Cover only 7% of the earth’s surface, but can contain up to half of the world’s terrestrial plant and animal species
To date, human activities have destroyed or degraded more than half of the earth’s tropical rain forests
Why should you be concerned about the disappearance of tropical rain forests?
Effect 1 - Biodiversity Loss
Effect 2 - Climate Change
Warms the atmosphere and speeds up climate change.
Fewer plants using photosynthesis to remove human-generated emissions of carbon dioxide (CO2)
Resulting increased levels of CO2 in the atmosphere contributes to atmospheric warming and climate change,
Effect 3 - System Change and Tipping Point
Large-scale losses of tropical rain forests can change regional weather pattern in ways that can prevent the forest from returning in cleared or degraded areas.
When this irreversible ecological tipping point is reached, the tropical rain forests in such areas become drier and less-diverse tropical grasslands
Earth’s life-support system has four spherical components that interact with each other.
Life is sustained by the cycling of nutrients and energy between and through these systems.
Atmosphere: composed of the troposphere and the stratosphere.
Hydrosphere: water at or near the earth’s surface (ice, water, and water vapor).
Geosphere: composed of a hot core, a thick, mostly rocky mantle, and a thin outer crust.
Biosphere: wherever life is found within the other three spheres.
The one-way flow of high-quality energy Solar energy principle of sustainability Greenhouse effect
The cycling of nutrients Chemical cycling principle of sustainability
Gravity
Greenhouse Earth. High-quality solar energy flows from the sun to the earth. It is degraded to lower-quality energy (mostly heat) as it interacts with the earth’s air, water, soil, and life forms, and eventually some of it returns to space.
Certain gases in the earth’s atmosphere retain enough of the sun’s incoming energy as heat to warm the planet in what is known as the greenhouse effect.
Ecology: how living organisms (biotic components) interact with one another and with the nonliving (physical and chemical) environment (abiotic component).
Biotic component consists of nested levels of biological organization:
Producers
Photosynthesis
Producers capture solar energy and use it
Convert carbon dioxide (CO₂) and water (H₂O) into carbohydrates such as glucose (C₆H₁₂O₆), which store chemical energy
Oxygen (O₂) released as a byproduct of this process accumulates in the atmosphere, making aerobic life possible for most organisms
Consumers
Several major consumer types are commonly recognized:
Decomposers are consumers that obtain energy and nutrients by breaking down the wastes and remains of plants and animals.
They are a subset of heterotrophs and are primarily bacteria and fungi.
Through decomposition, these organisms convert organic matter into inorganic nutrients that are returned to the soil, water, and air, where they can be reused by producers.
Detritivores obtain energy and nutrients by feeding directly on detritus—the wastes and dead bodies of other organisms.
By physically fragmenting organic material, detritivores help convert large, complex remains (such as fallen tree trunks) into simpler forms that can be further decomposed into inorganic nutrients usable by plants.
In natural ecosystems, wastes and dead organisms are not discarded; they function as resources that support nutrient cycling, consistent with the chemical cycling principle of sustainability.
Producers, consumers, and decomposers all rely on cellular respiration to release the chemical energy stored in glucose and other organic compounds.
In most organisms, this occurs through aerobic respiration, which uses oxygen to convert glucose back into carbon dioxide and water, releasing energy that fuels growth, maintenance, and reproduction.
Ecosystems—and the biosphere as a whole—are sustained by two fundamental processes:
Together, these processes reflect two core scientific principles of sustainability: energy flows through ecosystems, while nutrients cycle within them.
Soil is a complex, living system composed of:
Soil is one of Earth’s most important forms of natural capital.
Although it is technically renewable, soil forms extremely slowly, making the protection and renewal of topsoil critical for long-term sustainability.
Energy and matter behave differently in ecosystems:
Energy flows through ecosystems.
Matter cycles within them.
Gross Primary Productivity (GPP)
Net Primary Productivity (NPP)
Energy remaining after producers use some for respiration
\[\text{NPP} = \text{GPP} - \text{Respiration by producers}\]
Represents biomass available to consumers
Net primary productivity (NPP) differs dramatically across terrestrial and aquatic ecosystems.
Ecosystems with warm temperatures, ample sunlight, and sufficient water (e.g., tropical rainforests, swamps, marshes, coral reefs) tend to have high NPP.
Deserts, tundra, and open ocean regions generally have low NPP per unit area.
Although the open ocean has low NPP per square meter, its enormous area makes it a major contributor to global primary production.
Only energy stored as NPP (not GPP) is available to support consumers and higher trophic levels.
The hydrologic cycle moves water continuously among the atmosphere, land, and oceans.
Although water is continuously recycled, only a small fraction is accessible freshwater; most is in oceans, ice, or deep underground.
Carbon cycles among the atmosphere, biosphere, oceans, and geosphere.
Atmospheric CO₂ is a greenhouse gas and plays a central role in regulating Earth’s climate.
Nitrogen is essential for proteins and DNA, but most organisms cannot use atmospheric nitrogen (N₂) directly.
Microorganisms drive most nitrogen transformations.
Acid rain forms when sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) are released into the atmosphere and react with water vapor to form sulfuric and nitric acids.
These acids return to Earth through precipitation (rain, snow, sleet, or dry deposition).
Impacts include:
An algal bloom is a rapid increase in algae, usually triggered by excess nutrients (especially nitrogen and phosphorus).
When blooms die and decompose: - Oxygen is depleted - Fish and other aquatic organisms may die - Ecosystem structure is disrupted
Regulation of nutrient pollution in some regions has reduced the frequency and severity of blooms, but they remain a widespread issue.
Phosphorus is an essential nutrient for DNA, ATP, and cell membranes.
Unlike carbon and nitrogen, phosphorus: - Does not have a major atmospheric phase - Cycles primarily through rocks, soils, water, and living organisms
Key processes
Ecologists use multiple complementary approaches:
Field research
Controlled experiments
Modeling
Mathematical and computational models
Used when systems are too large, slow, or complex to manipulate directly
Laboratory systems may include:
Advantages
Limitations
