Food Web Assembly Rules for Generalized Lotka-Volterra Equations

In food webs, many interacting species coexist despite the restrictions imposed by the competitive exclusion principle and apparent competition. For the generalized Lotka-Volterra equations, sustainable coexistence necessitates nonzero determinant of the interaction matrix. Here we show that this requirement is equivalent to demanding that each species be part of a non-overlapping pairing, which substantially constrains the food web structure. We demonstrate that a stable food web can always be obtained if a non-overlapping pairing exists. If it does not, the matrix rank can be used to quantify the lack of niches, corresponding to unpaired species. For the species richness at each trophic level, we derive the food web assembly rules, which specify sustainable combinations. In neighboring levels, these rules allow the higher level to avert competitive exclusion at the lower, thereby incorporating apparent competition. In agreement with data, the assembly rules predict high species numbers at intermediate levels and thinning at the top and bottom. Using comprehensive food web data, we demonstrate how omnivores or parasites with hosts at multiple trophic levels can loosen the constraints and help obtain coexistence in food webs. Hence, omnivory may be the glue that keeps communities intact even under extinction or ecological release of species

Browser Fingerprinting Using Web Assembly

Hlavným cieľom tejto bakalárskej práce, je implementácia identifikácie zariadení, pomocou technológie Web Assembly. V práci si rozoberieme už existujúce metódy identifikácie zariadení, metódy na zabránenie identifikácie a spôsoby, ako tieto rôzne zábrany obísť. Tak isto sa zoznámime s prehliadačom Brave, ktorý sa snaží zredukovať identifikáciu zariadení na internete. Vysvetlíme si, ako funguje Web Assembly, aké sú jeho pozitíva, negatíva a či budeme schopný vďaka tejto novej technológii obísť rôzne obrany proti identifikácii zariadení. Ďalej sa zoznámime s niekoľkými webovými API, ktoré budeme využívať pri identifikácii zariadení a predstavíme si aj pár rozšírení, ktorých cieľom je zabrániť, alebo úplne obmedziť získanie identifikácie zariadení. Už existujúce bezpečnostné rozšírenia, obmedzujú činnosť Web Assembly, napríklad táto práca ukazuje, že rozšírenie Web API Manager dokáže neutralizovať testovaciu stránku implementovanú v rámci práce.The main goal of this bachelor thesis is the implementation of device identification using Web Assembly technology. In this work we are discussing the existing methods of device identification, methods to prevent identification and ways to circumvent these barriers. We are also getting acquainted with the Brave browser, which seeks to reduce the identification of devices on the Internet. We are explaining how Web Assembly works, what are its positives, negatives and if we are able to bypass various defences against device identification thanks to this new technology. Next, we are looking at the several web APIs we are using to identify devices, and we are introducing a few extensions designed to prevent or completely limit device identification. Existing security extensions limit the activity of the Web Assembly, for example this work shows that the Web API Manager extension can neutralize the test page implemented in this work.

Unique gear design provides self-lubrication

Composite gear configuration provides a reliable automatic means for replenishing gear mechanism lubricants that dissipate in the harsh environment of space. The center or hub section of the gear consists of a porous, oil impregnated material, and the outer or toothed section has radially drilled passages to cause the oil to gradually flow to the gear teeth surface

Effect of multiple disturbances on food web vulnerability to biodiversity loss in detritus-based systems

Global biodiversity is affected by human pressure and climate change, and the present rate of biodiversity loss is probably higher than ever before. Community composition is also changing, and interspecific interactions are under severe pressure. The extinction of one species within a food web can result in further secondary extinctions, due to bottom-up effects that can be even more intense and less predictable than the direct effects of disturbance, undermining our capacity for ecosystem management and conservation. Here we investigated a metric for assessing the structural stability of food webs in the face of species loss, referred to as "Resistance'', based on two fundamental web properties: (1) the proportion of key species in the web, a "key'' species being one whose deletion leads to at least one secondary extinction, and (2) the mean number of secondary extinctions observed per key species deletion. We compared web Resistance with web Robustness (Dunne et al. 2002) based on 12 detritus-based riverine food webs under four species extinction scenarios on various temporal and spatial scales. We investigated the effect of multiple disturbances (extreme flood and river basin urbanization) on community vulnerability to biodiversity loss, assessing the behavior of Robustness and Resistance under the applied species extinction scenarios and testing their dependence on web topology. We estimated the contribution of the rarest and the most dominant species, and that of the most and least connected species, to web Resistance. Urbanization negatively affected community vulnerability to biodiversity loss. Only food web Resistance showed a significant flood effect and interaction between flood and urbanization. The most connected species contributed the most to food web resistance, whereas the rarest and the most abundant species had a similar, intermediate structural importance. Both food web Resistance and the role of selected key species varied across web description scales. Food web Resistance values were coherent across species extinction scenarios, demonstrating the suitability of the proposed approach for quantifying community vulnerability to species loss and the importance of considering food webs in monitoring and impact assessment programs. The approach is thus seen to be a promising research pathway supporting ecosystem management

Robust Patterns in Food Web Structure

We analyze the properties of seven community food webs from a variety of environments--including freshwater, marine-freshwater interfaces and terrestrial environments. We uncover quantitative unifying patterns that describe the properties of the diverse trophic webs considered and suggest that statistical physics concepts such as scaling and universality may be useful in the description of ecosystems. Specifically, we find that several quantities characterizing these diverse food webs obey functional forms that are universal across the different environments considered. The empirical results are in remarkable agreement with the analytical solution of a recently proposed model for food webs.Comment: 4 pages. Final version to appear in PR

Permanence Does Not Predict the Commonly Measured Food Web Structural Attributes.

Food web assembly algorithms show great promise for investigating issues involving the dynamics of whole webs, such as succession, rehabilitation, and invasibility. Permanence, which requires that all species densities remain positive and finite, has been suggested as a good stability constraint. This study tests the validity of the permanence constraint by comparing real webs and model webs from the literature to the predictions of three assembly algorithms: one constrained by permanence and feasibility, one constrained by feasibility alone, and one with no dynamical constraint. It is found that the addition of the permanence constraint does not improve the predictive ability of the algorithm. Its main effect is to increase the efficiency of species selected for the web. Dynamically constrained webs have lower connectance and indistinct trophic levels compared to real webs and webs from other models, which is a consequence of omitting species’ physiology. Although webs are less likely to be permanent if they have high omnivory and cycling, the web‐building process circumvents this constraint. The challenges of testing and justifying system‐level hypotheses, including isolating and detecting their effects, are discussed