Changes of the functional responses of the rotifers Brachionus rubens and Brachionus calyciflorus with particle sizes

Abstract

Effects of size and concentration of food particles on clearance and ingestion rates were studied for the rotifer species Brachionus rubens and Brachionus calyciflorus. Food algae of varying sizes were offered in short-term radiotraccr experiments. For small particles, below the optimal size, feeding was best described by the rectilinear model with constant maximal clearance rates (~1 ind-' h--l) below and constant maximal ingestion rates (ng C ind-' h-l) above a critical concentration. In this size range, the maximal clearance rate increased and the critical concentration decreased with particle size. For particles larger than the optimal size, feeding could best be described by a curvilinear model. In this size range, clearance rates decreased continuously with food concentration, maximal ingestion rams were lower than those for small particles, and ingestion rates could even decrease in high concentrations of big particles. These findings suggest diff trent mechanisms in feeding on small and large particles and help to reconcile some seemingly contradictory results of previous studies.The functional response of planktonic suspension feeders usually can be described by one of three basic models. These models represent different feeding strategies, and the differences are most obvious from the clearance rates (Fig. 1). In the case of the rectilinear IBlackman model ( (Fig. lb), which can be expressed by the Michaelis-Menten or Ivlev (1955) equations, is characterized by continuously decreasing clearance rates. It is also conceivable that clearance rates decrease at low food concentrations (Fig. lc;Lehman 1976;Lam and Frost 1976). The resulting ingestion rates correspond to Holling's ( I 959) type 1, 2, and 3 functional responses.

Combined effect of temperature and food concentration on the grazing rate of the rotifer Brachionus plicatilis

“…1, 2); this is consistent with other work for B. plicatilis (B. ) and for other species of Brachionus fed optimal-sized prey (Rothhaupt 1990b). However, others suggest that Holling type 1 (rectilinear; Korstad et al 1989) or Holling type 3 (sigmoidal; Navarro 1999) responses better ®t the functional response for B. plicatilis.…”

“…However, others suggest that Holling type 1 (rectilinear; Korstad et al 1989) or Holling type 3 (sigmoidal; Navarro 1999) responses better ®t the functional response for B. plicatilis. In practice, it is di cult to distinguish di erences between these responses, and for most aquaculture purposes and ecosystem modelling there is little need to do so; nevertheless Rothhaupt (1990b) has approached this problem, recognising that prey size may alter the shape of the response. To test this hypothesis adequately would require substantially more rate measurements at low food concentrations than were collected in this study.…”

“…First, although generalities can be made, our data should ideally only be applied to grazing rates for B. plicatilis feeding on I. galbana. Feeding rate can vary with food quality (Doohan 1973) and cell type and size (Starkweather 1980;Rothhaupt 1990b;B. Hansen et al 1997;Navarro 1999).…”

Investigation of a rotifer (Brachionus calyciflorus) - green alga (Scenedesmus pectinatus) interaction under non- and nutrient-limited conditions

“…The clearance rates that were estimated of Brachionus feeding on non-limited S. pectinatus were similar to those that preyed on P-limited food. Because clearance rates drop continuously with food concentration above a critical concentration (Rothhaupt 1990a), the similar clearance rates in this case could be the result of the larger animals in non-limited conditions that through higher feeding activity might have outbalanced expected lower clearance rates. On the other hand, it remains possible that in both non-limited and P-limited conditions lower clearance rates were obtained, but that these were not detected in the experimental set-up employed in the current study.…”

“…The highest clearance rates were found for B. calyciflorus feeding on N-limited food and significantly lower clearance rates for animals feeding on P-limited and non-limited S. pectinatus. The difference in clearance rates for Brachionus feeding on N-limited and P-limited S. pectinatus can be explained from the differences in food concentrations (Rothhaupt 1990a). The clearance rates that were estimated of Brachionus feeding on non-limited S. pectinatus were similar to those that preyed on P-limited food.…”