Differential response of nematode colonist communities to the intertidal placement of dredged material

The use of fine-grained maintenance dredged material for habitat enhancement has increased in recent years, particularly recharge schemes which provide a means of combating the erosion of intertidal flats and saltmarsh. This article investigates the development of meiofaunal nematode communities following a natural experiment in 2003, when fine-grained dredged material was deposited concurrently at four adjacent intertidal recharge sites on the southeast coast of the United Kingdom. A 12-month survey of nematode assemblages was carried out to compare univariate, multivariate, allometric and functional attributes of colonist communities in relation to the different environmental conditions prevailing at the four sites. Developing assemblages were increasingly affected by the spatial differences in the elevation, consolidation and exposure of bed material. The results indicated that the colonisation sequence was the result of random settling of suspended nematodes, sequential reproduction and differential survival and reproductive success of colonising species. For the first time, this experiment provided insights into the development of adaptive and functional types of meiofaunal nematodes following the intertidal deposition of uncontaminated fine-grained dredged material. This, in turn, will contribute considerably to the development of ecological models of the evolution of the large-scale placement of muddy dredged material in the intertidal environment.     

Expression of parasite virulence at different host population densities under natural conditions

It has recently been suggested that the expression of parasite virulence depends on host population density, such that infected hosts have a higher sensitivity to density, and thus reach their carrying capacity earlier than uninfected hosts. In this scenario, parasite-induced reduction in fitness (i.e., virulence) increases with host density. We tested this hypothesis experimentally, using outdoor mesocosm populations of Daphnia magna infected by the microsporidian Octosporea bayeri. Contrary to the prediction, virulence was independent of host density. In a competition experiment with initial prevalence of 50%, O. bayeri reduced the competitive ability of infected Daphnia within the asexual growth phase independent of initial host population density. In an additional experiment we set up populations with 100% and 0% prevalence and followed their population dynamics over the whole season. Consistent with the competition experiment, we found no difference in population dynamics within the asexual growth phase of the host, suggesting that infected hosts are not more sensitive to density than uninfected hosts. The additional experiment, however, included more than the initial growth phase as did the competition experiment. Eventually, after 100 days, 100% infected populations assumed a reduced carrying capacity compared to uninfected populations. We identify and discuss three reasons for the discrepancy between our experiment and the predictions.     

Ecotype-specific improvement of nitrogen status in European grasses after drought combined with rewetting

Drought stress and associated low soil moisture can decrease N status of forage plants by reducing nitrogen (N) uptake. Conversely, rainfall and associated favorable soil moisture can improve plant N status. Yet, it is unclear to which degree drought combined with rewetting can buffer negative effects of drought on N status of forage plants and their populations. Here, we compared shoot N status (N concentration, total N uptake and C/N ratio) of four temperate grass species. Particularly, we investigated ecotypes (populations) grown from seeds from four to six European provenances/species after a drought treatment combined with rewetting (10 day harvest delay) versus continuously watered conditions for control.The experimental combination of drought and rewetting significantly increased shoot N concentration (+96%), N uptake (+31%); and decreased C/N ratio (−46%), biomass production (−29%) and C concentration (−1.4%) compared to control. Shoot N status was found to be different between target grass species and also within their populations under drought combined with rewetting treatment. Presumably drought-adapted populations did not perform better than populations from moist sites indicating no evidence of local adaptation.The drought combined with rewetting event could buffer the negative effects of drought. Shoot N status of grasses after drought and rewetting even exceeded control plants. This surprising finding can potentially be explained by higher N uptake, lack of growth dilution effects or delayed plant maturation. Furthermore, within-species shoot N status responses to drought combined with rewetting event were ecotype-specific, hinting at diverse responses of different population. For rangeland management, we recommend that if a drought event occurs during the growing season, harvesting should be delayed beyond a following rain event.     

Small rodent winter survival: snow conditions limit access to food resources

1. In Fennoscandia during winter small rodents spend most of their time in the subnivean space, between the snow cover and the ground. The subnivean space is probably not a uniform habitat, but broken into accessible and inaccessible patches by ice covering the vegetation. This might reduce access to otherwise available food resources. 2. To test whether ice formations reduce access to food and thus limit winter survival of small rodents, we conducted an experiment where we increased subnivean space by adding corrugated aluminium sheets on the ground before onset of winter. The sheets prevented ice formation, thus mimicking natural occurring subnivean space, and providing more room for animals living in the subnivean space to forage. 3. During the experiment 142 Microtus oeconomus were passive induced transponder (PIT)-tagged, and a system consisting of fixed tube-shaped antennas and PIT-tag readers were used to provide data to analyse winter survival and individual subnivean space use. The extent of winter grazing was measured after snow melt by examining percentage area grazed. 4. The treatment resulted in increased survival which corresponded well with significantly higher space use and more grazing under the sheets. 5. Females showed a positive correlation between probability of survival and body mass while no such effect was observed in males. 6. The results suggest that the snow cover reduces survival in winter by physically enclosing the vegetation in ice and thus reducing access to otherwise available food resources. The amount of ice and its configuration might vary between years due to changing weather patterns. Our results offer a mechanistic explanation for variations in winter survival and suggest incorporating climate variables in future small rodent models. 7. Directional and long-term changes in climate might result in increased ice formation in the subnivean system. Such deterioration may lead to reduced winter survival and act by stabilizing population dynamics and dampening vole cyclicity.     

Investigation of Micro-wear and Micro-friction Properties for Bionic Non-smooth Concave Components

Five kinds of 45^# steel samples with concave features on the surface were manufactured using Laser Texturing Technology (LIT). Optimum design theory was used to design the experiment, and a two-level orthogonal table-L16 (2^15) design was adopted , Micro-wear and micro-friction experienced by samples with concave surface features and samples with smooth surfaces were compared experimentally. The wear resistance of samples with concave surface features was increased most,and different surface morphologies had different effects on f~iction and wear properties.     

Evolving Scientific Epistemologies and the Artifacts of Empirical Philosophy of Science: A Reply Concerning Mesosomes

In a 1993 paper, I argued that empirical treatments of the epistemologyused by scientists in experimental work are too abstract in practice tocounter relativist efforts to explain the outcome of scientificcontroversies by reference to sociological forces. This was because, atthe rarefied level at which the methodology of scientists is treated byphilosophers, multiple mutually inconsistent instantiations of theprinciples described by philosophers are employed by contestingscientists. These multiple construals change within a scientificcommunity over short time frames, and these different versions ofscientific methodology can determine the outcome of a controversy. Iillustrated with a comparatively detailed analysis of the methodologyused by biologists debating the existence of an entity called thebacterial mesosome between the mid-1950s and the mid-1970s. This 1993piece has drawn several critiques in the philosophical literature. Inthis present piece I respond to these critiques and argue that they failto address the core argument of the original paper, and I reflectfurther on the methodologies of philosophers of science pursuingempirical or `naturalistic' epistemology.