Niche diversification of Sphagnum relative to environmental factors in northern Minnesota peatlands

Abstract

The peatlands sampled in this study are located in northern Minnesota and include 32 stands positioned in seven sites in the Red Lake peatland and Lake Itasca areas. Surface water chemistry ranges from pH values of 4.6 to 7.4, with corrected conductivity of 53 to 476 μohms cm−1 and calcium of 6.9 to 44.5 ppm. Six broad physiognomic landscape units are delimited based on quantitative analysis of the vegetation; these range from ombrotrophic ovoid islands to strongly minerotrophic forested fens. These landscape units can best be further divided or themselves characterized by the dominant Sphagnum species. Calculations of niche breadth across eight microhabitat axes and niche overlap for four microhabitat axes (pH, corrected conductivity, height above H2O level, and shade) for 13 species of Sphagnum suggest independent species utilization of the gradients. Among the mire-expanse species, niche breadths become narrower from hollow to hummock along calcium and pH gradients, whereas broadest niche breadths are present for midhummock species along the height gradient. For the taxonomically close species, S. fallax and S. angustifolium, niche overlap is greatest for conductivity and pH, whereas overlap is least along the height gradient. Quantification of niche breadth and niche overlap indicates considerable niche diversification along these microhabitat gradients, with individual species interacting independently to different gradients. These differing niche breadths along several different gradients suggest that these species of Sphagnum are largely equilibrium species, not opportunistic ones. In general, niche overlap is smaller in mire habitats where an abundance of bryophytes coexist with Sphagnum and highest in mire-expanse situations where Sphagnum is dominant.

<p><strong>Niche Breadth and Overlap of <em>Sphagnum </em>Species in Costa Rica</strong></p>

“…Sphagnum magellanicum is confirmed by the studies of Vitt and Slack (1984), McQueen (1990), and the present study to have a broad niche breadth compared to most species. In each study, this species has the second highest niche breadth.…”

“…The results of the present study and those of Vitt and Slack (1984) and McQueen (1991) suggests independent utilization of different microgradients. The greater similarity of the Costa Rican niche values to the niche values of Sphagnum species in North America than to the niche values reported for South America may be accounted for by diversity.…”

“…The number of quadrats used depended on the area of the site. Cover values were estimated using Daubenmire's (1959) canopy method as employed by Vitt and Slack (1984). Voucher specimens are in the University of Vermont herbarium (VT) and the New York Botanical Garden (NY).…”

“…Wolfe and McQueen (1992) reported that S. magellanicum and S. sanctojosephense are the most common species in the páramo habitats of Costa Rica. Although they did not calculate niche breadth and niche overlap, Wolfe and McQueen believed that their data suggest niche diversification along microhabitat gradients and independent species utilization of the gradients similar to the studies of Vitt and Slack (1984) and McQueen (1990).…”

Hydro-ecology of groundwater-dependent ecosystems: applying basic science to groundwater management

“…Species in bold ultimately were deleted from the final indicator list because they grow across a range of wetland types with different hydrologic regimes and thus are poor indicators for fen hydrology. (2007); aa : Szumigalski and Bayley (1996); bb: Szumigalski and Bayley (1997);cc: van Diggelen et al (1991); dd: Vitt and Slack (1984); ee: Wassen and Barendregt (1992) ; ff: no data found.…”