The reticulating phylogeny of island biogeography theory

Abstract

Biogeographers study all patterns in the geographic variation of life, from the spatial variation in genetic and physiological characteristics of cells and individuals, to the diversity and dynamics of biological communities among continental biotas or across oceanic archipelagoes. The field of island biogeography, in particular, has provided some genuinely transformative insights for the biological sciences, especially ecology and evolutionary biology. Our purpose here is to review the historical development of island biogeography theory during the 20th century by identifying the common threads that run through four sets of contributions made during this period, including those by Eugene Gordon Munroe (1948, 1953), Edward O. Wilson (1959, 1961), Frank W. Preston (1962a,b), and the seminal collaborations between Wilson and Robert H. MacArthur (1963, 1967), which revolutionized the field and served as its paradigm for nearly four decades. This epistemological account not only reviews the intriguing history of island theory, but it also includes fundamental lessons for advancing science through transformative integrations. Indeed, as is likely the case with many disciplines, island theory advanced not as a simple accumulation of facts and an orderly succession of theories and paradigms, but rather in fits and starts through a reticulating phylogeny of ideas and alternating periods of specialization and reintegration. We conclude this review with a summary of the salient features of this scientific revolution in the contest of Kuhn's structure, which strongly influenced theoretical advances during this period, and we then describe some of the fundamental assumptions and tenets of an emerging reintegration of island biogeography theory.

FIGURE 1. DARLINGTON‘S THEORY OF SELECTIVE IMMIGRATION

According to Darlington’s (1957) model, (A) species populations are distributed in a nested fashion among islands of increasing isolation from their mainland source. Publication of this model was soon followed by Wilson’s (1959) empirical demonstration of the nested pattern for four species of ponerine ants (B). In part (A), immigration abilities of species A > B > C > D; in part (B), distribution patterns suggest that immigration abilities of species 4 > 3 > 2 > 1. (Illustrations redrawn by Lomolino et al. 2006; reproduced with permission from Sinauer.)

FIGURE 2. WILSON’S CONCEPT OF SPECIES SATURATION AND ISLAND AREA

According to Wilson, the relationship between the number of ponerine and cerapachyine ant species and island area resulted from the tendency for insular faunas to be in “saturated or near-saturated conditions,” approaching an upper limit “set by the size of the islands” (1961:170–171).

FIGURE 3. ROBERT MACARTHUR‘S FIRST GRAPHICAL MODEL OF DYNAMIC EQUILIBRIUM ON ISLANDS

Using data supplied by Ruth Patrick from her then unpublished studies on the colonization of glass slides by freshwater diatoms (see Patrick 1968), Robert H. MacArthur sketched the first graphical equilibrium model illustrating how species richness should vary with island area (second column, labeled “is. small (or) is. large” (i.e., small or large islands, respectively), affecting extinction rates, and two curves labeled “ext.”) and isolation (simulated by enclosures with small or large openings; first column, affecting immigration rates, two curves labeled “immigr. of new sp.”). Illustration from a scan by Swanson (2000) of a note from MacArthur to E. O. Wilson dated 27 April 1962, which included the following: “But I did want to tell you my ideas about a model of number of species so that you can improve it while I am away. … Basically, unless immigration and local species extinctions are much rarer than I guess, they must about balance” (see Wilson 1994:250; Swanson 2000:89–90). (From the Robert Helmer MacArthur [1930–1972] Papers, Department of Ecology and Evolutionary Biology, Princeton University.)