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Predation Effects (predation + effects)

Distribution by Scientific Domains
Life Sciences100%

Selected Abstracts

Survival of Escherichia coli O157:H7 in private drinking water wells: influences of protozoan grazing and elevated copper concentrations

FEMS MICROBIOLOGY LETTERS, Issue 1 2002
Rebekka R.E Artz
Abstract The survival characteristics of Escherichia coli O157:H7 in private drinking water wells were investigated to assess the potential for human exposure. A non-toxigenic, chromosomally lux -marked strain of E. coli O157:H7 was inoculated into well water from four different sites in the North East of Scotland. These waters differed significantly in their heavy metal contents as well as nutrient and bacterial grazer concentrations. Grazing and other biological factors were studied using filtered (3 and 0.2 ,m) and autoclaved water. The survival of E. coli O157:H7 was primarily decreased by elevated copper concentrations. This hypothesis was supported by acute toxicity assay data. In addition, significant protozoan predation effects were observed in untreated water when compared with survival rates in filtered water. The combination of these two factors in particular determines the survival time of the pathogen in a private water well. It therefore appears that wells with higher water quality as assessed using the European Union Drinking Water Directive standards will also allow survival of E. coli O157:H7 for much longer periods. [source]

Long-term responses of zooplankton to invasion by a planktivorous fish in a subarctic watercourse

FRESHWATER BIOLOGY, Issue 1 2009
PER-ARNE AMUNDSEN
Summary 1.,Introduced or invading predators may have strong impacts on prey populations of the recipient community mediated by direct and indirect interactions. The long-term progression of predation effects, covering the invasion and establishment phase of alien predators, however, has rarely been documented. 2.,This paper documents the impact of an invasive, specialized planktivorous fish on its prey in a subarctic watercourse. Potential predation effects on the crustacean plankton, at the community, population and individual levels, were explored in a long-term study following the invasion by vendace (Coregonus albula). 3.,Over the 12-year period, the density and species richness of zooplankton decreased, smaller species became more abundant and Daphnia longispina, one of the largest cladocerans, was eliminated from the zooplankton community. 4.,Within the dominant cladocerans, including Daphnia spp., Bosmina longispina and Bosmina longirostris, the body size of ovigerous females and the size at first reproduction decreased after the arrival of the new predator. The clutch sizes of Daphnia spp. and B. longirostris also increased. 5.,Increased predation pressure following the vendace invasion induced many effects on the crustacean zooplankton, and we document comprehensive and strong direct and indirect long-term impacts of an introduced non-native predator on the native prey community. [source]

Reproductive potential and seedling establishment of the invasive alien tree Schinus molle (Anacardiaceae) in South Africa

AUSTRAL ECOLOGY, Issue 6 2009
DONALD M. IPONGA
Abstract Schinus molle (Peruvian pepper tree) was introduced to South Africa more than 150 years ago and was widely planted, mainly along roads. Only in the last two decades has the species become naturalized and invasive in some parts of its new range, notably in semi-arid savannas. Research is being undertaken to predict its potential for further invasion in South Africa. We studied production, dispersal and predation of seeds, seed banks, and seedling establishment in relation to land uses at three sites, namely ungrazed savanna once used as a military training ground; a savanna grazed by native game; and an ungrazed mine dump. We found that seed production and seed rain density of S. molle varied greatly between study sites, but was high at all sites (384 864,1 233 690 seeds per tree per year; 3877,9477 seeds per square metre per year). We found seeds dispersed to distances of up to 320 m from female trees, and most seeds were deposited within 50 m of putative source trees. Annual seed rain density below canopies of Acacia tortillis, the dominant native tree at all sites, was significantly lower in grazed savanna. The quality of seed rain was much reduced by endophagous predators. Seed survival in the soil was low, with no survival recorded beyond 1 year. Propagule pressure to drive the rate of recruitment: densities of seedlings and sapling densities were higher in ungrazed savanna and the ungrazed mine dump than in grazed savanna, as reflected by large numbers of young individuals, but adult : seedling ratios did not differ between savanna sites. Frequent and abundant seed production, together with effective dispersal of viable S. molle seed by birds to suitable establishment sites below trees of other species to overcome predation effects, facilitates invasion. Disturbance enhances invasion, probably by reducing competition from native plants. [source]

Variable strength of top-down effects in Nothofagus forests: bird predation and insect herbivory during an ENSO event

AUSTRAL ECOLOGY, Issue 4 2009
C. NOEMI MAZIA
Abstract Predators are thought to play a key role in controlling herbivory, thus having positive indirect effects on plants. However, evidence for terrestrial trophic cascades is still fragmentary, perhaps due to variation in top-down forces created by environmental heterogeneity. We examined the magnitude of predation effects on foliar damage by chewing insects and mean leaf size, by excluding birds from saplings in ,dry' and ,wet'Nothofagus pumilio forests in the northern Patagonian Andes, Argentina. The experiment lasted 2 years encompassing a severe drought during the La Niņa phase of a strong El Niņo/Southern Oscillation event, which was followed by unusually high background folivory levels. Insect damage was consistently higher in wet than in dry forest saplings. In the drought year (1999), bird exclusion increased folivory rates in both forests but did not affect tree leaf size. In the ensuing season (2000), leaf damage was generally twice as high as in the drought year. As a result, bird exclusion not only increased the extent of folivory but also significantly decreased sapling leaf size. The latter effect was stronger in the wet forest, suggesting compensation of leaf area loss by dry forest saplings. Overall, the magnitude of predator indirect effects depended on the response variable measured. Insectivorous birds were more effective at reducing folivory than at facilitating leaf area growth. Our results indicate that bird-initiated trophic cascades protect N. pumilio saplings from insect damage even during years with above-normal herbivory, and also support the view that large-scale climatic events influence the strength of trophic cascades. [source]