Ecology: Populations, Communities, and Energy Transfers

Vocabulary practice flashcards covering ecological concepts from IB Biology topics C4.1 and C4.2, including population dynamics, sampling methodology, interspecific relationships, energy flow, and biogeochemical cycling.

Population

An interacting group of organisms of the same species that inhabit the same geographical area and are capable of breeding with one another without reproductive isolation.

Community

A group of populations of different species living together and interacting with each other within a given area, representing the biotic component of an ecosystem.

Ecosystem

A biological system formed by the interaction of a community of living organisms (biotic component) with their physical environment or habitat (abiotic component).

Natality

The birth rate within a population, serving as one of the two primary processes that increases population size.

Mortality

The death rate within a population, serving as one of the two primary processes that decreases population size.

Immigration

The movement and integration of individuals into an area from elsewhere, resulting in an increase in population size.

Emigration

The departure of individuals permanently out of an area to settle elsewhere, leading to a reduction in population size.

Sampling Error

The difference between an estimated population size and the true population size, which can be minimized by collecting more samples or enlarging the sampling area.

Random Sampling

A sampling technique in which sample locations are chosen completely at random (such as through randomly generated grid coordinates) to avoid selection bias.

Systematic Sampling

A sampling technique in which sampling points are chosen at uniform, fixed intervals along a transect or area, allowing population distribution to be measured against an environmental gradient.

Quadrat

A square frame of known dimensions placed on the ground to count individuals or estimate percentage coverage of non-motile (sessile) organisms.

Lincoln Index

A mathematical formula ($\text{Population Size} = M \times N \times R^{-1}$) used alongside capture-mark-release-recapture to estimate the population size of motile organisms.

Sigmoid Population Growth Curve

An S-shaped growth curve displayed by populations in resource-limited environments, comprising an exponential phase, a transitional phase, and a plateau phase.

Carrying Capacity ($\kappa$)

The maximum population size of a species that an environment can sustain indefinitely, corresponding to the plateau phase where populations oscillate around a stable mean.

Exponential Growth Phase

The early stage of sigmoidal population growth characterized by rapid, accelerating growth due to an overabundance of resources and negligible environmental resistance.

Transitional Phase

The intermediate phase of a population growth curve where the rate of population increase slows as environmental resistance and competition for resources intensify.

Plateau Phase

The stable equilibrium phase of a population growth curve where natality plus immigration equals mortality plus emigration, maintaining numbers at carrying capacity.

Density-Dependent Factors

Environmental factors (such as predation, access to habitat, nutrient availability, disease spread, and waste accumulation) whose limiting effect strengthens as population density increases.

Intraspecific Interactions

Ecological relationships occurring between individuals of the same species, encompassing both cooperative behaviors (e.g., hunting packs) and competitive interactions (e.g., vying for mates or territory).

Interspecific Competition

An ecological interaction occurring when distinct species compete directly for physical territory or indirectly through the depletion of shared, limited resources.

Chi-Squared Test ($\chi^2$)

A statistical hypothesis test ($\chi^2 = \sum \frac{(O - E)^2}{E}$) applied to quadrat contingency data to determine whether an association between two co-occurring species is statistically significant.

Endemic Species

An organism that is native and naturally indigenous to a defined geographic area or ecosystem.

Invasive Species

A non-native (alien) species introduced to an ecosystem that outcompetes endemic species and disrupts food webs due to rapid reproduction, wide fundamental niches, and an absence of natural predators.

Top-Down Control

Population regulation within a community where apex predators or higher trophic levels exert predatory pressure, producing alternating, oscillating effects down the food chain.

Bottom-Up Control

Population regulation within a community where the availability of primary nutrients or producer biomass at the base restricts the growth of all higher trophic levels.

Symbiosis

A close, persistent, and long-term biological interaction between organisms of two different species.

Mutualism

A symbiotic relationship between two different species in which both participating organisms derive an adaptive or nutritional benefit ($+$/$+$).

Commensalism

A symbiotic relationship in which one organism benefits from the association while the other remains entirely unaffected ($+$/$0$).

Parasitism

A symbiotic relationship in which one organism (the parasite) lives on or inside another (the host) to gain resources, harming the host in the process ($+$/$-$).

Pathogenicity

The capacity of infectious agents (such as bacteria, fungi, protozoa, or viruses) to establish disease by disrupting the homeostatic processes of a host organism.

Allelopathy

A chemical interaction, common in plants, wherein an organism secretes secondary metabolites into the soil or air that influence the growth, survival, or germination of neighboring species.

Antibiotics

Biological chemical compounds synthesized and released by organisms (such as fungi) to kill or inhibit the growth of competitive bacterial prokaryotes.

Zone of Inhibition

A clear circular area on a bacterial culture plate surrounding an antibiotic-producing fungal colony or disk where bacterial growth has been impeded.

Open System

An energy system, such as a natural ecosystem, capable of exchanging both energy and matter across its boundaries with the surrounding environment.

Closed System

A thermodynamic system that exchanges energy (such as sunlight or heat) with its exterior environment but cannot exchange matter.

Photoautotroph

An autotrophic organism that uses sunlight as an external energy source to synthesize organic compounds from carbon dioxide and water via photosynthesis.

Chemoautotroph

An autotrophic organism that derives metabolic energy from the oxidation of inorganic chemicals (e.g., hydrogen sulfide, ammonia, or iron oxide) to synthesize carbon compounds in lightless ecosystems.

Cell Respiration

The biochemical oxidation of carbon compounds to release energy that is transferred to adenosine triphosphate ($\text{ATP}$) to power cellular work.

Trophic Level

The sequential feeding rank or relative energetic position that an organism occupies within a food chain or food web.

Producer

An autotrophic organism occupying the first trophic level that manufactures organic molecules from simple inorganic precursors using external energy.

Consumer

A holozoic heterotroph that obtains organic carbon compounds by ingesting other living or recently killed organisms and digesting them internally.

Saprotroph

A heterotrophic decomposer (such as fungi or certain bacteria) that absorbs dissolved organic nutrients from non-living or dead organic matter through external enzyme digestion.

Food Chain

A linear diagram illustrating the one-way direction of chemical energy and biomass transfers as organisms feed on lower trophic levels.

Food Web

A complex network of interconnected food chains reflecting the reality that organisms frequently consume multiple food sources and occupy multiple trophic levels.

Pyramid of Energy

A stepped graphical diagram representing the energy content available per unit area per unit time ($\text{J}\cdot\text{m}^{-2}\cdot\text{year}^{-1}$) at each successive trophic level, which can never be inverted.

Biomass

The total dry mass of organic material and carbon compounds found within the tissues of an individual organism or an entire trophic level.

Gross Primary Production (GPP)

The total amount of chemical energy or biomass generated by autotrophs in an ecosystem over a specific unit of time.

Net Primary Production (NPP)

The remaining producer biomass incorporated into plant tissues that is available to primary consumers after subtracting the energy lost via autotrophic cell respiration.

Secondary Production

The rate at which biomass is generated and accumulated by heterotrophic organisms (consumers and decomposers) through assimilation of ingested food.

Carbon Flux

The rate of transfer of carbon between distinct ecological reservoirs (sinks and sources), quantitatively measured in gigatonnes.

Compensation Point

The specific light condition at which the rate of carbon fixation via photosynthesis exactly equals the rate of carbon release via cellular respiration in a photosynthetic organism.

Combustion

An exothermic chemical reaction occurring when organic matter or fossil fuels are burned in the presence of oxygen, releasing carbon dioxide, water, and heat into the environment.

Keeling Curve

A continuous historical record of global atmospheric $\text{CO}_2$ concentrations demonstrating an overarching anthropogenic rise alongside annual fluctuations driven by seasonal photosynthetic shifts.