1. The range of factors which may influence the wide variation in the structure of pond communities is reviewed.2. Factors explaining the variation in numbers of macroinvertebrate and macrophyte taxa are investigated, using multiple regression analysis, for a group of ponds in which biogeographical effects are likely to be minimal.3. Numbers of macroinvertebrate taxa in these ponds are highly correlated with pH and probably, therefore, with other associated aspects of water chemistry.4. Many invertebrate taxa, from species to entire phyla, were not found below pH 5.5, but few characteristically 'acidophilic" taxa were apparent.5. Details of species composition of the macroinvertebrate fauna differ widely even between ponds of similar pH.6. The diversity and composition of macrophyte communities are not adequately predicted by any of the factors investigated.
Utricularia vulgaris growing at Wicken Fen, England, showed rapid turnover of the trapping apparatus. New groups of leaves, each bearing many traps, were produced at a rate of 1.4-2.8 groups per day from April to September, 1987. Old leaves decayed at a comparable rate, so that individual leaves survived for less than 50 days. In July, trapping efficiency of individual bladders was greatest between 1 and 6 days of age and then declined rapidly. Very few traps more than 19 days old could capture prey and most were lost from the leaves within 32 days. The lifespan of traps was closely related to their size and position on the leaves. Because of the rapidity of changes in trap condition with age, trap age is a vital consideration in any studies of the functional ecology of U. vulgaris.
SUMMARYThe partitioning of biomass between traps and leaves is a measure of the investment in carnivory of Utricularia vulgaris and is dependent on the relative values of three attributes: trap size, trap number and leaf size.Marked seasonal and individual variations in trap size, trap number and leaf size occur within a small population of U. vulgaris at Wicken Fen, Cambridgeshire, UK, with some plants consistently having fewer traps per leaf than others, and some smaller leaves than others, throughout the growing season. However, the three attributes vary independently, so that all combinations over the observed ranges of trap size, trap number and leaf size occur simultaneously in the population.In spite of the variation in the three constituent factors, the proportion of biomass invested in traps is close to 50"o in the majority of plants and throughout most of the growing season. The contribution of traps to total biomass cannot be predicted from the number of traps per leaf.Although the proportion of biomass represented by traps is the most useful measure of a plant's investment in carnivory, the precise way in which the biomass is partitioned between a variable number of traps of different sizes may also be an important consideration in cost-benefit analyses.
SUMMARYThe rootless submerged carnivorous hydrophyte Utricularia vulgaris L. is a potentially useful subject for tbe quantitatii'e study of foliar nutrient uptake and u.se, because known quantities of nutrients can be supplied precisely to individual leaves. We report here resuits obtained by band-feeding prey labelled witb ^^K and ^^P to leaves of known age in plants growing in near-natural conditions.Prey-derived ^*N was rapidly taken up and translocated: in plants fed via 3-d-old leaves, about 30 "" of tbe preŷ^N appeared in tbe immature parts of the plant \vithin 2 d. Almost a)l parts of the plant that were immature at the time of feeding received and retained prey ^'N throughout the 20 d experiment. Some backward translocation of ^-^N was observed, but only up to the second day after feeding.^P was also taken up and translocated rapidly, but was not retained by young tissues after they had become mature. Backward translocation of ^^P was observed into side-shoot meristems and flowers arising on parts of the plant older tban the fed leaves. This is in contrast to '^N uptake, where side-sboot buds and flowers received labelled nitrogen only if they arose on parts of the plant younger than the fed leaves.
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