Island ecology of arthropods : II. Niches and relative abundances of Seychelles ants (Formicidae) in different habitats.

1. The ant fauna of 3 islands of the Central Seychelles was studied by means of pitfall traps. The number of species and their abundances were investigated in relation to differences in island size, habitats, and microclimate conditions. In addition the effects of these factors on niche breadth and niche overlap were studied. 2. Nineteen and species were collected that belonged to 14 genera in 4 subfamilies (Table 2). Different numbers of species were found on different islands (Table 1). There are no significant correlations between the numbers of species, sizes of islands, and the available resources. The distribution of congeneric species agrees with the expected increase in 'relative diversity' on smaller islands (Fig. 3). 3. Species diversity and species distribution depend to some extent on habitat differences. This was evaluated by phytosociologic methods and microclimatic measurements. The composition of the ant fauna on different islands is more constant in undisturbed, autochthonous habitats than in those habitats that are strongly influenced by man. 4. Specific niche breadth and relative abundance of ant species showed a significantly positive correlation. Within comparable habitats, average niche breadth and niche overlap are greatest on the smallest island. Because the relative density also increases on this island, one cannot speak of a lower ecologic saturation compared with the larger islands.