Chapter 4Chapter 4

Ecosystems: Ecosystems: What What Are They and How Do Are They and How Do

They Work?They Work?

ECOLOGY

•Ecology is the study of the connection between organisms and their living and non-living environments.•The average number of organisms that can be sustained in an ecosystem is known as carrying capacity.•Food, water, and shelter are known as limiting factors.

BiosphereBiosphere

Ecosystems

Communities

Populations

Organisms

LEVELS

of

ORGANIZATION

FOCUSED

on

in

ECOLOGY

Species is the lowest on this hierarchy and Biosphere is the largestSpecies is the lowest on this hierarchy and Biosphere is the largest.

Vegetationand animals

Soil

Rock

Biosphere

Crust

core

Mantle

Lithosphere(crust, top of upper mantle) Hydrosphere

(water)

Atmosphere (troposphere, stratosphere)(air)

Biosphere(Living and dead

organisms)

Crust(soil and rock)

Oceanic crust Continental crust

Lithosphere

Upper mantle

Asthenosphere

Lower mantle

Solarradiation

Energy in = Energy out

Reflected byatmosphere (34%)

UV radiation

Absorbedby ozone

Absorbedby the earth

Visiblelight

Lower stratosphere(ozone layer)

Troposphere

Heat

Greenhouseeffect

Radiated byatmosphere

as heat (66%)

Earth

Heat radiatedby the earth

Solar Capital

ECOLOGY

•Abiotic – All of the non-living elements in an ecosystem like air, water, and temperature.

•Biotic – All of the living elements in an ecosystem.

Biotic Factors in an Aquatic Ecosystem

• Sunlight

• Temperature

• Precipitation

• Wind

• Latitude (distance from equator)

• Altitude (distance above sea level)

• Fire frequency

• Soil

• Light penetration

• Water currents

• Dissolved nutrient concentrations (especially N and P)

• Suspended solids

• Salinity

Abiotic Factors in Terrestrial and Aquatic Ecosystems

Ecotones: Ecosystem Boundaries

Tolerance• Range of Tolerance: range of chemical and

physical conditions that must be maintained for populations of a particular species to stay alive and grow, develop, and function normally.

• Law of Tolerance: the existence, abundance, and distribution of a species in an ecosystem are determined by whether the levels of one or more physical or chemical factors fall within the range tolerated by the species.

Po

pu

lati

on

Siz

e

Low High Temperature

Zone ofintolerance

Zone ofphysiological stress

Optimum range Zone ofphysiological stress

Zone ofintolerance

Noorganisms

Feworganisms

Lower limitof tolerance

Abundance of organismsFew

organismsNo

organisms

Upper limitof tolerance

Range of tolerance for a population of organisms, such as fish,to an abiotic environmental factor—in this case, temperature.

Ecology

• Biodiversity is the number and variety of organisms found within a certain region.

• Extinction is when a species is no longer in existence.

• Endangered means a species is in danger of extinction throughout all of a significant portion of its range.

ECOLOGY

Food Chain – A chain illustrating the organisms and their food source.

Grass grasshopper bird

A food chain

illustrates the transfer of energy from one trophic

level to the next.

ECOLOGY

Food Web – multiple chains assembled into one large web.

ECOLOGY

Ecological Pyramid

A food chain

that shows the relationship between the organisms in each trophic

level.

The figures represent number of individuals counted at each trophic

level.

Ecological Pyramid of Numbers

• The total dry weight of organisms in a particular trophic level is referenced as biomass.

Ecological Pyramid of Biomass

BIOMASS=

# of organisms x

the weight of an average individual

Ecological Pyramid of Energy

• Energy in ecosystems flows from producers to consumers.

• Energy is depicted in kilocalories.

• Ecological efficiency: % of usable energy transferred from one trophic level to the next. (Average is about 10%.)

Ecological Pyramid of Energy

Nutrient Cycles• Cycling of materials between the

environment and organisms.• Chemical and biological processes.• Examples:

– Water cycle– Carbon cycle– Nitrogen cycle– Phosphorus cycle– Sulfur cycle– Oxygen cycle

Precipitation

Precipitationto ocean Evaporation

EvaporationFromocean

Surface runoff(rapid)

Ocean storage

Condensation

Transpiration

Rain clouds

Infiltration andpercolation

Transpirationfrom plants

Groundwater movement (slow)

Groundwater movement (slow)

RunoffRunoff

Surface runoff (rapid)Surface runoff (rapid)

Precipitation

Water (Hydrologic) Cycle

Carbon Cycle

Nitrogen Cycle

Nitrogen Cycle• Nitrogen Fixation: bacteria convert

nitrogen to ammonia• Nitrification: bacteria convert

ammonia to nitrite and nitrate, which are used by plants

• Assimilation: plant roots absorb ammonia and nitrate

• Ammonification: decomposers convert dead organisms and waste to simpler compounds

• Denitrification: bacteria convert ammonia back into nitrite and nitrate, which are released into the air (cycle begins again)

Phosphorus Cycle

Phosphate Mining

Fertilizer containing phosphates

Animal waste

Phosphate Rock

Dissolved PhosphatesAnimal Excretion

Erosion

Uplifting into rocks

The Sulfur Cycle