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123.
Non-host organisms affect transmission processes in two common trematode parasites of rocky shores 总被引:1,自引:0,他引:1
Katrin Prinz Thomas C. Kelly Ruth M. O’Riordan Sarah C. Culloty 《Marine Biology》2009,156(11):2303-2311
The transmission of free-living trematode stages is mediated by various environmental factors, of which the presence of ambient
organisms within the host space is a potential major determinant. In two laboratory mesocosm experiments, we investigated
the influence of four intertidal rocky shore species on transmission success of cercariae of the digenean trematodes Echinostephilla
patellae (encysting in the tissue of blue mussels Mytilus edulis) and Parorchis
acanthus (encysting on mussel shells). Encystment success of both parasite species was significantly lower in the presence of test
organisms when compared to controls. Observations revealed that barnacles Austrominius
modestus actively filtered cercariae, whereas the larvae were obstructed by the seaweeds Corallina
officinalis and Fucus
serratus. Anemones Actinia
equina both physically disturbed and consumed cercariae. In a further laboratory experiment, grazing gastropods (Littorina
littorea, Patella
vulgata, and Gibbula
umbilicalis) were found to significantly reduce the numbers of P. acanthus metacercariae in artificially prepared dishes by ingestion of cysts. Our results suggest that non-host organisms may play
a key role in regulating the transmission of free-living trematode stages in rocky shore ecosystems, which is especially important
with regard to the relative diversity and density of species in these habitats. The findings also emphasize the need to include
parasites into marine food webs, since cercariae seem to be consumed by certain organisms to a considerable extent and could
possibly represent an important energy source. 相似文献
124.
Katrin M. Meyer Wolf M. Mooij Matthijs Vos W.H. Gera Hol Wim H. van der Putten 《Ecological modelling》2009,220(19):2594-2597
Addressing complex ecological research questions often requires complex empirical experiments. However, due to the logistic constraints of empirical studies there is a trade-off between the complexity of experimental designs and sample size. Here, we explore if the simulation of complex ecological experiments including stochasticity-induced variation can aid in alleviating the sample size limitation of empirical studies. One area where sample size limitations constrain empirical approaches is in studies of the above- and belowground controls of trophic structure. Based on a rule- and individual-based simulation model on the effect of above- and belowground herbivores and their enemies on plant biomass, we evaluate the reliability of biomass estimates, the probability of experimental failure in terms of missing values, and the statistical power of biomass comparisons for a range of sample sizes. As expected, we observed superior performance of setups with sample sizes typical of simulations (n = 1000) as compared to empirical experiments (n = 10). At low sample sizes, simulated standard errors were smaller than expected from statistical theory, indicating that stochastic simulation models may be required in those cases where it is not possible to perform pilot studies for determining sample sizes. To avoid experimental failure, a sample size of n = 30 was required. In conclusion, we propose that the standard tool box of any ecologist should comprise a combination of simulation and empirical approaches to benefit from the realism of empirical experiments as well as the statistical power of simulations. 相似文献
125.
Avian magnetic compass: fast adjustment to intensities outside the normal functional window 总被引:1,自引:0,他引:1
To determine how fast birds can adapt to magnetic intensities outside the normal functional window of their magnetic compass,
we tested migratory birds in a magnetic field of 92,000 nT, twice the intensity of the local geomagnetic field at the test
site in Frankfurt a.M., Germany. In the local field, robins showed a significant preference of their southerly migratory direction,
whereas in the 92,000-nT field, they were initially disoriented. However, when the birds were preexposed to 92,000 nT for
1 h before being tested, they were able to orient under this intensity, and their behavior did not differ from that in the
geomagnetic field. These data show that birds require only a short time to adjust to magnetic intensities, which they cannot
spontaneously use for orientation. Interpreting these findings in view of the radical pair model (Ritz et al. 2000), this means that they can learn rather quickly to interpret novel activation patterns on their retina. 相似文献
126.
Fertilization exceeding crop requirements causes an accumulation of phosphorus (P) in soils, which might increase concentrations of dissolved and colloidal P in drainage. We sampled soils classified as Typic Haplorthods from four fertilization experiments to test (i) whether increasing degrees of phosphorus saturation (DPS) increase concentrations of dissolved and colloidal P, and (ii) if critical DPS levels can be defined for P release from these soils. Oxalate-extractable concentrations of P, iron (Fe), and aluminum (Al) were quantified to characterize DPS. Turbidity, zeta potential, dissolved P, and colloidal P, Fe, Al, and carbon (C) concentrations were determined in water and KCl extracts. While concentrations of dissolved P decreased with increasing depth, concentrations of water-extractable colloidal P remained constant. In topsoils 28 +/- 17% and in subsoils 94 +/- 8% of water-extractable P was bound to colloids. Concentrations of dissolved P increased sharply for DPS > 0.1. Colloidal P concentrations increased with increasing DPS because of an additional mobilization of colloids and due to an increase of the colloids P contents. In addition to DPS, ionic strength and Ca(2+) affected the release of colloidal P. Hence, using KCl for extraction improved the relationship between DPS and colloidal P compared with water extraction. Accumulation of P in soils increases not only concentrations of dissolved P but also the risk of colloidal P mobilization. Leaching of colloidal P is potentially important for inputs of P into water bodies because colloidal P as the dominant water-extractable P fraction in subsoils was released from soils with relatively low DPS. 相似文献