height, lying a further 180 km further out in the
Pacific. We might be interested in analysing how
biological properties of these islands, such as species
richness and endemism, relate to properties such as
island area, altitude, and isolation. However, when
Masatierra first arose from a hotspot on the Nazca
plate some 4 Ma (millions of years ago), it probably
formed an island of some 1000 km^2 and perhaps
3000 m in height (Stuessy et al. 1998). Since then, it
has been worn down and diminished in area by sub-
aerial erosion, wave action, and subsidence, losing
both habitats and species in the process. Modelling
efforts that ignore this environmental history would
be liable to produce quite misleading accounts of
factors controlling biotic diversification on such
islands (Stuessy et al. 1998).
The third chapter, on The biogeography of island
life, concentrates on the biogeographical affinities
and peculiarities of island biotas—a necessary step
before the processes of evolution on islands are
tackled. The chapter thus begins in the territory of
historical biogeographers concerned with tracing
the largest scales from the space–time plot (Fig. 1.2)
and with working out how particular groups and
lineages came to be distributed as they are. This ter-
ritory has been fought over by the opposing schools
of dispersalist and vicariance biogeography. Island
studies have been caught up in this debate in part
because they seemingly provide such remarkable
evidence for the powers of long-distance dispersal,
whereas rejection of this interpretation requires
alternative (vicariance) hypotheses for the affinities
of island species, invoking plate movements
and/or lost land bridges, to account for the break-
ing up of formerly contiguous ranges. Some of the
postulated land-bridge connections now appear
highly improbable; nevertheless the changing
degrees of isolation of islands over time remains of
central importance to understanding the biogeog-
raphy of particular islands. As will be seen, the vic-
ariance and dispersalist hypotheses have been put
into too stark an opposition; both processes have
patently had their part to play (Stace 1989; Keast
and Miller 1996).4 THE NATURAL LABORATORY PARADIGM
Figure 1.1There are many different types of islands
in addition to those found in the world’s oceans. This
figure illustrates just a few of these (based on an
original in Wilson and Bossert 1971).