Knobcone pine response to shading from competing chaparral shrubs following stand-replacing wildfire

In northern California, fire regimes are shifting towards more frequent and larger severe wildfire. There is growing concern that this shift poses a threat to biodiversity in the form of cover type change at the landscape scale, resulting in the extirpation of some species in favor of +AD617:AD649well-adapted ones. In northern California, mature serotinous conifers, such as knobcone pine (Pinus attenuata), and resprouting shrub species easily regenerate in severe patches of any size. There is no general consensus regarding the effects of shrub competition on conifer recruitment; conifer response varies with shade tolerance and other abiotic factors. Knobcone pine and chaparral shrubs are universally shade intolerant, and we expect shading to be the main driver of inter-species competition. We examined knobcone pine regeneration on lower slopes within the 2018 Carr and Delta fires at the third and fourth post-fire years, as well as the 2008 Motion Fire at the 14th post-fire year, focusing on two measurements of shrub shading: inter-shrub porosity (% shrub cover) and intra-shrub porosity (species-specific crown density). Our response variables included recruitment success (recruits per ovulate cone) and growth (height). We found (1) there were few pine recruits under shrubs, with the bulk of the shrub-induced morality of knobcone pine occurring before the third growing season; (2) knobcone pine averaged about 6 established recruits per burned parent tree; and (3) the recruits were expected to persist despite limited growth and reach the shrub canopy by about the seventh year after fire. We conclude that competition with shrubs on lower slopes in northern California does not sufficiently impede the post-fire increase in serotinous pine density to limit subtle expansion into chaparral

Modeling the effect of striped bass (Morone saxatilis) on the population viability of Sacramento River winter-run chinook salmon (Onchorhynchus tshawytscha)

We estimated the impact of striped bass (Morone saxatilis) predation on winter-run chinook salmon (Oncorhynchus tshawytscha) with a Bayesian population dynamics model using striped bass and winter-run chinook salmon population abundance data. Winter-run chinook salmon extinction and recovery probabilities under different future striped bass abundance levels were estimated by simulating from the posterior distribution of model parameters. The model predicts that if the striped bass population declines to 512,000 adults as expected in the absence of stocking, winter-run chinook salmon will have about a 28% chance of quasi-extinction (defined as three consecutive spawning runs of fewer than 200 adults) within 50 years. If stocking stabilizes the striped bass population at 700,000 adults, the predicted quasi-extinction probability is 30%. A more ambitious stocking program that maintains a population of 3 million adult striped bass would increase the predicted quasi-extinction probability to 55%. Extinction probability, but not recovery probability, was fairly insensitive to assumptions about density dependence. We conclude that winter-run chinook salmon face a serious extinction risk without augmentation of the striped bass population and that substantial increases in striped bass abundance could significantly increase the threat to winter-run chi-nook salmon if not mitigated by increasing winter chinook salmon survival in some other way

Dislocation interactions and crack nucleation in a fatigued near-alpha titanium alloy

Dislocation interactions at the crack nucleation site were investigated in near-alpha titanium alloy Ti-6242Si subjected to low cycle fatigue. Cyclic plastic strain in the alloy resulted in dislocation pile-ups in the primary alpha grains, nucleated at the boundaries between the primary alpha and the two-phase regions. These two phase regions provided a barrier to slip transfer between primary alpha grains. We suggest that crack nucleation occurred near the basal plane of primary alpha grains by the subsurface double-ended pile-up mechanism first conceived by Tanaka and Mura. Superjogs on the basal dislocations were observed near the crack nucleation location. The two phase regions showed direct transmission of dislocations between secondary alpha plates, transmitted through the beta ligaments as , which then decompose into dislocation networks in the beta. The beta ligaments themselves do not appear to form an especially impenetrable barrier to slip, in agreement with the micropillar and crystal plasticity investigations of Zhang et al

Hyper-efficient model-independent Bayesian method for the analysis of pulsar timing data

A new model independent method is presented for the analysis of pulsar timing data and the estimation of the spectral properties of an isotropic gravitational wave background (GWB). We show that by rephrasing the likelihood we are able to eliminate the most costly aspects of computation normally associated with this type of data analysis. When applied to the International Pulsar Timing Array Mock Data Challenge data sets this results in speedups of approximately 2 to 3 orders of magnitude compared to established methods. We present three applications of the new likelihood. In the low signal to noise regime we sample directly from the power spectrum coefficients of the GWB signal realization. In the high signal to noise regime, where the data can support a large number of coefficients, we sample from the joint probability density of the power spectrum coefficients for the individual pulsars and the GWB signal realization. Critically in both these cases we need make no assumptions about the form of the power spectrum of the GWB, or the individual pulsars. Finally we present a method for characterizing the spatial correlation between pulsars on the sky, making no assumptions about the form of that correlation, and therefore providing the only truly general Bayesian method of confirming a GWB detection from pulsar timing data.Comment: 9 pages, 4 figure

The relationship between the dominant eye and refractive error in anisometropia

The relationship between the dominant eye and refractive error in anisometropi

Avian Habitat Use in a Chronosequence of Bottomland Hardwood Forest Restoration Sites

Since the 1950s, anthropogenic activity has caused the loss of millions of hectares of bottomland hardwood forest in the Upper Mississippi River Valley, causing population declines in bird populations. Restoration of these forest stands has been ongoing for the past 2 decades. We assessed bird species presence on sites in the Upper Mississippi River Valley to quantify diversity and relate presence to habitat conditions and sites’ age since restoration. We observed higher mean diversities at mature bottomland-forest sites during the spring and autumn, but nested ANOVAs indicated no significant differences among restoration-age categories during spring. During the autumn, the 15–23-y and the mature bottomland-forest categories were significantly different from th

A fourth account of centipede (Chilopoda) predation on bats

With an incident in Palo Duro Canyon, Texas, USA, Scolopendra heros Girard (Chilopoda: Scolopendromorpha: Scolopendridae) becomes the third centipede species known to prey on bats; S. gigantea Linnaeus and S. viridicornis Newport have been so documented in Venezuela and Brazil, respectively. The Texas predation was interrupted by the predator/prey pair’s falling around 15–20 m from the canyon wall and, perhaps also, by human presence where they landed. The centipede uncoiled and retreated to shelter under a nearby rock and, after initial immobilization, so did the bat. Con un incidente en Palo Duro Canyon, Texas, Estados Unidos, Scolopendra heros Girard (Chilopoda: Scolopendromorpha: Scolopendridae) se convierte en el tercer ciempiés que se sabe depreda murciélagos; S. gigantea Linnaeus y S. viridicornis Newport han sido documentados mostrando este comportamiento en Venezuela y Brasil, respectivamente. El incidente de Texas fue interrumpido por el despeñamiento del par depredador/presa unos 15–20 m desde la pared del cañón y, al parecer, por la presencia humana en el sitio de caída. El ciempiés se desenrolló y retiró para refugiarse bajo una roca cercana. Tras permanecer inmóvil inicialmente, el murciélago hizo lo mismo