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species numbers may change in fragments follow-
ing isolation, we still have a poor grasp of the over-
all implications for diversity on a regional scale of
the ongoing processes of ecosystem fragmentation.
Nonetheless, it is clear that habitat loss and frag-
mentation threatens many species with local,
regional and ultimately global extinction. It is also
evident that the processes of ecosystem response
can take considerable periods (often decades) to
play out, meaning that today’s fragmentation is
storing up numerous extinctions for the future.
However, taking a more positive approach to the
problem, the fact that responses are often lagged
means that there is an opportunity for mitigation
measures to be put in play, to reduce the so-called
‘extinction debt’, providing society cares enough to
act. Insofar as island effects are driving species
losses, the key is to prevent previously contiguous
and extensive ecosystems from becoming too iso-
lated: reserve systems need to be embedded in
wildlife friendly landscapes wherever possible.
If the catalogue of known extinctions is drawn up
for the period since AD1600, it can be seen that for

animal taxa that are relatively well known (e.g.

mammals, birds, and land snails), the majority of

losses have been of island species (Fig. 1.3). Today,

some of the greatest showcases for evolution are in

peril, with many species on the verge of extinction.

Why is this? These issues and some conservation

responses are explored in the final two chapters of

the book, Anthropogenic losses and threats,andIsland

remedies. There is mounting evidence that

humans are repeat offenders when it comes to

extinguishing island endemics. Wherever we have

colonized islands, whether in the Pacific, the

Caribbean, the Atlantic, the Indian Ocean, or the

Mediterranean, we have impacted adversely on

the native biota, and often on the ecosystem servi-

ces on which we ourselves rely (Diamond 2005).

Here we ask the question: are islands inherently

fragile, or are island peoples peculiarly good at

extinguishing species? In some senses, island biotas

are indeed fragile, but very often the demise of

endemic taxa can be traced to a series of ‘hard

knocks’ and the so-called synergistic interactions

between a number of alien forces, such that the

8 THE NATURAL LABORATORY PARADIGM

Number of species

100

80

60

40

20

0

1600–

1629

1630–

1659

1660–

1689

1690–

1719

1720–

1749

1750–

1779

1780–

1809

1810–

1839

1840–

1869

1870–

1899

1900–

1929

1930–

1959

1960–

Islands

Continents

No date

Figure 1.3Time series of extinctions of species of molluscs, birds, and mammals from islands and continents since about AD1600.
(Redrawn from Groombridge 1992, Fig. 16.5.)