Biodiversity & Conservation

MarLIN Glossary

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R

R-strategy
A life strategy which allows a species to deal with changes of climate and food supply by responding to suitable conditions with a high rate of reproduction. R-strategists are continually colonizing habitats of a temporary nature. (From Baretta-Bekker et al., 1992). Cf. 'K-strategy'.

Radial
Symmetrical about any plane passed perpendicular to the oral/aboral axis (Barnes et al., 1993).

Radially
In a 'radial' manner. See 'radial'.

Radius
Barnacle shell plate feature. Lateral projection of comparmental plate, overlaps ala of adjoining plate (pl. radii).

Ramus
The main horizontal part of the lower jaw (Barnes et al., 1993).

Rapids
Strong tidal streams resulting from a constriction in the coastline at the entrance to, or within the length of, an enclosed body of water such as a sea loch. Depth is usually shallower than 5 m (based on Hiscock 1990).

Rarity (conservation Assessment)
Seldom found or occurring. 'Rarity' needs to take account of the type of distribution and abundance which would be expected of a particular habitat, community, taxonomic group or species and any historical information about past numbers.

Rarity (species)
"The current status of an organism which, by any combination of biological or physical factors, is restricted either in numbers or area to a level that is demonstrably less than the majority of other organisms of comparable taxonomic entities" (Gaston, 1994). (See also 'nationally rare', 'nationally scarce').

Recent Colonist
A species which, without any human intervention, has extended its natural geographical range (q.v.) in recent times and which has established new self-maintaining and self-regenerating populations in the wild (cf. 'non-native'; 'vagrant').

Recoverability
The ability of a habitat, community or individual (or individual colony) of species to redress damage sustained as a result of an external factor.

Recruitment (population Biology)
Term used for the arrival of young in a given population per unit of time (based on Baretta-Bekker et al., 1992).

Red Data Book Species
A species listed in catalogues published by the IUCN or by national agencies, listing species which are rare, endangered or vulnerable to extinction globally or nationally.

Red List Species
A species identified as 'Extinct', 'Extinct in the wild', 'Critically endangered', 'Endangered', 'Vulnerable', 'Lower risk', 'Data deficient' or 'Not evaluated' according to criteria laid down in the IUCN Red List Categories (International Union for the Conservation of Nature and Natural Resources, 1994).

Refugium
Plural of 'refugia'.

Regeneration
Replacement by compensatory growth and differentiation of lost parts of an organism (Barnes et al., 1993).

Regional Importance

1) Species conservation - species which are unrecorded or recorded at only a few locations in similar physiographic situations in other parts of Britain. Species recorded in higher abundance in the site under consideration than in any other part of the region. Species which are at the geographical limits of their distribution might be included in this category. (Davies et al., 1990, based on Hiscock & Mitchell, 1989). Cf. 'regional importance: biotopes or areas' 'international importance', 'local importance', 'national importance' (biotopes or areas and species).

2) biotope and area conservation - Biotopes or areas which are widespread in similar situations but for which this is a good example in the coastal sector (q.v.) under consideration. Regional importance was, until 1995, defined for communities as being "Communities which are present in similar physiographic situations in Britain but which are outstandingly good examples of their type in the location under consideration, or are as good as examples of similar communities present elsewhere in Britain. Communities recorded at only a few locations in the same biogeographic region." (Davies et al., 1990, based on Hiscock & Mitchell, 1989). (Cf. 'regional importance: species', 'international importance', 'local importance', 'national importance' (biotopes or areas and species)).

Reintroduction
A species which has been reintroduced by human agency, deliberate or otherwise, to an area within its natural geographical range (q.v.) but where it had became extinct in historical times.

Relict Species
A species believed to have been previously more widely distributed but now restricted to a limited number of locations where populations are probably self-sustaining, for example,Thyasira gouldi, Leptopsammia pruvoti.

Representativeness
In conservation assessment -typical of a feature, habitat or assemblage of species. Representative examples are identified from the range of natural or semi-natural habitats and associated communities (biotopes) within a biogeographically distinct area or the boundaries of a national territory.

Resident
A permanent inhabitant, non-migratory.

Resilience
The ability of an ecosystem to return to its original state after being disturbed (from Makins, 1991) (cf. 'constancy', 'persistence', 'stability').

Resistance
The degree to which a variable is changed following perturbation (Pimm, 1984). The tendency to withstand being perturbed from the equilibrium (Connell & Sousa, 1983). (cf. 'Stability'; 'adjustment stability'.)

Reticulate
In the form of a mesh or net (Prescott, 1969).

Rhinophore
Singular of 'rhinophores'.

Rhinophores
Pair of tentacles or processes posterior to the cephalic tentacles of opisthobranch molluscs. The rhinophores are primarily sensory in function and vary greatly in shape between species, and in dorid nudibranchs can be retracted into basal sheaths (Stachowitsch, 1992; Picton & Morrow, 1994).

Rhizoid
A hair-like structure forming the root and anchorage point of certain algae (Abercrombie et al., 1973).

Rhizoids
Plural of 'rhizoid'.

Rhomboid
A oblique-angled parallelogram in which adjacent sides are of unequal lengths (OED, 2008).

Ria
A drowned river valley in an area of high relief; most have resulted from the post-glacial rise in relative sea-level (based on Allaby & Allaby, 1990). As defined for the EC Habitats Directive, 'rias and voes' are "drowned river valleys (not of glacial origin) with relatively deep narrow well-defined channels which are predominantly marine throughout".

Richness (species)
The number of species in a community, habitat or sample (cf. 'diversity'; 'evenness').

Ripple
A small ridge <10 cm high formed on top of a layer of sediment (usually sand) as a result of wave action or water currents (cf. 'dune').

Risk Assessment
An evaluation of the possibility of undesired events and the probability of harm being caused.

Rockmill
A hollow or pit in a rock surface within which pebbles or boulders are moved by currents or wave action, causing scouring and deepening of the hollow, and forming a smooth surface uncolonized by benthic organisms.

Rockpool
A depression in the littoral zone of a rocky seashore, where, during low tide, seawater is left behind (based on Baretta-Bekker, Duursma & Kuipers 1992).

Rostrum
In most crustaceans an anterior extension of the carapace which projects between the eyestalks. In barnacles the rostrum is the anterior shell plate.

RoxAnn
An acoustic ground discrimination system, based on sonar, which provides information on seabed relief and features.

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Glossary references