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Invasive predators not only cause native prey populations to decline but can also induce evolutionary changes in their behaviour in a short time scale. However, few studies have reported these rapid responses. This could be because strong predation pressure by invasive species often causes the extinction of native prey before an evolutionary effect can be detected. Recently, eradication projects successfully removed invasive predators and resulted in the recovery of native prey. We predicted that rapid responses can be detected by evaluating the behavioural traits of native prey populations having different histories of predator invasion. We examined the behavioural responses of a native frog, the Amami tip‐nosed frog (Odorrana amamiensis), to an invasive mongoose (Herpestes auropunctatus) on Amami Island, Japan. The native frog population was reduced by the mongoose; however, the eradication project leads to the recovery of the native frog population, thereby providing an opportunity to evaluate the evolutionary impact of the invasive species. We hypothesized that spatial differences in flight initiation distance (FID) can be explained by spatial patterns of past mongoose predation pressure. We used a spatial model based on generalized least squares regression methods to test the effects of potential factors on FID. We then performed model comparison and model averaging. We found that the native frog became more sensitive to the approach of a potential predator as the historical impact of the mongoose increased, suggesting that past strong predation pressure by the mongoose drove a rapid behavioural response in the native frog. Our study suggests that rapid behavioural responses of other native species can be detected not only after successful eradication projects, but also on currently invaded sites with different invasion histories. [ABSTRACT FROM AUTHOR]

The distribution of cracks strongly affects the hydro-mechanical behavior and strength of soil. In order to characterize the distribution of cracks in undisturbed expansive soil, X-ray computed tomography (X-ray CT) tests were carried out for one type of undisturbed expansive soil from Mile City, China. Seven undisturbed specimens retrieved from depths between 1 and 4.7 m were used to study the evolution of cracks along the drying path. The characteristics of the cracks were quantitatively studied by 3D parameters extracted from CT images by commercial software. The test results suggested that, with an increase in suction, the total volume of the cracks gradually increased, and one large crack formed due to the merging of sub-cracks before the shrinkage limit. When the suction was larger than the suction corresponding to the shrinkage limit, degradation of the cracks caused by the collapse of the soil structure was observed. Meanwhile, due to the development of sub-cracks, the crack anisotropy caused by the typically oriented primary cracks decreased along the drying path. Finally, a conceptual model of crack development for undisturbed Mile clay was proposed based on the evolution of crack volume, number, shape, and orientation.

In the geological disposal of high-level radioactive waste, bentonite buffer materials are required to have self-sealing property, which is the ability to fill gaps by swelling deformation between the buffer material and the waste containment vessel or surrounding bedrock. Self-sealing property was evaluated based on the pressure generated after the gap filling under the assumption of constant dry density and water content in the specimen and buffer material. On the other hand, it takes tens to hundreds of years for the transitional period until the buffer contacts with groundwater, fills the gap, and the internal state converges to a uniform state. To assess changes more accurately in the condition of the buffer material, it is necessary to evaluate time courses in the density and water content of the buffer material because of groundwater infiltration and swelling deformation. From these, the authors developed an experimental apparatus for swelling deformation of bentonite, which consists of a mould with 2 mm-thick stacked rings. It is aimed to evaluate the distribution of dry density, water content, and degree of saturation inside the specimen by cutting the specimen with a 2 mm thick ring after the end of experiment. In this paper, results of preliminary experiments to confirm the applicability of this apparatus to swelling deformation test of bentonite was firstly described. Then, experiments were conducted on compacted bentonite specimens using this apparatus, and changes in the dry density and water content distribution inside the specimens were evaluated in terms of swelling deformation behaviour.