Unit 8 · Ecology

Behavioral and physiological response ● (core concept) — Organisms respond to changes in their internal or external environment through behavioral and physiological mechanisms, and exchange information with one another in response to internal changes and external cues, which can change behavior. (Knowledge of specific mechanisms is beyond AP scope.)

Communication signals ● (core concept) — Organisms communicate through various mechanisms — visual, audible, tactile, electrical, and/or chemical signals. Signaling behaviors can produce changes in other organisms' behavior and result in differential reproductive success.

Innate and learned behavior ● (core concept) — Fitness favors innate (inborn) and learned behaviors that increase survival and reproductive success. Responses to information and communication are vital to natural selection and evolution.

Behavior examples ○ — Illustrative (suggested, not required) CED behavior examples: photoperiodism and phototropism in plants; taxis and kinesis in animals; nocturnal and diurnal activity; fight-or-flight response; predator warnings; plant responses to herbivory; territorial marking; coloration in flowering plants and animals; bird songs; pack, herd, flock, and schooling behaviors; colony and swarming behavior in insects; kin selection; parent-offspring interactions; courtship and mating behaviors; foraging by bees and other animals.

Endotherm ● (core concept) — An organism that uses thermal energy generated by metabolism to maintain homeostatic body temperatures.

Ectotherm ● (core concept) — An organism that lacks efficient internal mechanisms for maintaining body temperature, though it may regulate temperature behaviorally by moving into the sun or shade or by aggregating with other individuals.

Energy budget ● (core concept) — A net gain in energy results in energy storage, growth of the organism, and increased reproductive output; a net loss in energy results in loss of mass, a decrease in reproductive output, and eventually death.

Reproductive strategies in response to energy availability ● (core concept) — Different organisms use various reproductive strategies in response to energy availability. Some organisms alternate between asexual and sexual reproduction in response to energy availability.

Levels of ecological organization ● (core concept) — Populations, communities, ecosystems, and biomes — the ecological levels through which energy flows and matter cycles.

Biogeochemical cycle ● (core concept) — Energy flows through ecosystems, while matter and nutrients cycle between the environment and organisms via biogeochemical cycles. The cycles are essential for life, demonstrate the conservation of matter, and are interdependent. Biogeochemical cycles include abiotic and biotic reservoirs, and processes that cycle matter between reservoirs.

Hydrologic cycle ● (core concept) — Water movement and storage within the hydrosphere. Reservoirs include oceans, surface water, the atmosphere, and living organisms. Processes include evaporation, condensation, precipitation, and transpiration.

Carbon cycle ● (core concept) — The recycling of carbon atoms through Earth's biosphere into organisms as carbohydrates and back into the atmosphere as carbon dioxide. At the highest levels it simplifies into photosynthesis, cellular respiration, decomposition, and combustion.

Nitrogen cycle ● (core concept) — Cycling of nitrogen through steps including nitrogen fixation, assimilation, ammonification, nitrification, and denitrification, performed by microorganisms in the soil. The largest reservoir of nitrogen is the atmosphere; in nitrogen fixation, nitrogen gas (N2) is fixed into ammonia (NH3), which ionizes to ammonium (NH4+).

Phosphorus cycle ● (core concept) — Weathering of rocks releases phosphate (PO4 3−) into soil and groundwater. Producers take in phosphate, which is incorporated into biological molecules; consumers transfer phosphate by eating producers. Phosphorus returns to the soil via decomposition of biomass or excretion.

Trophic level ● (core concept) — Feeding levels in an ecosystem: producers; primary, secondary, tertiary, and quaternary consumers; and decomposers.

Autotroph ● (core concept) — An organism that captures energy from physical or chemical sources. Photosynthetic organisms capture sunlight, contributing to primary productivity; chemosynthetic organisms capture energy from small inorganic molecules, which can occur in the absence of oxygen.

Heterotroph ● (core concept) — An organism that obtains energy by consuming organic matter — including carnivores, herbivores, omnivores, decomposers, and scavengers. Heterotrophs metabolize carbohydrates, lipids, and proteins as sources of energy.

Primary productivity ● (core concept) — The rate at which photosynthetic organisms capture sunlight energy and convert it into biomass; the energy input that supports an ecosystem.

Energy flow examples ○ — Illustrative (suggested, not required) CED energy-flow examples: food chains/webs, trophic pyramids/diagrams, seasonal reproduction in animals and plants, life-history strategies (biennial plants, reproductive diapause).

Population ● (core concept) — Individual organisms of the same species that interact with one another and with the environment in complex ways.

Birth rate and death rate ● (core concept) — Population growth dynamics depend on birth rate, death rate, and population size. Relevant equation: dN/dt = B − D, where B is birth rate and D is death rate.

Exponential growth ● (core concept) — Reproduction without constraints results in the exponential growth of a population. Relevant equation: dN/dt = rmax·N, where rmax is the maximum per capita growth rate.

Carrying capacity ● (core concept) — The sustainable abundance of a species that can be supported by the ecosystem's total available resources (K in the logistic growth equation).

Density-dependent factor ● (core concept) — Limits to population growth whose effect intensifies as population density rises (e.g., competition, disease).

Density-independent factor ● (core concept) — Limits to population growth that act regardless of population density (e.g., natural disasters, climate extremes).

Logistic growth ● (core concept) — The growth pattern that typically ensues as density-dependent and density-independent limits are imposed. Relevant equation: dN/dt = rmax·N·((K−N)/K), where K is carrying capacity.

Community ● (core concept) — Groups of interacting populations of different species that change over time based on the interactions between those populations.

Species composition and diversity ● (core concept) — Community structure is measured and described in terms of the species present (species composition) and the variety and relative abundance of species (species diversity).

Simpson's diversity index ● (core concept) — Diversity Index = 1 − Σ(n/N)², where n is the total number of organisms of a particular species and N is the total number of organisms of all species.

Predator-prey interaction ● (core concept) — An interaction between organisms in which one hunts and eats another; can drive population dynamics.

Cooperation ● (core concept) — An interaction in which organisms work together; cooperative behavior tends to increase the fitness of the individual and the survival of the population.

Trophic cascade ● (core concept) — A feeding interaction that ripples through trophic levels — changes in a top predator's population affect the populations below it.

Niche partitioning ● (core concept) — The division of resources among species to reduce competition, allowing species to coexist in a community.

Competition ● (core concept) — Interaction between organisms competing for the same limited resources; can drive population dynamics.

Symbiosis ● (core concept) — A close, long-term interaction between two species, including parasitism, mutualism, and commensalism; can drive population dynamics.

Parasitism ● (core concept) — A symbiotic relationship in which one organism benefits at the expense of the other.

Mutualism ● (core concept) — A symbiotic relationship in which both organisms benefit.

Commensalism ● (core concept) — A symbiotic relationship in which one organism benefits and the other is neither helped nor harmed.

Ecosystem resilience ● (core concept) — Natural and artificial ecosystems with fewer component parts, and with little diversity among the parts, are often less resilient to changes in the environment.

Keystone species ● (core concept) — A species whose effects on the ecosystem are disproportionate relative to its abundance. When keystone species are removed, the ecosystem often collapses. Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining ecosystem diversity.

Adaptation ● (core concept) — A genetic variation favored by selection that manifests as a trait providing an advantage to an organism in a particular environment.

Heterozygote advantage ● (core concept) — A situation in which the heterozygous genotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype.

Random mutation ● (core concept) — Mutations are not directed by specific environmental pressures.

Invasive species ● (core concept) — A species whose intentional or unintentional introduction allows it to exploit a new niche free of predators or competitors, or to outcompete native species for resources, affecting ecosystem dynamics.

Biomagnification ● (core concept) — The increasing concentration of a substance (such as a toxin) in organisms at successively higher trophic levels. Human activities driving biomagnification can cause extinctions.

Eutrophication ● (core concept) — Nutrient enrichment of a body of water (often from runoff), causing algal blooms and oxygen depletion. Human activities driving eutrophication can cause extinctions.

Biogeography ● (core concept) — The study of the geographic distribution of species; biogeographical studies illustrate habitat change and ecosystem distribution caused by geological and meteorological events.

Ecosystem disruption examples ○ — Illustrative (suggested, not required) CED disruption examples: invasive species (kudzu, zebra mussels); disease (Dutch elm disease, potato blight); human activities (global climate change, logging, urbanization, monocropping); geological/meteorological events (El Niño, continental drift, meteor impact on dinosaurs).