Gametophyte ecology and demography of epiphytic and terrestrial tropical ferns.

Factors that influence the distribution of ferns are poorly understood and likely reflect the ecology of both the sporophyte and the gametophyte generation. Little study has been done on the ecology of the gametophyte generation, especially in regard to tropical species. The goal of this study was to examine demography and the influence of light and disturbance on the distribution of the gametophytes of several tropical epiphytic, hemiepiphytic, and terrestrial fern species. Through a series of observational and experimental studies, we found that increased terrestrial gametophyte density and richness were related to both increased light and disturbance. By contrast, increased light had no influence, and increased disturbance negatively affected epiphytic density. Over a 25-mo demographic study, epiphytic and hemiepiphytic species had significantly greater longevities and lower recruitment rates than terrestrial species. Such unique strategies may have evolved in response to different disturbance regimens between the two habitats. Terrestrial species encounter and are adapted to more frequent disturbance and have invested in rapid gametophyte growth and recruitment. Epiphytic species may be more influenced by bryophyte competition, and in habitats of relatively low disturbance, they have invested in greater size and longevities. In such systems, gametophytes are able to survive for years waiting for favorable recruitment conditions.