On the use of split moving window analysis for boundary detection in ordered dataseries from benthic communities

The capacity of Split Moving Window (SMW) boundary analysis was tested to detect the depth of the transition of a littoral to a profundal invertebrate community in two datasets that were ordered along a depth gradient. The littoral community was dominated byPolypedilum nubeculosum agg.,Potamopyrgus jenkinsi andGlyptotendipes cf.pallens. The species richness of the profundal community was much lower. Its fauna was dominated byChironomus cf.plumosus andChaoborus flavicans. The transition could be detected with small window sizes. The discontinuities are located at the same depth as the oxygen stratification. We conclude that SMW can be used to study artificial transects. Noisy datasets should be transformed to reduce the variation. The scale dependence of SMW is an advantage. Information about the nature of a discontinuity (transition, trend or local discontinuity) can be obtained by increasing the window size. The location of discontinuities that are detected at the edge of a series, with large windows, should be interpreted carefully due to the existence of a blind zone.     

Depressed monocyte polarization and clustering of dendritic cells in patients with head and neck cancer: In vitro restoration of this immunosuppression by thymic hormones

The in vitro restoring effects of a thymic hormone preparation, TP-1, on defective monocyte and dendritic cell function in patients with head and neck squamous cell carcinoma (HNSCC) have been examined. TheN-formylmethionyl-leucyl-phenylalanine(fMLF)-induced polarization of monocytes isolated from the peripheral blood was significantly lower (a mean of 19%) than the polarization of monocytes isolated from healthy controls (a mean of 33%). After the in vitro addition of TP-1 this defective polarization was improved to the normal value of 33% polarized monocytes. The capability of dendritic cells prepared from the blood to form cellular clusters with allogeneic cells was impaired in 26/44 patients. In vitro addition of TP-1 again had restoring effects. The original defective dendritic cell clustering of 97 clusters/six microscopic fields (mean) was improved to a value of 121 clusters. The defects in monocyte polarization and clustering of dendritic cells could be ascribed to the presence in serum of a tumor-derived low-molecularmass factor low-M _r factor; <25 kDa) sharing structural homology with p15E, the capsular protein of murine and feline leukemogenic retroviruses. The incubation of low-M _r factor from the serum of HNSCC patients with healthy donor monocytes resulted in a significantly higher inhibition of fMLF-induced monocyte polarization than did incubation with control low-M _r factor (a mean of 42 versus 16% inhibition). This suppressive effect of patient low-M _r factor was abrogated with a mixture of two monoclonal antibodies against p15E as well as with TP-1. The observations here reported on the in vitro effects of TP-1 on depressed monocyte and dendritic cell function in HNSCC have provided one of the rationales for a TP-1 therapeutic pilot trial recently started in HNSCC patients.     

On the reliability of Ponar grab samples for the quantitative study of benthic invertebrates in ponds

We present observations on the variability of sediment penetration depth by the Ponar grab sampler, which lead us to question the reliability of grab samples in the quantitative study of freshwater benthos. Penetration depth of the Petite Ponar grab depends on substrate type, and correlates with the amount of organic carbon, the water content and the granulometry of the sediment. Since these factors can also influence faunal composition and vertical distribution in the sediment, it is important to study the performance of the sampler before a biological explanation for the observed pattern is given. At the site studied, a case study was performed, in which variable grab penetration did not influence biological interpretation because the penetration depth of the grab followed that of the organisms under study.Research Assistant of the Belgian National Fund for Scientific Research (N.F.W.O.)Research Assistant of the Belgian National Fund for Scientific Research (N.F.W.O.)     

The oxygen uptake of Sarotherodon niloticus L. and the oxygen binding properties of its blood and hemolysate (Pisces: Cichlidae)

The oxygen consumption of Sarotherodon niloticus L. was found to decline below a critical oxygen concentration of about 2 mg O2/l. An important influence of CO2 on the oxygen affinity of whole blood was observed at all temperatures between 20 and 35 degrees C for gas mixtures containing 5.6% CO2. Purified hemolysate showed extremely high oxygen affinities (p50 = 1.08 mmHg at pH 8.2 and 20 degrees C). Low cooperativity was observed at all temperatures from 20 to 35 degrees C, and pH values between 6.5 and 8.2. The Bohr effect proved to be important at pH values lower than pH 7.5 (phi = delta log P50/delta pH = -0.58 between pH 6.5 and 7.0 at 35 degrees C). The oxygen affinities show high thermal sensitivity without a marked pH influence (delta H value for overall oxygenation at pH was -71.7 kJ/mol). The obtained results are interpreted as adaptations to diurnal variations in ambient temperature and oxygen availability.     

Metapopulation viability of an endangered holoparasitic plant in a dynamic landscape

By creating transient patch mosaics, disturbance can influence the dynamics of interacting populations in many ecosystems. In European heathland, traditional land use created such dynamic systems favourable for both early and later successional species. Little empirical evidence is, however, available on the impact of current management on metapopulations occurring in such landscapes. This paper looks at the metapopulation viability of the endangered holoparasite Cuscuta epithymum, a species that typically occurs in early successional stages of recently managed heathlands. We used both observational and experimental data from a 4‐yr study to parameterise a spatially explicit metapopulation model. This model explores the impact of demographic characteristics and spatiotemporal landscape patterns created by management events on metapopulation viability. Both occasional long‐distance dispersal and dormant seeds are shown to be critical for the long‐term survival of C. epithymum in a dynamic heathland landscape subjected to a fixed rotational mowing of 15 yr. A relatively high management frequency (<15 yr between two consecutive mowing events) appeared to be necessary to sustain a viable C. epithymum metapopulation. When there is a longer interval between management events, grazing can counterbalance the negative effects of vegetation succession. Our results indicate that small‐scale cyclical management events combined with extensive grazing are the most appropriate management strategy to maintain viable populations of C. epithymum instead of the current large‐scale management events. Our results further emphasise the importance of incorporating both spatiotemporal patch availability and key demographic characteristics, especially seed banks, for a realistic view of metapopulation dynamics in disturbed landscapes. This study clearly demonstrates the usefulness of metapopulation models to understand the impact of management events and to provide new ecological insights into processes acting at a landscape scale.