Symposium summary: Island biogeography

Abstract

ISSN 1948‐6596 news and update symposium summary Island biogeography A contributed session at the 5th International Biogeography Society Conference – Heraklion, Greece, 7–11 January 2011 It is now almost 50 years since the publication of Robert H. MacArthur and Edward O. Wilson’s 1963 paper, An Equilibrium Theory of Insular Zo‐ ogeography which led to their famous book, The Theory of Island Biogeography (MacArthur and Wilson 1967). These publications were instrumen‐ tal in a switch from a static, historically oriented biogeography, based in the direct interpretation of the data collected in the field, to a ‘dynamic’ equilibrium paradigm, based on a synthetic ap‐ proach to biogeographical processes. By their nature, the processes underlying biogeographic distributions and evolution on (remote) islands occur on large scales of time and space and remain among the most difficult to study and understand. Although some of the top‐ ics emphasized by MacArthur and Wilson still re‐ main relatively unexplored, recent advances in island theory demonstrate that we are moving towards a new synthesis, identifying and incorpo‐ rating aspects of the island systems that were not considered in the past. All the talks in the island biogeography session pointed in this direction. One of the first lessons taught to us by Wal‐ lace, decades before MacArthur and Wilson, is that comparisons among different archipelagos and biogeographic regions of the globe can offer significant insights and increase our understand‐ ing of the processes regulating biodiversity across time and space (see Wallace 1887). Daniel Car‐ stensen and colleagues compared the bio‐ geographical patterns of birds in Wallacea and the West Indies, adopting a network approach to detect biogeographical modules (i.e. sub‐regions of islands compartmentalized on the basis of a common avifauna) and the roles of each island according to its spatial location and the topology of the geographical network. They discussed the relative importance of island features and species richness on the local and regional fauna of the two biogeographical regions. Similarly, Silvia Aranda and co‐workers compared, within the framework of the Theory of Island Biogeography, the effects of area, isolation, geological age and climate on bryophyte species richness on Macaronesian Is‐ lands. They provided evidence that, in addition to area, it is necessary to quantify other variables that are also critical for the establishment of bio‐ diversity and at the same time have high explana‐ tory power (such as island age and climate), if we are to build up a more predictive science of spe‐ cies richness variation across island systems. However, island area remains the most powerful single variable in explaining variation in the number of species occupying an island and the species–area relationship (SAR) is one of ecology’s few laws. Even and Kathleen Tjorve showed that we should consider with caution the common assumption that the power law of Arrhenius is appropriate for both sample‐area (mainland) SARs and isolate (island) SARs. Especially regarding iso‐ late SARs, they argue that the form of the rela‐ tionship is actually sigmoid when the finest scales are included. Based on this assumption, they pro‐ posed a new species–area model and presented results from different archipelagos and taxa. Fifty years ago E.O Wilson, studying Mela‐ nesian ants, coined the term ‘taxon cycle’ to de‐ scribe ‘the inferred cyclical evolution of species [of Melanesian ants], from the ability to live in mar‐ ginal habitats and disperse widely, to preference for more central, species‐rich habitats with an as‐ sociated loss of dispersal ability, and back again’ (Wilson 1961). However, the taxon cycle has, until recently, been difficult to test (see Rick‐ lefs and Bermingham 2002). Evan Economo and Eli Sarnat evaluated taxon cycle predictions with a new dataset on habitat distributions of the entire Fijian ant fauna and a community phylogeny for one of the genera present in that archipelago. They provided evidence that as lineages progress to higher levels of endemism, they undergo shifts from marginal to interior primary habitats, from ecological generalism to specialization, and from frontiers of biogeography 3.1, 2011 — © 2011 the authors; journal compilation © 2011 The International Biogeography Society