Species Richness of Mammals Inhabiting Nearshore Archipelagoes: Area, Isolation, and Immigration Filters

Abstract

Patterns in community structure of non-volant mammals on islands of the Drummond Archipelago (northwestern Lake Huron) were compared to those of insular mammals in-habiting three other nearshore archipelagoes to test the hypothesis that species-area and species-isolation relationships are strongly influenced by the nature of the immigration filter. All four archipelagoes shared similar habitats and nearly identical species pools, but differed substantially in characteristics of their filters. Islands of the Drummond Archipelago tended to have more species per area and more species per degree of geographic isolation. The rate of decline in species richness with increasing isolation was similar and relatively low for islands of the Drummond Archipelago and central Lake Michigan. In comparison to these lacustrine archipelagoes, which had relatively weak filters (high immigration rates), mammalian species richness declined much more rapidly with isolation of islands along the coast of Maine and the St. Lawrence River, where strong currents and instability of ice-cover impede immigration. These insights may have special relevance for conservation of endangered species, many of which are restricted to ecosystems fragmented and isolated at a scale similar to that of nearshore archipelagoes.