impoverishment The characteristic by which
islands have fewer species per unit area than the
mainland in comparable ecosystems, a distinction
that is more marked the smaller the island.
inbreeding depression A reduction of the fitness
in a normally outbreeding population as a
consequence of increased homozygosity due to
inbreeding.
incidence functions Biogeographical tool for
describing how the probability of occurrence of a
species varies with selected characteristics of
islands (species richness, area, isolation, etc.).
introduction The voluntary or accidental human-
assisted movement of individual species into a site
that lies outside their natural, historical range.
introgressive hybridization (or introgression)
The incorporation of genes of one species into the
gene pool of another species.
invader complex Whereby introduced species
preferentially establish interactions with other
introduced species.
invasion The spread of a naturalized exotic
species into natural or semi-natural habitats, hence
‘invasive species’.
island rule The tendency for a graded series of
changes in the size of island vertebrate species in
relation to mainland congeners, such that small-
bodied species tend to get larger, and vice versa.
island sterilization Process occurring when
destructive volcanic ash flows are deposited over
an entire island, completely eliminating the existing
biota. It implies that colonization has to begin again
from nothing.
isolating mechanism Any structural, physiologi-
cal, ecological, or behavioural mechanism that
blocks or strongly interferes with gene exchange
between two populations.
isostatic sea level changes Changes in sea level
due to the relative adjustment of the elevation of
the land surface (e.g. (1) due to the removal of mass
from the land causing uplift, as when an icecap
melts, or (2) by tectonic uplift).
keystone species Species supplying a vital
resource or holding a crucial function in an ecosys-
tem, such that alteration in its numbers has a radi-
cal impact on key functional properties of the
ecosystem.
kipuka Hawaiian term for a remnant of an old
forest ecosystem that has been isolated by a new
lava flow.
lag time The time taken for the relaxation or
decrease of species richness following fragmenta-
tion (i.e. time taken to pay the extinction debt).
landscape Spatial concept, in ecology referring to
the interacting complex of systems on and close to
the Earth’s surface, including parts of the atmos-
phere, biosphere, hydrosphere, lithosphere, and
pedosphere.
landslides Gravitational instabilities that in the
most spectacular cases can lead to the collapse of
the slopes of an island, producing debris ava-
lanches of hundreds of km^3 into the sea. Such col-
lapses may occur unexpectedly and suddenly and
may lead to the disappearance of a significant part
of an island in minutes.
late successional species Species that occur
primarily in, or are dominant in, the late stages of
succession.
laurisilva Relict subtropical evergreen montane
cloud forest typical of the Macaronesian islands,
dominated by Laureaceae tree species: formerly
much more widely distributed.
lignification The acquirement of a woodiness in
insular plant species derived from herbaceous
continental ancestors.
Macaronesia Biogeographical region of the
Palearctic comprising the Atlantic Ocean volcanic
archipelagoes of the Azores, Madeira, the
Salvage Islands, the Canaries, and the Cape Verde
Islands.
Makatea islands Islands formed by young volca-
noes, with raised coral reef uplifted to a few metres
above sea level.
marine transgression The flooding of the land by
the sea due to a rise in the sea level, either by an
absolute sea-level change (interglacial periods) or
by tectonic subsidence.
mesopredator release The increasing number of
smaller omnivores and predators due to the
absence of larger predators: a phenomenon that can
result from habitat fragmentation.
metapopulation A population of geographically
separated subpopulations interconnected by
patterns of gene flow, extinction and recolonization.346 GLOSSARY