Abstract

Integrated predation (number of prey cells eaten per surface area and time) must be calculated to study the impact of predation in stratified systems where predator and prey populations are not uniformly distributed along the vertical axis. We considered the effect of the vertical distribution of populations and the functional response of the predator in this calculation. We developed seven algorithms which take into account both, one, or neither factor. Two cases of predation in the metalimnion of Lake Cisó (Banyoles, Spain) are used as examples to illustrate the limitations and advantages of the different approaches. In the first example (the rotifer Anuraeopsis fissa feeding on phototrophic purple bacteria) the vertical distribution of populations is very important (the populations were highly segregated), whereas use of the functional response makes very little difference. In the second example (the ciliate Coleps hirtus feeding on Cryptomnonas phaseolus ) the situation is reversed: the important factor is use of the functional response (the prey abundance was very high compared to the half saturation constant of ingestion for the predator).

Ramon Massana

Staff scientist

I am microbial ecologists with a deep interest in protist ecology and evolution