The dynamic consequences of invasion: negative plant-soil feedbacks on natives increase ver the time course of invasion

*a) Background/Questions/Methods*
Exotic species can negatively impact native community members, directly through interference competition, or indirectly by altering interactions between native species and other species such as pathogens and mutualists. Soil microbial communities have been shown to respond to invasive species, yet are relatively stable and may take time to respond to perturbations. For this reason, microbe-mediated effects of invasives on natives may take time to develop and may change throughout the invasion process. Few studies have investigated how species interactions between natives and exotics change during invasions.

_Acer platanoides_ was introduced into the US from Europe in 1756 and has since invaded intact forests, lowering understory diversity and inhibiting native tree species regeneration. We hypothesize that _A. platanoides_ invasion will decrease seedling survival in the native _A. saccharum_ by changing the soil microbial community through plant-soil feedbacks (PSF), and this relationship will intensify over the course of an invasion. We collected soil samples from beneath the canopies of both species co-occurring in Michigan forests that had been invaded by _A. platanoides_ for varying time periods. In the greenhouse, we inoculated seedlings of both species with the microbial communities to determine how the soil community affects seedling survival and growth.

*b) Results/Conclusion*
The microbe-mediated negative effects of _A. platanoides_ on survival of the native congener _A. saccharum_ increased with increasing invasion age (negative correlation between invasion age and _A. saccharum_ survival; r = -0.806, R^2^ = 0.65, p = 0.032). This result was not related to _A. platanoides_ density, suggesting that age of invasion drives this pattern. Contrastingly, invasion age did not significantly influence survival of _A. platanoides_ seedlings, indicating that _A. platanoides’_ PSF impacts native species but not on conspecific regeneration. Overall, _A. platanoides_ seedlings had increased growth (more and larger leaves) when grown in soil communities collected from the native _A. saccharum_, but _A. saccharum_ seedlings had reduced growth when grown in conspecific soil (p = 0.044). These results suggest that invasive species may have increased performance in exotic ranges by their ability to modify the soil microbial community in a manner that suppresses the growth of native species.

We show the microbial community cultivated by an invader alters the performance of a native plant species, and this effect increases over the course of an invasion. In future work, we plan to identify changes in microbial community composition and the relative abundances of mutualists versus antagonists in response to invasion to identify potential mechanisms

Asymptotic analysis of first passage time in complex networks

The first passage time (FPT) distribution for random walk in complex networks is calculated through an asymptotic analysis. For network with size $N$ and short relaxation time $\tau\ll N$, the computed mean first passage time (MFPT), which is inverse of the decay rate of FPT distribution, is inversely proportional to the degree of the destination. These results are verified numerically for the paradigmatic networks with excellent agreement. We show that the range of validity of the analytical results covers networks that have short relaxation time and high mean degree, which turn out to be valid to many real networks.Comment: 6 pages, 4 figures, 1 tabl

Can a State Funded Rural Economic Development Program Positively Impact the State’s Economy? A Case Study Application using Texas Department of Agriculture’s Rural Tourism Economic Development Program

In this paper, we review the tourism impact from supported tourism events and measure their economic value to the local economy. The economic values are the result of visitor spending and extrapolated to total event attendance creates economic values from the state-supported event. Communities receiving funding were responsible for collecting visitor surveys to measure consumer spending as well as the community completing a survey to record the investment cost of the event. The results were that state support represented 14 percent of the total event investment and total event value from visitor spending was $7.8 million for 31 events. The state percent share in value represents$1.1 million and considering the program-expended funds of $147,276 there is a$7.50 return for every $1 of state funding. Economic impacts from the funds add additional value and measure total economic value to Texas. We conclude that state supported programs focusing in the area of partial marketing support can create positive return on investment value of state funding.tourism, economic development, Texas tourism, state sponsored tourism, Agribusiness, Agricultural and Food Policy, Community/Rural/Urban Development, Marketing,

Internal Gravity Waves Modulate the Apparent Misalignment of Exoplanets around Hot Stars

We propose that the observed misalignment between extra-solar planets and their hot host stars can be explained by angular momentum transport within the host star. Observations have shown that this misalignment is preferentially around hot stars, which have convective cores and extended radiative envelopes. This situation is amenable to substantial angular momentum transport by internal gravity waves (IGW) generated at the convective-radiative interface. Here we present numerical simulations of this process and show that IGW can modulate the surface rotation of the star. With these two- dimensional simulations we show that IGW could explain the retrograde orbits observed in systems such as HAT-P-6 and HAT-P-7, however, extension to high obliquity objects will await future three- dimensional simulations. We note that these results also imply that individual massive stars should show temporal variations in their v sini measurements.Comment: 6 pages, 2 figures, Accepted for publication in ApJ

Carbon Rich Extremely Metal Poor Stars: Signatures of Population-III AGB stars in Binary Systems

We use the Cambridge stellar evolution code STARS to model the evolution and nucleosynthesis of zero-metallicity intermediate-mass stars. We investigate the effect of duplicity on the nucleosynthesis output of these systems and the potential abundances of the secondaries. The surfaces of zero-metallicity stars are enriched in CNO elements after second dredge up. During binary interaction, such as Roche lobe overflow or wind accretion, metals can be released from these stars and the secondaries enriched in CNO isotopes. We investigate the formation of the two most metal poor stars known, HE 0107-5240 and HE 1327-2326. The observed carbon and nitrogen abundances of HE 0107-5240 can be reproduced by accretion of material from the companion-enhanced wind of a seven solar star after second dredge-up, though oxygen and sodium are underproduced. We speculate that HE 1327-2326, which is richer in nitrogen and strontium, may similarly be formed by wind accretion in a later AGB phase after third dredge-up.Comment: 16 pages, 1 figure, 7 tables, accepted by MNRA

Fronthaul-Constrained Cloud Radio Access Networks: Insights and Challenges

As a promising paradigm for fifth generation (5G) wireless communication systems, cloud radio access networks (C-RANs) have been shown to reduce both capital and operating expenditures, as well as to provide high spectral efficiency (SE) and energy efficiency (EE). The fronthaul in such networks, defined as the transmission link between a baseband unit (BBU) and a remote radio head (RRH), requires high capacity, but is often constrained. This article comprehensively surveys recent advances in fronthaul-constrained C-RANs, including system architectures and key techniques. In particular, key techniques for alleviating the impact of constrained fronthaul on SE/EE and quality of service for users, including compression and quantization, large-scale coordinated processing and clustering, and resource allocation optimization, are discussed. Open issues in terms of software-defined networking, network function virtualization, and partial centralization are also identified.Comment: 5 Figures, accepted by IEEE Wireless Communications. arXiv admin note: text overlap with arXiv:1407.3855 by other author