Assessment of European streams with diatoms, macrophytes, macroinvertebrates and fish: a comparative metric-based analysis of organism response to stress

1. Periphytic diatoms, macrophytes, benthic macroinvertebrates and fish were sampled with standard methods in 185 streams in nine European countries to compare their response to degradation. Streams were classified into two main stream type groups (i.e. lowland, mountain streams); in addition, the lowland streams were grouped into four more specific stream types. 2. Principal components analysis with altogether 43 environmental parameters was used to construct complex stressor gradients for physical–chemical, hydromorphological and land use data. About 30 metrics were calculated for each sample and organism group. Metric responses to different stress types were analysed by Spearman Rank Correlation. 3. All four organism groups showed significant response to eutrophication/organic pollution gradients. Generally, diatom metrics were most strongly correlated to eutrophication gradients (85% and 89% of the diatom metrics tested correlated significantly in mountain and lowland streams, respectively), followed by invertebrate metrics (91% and 59%). 4. Responses of the four organism groups to other gradients were less strong; all organism groups responded to varying degrees to land use changes, hydromorphological degradation on the microhabitat scale and general degradation gradients, while the response to hydromorphological gradients on the reach scale was mainly limited to benthic macroinvertebrates (50% and 44% of the metrics tested correlated significantly in mountain and lowland streams, respectively) and fish (29% and 47%). 5. Fish and macrophyte metrics generally showed a poor response to degradation gradients in mountain streams and a strong response in lowland streams. 6. General recommendations on European bioassessment of streams were derived from the results.     

Differential mortality of wintering shorebirds on the Banc d'Arguin, Mauritania, due to predation by large falcons

Predators may influence many aspects of the daily life and seasonal movements of their prey. Here we quantify direct, and evaluate indirect effects of predation by three falcon species (Lanner Falcon Falco biarmicus , Barbary Falcon Falco pelegrinoides and Peregrine Falcon Falco peregrinus ) on coastal shorebirds wintering on the Banc d'Arguin, Mauritania, an area hosting approximately 30% of the East Atlantic Flyway population of shorebirds. On the basis of 754 h of observation over five winters, 97 witnessed attacks and 585 collected prey remains, we show that shorebirds were safer in larger flocks, which tended to be attacked less often. Furthermore, species that forage relatively close to shore and in small flocks were depredated more often than expected from their relative abundance. In three species, Red Knot Calidris canutus canutus , Bar-tailed Godwit Limosa lapponica taymyrensis and Dunlin Calidris alpina , the juveniles were more vulnerable than adults. We estimated that on average 1% of the juvenile and 0.1% of the adult Red Knots present were killed by large falcons each winter. For Red Knots we simultaneously quantified annual survival on the basis of an individual colour-marking programme: mortality due to predation by falcons accounted for an estimated 6.2% (juveniles) and 0.8% (adults) of annual mortality. We suggest that juvenile Red Knots are 10 times as likely to be killed by falcons because they use riskier habitats, i.e. early and late tide foraging areas closer to shores where surprise attacks are both more common and more successful. These results indicate that the strength of indirect effects of predation operating in a shorebird population largely outweigh the effects of mortality per se .     

Multiplication and distribution of iris severe mosaic virus in secondarily-infected iris bulbs after stress induced by heat and wounding

In freshly-lifted iris bulbs infected with iris severe mosaic virus (ISMV), virus was not always detected in the basal plate and rarely in bulb scale tissue. After exposing the bulbs to stress (wounding or high-temperature treatment) the sensitivity of virus detection was enhanced. The improved detection of viral antigen after local stress (wounding) coincided with an increase of viral RNA synthesis. When general stress (high-temperature treatment) was applied, the virus could be reliably detected in the basal plate, and usually in vascular bundles and surrounding tissue. Virus was detected in the upper part of the bulb scale when such tissues were detached from the basal plate. Thus, virus must have been present in the scales in localised spots, albeit at a very low concentration, and multiplication is likely to be the main factor involved in the improved sensitivity of viral detection. The distribution of ISMV in the bulb after local or general stress treatment is discussed.     

Taxon-specific reaction norms to predator cues in a hybrid Daphnia complex

1. Previous studies have shown that interspecific hybridisation is common among taxa from the Daphnia galeata/hyalina/cucullata species complex. We investigated the influence of predator kairomones on the morphology and life histories of nine clones belonging to three taxa (pure D. galeata, F₁ hybrids between D. galeata and D. hyalina, and backcrossed D. hyalina) of this species complex. Predators exerting positive (fish) and negative (Chaoborus larvae) size‐selective predation were tested. 2. The most responsive traits were size at maturity and size of neonates. Despite large between‐clone variation, discriminant analysis revealed that the three taxa were distinct from each other in key life‐history traits. F₁ hybrids did not react in an intermediate way compared to the other taxa: the multivariate distances between F₁ hybrids and either taxon were larger than between pure D. galeata and backcrossed D. hyalina. 3. The average plasticity (calculated across all traits) was similar for all three taxa. With regard to the size at maturity and neonate body size, the strength of the response was a function of the intrinsic values of these traits expressed in the control. For example, for size at maturity, smaller individuals showed a significantly stronger reaction to Chaoborus kairomones than larger ones. 4. Finally, we monitored seasonal changes in body size, egg number and population density of pure D. galeata and F₁ hybrids in Greifensee (Switzerland). The two taxa experienced similar seasonal changes in body size but, on some sampling dates, they differed in mean egg number. The observed seasonal changes in Daphnia body size were consistent with what would be expected if the predator assemblage shifted from fish to Chaoborus over the course of the summer. The fluctuations in the frequencies of Daphnia taxa, however, were not related to seasonal variation in Daphnia body size. 5. Experimental data suggest that temporally heterogeneous predation regimes might be an important condition stabilising the co‐occurrence of Daphnia hybrids with parental taxa. Predation regimes, however, cannot solely explain dynamic changes in taxon frequency in Greifensee.     

Influence of growth rate retardation on time budgets and energetics of Arctic Tern Sterna paradisaea and Common Tern S. hirundo chicks

Time budgets of free-living chicks of Arctic Terns Sterna paradisaea and Common Terns S. hirundo throughout development are presented with special reference to changes in time allocation when growth rate varies. Chicks of both species were inactive most of the time observed (87%). Time allocated to the different behaviours changed during development and was generally better correlated with body mass than age. Slower growing nestlings were brooded more and allocated more time to quiescence and less time to locomotion, preening, begging and attacking (the latter two significant only for the Arctic Tern). The energetic implications of variation in time budgets with age and growth rate were considered. Parental brooding resulted in an average energy saving of nearly 40% of an individual nestling's thermoregulatory costs. Whereas thermoregulatory costs remained nearly unchanged in Arctic Tern chicks, these were negatively correlated with growth rate in Common Terns. Tentatively, we estimated a 30% reduction in a nestling's total energy requirement for a 50% reduction in average growth rate for both species.     

Higher parasite resistance in Daphnia populations with recent epidemics

Natural populations often show genetic variation in parasite resistance, forming the basis for evolutionary response to selection imposed by parasitism. We investigated whether previous epidemics selected for higher resistance to novel parasite isolates in a Daphnia galeata–microparasite system by comparing susceptibility of host clones from populations with varying epidemic history. We manipulated resource availability to evaluate whether diet influences Daphnia susceptibility as epidemics are common in nutrient‐rich lakes. Exposing clones from 10 lakes under two food treatments to an allopatric protozoan parasite, we found that Daphnia originating from lakes (mainly nutrient rich) with previous epidemics better resist infection. Despite this result, there was a tendency of higher susceptibility in the low food treatment, suggesting that higher resistance of clones from populations with epidemic background is not directly caused by lake nutrient level. Rather, our results imply that host populations respond to parasite‐mediated selection by evolving higher parasite resistance.