Nonlinearity in the predation risk of prey mobility.

Odorous waste products such as urine and faeces are unavoidable for most animals and are widely exploited by predators and their prey. Consequently, waste accumulations can be risky and prey which increase their mobility in order to disperse and dilute their waste should avoid a high predation risk until this benefit is balanced by the increasing risks of random predator encounter. This hypothesis was tested for voles (Microtus spp.) in Finland which are vulnerable to predation due to the scent and ultraviolet attractiveness of their urine. The mortality and mobility of radio-collared voles showed a U-shaped relationship, regardless of vole sex, species or population cycle phase. The low risks for prey making intermediate movements suggest that predation risk can exert strong selective pressures on prey such that they have little respite from the risk of being killed.

Gastrin and gastric acid secretion in renal failure.

In 10 anephric patients awaiting transplantation, 15 patients with chronic renal failure and 30 patients with acute renal failure, daily basal plasma gastrin levels and basal and stimulated gastric acid secretion were measured. Significant elevated plasma gastrin levels were found in all of the anephric patients and in 50 percent of the patients with acute and 55 percent of those with chronic renal failure. Elevated plasma gastrin levels decreased to normal after kidney transplantation or when kidney function returned to normal in the patients with acute renal failure. Gastric acid secretion studies showed a consistent pattern in all three groups of patients with a low basal acid output, a high basal intragastric pH and a very significant peak acid output, perhaps secondary to elevated plasma gastrin levels due to inadequate renal inactivation of gastrin. This may partly explain the increased incidence of gastrointestinal bleeding and gastritis seen in patients with different degrees of renal failure.

Ultraviolet properties of Australian mammal urine.

The exploitation of predator signals by potential prey is well researched, but relatively little is known about how predators exploit chemical cues (either deliberate signals or waste by-products) produced by their prey. In Finland, the urine of some small rodents ( Microtus spp. and Clethrionomys spp.) is reflective in the ultraviolet range of wavelengths, and diurnal raptors with ultraviolet vision use these urine marks to track their rodent prey. This study examines the potential for such a phenomenon in Australian systems by studying the ultraviolet properties of urine from 13 native and introduced mammal species that are variously preyed upon by raptors. Urine from all 13 species displayed various levels of ultraviolet absorbance in their urine and fluorescence in the ultraviolet range. However, no signs of ultraviolet hyper-reflectance were detected, suggesting that the urine of European voles have unique ultraviolet properties. Ultraviolet-sensitive predators in Australia may be able to distinguish between species based on variation in the ultraviolet absorbance of their urine, but ultraviolet properties did not differ between prey and non-prey species, nor marsupial and placental groups. Moreover, because many natural surfaces are ultraviolet absorbing, it is unlikely that raptors could rely upon the ultraviolet properties of urine to target key prey species.