Adaptive Aspects of Insular Evolution, A Symposium

Abstract

ADAPTIVE ASPECTS OF INSULAR EVOLUTION was the theme chosen by the Association for Tropical Biology for its third international symposium, June 15-19, 1969. Appropriately enough, the symposium was held on a tropical island: at the University of Puerto Rico, Mayagiiez, where over 100 persons convened to hear presentations by an outstanding group of 17 participants assembled by Professor Ernst Mayr, Director of Harvard University's Museum of Comparative Zoology. The tone of the conference was set most effectively when Sherwin Carlquist of the Rancho Santa Ana Botanic Garden and Terrell H. Hamilton of the University of Texas broadly outlined the more important factors responsible for the characteristics of island floras and faunas, respectively. Their introductions re-emphasized how very suitable insular situations are for detailed studies of evolutionary processes, including dispersal, colonization, adaptation, competition, and extinction. With a refreshing balance of botanical and zoological viewpoints, the speakers who followed discussed various aspects of these topics and provoked considerable thoughtful and spirited debate. One of the central topics of the conference was the delimitation of some of the more important genetic and ecological characteristics of successful colonizing species. A recurrent theme was that an insular situation, be it an island or a mountain, may be remote for some species and at the same time very near for others, depending upon their ecological requirements. For certain plants, G. Ledyard Stebbins of the University of California, Davis, found that polyploidy apparently facilitates island colonization. Tremendous quantities of highly dispersible spore propagules were most responsible for the colonizing success of ferns, according to Rolla M. Tryon of Harvard University; he felt this high vagility largely accounted for the relatively low levels of endemicity characteristic of insular fern floras. Based on chromosome banding patterns, the report by Hampton L. Carson of Washington University centered upon certain genetic properties of successful species founders and subspecies colonizers in the genus Drosophila on the Hawaiian Islands. Ernest E. Williams of Harvard IJniversity reviewed his data on the invasion patterns of West Indian Anolis lizards and stressed the relation between the number of ecomorphs occurring on a given island and the structural habitats present. Carabid beetle species most successful in colonizing the West Indies were characterized by Philip J. Darlington, Jr., of Harvard University as being small, winged, and frequently associated with fresh water. Many of the talks focused directly or indirectly on the types of adaptive adjustments made to insular conditions by various floral and faunal elements following successful colonization; effects of impoverishment upon adaptive radiation, niche dimensions, and ecological and behavioral shifts were recurrent topics. Among those presenting new experimental data bearing on these phenomena were Allen Keast of Queens University, speaking on Tasmanian birds, Allen J. Kohn of the University of Washington on the carnivorous marine snail Conus, and Thomas Schoener of Harvard University on West Indian Anolis lizards. The composition, adaptations, and relationships of three very different insular floral communities were the principal subjects of Olov Hedberg of the University of Uppsala, Richard A. Howard of Harvard University, and Bassett Maguire of the New York Botanical Garden. Hedberg characterized the alpine flora of African mountains with particular reference to the rather striking adaptations to the extreme daily temperature fluctuations. Howard focused on the dwarf elfin forest of the higher elevations of Puerto Rico and the possible factors responsible for this peculiar floristic