Ecology, populations and environmental change definitions

Populations and their limits

Population

All the organisms of one species living in the same place at the same time, able to breed with one another.

Community

All the populations of all the species living in the same place at the same time.

Habitat

The place where an organism lives: a rock pool, a hedgerow, the gut of a cow.

Ecosystem

A community together with the non-living surroundings it interacts with, treated as one working unit.

Abiotic factor

A non-living influence: temperature, light, pH, water, oxygen, wind, soil depth.

Biotic factor

A living influence: competitors, predators, prey, parasites, pathogens, mates.

Carrying capacity

The population size that a particular environment can support over a sustained period, given the resources available in it.

Exponential growth

Growth in which the population multiplies by a constant factor per unit time, so the number added per unit time keeps increasing.

Niche

The role a species plays in its community: all the conditions it can tolerate and all the resources it uses, including where it lives, what it eats, what eats it and when it is active.

Competitive exclusion principle

Two species cannot occupy the same niche in the same place indefinitely; the better competitor eliminates the other.

Nutrient cycles: nitrogen, phosphorus and eutrophication

Nitrogen fixation

The reduction of nitrogen gas to ammonia, by nitrogen-fixing bacteria such as Rhizobium, by lightning, or industrially in the Haber process.

Ammonification

The release of ammonium from the nitrogen-containing compounds in dead organisms, faeces and urine, by saprobionts.

Nitrification

The oxidation of ammonium to nitrite and then to nitrate by nitrifying bacteria, Nitrosomonas and Nitrobacter, which needs oxygen.

Denitrification

The conversion of nitrate to nitrogen gas by bacteria respiring anaerobically with nitrate in place of oxygen, which returns nitrogen to the atmosphere.

Saprobiont

An organism that obtains its energy from dead material by secreting enzymes onto it and absorbing the soluble products.

Mycorrhiza

A mutualistic association between a fungus and a plant root, in which the fungus increases the surface area for absorbing water and mineral ions and receives organic compounds in return.

Eutrophication

Nutrient enrichment of a body of water, usually by nitrate or phosphate. It leads to an algal bloom, the death of plants beneath it, a rise in aerobic decomposers and a fall in dissolved oxygen.

Algal bloom

A rapid increase in the population of algae and cyanobacteria at the surface of a body of water, once a limiting nutrient is supplied.

Succession and environmental change

Succession

The change over time in the species occupying an area, in which each community alters the environment and makes it more suitable for the community that follows.

Pioneer species

The first species to colonise a bare surface, adapted to survive there when almost nothing else can.

Seral stage

One identifiable community in the sequence of a succession; the whole sequence is a sere.

Climax community

The relatively stable community a succession reaches under the local climate, which persists until something disturbs it.

Plagioclimax

A community held at a stage short of its climax by a repeated interference, usually human or from grazing animals.

Deflected succession

Succession that has been diverted from its natural course by an ongoing external factor.

Point quadrat

A frame holding a row of pins lowered vertically through vegetation; each species a pin touches is recorded, and hits per pin give percentage cover.

Gridded quadrat

A frame quadrat divided into a grid of small squares, usually 100, used to estimate percentage cover or frequency by counting squares.

ACFOR scale

A subjective five-point scale of abundance: Abundant, Common, Frequent, Occasional, Rare.

Post-mortem interval

The time that has passed since death.

Rigor mortis

The stiffening of muscles after death, caused by myosin heads staying bound to actin once ATP has run out.

Autolysis

The digestion of cells by their own enzymes, released from lysosomes after death.

Forensic entomology

The use of insects found on a body, their species and stage of development, to estimate the time since death.

Instar

One of the larval stages of an insect, separated from the next by a moult.

The carbon cycle and climate change

Carbon store

A place where carbon is held, such as the atmosphere, living organisms, soil, the oceans, sedimentary rock or fossil fuels.

Carbon transfer

A process that moves carbon from one store to another, such as photosynthesis, respiration, decomposition or combustion.

Fossil fuel

Coal, oil or natural gas, formed over millions of years from the remains of organisms that were buried in low-oxygen conditions before decomposers could break them down fully.

Proxy record

Evidence preserved from the past, such as pollen in peat or tree rings, from which a condition that was not measured directly, such as temperature, is inferred.

Dendrochronology

Dating wood by counting and matching its annual growth rings, whose widths also record the growing conditions of each year.

Ice core

A cylinder of ice drilled from an ice sheet, in which bubbles of trapped air preserve the composition of the atmosphere when each layer formed.

Climate model

A computer simulation of the atmosphere, oceans, land and ice built from physical laws, used to project future climate under a given set of inputs.

Emissions scenario

A stated assumption about future emissions of greenhouse gases, based on population, energy use and policy, which a climate model is run on.

Peer review

The evaluation of a scientific paper by independent experts in the same field before it is published, to check that its methods, analysis and conclusions are valid.

Scientific journal

A publication in which researchers report their methods, data and conclusions, usually after peer review, so that others can check and repeat the work.

Scientific conference

A meeting at which researchers present and discuss their work, often before publication, and have it questioned by others in the field.

Development rate

How fast an organism passes through a stage of its development, measured as 1 ÷ the time the stage takes, for example 1 ÷ the time for half a batch of eggs to hatch.

Managing ecosystems sustainably

Sustainable yield

The amount that can be harvested from a population in a given period without reducing the size of that population, so the same harvest can be repeated indefinitely.

Maximum sustainable yield

The largest sustainable yield available from a population. In the simple logistic model it occurs at about half the carrying capacity, where net growth is greatest; that position depends on the model's assumptions.

Sustainable management

Using an ecosystem so that its resources are still available to future generations, and the ecosystem itself is not degraded.

Reforestation

Replanting or allowing the regrowth of trees on land where forest has recently been cleared.

Biofuel

A fuel made from recently grown biomass, such as bioethanol from fermented crop sugars or biodiesel from plant oils.

Carbon neutral

Describes a process that adds no net carbon dioxide to the atmosphere, because the carbon it releases is balanced by carbon taken up.

Sustainable resource

A resource used no faster than it is replaced, so that it remains available to future generations.