Suchergebnisse

Numerical uncertainty ranges are often used to convey the precision of a forecast. In three studies, we examined how users perceive the distribution underlying numerical ranges and test specific hypotheses about the display characteristics that affect these perceptions. We discuss five primary conclusions from these studies: (1) substantial variation exists in how people perceive the distribution underlying numerical ranges; (2) distributional perceptions appear similar whether the uncertain variable is a probability or an outcome; (3) the variation in distributional perceptions is due in part to individual differences in numeracy, with more numerate individuals more likely to perceive the distribution as roughly normal; (4) the variation is also due in part to the presence versus absence of common cues used to convey the correct interpretation (e.g., including a best estimate increases perceptions that the distribution is roughly normal); and (5) simple graphical representations can decrease the variance in distributional perceptions. These results point toward significant opportunities to improve uncertainty communication in climate change and other domains.

Home range in the swamp wallaby, Wallabia bicolor (Marsupialia : Macropodoidea) was examined using
radio-tracking in a 150-ha remnant of mixed eucalypt forest at Healesville, Victoria. Three methods
were used to calculate home-range size: minimum convex polygons, fourier transform MAP(O.95) and
MAP(0.50) estimation, and harmonic mean 50% isopleths and 95% isopleths. The minimum convex
polygon method produced the largest estimate of home-range area (16.01 +/-.45 ha). Each method
required a different number of fixes before home-range area estimates reached an asymptote. These data
showed that W. bicolor have small, overlapping home ranges and that the shape of the home range
varied between individuals. Home-range area was larger than previously reported for this species, and
there was no significant difference between the sexes in home-range size.

Abstract
The unprecedented growth rate in human population and the increasing movement of people to urban areas is causing a rapid increase in urbanisation globally. Urban environments may restrict or affect the behaviour of many animal species. Importantly, urban populations may change their spatial movement, particularly decreasing their home ranges in response to habitat fragmentation, the presence of landscape barriers and the availability and density of resources. Several species-specific studies suggest that urban animals decrease their home ranges compared with their non-urban counterparts; however, it remained unclear whether this pattern is widespread across taxa or is instead restricted to specific taxonomic groups. Consequently, we conducted a meta-analysis, collecting 41 sets of data comparing home ranges in both natural and urban environments in 32 species of reptiles, birds and mammals. We calculated effect sizes as the difference in animal home range sizes between natural and urban environments. We found that the home ranges were smaller in urban environments compared with natural environments (mean effect size = −0.844), and we observed a similar result when considering birds and mammals separately. We also found that home range sizes were not significantly affected when disturbance in urban areas was minimal, which suggests that many species may be able to tolerate low levels of disturbance without changing their movement patterns. Our study thus indicates that increasing levels of urbanisation restrict the spatial movement of species across taxa; this information is relevant for ecological studies of further urban species as well as for the development of management strategies for urban populations.

The home range and movements of the allied rock wallaby, Petrogale assimilis, a small macropod of
the seasonally wet-dry tropics of Queensland, were studied over a 22-month period. There was no
significant difference in the size of home ranges (95% isopleth) or core areas (65% isopleth) of males
and females. Home ranges were generally elliptical with a mean size of 11.9 ha. Season had a major
effect on home ranges. The following measures were all significantly greater in the dry seasons than
in the wet seasons: home-range size (larger), home-range shape (more elongate), distance moved by
females when feeding (longer), distance between shelter site and home-range centre of activity (longer).
Feeding movements of males did not vary seasonally and were as long as dry-season movements of
females, suggesting that movements of males are primarily determined by behavioural rather than
physiological considerations. The overlap of rock-wallaby home ranges varied little between the sexes
or seasons and averaged 38%. Core areas overlapped by an average of 22%; however, feeding adult
rock-wallabies rarely met other conspecifics, except their partners. A comparison of the fixes of
unpaired wallabies that had overlapping home ranges showed that temporal separation was occurring.
In contrast, the home ranges of consort pairs showed extremely high temporal and spatial overlap.
Rock-wallabies exhibited strong fidelity to their home ranges. The overlap of the seasonal home ranges
and core areas of each individual rock wallaby averaged 68% and 52%, respectively. However, the
seasonal home range of a socially immature adult male altered in location and size as he matured
socially until it stabilised when he obtained a permanent consort.

Common brushtail possums
(Trichosurus vulpecula) are intractable pests in New
Zealand. The effectiveness of local control can be limited by immigration,
some of which has been attributed to a 'vacuum effect' –
directed movements induced by the control itself. To characterise the vacuum
effect we examined changes in the home ranges of trapped possums following
control in a 6-ha block at one end of a 13-ha forest patch on farmland near
Dunedin, New Zealand. We also monitored a sample of possums by
radio-telemetry. After control, the density was 3
ha–1 inside the removal area and 16
ha–1 outside. During the year after the removal,
29% of possums within 100 m of the boundary of the removal area
(n = 38) shifted their range centre at least 50 m
towards it. The effect diminished rapidly with distance: only 1 of 28 animals
moved more than 200 m from the boundary. The size of the previous range was a
significant predictor of movement among males, but this may be partly a
sampling artifact. We measured a net flux of 69 possums
km–1 across the boundary in the 12 months after
control, and possums settled on average 44 6.9 m inside the boundary. The
vacuum effect in brushtail possums appears largely confined to home-range
adjustments by individuals with ranges overlapping the area of reduced
density. This limits its potential role in population recovery.

Context. Understanding how the individual movement patterns and dispersion of a population change following wildlife management interventions is crucial for effective population management.
Aims. We quantified the impacts of two wildlife management strategies, a lethal intervention and a subsequent barrier intervention, on localised populations of the two most common macropod species in Tasmania, the Tasmanian pademelon (Thylogale billardierii) and the red-necked wallaby (Macropus rufogriseus rufogriseus). This manipulation allowed us to examine two competing hypotheses concerning the distribution of individuals in animal populations – the Ideal Free Distribution (IFD) hypothesis and the Rose Petal (RP) hypothesis. We predicted that the RP would be supported if individuals maintained their previous home ranges following intervention, whereas the IFD would be supported if individuals redistributed following the management interventions.
Methods. The movement patterns of T. billardierii and M. r. rufogriseus were tracked using GPS technology before and after the two management interventions.
Key results. Following lethal intervention, pademelons and wallabies (1) maintained their home-range area, (2) increased their utilisation of agricultural habitat and (3) shifted their mean centroid locations compared with the pre-intervention period. Following barrier intervention, pademelons and wallabies (1) maintained their home-range area, (2) decreased their utilisation of agricultural habitat and (3) shifted their mean centroid locations compared with the pre-intervention period.
Conclusions. On the basis of the individual responses of macropods to the management strategies (1) lethal intervention appeared to induce small shifts in home-range distributions of those remaining individuals in the population with home ranges overlapping the areas of lethal intervention and (2) barrier intervention is likely to induce whole-scale population movements of the animals that survive the lethal intervention in their search of an alternative food source. Both species displayed spatial and temporal shifts in their home-range distributions in response to lethal and barrier interventions that appear to conform broadly to predictions of IFD, at least in the timeframe of the present experiment.
Implications. Wildlife management strategies, which are increasingly constrained by ethical, socio-political and financial considerations, should be based on ecological and behavioural data regarding the likely responses of the target population.