Body Size, Food Concentration, and Population Growth in Planktonic Rotifers

Abstract

Population growth rates of eight species of planktonic rotifers were assessed for five to seven food concentrations using daily renewed batch cultures. The food concentration for which population growth rate was zero (the threshold food level) varied by a factor of 17 among species. The log of threshold food concentration was positively and significantly related to the log of body mass. Similarly, a strong positive log—log relationship was found between rotifer body mass and the food concentration supporting one—half the maximum population growth rate (°max/2); this food concentration varied by a factor of 35 among species. There was a positive relationship between rotifer body mass and maximum population growth rate. Because the smallest species have the lowest threshold food levels and the food levels necessary for them to attain °max/2 are lowest, they appear well adapted to living in food—poor environments. Large species appear to be restricted to food—rich environments but may thrive there because of their high reproductive potential. These conclusions are consistent with observations on species distribution and community structure of rotifers in nature.

Interactive effect of temperature and food concentration on growth rate: A test case using the small freshwater ciliate Urotricha farcta

“…This curve has three main attributes: (1) the food concentration where population growth equals mortality (the threshold level xЈ); (2) the maximum growth rate that reaches an asymptote at high prey levels ( max ); and (3) the rate at which the growth rate approaches this maximum level, indicated by the initial slope of the curve (␣). These important ecophysiological parameters can be used to assess the competitive ability of zooplankton (Lampert 1977b;Stemberger and Gilbert 1985;Gliwicz 1990;Montagnes 1996).…”

“…For instance, predictive equations have been developed to estimate maximum growth rates of ciliates of a given size at a given temperature (e.g., Montagnes 1996 and references therein). Likewise, the half saturation constant and the initial slope of the numerical response (Stemberger and Gilbert 1985;Rothhaupt 1990) are indications of an organism's ability to exploit low food concentrations; maximizing the ability to respond to low food levels has been used to predict competitive advantage between species (e.g., Stemberger and Gilbert 1985;Rothhaupt 1990).…”

“…All three of these aspects of the numerical response can be combined to compare the selective advantage of different taxa on a persistence versus opportunistic strategy continuum (Taylor 1978), analogous to the r/K selection theory (MacArthur and Wilson 1967;Stemberger and Gilbert 1985;Rothhaupt 1990;Walz 1993Walz , 1995. That is, a persistent species, adapted to low food concentrations, would predictably have a low threshold concentration (xЈ), a rapid increase to its maximum growth rate (␣), and a low maximum growth rate ( max ).…”

“…3, the expression max /k, is a measure of the initial slope of the numerical response curve (Stemberger and Gilbert 1985;Rothhaupt 1990). This slope is thus an indicator of the affinity between the prey and predator.…”

Life history and fatty acid composition of the marine rotifer Synchaeta cecilia valentina fed different algae

“…At 20°C and using Tetraselmis suecica as food, R. reduces when the algal concentration increases by 66% (2.10 to 3.49 1-19 ml-' dry wt), whereas exactly the opposite happens at 24OC (Oltra & Todoli 1997). Optimum thresholds of food concentration have been observed in several freshwater species of rotifers (Stemberger & Gilbert 1985) as well as in the euryhaline species Brachionus plicatilis and Encentrum linnhei (Schmid-Araya 1991).…”