DENSITY‐DEPENDENT GROWTH, ECOLOGICAL STRATEGIES, AND EFFECTS OF NUTRIENTS AND SHADING ON BENTHIC DIATOM SUCCESSION IN STREAMS¹

Abstract

The importance of immigration, growth, and competition for nutrients and light in benthic diatom succession was studied in experimental channels in a low‐nutrient stream. Diatom accumulation was greater in channels enriched with nitrate and phosphate (NP) than in control channels, reaching about 5 × 106 and 2 × 106 cells‐cm−2, respectively, after 30 d. Shading during late stages of community development reduced algal standing crop. Synedra ulna (Nitz.) Ehr. and Achnanthes minutissima Kütz. were codominant during early stages of community development in both habitats, but succession to an A. minutissima‐dominated community was much faster in NP‐enriched than in control conditions. Species dominating early stages tended to immigrate quickly, whereas species that increased in relative abundance during community development had either fast growth rates or fast immigration and average growth rates. Decreases in growth rates indicated resource supply became limiting during community development in control and enriched channels. Density‐dependent competition was indicated because nutrient concentrations in the water column and light did not decrease during the 30‐d study. Species autecologies were defined by effects of nutrient enrichment, shading, and community development on species growth rates. Differing autecologies of early and late succession species indicated that competition for nutrients was more important than competition for light. Species autecologies also indicated ecological strategies. The species most stimulated by nutrient enrichment were least able to maintain growth rates as algal abundances on substrata increased. In addition, these species that best sustained their growth rates during succession tended to have the highest immigration rates, indicating that drift and immigration may have been an important mechanism of persistence for some populations when resources become limiting within thick benthic mats.

Benthic community dynamics during summer low‐flows in two rivers of contrasting enrichment 1. Periphyton

“…This observation conforms with expectations of the Intermediate Productivity Hypothesis, predicting higher taxonomic richness at higher (but not extreme) levels of growth-limiting resources such as nutrients, space or light (Grime 1979;Waide et al 1999). Several experimental studies using periphyton have also shown that successional rates increase with higher nutrient supply (e.g., Pringle 1990;Stevenson et al 1991). Moreover, Pringle (1990) found higher taxon richness of periphyton in enriched waters than in unenriched waters.…”

Modelling diatom life forms and ecological guilds for river biomonitoring

“…The adnate life form encompasses the mobile and most of the low-profile diatoms. They are fast-growing species which could be favoured at high levels of nitrate because of nutrient stimulation but are less competitive in dense mature biofilms (Stevenson et al, 1991). Stalked diatoms appear to have an advantage when NO 3 À levels are low, meanwhile adnate diatoms could profit from decreased competition from stalked diatoms when NO 3 À levels are high.…”

Effect of a dam on epilithic algal communities of a mountain stream: before-after dam construction comparison

“…At the upstream site, mainly during the high water period, floods may have caused sloughing of life forms from the outer layers of the biofilm, thus resetting the algal community to early successional stages, as in Oemke and Burton (1986), Peterson and Stevenson (1992) and Peterson (1996). McCormick and Stevenson (1991) and Stevenson et al (1991) proposed that, during succession, benthic algal dominance change from species with high immigration abilities or disturbance resistant, such as Cocconeis spp., to species that predominate with limiting resources and high population densities, such as stalked species. In lotic ecosystems, where the spatial heterogeneity shaped by the current maintains a patch dynamics (Townsend, 1989) and temporal variation in the discharge produces periodical disturbances, the life forms of early and late-successional species represent ecological viable strategies.…”