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Chapter 4 Ecosystems: What Are They and How Do They Work?. © Brooks/Cole Publishing Company / ITP. Key Concepts. Basic ecological principles. Major components of ecosystems. Matter cycles and energy flow. Ecosystem studies. Principles of Sustainability. 4-1 THE NATURE OF ECOLOGY.

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Chapter 4

Ecosystems: What Are They and How Do They Work?

© Brooks/Cole Publishing Company / ITP


Key Concepts

  • Basic ecological principles
  • Major components of ecosystems
  • Matter cycles and energy flow
  • Ecosystem studies
  • Principles of Sustainability
4 1 the nature of ecology
  • Ecology- study of relationships between organisms and their environment
    • Ecology examines how organisms interact with their nonliving (abiotic) environment such as sunlight, temperature, moisture, and vital nutrients
    • Biotic interaction among organisms, populations, communities, ecosystems, and the ecosphere
the nature of ecology
The Nature of Ecology
  • Ecosystem organization
  • Organisms
  • Populations
  • Communities
  • Ecosystems
  • Biosphere

Fig. 4-2 p. 57



  • organism: any form of life.
  • organisms are classified into species.
  • species: groups of organisms that resemble each other, and in cases of sexually reproducing organisms, can potentially interbreed.
  • estimates of 5 to 100 million species, most are insects & microorganisms; so far only about 1.8 million named; each species is the result of long evolutionary history.
  • wild species: population that exists in its natural habitat (= native species).
  • domesticated or introduced species: population introduced by humans (= non–native species).


  • population: a group of interacting individuals of the same species.
  • examples: sunfish in a pond, white oak trees in a forest, people in a city;
  • habitat: the place where a population usually lives.
  • genetic diversity: in natural populations individuals vary in their genetic makeup.

© Brooks/Cole Publishing Company / ITP



  • community: populations of all species living together in a given area.
    • a biological community is a complex interacting network of plants, animals and microorganisms.
    • example: redwood forest community, consisting of populations of redwoods & other trees, shrubs and herbaceous species, animals and microorganisms.

© Brooks/Cole Publishing Company / ITP


Ecosystems & Ecosphere

ecosystem: a community of different species interacting with one another & with their non–living environment of matter & energy.


a patch of woods, a lake or pond, a farm field, an entire watershed in a tropical rain forest.

ecosphere (=biosphere): all of Earth's ecosystems together.

© Brooks/Cole Publishing Company / ITP

what is life

OBJ 4. 1

What is Life?
  • All life shares a set of basic characteristics
    • Made of cells that have highly organized internal structure and functions
    • Characteristic types of deoxyribonucleic acid (DNA) molecules in each cell
living organisms
Living Organisms
  • Capture and transform matter and energy from their environment to supply their needs for survival, growth, and reproduction
  • Maintain favorable internal conditions, despite changes in their external environment through homeostasis, if not overstressed
living organisms1
Living Organisms
  • Perpetuate themselves through reproduction
  • Adapt to changes in environmental conditions through the process of evolution

OBJ 4. 2


Earth's major components

Fig. 4–7


OBJ 4. 3

What Sustains Life?

Energy From Sun

one–way flow of usable energy from sun, through feeding interactions, to low–quality forms (heat)

Fig 4-9

© Brooks/Cole Publishing Company / ITP

Cycling of Matter

* the continual flow of matter between the nonliving environment & living organisms;


* enables Earth to hold its atmosphere; causes downward movement of matter in nutrient cycles.



  • biome: large regions characterized by a distinct climate & specific life–forms, especially vegetation, adapted to the region.
    • major biomes:
    • temperate grassland, temperate deciduous forest, desert, tropical rain forest, tropical deciduous forest, tropical savannah, coniferous forest, tundra
  • aquatic life zone: major marine or freshwater portion of the ecosphere, containing numerous ecosystems.
    • major aquatic life zones:
    • lakes, streams, estuaries, coastlines, coral reefs, & the deep ocean

© Brooks/Cole Publishing Company / ITP


OBJ 4. 4

Major Components of Ecosystems

  • abiotic: non–living components
    • examples: water, air, nutrients, & solar energy
  • biotic: living components (=biota)
    • examples: plants, animals, & microorganisms

© Brooks/Cole Publishing Company / ITP


Major Components of Ecosystems

Major components of aquatic ecosystems.

Fig. 4–11

© Brooks/Cole Publishing Company / ITP


Major Components of Ecosystems

Major components of terrestrial ecosystems.

Fig. 4–12

© Brooks/Cole Publishing Company / ITP

range of tolerance

OBJ 4. 5

Range of Tolerance

Variations in it’s physical and chemical environment

  • Differences in genetic makeup, health, and age.
  • Ex: trout has to live in colder water than bass

Law of Tolerance

The survival, growth, & reproduction of organisms is determined, in part, by maximum & minimum tolerance limits for physical conditions such as temperature.

Fig. 4–13

© Brooks/Cole Publishing Company / ITP

limiting factor
Limiting Factor
  • More important than others in regulating population growth
    • Ex: water light, and soil
    • Lacking water in the desert can limit the growth of plants
limiting factor principle
Limiting Factor Principle
  • too much or too little of any abiotic factor can limit growth of population, even if all the other factors are at optimum (favorable) range of tolerance.
    • Ex: If a farmer plants corn in phosphorus-poor soil, even if water, nitrogen are in a optimum levels, corn will stop growing, after it uses up available phosphorus.
dissolved oxygen content
Dissolved Oxygen Content
  • Amount of oxygen gas dissolved in a given volume of water at a particular temperature and pressure.
    • Limiting factor of aquatic ecosystem
components of an ecosystem producers

OBJ 4. 6


Producers or autotrophs- makes their own food from compound obtained from environment.

  • Ex: plant gets energy or food from sun
consumers or heterotrophs
Consumers or Heterotrophs
  • Obtain energy and nutrients by feeding on other organisms or their remains
  • Herbivores (plant-eaters) or primary consumers
  • Feed directly on producers
    • Deer, goats, rabbits

  • Carnivores (meat eater) or secondary consumers
  • Feed only on primary consumer
    • Lion, Tiger
  • Tertiary (higher-level) consumer
  • Feed only on other carnivores
    • Wolf
  • Omnivores- consumers that eat both plants and animals
    • Ex: pigs, humans, bears
  • Scavengers- feed on dead organisms
    • Vultures, flies, crows, shark
  • Detritivores- live off detritus
    • Detritus parts of dead organisms and wastes of living organisms.
  • Detritus feeders- extract nutrients from partly decomposed organic matter plant debris, and animal dung.
  • Decomposers - Fungi and bacteria break down and recycle organic materials from organisms’ wastes and from dead organisms
    • Food sources for worms and insects
    • Biodegradable - can be broken down by decomposers

Fig. 4–16

© Brooks/Cole Publishing Company / ITP


OBJ 4. 7

Food Web

  • Complex network of interconnected food chains
  • Food web and chains
    • One-way flow of energy
    • Cycling of nutrients through ecosystem
Grazing Food Webs
    • Energy and nutrients move from plants to herbivores
    • Then through an array of carnivores
    • Eventually to decomposers

(100,000 Units of Energy)

Grazing Food Webs
    • Energy and nutrients move from plants to herbivores
    • Then through an array of carnivores
    • Eventually to decomposers

(1,000 Units of Energy)

Grazing Food Webs
    • Energy and nutrients move from plants to herbivores
    • Then through an array of carnivores
    • Eventually to decomposers

(100 Units of Energy)

Grazing Food Webs
    • Energy and nutrients move from plants to herbivores
    • Then through an array of carnivores
    • Eventually to decomposers

(10 Units of Energy)

Grazing Food Webs
    • Energy and nutrients move from plants to herbivores
    • Then through an array of carnivores
    • Eventually to decomposers

(1 Units of Energy)

Detrital Food Webs
    • Organic waste material or detritus is the major food source
    • Energy flows mainly from producers (plants) to decomposers and detritivores.

OBJ 4. 8

Photosynthesis & Respiration

  • photosynthesis: complex chemical reaction in plants, in which solar radiation is captured by chlorophyll (& other pigments) & used to combine carbon dioxide & water to produce carbohydrates (e.g., glucose), other organic compounds, & oxygen.
    • carbon dioxide + water + solar energy glucose + oxygen
    • 6 CO2 + 6 H2O + solar energy C6H12O6 + O2
  • aerobic respiration: complex process that occurs in the cells of organisms, in which organic molecules (e.g., glucose) are combined with oxygen to produce carbon dioxide, water, & energy.
    • glucose + oxygen carbon dioxide + water + energy
    • C6H12O6 + O2 6 CO2 + 6 H2O + energy
    • Anaerobic Respiration or Fermentation: Breakdown of glucose in absence of oxygen

© Brooks/Cole Publishing Company / ITP

Producers transmit 1-5% of absorbed energy into chemical energy, which is stored in complex carbohydrates, lipids, proteins and nucleic acid in plant tissue
  • Bacteria can convert simple compounds from their environment into more complex nutrient compound without sunlight
    • Ex: becomes consumed by tubeworms, clams, crabs
    • Bacteria can survive in great amount of heat

OBJ 4. 9

  • Genetic diversity
  • Species diversity
  • Ecological diversity
  • Functional diversity
second law of energy

OBJ 4. 10

Second Law of Energy
  • Organisms need high quality chemical energy to move, grow and reproduce, and this energy is converted into low-quality heat that flows into environment
    • Trophic levels or feeding levels- Producer is a first trophic level, primary consumer is second trophic level, secondary consumer is third.
    • Decomposers process detritus from all trophic levels.


Food chains involve a sequence of organisms, each of which is the food for the next.

Fig. 4–18

© Brooks/Cole Publishing Company / ITP


Food Webs & Energy Flow

Example of some of the complexity of a food web in Antarctica.

Fig. 4–19

© Brooks/Cole Publishing Company / ITP


Generalized Energy Pyramid

In nature, ecological efficiency varies from 5% to 20% energy available between successive trophic levels (95% to 80% loss). About 10% efficiency is a general rule.

Fig. 4–21

© Brooks/Cole Publishing Company / ITP


Generalized Energy Pyramid

Annual pyramid of energy flow (in kilocalories per square meter per year) for an aquatic ecosystem in Silver Springs, FL.

Fig. 4–20

© Brooks/Cole Publishing Company / ITP

  • Dry weight of all organic matter contained in organisms.
    • Biomass is measured in dry weight
      • Water is not source of energy or nutrient
    • Biomass of first trophic levels is dry mass of all producers
    • Useable energy transferred as biomass varies from 5%-20% (10% standard)
pyramid of biomass
Pyramid of Biomass

Storage of biomass at various trophic levels of ecosystem

pyramid of numbers
Pyramid of Numbers

Number of organisms at each trophic level


gross primary productivity gpp
Gross Primary Productivity (GPP)

Rate in which producers convert solar energy into chemical energy (biomass) in a given amount of time

net primary productivity npp
Net Primary Productivity (NPP)
  • Rate in which energy for use by consumers is stored in new biomass of plants
    • Measured in kilocalories per square meter per year or grams in biomass
    • NPP is the limit determining the planet’s carrying capacity for all species.
    • 59% of NPP occurs in land / 41% occurs in ocean
nutrient cycles closed system energy flow open system







Energy Flow

OBJ 4. 11

Nutrient Cycles (Closed System) Energy Flow (Open System)

Open vs. Closed Systems

  • Closed System: a system in which energy, but not matter, is exchanged between the system & its environment.
    • Earth is a closed system - matter is neither lost nor gained (except negligible cosmic dust & meteorites) while energy flows through;
  • Open System: a system in which both energy & matter are exchanged between the system & its environment.
    • organisms are open systems because both matter & energy are exchanged with the environment.

© Brooks/Cole Publishing Company / ITP


Energy Flow & Nutrient Cycling

Life on Earth depends upon one–way flow of high–quality energy from sun & cycling of crucial elements.

Fig. 4–6

© Brooks/Cole Publishing Company / ITP


Energy Flow

The ultimate source of energy in most ecosystems is the sun.

Fig. 4–7

© Brooks/Cole Publishing Company / ITP


Nutrient Cycles

  • nutrient: any atom, ion, or molecule an organism needs to live, grow, or reproduce.
    • macronutrients needed in relatively large amountse.g., C, O, H, N, P, S, K, Ca, Mg, Fe
    • micronutrients needed in relatively small amountse.g., Na, Zn, Cu, Cl, I
    • nutrient cycles (= biogeochemical cycles) involve continual flow of nutrients from nonliving (air, water, soil, rock) to living organisms (biota) & back again.
    • nutrient cycles driven directly or indirectly by solar radiation & gravity.
    • Major cycles: hydrologic (water), carbon, oxygen, nitrogen, phosphorus and sulfur.

© Brooks/Cole Publishing Company / ITP

the sulfur cycle
The Sulfur Cycle

Fig. 4-34 p. 83


What on Earth is Soil?

  • outermost layer of our planet
  • Topsoil is the most productive
  • natural processes can take more than 500

years to form one inch of topsoil.

  • formed from rocks and decaying plants &




  •  varying amounts of organic matter
  •  minerals, and nutrients
  •  mineral particles (sand, silt, and clay)
  •  sample: 45 % minerals, 25 % water,
  • 25 % air, 5% organic matter
  •  loosen the soil, allowing O2 to penetrate
  •  hold soil together
  •  prevent erosion
  •  earthworms digest organic matter,
  • recycle nutrients, enrich soil
  •  fungi and bacteria help break down
  • organic matter in the soil

OBJ 4. 12

The major horizons are as follows.

O= organic matter on the soil surface that is in various states of decay.

A= the surface of the mineral soil that is composed of mineral and organic material.

E= the horizon between the surface and subsurface that has some part of it removed and transported to the subsurface by the flow of precipitation through the soil. Clay, iron, aluminum, and humus are most often the materials removed.

B= the subsurface zone where materials from the horizons above are deposited by the water that continually moves down from the surface.

C= A zone of partially weathered rock.

R = bedrock in its unchanged state.


An E horizon can develop in this area.

Bedrock can lie below the C horizon. In this position, the bedrock is called an R horizon.


Soil Characteristics

Horizon characteristics are used to name and classify soil.

Soil taxonomy defines diagnostic horizons that have certain properties, which reflect the soil forming processes that created them .

There is a set of surface and subsurface diagnostic horizons.

The main clues for identifying diagnostic properties of interest include texture, color, structure, consistency, and profile position.

Your soil judging worksheet will ask you to identify the soil forming factors and the soil diagnostic features that are evident in each of the soil bodies to be judged.



Texture is often the first characteristic soil scientists determine.

It is the relative proportion of sand, silt, & clay sized particles in the fine earth fraction of a soil horizon.

The fine earth fraction is all of the individual particles that are smaller than 2mm in diameter. Everything larger than sand is excluded.





2mm sand particle

magnified 133x

Clay particle


The three main methods for measuring texture are

Pipette method – laboratory procedure used by the National Soil Survey Lab in Lincoln, NE. It is time consuming and very accurate.

Hydrometer method – a reasonably accurate simple laboratory procedure often used in soil survey field offices to test the accuracy of the feel method.

Feel method – method used by soil scientists in the field, which involves feeling the soil with your fingers.

Requires practice and occasional calibration with the hydrometer method .

Soil survey scientists continually compare how they perceive various field samples using the feel method. This ensures consistent results from one scientist to another.