Variable prey development time suppresses predator-prey cycles and enhances stability

© 2016 John Wiley & Sons Ltd/CNRS. Although theoretical models have demonstrated that predator-prey population dynamics can depend critically on age (stage) structure and the duration and variability in development times of different life stages, experimental support for this theory is non-existent. We conducted an experiment with a host-parasitoid system to test the prediction that increased variability in the development time of the vulnerable host stage can promote interaction stability. Host-parasitoid microcosms were subjected to two treatments: Normal and High variance in the duration of the vulnerable host stage. In control and Normal-variance microcosms, hosts and parasitoids exhibited distinct population cycles. In contrast, insect abundances were 18-24% less variable in High- than Normal-variance microcosms. More significantly, periodicity in host-parasitoid population dynamics disappeared in the High-variance microcosms. Simulation models confirmed that stability in High-variance microcosms was sufficient to prevent extinction. We conclude that developmental variability is critical to predator-prey population dynamics and could be exploited in pest-management programs

Hot Streaks in Artistic, Cultural, and Scientific Careers

The hot streak, loosely defined as winning begets more winnings, highlights a specific period during which an individual's performance is substantially higher than her typical performance. While widely debated in sports, gambling, and financial markets over the past several decades, little is known if hot streaks apply to individual careers. Here, building on rich literature on lifecycle of creativity, we collected large-scale career histories of individual artists, movie directors and scientists, tracing the artworks, movies, and scientific publications they produced. We find that, across all three domains, hit works within a career show a high degree of temporal regularity, each career being characterized by bursts of high-impact works occurring in sequence. We demonstrate that these observations can be explained by a simple hot-streak model we developed, allowing us to probe quantitatively the hot streak phenomenon governing individual careers, which we find to be remarkably universal across diverse domains we analyzed: The hot streaks are ubiquitous yet unique across different careers. While the vast majority of individuals have at least one hot streak, hot streaks are most likely to occur only once. The hot streak emerges randomly within an individual's sequence of works, is temporally localized, and is unassociated with any detectable change in productivity. We show that, since works produced during hot streaks garner significantly more impact, the uncovered hot streaks fundamentally drives the collective impact of an individual, ignoring which leads us to systematically over- or under-estimate the future impact of a career. These results not only deepen our quantitative understanding of patterns governing individual ingenuity and success, they may also have implications for decisions and policies involving predicting and nurturing individuals with lasting impact

Asymptotic behavior and traveling waves for some population models

Since the 1970s, more and more mathematicians have been trying to propose reasonable models for the growth of species in all kinds of environments and for the spread of epidemic diseases, and to understand the long-term behavior of their modelling systems. This thesis, consisting of five chapters, mainly deals with the dynamics of population and epidemic models represented by some time-delayed ordinary and partial differential equations, and reaction-diffusion systems. -- In Chapter 1, we present some basic concepts and theorems, which involve the theories of monotone dynamics, uniform persistence, essential spectrum of linear operators, asymptotic speeds of spread and minimal traveling wave speed. -- Based on some specific competitive models, we formulate in Chapter 2 a class of asymptotically periodic delay differential equations, which models multi-species competition, and investigate the global dynamics of the model. More precisely, we established the sufficient conditions for competitive coexistence, exclusion and uniform persistence via theories of competitive systems on Banach spaces, uniform persistence, periodic and asymptotically periodic semiflows. -- Chapter 3 focuses on a nonlocal reaction-diffusion equation modelling the growth of a single species. For this model, we obtain a threshold dynamics and the global attractivity of a positive steady state. We also discuss the effects of spatial dispersal and maturation period on the evolutionary behavior in two specific cases. Our numerical investigation seems to suggest that the model admits a unique positive steady state even without monotonicity conditions. -- In Chapter 4, we consider an epidemic model represented by a reaction-diffusion equation coupled with an ordinary differential equation, which is proposed by Capasso et al. Here, the existence, uniqueness (up to translation) and global exponential stability with phase shift of bistable traveling waves are studied by phase plane techniques, monotone semiflow approaches and a detailed spectrum analysis. -- In Chapter 5, the asymptotic speeds of spread for solutions and traveling wave solutions to the integral version of the epidemic model in Chapter 4 are investigated. Our results show that the minimal wave speed for monotone traveling waves coincides with the asymptotic speed of spread for solutions with initial functions having compact supports. Some numerical simulations are also provided

Media alert in an SIS epidemic model with logistic growth

In general, media coverage would not be implemented unless the number of infected cases reaches some critical number. To reflect this feature, we incorporate the media effect and a critical number of infected cases into the disease transmission rate and consider an susceptible-infected-susceptible epidemic model with logistic growth. Our model analysis shows that early media alert and strong media effects are preferable to decrease the numbers of infected cases at endemic equilibria. Furthermore, we noticed that the model may have up to three endemic equilibria and bi-stability can occur in a threshold interval for the critical number. Note that the interval depends on parameters for the focal disease and the media effect. It is possible to roughly estimate the interval for re-emerging diseases in a given region. Therefore, the result could be useful to health policymakers. Global stability is also obtained when the model admits a unique endemic equilibrium

A nonautonomous impulsive stochastic population model with nonlinear interspecific competitive terms

Abstract In this paper, we formulate an nonautonomous impulsive population model with nonlinear interspecific competitive terms, and introduce the random perturbation of the birth rates of two species into this model. A good understanding of the extinction, stochastic permanence and global attractivity of system is obtained. Also, the limit of the average in time of the sample paths of every component of solutions is estimated. Numerical simulations are performed to justify our analytical results

Analysis of a negative binomial host–parasitoid model with two maturation delays and impulsive resource input

To study the interaction of parasitoids and their insect hosts in laboratory environment, we propose a mathematical model incorporating impulsive resource inputs, stage-structure, maturation times and negative binomial distribution of parasitoid attacks. According to the adaptability of the insect host to the environment, we obtain conditions under which the system is uniformly permanent in two cases, which guarantee that the host and its parasitoid can coexist. By applying fixed point theory, we show existence of the positive periodic solution where the host and its parasitoid can coexist, and also obtain the conditions that ensure the existence of the parasitoid-extinction periodic solution. Our numerical analysis confirms and extends our theoretical results. The simulations show that when the total amount of resource is fixed, a smaller amount of recourse inputs with a shorter period of impulsive delivery results in smaller oscillation amplitude in the insect host population. However, the development of parasitoid population is not affected by the resource management strategy. It is also demonstrated that larger maturation times, either the host's or the parasitoid's, lead to the decline of the parasitoid population. But larger parasitoid's maturation time does accelerate the host's population growth. These are helpful for us to acquire a deeper knowledge of the host–parasitoid interaction in laboratory environment

Transcriptome Analysis of Morus alba L. Flower Reveals Important Genes of Floral Sex Differentiation

Mulberry (Morus alba L.) is a perennial woody plant with significant economic benefits and ecological value. The floral character of mulberry has an important impact on the yield and quality to its fruits and leaves. However, little is known about the molecular mechanism of mulberry floral differentiation still now. The transcriptome data were obtained via Illumina HiSeq high-throughput sequencing from male and female inflorescences of the monoecious mulberry. A total of 26.21 Gb clean data were obtained, and as many as 100,177 unigenes with an average length of 821.66 bp were successfully assembled. In comparative-omics analysis, 1717 differentially expressed genes (DEGs) were identified between male and female flowers and only a quarter of the DEGs were highly expressed in female flowers. The KEGG pathway enrichment analysis revealed that DEGs were involved in glucose and lipid metabolism, hormone signal transduction, and the regulation of related transcription factors. In addition, many DEGs related to flower development and plant sex differentiation have also been detected, such as PMADS1/2, AGAMOUS, FLOWERING LOCUS T (FT), APETALA 2 (AP2), TASSELSEED2 (TS2), and ARABIDOPSIS RESPONSE REGULATOR 17 (ARR17). Finally, the expression patterns of selected 20 DEGs were validated by q-PCR and the results showed that the transcriptome data were highly reliable. This study shows that the differentiation of male and female flowers of mulberry is affected and regulated by multiple factors, with transcription factors and hormone signals playing a key role. Briefly, the current data provide comprehensive insights into the mulberry tree’s floral differentiation as well as a bioinformatics framework for the development of molecular breeding of mulberry

Composition and Morphology Modulation of Bimetallic Nitride Nanostructures on Nickel Foams for Efficient Oxygen Evolution Electrocatalysis

Metal-nitrides-based electrocatalysts for efficient oxygen-evolution have been extensively studied as one of the most promising candidates to fulfil the demand for future energy-conversion and storage. Herein, a series of NixCo1−xO- and NixCo1−xN-based nanostructures on nickel foams were reported to show excellent activities for oxygen-evolution reaction. The catalysts were prepared and modulated rationally via a facile-hydrothermal method, followed by high-temperature calcination under air or nitrogen atmosphere. The optimal bimetallic-nitride catalyst Ni0.3Co0.7N shows a small overpotential of 268 mV at 20 mA cm−2, and a Tafel slope of 66 mV dec−1 with good stability. The enhanced OER-performance is ascribed to the synergetic effect of the unique morphology and the intrinsic catalytic property of the nanostructure after nitridation