Effects of competitors and Chaoborus predation on the cladocerans of an eutrophic lake: an enclosure study

The role of large laboratory grown food competitors of the genus Daphnia as well as the predation impact of Chaoborus on the cladoceran community of an eutrophic lake was assessed in five in situ enclosure experiments. The hypothesis tested was that the outcome of competition and gape-limited predation on cladocerans is size dependent. According to the generally accepted assumptions on competition and invertebrate predation, large-bodied cladoceran taxa were expected to be less affected by competing congeners and by Chaoborus than were small-bodied taxa. Effects of the predator upon an assemblage of differently sized cladoceran taxa were much more pronounced than effects of competition. There was a tendency of predation and competition impact to decrease with cladoceran size, but predation pressure was also low for some small cladocerans and high for some large cladocerans. The general trends were further obscured by factors not or indirectly linked to body size

Estimating the impact of Chaoborus predation on zooplankton: A new design for in situ enclosures studies

We designed an experimental setup which permitted the selective exclusion of predatory Chaoborus larvae from mesocosms. With this new type of enclosure we could investigate the impact of Chaoborus on zooplankton and separate it from the effect of vertebrate predation by fish. The basic idea was to keep away Chaoborus larvae from enclosures by a mesh bottom or to let them penetrate enclosure bags open to the underlying water. The setup was tested in two very different lakes and proved to be adaptable to the specific lake requirements. Our design improves the simulation of lake conditions in the enclosures. First, predator densities are more natural and sec end, the animals are able to exhibit their normal DV

Zooplankton of a small eutrophic lake: impact of a biomanipulation attempt.

In a 3-year experiment carried out in the small eutrophic Plusssee (North Germany), we tested the hypothesis that large grazers as well as invertebrate predators are favoured by biomanipulation. The effect of piscivorous fish addition and removal of planktivores on zooplankton was estimated by ARIMA-modelling. The intervention analysis of zooplankton abundance data sets from a 13-year period revealed that invertebrate predators (Chaoborus and Leptodora) were more abundant during the biomanipulation period. However, large grazers of the genus Daphnia were not favoured. The small cladoceran Diaphanosoma occurred more frequently whereas the rotifer Asplanchna was reduced. Biomanipulation success was limited because most piscivores could not be successfully established. Biomanipulation to a certain extent reduced perch which fed on multiple prey but left roach as the most important planktivore on large grazers uncontrolled

Impact of weather on a lake ecosystem, assessed by cyclo-stationary MCCA of long-term observations.

Temperate lake ecosystems are generally characterized by a strong annual cycle, and the relationships between observations of such ecosystems and external forcing variables can exhibit a complex structure. Furthermore, the observational data record is often short. This makes it difficult to assess the relationships between external forcing factors and their impact on the biological succession. Cycle-stationary maximum cross-covariance analysis (MCCA) allows the effects of seasonality to be modeled in a flexible way, and we describe this statistical technique in detail. MCCA offers an objective method to approximate the high-dimensional total cross-covariance structure by defining "weighting" patterns. With a predictor set of reduced dimension, a suitable regression between forcing variables and ecological response variables can be set up. Cyclo-stationary MCCA is used here to analyze the influence of meteorological variables (air temperature, wind speed, global radiation, humidity, and precipitation) on 13 biological and biogeochemical indicator variables of Plussee, a small lake in northern Germany. The main weather influence on the indicator variables was found to be connected to winter temperature. From the covariance structure the following major signals were detected to be related to higher winter temperature: a more intense spring algal maximum, a higher zooplankton biomass during the algal maximum, a less intense loss of nutrients to the hypolimnion, a higher summer bloom together with changes in the nutrient concentrations, and stronger oxygen consumption in autum

Treatment Resistance Mechanisms of Malignant Glioma Tumor Stem Cells

Malignant gliomas are highly lethal because of their resistance to conventional treatments. Recent evidence suggests that a minor subpopulation of cells with stem cell properties reside within these tumors. These tumor stem cells are more resistant to radiation and chemotherapies than their counterpart differentiated tumor cells and may underlie the persistence and recurrence of tumors following treatment. The various mechanisms by which tumor stem cells avoid or repair the damaging effects of cancer therapies are discussed