CHAPTER 6

ECOSYSTEM

BALANCE

Relationships in the Ecosystem• All organisms need food to survive• Consumers that must actively hunt for other

organisms as a source of food are predators• The organisms hunted for food are called prey

Ex: the lynx and the snowshoe hare

Symbiosis• Symbiosis - two species

live closely together in an ecosystem. From ancient Greek – syn (with) biosis (living)

• Can take place between plant, animal, fungi, or any combination

Ex: crocodile and croc-bird, sucker fish and the shark, us and the Earth

Ecosystem Relationships

• Parasitisim – one organism feeds on the tissues or body fluids of another, called the host. Parasites may or may not cause harm to their hosts

• Ex: West Nile Disease is a virus that is passed from infected bird to other birds, mammals and even humans by the bite of a mosquito.

• The mosquito is also known as a vector because it needs blood meals to survive and reproduce

Parasitism

One organism (parasite) feeds directly from another organism (host).

The parasite benefits and the host is harmed (sometimes lethally).

Ex: tapeworm, hookworm, tick, bed bug

Commensalism• A relationship that

benefits one organism and neither helps nor hurts the other (neutral).

• Comes from the Latin com mensa “to share a table”

Ex: cattle egret feeds on insects stirred up as cattle or horses graze the grass for food.

Mutualism

• A relationship where both organisms help each other. Both organisms benefit in a “win-win relationship”.

Ex: legumes and nitrogen-fixing bacteria; pollinating plants by bees and butterflies, clownfish and the sea anenome

Ecological Succession

• The Earth is made of rock

• Lichens (fungus and algae) can live on bare rock

• Lichens secrete acid which breaks down the rock into soil

• Lichens are known as a pioneer community

Ecological Succession• Lichens are replaced by

grasses• Grasses further enrich the

soil allowing shrubs to grow• Pine trees replace shrubs• Deciduous trees

(oaks, maples, elms) replace pines

• Climax community – a community that does not experience additional succession

•

Secondary Succession

• Secondary succession — occurs when a community has been cleared by a major disturbance (fires, storms, human activity) that doesn’t destroy the soil

                                       

                  

Other Forms of Succession

Aquatic Succession Aquatic habitats also experience

succession Water gradually gain nutrients and

supports reeds and other water plants Organic matter (sediment) collects on

the lake floor More and more water plants cover the

surface of the lake When the lake fills in with sediment is

becomes a marsh Land plants gradually replace the

marsh plants to change the community into a fertile meadow

Island Succession Island succession occurs much

like it does on land Islands appear quickly after

volcanic eruptions Any organisms found on an island

usually arrive by water, wind or other organisms

Most islands have large bird populations

Organisms can adapt to fill many niches because there is no competition for resources (Galapagos finches)

Balance in the Ecosystem• All elements in an ecosystem are

connected to each other (abiotic and biotic factors)

• All processes in the ecosystem link together in a complex arrangement (food web)

• All natural ecosystems are STABLE – maintain a state of balance or equlibrium

• Systems that do not maintain equilibrium do not survive

Ecosystem Balance• Major disruptions cause major changes in

an ecosystem

• A new ecosystem will develop to replace the old one that was destroyed.

• Evolution of organisms is part of this development

• Organisms MUST adapt to majors changes or die out (face extinction)

Ecosystem Balance• Chaos Theory – mathematical explanation

of the effect small and large changes have on a particular ecosystem.

• Analyzing a complex system with both abiotic and biotic factors and multiple organisms can very very difficult.

• Hard to predict what the effect even one small change will have in the furture of an ecosystem.

BIOMES

• Biome – A major type of ecosystem with distinctive temperature range, rainfall and organisms

• Two kinds of biomes: terrestrial (land) and aquatic (water)

• Terrestrial biomes are classified by average temperatures and precipitation

• Aquatic biomes are classified by water depth, nutrient levels and location relative to land

Terrestrial BiomesDivided into 8

major biomes

• Desert and Tundra – very little water, small amount of biomass

Terrestrial Biomes• Forest – 75% of the

Earth’s biomass

3 forest biomes:

Coniferous (pine)

Deciduous (trees that lose leaves)

Rain (most water, 6% of all biomass)

Terrestrial Biomes

Grasslands –

22% of Earth’s land surface

8% of Earth’s biomass

Steppe – northern

Prairie - central

Savanna - southern

TERRESTRIAL BIOMES

TundraVery little water

Short shallow root plants

Permafrost

Coniferous ForrestPine forest

Moderate precipitation

Higher elevations

Deciduous ForrestHardwood trees that lose their leaves

Sufficient precipitation

Rain ForrestMost precipitation

Most plant and animal species on Earth

SteppeNorthern grasslands

Cooler temperatures

PrairieCentral portions of many continents

Large areas of grasses

SavannaWarmer, southern grasslands

Located near or below the equator

DesertVery little water

Poor soil or sand

Harsh temperatures

Classified by elevation

Terrestrial Biomes Fact SheetTundra Coniferous

ForrestDeciduous Forrest

Rain Forrest

Steppe Prairie Savanna Desert