Biogeography of milkweed butterflies (Nymphalidae: Danaidae) and mimetic patterns on tropical Pacific archipelagos

Distributions of danaine butterfly species and associated mimetic patterns were compared among fifteen archipelagos of the tropical Pacific Ocean, and within five major archipelagos (the Bismarcks, Fiji, East and West Solomon Islands, and Vanuatu). Using both simple and stepwise linear regression analysis, variation in the total number of danaine species and number of mimetic patterns was assessed with respect to island size, isolation and elevation. Relative to interarchipelago distributions, the distribution of danaine species and number of mimetic patterns on islands within archipelagos exhibited less dependence upon interisland distance and island area. Geographical features influencing the number of mimetic patterns were similar to those of danaines as a whole. Analysis of residuals from stepwise linear regression suggested that factors influencing danaine distributions were different from those for nondanaine butterflies. This result is consistent with the hypothesis of enhancement of danaine species establishment through Mullerian mimicry, although other factors such as host plant availability and similar habitat use may also be important.