ESS Topic 2: Ecology, Energy Flow, Biogeochemical Cycles, and Biomes

Comprehensive vocabulary flashcards covering key concepts from Environmental Systems and Societies (ESS) Topic 2, including population dynamics, ecological niches, thermodynamics, energy flow, biogeochemical cycling, and biomes.

Population

A group of organisms of the same species living in the same area at the same time, capable of interbreeding.

Population Density

The number of individuals of a species per unit area.

Carrying Capacity ($K$)

The maximum size of a population that can be sustainably supported by a given area, determined by competition for limited biotic and abiotic resources.

Limiting Factors

Environmental factors that slow down population growth and limit the numbers of a particular population.

Density-Independent Factors

Limiting factors that affect a population regardless of its size, such as rainfall, temperature, acidity, salinity, and catastrophic events like fires and floods.

Density-Dependent Factors

Limiting factors that regulate population size around carrying capacity ($K$) whose impact increases as population density increases, such as competition, predation, and disease.

Biosphere

The global ecological system comprising all parts of Earth where life exists, from the upper atmosphere to deep within the crust.

Community

A collection of interacting populations of different species living together within an ecosystem.

Habitat

The geographical and physical location where a community, species, population, or organism lives, providing the conditions needed for survival.

Keystone Species

A species that exerts a disproportionate impact on its community structure relative to its abundance, with its loss risking ecosystem collapse.

Ecological Niche

The unique ecological role and position of a species within an ecosystem, encompassing all its biotic and abiotic interactions, habitat requirements, behaviors, and resource acquisition.

Fundamental Niche

The full potential range of physical and chemical conditions and resources a species could theoretically occupy in the absence of biotic competition or predation.

Realized Niche

The actual narrower portion of the fundamental niche that a species occupies in nature due to biotic interactions such as competition.

Herbivory

A biological interaction in which an animal consumer feeds primarily on plant tissues or photosynthetic organisms.

Predation

A biological interaction where one animal (predator) hunts, kills, and consumes another animal (prey).

Parasitism

A symbiotic relationship between two species where one organism (the parasite) lives on or inside another (the host), obtaining nutrients at the host's expense.

Mutualism

An ecological relationship between two organisms of different species in which both individuals derive mutual benefit.

Dichotomous Key

A stepped identification tool composed of paired, contrasting statements based on physical characteristics that lead user choices toward the correct organism identification.

J-Curve

An exponential growth curve illustrating a population growing at its maximum theoretical rate under ideal conditions with unlimited resources.

S-Shaped Curve (Sigmoid Growth Curve)

A population growth model shaped by density-dependent limiting factors that restrict exponential growth, leveling the population off at carrying capacity ($K$) through lag, exponential, transitional, and plateau phases.

Tipping Point

A critical threshold where a relatively small shift in a system parameter causes a disproportionately large and often irreversible transition to a new equilibrium state.

Background Extinction

The standard, ongoing, low-level rate of species extinction that occurs continuously throughout geological history as a result of normal evolutionary and environmental changes.

First Law of Thermodynamics

The physical law of conservation of energy stating that energy cannot be created or destroyed, only transformed from one form to another.

Second Law of Thermodynamics

The physical law stating that every energy transformation increases entropy, dissipating useful energy into degraded, less accessible forms like heat.

Biomass

The total mass of dry organic matter of living or recently living organisms within a given area or ecosystem.

Photosynthesis

The metabolic pathway by which autotrophs capture light energy to synthesize organic molecules such as glucose from carbon dioxide and water: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$.

Cellular Respiration

The biochemical breakdown of organic molecules such as glucose in living cells to release usable metabolic energy ($ATP$) alongside heat: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$.

Autotroph

An organism that synthesizes organic matter from inorganic substances using energy from light or chemical reactions (also known as a producer).

Heterotroph

An organism that obtains organic carbon compounds and chemical energy by feeding on other living organisms or organic matter (also known as a consumer).

Detritivore

An organism that ingests dead particulate organic material (detritus) and digests it internally to extract nutrients and energy.

Saprotroph

A decomposer that feeds by secreting extracellular digestive enzymes into dead or decaying organic substrate and absorbing the soluble breakdown products.

Productivity

The rate at which new biomass or energy is generated and accumulated by organisms per unit area per unit time in an ecosystem.

Gross Productivity ($GP$)

The total assimilation of energy or accumulation of biomass per unit area per unit time, before any respiratory losses.

Net Productivity ($NP$)

The gain in energy or biomass per unit area per unit time remaining after deducting metabolic respiration losses ($NP = GP - R$).

Maximum Sustainable Yield

The maximum harvestable rate of a resource, equivalent to the net productivity of the population or trophic level, that does not impair future regeneration.

10% Rule

The ecological guideline stating that only about $10\%$ of chemical energy is transferred from one trophic level to the next, with the remaining $90\%$ lost largely as metabolic heat.

Pyramid of Numbers

An ecological pyramid displaying the absolute or relative count of individual organisms present at each successive trophic level within a food chain.

Pyramid of Biomass

An ecological pyramid representing the total dry mass of living organic material present at each trophic level at a particular snapshot in time.

Pyramid of Productivity (Pyramid of Energy)

An ecological pyramid illustrating the rate of energy flow through each trophic level over a fixed duration, which is always upright due to the Second Law of Thermodynamics.

Bioaccumulation

The progressive build-up and increasing concentration of a non-biodegradable substance or toxin within the tissues of an individual organism over its lifetime.

Biomagnification

The increasing concentration of persistent, non-biodegradable contaminants in organisms at successively higher trophic levels along a food chain.

Microplastics

Plastic particles with a diameter less than $5\,\text{mm}$ resulting from commercial manufacturing or the fragmentation of larger plastic waste.

Biogeochemical Cycles

Closed pathways through which essential chemical elements (including carbon, nitrogen, and phosphorus) cycle continuously between the biotic and abiotic spheres.

Carbon Sink

A natural or artificial reservoir that absorbs and accumulates more carbon than it releases over a specified period.

Carbon Source

A reservoir or process that releases more carbon dioxide into the surrounding environment than it absorbs.

Residence Time

The average duration that an individual atom or molecule of an element resides within a specific reservoir or store before cycling out.

Carbon Sequestration

The process of capturing atmospheric carbon dioxide and fixing it into long-term organic or inorganic reservoirs, such as wood tissue, soils, or geological formations.

Ocean Acidification

The ongoing decrease in oceanic $pH$ driven by the absorption of anthropogenic atmospheric carbon dioxide, diminishing the availability of carbonate ions required by calcifying organisms.

Forest Carbon Offsets

Tradeable credits where one unit equals one metric ton of carbon dioxide emissions sequestered or avoided through forest conservation, afforestation, or land management projects.

Climate

The statistical distribution and average pattern of weather conditions over extended periods, conventionally calculated across a span of approximately $30\,\text{years}$.

Weather

The day-to-day state of the atmosphere at a specific location and short-term interval, characterized by metrics such as temperature, humidity, wind, and precipitation.

Biome

A broad geographic category of comparable ecosystems defined by distinctive regional climatic patterns, limiting factors, and dominant plant formations.

Ecotone

A transitional boundary area of gradual environmental change where two neighboring biomes or ecosystems blend together.

Insolation

The total amount of incoming solar radiation intercepted by a unit area of Earth's surface over a defined interval, determined by latitude, planetary curvature, and axial tilt.

Thermohaline Circulation

Large-scale deep-ocean currents driven by global density differences that arise from variations in seawater temperature and salinity.

Tri-Cellular Model

A conceptual framework explaining planetary atmospheric circulation and climate zones through three distinct convection cells (Hadley, Ferrel, and Polar) in each hemisphere.

Hadley Cell

The tropical atmospheric circulation loop between $0^\circ$ and $30^\circ$ latitude, characterized by warm air rising at the equator and sinking as dry air in the subtropics.

Ferrel Cell

The mid-latitude circulation cell operating between $30^\circ$ and $60^\circ$ latitude that rotates in reverse direction relative to the adjacent Hadley and Polar cells.

Polar Cell

The high-latitude circulation cell between $60^\circ$ and $90^\circ$ latitude, where frigid air sinks at the poles, moves equatorward at the surface, and rises around $60^\circ$.