density compensation Higher than normal
densities of a species on an island: typically
explained as an outcome of the lower overall rich-
ness of the island assemblage.
density overcompensation A situation where
density compensation occurs to an apparently
excessive degree in one or more species.
density stasis A situation where the overall
population of the community on the island is less
than that of the reference mainland system, such
that population sizes per species are the same as the
mainland.
diffuse competition Community-wide interspe-
cific competition among a group of species, subject-
ing each species to a range of competitive pressures
exerted by other species.
dioecious species Having the sexes in separate
individuals.
diplochory Plant species with two different dis-
persal mechanisms.
disassembly The process of a community/habitat
patch losing species as, for instance, a result of
habitat loss and increased isolation due to habitat
fragmentation.
disharmony A characteristic of island biotas,
such that they are biased in their representation of
higher taxa compared to nearby mainland source
areas.
disjunction A distribution pattern exhibited by
taxa that have populations that are geographically
separated.
dispersal The movement of organisms away from
their point of origin.
disturbance Any relatively discrete event in time
that removes organisms and opens up space which
can be colonized by individuals of the same or dif-
ferent species.
dwarfism The tendency for some isolated popu-
lations to undergo significant decreases in body
size in comparison to their conspecifics on the
mainland (also termed nanism).
ecological release A colonizing species
encounters an environment in which particular
competitors or other interacting organisms, such
as predators, are absent, and being released
from these constraining forces responds, e.g. by
expanding its feeding niche, or losing defensive
traits.
ecological trap The preference of some species for
breeding in edge habitats even though mortality is
higher there than in the fragment.
ecoregion Major ecosystem type prevalent across
a region, resulting from large-scale predictable pat-
terns of solar radiation and moisture, which in turn
affect the kinds of local ecosystems and animals
and plants found there.
ecotone The transition zone between two adja-
cent communities/habitats, which typically shows
a mix of the properties of each.
ecosystem transformer An introduced species
that becomes naturalized, and invasive, and which
significantly alters ecosystem properties, thus
impacting on native species.
ecotourism Tourism based on an interest in observ-
ing nature, preferably with minimal ecological
impact.
edge effect In fragmented landscapes, the edge of
a habitat patch typically has altered physical and
biotic properties, which extend some way towards
the core of the habitat patch.
effective population size The proportion of
the adult population that actually participates in
breeding.
El Niño–Southern Oscillation (ENSO) Climatic
anomalies yielding significant changes in rainfall,
temperature, humidity, and storm patterns over
much of the tropics and subtropics, due to the inva-
sion of warm surface waters from the western part
of the equatorial Pacific basin to the eastern part,
disrupting the upwelling along the western coast of
South America.
empty niche In the island context, refers to the
lack of representation of a particular mainland
ecological guild or niche, providing evolutionary
opportunities for colonizing taxa to exploit the
vacancy.
en echelonlines Short lines of crustal weakness,
which are sub-parallel to each other.
endemic A taxon restricted to a given area,
whether a mountain top, island, archipelago, conti-
nent, or zoogeographic region.
entomochory Dispersal by insects.344 GLOSSARY