Nonequilibrium Diversity Dynamics of the Lesser Antillean Avifauna

Abstract

MacArthur and Wilson's model of island diversity predicts an increase in the number of species until colonization and extinction are balanced at a long-term steady state. We appraise this model on an evolutionary time scale by molecular phylogenetic analysis of the colonization of the Lesser Antilles by small land birds. The pattern of accumulation of species with time, estimated by genetic divergence between island and source lineages, rejects a homogeneous model of colonization and extinction. Rather, our results suggest an abrupt, roughly 10-fold increase in colonization rate or a 90% mass extinction event 0.55 to 0.75 million years ago.MacArthur and Wilson's (1) equilibrium theory of biogeography explains the number of species on islands as representing a balance between colonization and extinction. Accordingly, the biota of an island reaches a steady state at which the appearance of new species equals the disappearance of residents. Lack (2) argued instead that colonization was not limiting and that the ecological space on islands was filled with established populations that resisted replacement by new colonists. Both theories hold that the number of species on an island should be stable over long periods, but they differ with respect to the rate of accumulation of species and the prediction of species turnover.

Seeing the Forest for the Trees: The Limitations of Phylogenies in Comparative Biology

“…At face value, LTT plots suggest an ever-increasing species richness through time (Ricklefs, 2007), yet we know that can't be, because clades wax and wane through time (Gould et al, 1977;German et al, 1987;Foote, 2007). Although some topologies have been interpreted as suggestive of past mass extinction events (e.g., Ricklefs and Bermingham, 2001), current approaches generally cannot infer an ongoing decline in species richness.…”

“…At face value, LTT plots suggest an ever-increasing species richness through time (Ricklefs, 2007), yet we know that can't be, because clades wax and wane through time (Gould et al, 1977;German et al, 1987;Foote, 2007). Although some topologies have been interpreted as suggestive of past mass extinction events (e.g., Ricklefs and Bermingham, 2001), current approaches generally cannot infer an ongoing decline in species richness.Recently, Quental and Marshall (2010) investigated the efficacy of these methods. Using cetaceans, which thanks to their size and aquatic habits, have an extraordinarily complete fossil record, these authors compared diversity dynamics through time based on the fossil record versus those inferred from a molecular phylogenetic study that included almost every living cetacean species (Steeman et al, 2009).…”

Molecular phylogeography reveals island colonization history and diversification of western Indian Ocean sunbirds (Nectarinia: Nectariniidae)

“…Conversely, expanses of open ocean are easy to identify as barriers to gene flow. Species-level phylogenies in island settings can potentially provide useful insights into the rate of species diversification or lineage accumulation with time (Barraclough and Nee, 2001;Ricklefs and Bermingham, 2001), and into the mode of speciation (Coyne and Price, 2000;Turelli et al, 2001;Via, 2001), in particular the role of geography (Barraclough and Vogler, 2000;Hewitt, 2001). Potentially they might also indicate the vulnerability of species to extinction and provide information on rates of population turnover in island communities.…”

“…Archipelagos also provide the opportunity to trace the evolutionary history of multiple evolutionary lineages in the same geographical setting. This can provide ÔreplicatesÕ for the testing of evolutionary hypotheses, and improve our understanding of the relative contribution of local, regional, and historical processes, as well as unique events and circumstances, to community diversity (Arnold, 2000;Bermingham and Moritz, 1998;Juan et al, 2000;Ricklefs, 1987;Ricklefs and Bermingham, 2001).…”

Islands as model systems in ecology and evolution: prospects fifty years after MacArthur‐Wilson

“…An alternative way to approach non-equilibrium theory is simply to study the transient behaviour of models that would in theory eventually equilibrate, but do not have the opportunity due to lack of time or continuous environmental change (i.e. unattained equilibrium, Box 6; Ricklefs & Bermingham 2001).…”