Turbidity influences individual and group level responses to predation in guppies, Poecilia reticulata

© 2015 The Association for the Study of Animal Behaviour. Increasing turbidity (either sedimentary or organic) from anthropogenic sources has significant negative impacts on aquatic fauna, both directly and indirectly by disrupting behaviour. In particular, antipredator responses of individuals are reduced, which has been attributed to a reduced perception of risk. Here, we explored the effect of turbidity on shoaling behaviour, which is known to carry important antipredator benefits, predicting that fish in turbid water should show reduced shoal cohesion (increased interindividual distances) and reduced responses to a simulated predatory threat. We explored both the individual and shoal level responses to a predation threat at four different levels of turbidity. At the shoal level, we found that shoals were less cohesive in more turbid water, but that there was no effect of turbidity on shoal level response to the predation threat. At an individual level, guppies in turbid water were more likely to freeze (rather than dart then freeze), and those that darted moved more slowly and over a shorter distance than those in clear water. Fish in turbid water also took longer to recover from a predation threat than fish in clear water. We suggest that because fish in turbid water behaved in a manner more similar to that expected from lone fish than to those in a shoal, the loss of visual contact between individuals in turbid water explains the change in behaviour, rather than a reduced perception of individual risk as is widely supposed. We suggest that turbidity could lead to a reduced collective response to predators and a loss of the protective benefits of shoaling

Turbidity weakens selection for assortment in body size in groups

Prey animals commonly associate with similar-looking individuals to reduce predation risk, via a reduction in predator targeting accuracy (the confusion effect) and preferential targeting of distinct individuals (the oddity effect). These effects are mediated by body size, as predators often preferentially select large-bodied individuals, which are therefore at an increased risk within a group. The selection pressure to avoid oddity by associating with similar sized group mates is stronger for large individuals than small. This selection depends on the ability of both predators and prey to accurately assess body size and respond accordingly. In aquatic systems, turbidity degrades the visual environment and negatively impacts on the ability of predators to detect (and consume) prey. We assessed the effect of algal turbidity on predator–prey interactions in the context of the oddity effect from the perspective of both predator and prey. From a predator’s perspective, we find that 9-spined sticklebacks preferentially target larger Daphnia in mixed swarms in clear water, but not in turbid water, although the difference in attack rates is not statistically significant. When making shoaling decisions, large sticklebacks preferentially associate with size-matched individuals in clear water, but not turbid water, whereas small individuals showed no social preference in either clear or turbid water. We suggest that a reduced ability or motivation to discriminate between prey in turbid water relaxes the predation pressure on larger prey individuals allowing greater flexibility in shoaling decisions. Thus, turbidity may play a significant role in predator–prey interactions, by altering predator–prey interactions

'Selfish herds' of guppies follow complex movement rules, but not when information is limited

Under the threat of predation, animals can decrease their level of risk by moving towards other individuals to form compact groups. A significant body of theoretical work has proposed multiple movement rules, varying in complexity, which might underlie this process of aggregation. However, if and how animals use these rules to form compact groups is still not well under- stood, and how environmental factors affect the use of these rules even less so. Here, we evaluate the success of different movement rules, by comparing their predictions with the movement seen when shoals of guppies ( Poecilia reticulata ) form under the threat of predation. We repeated the experiment in a turbid environment to assess how the use of the movement rules changed when visual information is reduced. During a simulated predator attack, guppies in clear water used complex rules that took multiple neighbours into account, forming compact groups. In turbid water, the difference between all rule predictions and fish movement paths increased, particularly for complex rules, and the resulting shoals were more fragmented than in clear water. We conclude that guppies are able to use complex rules to form dense aggregations, but that environmental factors can limit their ability to do so

Solving the Ubiquitous Problem of Stellar Radii

This thesis will address the problem of measuring stellar radii, which is ubiquitous across many fields of modern astrophysics. A technique is introduced which integrates the area beneath the stellar spectral energy distribution (SED) of a star to measure its luminosity, and the shape of the SED to measure its temperature - from which follows its radius. This method addresses many of the problems facing of existing methods, which are reviewed, as it provides accurate measurements of stellar radius using only multiband photometry and precision parallaxes. It is well known that the radii and temperatures of M-dwarf prescribed by models are in disagreement with observations, both on the pre-main-sequence (pre-MS) and the main-sequence (MS). This methodology is applied to pre-MS M-dwarfs in the Pleiades and Praesepe clusters to perform a direct comparison to the radii predicted by stellar interiors. Assessment of the physicality and accuracy of the stellar atmosphere models is also performed by comparing synthetic spectra generated from them to flux--calibrated spectroscopic observations. The parameters for the synthetic spectra are provided by the SED fitting, allowing verification of the methodology itself to be performed. The advent of Gaia DR2 means that reliable distances are now available for field M-dwarfs, permitting the extension of this investigation to MS stars. Through this investigation, the nature of radius inflation in MS M-dwarfs is studied as a function of mass. This crucially allows insight into the physics behind the observed radius inflation, allowing current theories underpinning radius inflation to be critically assessed. The conclusion of this investigation is that magnetic models are currently unable to explain radius inflation in M-dwarfs. Given the successful application of the SED fitting methodology in measuring the stellar radii of miscellaneous field stars, this work is built upon to address the problem of determining the stellar parameters of exoplanet host radii. In doing so, it is demonstrated that the SED fitting technique extends well to the mass range of stars currently being scrutinised to discover and characterise exoplanets. Given its wide applicability for exoplanet host characterisation, the potential systematic errors that may prove problematic are reviewed and methods for their mitigation are suggested

Incentives to Incarcerate: Corporation Involvement in Prison Labor and the Privatization of the Prison System

The United States has the highest incarceration rate in the entire world. The United States accounts for approximately 5% of the world’s population, yet it accounts for 25% of the world’s prisoners. Not only does the United States mercilessly incarcerate its own citizens, it disproportionately incarcerates African American and Latino men. This fact on its own is disturbing; however, when it is coupled with the fact that corporations profit from and lobby for an overly aggressive and ineffective criminal justice system, makes these statistics even more horrendous. Private prison companies such as Corrections Corporation of America and GEO Group admit that their business model is dependent on the incarceration of massive numbers of human beings and that leniency in criminal punishment would adversely affect profits. The capitalist mentality which is essential for these corporations to stay in business is inherently incompatible with human rights

Alien Registration- Morrell, Charles S. (Hampden, Penobscot County)

https://digitalmaine.com/alien_docs/8220/thumbnail.jp

Handedness in fiddler crab fights

Asymmetric weapons are common in bilateral animals and, in some species, they can occur on either the left- or the right-hand side of the body (lateralization). Fiddler crabs (Uca spp, Decapoda: Ocypodidae) have an enlarged claw that is used in male–male combat over territories and in courtship displays. Males can be either right- or left-handed, and most species have a 1:1 ratio. Past studies have found little effect of handedness on fighting success, fight duration or other measures of combat. Here we show that, while handedness per se, does not affect fighting, handedness matching has a significant effect. In Uca mjoebergi, fights between different-handed males were more likely to escalate to grappling, suggesting that it is harder for the combatants to determine the winner. We suggest that the positioning of the claws during fighting creates distinct forces that result in different outcomes for same- versus different-handed fights. This can represent a strong selective pressure in populations with an uneven handedness distribution where the handedness minority will often engage in different-handed fights. We discuss these results in light of the selective forces that may act on handedness distribution in fiddler crabs

Ion-exchanged waveguide add/drop filter

An add/drop filter is fabricated using ion-exchanged waveguides and photowritten Bragg gratings. The device exhibits 20 dB extinction ratios and 3 dB bandwidths of 0.4 nm (100 GHz)

Applications of matrix derivatives to optimization problems in statistical pattern recognition

A necessary condition for a real valued Frechet differentiable function of a vector variable have an extremum at a vector x sub 0 is that the Frechet derivative vanishes at x sub 0. A relationship between Frechet differentials and matrix derivatives was established that obtains a necessary condition on the matrix derivative at an extrema. These results are applied to various scalar functions of matrix variables which occur in statistical pattern recognition