Biology subjects

Grimm, V.

Publications and source records attributed to Grimm, V..

7 recordsLinked to original sources

bioRxiv2023

Modelling the transmission and spread of yellow fever in forest landscapes with different spatial configurations

Yellow fever (YF) is a major public health issue in tropical and subtropical areas of Africa and South America. The disease is caused by the yellow fever virus (YFV), an RNA virus transmitted to humans and other animals through the bite of infected mosquitoes (Diptera: Culicidae). In Brazil and other South American countries, YFV is restricted to the sylvatic cycle, with periodic epizootic outbreaks affecting non-human primate (NHP) populations and preceding the emergence of human infections in areas close to forests. In recent epizootic-epidemic waves, the virus has expanded its range and spread across highly fragmented landscapes of the Brazilian Atlantic coast. Empirical evidence has suggested a possible relationship between highly fragmented areas, increased risk of disease in NHP and humans, and easier permeability of YFV through the landscape. Here, we present a hybrid compartmental and network-based model to simulate the transmission and spread of YFV in forest landscapes with different spatial configurations (forest cover and edge densities) and apply the model to test the hypothesis of faster virus percolation in highly fragmented landscapes. The model was parameterized and tested using the pattern- oriented modelling approach. Two different scenarios were simulated to test variations in model outputs, a first where the landscape has no influence on model parameters (default) and a second based on the hypothesis that edge density influences mosquito and dead-end host abundance and dispersal (landscape-dependent). The model was able to reproduce empirical patterns such as the percolation speed of the virus, which presented averages close to 1 km/day, and provided insights into the short persistence time of the virus in the landscape, which was approximately three months on average. When assessing the speed of virus percolation across landscapes, it was found that in the default scenario virus percolation tended to be faster in landscapes with greater forest cover and lower edge density, which contradicts empirical observations. Conversely, in the landscape- dependent scenario, virus percolation was faster in landscapes with high edge density and intermediate forest cover, supporting empirical observations that highly fragmented landscapes favour YFV spread. The proposed model can contribute to the understanding of the dynamics of YFV spread in forested areas, with the potential to be used as an additional tool to support prevention and control measures. The potential applications of the model for YFV and other mosquito-borne diseases are discussed.

ecology↗

bioRxiv2021

Tropical forest dynamics correspond to fair games in economic theory of financial markets

Ecological and economic systems both comprise of autonomous adaptive agents. It is thus possible that similar mechanisms determine the organization of both these complex systems. Indeed several economic theories have already been successfully applied in an ecological context. Here we show that efficient market theory in economics, where future earnings are distributed between competitors by a fair game, corresponds to fitness-equalizing mechanisms of coexistence in ecology. In contrast to stabilizing mechanisms, which promote coexistence by giving each species an equilibrium abundance that is resilient to perturbations, equalizing mechanisms promote coexistence without such resilience by minimizing the net fitness differences between species. However, identifying stabilizing and equalizing mechanisms from the short time-series data that are typically available in ecology is challenging. We used techniques from economics that are applied to collections of short time-series from a system. We found that observed species abundance dynamics in a neotropical forest are generally in agreement with efficient market theory implying a dominant role of equalizing mechanisms, which finding quantifies and supports what was generally believed about that specific forest system. Our study highlights that complex systems from ecology and economics share common features suggesting the possibility of further synergy between ecology and economics in future.

ecology↗

bioRxiv2021

Stabilising microbial communities by looped mass transfer

Creating structurally and functionally stable microbiomes would be greatly beneficial to biotechnology and human health but so far has proven challenging. Here, we propose a looped mass transfer design that keeps microbiomes constant over long periods of time. The effluent of five parallel reactors that began with the same inoculum, was mixed in a reactor that represented a regional pool. Part of this pool was transferred back to the five reactors. Community dynamics were monitored and visualized by quantitative microbial flow cytometry and selected taxonomic sequencing of whole communities and sorted subcommunities. The rescue effect, known from metacommunity theory, was the main stabilizing mechanism that led to the survival of subcommunities with zero netgrowth, especially at high mass transfer rates. The looped mass transfer approach promises to overcome notorious stochastic structural fluctuations in bioreactors and has the potential to design and stabilize communities that can perform desired functions.

microbiology↗

bioRxiv2020

Nafamostat Mesylate in lipid carrier for nasal SARS-CoV2 titer reduction in a hamster model

Severe acute respiratory syndrome corona virus 2 (SARS-CoV-2) has been responsible for the largest pandemic in recent decades. After seemingly being in control due to consequent lock-downs and social distancing, the majority of countries faces currently a second wave of exponentially increasing infections, hospital referrals and deaths due to SARS-CoV-2-mediated disease (COVID-19). To date, no effective vaccination has been found, and wearing masks and social distancing are the only effective approaches to reduce further spreading. However, unwillingness in the societies to distance again and consequently wear masks might be reasons for the second SARS-CoV-2 infection wave. User-friendly chemicals interfering at the host site with viral entry might be an approach to contain the pandemic. In addition, such an approach would work synergistic with vaccinations that miss new virus mutants. Nafamostat (NM) has been shown in vitro to interfere with cellular virus entry by inhibition of the host transmembrane protease serine 2 (TMPRSS2), an enzyme required for SARS-CoV-2 spike protein cleavage, a prerequisite for cell entry. We hypothesized that nasal application of NM in a liposomal layer (as additional mechanical barrier) could lower the nasal viral load and subsequently reduce the severity of COVID-19. We found, indeed, that nasal viral load one day post single NM application, was lowered in a hamster SARS-CoV-2 infection model. However, severity of subsequent local tissue destruction and weight loss due to pneumonitis was not favorably altered. In conclusion, a single NM application reduced nasal viral load, but did not favorably improve the outcome of COVID-19, likely due to the short half-time of NM. Improvement of NM stability or repetitive application (which was not permitted in this animal model according to Dutch law) might circumvent these challenges.

microbiology↗

bioRxiv2019

Honeybee colony performance affected by crop diversity and farmland structure: a modelling framework

Forage availability has been suggested as one driver of the observed decline in honeybees. However, little is known about the effects of its spatiotemporal variation on colony success. We present a modelling framework for assessing honeybee colony viability in cropping systems. Based on two real farmland structures, we developed a landscape generator to design cropping systems varying in crop species identity, diversity, and relative abundance. The landscape scenarios generated were evaluated using the existing honeybee colony model BEEHAVE, which links foraging to in-hive dynamics. We thereby explored how different cropping systems determine spatiotemporal forage availability and, in turn, honeybee colony viability (e.g., time to extinction, TTE) and resilience (indicated by, e.g. brood mortality). To assess overall colony viability, we developed metrics, PH and PP, which quantified how much nectar and pollen provided by a cropping system per year was converted into a colonys adult worker population. Both crop species identity and diversity determined the temporal continuity in nectar and pollen supply and thus colony viability. Overall farmland structure and relative crop abundance were less important, but details mattered. For monocultures and for four-crop species systems composed of cereals, oilseed rape, maize and sunflower, PH and PP were below the viability threshold. Such cropping systems showed frequent, badly timed, and prolonged forage gaps leading to detrimental cascading effects on life stages and in-hive work force, which critically reduced colony resilience. Four-crop systems composed of rye-grass-dandelion pasture, trefoil-grass pasture, sunflower and phacelia ensured continuous nectar and pollen supply resulting in TTE > 5 years, and PH (269.5 kg) and PP (108 kg) being above viability thresholds for five years. Overall, trefoil-grass pasture, oilseed rape, buckwheat and phacelia improved the temporal continuity in forage supply and colonys viability. Our results are hypothetical as they are obtained from simplified landscape settings, but they nevertheless match empirical observations, in particular the viability threshold. Our framework can be used to assess the effects of cropping systems on honeybee viability and to develop land-use strategies that help maintain pollination services by avoiding prolonged and badly timed forage gaps.

ecology↗

bioRxiv2019

While shoot herbivory mitigates, root herbivory exacerbates eutrophication’s impact on diversity in a grassland model

1Eutrophication is widespread throughout grassland systems and expected to increase during the Anthropocene. Trophic interactions, like aboveground herbivory, have been shown to mitigate its effect on plant diversity. Belowground herbivory may also impact these habitats response to eutrophication, but the direction of its influence is much less understood, and likely to depend on factors such as the herbivores preference for dominant species and the symmetry of belowground competition. If preferential towards the dominant, fastest growing species, root herbivores may reduce these species relative fitness and support diversity during eutrophication. However, as plant competition belowground is commonly considered to be symmetric, root herbivores may be less impactful than shoot herbivores because they do not reduce any competitive asymmetry between the dominant and subordinate plants.\n\nTo better understand this system, we used an established, two-layer, grassland community model to run a full-factorially designed simulation experiment, crossing the complete removal of aboveground herbivores and belowground herbivores with eutrophication. After 100 years of simulation, we analyzed communities diversity, competition on the individual-level, as well as their resistance and recovery. The model reproduced both observed general effects of eutrophication in grasslands and the short-term trends of specific experiments. We found that belowground herbivores exacerbate the negative influence of eutrophication on Shannon diversity within our model grasslands, while aboveground herbivores mitigate its effect. Indeed, data on individuals above- and belowground resource uptake reveals that root herbivory reduces resource limitation belowground. As with eutrophication, this shifts competition aboveground. Since shoot competition is asymmetric--with larger, taller individuals gathering disproportionate resources compared to their smaller, shorter counterparts--this shift promotes the exclusion of the smallest species. While increasing the root herbivores preferences towards dominant species lessens their negative impact, at best they are only mildly advantageous, and they do very little reduce the negative consequences of eutrophication. Because our models belowground competition is symmetric, we hypothesize that root herbivores may be beneficial when root competition is asymmetric. Future research into belowground herbivory should account for the nature of competition belowground to better understand the herbivores true influence.

ecology↗

bioRxiv2019

Resilience trinity: safeguarding ecosystem services across three different time horizons and decision contexts

Ensuring ecosystem resilience is an intuitive approach to safeguard future provisioning of ecosystem services (ES). However, resilience is an ambiguous concept and difficult to operationalize. Focusing on resilience mechanisms, such as diversity, network architectures or adaptive capacity, has recently been suggested as means to operationalize resilience. Still, the focus on mechanisms is not specific enough because the usefulness of a mechanism is context-dependent. We suggest a conceptual framework, resilience trinity, to facilitate management of resilience mechanisms in three distinctive decision contexts and time-horizons. i) reactive, when there is an imminent threat to ES resilience and a high pressure to act, ii) adjustive, when the threat is known in general but there is still time to adapt management, and iii) provident when time horizons are very long and the nature of the threats is uncertain, leading to a low willingness to act. This emphasizes that resilience has different interpretations and implications at different time horizons which however need to be reconciled. The inclusion of time into resilience thinking ensures that longer-term management actions are not missed while urgent threats to ES are given priority.

ecology↗