offspring that will emigrate to less favourable
habitats where sink populations, with negative
demography, can be maintained.
specialist species A species that uses a relatively
small proportion of the available resource types.
speciation The process in which two or more
contemporaneous species evolve from a single
ancestral population.
species swarm A large number of closely related
species occurring together in an area (e.g. an archi-
pelago) and derived by multiple splitting of an
ancestral stock.
species–area relationship (SAR) The relationship
between the number of species and the area of the
sample or island; within this simple idea, a variety
of important distinctions exist, which are often not
properly recognized.
species turnover The product of opposing rates
of species immigration to and species extinction
from an island. Where these rates precisely balance
this forms a dynamic equilibrium, with species
richness remaining constant through time but
species composition continually altering.
stepping stones Island or island groups that
facilitate the dispersal of species across oceans by
their intermediate geographic position between a
continental source pool and an island of interest.
stratovolcano The composite cone built by a
volcano that emits both molten and solid materials,
and builds up a steep-sided cone.
subduction The process by which lithosphere-
bearing oceanic crust is destroyed in plate tectonics
by the movement of one plate beneath another to
form a marine trench. The process leads to the
heating and subsequent re-melting of the lower
plate, in turn generating volcanic activity, typically
forming an arc of volcanic islands above the area of
subduction.
subfossil A dead organism that is not truly fos-
silized.
subsidence The downward movement of
an object relative to its surroundings. Subsidence
of the lithosphere can be due to increased mass
(e.g. increased ice, water, or rock loading) or due to
the movement of the island away from mid-ocean
ridges and other areas that can support anomalous
mass.
succession Refers to directional change in
(mostly) plant communities following significant
ecosystem disturbance, or following the creation of
an entirely new land surface area.
successional turnover In an island ecological
context, refers to species turnoverattributable to
successional processes.
supertramp A species that has excellent coloniz-
ing abilities but is a poor competitor in diverse
communities.
sustainable development Development that
meets the needs of the present generation without
compromising the ability of future generations to
meet their own needs.
sweepstake dispersal route The least favourable
of potential migration pathways in that it can only
be traversed very infrequently and with great
difficulty, or only under circumstances that occur
very rarely.
sympatric speciation The differentiation of two
reproductively isolated species from one initial pop-
ulation within the same local area, in which much
gene flow potentially could or actually does occur.
taxon cycle A proposed series of ecological and
evolutionary changes in a newly arrived colonist on
an isolated island, from the state of being indistin-
guishable from its mainland relatives to that of a
highly differentiated endemic, to extinction and
replacement by new colonists.
tephra A collective term for all the unconsoli-
dated, primary pyroclastic products of a volcanic
eruption, independent of grain size.
territoriality Behaviour related to the defence of a
specified area (the territory) against intruders.
Tertiary A period of geological time lasting from
c.65 Ma to the beginning of the Quaternary.
translocation programmes Attempts at species
conservation involving the movement of a number
of individuals into an area from which the species
is currently lacking (typically having once been
present).
trophic cascade The chain of knock-on extinc-
tions following the loss of one or a few species that
play a critical role (e.g. as a pollinator) in ecosystem
functioning.
trophic level Position in a food chain determined
by the number of energy transfer steps to that level.GLOSSARY 349