Predator-prey interactions between brown trout Salmo trutta and native and introduced amphipods; their implications for fish diets

An attempt to improve the food base for brown trout Salmo trutta in Northern Ireland was made in 1958.59 by deliberately introducing English Gammarus pulex into several Irish rivers. In addition. another amphipod Crangonyx pseudogracilis, was later accidently introduced into II ish waters. Our study represents the first attempt to examine the trophic interactions between a native fish predator (S. trutta) and an array of these native (Gammarus duebeni celticus) and introduced (G. pulex and C. pseudogracilis) amphipods. Feeding experiments, involving young brown trout predators and ampiphod prey, revealed that the fish actively selected C. pseudogracilis relative to two alternative Gammarus prey species. Although the trout encountered the Gammarus species more than C. pseudogracilis, they were eaten less than Crangonyx. Difficulties in handling and ingestion of Gammarus by trout may be a. key component of the preference fbr the smaller, more easily handled Crangonyx. The microdistribution of the species was altered by the fish, due to predation being greater in particular microhabitats, Our study showed that the introduction of the herbivorous C. pseudogracilis into Irish freshwaters may represent a useful addition to fish diets. particularly for small and/or juvenile fish. The reprecussions of the deliberate introduction of G. pulex are less clear. It may improve feeding for fish. but only if it can coexist with indigenous macroinvertebrates and thus ultimately improve the range and quantity of possible food items in predator diets. Alternatively, being highly predatory towards other macroinvertebrates including G. d. celticus and C. pseudogracilis. G. pulex may be deleterious to the diversity of the resident benthic community and hence reduce the diversity of prey available to fish predators.

The effect of increased dietary fruit and vegetable consumption on endothelial activation, inflammation and oxidative stress in hypertensive volunteers

Background and aims

Public health campaigns recommend increased fruit and vegetable (FV) consumption as an effective means of cardiovascular risk reduction. During an 8 week randomised control trial among hypertensive volunteers, we noted significant improvements in endothelium-dependent vasodilatation with increasing FV consumption. Circulating indices of inflammation, endothelial activation and insulin resistance are often employed as alternative surrogates for systemic arterial health. The responses of several such biomarkers to our previously described FV intervention are reported here.
Methods and results

Hypertensive volunteers were recruited from medical outpatient clinics. After a common 4 week run-in period during which FV consumption was limited to 1 portion per day, participants were randomised to 1, 3 or 6 portions daily for 8 weeks. Venous blood samples for biomarker analyses were collected during the pre and post-intervention vascular assessments. A total of 117 volunteers completed the 12 week study. Intervention-related changes in circulating levels of high sensitivity C-reactive protein (hsCRP), soluble intracellular adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), von Willebrand factor (vWF) and plasminogen activator inhibitor-1 (PAI-1) did not differ significantly between FV groups. Similarly, there were no significant between group differences of change in homeostasis model assessment (HOMA) scores.
Conclusions

Despite mediating a significant improvement in acetylcholine induced vasodilatation, increased FV consumption did not affect a calculated measure of insulin resistance or concentrations of the circulating biomarkers measured during this study. Functional indices of arterial health such as endothelium-dependent vasomotion are likely to provide more informative cardiovascular end-points during short-term dietary intervention trials.

Interactions between invasive and native crustaceans: differential functional responses of intraguild predators towards juvenile hetero-specifics

Intraguild predation (IGP) between invasive and native species can lead to species exclusions or co-existence, dependent on the direction and strength of the interaction. Recently, derivation of 'functional responses' has been identified as a means of comparing the community impacts of invasive and native species. Here, we employ a novel use of this functional response methodology to evaluate any IGP asymmetries between the invasive Ponto-Caspian amphipod Echinogammarus ischnus and the North American native Gammarus fasciatus. The direction and magnitude of intraguild predation of adult males on hetero-specific adult females has previously been shown to reverse across a water conductivity gradient. This partially explains field patterns, but does not predict the co-existence of the two species observed in many habitats and locations. Here, we compared intraguild predation by both species on each other's juveniles in high- and low- conductivity water. G. fasciatus has a higher type II functional response towards E. ischnus juveniles compared to the reciprocal interaction. Conductivity did not influence the predation rate on juveniles of either E. ischnus or G. fasciatus. Thus, the male/female IGP advantage to the native G. fasciatus in low conductivity water is compounded by a juvenile IGP asymmetry, which also counteracts the male/female IGP advantage to E. ischnus in high conductivity waters, helping to explain field patterns of exclusion and co-existence. Thus, complex asymmetries in mutual IGP associated with inherent species differences, environmental modulation, and life-history effects can help us understand and predict the population and community level outcomes of species invasions.

Trophic interactions and consequent impacts of the invasive fish Pseudorasbora parva in a native aquatic foodweb: a field investigation in the UK

Introduction of the invasive Asian cyprinid fish Pseudorasbora parva into a 0.3 ha pond in England with a fish assemblage that included Cyprinus carpio, Rutilus rutilus and Scardinius erythrophthalmus resulted in their establishment of a numerically dominant population in only 2 years; density estimates exceeded 60 ind. m(-2) and they comprised > 99% of fish present. Stable isotope analysis (SIA) revealed significant trophic overlap between P. parva, R. rutilus and C. carpio, a shift associated with significantly depressed somatic growth in R. rutilus. Despite these changes, fish community composition remained similar between the ponds. Comparison with SIA values collected from an adjacent pond free of P. parva revealed a simplified food web in P. parva presence, but with an apparent trophic position shift for several fishes, including S. erythrophthalmus which appeared to assimilate energy at a higher trophic level, probably through P. parva consumption. The marked isotopic shifts shown in all taxa in the P. parva invaded pond (C-13-enriched, N-15 depleted) were indicative of a shift to a cyanobacteria-dominated phytoplankton community. These findings provide an increased understanding of the ecological consequences of the ongoing P. parva invasion of European freshwater ecosystems.

Barriers to increasing fruit and vegetable intakes in the older population of Northern Ireland: low levels of liking and low awareness of current recommendations

Objective: To investigate barriers to increasing fruit and vegetable (f + v) intakes in a large sample of the older population of Northern Ireland (NI), in relation to current intakes.