Ecosystems & Communities: Organisms and their Environments

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Ecosystems & Communities:Organisms and their Environments

Chapter 15

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Ecosystems have living and non-living components

15.1 What are ecosystems?

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15.1 What is an Ecosystem?• A community of biological organisms plus the non-

living components with which the organisms interact.• Living organisms are not self-sufficient. They need

energy and raw materials.

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15.1 What is an Ecosystem?• The biotic environment consists of all the living

organisms within an area and is often referred to as a community.

• The abiotic (aka non-living or physical) environment, often referred to as the organisms’ habitat, consists of:• the chemical resources of the soil, water, and air,

such as carbon, nitrogen, and phosphorus• the physical conditions, such as the temperature,

salinity (salt level), moisture, humidity, and energy sources

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Which scenario below exemplifies an ecosystem?1. A group of organisms of the same species living in the

same place at the same time2. Different species interacting together at the same

place and time3. Different species interacting with each other at the

same time in a desert4. A smaller species living on a larger species in a

mutually beneficial relationship

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Take-Home Message 15.1• An ecosystem is all of the living organisms in a habitat

as well as the physical environment. Ecosystems are found not just in obvious places such as ponds, deserts, and tropical rainforests but also in some unexpected places, like the digestive tracts of organisms or the shell of a beetle.

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Challenge Question 15.1• An ecosystem is made of two components: the biotic

environment, or community, consisting of the living organisms within an area, and the physical environment, or the habitat in which these organisms live. A habitat consists of its chemical resources of the soil, water, and air as well as its physical conditions. List some of the aspects that make up the physical conditions of a habitat.

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Ecosystems have living and non-living components

15.2 A variety of biomes occur around the world, each determined by temperature and rainfall.

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15.2 A variety of biomes occur around the world, each determined by temperature and rainfall.• What is the average temperature?• What is the average rainfall (or other precipitation)?• Is the temperature relatively constant or does it vary

seasonally?• Is the rainfall relatively constant or does it vary

seasonally?

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Tropical Rain Forest

• forest of tall trees in a region of year-round warmth• ~ 125 to 660 cm yearly rainfall• temperature ranges from 20 °C - 34 °C• average humidity 77 - 88%• rainfall > 250 cm/year (may be a brief dry season) • almost all rain forests lie near the equator

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• < 6% of Earth's land surface• > 50% of all the world's plant and animal species live in

tropical rain forests• produce ~40% of Earth's oxygen• ~70% of the plants in the rainforest are trees• ~25% of all the medicines we use come from rainforest

plants

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Indicator Species

• any biological species that defines a trait or characteristic of the environment• may delineate an ecoregion • could indicate an environmental condition such as

a disease outbreak, pollution, species competition or climate change

• can be among most sensitive species in a region; sometimes act as early warning to monitoring biologists

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Tropical Rain Forest – Indicator Plant Species

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Tropical Rain Forest – Indicator Animal SpeciesGorilla

Gorilla gorilla

Orangutan (Pongo pygmaeus)

Spider MonkeyAteles geoffreyi

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Tropical Rain Forest – Indicator Animal Species2-toed sloth

Cholepus hoffmanni

Three-toed Sloth (Bradypus variegatus) with baby - Costa Rica

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Tropical Rain Forest – Indicator Animal Species

Collared AracariPteroglossus torquatus

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Grasslands (Prairie)

• 2 different types • tall-grass: humid & very wet• short-grass: dry; hotter summers and colder winters

than the tall-grass prairie• found in middle latitudes in the interiors of continents• either moist continental climates or dry subtropical

climates• Argentina - grasslands are known as pampas• grasslands in southern hemisphere tend to get more

precipitation than those in the northern hemisphere

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Grasslands (Prairie)• temperatures range from -40° F 70° F• growing season and a dormant season

• growing season is when there is no frost and plants can grow (which lasts from 100 to 175 days)• tropical and subtropical grasslands the length of

the growing season is determined by how long the rainy season lasts

• temperate grasslands the length of the growing season is determined by temperature (≥ 50° F)

• dormant (not growing) season: nothing can grow because its too cold

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Grasslands (Prairie)• average rainfall per year ranges from 10 - 30 inches

• tropical and sub-tropical grasslands: average rainfall per year ranges from 25 - 60 inches

• amount of rainfall is very important in determining which areas are grasslands • hard for trees to compete with grasses in places

where the uppers layers of soil are moist during part of the year but where deeper layer of soil are always dry.

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Grasslands– Indicator Plant SpeciesOld Field Habitat, Ohio

Grassland, North Dakota

Ironweed (Vernonia sp.) with Hedge Bindweed

Vine (Calystegia sepium)

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Grasslands– Indicator Plant Species

Ironweed (Vernonia sp.)

Joe Pye WeedEupatorium purpureum

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Grasslands – Indicator Plant Species

Common TeaselDipsacus fullonum Queen Anne's Lace (Daucus carota)

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Grasslands – Indicator Animal Species

Bison (Bison bison) on the range, Theodore Roosevelt National Park, North Dakota

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Przewalski's horse (Equus caballus przewalskii), The Wilds, Ohio

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Taiga• Russian word for forest • largest biome in the world• Eurasia, North America• located just below the tundra biome• many coniferous trees • aka boreal forest; Boreal was the Greek goddess of the

North Wind

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Taiga• winter temperature range is -54 to -1° C (-65 to 30° F)• summer: -7° C (20° F) to 21° C (70° F)• summers are very short (50 - 100 frost free days) • average yearly precipitation: 30 - 85 cm (12 - 33 in)• main seasons are winter and summer

• spring and autumn are very short • weather is either hot and humid or very cold

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Taiga

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Taiga – Indicator Plant Species

Balsam FirAbies balsamea

Black SprucePicea mariana

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Taiga – Indicator Plant Species

Jack PinePinus banksiana

Paper BirchBetula papyrifera

White PoplarPopulus alba

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Taiga – Indicator Animal Species

American Black BearUrsus americanus

Bald EagleHaliaeetus leucocephalus

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Taiga – Indicator Animal Species

Long-eared OwlAiso otus

Snowshoe RabbitLepus americanus

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Desert• cover about one fifth of Earth's land surface

• hot and dry: near Tropic of Cancer/Tropic of Capricorn• cold: near the Arctic

• temperature• hot & dry: ~ 25° C to ~ 49° C• cold: -2 to 4° C (winter) 21 to 26° C (summer)

• precipitation • hot & dry: very little rainfall and/or concentrated

rainfall in short periods between long rainless periods (< 15 cm/year)

• cold: 15 - 26 cm/year

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Desert

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Desert – Indicator Plant Species

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Saguaro Cactus Carnegiea gigantea

Fishhook Cactus Mammillaria microcarpa

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Trichomes

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Desert – Indicator Animal Species

Zebratail Lizard - Callisaurus draconides

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Rock hyrax (Procavia capensis)

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Bactrian Camel, Camelus bactrianus

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Temperate Deciduous Forest

• temperature: 0 - 20 C• precipitation: ~ 50 – 200 cm/year

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Temperate Deciduous Forest

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Temperate Deciduous ForestIndicator Plant Species

Oaks (Quercus sp.)

Dutchman's-BreechesDicentra cucullaria

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Temperate Deciduous ForestIndicator Plant Species

SassafrasSassafras albidum

RedbudCercis canadensis

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Temperate Deciduous Forest – Succession• orderly succession of communities to a climax

community (biome)• two main types of succession:

• primary succession: begins with bare rock exposed by geologic activity

• secondary succession: begins on soil from which previous community has been removed (by fire, agriculture, etc.)• secondary succession can proceed much faster

because the soil has been prepared by the previous community

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Temperate Deciduous ForestIndicator Animal Species

American ToadBufo americanus

Box Turtle

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Eastern Chipmunk Tamias striatus

Eastern Gray SquirrelSciurus carolinensis

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Yellow-breasted chatIcteria virens

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Tundra• annual average temperature < 5 C• precipitation (mostly in the form of snow) < 100 mm/year• summer is brief

• temperatures above freezing last only a few weeks at most

• "warm" summer coincides with periods of almost 24 hour daylight, so plant growth can be explosive

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Tundra

Anaktuvuk Pass, Alaska

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Tundra – Indicator Plant Species

Arctic Tundra Wildflowers - Alaska

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Tundra – Indicator Plant Species

Lichen

Polytrichum Moss(photographed in Ohio, not on the

Tundra)

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Tundra – Indicator Animal Species

Reindeer Rangifer tarandus

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Tundra – Indicator Animal Species

Caribou On Autumn Tundra Denali National Park Alaska

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Savanna• rolling grassland scattered with shrubs and isolated trees

• found between a tropical rainforest and desert biome• not enough rain falls on a savanna to support forests• found in a wide band on either side of the equator on

the edges of tropical rainforests• warm temperature year round• very long dry season (winter): ~ 10 cm rain; none at all

from Dec - Feb• very wet season (summer): ~ 35-65 cm rain

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Savanna

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Savanna – Indicator Plant Species

BaobabAdansonia digitata

Umbrella Thorn AcaciaAcacia tortillis

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Savanna – Indicator Animal Species

Savanna ElephantLoxodonta africana

Black MambaDendroaspis polylepis

LionPanthera leo

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Chaparral• winter: mild and moist, but not rainy• summer: very hot and dry. • annual temperature range: between -1° and 38° C• annual precipitation: ~ 25-45 cm, mostly in the winter

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Chaparral

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Chaparral – Indicator Plant Species

Blue OakQuercus douglasii

Common SagebrushArtemisia tridentata

Olive TreeOlea europaea

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Chaparral – Indicator Animal Species

Black-tailed JackrabbitLepus californicus

Golden JackalCanis aureus

Spotted SkunkSpilogale gracilis

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The Freshwater Biome• low salt concentration — usually less than 1%• plants and animals in freshwater regions are adjusted to

the low salt content and would not be able to survive in areas of high salt concentration (i.e., ocean)

• 3 different types of freshwater regions:• ponds and lakes• streams and rivers• wetlands

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The Freshwater Biome – Ponds and Lakes

From left: a view across Manzanita Lake toward Mt. Lassen, California; a forest pond near Donnelly, Idaho; a Great Blue Heron; Paranagat Lake, southeastern Nevada.

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The Freshwater Biome – Streams and Rivers

From left: McArthur-Burney Falls State Park, California; trout; Green River, Utah; Brooks River, Alaska.

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The Freshwater Biome - Wetlands

From left: Pescadero Marsh, California; coastal marsh at Umpqua Dunes, Oregon; trees and bogs on Esther Island, Alaska.

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The Marine Biome• cover about three-fourths of the Earth's surface • marine algae supply much of the world's oxygen supply

and take in a huge amount of atmospheric carbon dioxide

• evaporation of the seawater provides rainwater for the land

• 3 different types of marine regions:• oceans• coral reefs• estuaries

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The Marine Biome - Oceans

From left: mussels, worms, and a spider crab at a hydrocarbon seep community in the Gulf of Mexico; a sea fan and brain coral in the Florida Keys National Marine Sanctuary; a school of Atlantic amberjack off North Carolina.

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The Marine Biome – Coral Reefs

From left: reef life in the Gulf of Aqaba, Red Sea; a reef at Fanning Island atoll in the central Pacific; a reef in the Florida Keys National Marine Sanctuary.

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The Marine Biome - Estuaries

From left: Mangrove roots, south Florida; wetlands and tidal streams in the Ashe Island area, ACE Basin National Estuarine Research Reserve, South Carolina; a salt marsh in Winyah Bay National Estuarine Research Reserve, South Carolina.

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Ecological Notes

These are the biomes, in order of their productivity (highest first)

1. estuaries and tropical rain forest (highest)2. temperate forest3. agricultural land4. temperate grassland5. lakes and streams6. coastal zone7. tundra8. open ocean9. desert (lowest)

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Ecological Notes

In order to be productive and have a lot of living material standing around (biomass), an ecosystem has to have 4 basic necessities for plant life to thrive (if there are enough plants, the ecosystem will also support a lot of animals). The four things are:

1. Sunlight2. Nutrients3. Warm temperatures4. Water

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Biomes Video

http://www.thewildclassroom.com/video/index.html

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Take-Home Message 15.2• Biomes are the major ecological communities of earth,

characterized mostly by the vegetation present. Different biomes result from differences in temperature and precipitation, and the extent to which they vary from season to season.

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Challenge Question 15.2• Terrestrial biomes are determined by the temperature

and precipitation amounts as well as whether those factors are constant or vary by season. By contrast, how are aquatic biomes determined?

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Physical forces interacting create weather

15.3 Global air circulation patterns create deserts and rain forests.

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Water also cycles through ecosystems. It continually moves from the ocean to the air and land, then returns to the ocean in a cyclic pattern.

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Take-Home Message 15.3• Global patterns of weather are largely determined by the

earth’s round shape. Solar energy hits the equator at a more direct angle than at the Poles, leading to warmer temperatures at lower latitudes. This temperature gradient generates atmospheric circulation patterns that result in heavy rain at the equator and many deserts at 30° latitude.

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Challenge Question 15.3• Global weather patterns are mainly determined by the

amount of solar energy falling on an area. The amount of solar energy that falls on an area largely depends on the angle at which this light hits the earth. Explain what this means.

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15.4 Local topography influences the weather.

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15.4 Local topography influences the weather• High altitudes have lower temperatures

• With increasing elevation, the air pressure drops—this is because the weight of the atmosphere becomes lower as altitude increases.

• When pressure is lower, the temperature drops. For each 1000 meters above sea level, the temperature drops by about 6° C.

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15.4 Local topography influences the weather

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• Asphalt, cement, and tops of buildings absorb heat, raising the temperature.

• Tall buildings force wind downward.

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Which place would you expect to have the highest temperature during the summer?

1. Denver, Colorado (the mile high city)2. Dallas, Texas (large city)3. Farmer’s Branch, Texas (small town outside of

Dallas)4. Freeport, Maine (small town)

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Take-Home Message 15.4• Local features of topography influence the weather. With

higher altitude, the temperature drops. On the windward side of mountains, rainfall is high; on the backside, descending air reduces rainfall, causing rain shadow deserts. Urban development increases the absorption of solar energy, leading to higher temperatures, and creates wind near the bottom of tall buildings.

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Challenge Question 15.4• A rain shadow is a dry region on the landward side of a

mountain range. How is it formed?

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15.5 Ocean currents affect the weather.

15.5 Ocean currents affect the weather• water is continuously moving and mixing due to a

combination of forces • wind• earth’s rotation• gravitational pull of the moon• temperature• salt concentration

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15.5 Ocean currents affect the weather

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15.5 Ocean currents affect the weather• Why do beach communities have milder weather than

more inland communities?• Beaches on the east coast of the United States have

warmer water than west coast beaches at the same latitudes – why?

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Water can affect the climate in which example below?

1. Ecosystems located near large bodies of water2. El Niño3. Temperatures in Europe compared to North America4. All of the above

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Take-Home Message 15.5• Oceans have global circulation patterns. Disruptions in

these patterns occur every few years and can cause extreme climate disruptions around the world.

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Challenge Question 15.5• Why is most of Europe significantly warmer than regions

in Canada at the same latitude?

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Energy and chemicals flow within ecosystems

15.6 Energy flows from producers to consumers.

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First Stop: Primary Producers

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First Stop: Primary Producers• ecosystem: producers or consumers

• primary producers: plants, algae (some), bacteria • convert light energy from sun into chemical energy

through photosynthesis• chemical energy = food

• consumers eat or absorb their food• energy stored in chemical bonds of carbohydrate,

protein, and lipid molecules is captured and harnessed for consumers’ own movement, reproduction, and growth

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Second Stop: Primary Consumers – the Herbivores

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Third Stop: Secondary Consumers – the Carnivores

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Fourth Stop: Tertiary Consumers – the “Top” Carnivores

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Food Chain

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Food Web

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Food Web

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Food Chains & Food Webs• A change in one link in a food chain will affect the other

links. • The table on the next slide gives one example of a food

chain and the trophic levels represented in it:

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Food Chains & Food Webs

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GRASS

GRASSHOPPER

TOAD

SNAKE

HAWK

BACTERIA

IN GENERAL,

AUTOTROPHS (PRODUCERS)

HERBIVORES(PRIMARY

CONSUMERS)

CARNIVORES(2, 3, ETC.)

DECOMPOSERS

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Chain Reaction Game

http://www.ecokids.ca/pub/eco_info/topics/frogs/chain_reaction/play_chainreaction.cfm

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Energy Flows through a Food Web• Losses at every “step” in a food chain

• Inefficiency of energy transfers

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A grasshopper eats a plant. A mouse eats the grasshopper. A snake eats the mouse. A hawk could eat the snake or the mouse. In this food web, how would we categorize the hawk?

1. Producer2. Primary consumer3. Secondary consumer4. Tertiary consumer5. Quaternary consumer6. 4 and 5

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Take-home message 15.6• Energy from the sun passes through an ecosystem in

several steps. • First, it is converted to chemical energy in

photosynthesis. • Herbivores then consume the primary producers, the

herbivores are consumed by carnivores, and the carnivores, in turn, may be consumed by top carnivores.

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Take-home message 15.6• Detritivores and decomposers extract energy from

organic waste and the remains of organisms that have died.

• At each step in a food chain, some usable energy is lost as heat.

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15.7 Energy pyramids reveal the inefficiency of food chains.

Biomass• biomass: total weight of all living organisms in a given

area• only about 10% of the plants in an ecosystem is

converted into biomass• Food Energy Pyramid

• flow of energy through a food chain• trophic level: position that an organism occupies in a

food chain - what it eats, and what eats it• African savannas and grasslands sustain more species

of higher-order carnivores than any other terrestrial ecosystem

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Food Energy Pyramids• flow of energy through a food chain• trophic level: position that an organism occupies in a

food chain - what it eats, and what eats it

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You go out to eat at a fancy restaurant. You have a salad, salmon, and for dessert ice cream! Which part of the meal was the most energy efficient food for you to eat?

1. Salad 2. Salmon3. Ice cream 4. 2 and 3

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Take-home message 15.7• Energy from the sun passes through an ecosystem in

several steps known as trophic levels. • Energy pyramids reveal that the biomass of primary

producers in an ecosystem tends to be far greater than the biomass of herbivores.

• The biomass transferred at each step along the food chain tends to be only about 10% of the biomass of the organisms being consumed, due to energy lost in cellular respiration.

• As a consequence of this inefficiency, food chains rarely exceed four levels.

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15.8 Essential chemicals cycle through ecosystems.

Chemical Reservoirs• Each chemical is stored in a non-living part of the

environment.

• Organisms acquire the chemical from the reservoir, a non-living part of the environment.

• The chemical cycles through the food chain (biogeochemical cycles).

• Eventually, the chemical is returned to the reservoir.

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The Most Important Chemical Cycles

1) Carbon2) Nitrogen3) Phosphorus4) Sulfur

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Carbon Cycle Game

http://www.windows2universe.org/earth/climate/carbon_cycle.html

Fossil Fuels• created when large numbers of organisms die and are

buried in sediment lacking oxygen• In absence of oxygen, at high pressures, and after very

long periods of time, organic remains are ultimately transformed into coal, oil, and natural gas

• burning coal, oil, and natural gas releases large amounts of carbon dioxide• increases average CO2 concentration in the

atmosphere• current level of CO2 in the atmosphere is the highest it

has been in almost half a million years

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Global CO2 levels are rising in general, but they also exhibit a sharp rise and fall within each year – why?

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Fertilizers• Because it is necessary for the production of every plant

protein, and because all nitrogen must first be made usable by bacteria, plant growth is often limited by nitrogen levels in the soil.

• For this reason, most fertilizers contain nitrogen in a form usable by plants.

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Sulfur Cycle• component of protein • cycles in both a gas and sedimentary cycle• source : earth's crust• enters the atmosphere as hydrogen sulfide (H2S)

during fossil fuel combustion, volcanic eruptions, gas exchange at ocean surfaces, decomposition

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Sulfur Cycle• H2S is immediately oxidized to sulfur dioxide (SO2) • SO2 + water vapor H2SO4 (falls to earth in rain) • sulfur in soluble form is taken up by plant roots,

incorporated into amino acids such as cysteine• travels through food chain • eventually released through decomposition

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How is carbon recycled back to the atmosphere in the carbon cycle?

1. It is “fixed” by bacteria.2. It is a product of cellular respiration.3. Burning of fossil fuels.4. 2 and 3.5. All of the above.

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Why do commercial fertilizers usually contain usable forms of nitrogen and phosphorous?

1. These chemicals are not efficiently recycled in the soil.

2. Nitrogen and phosphorous need to be “fixed” by bacteria or the plant.

3. Nitrogen and phosphorous are found at high levels in the atmosphere but not in the soil.

4. Nitrogen and phosphorous only enter the soil through erosion.

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Take-home message 15.8• Chemicals essential to life—including carbon,

nitrogen, and phosphorus—cycle through ecosystems.

• They are usually captured from the atmosphere, soil, or water by growing organisms; passed from one trophic level to the next as organisms eat other organisms; and returned to the environment through respiration, decomposition, and erosion.

• These cycles can be disrupted as human activities significantly increase the amounts of the chemicals utilized or released to the environment.

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Species interactions influence the structure of communities.

15.9 Interacting species evolve together.

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Natural Selection• Causes organisms to become better adapted to their

environment

• Does not distinguish between biotic and abiotic resources as selective forces

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Coevolution• two (or more) species reciprocally affect each

other’s evolution• likely to happen when different species have

close ecological interactions with one another including:• predator/prey• parasite/host• competitive species• mutualistic species

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Penicillin was first isolated from a fungus growing on a plate of bacteria. This is an example of an adaptation of the fungus to fight off the bacteria. This interaction could be described as:

1. coadaptation.2. coevolution.3. symbiosis.4. predation.

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Take Home Message 15.9• In producing organisms better adapted to their

environment, natural selection does not distinguish between biotic and abiotic resources as selective forces.

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15.10 Each species’ role in a community is defined by its niche.

More than just a place for living, a niche is a complete way of living

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More than just a place for living, a niche is a complete way of living• Fundamental niche: the full range of environmental

conditions under which a species can live

• Realized niche: where and how a species is actually living

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Take Home Message 15.10• A population of organisms in a community fills a unique

niche, defined by the manner in which they utilize the resources in their environment.

• Organisms do not always completely fill their niche; competition with species that have overlapping niches can reduce their range.

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15.11 Competition can be hard to see, but it still influences community structure.

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Why is competition hard to see in nature?

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How can two very similar species avoid the consequences of competitive exclusion principle?

1. avoid predation 2. one species will become locally extinct 3. character displacement will occur 4. 2 and 3 5. all of the above

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Take Home Message 15.11• Populations with completely overlapping niches cannot

coexist forever.

• Competition for resources occurs until one or both species evolve in ways that reduce the competition, through character displacement, or until one becomes extinct in that location.

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15.12 Predation produces adaptation in both predators and their prey.

Predation• interaction between two species in which one species

eats the other• one of most important forces shaping composition and

abundance of species in a community

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Why do exotic species often flourish when released into novel habitats, even though natural selection has not adapted them to this new environment?

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Prey Adaptations for Reducing Predation• physical

• mechanical• chemical• warning coloration• camouflage mechanisms

• behavioral• passive and active behaviors

• hiding • escaping• alarm calling• fighting back

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1) Mechanical Defenses

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2) Chemical Defenses

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3) Warning Coloration

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4) Camouflage

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Predator adaptations for enhancing predation

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• toxic-avoidance methods • sensory perception

• faster running ability

• mimicry

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Why don’t predators become so efficient at capturing prey that they drive the prey to extinction?

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• predator adaptations are rarely so efficient that prey are driven to extinction

• “escape ability” in prey is stronger than selection for “capture ability” in predator

• cost of losing is much higher for prey

The gazelle can change direction very quickly while being chased by a cheetah (fastest land animal). The gazelle uses which method of defense listed below?

1. Mechanical defense2. Camouflage3. Behavioral4. Warning Coloration5. Chemical defense

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Take Home Message 15.12• Predators and their prey are in an evolutionary arms

race.

• As physical and behavioral features evolve in prey species to reduce their predation risk, predators develop more effective and efficient methods of predation.

• The coevolutionary process can result in brightly colored organisms, alarm calling, and many types of mimicry.

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THANK YOU TO…• http://www.blueplanetbiomes.org• http://www.marietta.edu/~biol/biomes/biome_main.htm• http://www.ucmp.berkeley.edu/exhibits/biomes/• http://www.tburg.k12.ny.us/mcdonald/foodch1.htm• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/

FoodChains.html• http://ic.galegroup.com/ic/scic/ReferenceDetailsPage/

ReferenceDetailsWindow?displayGroupName=Reference&disableHighlighting=false&prodId=SCIC&action=e&windowstate=normal&catId=&documentId=GALE%7CCV2644030753&mode=view&userGroupName=catholiccenhs&jsid=71a9d03928f7c22aa5cc70824a0bbc99

http://www.blueplanetbiomes.org/

http://www.marietta.edu/~biol/biomes/biome_main.htm

http://www.ucmp.berkeley.edu/exhibits/biomes/

http://www.tburg.k12.ny.us/mcdonald/foodch1.htm

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FoodChains.html

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FoodChains.html

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Ecosystems & Communities: Organisms and their Environments