Effects of winter food supplementation on reproduction, body mass, and numbers of small mammals in montane Australia

Abstract

We used a food-supplementation experiment to test the hypothesis that small-mammal populations are food-limited during winter in southeastern Australia. We trapped small mammals along 120- to 150-m transects at 12 creek and 12 ridgetop sites (representing high- and low-quality habitats) for 2 months prior to winter and 2 months during winter. High-quality food (peanut butter, honey, oats, and dried cat food) was provided ad libitum for 7 weeks during winter at four sites in each habitat. Eight sites were provided with empty feeding tubes and eight were untreated. Seven weeks of food supplementation caused numerical increases of 4.0- and 5.0-fold for the rodents Rattus fuscipes and Rattus lutreolus, respectively. Increases were due largely to immigration, and were only observed in the high-quality creek habitats (R. lutreolus were exclusively captured at creek sites). Food supplementation also led to an increase in body mass and reversed the hiatus in winter breeding for rodents. These results suggest that populations of both species are limited by winter food availability. However, survival rates (indexed from recapture rates) were not affected by food supplementation. Mean body mass of the marsupial Antechinus stuartii also increased with food supplementation, but other demographic parameters showed no response; numbers declined at creek sites after additional food was provided. Trapping-revealed measures of interspecific association showed that A. stuartii avoided areas of high rat numbers after additional food was provided. It is thus likely that interference competition from the much larger and more abundant rodents forced A. stuartii out of the food-supplemented creek sites, hence mediating the direct effects of food supplementation on this species.

The island syndrome and population dynamics of introduced rats

“…However, in forest, mouse density conversely decreased in summer. Asymmetrical interspecific competition in summer with the higher density of rats in the forest could explain this, possibly forcing the inferior competitor to emigrate as others have observed (Banks and Dickman 2000). In winter, when rat densities were lower, mice were only limited by resource availability.…”

“…The effect of insularity and latitude on body-size, the 'island rule', has received much attention, and changes in body-size of rodents have been variously attributed to Table 4 and mouse densities, not presented) extrinsic (latitude, Yom-Tov et al 1999;climate, Millien and Damuth 2004) and intrinsic (resource availability, Banks and Dickman 2000;predation, Norrdahl et al 2004) factors, or trade-offs, among them (Palkovacs 2003). Because our islands shared similar climates and lie within the same biogeographic region, we do not believe extrinsic factors are likely explanations for differences in body condition.…”

Population and behavioural responses of native prey to alien predation

“…Again, this seems unlikely. Both species are food-limited in winter (Banks and Dickman 2000); our experiments were carried out in summer when natural food resources are maximal and food shortages are least likely to occur (Dickman 1989). Third, both species may have become habituated to fox odour over time.…”

Competition and habitat use in native Australian Rattus: is competition intense, or important?

“…Both study species occur along the eastern seaboard of Australia, and achieve high population densities (>10 ha -1 ) in some coastal areas and upland localities such as the Blue Mountains (Banks 1991). Both species eat green plant material; R. lutreolus takes primarily monocotyledonous plants, while R. fuscipes includes considerable arthropod, seed and fungal material in the diet (Warneke 1971;Stewart 1979;Luo 1993).…”