ESS terms in Ecology

A non-living physical or chemical component of an ecosystem that affects living organisms, such as temperature, light, pH, salinity, dissolved oxygen or soil texture.

The number of individuals of a species in a given area, or a relative measure of how common it is.

The height of a place above sea level; temperature usually falls as altitude increases, producing zones of vegetation on mountains.

A compound of nitrogen and hydrogen (NH₃) made by nitrogen fixation and by the Haber process; the starting material for most synthetic nitrogen fertilisers.

The release of ammonium from the nitrogen-containing organic compounds in dead organisms and wastes, carried out by decomposers.

The positively charged ion NH₄⁺, formed when ammonia dissolves in soil water; a form of inorganic nitrogen released by decomposition and used by nitrifying bacteria.

Conditions in which oxygen is absent or very scarce, such as waterlogged soils, swamp sediments and animal guts, where only organisms that do not need oxygen can respire.

The large-scale movement of air around the Earth that transfers heat from the equator towards the poles, driven by unequal heating of the Earth's surface.

An organism that synthesises its own organic compounds from inorganic carbon and other elements, using energy from light or from inorganic chemical reactions.

A transect along which quadrats are placed, either continuously or at regular intervals, to record abundance along an environmental gradient.

The system of naming each species with two words, the genus name with a capital letter followed by the species name in lower case, both written in italics or underlined.

The increase in concentration of a persistent substance in an organism over its lifetime, because it is absorbed faster than it is broken down or excreted.

The continuous movement of a chemical element such as carbon or nitrogen between living organisms and the atmosphere, hydrosphere and lithosphere, which keeps the element available to living things.

The definition of a species as a group of organisms that can interbreed in nature and produce fertile offspring, and that are reproductively isolated from other such groups.

The increase in concentration of a persistent substance at each successive trophic level of a food chain, because biomass is lost in respiration while the substance is retained.

The mass of organic matter in an organism, population or trophic level, usually measured as dry mass per unit area, such as g m⁻² or kg m⁻².

A group of comparable ecosystems that have developed in similar climatic conditions in different parts of the world and so share similar vegetation structure and adaptations.

A change in where a biome occurs as the climate changes, generally a movement towards the poles and to higher altitudes as the climate warms.

The part of the Earth where life exists, including the lower atmosphere, the oceans and fresh waters, and the soil and upper rocks; an ecological system made of individuals, populations, communities and ecosystems.

The state of the living part of the Earth system, including the diversity of genes and species and the ability of ecosystems to function; one of the planetary boundaries.

A living component of an ecosystem that affects other organisms, such as food supply, predators, competitors, parasites, pathogens and mutualistic partners.

A pattern of population change in which rapid growth overshoots the carrying capacity and is followed by a sudden crash, often because resources have been used up.

A biome of high mid-latitudes dominated by coniferous trees, with long cold winters, short mild summers and low productivity limited by temperature and the short growing season.

The process by which organisms such as corals, molluscs and some plankton build shells or skeletons of calcium carbonate from calcium and carbonate ions dissolved in seawater.

A compound of calcium, carbon and oxygen (CaCO₃) that marine organisms use to build shells and skeletons, and the main component of limestone and chalk.

The measurement of the energy content of a material by burning a dried sample completely, often in a bomb calorimeter, and measuring the heat released.

A method of estimating the size of a mobile animal population by capturing, marking and releasing a sample, then recording how many marked individuals appear in a second sample.

The biogeochemical cycle by which carbon moves between the atmosphere, organisms, soils, oceans and rocks through processes such as photosynthesis, respiration, decomposition, dissolving and combustion.

The process of capturing carbon dioxide from the atmosphere or from emissions and storing it in solid or liquid form, for example in plant biomass, soils, rocks or underground reservoirs.

An animal that feeds mainly on other animals, as a secondary or higher consumer.

The maximum size of a population of a species that an environment can support over a long period, determined by competition for limited resources.

The process in all living cells that releases energy from glucose and other organic compounds for cell activities, producing carbon dioxide and water and losing some energy as heat.

An autotroph, usually a bacterium or archaeon, that makes organic compounds using energy released by exothermic inorganic chemical reactions rather than light.

The process by which chemoautotrophs make organic compounds from carbon dioxide using energy from oxidising inorganic substances such as hydrogen sulfide.

A group of organisms made up of a common ancestor and all of its descendants, which share characteristics inherited from that ancestor.

A branching diagram showing the probable evolutionary relationships between groups of organisms, in which each branching point represents a common ancestor.

The arrangement of organisms into groups on the basis of their shared characteristics, which allows efficient identification and the prediction of other characteristics.

The average atmospheric conditions of a place, such as temperature, precipitation, humidity and wind, calculated over a long period, usually about 30 years.

A graph showing the average monthly temperature of a place as a line and its average monthly precipitation as bars, usually based on about 30 years of data.

The relatively stable community at the end of a succession, in steady-state equilibrium with the climate and soils of the area.

The arrival and establishment of a species in an area where it did not previously live, for example plants spreading onto newly exposed rock.

The burning of a fuel or organic matter in oxygen, a transformation that releases energy as heat and light and returns stored carbon to the atmosphere as carbon dioxide.

An ancestral species from which two or more later species or groups have evolved, shown as a node on a cladogram.

A collection of interacting populations of different species living in the same area at the same time.

An interaction in which organisms of the same or different species need the same limited resource, such as food, water, light or space, so that each gets less.

An organism that obtains its energy and carbon compounds by feeding on other organisms or their remains, rather than making its own food.

A temperate climate type far from the sea, with a large annual temperature range, cold winters, warm or hot summers and lower precipitation, often peaking in summer.

A shallow, warm-water marine ecosystem built from the calcium carbonate skeletons of corals, with very high productivity and species diversity despite nutrient-poor surrounding water.

The apparent deflection of moving air and water caused by the Earth's rotation: to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

An electronic device that records measurements from one or more sensors automatically at set time intervals, allowing conditions to be monitored continuously over long periods.

Dichlorodiphenyltrichloroethane, a persistent, fat-soluble organochlorine insecticide that biomagnifies in food chains; its breakdown product DDE causes eggshell thinning in birds of prey.

An organism, mainly a bacterium or fungus, that breaks down dead organic matter into inorganic substances, releasing nutrients back into the soil, water or air.

The breakdown of dead organic matter into simpler inorganic substances by decomposers and detritivores, which releases nutrients and carbon dioxide.

The conversion of nitrate back into nitrogen gas by denitrifying bacteria in anaerobic conditions such as waterlogged soils, returning nitrogen to the atmosphere.

A factor whose effect on a population's birth or death rate increases as population density increases, such as competition, predation and disease.

A factor whose effect on a population does not depend on its density, such as extreme weather, fire, floods or volcanic eruptions.

The drying out of an organism or a habitat through loss of water, a major stress for organisms exposed to air at low tide or on dry soils.

An animal that ingests dead organic matter such as fallen leaves, faeces and dead bodies, breaking it into smaller pieces, as earthworms and woodlice do.

An identification tool made of a series of numbered questions, each with two alternative answers that lead either to another question or to the name of an organism.

The amount of oxygen gas dissolved in water, usually measured in milligrams per litre, which aquatic organisms need for respiration.

An event, natural or human, such as fire, flood, storm, grazing or clearing, that removes or damages part of a community and changes the resources available.

A method of identifying a species by sequencing a short, standard section of its DNA and comparing it with a reference library of sequences from known species.

The mass of a sample after all its water has been removed by drying to constant mass, used as a measure of the organic matter it contains.

The percentage of the energy received by one trophic level that is passed on to the next; typically 10% or less, but it varies between ecosystems, levels and species.

A diagram of stacked horizontal bars, one per trophic level, whose widths show the relative numbers, biomass or energy at each level.

A community of interdependent organisms and the physical environment with which it interacts.

An organism that creates, modifies or maintains habitat by changing the physical environment, such as beavers building dams or elephants pushing over trees.

The extent to which an ecosystem keeps its natural structure, species composition and processes, such as nutrient cycling, so that it can function and recover from disturbance.

A transition zone between two communities or biomes, where species from both occur and the community changes along an environmental gradient.

The removal from the gut of undigested food that was never absorbed into the body, as faeces.

The warm phase of ENSO, in which the Walker circulation weakens or reverses, warm water spreads east across the tropical Pacific and upwelling off western South America decreases.

The irregular fluctuation in winds and sea-surface temperatures across the tropical Pacific Ocean between El Niño, neutral and La Niña states, which affects weather in many parts of the world.

The one-way movement of energy through an ecosystem, entering mainly as sunlight, passing between trophic levels as chemical energy in food, and leaving as heat.

A systems diagram showing energy entering, passing between and leaving trophic levels, with arrows whose widths are often drawn in proportion to the size of each flow.

A measure of the disorder of a system and of how spread out its energy is; it increases in every energy transformation as energy is degraded to heat.

A gradual change in one or more abiotic factors, such as temperature, exposure or soil moisture, across a distance in space.

Growth of a population by a constant proportion in each time period, so that numbers double at regular intervals and the growth curve becomes ever steeper.

The phase of an S-shaped growth curve in which a population grows rapidly and at an increasing rate because resources are plentiful.

The permanent disappearance of a species, when its last individual dies.

The number of species that become extinct in a given period, often expressed as extinctions per million species per year and compared with the natural background rate.

A process in succession in which one species changes the conditions, for example by adding nitrogen or organic matter to the soil, in a way that helps other species to establish.

The cell of atmospheric circulation between about 30° and 60° latitude, in which air sinks in the subtropics, moves poleward at the surface and rises near 60°.

The physical law that energy can be transformed from one form to another but cannot be created or destroyed, so the total energy entering a system equals the total leaving or stored.

A sequence of organisms in which each feeds on the one before, showing the path of energy and biomass from a producer to higher consumers.

A network of interconnected food chains in an ecosystem, showing all the feeding relationships, including species that feed at more than one trophic level.

A carbon-rich fuel such as coal, oil or natural gas, formed over millions of years from the partly decomposed remains of ancient organisms buried in sediments.

The full range of conditions and resources in which a species could survive and reproduce if there were no limiting biotic factors such as competition or predation.

A group of closely related species that share many characteristics; the first part of a binomial name, written with a capital letter.

The total rate at which producers fix energy or carbon by photosynthesis or chemosynthesis per unit area per unit time, before respiratory losses.

The total gain in biomass or energy by an organism or trophic level per unit area per unit time, before any is lost in respiration.

The rate at which consumers absorb energy or biomass from food, equal to food ingested minus faecal losses, per unit area per unit time.

The industrial process that combines nitrogen from the air with hydrogen, at high temperature and pressure over an iron catalyst, to make ammonia, mainly for fertilisers.

The location in which a community, species, population or organism lives, including its physical features and the type of ecosystem that meets its needs.

The cell of atmospheric circulation between the equator and about 30° latitude, in which warm air rises at the equator, moves poleward at height and sinks in the subtropics.

A method for estimating primary productivity on land by harvesting, drying and weighing the plant biomass in sample plots at intervals and calculating the gain per unit area per unit time.

An animal that feeds on living plants or algae, so it is a primary consumer.

An interaction in which an animal feeds on plants or algae, benefiting the herbivore and harming the plant.

An organism that cannot make its own organic compounds and obtains them by feeding on other organisms or their remains.

A biome with very low and unreliable precipitation, usually under about 250 mm a year, and high daytime temperatures, in which water is the main limiting factor.

The maximum number of people an area or the Earth can support sustainably, given its resources, technology and level of consumption; difficult to estimate and changing over time.

An opening in the sea floor, usually at a spreading ridge, from which hot, mineral-rich water emerges, supporting food webs based on chemosynthetic bacteria.

A plant, such as a pitcher plant or sundew, that traps and digests insects to obtain nitrogen and other nutrients missing from the waterlogged, nutrient-poor soils where it grows.

The amount of incoming solar radiation reaching a given area of the Earth's surface, which varies with latitude, season, time of day and cloud cover.

Competition between individuals of different species for the same limited resource.

The belt of low pressure near the equator where the trade winds of the two hemispheres meet and warm, moist air rises, bringing heavy convectional rain; it moves north and south with the seasons.

Competition between individuals of the same species for the same limited resource.

A growth curve in which population size rises ever more steeply with time, showing exponential growth with no limiting factors.

A species that reproduces late and produces few large offspring with much parental care and a high chance of survival, adapted to stable environments near carrying capacity.

A species that has a disproportionately large effect on the structure of its community relative to its abundance, so that its removal can cause the community to change greatly or collapse.

A method of sampling stream invertebrates by disturbing the stream bed with the feet for a set time just upstream of a net held against the current.

A graph that shows how the abundance of each species changes along a transect, with the width of each band proportional to its abundance at each point.

The cool phase of ENSO, in which the Walker circulation and the trade winds strengthen, cold upwelling off western South America increases and the western Pacific becomes wetter.

The first phase of an S-shaped growth curve, in which a population grows slowly because there are few individuals to reproduce.

The angular distance of a place north or south of the equator, measured in degrees from the centre of the Earth, from 0° at the equator to 90° at the poles.

A plant of the pea and bean family, such as clover, beans, peas, lentils and soya, whose root nodules hold nitrogen-fixing bacteria.

The sequence of stages an organism passes through from the start of its life to reproduction and death, including its timing and lifespan.

A method for measuring aquatic primary productivity by comparing the change in dissolved oxygen in clear and darkened bottles of water incubated together for a set time.

A sedimentary rock made mostly of calcium carbonate, often from the shells and skeletons of marine organisms; the largest carbon store on Earth, holding carbon for hundreds of millions of years.

The environmental factor, abiotic or biotic, that is in shortest supply relative to need and therefore restricts the growth, abundance or distribution of a population.

A method of estimating the size of a population of mobile animals from capture-mark-release-recapture data, calculated as (M × N) ÷ R.

A transect along which every organism touching the line is recorded at set intervals.

A temperate climate type near oceans, with a small annual temperature range, mild winters, cool summers and precipitation spread throughout the year.

The largest harvest that can be taken from a population or trophic level every year without reducing its future availability, equal to its net productivity.

The production of methane by methanogenic microorganisms that break down dead organic matter in anaerobic conditions, for example in wetlands, rice paddies and the stomachs of ruminants.

Plastic particles smaller than 5 mm, from broken-down plastic items or made small, which are eaten by many organisms and can carry adsorbed pollutants into food chains.

A seasonal reversal of winds that brings a distinct wet season, as when the ITCZ moves away from the equator in summer and draws moist air over land.

A close relationship between two species in which both benefit, such as mycorrhizal fungi exchanging minerals for sugars with plant roots.

The rate at which producers store energy or biomass after their own respiratory losses, per unit area per unit time; NPP = GPP − R.

The gain in biomass or energy by an organism or trophic level per unit area per unit time that remains after respiratory losses; NP = GP − R.

The rate at which consumers store energy or biomass in new tissue after respiratory losses, per unit area per unit time; NSP = GSP − R.

The particular set of abiotic and biotic conditions and resources on which an organism or population depends, including how it obtains food and all the interactions that affect its survival and reproduction.

The conversion of ammonium into nitrite and then nitrate by nitrifying bacteria in aerobic soil and water.

The ion NO₂⁻, an intermediate form of inorganic nitrogen produced from ammonium and then converted into nitrate during nitrification.

The biogeochemical cycle by which nitrogen moves between the atmosphere, soils, water and organisms, largely through transformations carried out by bacteria.

The conversion of unreactive nitrogen gas (N₂) from the atmosphere into ammonia or ammonium, carried out by nitrogen-fixing bacteria, by lightning or industrially by the Haber process.

Bacteria that convert atmospheric nitrogen into ammonia, either living freely in soil and water or in mutualistic association with plants, such as Rhizobium in the root nodules of legumes.

Describes a substance that decomposers cannot break down, or break down only very slowly, so it persists in the environment for years.

The ongoing decrease in the pH of seawater caused by the oceans absorbing carbon dioxide from the atmosphere, which also lowers the concentration of carbonate ions.

A continuous, directed movement of seawater, driven by wind, the Earth's rotation and differences in water density, that transfers heat around the globe.

A measure of ENSO used by NOAA: the three-month running mean of the sea-surface temperature anomaly in the central equatorial Pacific (the Niño 3.4 region).

An animal that feeds on both plants and animals, so it can occupy more than one trophic level.

A carbon compound made by living organisms, such as glucose, proteins and fats, that stores chemical energy and forms biomass.

A relationship in which one organism, the parasite, lives on or in another, the host, and feeds from it, harming the host, usually without killing it quickly.

A microorganism or virus that causes disease in its host, such as a bacterium, virus, fungus or protist.

A waterlogged soil made of partly decomposed plant material that builds up because anaerobic conditions slow decomposition; a large carbon store that becomes a source when drained or burned.

An estimate of the percentage of the area within a quadrat that is covered by a particular species, seen from above.

The percentage of sampling units, such as squares within a quadrat or whole quadrats, in which a species is present.

Ground that remains at or below 0 °C for at least two consecutive years, found beneath tundra and boreal forest, which stores large amounts of organic carbon.

A carbon-based chemical, such as DDT or PCBs, that resists breakdown, dissolves in fats, travels long distances and builds up in food chains.

A scale from 0 to 14 that measures how acidic or alkaline a solution or soil is; 7 is neutral, lower values are acidic and higher values alkaline.

A loss of synchrony between the timing of linked life-cycle events, such as a food peak and the demand of its consumers, caused by species responding differently to environmental change.

An autotroph that uses light energy to make organic compounds by photosynthesis, such as a green plant, alga or cyanobacterium.

The process by which producers use light energy to convert carbon dioxide and water into glucose and oxygen, transforming light energy into chemical energy.

The first community to become established on a newly exposed or disturbed surface at the start of succession, made up of pioneer species.

A species that is first to colonise bare ground or rock, able to tolerate harsh conditions such as lack of soil, nutrients and water, and often an r-strategist.

A container sunk level with the ground surface so that small animals walking across the ground fall in and can be counted.

A stable community that develops when human activity, such as burning, grazing or mowing, stops or diverts succession before the climatic climax is reached.

The final phase of an S-shaped growth curve, in which births roughly equal deaths and the population fluctuates around the carrying capacity.

The cell of atmospheric circulation between about 60° latitude and the pole, in which cold, dense air sinks at the pole and flows towards lower latitudes at the surface.

The identification and counting of pollen grains preserved in layers of peat or lake sediment, used to reconstruct past vegetation and the changes of succession.

A group of persistent, fat-soluble industrial chemicals once used in electrical equipment, which biomagnify in food chains and harm the immune and reproductive systems of top predators.

A group of organisms of the same species living in the same area at the same time, which are capable of interbreeding.

The number of individuals of a species per unit area or per unit volume.

The changes in the size, density and structure of populations over time, and the birth, death and migration processes that cause them.

An interaction in which one animal, the predator, kills and eats another, the prey.

A consumer that feeds on producers and so occupies the second trophic level, such as a herbivore.

The rate of production of biomass by autotrophs using an external energy source and inorganic carbon, per unit area per unit time, such as kg C m⁻² yr⁻¹.

Succession on a newly formed surface with no soil and no previous community, such as new volcanic rock, a glacial moraine, wind-blown sand or freshly deposited silt.

An organism, such as a plant, alga or photosynthetic bacterium, that makes its own organic compounds from inorganic substances and forms the first trophic level.

The rate at which biomass or energy is gained by an organism, trophic level or ecosystem, per unit area per unit time.

An ecological pyramid showing the standing crop of biomass at each trophic level per unit area at one time, usually in g m⁻² of dry mass.

An ecological pyramid showing the energy flowing into each trophic level per unit area per unit time, usually in kJ m⁻² yr⁻¹; it is never inverted.

An ecological pyramid showing the number of individual organisms at each trophic level per unit area at one time.

A square frame of known area, often divided into smaller squares, used to sample non-mobile or slow-moving organisms.

A species that reproduces early and produces many small offspring with little parental care, adapted to colonise unstable or new habitats and use short-lived resources.

A dry area on the sheltered side of a mountain range, where air that has lost its moisture rising over the mountains descends and warms.

A sampling method in which every point in the study area has an equal chance of being chosen, usually by using random numbers as grid coordinates.

All forms of nitrogen other than unreactive nitrogen gas (N₂), such as ammonia, ammonium, nitrate and nitrous oxide, which living things can use or which can pollute air and water.

The actual range of conditions and resources in which a species exists, usually smaller than its fundamental niche because of competition and other interactions.

The average length of time that an atom of an element, such as carbon, remains in a particular store before moving to another store.

The energy or biomass used in cellular respiration by an organism or trophic level and lost as heat, the R in NP = GP − R.

A small swelling on the root of a plant such as a legume or alder that houses nitrogen-fixing bacteria in a mutualistic relationship with the plant.

A plant-eating mammal, such as a cow, sheep or goat, with a multi-chambered stomach in which microorganisms ferment plant material, producing methane.

A sigmoid growth curve with lag, exponential, transitional and plateau phases, in which population growth slows and levels off at the carrying capacity.

The concentration of dissolved salts in water or soil, usually measured in parts per thousand or as electrical conductivity.

The process of collecting data from a small, representative part of a population or area in order to estimate a characteristic of the whole.

An organism, mainly a fungus or bacterium, that feeds by secreting digestive enzymes onto dead organic matter and absorbing the products.

A tropical grassland biome with scattered trees, high temperatures all year and a long dry season, often maintained by fire and grazing as well as climate.

An animal that feeds on the dead bodies of animals it has not killed itself, such as a vulture.

The temperature of the water at or near the surface of the ocean, which controls evaporation, storm formation and the exchange of heat between the ocean and the atmosphere.

The physical law that every energy transformation degrades some energy into less useful forms, mainly heat, so no transformation is 100% efficient and entropy increases.

A consumer that feeds on primary consumers and so occupies the third trophic level.

The rate at which consumers gain biomass from carbon compounds absorbed and assimilated from the food they ingest, per unit area per unit time.

Succession on bare soil where a community existed before but was removed or destroyed, for example abandoned farmland or forest after a severe fire.

One of the series of communities, or seral stages, that replace each other during succession, from the pioneer community to the climax community.

The management of forests and plantations to grow and harvest trees for timber, fuel and other products.

A store that takes in more of an element than it releases over a period of time, so that the amount held in it is increasing; a net accumulation.

A store that releases more of an element than it takes in over a period of time, so that the amount held in it is decreasing; a net release.

A group of organisms that can interbreed and produce fertile offspring.

The biomass or number of organisms present in a trophic level or area at one particular time, as opposed to the rate at which it is produced.

A rise in sea level above the normal tide caused by the strong winds and low pressure of a storm, which can flood low-lying coasts.

A sampling method in which the area is divided into distinct zones and random samples are taken within each zone, usually in proportion to its size.

The replacement of one community by another in an area over time, as each community changes the biotic and abiotic conditions so that others can colonise and outcompete it.

The amount of a renewable resource that can be harvested per unit time without reducing the stock or its ability to provide the same yield in future.

A strong, wide net swept through long grass or low vegetation to collect insects and other invertebrates.

A sampling method in which samples are taken at regular intervals in space or time, such as every 5 m along a line or at every point of a grid.

A group of organisms at any level of classification, such as a kingdom, phylum, class, order, family, genus or species.

The science of naming, describing, identifying and classifying organisms into groups.

A forest biome of the mid-latitudes with warm summers, cool or cold winters and rain spread through the year, often dominated by broadleaved trees that lose their leaves in winter.

A grassland biome of continental interiors in the mid-latitudes with hot summers, cold winters and too little rain to support forest, such as the prairies and steppes.

A rough generalisation that about 10% of the energy at one trophic level passes to the next; real efficiencies vary widely, so it is neither fixed nor a true average.

A consumer that feeds on secondary consumers and so occupies the fourth trophic level.

The regulation of a community by organisms at higher trophic levels, such as predators or large herbivores, which limits the abundance of the organisms they eat.

The steady surface winds that blow from the subtropical high-pressure belts towards the equator, from the north-east in the Northern Hemisphere and the south-east in the Southern Hemisphere.

A line laid across a study area, usually along an environmental gradient, along which samples are taken at regular intervals.

The phase of an S-shaped growth curve in which population growth slows as resources become limited and competition, predation and disease increase.

The edge beyond which trees cannot grow, set by low temperatures and a short growing season, found at high latitudes and at high altitudes on mountains.

A model of atmospheric circulation in which each hemisphere has three cells of moving air, the Hadley, Ferrel and polar cells, explaining global belts of pressure, wind and rainfall.

The position an organism occupies in a food chain, counted by the number of feeding steps between it and the producers at the base.

A rapidly rotating storm system with a low-pressure centre that forms over warm tropical oceans; it is called a hurricane, typhoon or cyclone once sustained winds exceed 119 km/h.

A forest biome near the equator with high temperatures and heavy rainfall all year, very high net primary productivity and the highest terrestrial species diversity.

A funnel with a mesh and a lamp above it, used to extract small invertebrates from soil or leaf litter as they move away from heat and light.

A treeless biome of high latitudes or high altitudes with long, very cold winters, a short growing season, low precipitation and often permafrost below the surface.

The hypothesis, proposed by Frans Vera in 2000, that large wild herbivores kept much of lowland temperate Europe as a mosaic of open grassland, scrub and woodland rather than closed forest.

The east–west loop of atmospheric circulation over the tropical Pacific, with air rising over the warm western Pacific and sinking over the cooler eastern Pacific.

The state of the atmosphere at a particular place and time, or over a short period, described by temperature, humidity, air pressure, wind speed and precipitation.

A graph that plots mean annual precipitation against mean annual temperature and shows which terrestrial biome is likely to develop under each combination of the two.

The change in community composition along an environmental gradient, such as altitude, latitude, tidal level or distance from a water source.