ENVIRONMENTAL SCIENCE 13e

CHAPTER 3:Ecosystems: What Are They and How Do They Work?

Core Case Study: Tropical Rainforests Are Disappearing (1)

• Found near the equator

• 2% land surface

• ~50% world’s known terrestrial plant and animal species

• ≥50% destroyed or disturbed by humans– Cutting trees– Growing crops– Grazing cattle– Building settlements

Core Case Study: Tropical Rainforests Are Disappearing (2)

• Consequences of disappearing tropical rainforests1. Decreased biodiversity as species become

extinct

2. Accelerated global warming: fewer trees to remove carbon dioxide from the atmosphere

3. Changes regional weather patterns: can lead to increase in tropical grasslands

3-1 What Keeps Us and Other Organisms Alive?

• Concept 3-1A The four major components of the earth’s life-support system are the atmosphere (air), the hydrosphere (water), the geosphere (rock, soil, sediment), and the biosphere (living things).

• Concept 3-1B Life is sustained by the flow of energy from the sun through the biosphere, the cycling of nutrients within the biosphere, and gravity.

Earth Has Four Major Life-Support Components

• Atmosphere

• Hydrosphere

• Geosphere

• Biosphere

Three Factors Sustain Life on Earth

• One-way flow of high-quality energy from the sun

• Cycling of matter or nutrients through parts of the biosphere

• Gravity

Solar Energy Reaching the Earth

• Electromagnetic waves– Visible light

– UV radiation

– Heat

• Natural greenhouse effect

• Energy in = energy out

• Human-enhanced global warming

3-2 What Are the Major Components of an Ecosystem?

• Concept 3-2 Some organisms produce the nutrients they need, others get the nutrients they need by consuming other organisms, and some recycle nutrients back to producers by decomposing the wastes and remains of organisms.

Ecology

• How organisms interact with biotic and abiotic environment

• Focuses on specific levels of matter:– Organisms

– Populations

– Communities

– Ecosystems

– Biosphere

Living and Nonliving Components (1)

• Abiotic – Water

– Air

– Nutrients

– Solar energy

– Rocks

– Heat

Living and Nonliving Components (2)

• Biotic– Plants

– Animals

– Microbes

– Dead organisms

– Waste products of dead organisms

Trophic Levels (1)

• Producers – autotrophs–Photosynthesis

• Consumers – heterotrophs–Primary - herbivores–Secondary - carnivores–Third-level

• Omnivores

Trophic Levels (2)

• Decomposers– Release nutrients from the dead bodies

of plants and animals

• Detrivores – Feed on the waste or dead bodies of

organisms

Production and Consumption of Energy

• Photosynthesis

• Carbon dioxide + water + solar energy glucose + oxygen

• Aerobic respiration

• Glucose + oxygen carbon dioxide + water + energy

Energy Flow and Nutrient Recycling

• Ecosystems sustained through:– One-way energy flow from the sun

– Nutrient recycling

Science Focus: Invisible Organisms (1)

• Microorganisms/Microbes– Bacteria

– Protozoa

– Fungi

– Phytoplankton

Science Focus: Invisible Organisms (2)

• Microbes can cause disease– Malaria– Athlete’s foot

• Microbes are also beneficial– Intestinal flora– Purify water– Phytoplankton remove carbon dioxide

from the atmosphere

3-3 What Happens to Energy in an Ecosystem?

• Concept 3-3 As energy flows through ecosystems in food chains and webs, the amount of chemical energy available to organisms at each succeeding feeding level decreases.

Energy Flow in Ecosystems

• Trophic levels

• Food chain – Sequence of organisms, each of which

serves as a source of food for the next

• Food web – Network of interconnected food chains

– More complex than a food chain

Usable Energy by Trophic Level

• Energy flow follows the second law of thermodynamics – energy lost as heat

• Biomass decreases with increasing trophic level

• Ecological efficiency – typically 10%

• Pyramid of energy flow

Two Kinds of Primary Productivity

• Gross primary productivity (GPP)• Net primary productivity (NPP)• Planet’s NPP limits number of

consumers• Humans use, waste, or destroy 10-

55% of earth’s total potential NPP• Human population is less than 1% of

total biomass of earth’s consumers

3-4 What Happens to Matter in an Ecosystem?

• Concept 3-4 Matter, in the form of nutrients, cycles within and among ecosystems and in the biosphere, and human activities are altering these chemical cycles.

Biogeochemical Cycles

• Nutrient cycles

• Reservoirs

• Connect all organisms through time

Hydrologic Cycle

• Water cycle is powered by the sun1. Evaporation

2. Precipitation

3. Transpiration - evaporates from plant surfaces

• Water vapor in the atmosphere comes from the oceans – 84%

• Over land, ~90% of water reaching the atmosphere comes from transpiration

Science Focus: Water’s Unique Properties (1)

• Holds water molecules together – hydrogen bonding

• Liquid over a wide temperature range

• Changes temperature slowly

• Requires large amounts of energy to evaporate

Science Focus: Water’s Unique Properties (2)

• Dissolves a variety of compounds

• Filters out UV light from the sun

• Adheres to a solid surface – allows capillary action in plants

• Expands as it freezes

Carbon Cycle

• Based on carbon dioxide (CO2)• CO2 makes up 0.038% of atmosphere

volume • Major cycle processes

– Aerobic respiration– Photosynthesis– Fossil fuel combustion and deforestation

• Fossil fuels add CO2 to the atmosphere and contribute to global warming

Nitrogen Cycle

• Multicellular plants and animals cannot utilize atmospheric nitrogen (N2)

• Nitrogen fixation

• Nitrification

• Ammonification

• Denitrification

Phosphorus Cycle

• Does not cycle through the atmosphere• Obtained from terrestrial rock

formations• Limiting factor on land and in

freshwater ecosystems• Biologically important for producers

and consumers

Sulfur Cycle

• Most sulfur stored in rocks and minerals

• Enters atmosphere through:– Volcanic eruptions and processes– Anaerobic decomposition in swamps, bogs,

and tidal flats– Sea spray– Dust storms– Forest fires

3-5 How Do Scientists Study Ecosystems?

• Concept 3-5 Scientists use field research, laboratory research, and mathematical and other models to learn about ecosystems.

Field Research

• Collecting data in the field by scientists

• Remote sensing devices

• Geographic information systems (GIS)

Laboratory Research

• Simplified model ecosystems– Culture tubes– Bottles – Aquariums– Greenhouses– Chambers with controllable abiotic factors

• How well do lab experiments correspond with the greater complexity of real ecosystems?

Scientific Studies of Ecosystems

• Models– Mathematical

– Computer simulations

• Models need to be fed real data collected in the field- baseline data

• Models must determine relationships among key variables

Baseline Data to Measure Earth’s Health

• Needed to measure changes over time

• Lacking for many ecosystems

• Call for massive program to develop baseline data