Population stage structure of Hawaiian endemic fern taxa of Diellia (Aspleniaceae): implications for monitoring and regional dynamics

Abstract

Single census data were used to investigate the stage structure within populations of the endemic fern genus Diellia in the Hawaiian Islands. Populations were classified as "dynamic" (sporelings predominate), "normal", or " regressive" (mature plants predominate). Six taxa were studied: Diellia erecta Brack., Diellia erecta f. alexandri (Hillebr.) W.H. Wagner, Diellia falcata Brack., Diellia mannii (D.C. Eaton) W.J. Rob., Diellia pallida W.H. Wagner, and Diellia unisora W.H. Wagner. There were significant differences between the population stage structures of different taxa. The populations of D. erecta f. alexandri, and D. unisora represented regressive cases. Diellia pallida was represented by two regressive and one dynamic local population. The status of local populations of D. erecta and D. falcata varied from dynamic to regressive. Diellia erecta f. alexandri, D. mannii, D. pallida, and D. unisora are probably near extinction. Variation in local population conditions of D. erecta, D. falcata, and D. pallida may represent the history of local colonization and subsequent extinction events. The regional dynamics of these taxa correspond with the metapopulation model, since pteridophytes have good dispersal ability, and recruitment of Diellia species takes place only in moist years and is influenced by local disturbances. We conclude that stage structure of local populations can indicate the regional dynamics of a species. All local Diellia populations have to be considered as priority candidates for future conservation efforts.Key words: conservation, Diellia, Hawaiian Islands, metapopulation, population stage structure, regional dynamics.