Scale, succession and complexity in island biogeography: are we asking the right questions?

1 This paper offers a commentary on the development of island ecological theory since the publication of MacArthur & Wilson's equilibrium theory in the 1960s. I distinguish the simple model at the core of their Equilibrium Theory of Island Biogeography (ETIB) and the broader body of their theory, which embraces evolutionary as well as ecological patterns - all, however, within the overarching framework or assumption of equilibrium. 2 The basic problems with the ETIB have long been known, and its status as a ruling paradigm has been the subject of concern for more than two decades. With the development of nonequilibrium ideas in ecology, island biogeographers arguably now have viable theoretical frameworks to set alongside or around the ETIB. Four conditions are highlighted as extremes: i) dynamic equilibrium; ii) dynamic nonequilibrium; iii) 'static' equilibrium; and iv) 'static' nonequilibrium: together providing a conceptual framework for island ecological analyses. 3 The importance of scale is stressed and attention is drawn to Haila's spatial-temporal continuum as an organizational device. It is argued that the processes represented within the ETIB (and by extension, other island theories) may be prominent within only a limited portion of this continuum, while elsewhere they are generally subsumed by other dominant processes. 4 Colonization and ecosystem development of near-shore islands constitute just a special case of ecological succession, and thus the development of theories of island assembly may benefit accordingly from efforts to incorporate ideas from the ecological succession literature. 5 The desirability of specifying answerable questions is stressed, as is the need to build a greater degree of complexity into the development of island ecological models. Notwithstanding which, it is also recognized that key advances are often brought about by simple, but bold models, of the form exemplified elsewhere in this issue.