Are island forests vulnerable to invasive defoliators? Strength in simplicity

Abstract

Islands are profoundly interesting ecosystems in which to examine evolutionary patterns and processes. Their isolation and simplicity provide natural 'Ecotrons' in which to seek an understanding of the role of biological diversity in the functioning of ecosystems. Insular biotas are typically relictual, depauperate and disharmonic (Paulay 1994) and hold significantly less biodiversity than equivalent mainland habitats (Whittaker 1998). The MacArthur and Wilson (1967) theory of island biogeography also suggests that the continuous immigration and extinction of species on islands results in a dynamic equilibrium of constant species turnover. Not surprisingly it has become axiomatic to represent island ecosystems as simple, vulnerable, and particularly susceptible to the loss of endemic biodiversity following invasion by continental biota (MacArthur & Wilson 1967, Paulay 1994, Whittaker 1998, Primack 2002). Although empirically not well supported (Wilson 2001), the appealing logic of the equilibrium theory persists and has even been applied to insect: plant interactions (Janzen 1968, Opler 1974, Feeny 1976). However, the spectacular divergence of island biota has been recognized since Wallace (1858) and Darwin (1859). Collectively, islands hold greater biodiversity than the continents and the disproportionate endemicity of island flora, and co-evolved associate invertebrate fauna, suggests evolutionary time-scales of stability or predictability. © Springer Science+Business Media B.V. 2008.