We investigated patterns of resource partitioning between two brackish crustaceans (I. baltica and G. insensibilis) on trophic mosaics of fungal species colonizing vegetal detritus. Laboratory feeding experiments were carried out to assess consumption rates and diet selection of single individuals belonging to five populations. Adults of two co-occurring population of both G. insensibilis and I. baltica and one population of G. insensibilis, occurring alone in another habitat patch, were studied. Each individual were offered both fragments of Cymodocea nodosa conditioned by 8 fungal species and sterilized fragments as sole food source for 7 days. Both species preferred "conditioned" detritus but potential resource use was greater in G. insensibilis than in I. baltica. Individual niche breadth increased and phenotypic variability reduced in the allotopic sample. Trophic similarities were lower between individuals of co-occuring populations than between I. baltica and the allotopic G. insensibilis. The results suggest that co-occurrence is an important factor contributing to the enhancement of phenotypic variability and, consequently, to a trophic generalization at population level in G. insensibilis. It emphasizes the role of fungal patchiness on detritus in regulating resource partitioning between the two species. 相似文献
Light and first SEM observations on the pollen ofAegialitis indicate that the two species of the genus are clearly distinguishable from all other genera of the tribeStaticeae to whichAegialitis presently is relegated. Intraspecific exine or aperture dimorphism which appears frequently in this tribe, is not recorded in this genus.A. annulata andA. rotundifolia have distinct monomorphic pollen and show a great resemblance in exine features with the tribePlumbagineae, particularly species ofPlumbago. Considering these and other features, separate subtribal status forAegialitis within thePlumbagineae is proposed. 相似文献
Rhodopsin in bovine photoreceptor disk membranes was subjected to limited proteolysis by thermolysin, removing twelve amino acids from rhodopsin's carboxyl terminus. (1) The rate of proteolysis is significantly faster with rhodopsin following exposure to light than with unbleached rhodopsin, provided that the incubation conditions (pH, temperature) favor the formation of metarhodopsin II. (2) If the disk membranes are illuminated under conditions in which metarhodopsin I is the predominant photoproduct (pH 8.5, 0°C), no increase in the rate of proteolysis is observed compared to unilluminated membranes. (3) The light-induced increase in the rate of proteolysis is transient: it slowly decays in the dark to the original rate found for unbleached rhodopsin. The enhanced susceptibility to proteolysis appears to measure a conformational change at rhodopsin's cytoplasmic surface which is first exhibited at the metarhodopsin II stage. This and possibly other light-dependent changes may allow rhodopsin to mediate its signal as a light-receptor protein by binding to and activating certain rod cell enzymes. 相似文献
An enclosure experiment was conducted to assess the effects of a zooplankton elimination on the structure of a phytoplankton community. Phytoplankton biomass and production were higher in grazer-free enclosures, while the productivity per unit biovolume was lower. Exclusion of zooplankton favoured the majority of algal species, especially chrysophyceans (Dinobryon spp.) and the diatom Rhizosolenia, while mucilagineous green-algae were disfavoured. Middle sized algae (ESD 15–50 µm) and those with the largest Surface Area/Volume ratio were proportionally most favoured by the elimination of grazers.These differences in phytoplankton community structure are discussed in relation to effects of direct selective grazing and nutrient recycling by zooplankton. Some differences, as the immediate positive response of Dinobryon and Rhizosolenia, are probably caused by grazing release, while others, e.g. the response of mucilagineous species, might be caused by changed competitive relationships between the algae. 相似文献
The effects of contaminants and organic pollution on the chironomid communities of two basins in Lac St. Louis, a river-lake on the St. Lawrence River above Montreal, Quebec, were assessed and compared using lake classification theory techniques and morphological deformity indices based on the ligulae and antennae ofProcladius, the dominant surviving component of the south-shore communities. Contaminants from the industrial complex around Beauharnois, Quebec, have seriously degraded communities along the south-shore gradient while the introduction of untreated domestic wastes from Laprairie, Quebec, has seriously affected the communities of the Laprairie basin. The interaction between trophic and contaminant effects constitutes a classic example of the setback or deflection in the trajectory of ecological succession in biological communities hypothesized by ODUM (1981, 1985). 相似文献
One of the reasons suggested to explain the dominance of blue-greens in eutrophic lakes is that they are not used as food by zooplankton; and even when ingested, they are poorly utilized.
An increase in herbivores might be the expected result of biomanipulation of the aquatic food chain. This attempt at controlling the algae population is, however, destined to fail if zooplankton do not also utilize blue-greens as food. In this respect, a series of in-lake experimental results indicates that after the food chain has been biomanipulated, there is a decrease in blue-green density in periods when there is an increase in herbivores. Is this only an accidental result or are the two facts interrelated; in other words, can the decrease in the density of blue-greens be attributed to the increased use of them by zooplankton herbivores?
The suitability of blue-greens as food for zooplankton has been widely investigated by many authors with contrasting and inconclusive results. Two main factors seem to play important role in determining their suitability as food: the biochemical properties of the different species, or even different strains of the same species; and the shape and size of the colonies.
In particular, biochemical properties can result in toxic effects on zooplankton, while size and shape may strongly interfere with filtering, thus reducing the possibility of gathering food.
We report here the results of an experimental study designed to compare algal responses to short-term manipulations of zooplankton
in three California lakes which encompass a broad range of productivity (ultra-oligotrophic Lake Tahoe, mesotrophic Castle
Lake, and strongly eutrophic Clear Lake). To assess the potential strength of grazing in each lake, we evaluated algal responses
to a 16-fold range of zooplankton biomass. To better compare algal responses among lakes, we determined algal responses to
grazing by a common grazer (Daphnia sp.) over a range ofDaphnia densities from 1 to 16 animals per liter. Effects of both ambient grazers andDaphnia were strong in Castle Lake. However, neither ambient zooplankton norDaphnia had much impact on phytoplankton in Clear Lake. In Lake Tahoe, no grazing impacts could be demonstrated for the ambient zooplankton
butDaphnia grazing had dramatic effects. These results indicate weak coupling between phytoplankton and zooplankton in Clear Lake and
Lake Tahoe, two lakes which lie near opposite extremes of lake trophic status for most lakes. These observations, along with
work reported by other researchers, suggest that linkages between zooplankton and phytoplankton may be weak in lakes with
either extremely low or high productivity. Biomanipulation approaches to recover hypereutrophic lakes which aim only to alter
zooplankton size structure may be less effective if algal communities are dominated by large, inedible phytoplankton taxa. 相似文献