Small mammals reduce activity during high moon illumination under risk of predation by introduced predators

Predation influences prey survival and drives evolution of anti-predator behaviour. Anti-predator strategies by prey are stimulated by direct encounters with predators, but also by exposure to indicators of risk such as moonlight illumination and vegetation cover. Many prey species will suffer increased risk on moonlit nights, but risk may be reduced by the presence of dense vegetation. Determining the role of vegetation in reducing perceived risk is important, especially given predictions of increased global wildfire, which consumes vegetation and increases predation. We used remote cameras in southeastern Australia to compare support for the predation risk and habitat-mediated predation risk hypotheses. We examined the influence of moonlight and understorey cover on seven 20-2500 g mammalian prey species and two introduced predators, red foxes and feral cats. Activity of all prey species reduced by 40-70% with increasing moonlight, while one species (bush rat) reduced activity in response to increasing moonlight more sharply in low compared to high understorey cover. Neither predator responded to moonlight. Our findings supported the predation risk hypothesis and provided limited support for the habitat-mediated predation risk hypothesis. For prey, perceived costs of increased predation risk on moonlit nights outweighed any benefits of a brighter foraging environment.

Do body size, diet type or residence time explain habitat use in a vertebrate herbivore community?

Many theories attempt to explain patterns of community organisation among large herbivores. We explored the role of body size, diet type and residence time on habitat use in a community comprising four metatherians (western grey kangaroo, Macropus fuliginosus; eastern grey kangaroo, M. giganteus; red-necked wallaby, Notamacropus rufogriseus; swamp wallaby, Wallabia bicolor) and two eutherians (red deer, Cervus elaphus; European rabbit, Oryctolagus cuniculus) in south-eastern Australia. We used camera traps to estimate habitat occupancy, quantified habitat specialisation using relative entropy, and ran regressions using percentage grass consumed, log(mass) and log(time at site) as predictor variables and relative entropy as the response. If body size influenced habitat use, we predicted smaller species would occupy fewer habitats. If diet type influenced habitat use, we predicted intermediate feeders would use more habitats. If the time that a species had been present at a site predicted community organisation, newer species would use more habitats. None of these theories explained habitat use in our community. Red deer used a narrower range of habitats than expected, perhaps due to the poor suitability of habitats available in the Grampians. While interactions between our hypotheses are likely to be important, the body size model deserves further attention in this community.

Pathogenesis of anemia in rats with Walker 256 carcinosarcoma

The purpose of this study was to further clarify the pathophysiology of anemia in malignancy. To accomplish this end a total of 210 normal or splenectomized rats with or without the solid form of Walker 256 carcinosarcoma was studied. In vivo studies demonstrated that in stage I cancer (tumor weight less than 10% of body weight) a slightly shortened red cell survival resulted in a mild degree of anemia. With increasing tumor size, 51Cr red cells mass decreased further, in spite of extramedullary erythropoiesis and a slightly increased incorporation transferrin-bound iron into red cells. Splenectomized rats with stage II cancer developed a more profound degree of anemia associated with a significantly decreased incorporation of 59Fe into red cells. Marrow cell culture studies demonstrated that heme synthesis in response to erythropoietin in stage I cancer was not significantly different from normal, but in rats with stage II cancer (tumor weight greater than 10% of body weight) heme synthesis in response to erythropoietin was markedly decreased. In vitro studies demonstrated that plasma erythropoietin levels were appropriately increased in most rats with transplanted malignancy. These studies indicate that bone marrow heme synthesis in response to erythropoietin is impaired in rats with the anemia of advanced malignancy.