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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 differ- ent 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 candi- dates for future conservation efforts. Resume : Les auteurs ont utilise les donnees a simple consensus pour examiner la structure des stades des populations de fougeres endemiques appartenant au genre Diellia, aux iles Hawai. Ils ont classifie les populations en « dynami- ques » (ou predominent les plantules issues de spores), « normales » ou « regressives » (les plantes matures predomi- nent). Ils ont etudie six taxons : 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 et Diellia unisora W.H. Wagner. On observe des differences significatives dans les structures des stades de population chez les differents taxons. Les po- pulations du D. erecta f. alexandri et du D. unisora montrent des structures regressives. Chez le D. pallida on trouve deux populations regressives et une population dynamique locales. Le statut des populations locales des D. erecta et D. falcata varient, de dynamiques a 'regressifs'. Les D. erecta f. alexandri, D. mannii, D. pallida et D. unisora sont probablement pres de l'extinction. La variation des conditions subies par les populations locales des D. erecta, D. fal- cata et D. pallida pourraient representer l'histoire de la colonisation locale et les evenements subsequents de l'extinc- tion. La dynamique regionale de ces taxons correspond au modele des metapopulations, puisque les pteridophytes possedent une bonne capacite de dispersion, et que le recrutement des especes de Diellia a lieu uniquement au cours des annees humides, tout en etant influencee par les perturbations locales. Les auteurs concluent que la structure des stades des populations locales peuvent indiquer la dynamique regionale d'une espece. Toutes les populations locales de Diellia doivent etre considerees comme candidates prioritaires pour les efforts de conservation a venir. |
