0198566123.pdf

162 SCALE AND ISLAND ECOLOGICAL THEORY: TOWARDS A NEW SYNTHESIS

Box 6.2 Lomolino’s (2000) tripartite model of island biogeography

In a special issue on island biogeography

published in the journal Global Ecology and

Biogeographyin 2000, Mark Lomolino (2000a)

argued that given the acknowledged limitations

of the equilibrium theory, a new island model is

required, and that it should: (1) include feedbacks

among system components (as Bush and

Whittaker 1991), (2) acknowledge the role of

evolution (as Heaney 2000), and (3) be

species-based (Lomolino 2000b). He stated

‘Species vary in many ways that affect

immigration, extinction and speciation, and many

biogeographic patterns derive from, not despite,

differences among species. For example, the form

of the species-isolation and species–area

relationships may reflect very general patterns of

variation in immigration abilities and resource

requirements among species.’ (Lomolino

2000 a, p. 3).

Lomolino’s graphical model (see figure)

maintains the simplicity of MacArthur and Wilson’s

(1967) classic island biogeography scheme, but

pulls out a third dimension, explicitly recognizing

the role played by speciation in promoting species

richness, as a function of the island’s area and

isolation. In many respects this graphic merely

sketches out ideas contained within MacArthur

and Wilson’s (1967) monograph. As we saw, the

first statement of their model explicitly includes

speciation, and they went on to discuss how

particular taxa typically show the best patterns of

evolutionary radiation towards the periphery of

their spread across an ocean’s islands (they

termed this the ‘radiation zone’).

The graphic provides a useful summary of some

of the more important patterns and processes we

have discussed in the island ecology section, while

also pointing to the main process we have

Immigration

Island

characteristics

Isolation

Biogeographic

process

Speciation

Extinction

Area

0

a

b

0

c

d

Lomolino’s (2000a) tripartite model focuses on the relative importance of the three fundamental processes of biogeography: evolutionary

change, extinction, and dispersal. He notes that: (1) immigration rates should increase not only with proximity to a source region but also

with the vagility of the target species; (2) extinction rates should decrease with island area but increase with the target species’ resource

requirements (which may in turn be broadly related to body size, Bierdermann 2003); finally, (3) speciation rates should be more important

where extinction and immigration rates are lowest, and therefore will be greater on the largest and most isolated islands, but will decrease

with species vagility and resource requirements. The shading represents the relative levels of richness and the relative resistance to and

resilience of insular biotas following disturbance. The biotic characteristics of islands in the four corners (a, b, c, and d) are set out in the

table. (From Lomolino (2000a), Fig. 1.)