Oceanic Islands and Biogeographical Theory: A Review

T HE branch ofbiogeography concerned with life-forms and physiognomic formations was founded on the study of altitudinal zonation on mountains. These sharp local patterns were soon joined with broad regional patterns under a simple theory of climatic and, secondarily, edaphic determinism. Since physiognomy is supposed to show convergence in similar environments, regardless of origin, processes of migration and evolution have been of slight interest, and island biotas have been given no special attention. The modern development of the branch of biogeography concerned with species or other taxa and with regional associations of taxa began with the study of oceanic islands, where climatic gradients are weak and where the sharpest, most provocative patterns demand ecological and historical explanations. The neatly delimited and relatively comprehensible island biotas have evoked many hypotheses, some of which have been extrapolated to continental regions. The comprehensive theory needed to explain the welter of geographical patterns formed by the hundreds of thousands of plant and animal species is still incomplete. Islands continue to be drawn on as heavily as ever for general models, which have come to include mathematical formulations. The boldest recent attempt in this line is a formidable little book by Robert H. MacArthur and Edward 0. Wilson,' which is having a great impact in some quarters and which requires careful consideration. To put it in perspective, some previous theory will be sketched as background.