No abstract

It is important to unravel how invasive species impact native ecosystems in order to control them effectively. The presence of abundant exotic prey promotes population growth of invasive predators, thereby enhancing the predation pressure on native prey (hyper-predation). Not only the exotic prey but also feeding by humans is likely to cause “hyper-predation”. However, the contribution of artificial resources to this was underestimated in previous studies. Here, we combined fecal and stable isotope analyses to reveal short- and long-term food habits of free-ranging cats on Tokunoshima Island. Although 20.1% of the feral cat feces contained evidence of forest-living species, stable isotope analysis suggested that the cats were mostly dependent on artificial resources. In addition, a general linear model analysis showed that their diet was strongly correlated with landscape variables. These results indicate that the invasive free-ranging cats are aided by anthropogenic feeding, and they move from the human habituated area to natural areas with high biodiversity. These findings suggest the possibility of human feeding indirectly accelerates the effect of cat predation, and call for a further study on their demography. Cat management mainly involves trapping, but our findings show that educating local residents to stop feeding free-ranging cats and keeping pet cats indoors are also important.

We investigated maize (Zea mays) consumption by brown bears (Ursus arctos) in a subpopulation of eastern Hokkaido, Japan, using carbon stable isotope analysis of hair samples to better understand the pattern and scale of movement of the bears' crop-foraging behavior. We identified a total of 30 individuals (19 males and 11 females) using DNA analysis of the hair samples. Stable isotope analysis suggested that female bears that were more likely to consume maize lived closer to agricultural crop fields. Our statistical model also estimated that the relative maize consumption of female bears decreased rapidly as the distance to crop fields increased to 3-4 km, similar to the radius of the annual home range of female bears. In contrast, male bears that were more likely to consume maize lived both in forested areas and near crop fields. Even if male bears live in a forested area except during the maize harvest period, they appeared to be at risk of being killed by lethal control because they can move from forested areas to crop fields during the maize harvest period. Collecting hair samples of many bears in the population over several years may allow the effect of lethal control on population viability to be estimated non-invasively.

No abstract

We determined the magnitude of isotopic fractionation of carbon and nitrogen stable isotope ratios (as enrichment factors, Δδ(13)C and Δδ(15)N, respectively) between the tissues and diets of captive Japanese macaques (Macaca fuscata) using a controlled feeding experiment, to provide basic data for reconstructing their feeding habits. The Δδ(13)C and Δδ(15)N values, respectively, were 0.9 ± 0.2 ‰ (mean ± standard deviation, SD) and 3.0 ± 0.3 ‰ for whole blood, 1.3 ± 0.2 ‰ and 4.3 ± 0.3 ‰ for plasma, and 0.8 ± 0.2 ‰ and 3.0 ± 0.2 ‰ for red blood cells. However, the Δδ(13)C and Δδ(15)N values for hair were 2.8 ± 0.3 ‰ and 3.4 ± 0.2 ‰, respectively. No difference was detected in the δ(13)C and δ(15)N values of hair sampled from different parts of the body. We investigated the effects of diet on δ(13)C in growing hair by alternating the diet of the macaques each month between two diets that differed markedly in δ(13)C. Hair regrown after shaving repeatedly recorded the δ(13)C of the diet consumed during the time of hair growth. On the other hand, hair naturally grown during the diet-change experiment did not show a clear pattern. One possible reason is that the hair had grown abnormally under unnatural indoor conditions and showed complicated isotope signatures. To reconstruct the long-term feeding history of Japanese macaques, we need to further clarify the relationships between the stable isotope signature of diet and various body tissues.