application of fully integrated models that combine climatic suitability, habitat availability, population dynamics, and mechanistic movement
models of dispersal (39, 42). These may involve a
single species or two or more interacting species.
Ecological replacements
Biodiversity can increase ecosystem stability by
buffering the effects of environmental change,
resisting species invasions, and preventing sec-
ondary extinctions after species losses (43). Species
extinctions reduce interaction network diver-
sity (44) and can lead to cascading effects, in-
cluding the loss of other species and their biotic
interactions (45). Where only local extinction oc-
curs, critical ecosystem functions might be re-
instated through reintroductions; for example,
the reintroduction of wolves into Yellowstone Na-
tional Park in 1995–1996 restored direct effects
on their prey and a range of indirect effects (46).
The global extinction of a species, however, means
that restoration of functions might be achieved
only through introduction of functionally similar exotic species.
The 2013 IUCN guidelines define ecological
replacement as a form of conservation intro-
duction involving the release of an appropriate
substitute species to reestablish an ecological
function lost through extinction. Although the
rationale for ecological replacement is differ-
ent from that of assisted colonization, the two
terms have often been used interchangeably in
the literature [e.g., (47)]. Although, in some sit-
uations, an assisted colonization to prevent
extinction of the focal species could serve in
parallel to restore an ecosystem function outside
the indigenous range (47), in many cases, the
most appropriate ecological replacements might
not be endangered species. Recognition of eco-
logical replacement as a valid conservation tool
represents a departure from the single-species
focus that once characterized conservation trans-
locations and conforms more closely to the cur-
rent global conservation emphasis on restoring
natural processes rather than addressing only
extinction risk (48).
There has been interest in the replacement of
ecological functions once performed by extinct
SCIENCE
sciencemag.org 25 JULY 2014 • VOL 345 ISSUE 6195 409
Invertebrates Fish Amphibians Birds Mammals Reptiles
0
40
20
60
80
100
0
20
30
40
10
50
60
Percent of vertebrate species
Percent of
animal species Species translocated by IUCN regions Species translocated by taxon
26.4
13.2
20.1
18.8
7.6
4.9
4.9
1.7 1.9
<1
Species in nature
Species translocated
Fig. 2. Global and taxonomic range of conservation translocations.
The proportions of 303 species that have been translocated for conservation purposes, by IUCN region (main map—the larger the circle the
greater the proportion of species), and by taxon (inset bar chart: shaded
bars are proportions of species translocated out of the total of 303; unshaded bars are proportions of species in nature. Because invertebrate
species are estimated to be >99% of all animal species in nature, for clarity, the relative proportion of invertebrates in nature and the proportion
of invertebrate species that have been translocated out of the total of
303 animal species are presented on the right; the proportions relative
to vertebrate species only are on the left. [Data from (10).] The color
inset map shows the 10 IUCN regions; west to east, these are North
America and Caribbean, Meso-America, South America, North Africa,
Central and West Africa, East and Southern Africa, West Asia and the
Middle East, Europe and the Mediterranean, Asia, and Oceania (source
iucn.org). Data on the 303 species was derived from downloadable project summaries available at iucnsscrsg.org. Base map source: commons.
wikimedia.org
