Abstract. Determining the biological and environmental factors that limit the distribution and abundance of organisms is central to our understanding of the niche concept and crucial for predicting how species may respond to large-scale environmental change, such as global warming. However, detailed ecological information for the majority of species has been collected only at a local scale, and insufficient consideration has been given to geographical variation in intraspecific niche requirements. To evaluate the influence of environmental and biological factors on patterns of species distribution and abundance, we conducted a detailed, broadscale study across the tropical savannas of northern Australia on the ecology of three large, sympatric marsupial herbivores (family Macropodidae): the antilopine wallaroo (Macropus antilopinus), common wallaroo (M. robustus), and eastern grey kangaroo (M. giganteus). Using information on species abundance, climate, fire history, habitat, and resource availability, we constructed species' habitat models varying from the level of the complete distribution to smaller regional areas. Multiple factors affected macropod abundance, and the importance of these factors was dependent on the spatial scale of analyses. Fire regimes, water availability, geology, and soil type and climate were most important at the large scale, whereas aspects of habitat structure and interspecific species abundance were important at smaller scales. The distribution and abundance of eastern grey kangaroos and common wallaroos were strongly influenced by climate. Our results suggest that interspecific competition between antilopine wallaroos and eastern grey kangaroos may occur. The antilopine wallaroo and eastern grey kangaroo (grazers) preferred more nutrientrich soils than the common wallaroo (grazer/browser), which we relate to differences in feeding modes. The abundance of antilopine wallaroos was higher on sites that were burned, whereas the abundance of common wallaroos was higher on unburned sites. Future climate change predicted for Australia has the capacity to seriously affect the abundance and conservation of macropod species in tropical savannas. The results of our models suggest that, in particular, the effects of changing climatic conditions on fire regimes, habitat structure, and water availability may lead to species declines and marked changes in macropod communities.

Summary 1.Much recent research has focused on the use of species distribution models to explore the influence(s) of environment (predominantly climate) on species' distributions. A weakness of this approach is that it typically does not consider effects of biotic interactions, including competition, on species' distributions. 2.Here we identify and quantify the contribution of environmental factors relative to biotic factors (interspecific competition) to the distribution and abundance of three large, wide-ranging herbivores, the antilopine wallaroo ( Macropus antilopinus ), common wallaroo ( Macropus robustus ) and eastern grey kangaroo ( Macropus giganteus ), across an extensive zone of sympatry in tropical northern Australia. 3.To assess the importance of competition relative to habitat features, we constructed models of abundance for each species incorporating habitat only and habitat + the abundance of the other species, and compared their respective likelihoods using Akaike's information criterion. We further assessed the importance of variables predicting abundance across models for each species. 4. The best-supported models of antilopine wallaroo and eastern grey kangaroo abundance included both habitat and the abundance of the other species, providing evidence of interspecific competition. Contrastingly, models of common wallaroo abundance were largely influenced by climate and not the abundance of other species. The abundance of antilopine wallaroos was most influenced by water availability, eastern grey kangaroo abundance and the frequency of late season fires. The abundance of eastern grey kangaroos was most influenced by aspects of climate, antilopine wallaroo abundance and a measure of cattle abundance. 5. Our study demonstrates that where census and habitat data are available, it is possible to reveal species' interactions (and measure their relative strength and direction) between large, mobile and/ or widely-distributed species for which competition is difficult to demonstrate experimentally. This allows discrimination of the influences of environmental factors and species interactions on species' distributions, and should therefore improve the predictive power of species distribution models.

Since its introduction in 1997, robotic surgery has overcome many limitations, including setup costs and surgeon training. The use of robotics in general surgery remains unknown. This study evaluates robotic-assisted procedures in general surgery by comparing characteristics with its nonrobotic (laparoscopic and open) counterparts. Weighted Healthcare Cost and Utilization Project Nationwide Inpatient Sample data (2008, 2009) were used to identify the top 12 procedures for robotic general surgery. Robotic cases were identified by Current Procedural Terminology codes 17.41 and 17.42. Procedures were grouped: esophagogastric, colorectal, adrenalectomy, lysis of adhesion, and cholecystectomy. Analyses were descriptive, t tests, χ2s, and logistic regression. Charges and length of stay were adjusted for gender, age, race, payer, hospital bed size, hospital location, hospital region, median household income, Charlson score, and procedure type. There were 1,389,235 (97.4%) nonrobotic and 37,270 (2.6%) robotic cases. Robotic cases increased from 0.8 per cent (2008) to 4.3 per cent (2009, P < 0.001). In all subgroups, robotic surgery had significantly shorter lengths of stay (4.9 days) than open surgery (6.1 days) and lower charges (median $30,540) than laparoscopic ($34,537) and open ($46,704) surgery. Fewer complications were seen in robotic-assisted colorectal, adrenalectomy and lysis of adhesion; however, robotic cholecystectomy and esophagogastric procedures had higher complications than nonrobotic surgery ( P < 0.05). Overall robotic surgery had a lower mortality rate (0.097%) than nonrobotic surgeries per 10,000 procedures (laparoscopic 0.48%, open 0.92%; P < 0.001). The cost of robotic surgery is generally considered a prohibitive factor. In the present study, when overall cost was considered, including length of stay, robotic surgery appeared to be cost-effective and as safe as nonrobotic surgery except in cholecystectomy and esophagogastric procedures. Further study is needed to fully understand the long-term implications of this new technology.

Mammalian mating systems are thought to be shaped by the spatial distribution and abundance of key resources, which in turn influence the spacing behaviour of individuals. In particular, female home range size is predicted to reflect the availability of key resources. We documented the availability and distribution of food and shelter resources for two neighbouring populations of bobucks, or mountain brushtail possums, Trichosurus cunninghami, that were characterised by different mating systems: our "forest population" was socially monogamous, whereas the "roadside population" was polygynous. Both silver wattle, Acacia dealbata, the main food resource for bobucks, and den-trees, which provided shelter, occurred at significantly higher density at the roadside site. The pattern of distribution of these two resources also differed between the sites. Both food and den-trees were scattered evenly throughout the roadside habitat. In contrast, den-trees were located predominantly at one end of the forest site, while silver wattle trees were located at the other. There was no significant difference in the amount of silver wattle, or in the number of den-trees, located within the home ranges of individual females at the two sites. However, forest females had home ranges, on average, almost three times the size of those of roadside females. At the roadside site, the size of female home ranges varied inversely with the density of silver wattle, indicating that these females ranged over as large an area as necessary to gain access to sufficient silver wattle trees. There was no such relationship among forest females. These populations provide a clear example of resource distribution determining female home range size. This influenced the number of female home ranges a male's home range overlapped with, which in turn determined the mating system. Such clear links between resource availability and mating system have not previously been established in a marsupial.

In wildlife research, our ability to GPS track sufficient numbers of individuals is always limited by cost, which restricts inference of species-habitat relationships. Here, we describe the modification and use of a relatively new and inexpensive off-the-shelf GPS device, to provide detailed and accurate information on the movement patterns of individuals (mountain brushtail possums, Trichosurus cunninghami), including how movement varies through time, and how individuals interact with each other. Our results demonstrated that this technology has enormous potential to contribute to an improved understanding of the movement patterns and habitat preferences of wildlife at a fraction of the cost of traditional GPS technology.

Overall, robotic-assisted surgery has significantly reduced median LOS, complications, and mortality compared with nonrobotic surgery. Results of this study support the contention that robotic-assisted surgery is as safe as nonrobotic surgery and offers the surgeon an additional technique for performing cardiac surgery.

Detailed knowledge of how individuals use space when active and while sheltering is crucial to understanding the habitat requirements of a species. I present the first home-range estimates for bobucks, Trichosurus cunninghami, that are based on both nocturnal and diurnal radio-tracking fixes. I tracked 37 individuals (14 adult females, 14 adult males, three subadult females and six subadult males) between mid-1999 and late 2003 in a forest patch in the Strathbogie Ranges, south-eastern Australia. I collected a total of 9562 diurnal fixes (mean 309 fixes per adult) and 5211 nocturnal fixes (mean 169 fixes per adult). All individuals used multiple den-trees; adults used a mean of 7.2 den-trees per individual. Adult bobucks of both sexes had a mean home-range size of 6.0 ha. There were no significant differences in the mean number of den-trees used or in the mean home-range size of adult males and females. Subadults used significantly fewer den-trees and had significantly smaller home ranges than adults. This study demonstrates the importance of large and long-term datasets in accurately determining the habitat requirements of a population.

The demographic characteristics of populations are determined by the life-history strategies of their constituent individuals. Habitat characteristics, such as the availability of key resources, shape life-history strategies; thus habitat variation may result in intraspecific variability in demography. We studied two neighbouring populations of bobucks or mountain brushtail possums Trichosurus cunninghami within a fragmented forest system. One population occurred in a forest patch that was selectively logged in the last 40 years; the other occupied narrow strips of linear roadside remnant vegetation that have not been logged for at least 100 years. Many demographic parameters of the two populations were similar, and were consistent with those described previously for a bobuck population living in continuous forest. For example, both sexes were long-lived (at least 12 years), but there were fewer males in the oldest age classes at both sites. Most females produced one young per year and reproduction was highly seasonal. Females in the oldest age classes produced young, but none of these survived to pouch emergence. There were also marked differences between our two study populations: the sex ratio of adults was equal at the forest site but female-biased (1.7:1) at the roadside site. Forest males weighed significantly less than males at the roadside site and females at both sites. The peak of births occurred more than a month later at the roadside than at the forest site. The sex ratio of roadside offspring did not differ significantly from parity; however, the sex ratio of young at the forest site was significantly male-biased (62% of young). This demographic variation may be explained by differences in habitat characteristics (particularly logging history); a detailed investigation of resource availability at the two sites is warranted. Our results highlight the importance of studying multiple populations when attempting to describe the population ecology of a species.