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Niche Relationships of Mountain Stream Bryophytes

1985; American Bryological and Lichenological Society; Volume: 88; Issue: 1 Linguagem: Inglês

10.2307/3242643

1938-4378

Nancy G. Slack, Janice M. Glime,

Lichen and fungal ecology

Bryophyte community structure was studied in ten streams in the Adirondack Mountains of New York and adjacent areas over an elevation range of 625 m. Species composition, including frequency and cover and possible niche parameters including elevation, water temperature, pH, flow rate, incident light, substrate type and height above or depth below water level were measured. An ordination was done of the ten streams, and species diversity, niche breadth and niche overlap were calculated. Elevation and stream flow were important for niche separation between streams. Height and type of substrate including rock size were important niche parameters within streams. Characteristic height segregation was seen within streams for many species including several co-occurring members of the Brachytheciaceae and two morphologicalforms of Hygrophypnum ochraceum. The communities included 28 mosses, seven hepatics and one aquatic lichen. It is advantageous to be able to test interactions within a group ofbryophytes in a habitat dominated by bryophytes. Many habitats fill this requirement, but few have been studied in terms of community structure. Forest floor communities (Slack 1977; Lee & LaRoi 1979a, 1979b) and bogs and fens (e.g., Slack et al. 1980; Vitt & Slack 1984) have been analyzed. Although both forest floors and mires are often dominated by bryophytes in the ground layer, these habitats are complicated by the large number of non-bryophyte plant species also present. Mountain streams, the subject of the present study, are often virtually free of higher plants. This absence of multilayer plant association facilitates the study of bryophyte species interactions. Early studies of North American stream ecosystems emphasized the importance of allochthonous detritus as the major energy source. Naimer, in the 1982 meetings of the North American Benthological Society, was the first to report that bryophytes are important biological contributors to these systems since they constitute a major part of the primary productivity in lower order streams. Bryophytes are also important as a substrate for insects 007-2745/85/7-18$1.35/0 This content downloaded from 157.55.39.161 on Mon, 23 May 2016 05:23:21 UTC All use subject to http://about.jstor.org/terms 8 THE BRYOLOGIST [Volume 88 (Babcock 1949; Minkley 1963; Glime & Clemons 1972) and for algae (Douglas 1958) as well as a food source for insect larvae (Jones 1949). They thus contribute significantly, if indirectly, as food sources for fish. Certainly in mountain streams the bryophytes are the dominant organisms and their community structure is important to the dynamics of the stream ecosystem. In North America there have been no studies defining community structure or niche relationships of stream bryophytes. Existing studies report patterns of presence of bryophytes in streams (Glime 1968, 1970); discuss tolerance limits and responses of individual species (e.g., Conboy & Glime 1971; Glime 1971; Glime & Acton 1979; Glime 1982) or are species lists and descriptive ecology. An early British study by Tutin (1949) provides a starting point for selecting possible niche parameters. She studied vertical zonation in a mountain stream in the English Lake District and concluded that water supply, air humidity, aeration, light intensity and altitude may all be important in determining species composition of stream bryophyte communities. Since height above the water correlates with humidity (Craw 1976), height is an important parameter which can be measured. Niche breadth and niche overlap measures have been used to describe many animal and higher plant communities, but these useful methods of analysis have less often been applied to bryophytes (Slack 1982, 1984). Watson (1980) first applied niche breadth and overlap equations to one family of bryophytes, the Polytrichaceae, on Mt. Washington, New Hampshire. She elucidated niche or ecotope relationships between and within the Polytrichum and Polytrichastrum species in relation to environmental factors. Lee and LaRoi (1979) measured niche breadths and overlap for bryophytes in the Canadian Rockies over elevation and moisture gradients. Vitt and Slack (1984) recently measured niche breadths and overlap for 13 Sphagnum species in relation to eight microhabitat parameters in the Redlake Peatland in northern Minnesota. Four of these parameters were found to be important in niche diversification in Sphagnum. In the present study we have examined niche breadth, niche overlap, community similarity and species diversity. Niche parameters investigated include altitude, pH of water, water movement, substrate, and height above the water. DESCRIPTION OF THE STUDY AREA Ten streams were chosen, eight in the Adirondack Mountains, New York, and two for comparison south of the Adirondacks in Schenectady County, New York. The presence of bryophytes was the major criterion for inclusion in the study. Water movement was another criterion; very sluggish streams with almost no water movement were not included. Such streams sometimes do contain vascular plants. Within the Adirondack area a range of elevation (from 255 m to 825 m) was also a criterion for the choice of streams. The ten streams contained only bryophytes and one aquatic lichen, but no vascular plants. Most of the streams are small and lack names on area maps. Stream locations and characteristics are as follows: Stream 1-Essex Co., District 4, North Elba (4413'N, 73*52'W), 0.8 km above Cascade Mountain trailhead at Rt. 73, 0.6 km from road, elevation 825 m. A 1 m wide slow-moving stream; substrate granite rocks, fist to wheelbarrow size; canopy of Acer saccharum, Fagus grandifolia, Betula alleghaniensis; understory of Viburnum cassinoides, Acer spicatum. pH 6.8. Stream 2-Essex Co., District 4, North Elba (4413'N, 7352'W), just above Cascade Mountain trailhead, elevation 670 m. A 1 m wide slow-moving stream; granite rocks fist to bucket size; canopy of Betula papyrifera; understory of Acer spicatum. pH 6.5. Stream 3-Essex Co., District 4, North Elba (4417'N, 7456'W), Riverside Road, 0.8 km south of junction with Rt. 86, east side of road, elevation 524 m. A 4 m wide stream with rapid falls and moderate pools (17 cm/sec surface flow); granite boulders cement mixer size; canopy of Abies balsamea, Betula alleghaniensis, Acer spicatum, Sorbus americanus. pH 6.4. Stream 4-Essex Co., District 4, Keene (4412'N, 73049'W), the Garden at base of Johns Brook trail, stream just south of parking lot, elevation 425 m. A 1 m wide slow, intermittent stream; small granite and schist rocks egg to fist size; sparse canopy of Betula papyrifera, B. alleghaniensis, Tsuga canadensis. pH 6.8. Stream 5-Essex Co., District 4, Keene (449'N, 73052'W), stream just below (east of) Johns Brook Lodge, elevation 685 m. A 4 m wide stream with moderate flow (25 cm/ sec surface flow); granite boulders of wheelbarrow and cement mixer size; cover of Betula alleghaniensis, Abies balsamea, Picea rubens; understory of Acer spicatum, Acer pensylvanicum, Acer saccharum. pH 6.2. Stream 6-Essex Co., District 4, Keene (44010'N, 73052'W), stream above junction with trail up Big Slide Mountain, east of Johns Brook Lodge, elevation 745 m. A 4 m wide stream with rapid flow (50 cm/sec surface flow), granite bedrock with few boulders, wheelbarrow to cement mixer size; cover of Betula alleghaniensis, Betula papyrifera, Picea rubens, Abies balsamea, Acer saccharum. pH 6.1. Stream 7-Essex Co., District 4, Keene (449.5'N, 73052'W), stream along trail to Johns Brook Lodge about 0.8 km northeast of lodge, elevation 685 m. A 1 m wide stream with slow flow; granite bucket to cement mixer size boulders; cover of Betula alleghaniensis, Fagus grandifolia, Acer saccharum. pH 6.3. Stream 8-Essex Co., District 11, Schroon (43050'N, 7345'W), northeast corner of Schroon Lake, elevation 255 m. A 1 m wide stream with intermittent dry bed and small pools; granite bedrock and some cement mixer size boulders; cover of Tsuga canadensis, Acer saccharum, Betula papyrifera, B. alleghaniensis. pH 6.05. Stream 9-Schenectady Co., District 18, Glenville (4253'N, 741'W), Washout Creek, elevation 200 m. A 4 m wide stream with slow flow (8 cm/sec surface flow); Schenectady Sandstone and Shale bedrock; cover of Acer saccharum, Fraxinus americana, Carya ovata, Carpinus caroliniana, Tilia americana; understory of Hamamelis virginiana. pH 6.5-7.4. Stream 10-Schenectady Co., District 17, Glenville (4255'N, 745'W) Wolf Hollow Creek, elevation 200 This content downloaded from 157.55.39.161 on Mon, 23 May 2016 05:23:21 UTC All use subject to http://about.jstor.org/terms 1985] SLACK & GLIME: NICHE RELATIONSHIPS 9 m. A 4 m wide stream with slow flow (4 cm/sec surface flow); Schenectady Sandstone and Shale with numerous angular rocks; cover of Acer saccharum and Fraxinus americana. pH 7.3. The district numbers refer to botanical districts of New York State, based on latitude and longitude. See, for example, Ketchledge's Revised Checklist of Mosses of New York State (198 1) which uses these districts.