CHAPTER 8
Applied Island Biogeography
Kostas A. Triantis
1,2 and Shonil A. Bhagwat
2
1 Azorean Biodiversity Group, University of Azores, Terceira, Portugal
2 School of Geography and the Environment, University of Oxford, Oxford, UK
8.1 INTRODUCTION
When a nature preserve is set aside, it is destined
to become an island in a sea of habitats modifi ed
by man.
(Wilson & Willis, 1975 , p. 525)
Islands have played a central part in the development
of conservation theory. In particular, the Equilibrium
Theory of Island Biogeography (ETIB) (MacArthur &
Wilson, 1963, 1967 ; Wilson, 1969 ) has played a
pivotal role in diverse areas such as protected area
network design theory and predicting extinction rates.
The ETIB is a dynamic equilibrium model which postulates that the number of species of a given taxon
found on an island will be the product of opposing
forces leading respectively to the gain and loss of
species, and resulting in a continual turnover of the
species present on each island through time.
This is captured in MacArthur and Wilson ’ s famous
graphical model, in which immigration rate declines
exponentially and extinction rate rises exponentially as
an initially empty island fi lls up towards its equilibrium
richness value (shown by the intersection; Figure 8.1 ).
The immigration rate curve fl attens with increasing
island isolation and the extinction rate curve fl attens
with increasing area, thereby generating a family of
curves providing unique combinations of richness and
turnover for each combination of area and isolation.
The infl uence of the ETIB is marked not just by the
research it has inspired, but also by the theories and
applications it has spawned and infl uenced (e.g.
species – energy theory, metapopulation theory, island
assembly theory, neutral theory and stochastic niche
theory; reviewed in Whittaker & Fern á ndez - Palacios,
2007 ). Within a few years of publication, the application of the ETIB to the fi eld of conservation was being
vigorously debated by academics. One of the key
insights was the realization that terrestrial reserves
and national parks could be viewed as simply another
type of island ( ‘ habitat islands ’ ) surrounded by a ‘ sea ’
of human - altered landscapes. It logically followed that
these reserves would behave like islands cut off from
the mainland by rising sea levels, i.e. they would lose
species as they ‘ relaxed towards equilibrium ’ (Figure
8.1 ; Diamond, 1975a ; Wilson & Willis, 1975 ).
In the context of the ‘ crisis ’ discourse of conservation science from the 1970s onwards, several prominent conservation scientists turned to island theory
in the search for an ‘ off the shelf ’ general scientifi c
guide on protected area system design to assist in both
advocacy and implementation. If each protected area
might become, in time, an island surrounded by habitats modifi ed by man (Wilson & Willis, 1975 , p. 18),
and given a fi nite total area that can be set aside for
conservation as a natural landscape is being converted
to other uses, one of the basic questions is, ‘ What
confi guration of reserves should conservationists
advocate? ’
According to Margules & Pressey (2000) , reserves
have two main roles: they should sample or represent
the biodiversity of each region and they should
Conservation Biogeography
Edited by Richard J. Ladle and Robert J. Whittaker
© 2011 Blackwell Publishing Ltd. ISBN: 978-1-444-33503-3
Applied Island Biogeography
Kostas A. Triantis
1,2 and Shonil A. Bhagwat
2
1 Azorean Biodiversity Group, University of Azores, Terceira, Portugal
2 School of Geography and the Environment, University of Oxford, Oxford, UK
8.1 INTRODUCTION
When a nature preserve is set aside, it is destined
to become an island in a sea of habitats modifi ed
by man.
(Wilson & Willis, 1975 , p. 525)
Islands have played a central part in the development
of conservation theory. In particular, the Equilibrium
Theory of Island Biogeography (ETIB) (MacArthur &
Wilson, 1963, 1967 ; Wilson, 1969 ) has played a
pivotal role in diverse areas such as protected area
network design theory and predicting extinction rates.
The ETIB is a dynamic equilibrium model which postulates that the number of species of a given taxon
found on an island will be the product of opposing
forces leading respectively to the gain and loss of
species, and resulting in a continual turnover of the
species present on each island through time.
This is captured in MacArthur and Wilson ’ s famous
graphical model, in which immigration rate declines
exponentially and extinction rate rises exponentially as
an initially empty island fi lls up towards its equilibrium
richness value (shown by the intersection; Figure 8.1 ).
The immigration rate curve fl attens with increasing
island isolation and the extinction rate curve fl attens
with increasing area, thereby generating a family of
curves providing unique combinations of richness and
turnover for each combination of area and isolation.
The infl uence of the ETIB is marked not just by the
research it has inspired, but also by the theories and
applications it has spawned and infl uenced (e.g.
species – energy theory, metapopulation theory, island
assembly theory, neutral theory and stochastic niche
theory; reviewed in Whittaker & Fern á ndez - Palacios,
2007 ). Within a few years of publication, the application of the ETIB to the fi eld of conservation was being
vigorously debated by academics. One of the key
insights was the realization that terrestrial reserves
and national parks could be viewed as simply another
type of island ( ‘ habitat islands ’ ) surrounded by a ‘ sea ’
of human - altered landscapes. It logically followed that
these reserves would behave like islands cut off from
the mainland by rising sea levels, i.e. they would lose
species as they ‘ relaxed towards equilibrium ’ (Figure
8.1 ; Diamond, 1975a ; Wilson & Willis, 1975 ).
In the context of the ‘ crisis ’ discourse of conservation science from the 1970s onwards, several prominent conservation scientists turned to island theory
in the search for an ‘ off the shelf ’ general scientifi c
guide on protected area system design to assist in both
advocacy and implementation. If each protected area
might become, in time, an island surrounded by habitats modifi ed by man (Wilson & Willis, 1975 , p. 18),
and given a fi nite total area that can be set aside for
conservation as a natural landscape is being converted
to other uses, one of the basic questions is, ‘ What
confi guration of reserves should conservationists
advocate? ’
According to Margules & Pressey (2000) , reserves
have two main roles: they should sample or represent
the biodiversity of each region and they should
Conservation Biogeography
Edited by Richard J. Ladle and Robert J. Whittaker
© 2011 Blackwell Publishing Ltd. ISBN: 978-1-444-33503-3