n (Nz) molecules you just inhaled. absorb and hold o v e r f l o w s o f w a t e r f r o m d r e n c h i n g rains o r rapidly m e l t i n g snow. The W a t e r Cycle Sustains All Life C a r b o n Cycles a m o n g Living and Nonliving Things W a t e r ( H O ) is a n a m a z i n g substance that is necessary for life o n t h e earth. The h y d r o l o g i c cycle, also called the w a t e r Carbon is the basic b u i l d i n g b l o c k of t h e carbohydrates, c y c l e , collects, purifies, and distributes the earth?s fixed fats, proteins, DNA, and o t h e r organic c o m p o u n d s re- s u p p l y of water, as s h o w n i n Figure 3.14. quired f o r life. Various c o m p o u n d s of carbon circulate The sun powers t h e water cycle. I n c o m i n g solar energy t h r o u g h the biosphere, the atmosphere, and parts of the causes evaporation?the conversion of some of the liquid water hydrosphere, i n the c a r b o n c y c l e s h o w n i n Figure 3.15. i n the earth?s oceans, lakes, rivers, soi], and plants to vapor, A key c o m p o n e n t of the carbon cycle is carbon dioxide This w a t e r vapor rises i n t o the atmosphere, w h e r e it con- (CO,) gas. It makes u p about 0. 0 4 0 % o f the v o l u m e of the denses into droplets. G r a v i t y t h e n draws the water back to the earth?s troposphere. Carbon d i o x i d e {along w i t h w a t e r earth?s surface as precipitation (rain, snow, sleet, and dew). vapor i n the w a t e r cycle) affects the t e m p e r a t u r e of the M o s t p r e c i p i t a t i o n falling o n terrestrial ecosystems atmosphere t h r o u g h the greenhouse effect ( F i g u r e 3.3) becomes s u r f a c e r u n o f f. This w a t e r flows into streams, and thus plays a m a j o r role i n d e t e r m i n i n g t h e earth?s 7 6 @ CHAPTER 3 ECOSYSTEMS: W H A T ARE THEY A N D H O W D O THEY W O R K ?  Evaporation from ocean Precipitation to ocean Infiltration * and percolation |; into aquifer eMS t ) Come hte) C I Natural process oO Natural reservoir BE Human impacts ) Natural pathway > Pathway affected by human activities Xe FIGURE 3. 1 4 N a t u r a l capital: Simplified model of the water cycle, or hydrologic cycle, in which water circulates in various physical forms within the biosphere. The red arrows and boxes identify major effects of human activities on this cycle. C r i t i c a l t h i n k i n g : What are three ways in which your lifestyle directly or indirectly affects the hydrologic cycle? climate. If the carbon cycle removes t o o m u c h COQ, f r o m Typically, CO2 remains i n the atmosphere f o r 100 years o r the atmosphere, the atmosphere w i l l cool, and i f it gener- more. Some of the CO, i n the atmosphere dissolves i n t h e ates too m u c h COQ,, t h e atmosphere w i l l get w a r m e r. Thus, ocean. I n the ocean, decomposers release carbon that is even slight changes i n this cycle caused by natural o r h u - stored as insoluble carbonate minerals a n d rocks i n b o t t o m m a n factors can affect the earth?s climate, w h i c h helps sediment for long periods. M a r i n e sediments are the earth?s determine t h e types of life t h a t can exist in various places. largest store of carbon, m o s t l y as carbonates. Carbon is cycled t h r o u g h the biosphere by a combina- O v e r millions of years, some o f the carbon i n deeply tion o f photosynthesis by producers that removes CO, from buried deposits of dead plant m a t t e r a n d algae have been the air and water, and aerobic respiration by producers, con- converted into c a r b o n - c o n t a i n i n g fossil fuels such as coal, sumers, and decomposers that adds CO, in the atmosphere. oil, a n d n a t u r a l gas (Figure 3.15). I n a f e w h u n d r e d years, 77  QO Process O Reservoir D Pathway affected by humans D NaturalP athway Phosphates Phosphates In sewage in fertiizer Plate Phosphates tectonics mining waste Phosphate ?i| in rock t} (fossi bones, guano} Animais iconsumers) Phosphate dissolved in in shallow ocean sediments in d e e p ocean sediments, F I G U R E 3. 1 7 N a t u r a l c a p i t a l : Simplified model showing the circulation of various chemical forms o f phosphorus (mostly phosphates) in the phosphorus cycle, with major harmful human im- Pacts shown by the red arrows. (Yellow box sizes do not show relative reservoir sizes.) C r i t i c a l t h i n k i n g : W h a t are t w o ways in which the phosphorus cycle and the nitrogen cycle are linked? W h a t are t w o ways in which the phosphorus cycle and the carbon cycle are linked? A s w a t e r r u n s o v e r exposed rocks, it s l o w l y erodes H u m a n activities, i n c l u d i n g the r e m o v a l of large amounts a w a y i n o r g a n i c c o m p o u n d s t h a t c o n t a i n p h o s p h a t e ions. of phosphate from the earth to m a k e fertilizer, disrupt the W a t e r carries these i o n s i n t o t h e soil, w h e r e t h e y are a b - phosphorus cycle (see red arrows i n Figure 3.17). B y clearing s o r b e d b y t h e r o o t s of plants a n d by o t h e r p r o d u c e r s. Phos- tropical forests (Core Case Study), w e reduce phosphate p h a t e c o m p o u n d s a r e t h e n t r a n s f e r r e d by food w e b s f r o m levels i n tropical soils. Eroded topsoil a n d fertilizer washed p r o d u c e r s to c o n s u m e r s a n d e v e n t u a l l y t o d e t r i t u s feeders from fertilized crop fields, lawns, a n d golf courses carry large a n d decomposers. quantities of phosphate ions into streams, lakes, a n d oceans. W h e n phosphate and o t h e r phosphorus compounds There they stimulate the g r o w t h of producers such as algae w a s h i n t o t h e ocean, t h e y are deposited as m a r i n e sediment and various aquatic plants, w h i c h can upset chemicalc y c l i n g a n d c a n r e m a i n t r a p p e d f o r m i l l i o n s of years, O v e r time, and other processes i n bodies of water. A c c o r d i n g t o a num- g e o l o g i c a l processes can u p l i f t a n d expose these seafloor b e r of scientific studies, w e are d i s r u p t i n g the phosphorus deposits, f r o m w h i c h p h o s p h a t e can be e r o d e d a n d freed cycle because o u r inputs of phosphorus i n t o t h e environ- u p to r e e n t e r t h e p h o s p h o r u s cycle. m e n t ( p r i m a r i l y f o r use as fertilizer) have exceeded the M o s t soils c o n t a i n l i t t l e p h o s p h a t e , w h i c h o f t e n l i m i t s planet?s e n v i r o n m e n t a l l i m i t f o r phosphorus. p l a n t g r o w t h o n l a n d unless p h o s p h o r u s (as p h o s p h a t e salts m i n e d f r o m t h e e a r t h ) is a p p l i e d t o t h e soil as a fertil- CONSIDERT H I S... cee izer. L a c k o f p h o s p h o r u s also l i m i t s t h e g r o w t h of p r o d u c e r | p o p u l a t i o n s i n m a n y f r e s h w a t e r streams a n d lakes, T h i s is L E A R N I N G F R O M NATURE because p h o s p h a t e salts a r e o n l y s l i g h t l y soluble i n w a t e r ' Scientists study the water, carbon, nitrogen, and phosphorus a n d d o n o t release m a n y p h o s p h a t e i o n s to p r o d u c e r s i n cycles to help us learn how to recycle the wastes we create. a q u a t i c systems.. - -- 80 | CHAPTER 3. ECOSYSTEMS: WHAT ARE THEY ANO HOW DO THEY WORK?  bai? Planetary Boundaries For most of the past 10,000-12,000 years, earth?s life-support system,e s p e c i a l l y humans have been living in an era called produce food; (2) biodiversity loss from since 1950, replacing biologically diverse forests and the Holocene. During this era, we have In 2015 an international team of 18 grasslands with simplified fields of single enjoyed a favorable climate and other en- leading researchers in their fields published crops; (3) land system change from agri- vironmental conditions. This general sta- a paper estimating how close we are to culture and urban development; and bility allowed the human population to exceeding nine major planetary boundaries, (4) climate change from disrupting the grow, develop agriculture, and take over Or ecological tipping points, because of a large share of the earth?s land and carbon cycle, mostly by overloading human activities. They warn thatexceeding the atmosphere with carbon dioxide other resources (see Figure 1.8, p. 12). them could change how the planet oper- produced by the burning of fossil fuels. Most geologists contend that w e are ates and could trigger abrupt and long- There is an urgent need for more re- still living in the Holocene era, but some lasting or irreversible environmental changes. search to fill in the missing data on these scientists disagree. According to them, This could seriously degrade the earth's life- planetary boundaries. when the Industrial Revolution began Support system and our economies. (around 1750) w e entered an era called The researchers estimated that w e the Anthropocene, an era dominatedb y have exceeded four of theseplanetary humans. In this new era, our ecological CRITICAL A e boundaries. They are (1) disruption of the footprints have expanded significantly nitrogen and phosphorus cycles, mostly W h i c h t w o o f these b c u n d a r i e s d o you and are changing and stressing the from greatly increased use of fertilizers to t h i n k are t h e m o s t i m p o r t a n t ? CHECKPOINT FOR U N D E R S T A N D I N G 3. 4 w h a t w e k n o w about ecosystems has c o m e from such research, 1. Identify several ways that human activities are altering the Scientists use a variety o f m e t h o d s to s t u d y t r o p i c a l hydrologic cycle. forests (Core Case S t u d y ). Some b u i l d tall c o n s t r u c t i o n 2. Identify several harmful human activities that are altering the. cranes to reach the canopies. This, a l o n g w i t h c l i m b i n g carbon cycle. trees and installing rope w a l k w a y s b e t w e e n treetops, 3. Discuss t h e role t h a t bacteria play in the nitrogenc y c l e. helps t h e m i d e n t i f y a n d observe t h e d i v e r s i t y o f species living or feeding i n these treetop habitats. 4. Identify several harmful h u m a n activities t h a t are altering t h e : Ecologists carry out controlled experiments by isolating and phosphorus cycle. j changing a variable in part of an area and comparing the results with nearby unchanged areas. You learned abouta classic ex- ample of this i n the Core Case Study of Chapter 2 (p. 36). 3.5 H O W DO SCIENTISTS Scientists also use aircraft and satellites equipped w i t h sophisticated cameras and other remote sensing devices to STUDY ECOSYSTEMS? scan and collect data on t h e earth?s surface. T h e y use geo- graphic information system (GIS) software to capture, store, CONCEPT 3.5 Scientists use field research, laboratory research, analyze, a n d display this i n f o r m a t i o n. For example, GIS and mathematical and other models to learn about ecosystems software can convert digital satellite images i n t o global, and how much stress they can take. regional, and local maps. These maps s h o w variations i n vegetation, gross p r i m a r y productivity, soil erosion, defor- Some Scientists S t u d y N a t u r e Directly estation, air p o l l u t i o n emissions, w a t e r usage, d r o u g h t , flooding, pest outbreaks, a n d o t h e r variables. Scientists use field research, laboratory research, a n d Some researchers attach t i n y radio transmitters to ani- mathematical and o t h e r models to learn about ecosystems mals a n d use global positioning systems (GPSs) to track (Concept 3.5). Field research, sometimes called ?muddy- w h e r e and h o w f a r animals go. This technology is i m p o r - boots biology,? involves g o i n g into forests (see Chapter 2 tant f o r studying endangered species. Scientists also study opening photo, pp. 3 4 - 3 5 ) , oceans (see opening p h o t o this nature by using cell p h o n e cameras and m o u n t i n g t i m e - chapter), and other natural settings to study the structure lapse cameras o r video cameras o n Stationary objects o r of ecosystems and to learn w h a t happens i n them. M o s t of small drones. 31  a n d t h e r a t e at w h i c h t h e y use p h o t o s y n t h e s i s : c o m p l e x process secondary c o n s u m e r (carnivore), some of t h a t energy t h r o u g h i n t h e cells of g r e e n plants that o r g a n i s m t h a t feeds o n l y o n c e l l u l a r respiration. captures l i g h t e n e r g y a n d converts primary consumers. n i t r o g e n c y c l e : cyclic m o v e m e n t of it to c h e m i c a l b o n d energy. soil: complex mixture of nitrogen in different chemical p r i m a r y consumer (herbivore): i n o r g a n i c m i n e r a l s (clay, silt, f o r m s f r o m t h e e n v i r o n m e n t to o r g a n i s m t h a t feeds o n s o m e or pebbles, a n d s a n d ) , d e c a y i n g o r g a n i s m s and t h e n b a c k t o t h e all parts o f plants or o n o t h e r o r g a n i c m a t t e r , w a t e r , air, and environment. producers. living organisms. n u t r i e n t : any chemical a n p r o d u c e r ( a u t o t r o p h ) : organism stratosphere: second layer of the o r g a n i s m m u s t take i n to live, t h a t uses solar e n e r g y (green atmosphere, containing the ozone grow, or reproduce. plants) o r c h e m i c a l e n e r g y (some layer, which filters out most of the n u t r i e n t cycle (biogeochemical bacteria) to m a n u f a c t u r e t h e sun's harmful UV-light rays. c y c l e ) : n a t u r a l process t h a t recycles o r g a n i c c o m p o u n d s i t needs as s u r f a c e r u n o f f : w a t e r f l o w i n g off n u t r i e n t s i n various chemical forms nutrients from simple inorganic t h e fand i n t o bodies of surface f r o m t h e n o n l i v i n g e n v i r o n m e n t to water, c o m p o u n d s obtained f r o m the living organisms and t h e n back to environment. t e r t i a r y c o n s u m e r : animal the nonliving environment. t h a t feeds o n a n i m a l - e a t i n g p y r a m i d of energy f l o w (trophic o m n i v o r e : a n i m a l t h a t can use animals. p y r a m i d ) : d i a g r a m representing b o t h p l a n t s a n d a n i m a l s as f o o d the f l o w of energy t h r o u g h each t r o p h i c l e v e l : all organisms that sources. t r o p h i c level i n a food chain o r food are the same n u m b e r of e n e r g y P h o s p h o r u s c y c l e : cyclic web. W i t h each energy transfer, transfers a w a y f r o m t h e o r i g i n a l m o v e m e n t of phosphorus i n o n l y a small part (typically 1 0 % ) o f source o f e n e r g y (sun) t h a t enters different chemical forms from the t h e usable energy e n t e r i n g one an ecosystem. e n v i r o n m e n t t o organisms and t r o p h i c level is transferred to the t r o p o s p h e r e : i n n e r m o s t l a y e r of t h e n back t o t h e e n v i r o n m e n t. organisms at t h e n e x t t r o p h i c level. t h e atmosphere. Chapter Review Core Case S t u d y of each. (c) D i s t i n g u i s h b e t w e e n the l i v i n g a n d n o n - 1. W h a t are t h r e e h a r m f u l effects o f the clearing a n d l i v i n g c o m p o n e n t s i n ecosystems a n d g i v e t w o e x - d e g r a d a t i o n o f t r o p i c a l r a i n forests? amples of each. 4. (a) W h a t is a t r o p h i c l e v e l ? D i s t i n g u i s h a m o n g p r o - S e c t i o n 3.1 ducers (autotrophs), consumers (heterotrophs), 2. (a) W h a t a r e t h e t w o k e y c o n c e p t s f o r t h i s d e c o m p o s e r s , and d e t r i t u s f e e d e r s ( d e t r i t i - s e c t i o n ? (b) D e f i n e a n d d i s t i n g u i s h a m o n g t h e v o r e s ) , a n d give an e x a m p l e o f each. (b) S u m m a r i z e a t m o s p h e r e , troposphere, stratosphere, the process o f p h o t o s y n t h e s i s a n d e x p l a i n h o w it h y d r o s p h e r e , g e o s p h e r e , and b i o s p h e r e. provides us w i t h f o o d a n d the o x y g e n i n t h e air t h a t (c) W h a t t h r e e i n t e r c o n n e c t e d factors s u s t a i n l i f e w e breathe. (c) D i s t i n g u i s h a m o n g p r i m a r y c o n - o n t h e e a r t h ? (d) D e s c r i b e t h e f l o w o f e n e r g y to sumers (herbivores), carnivores, secondary con- a n d f r o m t h e e a r t h. (e) W h a t is t h e g r e e n h o u s e s u m e r s , t e r t i a r y c o n s u m e r s , and o m n i v o r e s , and e f f e c t a n d w h y is it i m p o r t a n t ? g i v e an e x a m p l e of each.. 5. {a) Explain the importance of microbes. (b) W h a t is Section 3.2 a e r o b i c r e s p i r a t i o n ? (c) W h a t t w o processes sustain 3. (a) W h a t are t h e t w o k e y concepts f o r this section? ecosystems and the biosphere and h o w are they linked? (b) D e f i n e e c o l o g y. D e f i n e o r g a n i s m , p o p u l a t i o n , c o m m u n i t y , and e c o s y s t e m , and give an example 6. W h a t is s o i l ? cA mw CUAPTER 2 ECOSYSTEMS: W H A T ARE THEY A N D H O W D O THEY W O R K ?