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1. Merging dynamical and structural indicators to measure resilience in multispecies systems

   https://doi.org/10.1111/1365-2656.13421  

   Medeiros, Lucas P.; Song, Chuliang; Saavedra, Serguei (February 2021, Journal of Animal Ecology)

   Abstract Resilience is broadly understood as the ability of an ecological system to resist and recover from perturbations acting on species abundances and on the system's structure. However, one of the main problems in assessing resilience is to understand the extent to which measures of recovery and resistance provide complementary information about a system. While recovery from abundance perturbations has a strong tradition under the analysis of dynamical stability, it is unclear whether this same formalism can be used to measure resistance to structural perturbations (e.g. perturbations to model parameters).Here, we provide a framework grounded on dynamical and structural stability in Lotka–Volterra systems to link recovery from small perturbations on species abundances (i.e. dynamical indicators) with resistance to parameter perturbations of any magnitude (i.e. structural indicators). We use theoretical and experimental multispecies systems to show that the faster the recovery from abundance perturbations, the higher the resistance to parameter perturbations.We first use theoretical systems to show that the return rate along the slowest direction after a small random abundance perturbation (what we call full recovery) is negatively correlated with the largest random parameter perturbation that a system can withstand before losing any species (what we call full resistance). We also show that the return rate along the second fastest direction after a small random abundance perturbation (what we call partial recovery) is negatively correlated with the largest random parameter perturbation that a system can withstand before at most one species survives (what we call partial resistance). Then, we use a dataset of experimental microbial systems to confirm our theoretical expectations and to demonstrate that full and partial components of resilience are complementary.Our findings reveal that we can obtain the same level of information about resilience by measuring either a dynamical (i.e. recovery) or a structural (i.e. resistance) indicator. Irrespective of the chosen indicator (dynamical or structural), our results show that we can obtain additional information by separating the indicator into its full and partial components. We believe these results can motivate new theoretical approaches and empirical analyses to increase our understanding about risk in ecological systems. 

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2. A trust model for spreading gossip in social networks: a multi-type bootstrap percolation model

   https://doi.org/10.1098/rspa.2019.0826  

   Bhansali, Rinni; Schaposnik, Laura P. (March 2020, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   null (Ed.)

   We introduce here a multi-type bootstrap percolation model, which we call T -Bootstrap Percolation ( T -BP), and apply it to study information propagation in social networks. In this model, a social network is represented by a graph G whose vertices have different labels corresponding to the type of role the person plays in the network (e.g. a student, an educator etc.). Once an initial set of vertices of G is randomly selected to be carrying a gossip (e.g. to be infected), the gossip propagates to a new vertex provided it is transmitted by a minimum threshold of vertices with different labels. By considering random graphs, which have been shown to closely represent social networks, we study different properties of the T -BP model through numerical simulations, and describe its implications when applied to rumour spread, fake news and marketing strategies. 

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3. Sweeping secular resonances and giant planet inclinations in transition discs

   https://doi.org/10.1093/mnras/stad3066  

   Zanazzi, J. J.; Chiang, E. (October 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT The orbits of some warm Jupiters are highly inclined (20°–50°) to those of their exterior companions. Comparable misalignments are inferred between the outer and inner portions of some transition discs. These large inclinations may originate from planet–planet and planet–disc secular resonances that sweep across interplanetary space as parent discs disperse. The maximum factor by which a seed mutual inclination can be amplified is of the order of the square root of the angular momentum ratio of the resonant pair. We identify those giant planet systems (e.g. Kepler-448 and Kepler-693) that may have crossed a secular resonance, and estimate the required planet masses and semimajor axes in transition discs needed to warp their innermost portions (e.g. in CQ Tau). Passage through an inclination secular resonance could also explain the hypothesized large mutual inclinations in apsidally-orthogonal warm Jupiter systems (e.g. HD 147018). 

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4. Weak Randomness in Graphons and Theons

   https://doi.org/10.1002/rsa.21261  

   Coregliano, Leonardo N; Malliaris, Maryanthe (January 2025, Random Structures & Algorithms)

   Call a hereditary family F of graphs strongly persistent if there exists a graphon W such that in all subgraphons W0 of W , F is precisely the class of finite graphs that have positive density in W0. Our first result is a complete characterization of the hereditary families of graphs that are strongly persistent as precisely those that are closed under substitutions. We call graphons with the self-similarity property above weakly random. A hereditary family F is said to have the weakly random Erdos–Hajnal property (WR) if every graphon that is a limit of graphs in F has a weakly random subgraphon. Among families of graphs that are closed under substitutions, we completely characterize the families that belong to WR as those with “few” prime graphs. We also extend some of the results above to structures in finite relational languages by using the theory of theons. 

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5. The calling songs of some katydids (Orthoptera, Tettigonioidea) from the tropical forests of Southeast Asia

   https://doi.org/10.3897/jor.32.84563  

   Tan, Ming Kai; Duncan, Jacob; Wahab, Rodzay bin; Lee, Chow-Yang; Japir, Razy; Chung, Arthur Y.; Baroga-Barbecho, Jessica B.; Yap, Sheryl A.; Montealegre-Z, Fernando (January 2023, Journal of Orthoptera Research)

   Katydids produce sound for signaling and communication by stridulation of the tegmina. Unlike crickets, most katydids are known to sing at ultrasonic frequencies. This has drawn interest in the investigation of the biophysics of ultrasonic sound production, detection, evolution, and ecology (including predator–prey interactions) of these katydids. However, most of these studies are based on species from the Neotropics, while little is known about katydid species from the hyperdiverse region of Southeast Asia. To address this, a concerted effort to document, record, and describe the calling songs of Southeast Asian katydids, especially species that call at ultrasonic frequencies, was made. A study spanning two years (2018–2020) in the Malay Peninsula (Singapore and Malaysia), Borneo (Brunei Darussalam and Sabah), and the Philippines revealed previously unknown calls of 24 katydid species from four subfamilies. The calling songs of Southeast Asian katydid species are highly diversified in terms of time and frequency. Call structure can range from isolated syllables (e.g.,Holochlora), continuous trills (e.g.,Axylus philippinus), to short pulse-trains (e.g.,Euanisous teuthroides) and complex echemes (e.g.,Conocephalusspp.), with 87.5% of species having ultrasonic peak frequencies and 12.5% being considered extreme ultrasonic callers (peak frequency >40 kHz). The call spectrum ranges from tonal (e.g., spectral entropy is 6.8 inCasignetasp. 2) to resonant (entropy is 8.8 inConocephalus cognatus). Of the 24 species whose calls are described here, we imaged and described the sound-producing structures of 18. This study provides a preliminary overview of the acoustic diversity of katydids in Southeast Asia, and the authors hope to inspire further investigation into the bioacoustics of little-known katydids from these areas. Amassing a database of calling songs and sound-producing organ illustrations from different species is important to address taxonomic impediments while advancing our knowledge about the bioacoustics of Southeast Asian katydids. 

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