Enviroweb HomeBiosphere Contents
Glossary
A-B-C-D-E-F-G-H-I-K-L-M-N-O-P-R-S-T-V-W-X-Z
Abiotic
Environmental factors that are nonliving components of the ecosystem.
Acetic acid
An organic acid produced by certain micro-organisms during the
decomposition of organic matter. Also known as ethanoic acid.
Acid
A substance which, on being dissolved in water produces hydrogen ions
at concentrations which exceed those found in pure water. Acids are
strongly corrosive and will dissolve metals from many natural
materials, e.g. rock.
Active surface
The term active surface is used in the text to denote the general
attributes of any form of surface.
Allogenic succession
Succession due to external factors. (See: Succession).
Amensalism
An ecological interaction where the competition is asymmetrical and
the interaction is negative for only one participant ( - 0
interaction).
Amino acids
An organic compound containing an amino group and a carboxyl group;
amino acids are the units or building blocks that make peptide and
protein molecules.
Ammonification
Conversion of an organic form of nitrogen (e.g. of protein) into the
inorganic ammonium (NH4+) ion.
Anaerobiosis
The state of being oxygen free. Describes the breakdown of sugars in
organic compounds in the absence of oxygen (releasing some energy and
producing organic acids and/or alcohol).
Aquatic ecosystem
Any ecosystem of which the principal component is water, such as
ponds, lakes, rivers, streams and oceans. Lawrence (1995)
Asexual reproduction
Reproduction which forms new individuals from a single individual
without the involvement of gametes. The offspring are genetically
identical to the parent and to each other. Parker (1984) Lawrence
(1995)
Assimilation
In autotrophic organisms it is the uptake of elements and simple
inorganic compounds such as carbon dioxide, nitrogen and water from
the environment and their incorporation into complex organic
compounds. In heterotrophs it is the conversion of digested food
material into complex biomolecules. Lawrence (1995)
Atmosphere
The gaseous envelope surrounding planets. The term is generally
applied to the whole body of terrestrial air. The earth's atmosphere
is composed mainly of nitrogen, oxygen, argon and carbon dioxide.
Autogenic succession
Succession occurring due to changes brought about by the presence of
vegetation itself.
Bacteria
A group of extremely metabolically diverse, prokariotic, unicellular
micro-organisms, usually possessing cell walls. They are ubiquitous in
soil and water. The many forms include parasitic and disease-causing
organisms and those which play an important part in the breakdown of
dead organisms. Lawrence (1995)
Biodiversity
The diversity of the natural world, ecological variety and richness.
Chambers (1994)
Biofilm
A thin film composed of micro-organisms and the substances they
produce, that adheres to surfaces such as river beds or pipe
interiors.
Biological fixation
With reference to nitrogen fixation: The process whereby atmospheric
elemental nitrogen is reduced to ammonia, and which is carried out in
the living world only by some free-living bacteria and cyanobacteria
(blue-green algae) and by a few groups of bacteria in symbiotic
association with plants.Lawrence (1995)
Biomagnification
The increasing concentration of a compound in the tissue of organisms
as the compound passes along the food chain; resulting from the
accumulation of the compound at each trophic level prior to its
consumption by organisms at the next trophic level. Begon, Harper
& Townsend (1986)
Biomass
The total mass or weight of all the living organisms in a given area
or population.
Biomes
A broad, regional type of ecosystem characterised by distinctive
climate and soil conditions and a biological community which is
adapted to those conditions.
Biosphere
The zone of air, land, and water (both in lakes and in the sea) at the
surface of the earth that is occupied by organisms.
Biotic
Applied to the living components of the biosphere or of an ecosystem,
as distinct from the non-living, abiotic, physical and chemical
components. Allaby and Allaby (1990)
Blue Green Algae
Common name for cyanobacteria. (See Cyanobacteria).
Lawrence (1995)
Boreal forests (Taiga)
A broad band of mixed deciduous and coniferous woodland that stretches
across most of northern North America, and Eurasia. Boreal forest is
also known as Taiga.
Carbohydrates
Compounds of carbon, oxygen and hydrogen, of general formula Cx(H2O)y,
including sugars (monosaccharides and disaccharides) and their
derivatives, and polysaccharides such as starch and cellulose.
Lawrence (1995)
Carbon
The basic element of organic life which, together with hydrogen and
oxygen, forms the fundamental molecules involved in organic
structures.
Carbon dioxide
A colourless, odourless gas at normal temperatures, composed of one
atom of carbon and two of oxygen. It makes up about 0.03% of the
atmosphere by weight. Carbon dioxide is consumed in photosynthesis by
green plants and produced by the respiration of plants and animals and
the burning of fossil fuel.
Carbonate
A mineral containing the chemical group CO3 e.g. calcite (CaCO3).
Carbonates are associated mainly with limestone and dolomite. Allaby
and Allaby (1990)
Carbonic acid
A very weak acid formed from carbon dioxide and water. Sharp (1990)
Carnivores
Animals that feed on other animals, especially the flesh-eating
mammals (Carnivora) such as dogs, cats, bears and seals, which feed on
meat or fish. Lawrence (1995)
Chaparral
The scrub of west California and adjacent regions, in which the leaves
of the trees and shrubs are evergreen, hard, thick, leathery and
usually small. These adaptations allow the plants to survive the
pronounced hot, dry season. Much of the chaparral has been derived by
disturbance, principally burning of an earlier forest cover. Allaby
(1994)
Chlorophyll
The green pigment in plants that functions in photosynthesis by
absorbing radiant energy from the Sun, predominantly from blue
(435-438nm) and red (670-680nm) regions of the spectrum. Allaby (1994)
Chloroplasts
The inclusion of (plastids) within plant cells which contain
chlorophyll.Begon, Harper & Townsend (1986)
Class
Taxonomic group into which a phylum or a division is divided, and
which is itself divided into orders. Lawrence (1995)
Climatic climax
A relatively stable, long-lasting ecosystem which is established after
a successional series, usually best suited to the climate of the area.
Climax
A relatively stable, long-lasting community reached in a successional
series; usually determined by climate and soil type.
Community
A general term applied to any grouping of populations of different
organisms found living together in a particular environment;
essentially, the biotic component of an ecosystem. Allaby (1994)
Colonisation
The successful establishment of an invading species in a
habitat.Allaby (1994)
Cyanobacteria
A large and varied group of photosynthesizing bacteria which were
formerly regarded as algae - hence the common name ‘blue green algae’.
They are believed to have been the first oxygen-producing organism.
Many species can fix atmospheric nitrogen. Some produce toxins which
can become a health hazard when algal blooms occur. Lawrence (1995)
Allaby (1994)
Decomposer
Organism such as a maggot or bacteria that takes part in the decay of
other organisms (plants and animals) by feeding on their remains.
Decomposition
The breakdown of complex organic material, undertaken by bacteria and
fungi. Leads to the production of humus.
Deforestation
The removal of forests. Deforestation is often the result of human
activities such as logging or farming and may lead to desertification.
Demes
A spatially discrete interbreeding of organisms with definable genetic
or cytological characters (i.e. a subpopulation of a species). Allaby
(1994)
Denitrification
Conversion of 'agriculturally useful' forms of nitrogen e.g. NO3-,
NH4+ to dinitrogen (N2) gas.
Deserts
Areas receiving less than 25cm of rain a year. The term is more
generally applied to any arid area. Deserts do not necessarily have a
hot climate: cold deserts do occur.
Differentiation
The increasing specialization of the organization of the different
parts of an embryo, as a multicellular organism develops from the
undifferentiated fertilized egg. Lawrence (1995)
Diffusion
The movement of a substance down a concentration gradient from high
concentration of the substance to low concentration, normally within
gaseous fluids. Diffusion is caused by random movement of the
particles of the substance so that ultimately it will lead to a
homogenous distribution of the substance in the fluid.
Direct interference
The addition or removal of a material or element from an ecosystem by
a plant which does not directly compete for it.
Diurnal
Daily; related to or performed in or lasting a day. Chambers (1994)
DNA
Deoxyribose nucleic acid (DNA) is found in the nuclei of cells and
carries the necessary hereditary information to enable highly specific
proteins to be constructed. Sharpe (1990)
Domain
A taxonomic rank introduced by Carl Woese in 1990 as the primary
division of living organisms.
Dynamic equilibrium
A state where, although the mean state is constant, the forces acting
continue to change and flux.In chemical terms dynamic equilibrium
refers to the state in which there is no change in composition, unless
there is a change in an external property.(e.g. temperature or
pressure). This state only exists where the downward and reverse
reactions are exactly balanced.
Ecosphere
See Biosphere.
Ecosystem
A specific biological community and its physical environment
interacting in an exchange of matter and energy.
Edaphic climax
The climax vegetation that occurs as a result of soil induced factors.
Elements
A substance which cannot be further divided by chemical methods. The
basic substances which build up chemical compounds. Sharpe (1990)
Environmental gradient
A continuum representing an factor such as mean annual precipitation,
soil fertility, growing season length, etc. Each species will have a
point on the continuum at which it experiences optimum growing
conditions, and a range of tolerance representing the conditions in
which it is able to survive.
Environmental spheres
See Atmosphere, Biosphere, Hydrosphere, Lithosphere, Mesosphere, Photosphere.
Enzymes
Molecules, usually proteins or nucleic acids, that act as catalysts in
biochemical reactions.
Epiphytic plants
Plants that live on the surface of other plants but do not derive
water or nourishment from them. Lawrence (1995)
Equilibrium
A state of even balance. Chambers (1994)
Erosion
The process of wearing away the land surface, by processes which
transport rock debris. Erosion frequently refers to the loss of soil
due to wind or as a result of washing away by water.
Essential elements
With reference to nutrition: elements necessary for the survival of
the organism.
Eukaryotes
Organisms with cells possessing a membrane-bound nucleus in which the
DNA is complexed with histones and organised into chromosomes, i.e.
protozoans, algae, fungi, plants and animals. Begon, Harper &
Townsend (1986)
Evolution
The development of new types of living organisms from pre-existing
types by the accumulation of genetic differences over long periods of
time. Lawrence (1995)
Extinction
The complete disappearance of a species from the earth.Lawrence (1995)
Facilitation model
This theory was put forward by Connell and Slatyer in 1977 but it is
based upon the 'classic' theory of succession. It suggests that
species that are being replaced in a succession will have altered
their environment so that it is less suitable for their own needs
whilst becoming more suitable for the needs of the replacing species.
For example, as a plant species develops it changes the microclimate
and soil around it due to both an increase in height, which produces
calm areas, and organic decomposition, which will increase the
fertility of the soil. Since this initial species may have been a
pioneer species especially tolerant of harsh environments, it may not
subsequently be able to survive competitively in the richer conditions
it has helped to create.
Family
Taxonomic group of related genera, related families being grouped into
orders. Familial names usually end in -aceae in plants and -idae in
animals. Lawrence (1995)
Food Chain
A linked feeding series in an ecosystem: the sequence of organisms
through which energy and materials are transferred, in the form of
food, from one trophic level to another.
Food conversion ratios
The percentage of consumed food converted to body weight.
Food web
A complex interlocking series of individual food chains. (See: Food
chain).
Fossil fuel
A fuel derived from the remains of ancient plant or animal life. The
main forms used are oil, gas and coal.
Fundamental niche
The full range of conditions across which a species could survive and
reproduce, in the absence of competition from other species.
Gametes
Reproductive cells produced by sexually reproducing organisms which
fuse with another gamete of opposite sex or mating type to produce a
zygote. Lawrence (1995)
Genetic information
The information for synthesizing RNA and protein, which is contained
in DNA and RNA. Lawrence (1995)
Genera
The plural of genus. Taxonomic group of closely related species,
similar and related genera being grouped into families. Generic names
are italicized in the scientific literature e.g. Homo (man), Canis
(wolves and dogs). Lawrence (1995)
Genes
The basic unit of inheritance, by which hereditary characteristics are
transmitted from parent to offspring. At the molecular level a single
gene consists of a length of DNA (or in some viruses RNA.) Each living
cell carries a full complement of the genes typical of the species.
Lawrence (1995)
Genus
One of the groups used in classifying organisms. Consists of a number
of similar species, and occasionally of one species only. Similar
genera are grouped in a family. Abercrombie, Hickman and Johnson
(1980)
Global carbon budget
The carbon available to global systems, and its distribution within
those systems.
Halosere
A sere which is developed under saline conditions.
Hardpan
Hardened soil horizon, usually found in the middle or lower parts of
the profile. Allaby and Allaby (1990)
Herbivores
An animal that feeds exclusively on plants. Lawrence (1995)
Higher plant
A plant of relatively greater complexity than the more simple, lower
plants. Higher plants contain a vascular system of transport vessels
including xylem. E.g. flowering
plants, conifers, ferns.
Horizons
With reference to soils: A horizontal layer that can be distinguished
from the layers below and above it. Identified by a coding system
using a capital letter, sometimes followed by a subscript, such layers
are used to diagnose soil types. Allaby and Allaby (1990)
Humus
Sticky, brown insoluble residue from the bodies of dead plants and
animals. Humus gives soil its structure, coating mineral particles and
holding them together. It also serves as a major source of plant
nutrients.
Hydrological cycle
The circulation of water - in liquid, solid, or vapour form - through
a series of reservoirs in the environment.
Hydrosere
A sere developed under (non-saline) wet conditions, such as lake
margins.
Hydrosphere
The total body of water of the earth, i.e. the oceans, rivers, lakes,
underground and atmospheric water.
Inhibitory effect
The ability to restrict the growth or potential for growth of
competitors; an effect caused by some organisms in competition for
nutrients.
Initial Floristic Competition theory
A succession theory which suggests that development at any one site
depends largely on who gets there first: there is not necessarily an
orderly progression because existing species will try to maintain
their hold on the site. (Egler 1954). It is also known as the
'Inhibition Model' (Connell and Slayter 1977).
Inorganic
With reference to chemistry: of, or relating to, compounds which do
not contain carbon. Also: not of animal or vegetable origin. Chambers
(1994)
Ions
Atoms or molecules that have acquired an electric charge by the loss
(cation; positive charge) or gain (anion; negative charge) of one or
more electrons. Allaby and Allaby (1990)
Keystone species
Species that have a key role in an ecosystem, affecting many other
species, and whose removal leads to a series of extinctions within the
system. Lawrence (1995)
Kingdom
With reference to taxonomy: the primary division of the living world,
until the category Domain was introduced above the level of Kingdom in
1990. Kingdoms are divided into phyla, for animals, and divisions for
plants and other organisms. Lawrence (1995)
Leaching
The removal and transport of elements in solution from and through a
soil.
Lichens
A composite organism formed from the symbiotic association of certain
fungi and a green alga (or cyanobacterium), forming a simple thallus
and found encrusting rocks, tree trunks etc., often in extreme
environmental conditions. Lawrence (1995)
Life cycle
A series of developmental changes undergone by the individuals
comprising a population, including fertilization, reproduction and the
death of those individuals. Allaby (1994)
Limiting nutrient
One of a number of nutrients essential for plant or algal growth, the
limited supply of which causes a halt to further growth as it is
depleted.
Lithosere
A sere which develops on rock.
Lithosphere
The rigid uppermost portion of the mantle plus the overlying crust of
the earth comprising surface rocks.
Litter
Accumulation of dead plant remains on the soil surface. Allaby and
Allaby (1990)
Litter layer
See Litter.
Lower plant
A plant of relatively little complexity.
Macronutrients
Nutrients required in large amounts by plants for growth: carbon,
hydrogen, oxygen, nitrogen, phosphorus, sulfur, potassium, calcium and
magnesium.
Mariculture
Mariculture is the growth of marine organisms (most commonly fish) in
captivity for food or other uses.
Marine
Of, in, near or concerned with the sea. Chambers (1994)
Mediterranean
Biome that occurs around latitude 35oN and 35oS and is associated with
warm temperate west coasts. Summers generally are hot and dry, winters
mild, cool and rainy. The climate is strongly influenced by westerly
air streams in winter and subtropical high pressure in summer. Allaby
(1994)
Megafauna
Animals that are large enough to be seen with the naked eye. Allaby
(1994)
Meiosis
A type of nuclear division which results in daughter nuclei each
containing half the number of chromosomes of the parent. Lawrence
(1990)
Mesosphere
Upper-atmospheric layer above the stratopause (at 50 km) through which
temperature decreases with height up to about 80 km, where temperature
reaches a minimum of about -90oC. Allaby and Allaby (1990)
Metabolism
The total of all the chemical reactions that occur within a living
organism.Allaby (1994)
Micro fauna
Animals less than 200um long, such as protozoa, only visible under the
microscope. Lawrence (1995)
Microclimate
The climate acting in a small area; a divergence through localised
conditions from the average climate for a region.
Microhabitat
The habitat developed in a small localised area which is adapted to
that site and situation; it may diverge markedly from the overall
ecosystem of the region.
Micronutrient
Elements required in small amounts by plants for growth. Elements are:
Fe, Na, Mn, Cu, Zn, Mo, B, Cl.
Microorganism
Any microscopic organism, including bacteria, viruses, unicellular
algae and protozoans, and microscopic fungi (yeasts and moulds).
Lawrence (1995)
Minerals
Naturally occurring homogenous inorganic substances of definite
composition and crystal structure.
Mitochondria
An energy-producing body, threadlike to spherical shape, present in
cytoplasm. Chambers (1994)
Mitosis
The normal process of nuclear division by which two daughter nuclei
are produced, each identical to the parent nucleus, resulting in two
daughter cells with identical nuclear contents. Allaby (1994)
Molar ratio
The ratio of each element within a molecule. For example, carbon
dioxide (CO2) has a molar ratio of 1:2.
Molecule
A molecule is composed of two or more bonded atoms. Molecules are
converted into other molecules during chemical reactions by breaking
chemical bonds between atoms: new chemical bonds between different
atoms are usually formed to create the product of a chemical reaction.
Monoclimax theory
The theory of monoclimax suggests that although there may be several
seres developing within a climatic region the ultimate result will be
convergence to a single climax form of vegetation, providing enough
time is given and the process is free from interference.
Mutations
A change in the structure or amount of the genetic material of an
organism.Allaby (1994)
Mutualistic interaction
A relationship between individuals of two different species in which
both species benefit from the association
Niches
The functional position of an organism in its environment, comprising
the habitat in which it lives, the period of time during which it
occurs and is active there, and the resources it obtains there. Allaby
(1994)
Nitrification
The oxidation of ammonium ion to nitrate, and the oxidation of nitrite
to nitrate, carried out chiefly by a few groups of soil bacteria
(nitrifiers) and also by a few species of fungi. Lawrence (1995)
Nitrogen cycle
The sum total of processes by which nitrogen circulates between the
atmosphere and the biosphere or any subsidiary cycles within this
overall process. Lawrence (1995)
Nucleic acids
A molecule that is composed of strings of NUCLEOTIDES forming a
POLYNUCLEOTIDE CHAIN. Nucleic acids act as the genetic material of
cells and occur as either DNA (two chains) or RNA (one chain). Hale
& Magham (1988)
Nutrient cycles
The exchanges of elements between the living and non-living components
of an ecosystem. Lawrence (1995)
Nutrients
Any substance that organisms take in and use for growth and
maintenance.
Obligate predator
An predator that is very specific in its prey.
Omnivores
Animals that eat both plant and animal food. Lawrence (1995)
Order
Classification of organisms. Consists of a number of similar families.
Similar orders are grouped into classes. Abercrombie, Hickman &
Johnson (1980)
Organic matter
Substances formed by living organisms, often the product of their
decay.
Oxalic acid (COOH2)
Also called ethanedioic acid (COOH2). An organic acid which is a
by-product of the bacterial decomposition of organic matter.
Oxidised
To combine with oxygen. Also means to lose electrons. Chambers (1994)
Oxygen (O)
A gas without taste, colour or smell, forming part of the air, water,
etc., supporting most forms of life and also necessary for combustion.
(Atomic number 8; symbol O). Chambers (1994)
Parasite
An organism that lives in, or on, another living organism and derives
subsistence from it, without rendering it any service in return.
Chambers (1994)
Perennial
A plant that lives more than two years. Chambers (1994)
Permafrost
The permafrost is permanently frozen ground which extends 2000-3000 km
south of the North Pole. It may be divided into three classes:i)
Continuous, in which the subsoil never thaws. ii) Discontinuous, where
patches of unfrozen ground occur. iii) Sporadic, where the area of
unfrozen ground dominates. Seasonally areas of permafrost may thaw in
their upper few centimetres allowing some plant growth.
Photosynthesis
The process by which green plants convert light energy into chemical
energy (food), through the use of chlorophyll. The main chemical
components are water and carbon dioxide.
Phylum
Classification of a primary group consisting of animals constructed on
a similar general plan, and thought to be evolutionarily related.
Lawrence (1995)
Physiographic climax
The climax vegetation that occurs as a result of terrain induced
factors.
Phytographic climax
The climax vegetation that occurs as a result of light induced
factors.
Phytoplankton
The small plants such as diatoms which float passively in seas and
lakes. They form the base of many marine food chains.
Photosphere
The visible surface of the sun. The average temperature of the
photosphere is 6000K.
Pioneer species
First species, usually mosses, lichens and micro-organisms that
colonize a bare site as the first stage in a primary succession.
Lawrence (1995)
Plagioclimax
A plant community arrested from seral development as a result of human
interference.
Plasmalemma
The membrane round the outside of a living cell.
Polyclimax Theory
A theory that other factors are as important as climate in governing
the climax vegetation. In any particular climatic region seres will
develop a set of climax vegetations because of these other factors.
Population
A group of individuals of a species living in a certain area. Lawrence
(1995)
Prairies
A temperate grassland of northern America dominated by xeromorphic
grasses, which fall into three groups based on stature (tall, mid, and
short) with a progressive decrease in rainfall. Allaby (1994)
Precipitation
With reference to the water cycle: Rain, hail, snow etc.
Chambers (1994)
Predator
A predator is any species which uses another species, the prey, as a
source of food. This ranges from algae feeding on bacteria through
herbivores feeding on food plants to carnivores feeding on herbivores.
The difference between a predator and a parasite is that a parasite
can only survive if its host survives, whereas a predator eats and
thereby kills its prey.
Prey
The creature or creatures that a predator hunts and kills as food.
Chambers (1994)
Primary Producer
An organism that synthesises food molecules from inorganic compounds
by using an external energy source: most primary producers are
photosynthetic.
Primary productivity
The rate at which biomass is produced by photosynthetic and
chemosynthetic autotrophs (mainly green plants) in the form of organic
substances. Allaby (1994)
Primary succession
The sequence of development of vegetation on land that has not
previously been influenced by vegetation (e.g. following lava flows,
glacial retreat, newly exposed rock surfaces, etc).
Proteins
One of the chief constituents of living matter, any one of a group of
large organic molecules containing chiefly, carbon, hydrogen, oxygen,
nitrogen and sulfur, and consisting of amino acids joined together by
peptide bonds. Lawrence (1995)
Protozoans
Any member of the phylum Protozoa, including unicellular or acellular
organisms. Hale & Margham (1988)
Productivity
The rate or efficiency of production of a given thing e.g.
biomass.Chambers (1994)
Psammosere
A sere developed on sands or dunes.
Psyllid
An insect of the genus Psylla, sap-sucking plant pests. Chambers
(1994)
Rain forests
Forest biomes that develop in areas with an annual rainfall of more
than 254cm. Lawrence (1995)
Realised niche
The range of conditions across which a species can be found. This is
smaller than the fundamental
niche due to competitive interactions with other species.
Relay Floristic Theory
See: Facilitation Model.
Respiration
The breakdown of chemicals (food) through oxidation to release energy
for life. The main components of the reaction are water, oxygen and
sugars. Note that nearly all living organisms respire, plants as well
as animals.
RNA
Ribonucleic acid, large linear molecule of varied composition, made up
of a single chain of a ribonucleotide subunits. Lawrence (1995)
Saline
Containing salt; a salt solution. Chambers (1994)
Savanna
Savanna or savannah. Tropical grassland areas situated between the
humid equatorial regions and the arid zone in the mid-latitudes.
Scree slope
A slope on which an accumulation of coarse rock debris, added to by
the weathering and release of fragments e.g. from a cliff face. Allaby
and Allaby (1990)
Secondary climax
The climax vegetation resulting from the re-colonisation of a
partially devastated climax vegetation.
Secondary consumers
A carnivore that preys upon herbivores. Allaby (1994)
Secondary sere
Second stage occurring in plant succession, initiated by the
disruption of a previously existing seral or climax community by some
major environmental disturbance and leading to a marked change in the
stable vegetation community e.g. fire. Allaby (1990)
Secondary succession
The succession of seres following the partial devastation of an area.
Sere
A sere is the sequential development of a plant community or group of
plant communities on the same site over a period of time. Succession
at any particular site will progress through a sequence of seral
stages.
Specialisation
The development of adaptations to a specific environment.
Species
A population of morphologically similar organisms that can reproduce
sexually among themselves but cannot produce fertile offspring when
mated with other organisms.
Stability
Ability of a community or ecosystem to withstand or recover from
changes or stresses imposed from outside. Lawrence (1995)
Standing crop
Standing crop is the biomass present at any one time in any specific
ecological component.
Steady state
The condition where the inputs and outputs (fluxes) of a reservoir
balance one another.
Steppes
Dry, grassy, treeless, uncultivated and sometimes salt plain, as in
central Europe and in Asia. Chambers (1994)
Stomata
Openings in epidermis of aerial part of plants, especially on
undersides of leaves, through which air and water vapour enters the
intercellular spaces, and through which carbon dioxide and water
vapour from respiration is released. Lawrence (1995)
Stone age
A stage of culture before the general use of metal, divided into the
Old Stone Age (Palaeolithic) and the New (Neolithic). Chambers (1994)
Stress
A physiological condition, usually affecting behaviour, produced by
excessive environmental or psychological pressures. Allaby (1990)
Subsere
A secondary sere which develops after partial devastation of a site.
Substrates
A substratum; a base, a medium on which an organism can grow. Chambers
(1994)
Succession
Succession refers to the sequential development of changes within a
plant community. This is a natural process in which the species found
in a given area change conditions to make the area less suitable for
themselves and more suitable for others. This continues until the
climax vegetation for an area dominates (See: Facilitation Model).
Symbiotic
Two organisms of different species living together in a persistent,
close, and usually obligatory, association, not necessarily to their
mutual benefit. Often used to describe an association in which both
partners benefit, which is more properly called mutualism. Lawrence
(1995)
System longevity
The ability of an ecosystem to survive wide shifts in the environment
due to its stability and diversity.
Systematics
The study of the identification, taxonomy and nomenclature of
organisms, including the classification of living things with regard
to their natural relationships, and the study of variation and the
evolution of taxa.Lawrence (1995)
Taxonomy
The science of classification, especially of living organisms, which
arranges organisms into hierarchical groupings. Lawrence (1995)
Temperate Forest
Deciduous summer forest dominated by broad-leafed hardwoods, which
occurs over large tracts in the mid-latitudes of Europe, North America
and eastern Asia, but which is restricted in the Southern hemisphere
to parts of Chilean Patagonia. Allaby (1994)
Temperate Grassland
A type of vegetation which includes in the northern hemisphere, the
North American prairies and the Eurasion Steppe; and in the southern
hemisphere, the veldt of South Africa, the pampas of Argentina, and
the Canterbury Plains of New Zealand. Allaby (1994)
Temperate regions
The parts of the earth of moderate temperature, between the tropics
and the polar circles. Chambers (1994)
Thunderstorm
A storm of fairly local scale in which strongly developed cumulonimbus
cloud produces thunder and lightning, usually with rain and strong,
gusting wind, and often with hail. Allaby and Allaby (1990)
Tolerance model
A succession theory proposed by Connell and Slatyer (1977) which
suggests that replacements in a succession are not necessarily
affected by earlier colonisers, and later species tend to be those
which can tolerate lower levels of resources than earlier species.
Topography
The detailed study, description or feature of a limited area. With
reference to land or the ocean bottom: a description of relief.
Chambers (1994)
Trace elements
Elements which are present, or needed, in extremely small
concentrations.
Transpiration
The evaporation of water from stomata in the aerial parts of plants, especially in the leaves. This
evaporation cools plants and creates a pressure gradient which helps
to enable the mass flow of water and dissolved nutrients upwards from
the roots of the plant.
Trophic level
A step in the movement of energy through an ecosystem: an organism's
feeding status in an ecosystem.
Tropical Grasslands
See Savanna
Tropical rain forests
Tropical rain forest is a species-rich biome consisting of stratified
communities of broad leaved shrubs, trees, epiphytes, lianas, numerous
insects, birds and other animals. Average monthly temperatures are
normally in excess of 25oC and the range of temperature variation is
small. Rainfall is abundant: between 1750 and 2500 mm per year,
depending on the topography.
Tundra
Tundra is a treeless arctic or alpine biome where permafrost, low
temperatures, high precipitation or wind have prohibited natural
forest vegetation. Tundra may also be created when man, fire or
animals destroy the natural forest and it fails to regenerate. High
tundra is characterised by ground which is bare except for sparse
lichen and grasses. Low tundra is characterised by a thick mat of
vegetation often saturated with water and dotted with small ponds.
Veldt
Open unforested, or thinly forested grass-country. Chambers (1994)
Viruses
A protein-coated particle of RNA or DNA, capable of increasing rapidly
inside a living cell. Chambers (1994)
Water column
A term used to describe the cross section of a body of water, with
particular reference to the different processes taking place at
various depths, e.g. the photic zone.
Water cycle
The cycle in which water from the sea evaporates into the atmosphere,
later condenses and falls to the Earth as rain or snow, then
evaporates directly back into the atmosphere, or returns to the sea by
rivers. Chambers (1994)
Weathering
The process by which rocks are broken down and decomposed by the
action of external agencies such as wind, rain, temperature changes,
plants, and bacteria. Note that the process acts in situ with no
transportation taking place and is therefore different from erosion.
Two forms of weathering, chemical and physical, can take place and
both may act at the same time.
Xeroseres
A sere which is developed in a dry, arid environment.
Xylem
Transport vessels found in the stems of all higher
plants. They transport water and dissolved nutrients upwards
from the roots to the leaves.
Zooplankton
Non-photosynthetic organisms and small invertebrate animals which are
microscopic in size and occupy the upper water layers in freshwater
and marine ecosystems. They live by eating smaller plants and or
animals.
Zygotes
Fertilized eggs. Lawrence (1995)
A-B-C-D-E-F-G-H-I-K-L-M-N-O-P-R-S-T-V-W-X-Z