Species Richness on the Nondisturbed Northwestern Hawaiian Islands

Abstract

An examination of selected ecological variables on the 18 low, sandy, non—disturbed islands of the northwestern Hawaiian Islands, and the vascular plants and birds, primarily seabirds, occurring there shows that species richness on low, sandy, oceanic islands is influenced by ecological diversity and is affected by variables similar to those on high, rocky islands. Species richness of vascular plants on these islands can be predicted by means of stepwise regression on the basis of area of vegetation, and to a lesser extent, elevation. In turn, variation in numbers of breeding species of seabirds, total species of seabirds, and total species of birds on these same islands can be predicted on the basis of number of species of vascular plants, and to a lesser extent, area of the island. Ecological diversity, although poor in quality, is of prime importance in regulating use of low, sandy, oceanic islands by any seabird. Although terrestrial bird use islands for obtaining food and for nesting whereas seabird use islands only as a nesting and roosting place, species of terrestrial birds and seabirds on islands are associated with similar ecological variables.

The numbers of land birds, waders, sea birds, land crustacea, and certain insects on the lagoon islands of Aldabra Atoll

“…Furthermore, for those of them that feed in the lagoon, such as the black-naped and crested terns (Diamond, 19711, isolated islands may be closer to the richest feeding areas than less isolated islands. By contrast with Amerson's (1975) findings for the sea birds of the north-west Hawaiian islands, the number of plant species on the Aldabran islands has no significant relationship to the number of breeding sea bird species. The discrepancy in these findings is probably the result of the different nesting habits of the species concerned.…”

“…For example, two studies have shown island area to be an important variable in determining bird species number (Hamilton,Barth 8c Rubinoff, 1964; Hamilton 8c Barth, 1965), with area probably producing its effect through its influence on plant species number (e.g. Abbott, 1974; Amerson, 1975; Harris, 1973;Power, 1972). In continental areas, bird species number is predicted best by diversity in the vertical and horizontal structure of the vegetation (Karr, 1968; MacArthur 8c MacArthur, 196 1 ; Pianka & Huey, 197 11, which are, in turn, related to the energy requirements of the birds.…”

Ecological Correlates of Insular Rodent Diversity

“…The number of vascular plant species is a good predictor of breeding bird diversity on the Galapagos Islands (Harris 1973), on the high, rocky California Channel Islands (Power 1972(Power , 1976, and on the low, sandy Hawaiian Islands (Amerson 1975). Plant diversity (but not shrub volume diversity) also accounts for much of the variation in lizard species diversity on islands in the Gulf of California (Case 1975).…”

Environmental Diversity

“…As Amerson (1975) found in his study of breeding birds on 18 sandy cays in the Hawaiian Islands. large islands have packed onto them more ecological niches than do small islands.…”