Hills and Streams: An Ecology of Hong Kong

Glossary

Glossary Biological terms which have not been defined in the text, or which appear in several different places, are defined below. The definitions are operational and refer to the manner or context in which terms have been used in this book. abaptation The process by which the characteristics of an organism were determined by the action of natural selection on its ancestors. Cr. adaptation. abiotic Non-living; usually applied to physical and chemical factors in an environment. Cf. biotic. adaptation A genetically-determined characteristic that enhances the ability of an organism to survive and reproduce in its environment; usually applied to beneficial features which are believed to have evolved as a result of natural selection acting on previous generations. The prefix ad- (Latin 'to') gives the erroneous impression that an organism is matched to present day environments. In reality, the characteristics of organisms are the result of the influence of past environments on the survival and reproduction of their ancestors. Cf. abaptation. alien species See exotic species. allochthonous Material entering one habitat (such as a stream) but 175 derived from another (the adjacent land); I.e., exogenous. Cr. autochthonous. alluvium An inorganic deposit of sand, silt and gravel which has been transported to the site by water. Cf. colluvium. altruistic Refers to an animal which undertakes actions which benefit other individuals at some cost to itself; i.e., the altruist is usually seen as making a sacrifice, such as foregoing reproduction while helping another individual to rear its young. amphibiotic Animals which spend part of their life cycle in water and the rest on land; includes amphibians and many stream insects which have aquatic juveniles and terrestrial adults. annual plants Species which can germinate, grow and set seed within one year; living for one year or less. aposemete A poisonous, dangerous or distasteful animal which is brightly coloured to advertise its unpleasant attributes; species with warning colouration are said to exhibit aposematism. arboreal Living in trees. aquatic Living in water, as opposed to terrestrial. autochthonous Material produced within a habitat (such as organic material produced as a result of photosynthesis by algae growing in a stream); i.e., endogenous. Cf. allochthonous. autotrophic Describes organisms which synthesize organic matter from inorganic materials, typically by the process of photosynthesis; also used of communities which are net producers of organic material and do not depend on allochthonous inputs. Cr. heterotrophic. Batesian mimicry Resemblance of a palatable or harmless species (the mimic) to an unpalatable or harmful species (the model, usually an aposemete); it is assumed that this deceives predators so conferring protection on the mimic. Cf. Mullerian mimicry. benthos The organisms which live on or in the bed of rivers, streams and reservoirs; bottom-dwelling or benthic organisms. 176 Glossary biomass The weight of living material (but including dead tissues of the bark and heart wood of living trees) usually expressed as dry weight per unit area (as are all biomass figures in this book). biota All of the living organisms occurring within a particular area; e.g., Hong Kong's biota. biotic Living; pertaining to the biological factors in an organism's environment, such as its natural enemies, breeding partners, competitors, prey and so on. Cf. abiotic. boundary layer The thin, relatively slow-moving layer of water just above the bed of a river, where speed of flow is reduced by friction. Carboniferous The geological period from 270 to 220 million years ago. canopy The uppermost continuous stratum or layer of vegetation in a forest. In effect, the crowns of the tallest trees. Cf. understorey. carnivore An animal which eats the flesh of other animals. carrion The dead bodies of animals. cellulose A complex polymer of glucose; i.e., a polysaccharide; the main constituent of plant cell walls. channelization Engineering work involving straightening the course of a river or stream, whereby the complex natural pattern of meandering or braided flow and irregular banks is replaced by a straight channel with uniform, smooth banks. chitin A complex polysaccharide (glucose polymer) which is laid down in chains and forms the major component of insect cuticles (exoskeletons). climax A community which has reached an apparently unchanging, steady state under particular environmental conditions; the presumed end point of a successional sequence. coevolution Reciprocal evolution of two interacting species whereby evolutionary change in one leads to a change in the other. 177 Glossary collector-filterer An aquatic animal which filters fine particles of organic matter...