Information on the distribution of 225 species of planktic, periphytic and benthic rotifers from diverse waters in south and central Sweden was analyzed for temperature preference and tolerance. Most rotifers have a very wide tolerance range. Certainly differences in temperature dependence exist between separate species. However, these differences are, in a regional material like this, generally less distinct than what has been found for the distribution within individual lakes.
Information on the distribution of planktic, periphytic and benthic rotifers from diverse waters in south and central Sweden was analysed for details on relationships to the trophic degree. Three factors were combined in order to get an estimation of the trophic degree: tot-P-content, electrolytic conductivity and content of dry matter. Indicators of oligotrophic and eutrophic environments are enumerated. As far as the planktic species are concerned, the results are largely compatible with those of earlier investigations (while the non-planktic forms were previously less known in this respect). Some eutrophy indicators have been reported as typical of saprobic environments. 6 16 40 100 251 631 1585 3981 10000 p S
The literature on variation inKerutella is reviewed. The old idea of a thorough endogenous control has to be rejected, but internal factors ought to play a certain role beside influences from current and previous environment. In certain cases there is probably a succession of genetically different clones during the course of the year (cf. King, 1972King, , 1977. but the seasonal variation in lake populations of, e.g., K. cochlearis ought to be mainly non-genetical. There is some evidence that temperature and food exert an influence on the morphology, via rate of growth, but probably other abiotic and biotic factors are at work as well. The existence of allometric relationships is clearly demonstrated for several species. The variation in spine length has been suspected by some authors to consititute just the function of size variation which is thus considered primary. Some of the variation found is obviously non-adaptive. An attempt is made at explaining the existence of discontinuous variation within a single lake. Implications on taxonomy and speciation are briefly discussed.
Rotifera should be especially suited for an analysis of habitat relations because this group contains such a high number of species, inhabiting diverse environments . Furthermore, rotifers are to a large extent cosmopolitan, implying that ecological barriers, rather than geographical, are decisive of their distribution . In this review a short characterization of the rotifer fauna in different habitats is given, whereby macroenvironments and microenvironments are reported separately . The macroenvironments are classified as follows : `harmonious' lakes and ponds, arctic and antarctic waters, hot springs, hypertrophic-saprobic environments, mires, strongly acidic waters, saline waters, temporary water bodies, subterranean waters, running waters, oceans, terrestrial environments . The following microenvironments are distinguished : macrophytes (housing periphytic rotifers), open water (with planktic forms), minerogenous sediments (with psammon and hyporheos), organogenous sediments, other organisms (i .e . parasites and epizoans) .Many rotifers are more or less euryecious, while relatively few are strongly restricted in their choice of habitat . In extreme environments a low number of species is found, but often a high number of individuals within these species . These rotifers are usually primary consumers, and for natural reasons extreme environments are characterized by a low number of trophic levels .In environments with a high species number the separate species differ very much in their morphology, making it difficult to find common traits which may be interpreted as adaptations to the respective habitats . The most apparent adaptations ought to be found among the planktic rotifers, and these adaptations seem to constitute largely a protection against predators . Rotifers in extreme environments are usually not very apart in a morphological or taxonomical respect, with their most close relatives living in `normal' habitats and sometimes euryecious (an apparent exception from this rule is formed by the class Seisonidea) . Adaptations to deviating chemical and physical environments may develop relatively rapidly (seen from a geological perspective), while the more fundamental changes (occurring during a longer period of time) seem to be a response to biotic factors (e .g ., the development of different types of trophi for facilitating food collection) .
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