The stream as a habitat templet for bryophytes: species' distributions along gradients in disturbance and substratum heterogeneity

Abstract

1. The structure of bryophyte communities in streams in relation to habitat characteristics,, especially disturbance, is described. Disturbance in rivers is quantified as movement of the stream bed, whereas in small streams water level fluctuation is used as an indicator of disturbance frequency. 2. Canonical correspondence analysis differentiated frequently disturbed sites from more stable ones. The existence of a disturbance gradient was confirmed in a subset of the study sites using long-term records of discharge variation. A parallel change was detected in the species composition of bryophyte communities with low-statured, potentially fast colonizers dominating the disturbed end and large perennial species the stable end of the gradient. 3. A consistent pattern of zonation of bryophyte species was found along the gradient from continually submersed to persistently dry conditions in small streams and lake outlets. An abrupt increase in species richness occurred at or just above the water line, where facultatively aquatic species tolerant of both conditions formed the bulk of the community. 4. The relationship between species richness and standing crop in stream bryophyte communities was consistent with the hump-backed model of Grime (1979), especially at the within-habitat scale. Quadrats of low and very high standing crop were characterized by low species richness, while peak richness was observed at intermediate standing crops. 5. A few perennial species (e.g. Fontinalis spp. and Rhynchostegium riparioides) capable of monopolizing space dominated the most stable habitats. Species composition in low biomass sites was more variable, yet only one basic growth-form (small-statured species with high allocation to spore production) seemed possible in these highly disturbed streams. In habitats of intermediate biomass, small-scale disturbances apparently allow the formation of a more varied bryophyte community. 6. A habitat templet for stream bryophyte life strategies and community structure is presented. Disturbance is proposed to be the factor filtering out traits unsuitable for a given environment. The potential of stream bryophytes for testing and developing general ecological theory is emphasized.

Can biological invertebrate traits resolve effects of multiple stressors on running water ecosystems?

“…Harsh, homogenous traits Habitat harshness as trait filter (Thienemann, 1918) Temporal heterogeneity = disturbance/stress Running water predictions (Southwood, 1977) Spatial heterogeneity = provision of refugia stream bryophytes (Muotka & Virtanen, 1995), stream and lake hydrophytes (Willby, Abernethy & Demars, 2000;Demars & Harper, 2005), benthic pond invertebrates (Verberk, Siepel & Esselink, 2008), marine benthic invertebrates (Bremner, Rogers & Frid, 2003b) or fluvial floodplain plants and birds (Bournaud, 1994;Pautou & Arens, 1994). These theoretical studies also stimulated work on applied aspects of trait responses to human-caused stressors (or release from stress after restoration) of organisms such as benthic stream invertebrates Dolédec et al, 1999), stream fish (Ferreira et al, 2007;Schmutz et al, 2007), benthic pond or lake invertebrates (Menetrey et al, 2005;Van Kleef et al, 2006), waterway hydrophytes (Willby, Pygott & Eaton, 2001), lagoon fish, benthic invertebrates, macrophytes and plankton (Mouillot et al, 2006;Pravoni, Da Ponte & Torricelli, 2008), marine benthic invertebrates (Bremner, Frid & Rogers, 2003a;Frid et al, 2008), marine fish (Jennings, Greenstreet & Reynolds, 1999), fluvial floodplain plants, molluscs and insects (Dziock, 2006;Foeckler et al, 2006;Henle et al, 2006) or forest birds (Hausner, Yoccoz & Ims, 2003).…”

Patterns of bryophyte diversity in humid coastal and inland cedar–hemlock forests of British Columbia

“…Logs provide habitat for many species of bryophytes, and different decay classes and sizes of logs support different communities Table 5. of bryophytes (Gustafsson and Hallingbäck 1988;Söderström 1988a). Disturbing these habitats can reduce bryophyte diversity dramatically (Muotka and Virtanen 1995).…”

“…The results of such research indicate the importance of substrates and habitats. Habitats such as streams, fens, and bogs exhibit unique patterns of bryophyte diversity (Slack and Glime 1985;Muotka and Virtanen 1995;. Vitt and Belland (1997) have shown that patterns of bryophyte diversity are strongly correlated to habitat type and scale of the investigation.…”

The relationship between species richness and taxonomic distinctness in freshwater organisms

“…For a description of the sampling methods, refer to Muotka and Virtanen (1995). Environmental variables of importance to bryophytes include habitat structure and water chemistry.…”