5 research outputs found
Major Roads: A Filter to the Movement of the Squirrel Glider Petaurus Norfolcensis
An understanding of the ecological effects of roads and related traffic in highly fragmented landscapes is critical because the viability of wildlife that persist through the adverse impact of habitat loss and fragmentation, due to causes such as agriculture or urban land-uses, may be further impaired by the presence of roads. The potential barrier effect can increase the level of population isolation, especially if traffic volume increases and roads are w3idened. This is particularly the case in landscapes where a large proportion of the habitat occurs in linear strips, such as in hedgerows or along roadsides or watercourses. Much of eastern Australia has been cleared and many threatened species occur in habitat adjacent to roads. Thus, management must minimize the negative effects of roads while maximizing their value for conservation. Gaps in habitat may result in impeded mobility of wildlife and potentially isolate populations, with subsequent consequences for population persistence. The squirrel glider Petaurus norfolcensis can be considered a model species for investigating the impact of roads on connectivity. A native arboreal marsupial, the squirrel glider has a very efficient way of locomotion which consists of gliding between trees, with very rare ventures on the ground, where the risk of predation is higher. Glider movement within home ranges and during dispersal is expected to occur along continuous vegetation, while cleared areas wider than the maximum gliding distance achievable could act as barriers. In this study we evaluated the filter effect of major roads on the squirrel glider in central Victoria (south-eastern Australia) using a combination of radiotracking and genetic techniques. We asked two important questions. First, does a major road act as a barrier or filter to the movement of gliders and if so, does the presence of tall trees between the carriageways facilitate their crossing. A total of 58 adult individuals were radiotracked at six sites along the Hume Freeway (central Victoria), and at two control sites (minor roads with low traffic volume and small or non-existent gap in canopy cover) over a period of six months. The six sites consisted of small roads lined with old growth trees and dissected by the freeway. Three of these sites also had tall trees present in the median section of the freeway. The percentage of animals crossing at sites with vegetated median was similar to that at control sites, with 70% and 79% of all animals observed on the opposite side of the road or the centre median at least once, respectively. In contrast, only one male glider (10% of all animals) was observed crossing at sites with non-vegetated median. Overall, females were less inclined to cross roads, even at control sites and the intensity of crossing was also higher for males than females. The presence of trees in the median of the freeway was thus demonstrated to be a very efficient method of improving connectivity for gliders. Data on dispersal collected via direct methods can be highly informative but also requires intense efforts in field work and usually long term studies. Genetic techniques are a useful alternative to infer dispersal events, through the use of spatial autocorrelation and relatedness/parentage analysis. These methods will be implemented to consolidate the preliminary results and estimate the net effect of observed crossings on gene flow. Mitigation structures consisting of rope bridges and poles are being constructed to improve mobility of gliders as well as a number of other arboreal species and their effectiveness will be monitored using a combination of techniques. These will include motion-detecting infrared cameras, implantable transponders and radiotracking. Data will be compared on a pre- post-mitigation basis and at treatment and control sites
Large Gaps in Canopy Reduce Road Crossing by a Gliding Mammal
Roads and traffic reduce landscape connectivity and increase rates of mortality for many species of wildlife. Species that glide from tree to tree may be strongly affected by roads and traffic if the size of the gap between trees exceeds their gliding capability. Not only are wide roads likely to reduce crossing rates, but mortality may also be increased if gliders that do cross have poor landing opportunities. The road-crossing behavior of 47 squirrel gliders (Petaurus norfolcensis) was investigated in southeast Australia using radio-tracking. The proportion of gliders crossing one or both roadways of a freeway where trees were present or absent from the center median was compared to that at single-lane country roads (control). The proportion of gliders crossing the road at control sites (77%) was similar to the proportion that crossed one or both roadways at the freeway with trees in the median (67%), whereas only a single male (6%) crossed the freeway where trees were absent from the median. The frequency of crossing for each individual was also similar at control sites and freeway sites with trees in the median. The almost complete lack of crossing at sites where trees were absent from the median was attributed to the wider gap in canopy (50 - 64 m vs. 5 - 13 m at sites with trees in the median). This suggests that traffic volume, up to 5,000 vehicles per day on each roadway, and the other characteristics of the freeway we studied are not in themselves complete deterrents to road crossing by squirrel gliders. This study demonstrates that retaining and facilitating the growth of tall trees in the center median of two-way roads may mitigate the barrier effect of roads on gliders, thus contributing positively to mobility and potentially to connectivity. This information will be essential for the assessment of road impacts on gliding species using population viability models
Recommended from our members
Quantifying and mitigating the barrier effect of roads and traffic on Australian wildlife
The network of highways, freeways, and other major roads in Australia and around the world continues to expand in length and width as new roads are built and existing roads widened. The effects of roads and traffic on the survival and movement of indigenous wildlife are potentially numerous and profound. Successful mitigation of these effects relies on the detailed definition of the nature and extent of the problem and appropriate analysis of the effectiveness of amelioration. Habitat loss across large areas of Australia has been so extensive that many landscapes currently support less than 5 to 10% of indigenous vegetation. Ironically, much of the remaining vegetation occurs adjacent to existing roads or in unused road reserves. Consequently, new roads will dissect these vegetation remnants, potentially disrupting the movement of animals along these linear corridors. Similarly, the widening of existing roads will typically result in the removal of valuable habitat for wildlife. In our study, we investigated the effect of a new road on the movement and ecology of the Squirrel Glider Petaurus norfolcensis in southeastern Australia. The squirrel glider is an endangered species restricted to forest and woodland in eastern Australia. Its primary form of movement is by gliding between trees. We radio-tracked nine individuals for a two-month period in the vicinity of a new dual-carriageway freeway and an existing single-carriageway highway. A total of 488 radio-tracking fixes revealed that animals were resident adjacent to both roads and that the rate of road crossing varied by sex and road width. Females were never observed to cross the dual carriageway, while a single male was located on opposite sides at a ratio of 1:0.4. Both females and males crossed the single carriageway regularly. Two of the nine gliders disappeared during the study. The results of this study are being used to design a major collaborative research project that aims to more fully quantify the negative effects of roads and traffic on Australian wildlife. At present, there is a poor understanding of the ecological effects of roads and traffic in Australian ecosystems and on Australian wildlife. In particular, we are focusing on the population-level effects in order to determine the extent that population viability has been reduced. A range of taxa with different levels of vulnerability are being studied, including arboreal marsupials, ground-dwelling mammals, geckoes, and invertebrates. We will incorporate studies of movement patterns with genetic techniques and metapopulation- viability analyses to elucidate effects at the population level. The project will then test the effectiveness of various mitigation measures by determining the extent to which population viability has been improved
Recommended from our members
Combining three approaches to quantify the barrier effect of roads: genetic analyses
The movement and dispersal of animals between populations is an important component of wildlife ecology and has been described as “the glue that holds local populations together.” Without adequate ability to disperse, the rate of movement of individuals and DNA between populations is reduced and these populations become isolated, increasing the risk of local extinction. Most research addressing the barrier effect of roads and traffic has focussed on the use of crossing structures by wildlife. Our study is a first for Australia and represents a unique collaboration to quantify the barrier effect in a highly fragmented landscape and (subsequently) the success of mitigation. The aims of the project are to use genetic techniques and empirical observations to quantify the barrier effect of roads on the movement and dispersal of mammals, reptiles, birds, and invertebrates and to assess the effectiveness of structures and road designs intended to mitigate the barrier effect. Quantitative modeling will also be implemented to predict the effects of reduced movement on population viability. A range of genetic markers is available for use in population biology to measure dispersal. Microsatellites are hypervariable and sensitive enough to be able to detect genetic differentiation in the short term and at small spatial scales, and are therefore appropriate to investigate genetic substructuring due to the presence of roads. Genetic analyses will be used at different scales of resolution. The genic approach will be employed for identifying population substructuring and patterns of gene flow at the population level. The genotypic approach will be used for finer-scale observations of dispersal of individuals. Direct methods still provide highly reliable data on dispersal parameters, although they rely on logistically difficult field observations. Trapping and radio tracking will be used in the present project to be combined with and strengthen the results obtained from genetic analyses. Repeated trapping will provide life history information which can aid in understanding the genetic data and contribute to the population viability models. Radio tracking will be used to collect information on daily movements of mammals in relation to foraging as well as dispersal and to assess the effectiveness of mitigation structures. Finally, quantitative population modelling will be conducted to estimate the effects of inhibited dispersal on population viability. Data from observations and genetic studies will be used to characterise populations in terms of age and stage structures, fecundity, survival, and dispersal. Data collected over three years will be used to characterise variability in the parameters to improve population modelling