Ecosystems & Environment

7/27/2019 Ecosystems & Environment

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Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Hewitt/Lyons/Suchocki/Yeh

Conceptual Integrated

Science

Chapter 21

ECOSYSTEMS ANDENVIRONMENT




This lecture will help you

understand:• Organisms and Their Environment

• Species Interactions

• Science and Society: Species Interactions

• Science and Society: Invasive Species• Energy Flow in Ecosystems

• Integrated Science: Materials Cycling

• Kinds of Ecosystems

• Change in an Ecosystem• Population Studies

• Human Population Growth




Organisms and Their Environment

Ecology is the study of how organismsinteract with their environments.

The environment includes abiotic (nonliving) and biotic (living) components.

We study ecology at many levels, includingthe individual, population, community, andecosystem.




Prairie dogs living in Nebraska represent:

A. A species

B. A populationC. A community


CHECK YOUR NEIGHBOR




Prairie dogs living in Nebraska represent:

A. A species

B. A population

C. A community


CHECK YOUR ANSWER




Species Interactions

Food chains and food webs describe which

species eat which other species. These feeding

levels—called trophic levels—include

producers and consumers.


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Species Interactions

Other types of species interactions include:

• Competition—species compete when their

niches overlap.

• Symbiosis—species may live in closeassociation with one another. A symbiotic

relationship may involve parasitism,commensalism, or mutualism.



Science and Society: Species

Interactions

Studies show that diverse communities aremore stable and more productive.

• More species means greater redundancy

in a community.• Diverse communities might be more

productive because different species use

resources in different ways.• It is harder for new species to successfully

invade a diverse habitat.



Science and Society: Invasive

SpeciesInvasive species are species that are introduced from

their native habitat into a new habitat and that proceed tothrive there. This results in harm to native species.

Invasive species:

• Usually are unintentionally introduced (at least thesedays)

• May out-compete or devour native species



Energy Flow in Ecosystems

All organisms need energy in order to grow, reproduce, and perform theactivities necessary for survival.

The amount of organic matter in an ecosystem is its biomass.

The rate at which an ecosystem’s producers build biomass is theecosystem’s primary productivity.



Energy Flow in Ecosystems

On average, only about 10 percent of the energy at onetrophic level becomes available to the next level. Theother 90 percent is:

• Uneaten organisms

• Heat lost to the environment• Feces

• Maintenance



Integrated Science: Energy Leaks

Where Trophic Levels Meet• Moving energy from one trophic level to another involves

a long series of chemical reactions.

• Because every chemical reaction involves some energyloss to the environment, we see why so much energyleaks from one trophic level to the next.



Kinds of Ecosystems

There are terrestrial and aquatic ecosystems.

Terrestrial ecosystems are called biomes.



Kinds of Ecosystems

There are eight biomes on Earth:

• Tropical forests

• Temperate forests• Coniferous forests

• Tundra

• Savannas

• Temperate grasslands• Chaparral

• Deserts

Ki d f E t



True or false? Deserts are not always

located in a band around 30 degrees north

latitude and 30 degrees south latitude.

Explain your answer to your neighbor.

Kinds of Ecosystems

CHECK YOUR NEIGHBOR

Ki d f E t



True. Deserts are defined by the low level of

precipitation they receive. Some deserts,

including the continent of Antarctica, are

located far from the equator. Like alldeserts, Antarctica receives very little

precipitation. When it falls, it is in the form

of snow.

Kinds of Ecosystems

CHECK YOUR ANSWER



Kinds of Ecosystems

Aquatic ecosystems include freshwater and

saltwater environments as well as

estuaries where freshwater and saltwater

meet.



Kinds of Ecosystems

All lakes and ponds can be divided into three zones:

• The littoral zone—close to the water surface and to shore, relativelywarm because of its exposure to sunlight.

• The limnetic zone—close to the water surface but far from shore,occupied largely by plankton, organisms that float in the water rather than swim actively.

• The profundal zone—deep water habitats in ponds and lakes. Mostorganisms in the profundal zone consume organic debris that driftsdown from above.



Kinds of Ecosystems

Species that live in the flowing waters of

rivers and streams usually have

adaptations that allow them to keep from

being washed away: hooks, suckers,strong swimming ability.

Algae often occupy the base of the food

chain in river and stream habitats.



Kinds of Ecosystems

Estuaries are habitats where freshwater rivers joinoceans.

Estuarine plants, such as certain seaweeds, marshgrasses, and mangroves, have adaptations thatallow them to deal with changing salinityconditions.



Kinds of Ecosystems

Ocean habitats are divided by either the depth in the water column or proximity to shore.

Many species are found in the pelagic zone—either in the photic zone close to the water surface or the deeper aphotic zone, whichreceives little sunlight and is much more limited in food availabilityand biodiversity.

The vast majority of marine species are found not in the pelagic zonebut in the benthic zone on the ocean bottom.



Kinds of Ecosystems

The intertidal zone: closest to shore, periodicallyunderwater and exposed to air as the tidemoves in and out. Many species, includingcertain barnacles, sea anemones, starfish, and

other species, are specialized for life in theintertidal zone.

The neritic zone: underwater marine habitats near

the coasts, such as coral reefs. The neritic zonecontains high levels of nutrients that havewashed into the water from land.

Farther out is the deeper oceanic zone.



Integrated Science: Materials

Cycling

Many substances on Earth travel through a

continuous cycle from living organisms to

the abiotic environment and back—these

are biogeochemical cycles.

Three of these cycles involve water, carbon,

and nitrogen.




CyclingThe water cycle:

• Water evaporates from theoceans into the atmosphere.

• Water is moved around theatmosphere by winds.

• Water precipitates as rain or snow over ocean or land.

• Water moves into the bioticworld when it is absorbed or swallowed by organisms. Someof this water then passes up thefood chain. The rest is returnedto the abiotic environment in avariety of ways, includingthrough animal respiration,perspiration, excretion, andelimination, and evaporationfrom plant tissue.





CyclingThe carbon cycle:

• Most of the inorganic carbon onearth exists as carbon dioxide and isfound either in the atmosphere or dissolved in ocean waters.

• Plants and other producers convertcarbon dioxide to glucose duringphotosynthesis.

• Carbon is returned to theenvironment by living organisms ascarbon dioxide, a product of cellular respiration.

• Because atmospheric carbondioxide traps heat on the planet, thishas resulted in global warming.





CyclingThe nitrogen cycle:• Nitrogen is found primarily as

nitrogen gas, the dominantcomponent of the Earth’satmosphere.

• In order for living organisms tomake use of nitrogen, it has tobe converted into usable form.Living organisms rely onbacteria to accomplish thistransformation. Nitrogen isconverted to ammonium by

nitrogen-fixing bacteria in soil,and then to nitrates bynitrifying bacteria.

• Nitrogen returns to the abioticenvironment when it isconverted back to nitrogen gasby denitrifying bacteria.




Change in an Ecosystem

Ecological succession describes how the

species composition of an ecosystem

changes after a disturbance.

Ecological succession is sometimes divided

into two types, primary succession and

secondary succession.





Primary succession: the colonization of bare land devoid of soil; may occur when new land is formed by volcanic activity or when a glacier’s retreatreveals bare rock.

Early colonizers of new habitat, known as pioneer species, must survive withfew nutrients and little existing organic matter, cope with direct sunlight, and

survive the variable temperatures that result from lack of cover.

Pioneer species are often succeeded by grasses, shrubs, and finally, trees.

Ecological succession culminates in a climax community .

During the process of succession, the total biomass of the ecosystem typicallyincreases, as does the number of species.









Secondary succession occurs when a disturbance destroys existing life

in a habitat, but leaves soil intact.

Examples: fires, abandonment of

old farmland

Because soil is already present,

secondary succession

proceeds more quickly

than does primarysuccession.





Intermediate disturbance hypothesis—

Regular disturbances, if not too extreme,

actually contribute to biodiversity because

different species make use of differenthabitats, and periodic disturbances

guarantee that there will always be habitat

at varying stages of recovery.




Population Studies

Population Studies




A population is a group of individuals

belonging to a single species that

occupies a certain area.

What are some populations in your area?

Discuss with your neighbor.

Population Studies

CHECK YOUR NEIGHBOR




Population Studies

Population size over time depends on four

variables—birth rate, death rate, the rate

of immigration into the population, and the

rate of emigration out of the population.




Population Studies

Exponential growth occurs when a

population grows at a rate that is

proportional to its size.




Population Studies

Logistic growth occurs when populationgrowth slows as it reaches the habitat’scarrying capacity, the maximum number

of individuals or maximum populationdensity the habitat can support.




Population Studies

Organisms have different life history strategies.

r-selected organisms produce a lot of offspring and invest little

in each offspring. For example, they provide little parental

care. Few of the offspring reach adulthood.

K-selected organisms produce a few offspring and provide a

great deal of investment in each. For example, they provide a

lot of parental care. Most of their offspring reach adulthood.

Of course, these are two extremes along a continuum.




Population Studies




Human Population Growth

Human population is currently about 6.5 billion.

Although world population continues to grow rapidly, the rate of growth has slowed, so that growth is no longer exponential.

Scientists now believe that if present trends continue, the globalhuman population will peak at around 10 billion soon after 2050.







A pyramid-shaped age structure diagram, such as that of Kenya, is a sign of a rapidly growing population. Most of the population is young and therefore at or approachingreproductive age.

The United States has an age structure that is much moreeven—its population is growing slowly.

In Italy, much of the population is older, and there arerelatively few children. Italy’s population is stable or evendeclining.








AIDS has affected world population more than anyother disease since the bubonic plague of theMiddle Ages.

AIDS strikes primarily adults of reproductive age.

Some of the countries struck hardest by AIDS,

including Botswana and South Africa, areexpected to experience population declines as aresult of the disease.

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