Comparative life history of aspidiaceous ferns in northern Japan with reference to fertility during sporophyte development in relation to habitats
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The life-cycle characteristics of ferns, in particular reproductive characteristics in relation to alternation of generations, have been studied in populations of 19 species of aspidiaceous ferns native to Hokkaido. The developmental age of the sporophyte was quantitatively expressed by the number of midrib branches of the leaf (NV; number of venation). The maximum developmental age (MNV) of the aspidiaceous ferns in Hokkaido ranged from 49 to 113. The initiation of fertility (IF) in the relative developmental age (RDA), percentages of any NV to the maximum NV of the leaf population) ranged from 15 to 65%. Ferns occurring on rocky cliffs initiated fertility at 15–21%, while ferns occurring on the forest floor initiated fertility at 41–65% in the RDA of a leaf population. Further observations were undertaken on 26 ferns of other families and revealed that there were correlations between habitat and maximum NV, and habitat and IF in the RDA. Ferns occurring on cliffs, on mossy rocks and on tree trunks, had lower maximum NV of the leaf and earlier initiation of fertility in the RDA, than those of ferns occurring on the forest floor, edge of forests and on grassland in Hokkaido. Ferns occurring in the exposed habitat seemed to behave as a r-strategist, while ferns occurring in the forest floor seemed to behave as a K-strategist.
Key wordsAspidiaceous ferns Comparative life history Fertility rate Initiation of fertility (IF) Phenomenological convergence Relative developmental age (RDA)
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