Omnivory by planktivores stabilizes plankton dynamics, but may either promote or reduce algal biomass

Classical models of phytoplankton–zooplankton interaction show that with nutrient enrichment such systems may abruptly shift from limit cycles to stable phytoplankton domination due to zooplankton predation by planktivorous fish. Such models assume that planktivorous fish eat only zooplankton, but there are various species of filter-feeding fish that may also feed on phytoplankton. Here, we extend these classical models to systematically explore the effects of omnivory by planktivorous fish. Our analysis indicates that if fish forage on phytoplankton in addition to zooplankton, the alternative attractors predicted by the classical models disappear for all realistic parameter settings, even if omnivorous fish have a strong preference for zooplankton. Our model also shows that the level of fish biomass above which zooplankton collapse should be higher when fish are omnivorous than when fish are zooplanktivorous. We also used the model to explore the potential effects of the now increasingly common practice of stocking lakes with filter-feeding fish to control cyanobacteria. Because omnivorous filter-feeding fish forage on phytoplankton as well as on the main grazers of phytoplankton, the net effect of such fish on the phytoplankton biomass is not obvious. Our model suggests that there may be a unimodal relationship between the biomass of omnivorous filter-feeding fish and the biomass of phytoplankton. This implies that to manage for reductions in phytoplankton biomass, heavy stocking or strong reduction of such fish is bes

Half-Integer Shapiro Steps in a Short Ballistic InAs Nanowire Josephson Junction

We report on half-integer Shapiro steps observed in an InAs nanowire Josephson junction. We observed the Shapiro steps of the short ballistic InAs nanowire Josephson junction and found anomalous half-integer steps in addition to the conventional integer steps. The half-integer steps disappear as the temperature increases or transmission of the junction decreases. These experimental results agree closely with numerical calculation of the Shapiro response for the skewed current phase relation in a short ballistic Josephson junction

Effects of climate on size structure and functioning of aquatic food webs

In aquatic food webs, the role of body size is notoriously strong. It is also well known that temperature has an effect on body size. For instance, Bergmann’s rule states that body size increases from warm to cold climates. This thesis addresses the question how climate shapes the size structure of fish and zooplankton communities, and how this affects the strength of the trophic cascade from fish to plankton. I combine three different approaches: a space-for-time substitution study of data from the 83 shallow lakes distributed along a latitudinal gradient in South America, simple mathematical models to explore climate effects on the dynamics of trophic interactions, and an experimental analysis of trophic interactions using outdoor mesocosms

To swim or not to swim: an interpretation of farmed mink's motivation for a water bath

How an animal’s behavioural (ethological) needs can be met is a pivotal issue in the assessment of welfare for captive animals. The value of swimming water for farmed mink is an example how scientific and societal questions relating to animal welfare can be answered. A number of studies have addressed the issue of the indispensability of swimming water for mink; however, so far with inconclusive evidence. In this paper, the results of these studies and related literature are reviewed. First, the biological definition of need is discussed. Subsequently, attention is paid to the effects of the presence, absence and the removal of swimming water on behavioural and physiological correlates of well-being including stereotypic and anticipatory behaviour and urinary cortisol. Thereafter we discuss individual differences in the use of swimming water, the price animals pay for access to a water bath, and the effect of access to swimming water on juvenile play. The main conclusions of the literature review are that 1) the use of a water bath for mink is most likely related to foraging behaviour (foraging areas: land and water); 2) absence of swimming water, without prior experience, does not lead to consistent changes in level of stereotypic behaviour, or anticipatory responses; 3) removal of a previously experienced water bath may induce short-term stress as indicated by behavioural parameters and elevated cortisol responses; 4) mink work hard for access to a swimming bath and running wheel in consumer demand studies. Other cage modifications such as tunnels and biting objects, may also provide environmental enrichment, if they are added to otherwise impoverished conditions; 5) There are individual differences in the use of swimming water: these are related in part to variation in prior experience of aquatic resources.; 6) As prior experience is important both with respect to individual use of swimming water and the response to deprivation, swimming water can not be described as biological need in the sense of a fixed requirement for survival. As swimming water appears to act as an incentive that induces its own motivation a more accurate term may be an “incentive induced or environmentally facilitated need”. Given the available evidence, it is not possible to conclude whether mink that have never experienced swimming water, suffer as a consequence of its absence. However, it is possible to predict that mink with access to water have improved quality of life, due to increased behavioural opportunities, in comparison to farmed mink without access to swimming water. In practical terms, it is still open to debate whether mink should be provided with swimming water, or if alternative, less valued, but easier to install and maintain forms of environmental enrichment, should be provided in mink housing. To clarify these issues a number of future studies would be valuable. These include; 1) whether specific environmental cues affect motivation to swim, such as the form of drinking water delivery systems ; 2) whether prior experience of swimming water affects its incentive value; in other words “can you miss what you never experienced?”; 3) do behavioural parameters such as stereotypic behaviour; rebound effects and vacuum activity have any general utility in assessing the value of absent resources; 4) what are preferences for and the value of alternative resources which may act as substitutes for swimming water. In addition we would recommend further work investigating: relationship between access to swimming water and positive indicators of welfare such as play and/or anticipatory behaviour; the effects of preventing the performance of rewarding behaviours and deprivation of a previous experienced resource; and health and hygeine issues related to provision of a water bath. In future work, it would be desirable to present be the actual percentages of animals using a water bath during the experiment and the use of power analyses, to aid their interpretation

Herbivory on freshwater and marine macrophytes: A review and perspective

Until the 1990s, herbivory on aquatic vascular plants was considered to be of minor importance, and the predominant view was that freshwater and marine macrophytes did not take part in the food web: their primary fate was the detritivorous pathway. In the last 25 years, a substantial body of evidence has developed that shows that herbivory is an important factor in the ecology of vascular macrophytes across freshwater and marine habitats. Herbivores remove on average 40-48% of plant biomass in freshwater and marine ecosystems, which is typically 5-10 times greater than reported for terrestrial ecosystems. This may be explained by the lower C:N stoichiometry found in submerged plants. Herbivores affect plant abundance and species composition by grazing and bioturbation and therewith alter the functioning of aquatic ecosystems, including biogeochemical cycling, carbon stocks and primary production, transport of nutrients and propagules across ecosystem boundaries, habitat for other organisms and the level of shoreline protection by macrophyte beds. With ongoing global environmental change, herbivore impacts are predicted to increase. There are pressing needs to improve our management of undesirable herbivore impacts on macrophytes (e.g. leading to an ecosystem collapse), and the conflicts between people associated with the impacts of charismatic mega-herbivores. While simultaneously, the long-term future of maintaining both viable herbivore populations and plant beds should be addressed, as both belong in complete ecosystems and have co-evolved in these long before the increasing influence of man. Better integration of the freshwater, marine, and terrestrial herbivory literatures would greatly benefit future research efforts

Exploring the impact of recipe cards for seafood at the point of sale

Food consumption and purchase behaviour are highly habituated, with food marketers often attempting to interrupt routine behaviour and thought patterns at the point of sale (POS) through aggressive sales promotion. In the case of food products, recipe cards are a common POS tactic, yet little research has examined the impact of recipe cards at POS. This research explores the impact of recipe cards at POS specifically in relation to seafood with data gathered through 11 face to face depth interviews with fishmongers. Results highlight the positive impact of recipe cards as marketing stimuli for seafood through two key roles: (1) risk reduction for consumers who lack knowledge about how to prepare and serve seafood; and (2) facilitating variety seeking for consumers who are looking for something different. Regardless of the consumers’ motivation for taking recipe cards, the fishmongers perceive that the cards have a positive impact on seafood sales

Effects of in-season uphill sprinting on physical characteristics in semi-professional soccer players

AIM: Soccer performance is determined by a number of physiological adaptations that can be altered by high intensity training. However, the effectiveness of using an uphill sprint based protocol has not been demonstrated for soccer players. We sought to determine the effectiveness of an in-season uphill sprint training (UST) programme on soccer related physiological outcomes. METHODS: 14 male soccer players (age: 22 ± 8 years, height: 1.81 ± 8 m, body mass: 76 ± 12 kg) underwent testing (5-10-5 agility drill, Yo-Yo Intermittent Recovery Test Level 1, leg and back dynamometry & 3km time trial) at baseline and after 6 weeks of UST or normal activity. Participants were allocated to a control (n=7) or UST (n=7) group. The UST group took part in twice weekly training consisting of 10 x 10 sec sprints with 60s recovery on a 7% gradient for 6 weeks. The control group maintained normal activity patterns. RESULTS: 3km time trial, strength, agility and Yo-Yo performance were all significantly improved pre to post following 6 weeks of UST (Agility 3%, d=1.3; Strength 10%, d=-3.2; VO2 max 3%, d=-1.4; 3-km TT 4%, d=1.3). In the control group 3km time trial, strength, agility and Yo-Yo performance remained unchanged after 6 weeks (Agility 0.1%, d=-0.2; Strength 2%, d=0.0; VO2 max -0.1%, d=0.0; 3-km TT 1.3%, d=0.3). CONCLUSION: Therefore in-season short duration UST is an effective way to improve soccer fitness in a time efficient manner