Structure factor of polymers interacting via a short range repulsive potential: application to hairy wormlike micelles

We use the Random Phase Approximation (RPA) to compute the structure factor, S(q), of a solution of chains interacting through a soft and short range repulsive potential V. Above a threshold polymer concentration, whose magnitude is essentially controlled by the range of the potential, S(q) exhibits a peak whose position depends on the concentration. We take advantage of the close analogy between polymers and wormlike micelles and apply our model, using a Gaussian function for V, to quantitatively analyze experimental small angle neutron scattering profiles of semi-dilute solutions of hairy wormlike micelles. These samples, which consist in surfactant self-assembled flexible cylinders decorated by amphiphilic copolymer, provide indeed an appropriate experimental model system to study the structure of sterically interacting polymer solutions

On the mismatch between salinity tolerance and preference for an invasive fish: A case for incorporating behavioral data into niche modeling

Many estuarine species are euryhaline, tolerating a broad range of salinity conditions, such that data on their salinity tolerances can provide little information about a species' distribution and abundance. This is particularly true for nonnative species, known to be tolerant of a broad range of conditions. Instead, data on a species' abiotic or habitat preferences may improve prediction of a nonnative species' potential range, if introduced or if undergoing range expansion. At minimum, information about abiotic preferences may be telling of areas where the probability of nonnative occurrence or density may be higher, and if present, of areas that confer higher fitness. In this study, the salinity preference of the nonnative African jewelfish (Hemichromis letourneuxi), a recent and rapidly-expanding invader in the Florida Everglades, was quantified in laboratory trials. Despite the broad salinity tolerance of African jewelfish (up to 50), trials show a strong preference for freshwater conditions. When presented with a salinity gradient, over 50% of observations in timed videotaped trials were collected in the lowest salinity chamber (0.3), suggesting an affinity for low salinity, which was unaffected by the sex or body condition of study fish. Fish clearly avoided mid and full salinity conditions. Findings suggest that their distribution may be considerably more limited, and that the species may have higher invasion success in oligohaline habitats, than predicted based on their salinity tolerance. Results have important implications for nonnative species niche modeling, and argue for better integration of behavior along with physiological responses when examining species distributions in dynamic environments. •We quantified the salinity preference of a nonnative fish in lab trials.•When exposed to a gradient, fish showed a consistent preference for 0.3 salinity.•Results suggest a more limited field distribution than based on salinity tolerance.•Findings argue for incorporating preference data when forecasting nonnative ranges

Bonefish in South Florida: status, threats and research needs

Bonefish (Albula vulpes) support a world-renowned fishery in South Florida, USA. However, fishing guides and anglers have been reporting significant declines in bonefish angling quality over that past three decades. In the absence of any long-term bonefish stock and ecosystem assessments, the cause of this decline in the fishery is unclear. Here we summarize our current knowledge of bonefish ecology in Florida and discuss potential causes of fishery decline. Reductions and alterations in freshwater flows from the Everglades have caused major changes in bonefish habitat, including acute (anoxic conditions) and chronic (ch