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Predator–prey interactions play major and direct roles in the structuring of zooplankton communities. Asplanchna usually predates ciliates, rotifers, cladocerans and sometimes even copepods, its predation may drive not only the ecological, but also the evolutionary dynamics of prey populations. In the present study, the life-table demography and the population growth of Asplanchna brightwelli were investigated at four temperatures (16, 20, 24 and 28°C) using Brachionus angularis as prey at four densities (10, 20, 30 and 40 ind.mL−1). The results showed that temperature affected significantly all the life-table demographic parameters (age-specific survivorship and fecundity, average lifespan, life expectancy at hatching, generation time, net reproductive rate and intrinsic rate of population increase) and the population growth rate obtained from the population growth studies, prey density affected the generation time, the net reproductive rate, the intrinsic rate of population increase and the population growth rate, and the interaction between temperature and prey density affected the generation time and the population growth rate. Both the average lifespan and the life expectancy at hatching were the longest at 16°C, the generation times were longer at lower temperatures (16 and 20°C) and higher prey densities (30 and 40 ind.mL−1), the net reproductive rates were higher at lower temperatures (16 and 20°C) and 20–40 ind.mL−1 of B. angularis, and the population growth rates were higher at 20°C under 20–40 ind.mL−1 of B. angularis.
Species richness of macrophytes of artificial and natural water bodies covering rivers, streams, canals and habitats with standing water was studied in two Central European biogeographical regions, Pannonian and Carpathian, represented by two model areas (the Borská nížina Lowland and the Turčianska Kotlina Basin). We found that: (i) the total number of macrophytes was higher in artificial water bodies compared to natural aquatic habitats in both regions and differences were statistically significant (P<0.05); and (ii) species richness of macrophytes is relatively low in both regions; slightly higher mean number was found in the Pannonian region (3.53) compared with the Carpathian region (3.06). Effects of environmental characteristics on species richness studied by generalized linear model (GLM) showed that explained variances of GLM were similar in both regions. The main drivers of the diversity pattern were those connected with the hydrology of water bodies, such as substrate characteristics and turbidity, less frequent were chemical characteristics, such as water conductivity and N-contents, whereas landscape characteristics manifested the smallest impact.
Reservoirs are subject to severe fluctuations in the water level from seasonal and interannual climatic variations, as well as abstraction for irrigation, hydropower, and drinking water. This can affect the matter and energy transfer through the food web, of which zooplankton is of crucial importance. We traced seasonal changes in the carbon and nitrogen stable isotope signatures of suspended particulate matter and crustacean zooplankton from a small Mediterranean reservoir. The δ13C and δ15N isotopic baseline signature of the lake varied seasonally, becoming more 13C-depleted and 15N-enriched in winter and less 13C-depleted and 15N-enriched values in the drier summer months, when external water inputs were negligible. Seasonal changes in the δ13C and δ15N SPM isotopic signature were well reflected in the herbivorous cladocerans. δ15N of the calanoid and cyclopoid copepods were at least 3‰ greater than for the herbivorous cladocera, suggesting their potential use as a food resource. δ13C of predatory copepods were also consistent with seasonal fluctuations in the δ13C SPM baseline, except during the heavy rains in early spring, when they were observably rich in lipids with a higher C/N ratio, suggesting that they had entered dormancy and were not actively feeding in the water column. This indicates the importance of taking into account not only the seasonality, but the community dynamics and trophic level of zooplankton taxa when interpreting stable isotope studies.
The studies of differences in life history and suitability of both water temperatures and trophic levels among rotifer sibling species improve our understanding of speciation, sibling species coexistence and possible niche differentiation over space and time, and consequences for the functioning of ecosystems induced by climate change and eutrophication. We collected Brachionus calyciflorus from Lake Baixiang and Lake Kongque, two tropical shallow lakes, in Xishuangbanna city, Yunnan, China, clonally cultured them in laboratory, and found that the B. calyciflorus complex contains two sibling species named sibling species BNA13 and BNB3 by phylogenetic analysis, and investigated the life-table parameters of the two sibling species BNA13 and BNB3 at four temperatures (16, 20, 24 and 28°C) and four algal densities (0.5, 1.0, 2.0 and 4.0×106 cells.mL−1). The results showed that the responses to increasing temperature and algal density for each of the life-table parameters differed with rotifer sibling species. Sibling species, temperature, algal density and their interactions almost all significantly affected the durations of juvenile period, embryonic development, reproductive period, post-reproductive period, mean lifespan, net reproductive rate, generation time and intrinsic rate of population growth. Sibling species significantly affected the age-specific survivorship. Temperature, algal density and their interaction and the interaction of sibling species and temperature significantly affected the age-specific fecundity. Regardless of the effects of temperature and algal density, the durations of juvenile period, embryonic development, reproductive period, post-reproductive period and mean lifespan, age-specific survivorship, net reproductive rate and generation time of the B. calyciflorus sibling species BNA13 were greater than those of BNB3, but the intrinsic rate of population growth of BNA13 was lower than those of BNB3. This suggests that the two B. calyciflorus sibling species adopted variable life history strategies, low population growth and high survivorship for sibling species BNA13, and high population growth and low survivorship for sibling species BNB3. Both the intrinsic rates of population growth of BNA13 and BNB3 were the highest at 28°C and 4.0×106 cells.mL−1 algal density, indicating that some adaptations of the B. calyciflorus sibling species BNA13 and BNB3 in tropical shallow lakes to water temperatures and trophic levels were similar, and they have the potential for coexistence in single waterbody of higher temperature and higher trophic level.
We investigated the distribution and dynamics of viruses, prokaryotes and small eukaryotic phytoplankton in Sidi Salem freshwater reservoir (Northern Tunisia). Samples were collected from the deepest station at different depths throughout the water column for 2 years (February 2009 to January 2011). The reservoir was characterized by seasonal alternations of thermal stratification and homothermy. Among the different microbial communities counted using flow cytometry (FCM), picocyanobacteria constituted an important autotrophic component since they were always present and their highest concentration reached 3.02 and 2.65×105 cells.mL−1 in March 2009 and June 2010, respectively. The heterotrophic prokaryotic communities (represented mainly by bacteria) were characterized by a clear separation between two subgroups referred to as high-DNA and low-DNA content populations, and the highest concentrations of heterotrophic bacteria (i.e., 3.8×107 cells.mL−1) were recorded in spring 2009. Several viral groups referred to as virus-like particles (VLP) groups 1, 2 and 3 could also be discriminated using FCM. VLP1 and VLP2 displayed a significant correlation with the heterotrophic bacteria (r=0.80 and 0.78, P<0.001) but seem to be independent from picocyanobacteria and/or chlorophyll a, suggesting these VLPs were mainly bacteriophages. At last, the virus to prokaryotic ratio could be high, especially in summer (mean=22, max=487), suggesting a strong coupling between bacteria and viruses, at least at certain periods of the year.
The role of both natural and artificial ponds in supporting biodiversity and as an infrequent habitat for aquatic organisms in urban areas may be greater than that in more rural landscapes. Moreover, biological succession and the dynamics of zooplankton can differ in urban ponds where we may observe a specific combination of environmental factors (e.g., an increase of eutrophication and pollution) compared to other water ecosystems. Therefore, ten urban artificial ponds were examined and the type of direct catchment area was established as the most important factor in the determination of zooplankton distribution. Different environmental factors structured zooplankton distribution between forest and meadow ponds. Low concentrations of oxygen as well as lack of fish, which was an effect of high concentrations of ammonium nitrogen, were responsible for the occurrence of littoral species and large crustacean species (e.g., Daphnia hyalina and Megacyclops viridis) in the case of forest ponds. Fish predation on large crustaceans and favourable food conditions (high concentration of chlorophyll a) created suitable conditions for the occurrence of pelagic species (e.g., Keratella cochlearis and K. quadrata) in the case of meadow ponds. Moreover, soon after the ice cover melted and before new macrophytes developed, previous-year dry rush stems created valuable refuge conditions for zooplankton in this type of pond. Despite anthropogenic pollution resulting from the close vicinity of the agglomeration of Poznań and unfavourable conditions attributed to the spring season a diverse zooplankton community occurred, reaching the level of 119 species in total.
Aquatic insects are widely distributed, and are especially diverse and abundant in tropical streams, where they play an important role in the food chain due to their diversity of feeding strategies, and the potential for the transfer of energy between aquatic and terrestrial environments. The intimate relationship found between these insects and environmental variables means that they are often used as bioindicatorss in environmental studies. We tested the hypothesis that the loss of environmental integrity in tropical streams will lead to a loss of species and a decline in the abundance of mayflies (Leptophlebiidae), in addition to a change in species composition, and the dynamics of population. Collect immature leptophlebiids in 18 streams representing different degrees of conservation, in the Brazilian Cerrado. The environmental integrity of the sites was assessed using a Habitat Integrity Index (HII), which generates values of zero (degraded) to one (preserved), based on soil use, the extension and conservation of riparian forest, as well as morphological features of the stream. A total of 4945 immature leptophlebiids were collected and identified as belonging to 16 species or morphospecies. On an average, a reduction of 0.1 in the value of the HII led to the loss of five specimens and one species. The composition of the communities varied systematically along the environmental gradient, with more sensitive species being found only when the index was above a threshold of 0.6. The importance of the riparian vegetation for the aquatic biota, especially its role in the mitigation of impacts from the surrounding matrix, supports the universal conservation of this type of habitat.
In the eutrophic Lake Kasumigaura in Japan, a trend of dissolved Si (DSi) concentration was detected over the last three decades, probably caused by the DSi release enhanced by an increase in sediment resuspension for the same period (Arai et al., Limnol., 13, 81–95, 2012). The present study described the long-term trends of the magnitude and seasonality of diatom blooms in the lake during 1981–2010 using the database and assessed the influencing factors for the trends by the numerical simulation of DSi and diatoms. The box model was developed based on the lake budgets (inflow, outflow, release and sedimentation) and the simple diatom growth model depending on DSi, temperature and light condition. As results, database analysis detected a long-term trend of increasing diatom abundance and a shift of blooming season from spring and autumn to the winter–spring period. Si could be regarded as a main nutrient factor limiting diatom growth by analyzing N:P:Si ratios. Our model simulation relatively well-reproduced the increasing trend and the shift of seasonality of DSi and diatoms, even though peaks of diatom blooms were underestimated in some years. Among input variables, the concentration of resuspended sediments radically increased. The model simulation with the input variables or parameters changed suggested as follows: (1) the recent DSi release from resuspended sediments enhanced diatom abundance and (2) the degradation of light condition caused by resuspension affected the shift of blooming season. These findings implicate the significance of the interactions between sediments and water to phytoplankton blooms.