Numerous species are adapted for colonization of insular fresh waters by using different mechanisms of active and passive dispersal, especially among oceanic islands at low latitudes. Over time, similar animal communities have assembled in many tropical streams and rivers on isolated islands. These freshwater communities are characterized by a relatively low number of species of fishes, decapods, gastropods and insects that typically have complex life cycles including passive, long-distance dispersal. These species often disperse during marine phases with drifting larvae or by rafting and aerial transport of resistant, dormant stages. Active dispersal is sometimes effective for relatively short-distance movements from one island’s streams to another island’s nearby drainage basin within an archipelago (a “stepping-stones” dispersal pattern). Identifying distinct differences among aquatic communities on “true oceanic” islands of different ages and geologic histories requires a longterm biogeographic perspective including the degree of spatial isolation of populations and differences in rates of speciation. Consequently, the total biodiversity of insular streams is a complex combination of dispersal from multiple sources of species from continents and other islands, as well as evolution of new endemics. Recolonization of streams following natural disturbances and the impacts of introduced species result in dynamic changes in species accumulation and turnover in these insular freshwater ecosystems. Analysis of dispersal to islands provides general perspectives on managing fragmented habitats, especially the effects of invasive species that also shed light on factors affecting the equilibrium composition of animal communities in island-like ecosystems on continents.
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