Key Terms in Ecology and Biology: Community, Succession, and Interactions

Abiotic factors

Non-living things or factors in an environment, such as air, temperature, water, and minerals.

Ammonification

The process where decomposers (fungi and prokaryotes) convert organic nitrogen from dead tissues or waste back into inorganic nitrogen as ammonia.

Anammox

Anaerobic ammonia oxidation; a process carried out by specific bacteria where ammonia is oxidized using nitrite as the electron acceptor to produce gaseous nitrogen.

Assimilation

The process by which plants take up ammonia or nitrates and use them to make important biological molecules like DNA and proteins.

Biosphere

A meta-ecosystem that contains all of the ecosystems that are in some way connected; often referred to as the whole Earth.

Biotic factors

Living things or factors in an environment, such as bacteria, plants, and animals.

Carbohydrates

Organic molecules that contain carbon, oxygen, and hydrogen, usually in a ratio of 1 to 2 to 1.

Community

All the living things (all populations of different species) that live in a defined area.

Denitrification

The anaerobic process that converts nitrate ($NO_3^-$) to nitrogen gas ($N_2$), removing bioavailable nitrogen from the ecosystem and returning it to the atmosphere.

Ecology

The study of how living things interact with each other and their environment.

Ecosystem

A system that includes all of the living things (biotic factors) in a community and the non-living things (abiotic factors) in that area.

Haber-Bosch process

An industrial process for making synthetic fertilizers by causing nitrogen gas ($N_2$) to react with hydrogen gas ($H_2$).

Heterocysts

Structures in some cyanobacteria that provide a low-oxygen environment for the nitrogenase enzyme to function.

Lipids

Organic molecules composed mainly of carbon, hydrogen, and oxygen, but containing a lower proportion of oxygen atoms than carbohydrates.

Nitrification

The process that converts ammonia ($NH_3$) into nitrates ($NO_3^-$), often involving an intermediate step of converting ammonia to nitrite ($NO_2^-$).

Nitrogen fixation

The process of converting atmospheric nitrogen gas ($N_2$) into biologically available nitrogen, such as ammonia ($NH_3$).

Nitrogenase

An enzyme complex found in nitrogen-fixing organisms that catalyzes the reduction of $N_2$ to $NH_3$ and is deactivated by the presence of oxygen.

Nucleic acids

Large molecules, such as DNA and RNA, that are made up of smaller molecules called nucleotides.

Organic molecules

Compounds generally found in living systems that contain molecules with a carbon-carbon covalent bond or a carbon-hydrogen covalent bond.

Population

The members of the same species that live in the same area.

Proteins

Giant macromolecules made up of amino acid building blocks; they contain carbon, hydrogen, oxygen, and nitrogen.

Absolute fitness

A measure of the ratio of a given genotype before and after selection.

Adaptations

Beneficial features arising by natural selection.

Autotrophs (Producers)

Organisms that make their own food by creating organic substances (such as glucose) from inorganic substances (such as carbon dioxide).

Chemoautotrophs

Autotrophs that use chemical energy (by oxidizing inorganic substances) rather than light to produce food.

Chemoheterotrophs

Organisms that must consume organic matter and utilize organic compounds as their energy source.

Commensalism

A long-term, close association between two species in which one benefits and the other is unaffected.

Competition

An interaction where organisms of two species use the same limited resource and hurt each other.

Ecological Community

All the populations of all the different species that live together in a particular area.

Ectosymbiosis

A relationship in which one species lives on the outside surface of the other.

Endosymbiosis

A relationship in which one of the symbiotic species lives inside the tissue of the other.

Fitness (Evolutionary)

A measure of reproductive success that reflects how well an organism is adapted to its environment.

Herbivory

A special case of predation in which the prey species is a plant.

Heterotrophs (Consumers)

Organisms that must consume organic matter.

Interspecific Interactions

Interactions between two or more different species in a community.

Mutualism

A long-term, close association between two species in which both partners benefit.

Niche

An organism's ecological role and requirements for survival and reproduction.

Parasitism

A long-term, close association between two species in which one (the parasite) benefits and the other (the host) is harmed.

Photoautotrophs

Autotrophs, such as plants, that use light as their energy source.

Photoheterotrophs

Heterotrophs (consumers of organic matter) that require light as their energy source.

Predation

An interaction where a member of one species (predator) eats all or part of the body of a member of another species (prey).

Relative Fitness

A measure of differential reproductive success, comparing the proportion of the next generation's gene pool descended from a particular organism (or genotype) against competing organisms.

Resource Partitioning

The evolution of species with overlapping niches to utilize less similar resources, minimizing competition.

Symbiosis

A general term for interspecific interactions in which two or more species live together in a long-term, intimate association.

Climax Community

A stable, unchanging final state of a community, primarily determined by an area's climate, which was once thought to be the result of succession.

Community Structure

The composition of a community, including the number of species, their relative numbers, and their patterns of interaction.

Ecological Succession

A series of progressive changes in the species that make up an ecological community over time.

Exponential Growth

A growth pattern described by a differential equation where the population grows without environmental constraints; as the population increases, the growth rate increases, creating a 'J' shaped curve.

Foundation Species

A species that plays a unique, essential role in creating and defining a community, often by modifying the environment so it can support other organisms (e.g., kelp, coral).

Keystone Species

A species that has a disproportionately large effect on community structure relative to its biomass or abundance, often preserving the balance of the community (e.g., Pisaster sea star).

Per Capita Population Growth Rate

The average growth rate per individual organism in a population, calculated as the population growth rate divided by the total population.

Pioneer Species

The hardy plants, lichens, and microbes with few soil requirements that are the first to colonize a new habitat, helping to break down rock into soil.

Primary Succession

A type of succession where newly exposed or newly formed rock is colonized by living things for the first time (e.g., after lava flows or glacier retreat).

Secondary Succession

A type of succession where an area that was previously occupied by living things is disturbed (e.g., by fire), then re-colonized following the disturbance.

Species Diversity

A measure of community complexity that is a function of both species richness (number of species) and species evenness (relative abundances).

Species Richness

The number of different species in a particular community.