0198566123.pdf

Remote island biotas differ from those of con-

tinents in a number of ways, being generally species-

poor and disharmonic (peculiar in taxonomic

composition), yet rich in species found nowhere

else, i.e. endemic to those islands. Although many

of these features are well known through the more

popular illustrations from island groups such as the

Galápagos, the global significance of island biodi-

versity is not so well appreciated. Data for a num-

ber of taxa are available that unequivocally

demonstrate that islands, particularly large and

remote islands, contribute disproportionately to

global biodiversity, i.e. they are biodiversity

‘hotspots’. Island biogeographers have, in recent

decades, continued to discover ‘new’ species on

islands, some from extant (i.e. living) populations,

others from fossils or subfossils. These new discov-

eries require a reappraisal of island biogeographi-

cal ideas and models. They also underline the

accelerated rate of attrition of island biotas through

human action, which qualifies many islands today

as ‘threatspots’ as well as centres of endemism.

Having explored the properties of the laborato-

ries, the second and third parts of the book examine

the ecological and evolutionary insights provided

by islands, moving from the finer spatial and tem-

poral frames of reference, to the coarser scales over

which evolutionary change operate (Fig. 1.2).

Table 1.1 picks out some of the dominant island

theories or themes and the typical island configura-

tions that, as will become clear later, appear to

match these themes (cf. Haila 1990). The first two,

adaptive radiation and the taxon cycle, are each

forms of evolutionary change: typically, the best

examples of island evolution are from very isolated,

high islands. The last three themes fall within what

may be termed island ecology. Island ecological

theories have applications to ‘habitat islands’

within continental land masses as well as to real

islands and, indeed, form an important part of the

contribution of biogeography to the problems of

conservation science (conservation biogeography

sensuWhittakeret al. 2001).

The separation of ecology from evolution is a

rather arbitrary one: evolution cannot work without

ecology to drive it; ecological communities operate

within the constraints of evolution. Nonetheless, we

find it helpful to distinguish theory that treats species

as essentially fixed units of analysis as ‘island ecol-

ogy’, and this we consider within the three chapters

of Part II. The first is an analysis of the macroecology

of islands (Chapter 4), focused on what we light-

heartedly term Species numbers games. Undoubtedly,

the most influential contribution to this literature has

been Robert H. MacArthur and Edward O. Wilson’s

(1967)The theory of island biogeography. MacArthur

THE NATURAL LABORATORY PARADIGM 5

Populations:

demography,

dynamics

Individual

behaviour

Space

Time

Evolutionary and

biogeographic

dynamics

(4)

(3)

(2)

(1)

Figure 1.2A scheme of different time–space scales of ecological
processes and criteria that define corresponding scales of insularity.
(1) individual scale; (2) population scale 1: dynamics; (3) population
scale 2: differentiation; (4) evolutionary scale. (Redrawn from Haila
1990, Fig. 1.)

Table 1.1Some prominent island biogeographical theories and the

geographical configurations of islands for which they hold greatest

relevance

Type of archipelago Prominent theories

Large, very distant Adaptive Radiation

Large, distant Taxon Cycle

Medium, mid-distance Assembly Rules

Small, near Equilibrium Model of Island

Biogeography

Small, very near Metapopulation dynamics