Niche Breadth and Overlap of Four Species of Sphagnum in Southern Ecuador

Abstract

Niche breadth and overlap values ofS. magellanicum, S. recurvum, S. sancto-joseph- ense, and S. subsecundum var. rufescens from four peatlands in southern Ecuador are similar to those reported for Sphagnum-dominated peatlands in North America. The pH, conductivity, and concentrations ofFe, K, Mg, Mn, Na, and P indicate that these peatlands are similar to intermediate or transitional poor fens in the Northern Hemisphere. Niche diversification of Sphagnum in North America has been investigated by Vitt and Slack (1984). They examined microhabitat parameters of conductivity, pH, Ca, K, Mg, Na, height above the water table, and shade for 13 Sphagnum species in northern Minnesota. Calculations of niche breadth and overlap suggested independent species utiliza- tion of the gradients. In the peatlands they exam- ined, they found that niche breadths of Ca and pH become narrower from hollow to hummock, but the broadest niche breadths were for midhummock spe- cies along the height gradient. Individual species appear to interact independently to different gra- dients. This led Vitt and Slack to conclude that species of Sphagnum are largely equilibrium species as opposed to fugitive species. Slack (1982) suggests that equilibrium species have well-defined niches distinct from close competitors, whereas fugitive species are characterized by strong niche overlap with similar species. Vitt and Slack (1984) noted an exception with one species, S. russowii Warnst., which they believe to be a fugitive species since it is found in a wider range of habitats than the other species. The broad niche overlap of such species is attributed to the ruderal nature (Andrus 1986). Andrus (1986) does not quite agree with Slack's (1982) interpretation that Sphagnum species are best classed as equilibrium species. He feels that this is probably more appropriate for species in well-de- veloped and slowly evolving peatlands. The distri- bution of Sphagnum in peatlands is envisioned by Slack (1982) as a function of colonizing ability and competitive interactions since the last disturbance event, with the establishment of Sphagnum as a short phase compared to growth of the Sphagnum in an established peatland, which is viewed as a relatively long-lived habitat. However, Andrus notes that periodic drought and fire are common phe- nomena in northern peatlands. Such disturbances create short-lived habitats that are often character- istic of fugitive species.