Search for: [Abstract = "Each effort for an ecological classification based on the concept of species always encounters serious difficulties. It is nevertheless necessary when data obtained for species are to be used for the construction of a complex system model composed of the trophic levels. Even the plankton, generally accepted as one of the most simple systems, can be subjected only with great difficulty to the trophic classification operations \(Fig 1\). The essence of this difficulty is the very unclear trophic status of each animal component of the system. Nevertheless such classification efforts are quite common nowadays \(works on IBP synthesis\) placing each zooplankton species into herbivores, carnivores, detritivores or omnivores, where only the last group seems reasonable as most species allotted to the three former groups in reality represent their own groups only in specific conditions, e.g. laboratory experiments.The type of food of a given species is largely dependent on three factors\: 1. Morphological and functional aspects of food uptake \(filter feeding, sedimentation or raptorial feeding, n.b. many species mak e use of two or even three mechanisms alternatively\). 2. Animal behaviour which determines its food selectivity\: a. ease of choice of a particular feeding zone, b. ease of choice of particular objects from the potential food variety. 3. Abundance of diverse types of food in the environment. The first two factors are essentially of species origin but even these may change quite a bit not only from stage to stage of individual development, but also from environment to environment differ ing in food sources. E.g. Chydorus sphaericusis a typical “scraper” when feeding on periphyton or large phytoplankton colonies\(Fryer 1968\), but acts as a typical filter feeder in limnetic environment wherethere are no large phytoplankton forms \(Gliwicz 1969c\). Also, a typical cyclopoidcopepod feeding almost exclusively on phytoplankton in natural conditions,will be a successful carnivore when animal food is more available. Here, whenconsidering the third factor, we come across the greatest difficulty. One cannever be sure whether a species, which in one lake is beyond all doubts a carnivore,is not by chance a typical herbivore in another lake, as is certainly the casewith Cyclops abyssorum tatricus \(compare Eppacher 1968 and Pechlaneretal. 1972\) or Heterocope saliens \(Monakov 1972\)."]

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