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Section: Ecology ; Topics: Biology of interactions, Ecology

Insights on the effect of mega-carcass abundance on the population dynamics of a facultative scavenger predator and its prey

Sidous, Mellina; Cubaynes, Sarah; Gimenez, Olivier; Drouet-Hoguet, Nolwenn; Dray, Stéphane; Bollache, Loïc; Madhlamoto, Daphine; Ngwenya, Nobesuthu Adelaide; Fritz, Hervé; Valeix, Marion

10.24072/pcjournal.420 - Peer Community Journal, Volume 4 (2024), article no. e53.
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The interplay between facultative scavenging and predation has gained interest in the last decade. The prevalence of scavenging induced by the availability of large carcasses may modify predator density or behaviour, potentially affecting prey. In contrast to behavioural mechanisms through which scavenging affects predation, the demographic effects of facultative scavenging on predator and prey populations remain poorly studied. We used the semi-natural experimental opportunity in Hwange National Park, Zimbabwe, where contrasted management measures (culling and artificial supply of water) have led to fluctuations in elephant carrion abundance, to identify the consequences of facultative scavenging on the population dynamics of a large mammalian carnivore, the spotted hyaena (Crocuta crocuta), and its prey. Using a 50-year dataset and Multivariate Autoregressive State Space models, we estimated hyaena and prey densities over four periods contrasted in elephant carrion availability due to management practices. Models that allow hyaena and their prey populations’ growth rate to vary depending on these four periods contributed significantly to explain variations in their density, which is consistent with an effect of management measures on the population dynamics of hyaena and its prey. Although our results support a predominant role of bottom-up mechanisms, whereby hyaena density is driven by herbivore density, itself driven by resources availability, some subtle patterns of densities could be interpreted as consequences of changes in predation pressure following changes in scavenging opportunities. We discuss why signals of prey and predator population dynamics decoupling are less likely to be observed in systems with a high diversity of prey, such as African savannas, and why inputs of mega-carcasses as pulsed resources hardly impacted top-down relationships in the long run. This study represents a first investigation of the long-term effects of carrion pulses, whose frequency may increase with climate changes, on the classical predator-prey coupling for large mammals.
Section: Animal Science ; Topics: Applied biological sciences, Computer sciences, Health sciences

Pig herd management and infection transmission dynamics: a challenge for modellers

Sicard, Vianney; Picault, Sébastien; Andraud, Mathieu

10.24072/pcjournal.403 - Peer Community Journal, Volume 4 (2024), article no. e52.
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The control of epidemics requires a thorough understanding of the complex interactions between pathogen transmission, disease impact, and population dynamics and management. Mechanistic epidemiological modelling is an effective way to address this issue, but handling highly structured and dynamic systems, remains challenging. We therefore developed a novel approach that combines Multi-Level Agent-Based Systems (MLABS) with spatial and temporal organization, allowing for a tuned representation of the transmission processes amongst the host population. We applied this method to model the spread of a PRRSv-like virus in pig farms, integrating the clinical consequences (conception and reproduction failures), in terms of animal husbandry practices. Results highlighted the importance to account for spatial and temporal structuring and herd management policies in epidemiological models. Indeed, disease-related abortions, inducing reassignments of sows in different batches, was shown to enhance the transmission process, favouring the persistence of the virus at the herd level. Supported by a declarative Domain-Specific Language (DSL), our approach provides flexible and powerful solutions to address the issues of on-farm epidemics and broader public health concerns. The present application, based on a simple Susceptible-Exposed-Infected-Recovered (SEIR) model, opens the way to the representation of more complex epidemiological systems, including more specific features such as maternally derived antibodies, vaccination, or dual infections, along with their respective clinical consequences on the management practices.
Section: Ecotoxicology & Environmental Chemistry ; Topics: Environmental sciences, Physiology

Assimilation efficiencies and elimination rates of silver, cadmium and zinc accumulated by trophic pathway in Gammarus fossarum

Gestin, Ophélia; Lopes, Christelle; Delorme, Nicolas; Garnero, Laura; Geffard, Olivier; Lacoue-Labarthe, Thomas

10.24072/pcjournal.426 - Peer Community Journal, Volume 4 (2024), article no. e51.
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To improve the assessment of metal toxicity in aquatic organisms, it is important to consider the different uptake pathways (i.e. trophic or aqueous). The bioaccumulation of dissolved metals such as Cd and Zn in gammarids is beginning to be well described. However, there are very few data on the contribution of the dietary pathway, and its associated toxicokinetic parameters. Among these, the assimilation efficiency (AE) is an essential parameter for the implementation of models that take the trophic pathway into account. This study aims to estimate the assimilation efficiencies and elimination rates of two types of food, i.e. alder leaves and chironomid larvae, contaminated with three metals (Ag, Cd and Zn) of major concern for the Water Framework Directive (WFD). The pulse-chase-feeding method was used. Gammarids were fed with alder leaves or chironomid larvae previously contaminated with ^110mAg, ¹⁰⁹Cd or ⁶⁵Zn, for a short period of time (1 to 5 hours), followed by an elimination phase of 14 days. At different time points, the gammarids were placed alive on the gamma detector to individually quantify whole body concentrations of ^110mAg, ¹⁰⁹Cd or ⁶⁵Zn. Our results indicate that: i) Cd has the highest assimilation efficiency (39% for leaves and 19% for larvae), followed by Zn (15% for leaves and 9% for larvae) and Ag (5% for leaves); ii) for Cd and Zn, the AE were higher when gammarids were fed with leaves than with larvae; iii) the elimination rates of metals seem to depend more on the food matrix than on the metal assimilated; and thus iv) the biological half-life calculated from the k_es is 5.1 days for Ag, between 4.9 and 13 days for Cd and between 3.8 and 13 days for Zn.
Section: Microbiology

Molybdate delays sulphide formation in the sediment and transfer to the bulk liquid in a model shrimp pond

Torun, Funda; Hostins, Barbara; De Schryver, Peter; Boon, Nico; De Vrieze, Jo

10.24072/pcjournal.421 - Peer Community Journal, Volume 4 (2024), article no. e50.
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Shrimp are commonly cultured in earthen aquaculture ponds where organic-rich uneaten feed and faeces accumulate on and in the sediment to form anaerobic zones. Since the pond water is rich in sulphate, these anaerobic conditions eventually lead to the production of sulphide. Sulphides are toxic and even lethal to the shrimp that live on the pond sediment, but physicochemical and microbial reactions that occur during the accumulation of organic waste and the subsequent formation of sulphide in shrimp pond sediments remain unclear. Molybdate treatment is a promising strategy to inhibit sulphate reduction, thus, preventing sulphide accumulation. We used an experimental shrimp pond model to simulate the organic waste accumulation and sulphide formation during the final 61 days of a full shrimp growth cycle. Sodium molybdate (5 and 25 mg/L Na₂MoO₄.2H₂O) was applied as a preventive strategy to control sulphide production before oxygen depletion. Molybdate addition partially mitigated H₂S production in the sediment, and delayed its transfer to the bulk liquid by pushing the higher sulphide concentration zone towards deeper sediment layers. Molybdate treatment at 25 mg/L significantly impacted the overall microbial community composition and treated samples (5 and 25 mg/L molybdate) had about 50% higher relative abundance of sulphate reducing bacteria than the control (no molybdate) treatment. In conclusion, molybdate has the potential to work as mitigation strategy against sulphide accumulation in the sediment during shrimp growth by directly steering the microbial community in a shrimp pond system.

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The network image was drawn by Martin Grandjean: A force-based network visualization CC BY-SA