Unit 8: Ecology

Ecology

The study of interactions between living things and their environments.

Biosphere

The entire part of Earth where living things exist.

Ecosystem

The interaction of living (biotic) and nonliving (abiotic) components in an area.

Community

A group of populations of different species interacting in the same area (biotic interactions only).

Population

A group of individuals of the same species living in the same area at the same time that are capable of interbreeding.

Abiotic factors

Nonliving environmental conditions (e.g., temperature, water availability, pH, salinity, light, nutrient levels).

Biotic factors

Living influences on an organism (e.g., predators, competitors, pathogens, potential mates).

Stimulus

A change in internal or external conditions that can trigger a response (e.g., light intensity, dehydration, chemical signal).

Endotherm

An organism that generates most body heat internally through metabolism, helping maintain a relatively stable internal temperature.

Ectotherm

An organism whose body temperature is strongly influenced by environmental temperature and often regulated behaviorally (e.g., basking, seeking shade).

Taxis

Directed movement toward or away from a stimulus source (e.g., positive phototaxis toward light).

Kinesis

Nondirectional movement where speed or turning rate changes with conditions (not steering toward a target).

Innate behavior (instinct)

Genetically programmed behavior that occurs without prior experience (includes reflexes and fixed action patterns).

Learned behavior

Behavior modified by experience; learning is a change in behavior brought about by experience.

Imprinting

A type of learning where young animals form a strong attachment during a specific early-life window based on environmental cues.

Critical period

A limited window of time when an organism is especially sensitive to certain cues (key to imprinting).

Habituation

Learning not to respond to a repeated, harmless stimulus.

Circadian rhythm

An internal daily biological cycle (“biological clock”) affecting behavior and physiology.

Pheromone

A chemical signal between members of the same species that affects behavior via olfactory receptors (e.g., mating, alarm, trail signals).

Agonistic behavior

Aggressive behavior resulting from competition for resources such as food.

Dominance hierarchy

A group “pecking order” that establishes which individuals are most dominant, often reducing constant fighting.

Territoriality

Defending a space to increase access to limited resources (has energy and injury costs).

Cooperative behavior

Group behaviors (e.g., group hunting, alarm calling) that can increase inclusive fitness, especially among relatives.

Altruistic behavior

Unselfish behavior that benefits another individual at a cost to the actor because it advances shared genes (often via relatives).

Tropism

Directional plant growth toward or away from a stimulus (a growth response, not relocation).

Phototropism

Directional plant growth response to light; shoots typically bend toward light.

Gravitropism

Directional growth response to gravity; stems show negative gravitropism (up), roots positive gravitropism (down).

Thigmotropism

Directional growth response to touch (e.g., vines wrapping around a support).

Auxin

A plant hormone that redistributes to create unequal growth; in shoots, higher auxin promotes cell elongation, bending the shoot.

Photoperiodism

A plant response in flowering/developmental timing based on day length and darkness.

Stomata

Openings in leaves controlled by guard cells; opening allows CO₂ in but increases water loss via transpiration.

Guard cells

Cells that regulate stomatal opening/closing by changing turgor pressure through ion movement and osmosis.

Acclimation

A reversible change within an individual’s lifetime in response to the environment (not heritable).

Adaptation

A heritable trait shaped by natural selection across generations.

Primary producer (autotroph)

An organism that converts inorganic carbon (often CO₂) into organic molecules, usually via photosynthesis (or chemosynthesis in some systems).

Consumer (heterotroph)

An organism that obtains energy and carbon by eating other organisms.

Decomposer

An organism that breaks down dead organic matter and waste, releasing nutrients back into the environment.

Trophic level

A feeding position in a food chain/web (e.g., producer, primary consumer, secondary consumer).

Food web

A network showing multiple interconnected pathways of energy transfer among organisms (more realistic than a single food chain).

10% rule

Rule of thumb that ~10% of energy at one trophic level becomes biomass available to the next level; most is used/lost as heat.

Energy pyramid

A diagram of energy available at each trophic level per unit area per unit time; always narrows upward.

Biomass pyramid

A diagram of total mass of living organic matter at each trophic level; can be inverted in aquatic systems where producers reproduce rapidly.

Gross primary productivity (GPP)

The total rate of photosynthesis/energy captured by producers; hard to measure directly because respiration occurs simultaneously.

Net primary productivity (NPP)

Producer biomass/energy remaining after respiration; NPP = GPP − R and sets the energy budget for the rest of the ecosystem.

Biogeochemical cycle

The movement of matter (e.g., carbon, nitrogen, phosphorus) between living organisms and the abiotic environment.

Nitrogen fixation

Conversion of atmospheric N₂ into ammonia (or related forms) by certain bacteria (free-living or symbiotic).

Carrying capacity (K)

The maximum number of individuals a habitat can support long-term; can change with environmental conditions.

Density-dependent factor

A limiting factor whose effects intensify as population density increases (e.g., competition, disease, predation).

Competitive exclusion principle

Two species cannot occupy exactly the same niche indefinitely in the same place; one will outcompete the other unless niches differentiate.

Eutrophication

Nutrient enrichment (often N and P) causing algal blooms and oxygen depletion as decomposition increases, leading to hypoxia and die-offs.