Chapter 3 Ecosystems: What Are

They and How Do They Work?

Ecology is a study of connections in nature. How organisms interact with one

another and with their nonliving environment.

ENERGY FLOW IN ECOSYSTEMS

Food chains and webs show how eaters, the eaten, and the decomposed are connected to one another in an ecosystem.

Figure 3-17Figure 3-17

Food Webs Trophic levels are

interconnected within a more complicated food web.

Food webs show us the complex interactions between many food chains.

Figure 3-18Figure 3-18

Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs

In accordance with the 2nd law of thermodynamics, there is a decrease in the amount of energy available to each succeeding organism in a food chain or web.

Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs

Ecological efficiency: percentage of useable energy transferred as biomass from one trophic level to the next.

Figure 3-19Figure 3-19

Producers: Basic Source of All Food

Most producers capture sunlight to produce carbohydrates by photosynthesis:

Chemosynthesis:

Some organisms such as deep ocean bacteria draw energy from hydrothermal vents and produce carbohydrates from hydrogen sulfide (H2S) gas .

Productivity of Producers: The Rate Is Crucial

Gross primary production (GPP) Rate at which an

ecosystem’s producers convert solar energy into chemical energy as biomass.

Figure 3-20Figure 3-20

Net Primary Production (NPP) NPP = GPP – R

Rate at which producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R).

Figure 3-21Figure 3-21

Photosynthesis: A Closer Look

Chlorophyll molecules in the chloroplasts of plant cells absorb solar energy.

This initiates a complex series of chemical reactions in which carbon dioxide and water are converted to sugars and oxygen.

Figure 3-AFigure 3-A

Consumers: Eating and Recycling to Survive

Consumers (heterotrophs) get their food by eating or breaking down all or parts of other organisms or their remains. Herbivores

Primary consumers that eat producers Carnivores

Primary consumers eat primary consumers Third and higher level consumers: carnivores that eat

carnivores. Omnivores

Feed on both plant and animals.

Populations, Communities, and Ecosystems

Members of a species interact in groups called populations.

Populations of different species living and interacting in an area form a community.

A community interacting with its physical environment of matter and energy is an ecosystem.

Factors That Limit Population Growth

Availability of matter and energy resources can limit the number of organisms in a population.

Figure 3-11Figure 3-11

Factors That Limit Population Growth

The physical conditions of the environment can limit the distribution of a species.

ECOSYSTEM COMPONENTS Life exists on land systems called biomes and in

freshwater and ocean aquatic life zones.

Figure 3-9Figure 3-9

Nonliving and Living Components of Ecosystems Ecosystems consist of nonliving (abiotic) and

living (biotic) components.

Figure 3-10Figure 3-10

Core Case Study: Have You Thanked the Insects Today?

Many plant species depend on insects for pollination. Insect can control other pest insects by eating them …if all insects disappeared, humanity probably could not last more than

a few months [E.O. Wilson, Biodiversity expert]. Insect’s role in nature is part of the larger biological community in

which they live.

Figure 3-1Figure 3-1

THE EARTH’S LIFE SUPPORT SYSTEMS

The biosphere consists of several physical layers that contain: Air Water Soil Minerals Life

Figure 3-6Figure 3-6

Fig. 3-6, p. 54

Lithosphere (crust, top of upper mantle)

RockSoil

Vegetation and animals

Atmosphere

Continental Crust

LithosphereUpper mantle

AsthenosphereLower mantle

Mantle

Core

Biosphere

Crust

Crust (soil and rock)

Biosphere (living and dead

organisms)

Hydrosphere (water)

Atmosphere (air)

What Sustains Life on Earth?

Solar energy, the cycling of matter, and gravity sustain the earth’s life.

Figure 3-7Figure 3-7

What Happens to Solar Energy Reaching the Earth?

Solar energy flowing through the biosphere warms the atmosphere, evaporates and recycles water, generates winds and supports plant growth.

Figure 3-8Figure 3-8

Two Secrets of Survival: Energy Flow and Matter Recycle

An ecosystem survives by a combination of energy flow and matter recycling.

Figure 3-14Figure 3-14

BIODIVERSITY

Figure 3-15Figure 3-15

Why Should We Care About Biodiversity?

Biodiversity provides us with: Natural Resources (food water, wood, energy, and

medicines) Natural Services (air and water purification, soil

fertility, waste disposal, pest control) Aesthetic pleasure

Biodiversity Loss and Species Extinction: Remember HIPPO

H for habitat destruction and degradation I for invasive species P for pollution P for human population growth O for overexploitation