0198566123.pdf

FORMS OF EQUILIBRIA AND NON-EQUILIBRIA 153

macroecological modelling approach

concerning factors like introduction effort and

predation (e.g. Blackburn et al. 2004, Cassey

et al. 2005b) or considering the detailed

context of turnover for particular islands

(Duncan and Blackburn 2002), such as the

impact of disease organisms and their carriers

on Hawaii (Pratt 2005).

We hope to have illustrated how difficult it

is to bring such arguments about the equilibrium

assumption to a clear conclusion. We are left,

nonetheless, with some intriguing observations.

First, plant species numbers on oceanic islands

appear to be capable of significant increases

withoutnecessarilyinvolving high turnover

(extinction) of native species. Second, the

proportional relationships seen in the figure

suggest that the slope (zvalue) of the ISARs

(island species–area relationships) have been

little changed despite the enrichment of the

floras and the turnover involved in the avifaunas.

Third, it seems the role of isolation is less

significant for determining island land bird

species numbers than predicted by the EMIB.

Log (extinct native species + 1) Log (extinct native species + 1)

Log (historic richness of species + 1) Log (historic richness of species + 1)

Log (extant naturalized species + 1)

Log (current richness of species + 1) Log (current richness of species + 1)

Log (extant naturalized species + 1)

0

0 0

1

2 1

2

0

1

2

3

4

1

2

3

4

12 0 1 2

012

34

1234

A - plants

B - plants

C - birds

D - birds

Species richness of vascular plants and land birds on oceanic islands. Triangles represent islands inhabited before European contact; circles
represent those that were not. (From Sax et al. 2002, Fig. 1.)