Environmental Science and Ecology: Key Concepts and Case Studies

Environment

All the living and nonliving things around us with which we interact.

Environmental science

The study of how the natural world works, how our environment affects us, and how we affect it.

Ecology

The branch of biology that studies relationships among organisms and between organisms and their environment.

Natural resources

Substances and energy sources that we take from our environment to survive.

Renewable natural resources

Resources that are replenished over short periods of time.

Nonrenewable natural resources

Resources that form much more slowly than we use them, and are finite in supply.

Ecosystem services

Processes provided by healthy ecosystems that support life and human economies.

Environmentalism

A social movement dedicated to protecting the natural world from harmful human actions.

Sustainability

A guiding principle of environmental science that means conserving resources so they remain available for future generations.

Natural capital

The Earth's total wealth of resources and ecosystem services.

Ecological footprint

The cumulative area of land and water required to provide the resources a person or population consumes and to dispose of the waste.

Overshoot

When humanity's demand on Earth's resources exceeds the planet's capacity to sustainably supply them.

Hypothesis

A statement that attempts to explain a phenomenon or answer a scientific question.

Experiment

An activity designed to test the validity of a hypothesis by controlling variables.

Dependent variable

The variable that is measured in an experiment.

Independent variable

The variable that is manipulated in an experiment.

Controlled experiment

An experiment where all variables except one are kept constant.

Control

The unmanipulated point of comparison in an experiment.

Theory

A widely accepted, well-tested explanation of natural phenomena that unifies many observations.

Ethics

The branch of philosophy that involves examining moral values and principles.

Environmental ethics

Application of ethical standards to the relationships between people and nonhuman entities.

Matter

All material in the universe that has mass and occupies space.

Atom

The smallest component of an element that maintains the element's chemical properties.

Element

A fundamental type of matter that has a given set of properties and cannot be broken down further.

Isotope

Atoms of the same element with different numbers of neutrons.

Ion

An atom or group of atoms with an electric charge due to gain or loss of electrons.

Molecule

A combination of two or more atoms held together by covalent bonds.

Compound

A molecule composed of atoms of two or more different elements.

Covalent bond

Atoms share electrons.

Ionic bond

Electrons are transferred from one atom to another, creating oppositely charged ions.

Hydrogen bond

A weak attraction between a hydrogen atom in one molecule and another atom in a different molecule.

Organic compounds

Compounds that contain carbon and are produced by living organisms.

Macromolecules

Large organic molecules including proteins, nucleic acids, carbohydrates, and lipids.

pH scale

Measures how acidic or basic a solution is (0-14).

Potential energy

Stored energy that can be released.

Kinetic energy

Energy of motion.

First Law of Thermodynamics

Energy cannot be created or destroyed—only transformed.

Second Law of Thermodynamics

Energy changes form, losing usable energy as heat (entropy increases).

Photosynthesis

Process by which autotrophs convert solar energy into chemical energy.

Cellular respiration

Organisms use oxygen to break down glucose and release energy.

Chemosynthesis

Process by which bacteria use energy from inorganic chemicals (like hydrogen sulfide) to produce sugars.

Tectonic plates

Sections of Earth's crust that move slowly across the mantle.

Divergent boundary

Plates move apart; new crust forms.

Convergent boundary

Plates collide; subduction or mountain formation occurs.

Transform boundary

Plates slide past each other.

Subduction zone

Area where one tectonic plate is forced beneath another.

Rock cycle

The process of creation, destruction, and transformation of rocks.

Evolution

Genetic change in populations of organisms across generations.

Natural selection

Process by which traits that enhance survival and reproduction become more common in a population.

Adaptation

A heritable trait that increases an organism's fitness.

Mutation

A random change in DNA that may create genetic variation.

Speciation

The process by which new species arise.

Allopatric speciation

Speciation due to geographic isolation.

Extinction

The disappearance of an entire species from Earth.

Biodiversity

Variety of life across all levels of organization (species, genes, ecosystems). Example: Tropical rainforests have high biodiversity.

Endemic species

Species found only in one place on Earth. Example: Lemurs in Madagascar.

Population ecology

Study of the dynamics of population change and factors that affect population size and density. Example: Tracking wolf population in Yellowstone.

Carrying capacity (K)

The maximum population size that an environment can sustain indefinitely. Example: Deer population limited by available food.

Limiting factors

Physical, chemical, or biological characteristics that limit population growth. Example: Water, temperature, food supply.

Density-dependent factors

Influences on population growth that vary with population density. Example: Disease, competition.

Density-independent factors

Influences on population growth independent of density. Example: Natural disasters, temperature.

r-selected species

Species with high reproductive rates, little parental care, and short lifespans. Example: Mosquitoes or dandelions.

K-selected species

Species with few offspring, high parental care, and long lifespans. Example: Elephants or humans.

Logistic growth

Population growth that slows as it approaches carrying capacity (S-shaped curve). Example: Population of deer stabilizing when food limits are reached.

Exponential growth

Population increases by a fixed percentage each year (J-shaped curve). Example: Bacteria multiplying in ideal conditions.

Habitat

The specific environment in which an organism lives, including living and nonliving elements. Example: A salamander's habitat is a moist forest floor under logs.

Niche

An organism's role in its environment—its habitat, resource use, and interactions. Example: Bees pollinate flowers and feed on nectar.

Specialist species

Organisms with very specific habitat or resource requirements. Example: Koalas eat only eucalyptus leaves.

Generalist species

Organisms that can use a wide variety of resources or habitats. Example: Raccoons and cockroaches thrive in many environments.

Competition

A relationship where multiple organisms seek the same limited resource. Example: Plants competing for sunlight in a dense forest.

Interspecific competition

Competition between members of different species. Example: Lions and hyenas competing for prey.

Intraspecific competition

Competition among members of the same species. Example: Deer competing for mates or territory.

Competitive exclusion

When one species outcompetes another, causing local extinction. Example: Zebra mussels outcompeting native mussels in the Great Lakes.

Resource partitioning

Species divide resources by specializing in different ways. Example: Birds feeding on different parts of the same tree.

Predation

One species (predator) kills and eats another (prey). Example: Wolves hunting elk.

Parasitism

A relationship where one organism benefits and the other is harmed. Example: Tapeworms in a mammal's intestines.

Herbivory

Animals feed on plants, affecting their growth and survival. Example: Caterpillars eating leaves.

Mutualism

Both species benefit from the interaction. Example: Bees pollinate flowers and receive nectar.

Commensalism

One species benefits, and the other is unaffected. Example: Moss growing on a tree trunk.

Trophic level

Rank in the feeding hierarchy of a food chain. Example: Producers → herbivores → carnivores → decomposers.

Producer (autotroph)

Organisms that use sunlight or chemicals to make their own food. Example: Grass or phytoplankton.

Consumer (heterotroph)

Organisms that gain energy by feeding on others. Example: Deer eating plants, lions eating deer.

Primary consumer

Organisms that eat producers (herbivores). Example: Rabbits eating grass.

Secondary consumer

Organisms that eat primary consumers (carnivores). Example: Snake eating a rabbit.

Tertiary consumer

Top predators that eat secondary consumers. Example: Hawk eating a snake.

Decomposer

Break down dead organic material and recycle nutrients. Example: Fungi and bacteria.

Detritivore

Consume detritus (waste, dead tissue). Example: Earthworms or millipedes.

Food chain

Linear series of feeding relationships. Example: Grass → grasshopper → frog → snake → hawk.

Food web

Network of interconnected feeding relationships. Example: Marine food web with fish, plankton, and whales.

Keystone species

Species with a strong influence on community structure. Example: Sea otters controlling sea urchin populations.

Trophic cascade

Indirect effects of predators on lower trophic levels. Example: Wolves controlling elk, which allows vegetation to recover.

Disturbance

An event that rapidly changes an ecosystem. Example: Fires, floods, hurricanes, logging.

Resistance

When a community resists change during a disturbance. Example: Old-growth forest maintaining structure after a small storm.

Resilience

A community changes in response but returns to its original state. Example: A forest regrowing after fire.

Succession

Predictable changes in species composition over time after disturbance. Example: Grass → shrubs → forest.

Primary succession

Occurs where no soil exists—pioneer species colonize first. Example: Lichens on bare rock after volcanic eruption.

Secondary succession

Occurs where soil remains after disturbance. Example: Reforesting after a forest fire.

Pioneer species

First species to colonize a disturbed area. Example: Mosses and lichens.

Climax community

Stable, mature community after succession. Example: A fully developed temperate forest.

Ecosystem

All organisms and nonliving entities that occur and interact in a particular area. Example: A coral reef or a tropical rainforest.