Ecological biogeography of southern ocean islands: species-area relationships, human impacts, and conservation.

Previous studies have concluded that southern ocean islands are anomalous because past glacial extent and current temperature apparently explain most variance in their species richness. Here, the relationships between physical variables and species richness of vascular plants, insects, land and seabirds, and mammals were reexamined for these islands. Indigenous and introduced species were distinguished, and relationships between the latter and human occupancy variables were investigated. Most variance in indigenous species richness was explained by combinations of area and temperature (56%)-vascular plants; distance (nearest continent) and vascular plant species richness (75%)-insects; area and chlorophyll concentration (65%)-seabirds; and indigenous insect species richness and age (73%)-land birds. Indigenous insects and plants, along with distance (closest continent), explained most variance (70%) in introduced land bird species richness. A combination of area and temperature explained most variance in species richness of introduced vascular plants (73%), insects (69%), and mammals (69%). However, there was a strong relationship between area and number of human occupants. This suggested that larger islands attract more human occupants, increasing the risk of propagule transfer, while temperature increases the chance of propagule establishment. Consequently, human activities on these islands should be regulated more tightly.