Arthropod generalist predators (AGP) are widespread and abundant in both aquatic and terrestrial ecosystems. They feed upon herbivores, detritivores, and predators, and also on plant material and detritus. In turn, AGP serve as prey for larger predators. Several prominent AGP have become invasive when moved by humans beyond their native range. With complex trophic roles, AGP have diverse effects on other species in their introduced ranges. The invaders displace similar native species, primarily through competition, intraguild predation, transmission of disease, and escape from predation and/or parasites. Invasive AGP often reach higher densities and/or biomass than the native predators they replace, sometimes strengthening herbivore regulation when invasive AGP feed on key herbivores, but sometimes weakening herbivore suppression when they eat key predators. The complexity and unpredictability of ecological effects of invasive AGP underscores the high risk of adverse consequences of intentional introductions of these species (e.g., for biological control or aquaculture).

Ecological Effects of Invasive Arthropod Generalist Predators

Scientific names: Acer negundo L., Aceraceae. Synonyms: Negundo aceroides Moench (1794), Negundo fraxinifolium (Nutt.) DC. (1824). Common names: Box-elder, ash-leaved maple, manitoba maple (GB and US), Eschen-Ahorn (DE), askbladet lon (DK), saarvaher (EE), Saarnivaahtera (FI), askhlynur (IS), uosialapis klevas (LT), Oslapu kļava (LV), Vederesdoorn (NL), asklonn (NO), klon jesionolistny, jesioklon (PL), asklonn (SE).

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NOBANIS -Invasive Alien Species Fact Sheet

Despite the common view that conditions in winter strongly influence survival and population size of fish, the ecology of salmonids has not been as extensively studied in winter as in other seasons. In this paper, we review the latest studies on salmonid winter survival, habitat use, movement and biotic interactions as they relate to the prevailing physical and habitat conditions in rivers and streams. The majority of research conducted on the winter ecology of salmonids has been carried out in small rivers and streams, where temperatures are above zero and where there is no ice. Investigations in large rivers, regulated and dredged rivers, and under conditions of different ice formations are almost totally lacking, presumably related to sampling difficulties with these systems. The studies-at-hand indicate that a multitude of physical and biological factors affect the survival, behavior, and habitat use of salmonids in winter. The general concept that winter functions as a critical period for the survival of young salmonids is not well supported by the literature. Instead, overwinter survival of juvenile fish appears to be context-dependent, related to specific habitat characteristics and ice regimes of streams. In general, over wintering salmonids prefer sheltered, low velocity microhabitats, are mainly nocturnal, and interact relatively little with conspecifics or interspecifics. Specific descriptions of microhabitat preferences of salmonids are difficult to make due to highly disparate results from the literature. We suggest that future research should be directed towards (1) being able to predict the dynamics of freezing and ice processes at different scales, especially at the local scale, (2) studying fish behavior, habitat use and preference under partial and full ice cover, (3) evaluating the impacts of man-induced environmental modifications (e. g. flow regulation, land-use activities) on the ecology of salmonids in winter, and (4) identifying methods to model and assess winter habitat conditions for salmonids. Copyright © 2007 John Wiley & Sons, Ltd.

Life in the ice lane : the winter ecology of stream salmonids

Spatial and temporal variability of streambed hydraulic conductivity in West Bear Creek, North Carolina, USA

Beaver (Castor canadensis) mitigate the effects of climate on the area of open water in boreal wetlands in western Canada

The genus Castor comprises two species: the Eurasian beaver Castor fibre , and the North American beaver Castor canadensis . Both species suffered from overexploitation, but have seen a revival since the 1920s due to increased protection and reintroduction programmes. Increases in the populations and distributions of species that are able to modify ecosystems have generated much scientific interest. Here we review the available literature concerning the possible ecological impact of beaver species in the Old and New World. 2. Beavers, being ecosystem engineers, are among the few species besides humans that can significantly change the geomorphology, and consequently the hydrological characteristics and biotic properties of the landscape. In so doing, beavers increase heterogeneity, and habitat and species diversity at the landscape scale. Beaver foraging also has a considerable impact on the course of ecological succession, species composition and structure of plant commu- nities, making them a good example of ecologically dominant species (e.g. keystone species). 3. Nevertheless, the strength of beavers' impact varies from site to site, depending on the geographical location, relief and the impounded habitat type. Consequently, they may not be significant controlling agents of the ecosystem in all parts of their distribution, but have strong interactions only under certain circumstances. We suggest that beavers can create important management opportunities in the Holarctic, and this review will help land man- agers determine the likely outcome of beaver activity.

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Ecological impact of beavers Castor fiber and Castor canadensis and their ability to modify ecosystems

Three separate effects on refuge use by signal crayfish Pacifastacus leniusculus and Atlantic salmon Salmo salar were examined: (1) the effect on Atlantic salmon of an addition of signal crayfish (doubling the total number of animals), (2) the effect on signal crayfish of an addition of Atlantic salmon and (3) intraspecific compared with interspecific competition, compared by holding total density of animals constant and varying the proportion of signal crayfish and Atlantic salmon in trials. Observations were made during winter, when both species are nocturnal. The proportion of Atlantic salmon sheltering was significantly lower in the presence than in the absence of signal crayfish when the interspecific treatment (Atlantic salmon plus signal crayfish) effected a doubling in density compared to the intraspecific treatment (Atlantic salmon alone). The proportion of signal crayfish sheltering was independent of the presence of Atlantic salmon. When total density was constant, the proportion of Atlantic salmon sheltering was significantly higher in intraspecific (52·8%) than interspecific trials (27·3%). Atlantic salmon out of shelter during the day in winter are believed to be very vulnerable to predators and the capacity for fish to share shelters with one another is known to be very low. Therefore, competition from crayfish for winter shelters may lead to detrimental effects on Atlantic salmon populations.

Competition for shelter among over-wintering signal crayfish and juvenile Atlantic salmon

Nutrient Restoration Using Atlantic Salmon Carcasses as a Component of Habitat Management in Scottish Highland Streams

Abstract Shock tubes are a crucial source of experimental data for the aerothermodynamic modelling of atmospheric entry vehicles. Notably, many chemical-kinetic and radiative models are validated directly against optical measurements from these facilities. Typically, the incident shock speed at the location of the experimental measurement is taken to be representative of the test slug; however, the shock velocity can vary substantially upstream of this location. These variations have been long posited as a source of disagreement with computational predictions, although a definitive link has proved elusive. This work describes a series of experiments which aim to isolate and confirm the importance of the shock deceleration effect. This is achieved by generating different shock trajectories and comparing the post-shock trends in atomic oxygen emission and electron density. These trends are shown to be directly linked to the upstream shock speed variations using a recently developed numerical tool (LASTA). The close agreement of the comparisons confirms the importance of shock speed variation for shock tube experiments; these findings have direct and potentially critical relevance for all such studies, both past and present.

The influence of shock speed variation on radiation and thermochemistry experiments in shock tubes

A fundamental aspect of atmospheric entry flow-fields is the complex interaction between non-equilibrium thermochemistry and radiation. Shock tubes provide a means of generating flight-representative shock-layers, which allows extraction of thermochemical rates and radiative intensities. Currently, the NASA Electric Arc Shock Tube (EAST) is the best source of such data. Although simple in principle, nuances of these experimental facilities can affect the observed results. Notably, electron densities and radiance levels in excess of equilibrium predictions have been observed at EAST for many years. The deceleration of the shock as it passes along the tube has been posited as a source of these discrepancies. In this work, a recently developed numerical methodology (LASTA) is applied to these results from the literature. Using the experimental shock speed profile as an input, trends in post-shock electron density are computed. Radiance throughout the shock-layer is also predicted by coupling the simulation to the NASA NEQAIR code. It is shown that the predictions of LASTA provide a good match to the magnitudes and trends of the experimental differences, confirming shock speed variation as their cause. 

Peter Collen

Papers

Ecological impact of beavers Castor fiber and Castor canadensis and their ability to modify ecosystems

Competition for shelter among over-wintering signal crayfish and juvenile Atlantic salmon

Nutrient Restoration Using Atlantic Salmon Carcasses as a Component of Habitat Management in Scottish Highland Streams

The influence of shock speed variation on radiation and thermochemistry experiments in shock tubes

Analysis of Shock Deceleration Effects on Radiation Experiments in the NASA Electric Arc Shock Tube