327Discussion
Summary
We found Least Concern and Data Defi cient island-restricted mammals that possess
a high combined score of λ (^) M and ED. This method can be the start to fi nding species
with a combination of phylogenetic rarity and long-term extinction risk due to
island isolation. Further analyses are needed, as global prioritizations risk overgen-
eralizing among distinct animals, and yet suitable datasets, spatial and otherwise,
are diffi cult to come by.
Island Studies
Islands represent less than 5 % of the earth’s land area , harbour 80 % of known spe-
cies extinctions since 1500 (Ricketts et al. 2005 ), and make up 39 % of today’s
IUCN Critically Endangered species (TIB 2012 ). Endangered island species, such
as those targeted and listed in the Threatened Island Biodiversity (TIB) database,
are currently of major concern due to invasive species. However, we can still exam-
ine the effects of isolation and area from an island point of view. On a global scale ,
this method aims to show which islands or species are most important for conserva-
tion, based on the spatial properties of the islands and the phylogenetic rarity of the
species themselves.
Islands are a natural laboratory for evolutionary specialization and adaptation,
because such an environment greatly shapes the select set of species living there in
such isolation (Losos and Ricklefs 2009 ). From a conservation perspective, islands
are unique because with less spatial area to begin with, they can only support smaller
populations to evolve on them (Diamond 1975 ; Frankham 1998 ). Furthermore,
recolonisation, the process responsible for maintaining population size from a larger
source population, decreases because of spatial isolation and size (MacArthur and
Wilson 1963 , 1967 ; Simberloff and Wilson 1970 ), and dispersal amongst islands
can be far more limited than on terrestrial “islands”. We expect that islands suffer
more from stochastic extinction processes, in addition to anthropogenic effects such
as introduced species, so they are on the whole in much greater need of immediate
conservation action. In fact, islands have previously been the focus of research on
prioritisation schemes for conservation planning (TIB 2012 ).
However, much complexity remains in studying islands. Most threatened species
have small geographic distributions, and the distributions of island species are inev-
itably smaller than the distributions of continental species (Manne et al. 1999 ). Yet,
some island populations can “show greater persistence than mainland populations
of the same species, notwithstanding their smaller range sizes” (Channell and
Lomolino 2000 ), perhaps refl ecting the advantages of living in sheltered isolation.
Another study found that island endemics are not relatively more threatened than
Metapopulation Capacity Meets Evolutionary Distinctness: Spatial Fragmentation...