the theoretical and operational principles of nature
conservation and the long history of the conserva-
tion movement are beyond our present remit. Our
purpose in this final section of the book is to con-
sider two broad themes. First, in the present chap-
ter, we examine the application of ideas derived
from island ecological biogeography to conserva-
tion problems. This research programme is focused
largely on the loss of species resulting from the
reduction in area and fragmentation of ‘natural’
habitats, and is based on the premise that island
ecological rules can be applied to ‘islands’ of par-
ticular habitat types within mainland landmasses.
This work forms part of the emerging field of
conservation biogeography (Whittaker et al. 2005).
Second, we return in the final two chapters to a
focus on real islands, examining the particular
conservation problems of oceanic islands and some
of the management solutions that have been devel-
oped. The rationale for focusing on such islands in
an island biogeography book is obvious, but this
focus is also justified by the wider significance of
islands as repositories of biodiversity and by the
extent to which island endemics feature in the lists
of recently extinct and currently endangered
species.
10.2 Habitats as islands
... the abundance of publications on the theory of island
biogeography and applications [of it] has misled many sci-
entists and conservationists into believing we now have a
ready-to-wear guide to natural area preservation...
(Shafer 1990, p. 102)It is generally accepted amongst conservation bio-
logists, that the ongoing fragmentation and reduc-
tion in area of natural habitats is a key driver of
terrestrial species extinctions at local, regional, and
global levels (Whitmore and Sayer 1992). The
remaining areas of more-or-less natural habitats are
increasingly becoming mere pockets within a sea of
altered habitat; in short, they are habitat islands. It
was therefore to island biogeography that many
scientists turned in the search for predictive models
of the implications of fragmentation and for guid-
ance as to how best to safeguard diversity.
The implications of increasing insularity for
conservation were recognized in the seminal works
of Preston (1962) and MacArthur and Wilson (1963,
1967), with Preston astutely observing that in the
long run species would be lost from wildlife pre-
serves, for the reason that they constitute reduced
areas in isolation. MacArthur and Wilson’s dynamic
(EMIB) model provided the theoretical basis to
develop this argument, allowing conservation
scientists to explore the outcomes of differing con-
figurations of protected areas, assuming them to act
as virtual islands in a ‘sea’ of radically altered and
thus essentially empty habitats. One early manifes-
tation of this research programme was the so-called
SLOSS debate, which posed the question ‘given the
opportunity to put a fixed percentage of land into
conservation use is it better to opt for a Single Large
Or Several Small reserves?’ Here the focus is on the
entire regional assemblage of species and how to
maximize the carrying capacity of the protected
area (i.e. habitat island) system. We will come back
to this debate a little later, as we have organized this
discussion to begin with the smallest units: popula-
tions of particular species.
The most basic question is: ‘how many individu-
als are enough to ensure the survival of a single iso-
lated (perhaps the last remaining) population? The
resulting figure is termed the minimum viable
population. We will consider this first. Many
species of conservation concern are not, however,
restricted to a single locality—or at least, not yet.
Rather, their survival in a region might be depend-
ent on a network of habitat islands. Most of this
book has been concerned with real islands in the
sea. Is it realistic to expect habitat islands within
continents to behave according to the same princi-
ples as real islands? Instead of the barrier of salt
water, a forest habitat island might be separated
from another patch of forest by a landscape of
meadows, hedgerows, and arable land. The impli-
cations for species movements between patches
might be radically different. As we have seen, how-
ever, this is probably too simple a distinction and
too simple a question. Scale of isolation is crucial, as
well as the nature of the intervening landscape fil-
ter. Mountain habitat islands within continents, but
surrounded by extensive arid areas, may be much252 ISLAND THEORY AND CONSERVATION