© 1974 by The Society for Integrative and Comparative Biology
Ecology and Evolution of Social Organization in Arctic Sandpipers
Museum of Vertebrate Zoology, University of California Berkeley, California 94720
Department of Biological Sciences, Dartmouth College Hanover, New Hampshire 03755
Department of Biology, University of Alaska Fairbanks, Alaska 99701
A comparative analysis of sandpiper social systems on arctic and subarctic breeding grounds (24 species in the family Scolopacidae, subfamily Calidridinae) shows four major patterns. In a majority of the species (15), populations are dispersed through a strongly developed territorial system, with strong monogamous pair bonds and only minor yearly fluctuations in numbers. The second pattern is seen in three species in which the female of a pair may lay two sets of eggs in quick succession, one for each member of the pair to incubate. This opens opportunities for facultative polygyny or polyandry (‘serial polygamy’) and for the evolutionary weakening of the strong pair bond seen in the first pattern. The third and fourth patterns are those of polygyny (three species) and promiscuity (three species). These six species show clumped dispersions; their year-to-year fluctuations tend to be strong; the males defend compressible, often small, territories; and high densities can occur locally. It is suggested that the pattern of overdispersion and monogamy represents a conservative mode of adapting to high-latitude environments, while the pattern of clumped dispersion with polygyny or promiscuity represents an opportunistic mode in that the birds are concentrated into breeding areas where and when weather, food, and/or some other environmental factors are particularly favorable. Apparently falling evolutionarily between these two basic patterns are several species conservative in their life-styles, but polygamous at least occasionally and showing some features of opportunism. There is thus a striking diversity of social systems in calidridine sandpipers, that is, in the styles of habitat exploitation they have evolved in the arctic and subarctic habitats to which their breeding is confined. A graphic model suggesting paths of evolutionary development and of interplay among factors considered critical in the evolution of these systems is proposed.