Abstract
Context
In highly fragmented landscapes, arboreal mammals are limited by their ability to move and disperse between core habitats. Connectivity modelling for multiple species allows scientists to identify the most efficient movement and/or dispersal pathway(s) to prioritise for conservation efforts.
Objectives
In this study, we evaluated the most cost-effective corridor pathway for eight species of arboreal mammals, with particular emphasis on an endangered population of greater gliders (Petauroides volans).
Methods
We use species distribution modelling and circuit theory to calculate connectivity in the landscape for each species. An all-species corridor was then modelled using a least cost path analysis. The final corridor was evaluated for all species through ground-truthing accessible segments.
Results
We identified that some segments of the corridor had low suitability for highly specialised species, and those with tree hollow requirements for denning. The all-species corridor also utilised an artificial crossing structure over a highway, and monitoring of this rope bridge found only two species (sugar gliders; Petaurus breviceps and ringtail possums; Pseudocheirus peregrinus) used the structure on occasion. Thus, the modelled corridor pathway was not suitable for all species, rather it was found to be more suitable for generalist species such as sugar gliders, ringtail possums, brown antechinus; Antechinus stuartii and brushtail possums; Trichosurus vulpecula.
Conclusions
Our study exemplifies the importance of ground-truthing in connectivity conservation studies to ensure conservation outcomes are realised. Furthermore, we provide detailed recommendations for relevant conservation managers, to improve the usage of these existing habitat corridors by arboreal species.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Introduction
Habitat loss and fragmentation are the most important threatening processes for mammalian species in the Anthropocene (Powers and Jetz 2019). Globally, 27% of mammal species are threatened with extinction because of habitat loss and decline in habitat quality (Schipper et al. 2008). Habitat fragmentation is the reduction in continuous habitat into smaller, disjunct patches within a dissimilar matrix (Haddad et al. 2015; Wilson et al. 2016). Remnant fragments are often too small and isolated to maintain viable populations of some species, and through environmental, demographic and genetic changes, a vortex of extinction can form (Gilpin and Soule 1986).
The effects of habitat fragmentation are particularly pronounced for arboreal species; particularly obligate canopy dependent species such as greater gliders. Obligate arboreal mammals have limited dispersal potential in a cleared matrix and are therefore most sensitive to habitat fragmentation (Keinath et al. 2017). Some of the consequence of reduced or limited population connectivity for arboreal mammals includes lowered effective population size and potential for genetic drift (Lancaster et al. 2011; Malekian et al. 2015). Morphological changes have been observed, such as reductions in body size due to the limited amount of habitat and resources available (Fietz and Weis-Dootz 2012). Ecologically, the abundance and distribution of an arboreal species can be reduced within a fragmented landscape as it is unable to facilitate movement and connectivity when the matrix contains no trees (Koprowski 2005; Isaac et al. 2014).
Wildlife corridor implementation is considered an important strategy to reconnect habitat patches in a fragmented landscape (Beier and Noss 1998; Mackey et al. 2010; Hilty et al. 2012). For arboreal species, there are examples where corridors are vital for their conservation acting to reconnect once isolated populations (Wilson et al. 2007; Soanes et al. 2017b; Jackson et al. 2020). There are nine published landscape corridors that have either been evaluated for use by arboreal species, or specifically created for arboreal species (Laurance and Laurance 1999; Williams-Guillén et al. 2006; Lees and Peres 2008; Haslem et al. 2012; Anitha et al. 2013; Taylor and Goldingay 2013; Taylor and Rohweder 2013; Teixeira et al. 2013; Soanes et al. 2017b). At smaller scales, artificial corridors have been installed, such as underpasses and overpasses for arboreal species (Taylor and Goldingay 2009; Weston et al. 2011; Goldingay et al. 2013, 2018; Teixeira et al. 2013; Yokochi and Bencini 2015; Chan et al. 2020; Garcia et al. 2022). Given the significance of connectivity for arboreal species in fragmented systems disturbed by agriculture and urban development, further investigation into identifying and evaluating the usage of different types of corridors is needed.
Maintaining and restoring landscape connectivity is one conservation strategy to mitigate the impacts of agricultural practices and urbanisation (Crooks and Sanjayan 2006). Using wildlife occurrence data, metrics of landscape connectivity can be derived from spatial models, and these modelling approaches provide a quantitative basis to identify potential corridors in fragmented landscapes (Pe’er et al. 2011; Pliscoff et al. 2020). Spatially explicit models such as species distribution models (Elith et al. 2011), least-cost path mapping (Sawyer et al. 2011a), models based on electric circuit theory (McRae et al. 2008), and various toolkits for GIS (Correa Ayram et al. 2016), are increasingly applied in designing regional scale corridors for various taxa and ecosystems (Braaker et al. 2014; Naidoo et al. 2018; Pliscoff et al. 2020). Readily available data such as topographic data (elevation, aspect, slope), soil and vegetation type, can be used to model habitat suitability and a matrix of habitat suitability for multiple species can then be combined to predict a corridor pathway that benefits multiple species (Elith et al. 2011; Brodie et al. 2015; Petsas et al. 2020; Pliscoff et al. 2020; Miranda et al. 2021).
Despite the prolific use of numerical modelling to identify corridor connectivity networks at regional scales, these corridor network models are rarely validated for their actual use by the target species (Kilbane et al. 2019). Landscape connectivity requires ground-truthing because of the limitations associated with ecological modelling. Some limitations include accounting for threatening processes and the presence of key resources that cannot be provided in continuous spatial layers. This is particularly relevant for species with obligate habitat requirements, such as tree hollow availability. Thus, on-ground assessments of habitat suitability of modelled corridors are essential for conservation managers, so as to effectively manage and prioritise their management actions.
In this study, a fragmented landscape impacted by agriculture and urbanisation, we used a multiple-species methodological framework (Pliscoff et al. 2020) to identify the most cost effective corridor pathway for targeted conservation activities. This study used species distribution modelling, electric circuit-based modelling, and a consensus of suitability, to quantify the functional connectivity of eight semi-arboreal and arboreal species. The central focus of the corridor was to connect an endangered species and isolated population of greater gliders (Petauroides volans) with contiguous landscape across nine kilometres of fragmented habitat. Evaluation of the modelled corridor was performed via ground-truthing the habitat suitability for all eight species and monitoring artificial crossing structures over and underneath the highway. This assessment of the corridor meant that data driven recommendations could be made for strategic conservation management purposes.
Materials and methods
Study site
Our study area focused on the fragmented agricultural landscape surrounding the township of Berry, in New South Wales (NSW), located 111 km south of Sydney, Australia (Fig. 1). This area is the location of a Great Eastern Ranges (GER) wildlife corridor project called the ‘Berry Bush Links’ (GER 2021). The Berry wildlife corridor aims to create additional habitat and connect the fragmented Seven Mile Beach National Park (SMBNP) with contiguous habitat 9 km to the west of the park (known as the ‘Illawarra Escarpment’). The area is characterised by mostly cattle and dairy farming, and low density rural residential properties. A major highway (up to 80 m wide) runs between the Illawarra Escarpment and Seven Mile Beach National Park (Fig. 1). The species identified as a priority for the corridor’s creation is the endangered greater glider. The population of greater gliders at Seven Mile Beach National Park (Fig. 1) was listed as an endangered population, primarily due to its isolation from other populations found locally and regionally (NSW Scientific Committee 2016). The geographical boundaries used in this study was the natural barrier of the Shoalhaven River (see southern end of map in Fig. 1), and the furthest northern end of Seven Mile Beach National Park (Fig. 1).
The study landscape near the township of Berry, NSW. The blue outline is the focus area of the Berry Bush Links project for the Berry wildlife corridor (GER 2021)
Connectivity model parameters
Our study used five key steps in producing an all-species corridor for the study landscape (Fig. 2). Using occurrence and environmental data, species distributions were first created. The probability of a species presence was then used to calculate a resistance surface, used in modelling connectivity models. A consensus map for connectivity for all species was then analysed using a least cost path to produce a final all species corridor (Fig. 2).
Key methodological steps used in the study to estimate the movement corridors for each of the eight species. Methodological framework was adapted from (Pliscoff et al. 2020)
Species data
This study focused on a group of eight native, arboreal marsupials (Table 1). The species ranged from those heavily reliant on trees and canopy for movement (gliding species) to more generalist species such as brown antechinus, ringtail possums, brushtail possums and southern bobucks (Table 1). Presence data was obtained using three different methods.
Firstly, empirical data was collected and primarily targeted small mammals (Gracanin et al. 2022). This involved live trapping and camera trapping at 164 sites, between August to November 2019, for a total of 4592 camera trap nights and 1148 live trap-nights (Gracanin et al. 2022). Further data was utilised from a long-term camera trap study in the landscape as well, that spanned over one year (November 2019–November 2020) and added up to 6517 camera trap nights (Gracanin and Mikac 2022a, b).
Secondly, spotlighting surveys were conducted for ringtail possums, brushtail possums, southern bobucks, greater gliders, feathertail gliders and eastern pygmy possums (Davey 1990; Wintle et al. 2006; Vinson et al. 2020a). This involved walking 100–500 m transects, depending on site size and private property limitations, with an AceBeam H30 4000 lm head torch. Spotlighting surveys were conducted by one observer (A.G.), walking at a speed of 5 min per 100 m, scanning for eyeshine in the canopy, mid-storey, and understorey. A pair of 8 × 40 pair of binoculars (Avalon 10 × 42 PRO HD) were used to aid in identifying species. The GPS coordinates of the animal were recorded by standing beneath where the animal was first sighted. All spotlighting surveys commenced one hour after last light. As feathertail gliders and eastern pygmy possums are often difficult to detect in dense forests such as rainforests, water stations were placed in trees (n = 8) for over a year to aid in detecting their presence (Mella et al. 2019). Water was used as “bait” for these species as they are rarely attracted to traditional small mammal baits of peanut butter, honey and oats (Huang et al. 1987; Tasker and Dickman 2001). The third method used for obtaining species occurrence data was through downloading records from the online database BioNet (NSW Government 2022). BioNet are validated records of species from qualified observers and uploaded to a central database as per NSW Scientific Licensing requirements. Data was downloaded from this database for all eight species, from 1980 to 2021.
Species distribution models
We used a multivariate approach, maximum entropy (Maxent), to correlate species presence and environmental variables to predict the distribution of species across the landscape (Elith et al. 2011). The distribution of all eight species were modelled with maximum entropy algorithm (Maxent) with the R package: ‘maxnet’ (Phillips et al. 2017). A ‘block’ partition scheme (k = 4) was selected for all analyses. The regularisation multiplier was set to between 1 and 5 (with steps of 0.5), and all feature classes (L, LQ, H, LQH, LQHP; L = linear, Q = Quadratic, H = hinge, and P = product) were selected. In total, 45 different models were built, run, and tested for each species. The model selection was based on the lowest delta corrected Akaike information criterion (AICc) (Supplementary 1). Occurrences were partitioned for training (70% of the total) and testing (30%) and pseudoabsences (10,000 background points) were randomly distributed across the study area. Five environmental variables were used in the modelling: elevation, slope, aspect (DCS Spatial Services 2022), soil (DPIE NSW 2020) and vegetation type (DPIE NSW 2013). Vegetation type was manually updated by comparing it to recent satellite imagery, and relevant habitat was added (with vegetation type validated in the field) or removed (where development had occurred). The spatial layer for vegetation type also included categories for agricultural land and urban land. All environmental layers were at a spatial resolution of 25 m.
Connectivity models
We employed circuit theory to identify potential corridors linking core areas within the landscape, using the software Circuitscape 4.0.5 (McRae and Shah 2009). Circuit theory links populations through multiple pathways, with connectivity potential increasing according to the density of pathways (McRae et al. 2008). The models produced from Maxent were converted by inverting the values of habitat suitability so that each pixel represented a resistant value ranging from 0 to 1 (higher values indicating more resistance). Using expert opinion, literature reviews, and field data (Zeller et al. 2012), the resistant values for rope bridges, underpasses, highways, and rivers, were manually changed to better reflect their impact as barriers (Supplementary 2). Values for highways and rivers wider than 25 m, were manually changed to better represent the barrier they pose for each species. For each species, the wildlife underpasses and rope bridges along the highway were assigned a resistant value that was calculated using the average resistance values from urban areas. This was because urban areas represent the closest surface type in similarity (e.g. concrete surfaces, wooden poles, street lights), and thus reflect a more appropriate value than using a value based on expert opinion alone (Zeller et al. 2012). Core habitat (nodes) were selected based on fragment size (> 50Ha) and the conservation status of the habitat. We selected core habitat that was either a large patch within the landscape, or sections representing a larger continuous landscape. Seven nodes were selected, and each were protected by government (NSW National Parks and Wildlife Service estate or local council reserves) or were private properties with conservation agreements. These nodes also represented the goal of the Berry Wildlife Corridor to connect the larger continuous landscape of the Illawarra Escarpment and surrounds, with the isolated Seven Mile Beach National Park. A graph-based connectivity metric, the Index of Integral Connectivity (IIC), was calculated for each model using Conefor Sensinode 2.6 (Saura and Torné 2009) to compare connectivity between species.
All species corridor
A consensus current map was created by averaging the eight normalised current maps for each species from Circuitscape (Monsimet et al. 2020; Petsas et al. 2020; Miranda et al. 2021). A least cost path analysis was performed on the all-species conductance map using Linkage Mapper (McRae and Kavanagh 2022).
Evaluation of proposed corridor
The final corridor network produced was evaluated by ground-truthing key habitat requirements for all eight species. Key habitat variables measured were: (1) feed tree composition; (2) noxious weed coverage; and (3) hollow availability for size classes < 5 cm, 5-10 cm and > 10 cm. Habitat surveys were performed at points along the final corridor network, that were spaced on average, 100 m apart. Each variable had a weighted value in terms of its relative importance for each species, so that the sum of values equated to a final index of suitability that ranged from zero (not suitable) to 1 (highly suitable) (Supplementary 3). We gave variables a higher weight if expert opinion, literature reviews, and field data were in agreement that the variable was highly influential in determining habitat value. Variables thought to be less important by experts or indicated by field data we gave a lower weight. From this, weighted habitat rankings for the segments of the final corridor for each species were calculated to indicate its value as both habitat and as movement corridors.
The monitoring of two rope bridges (between 18/4/2020 and 18/4/2022) and two underpasses (between 16/6/20 and 19/8/21) was also undertaken using motion sensor cameras (Fig. 3). Qualified tree climbers accessed rope bridges found over the highway and installed motion sensor cameras at each end (Spypoint Link S Cellular Solar Trail Camera). These cameras were solar powered (charging an internal lithium battery) and cameras uploaded photos daily to a server. This ensured continued, uninterrupted monitoring of two rope bridges. In the two underpasses, cameras (Browning Tail Cameras BTC-7-4 K) were positioned on the ceiling on either end of the passages and left to record the underpass floors for over one year. Additional cameras were positioned on wooden poles to face wooden bridges inside the underpasses (Fig. 3).
Results
Species distribution models
More generalist species had a greater and consistent coverage of habitat suitability, compared to more specialist species such as the greater glider, eastern pygmy possum and feathertail glider (Fig. 4). Both eastern pygmy possums and feather tail gliders had greater suitability at high elevations in more topographically diverse terrain, particularly favouring Illawarra Subtropical Rainforest. Ringtail possums, brushtail possums, antechinus, and sugar gliders, all had medium to high suitability values for most of the vegetation throughout the landscape. The southern bobuck showed a distinct preference for higher elevation habitat, and the greater glider had moderate to low suitability in available vegetation with most suitable habitat occurring along the Illawarra Escarpment.
MaxEnt species distribution maps for A Feathertail glider Acrobates pygmaeus; B Eastern pygmy possum Cercartetus nanus; C Brown antechinus Antechinus stuartii; D Sugar glider Petaurus breviceps; E Ringtail possum Pseudocheirus peregrinus; F Brushtail possum Trichosurus vulpecula; G Southern bobuck Trichosurus cunninghami; H Greater glider Petauroides volans
Potential connectivity models
For each species, connectivity models differed in the amount of area in the potential connectivity network (Fig. 5). Feathertail gliders and eastern pygmy possums were restricted to movements along and within the Illawarra Escarpment and surrounding national parks. Whereas ringtail possums, brushtail possums, antechinus, and sugar gliders, all had high levels of connectivity, with higher values in the IIC index. The greater glider had the least amount of connectivity of all the species.
Potential connectivity analysis for wildlife species within the study’s fragmented landscape, as based on circuit theory corridor implemented using Circuitscape. Focal fragments are shown in black, with yellow (low flow) and red (high flow) showing corridor flow intensity. A Feathertail glider Acrobates pygmaeus; B Eastern pygmy possum Cercartetus nanus; C Brown antechinus Antechinus stuartii; D Sugar glider Petaurus breviceps; E Ringtail possum Pseudocheirus peregrinus; F Brushtail possum Trichosurus vulpecula; G Southern bobuck Trichosurus cunninghami; H Greater glider Petauroides volans. Upper left corner values show Integral Index of Connectivity (IIC) from Conefor Sensinode 2.6
All species corridor
The final corridor as defined through least cost path analyses, focused on connecting all species between Seven Mile Beach National Park (SMBNP) and the Illawarra Escarpment (Fig. 6). The impact of the highway and river as strong barriers to movement were evident. The corridor identified did not utilise steppingstone fragments of habitat, instead riparian corridors and roadside habitat were selected. Sections of these thin linear corridors, and the rope bridges and underpasses, were identified as pinch points (Supplementary 4).
Rope bridge and underpass usage
Of the two underpasses only cameras from one underpass were not stolen, and this underpass recorded arboreal mammal species utilising the underpass. Trichosurus species was recorded crossing on 24 occasions in this underpass, however distinguishing features were difficult to discern on cameras. Based on nearby observations (less than 100 m away), T. vulpecula and T. cunninghami have been recorded in the area, thus the possums recorded on camera using the underpass are likely to be both species. Each possum record was of it using the floor, and not the wooden bridge installed inside the underpass for arboreal species. On two occasions, brown antechinus were recorded using the underpass tunnels.
Of the two rope bridges only two arboreal mammal species were recorded using the bridges (Fig. 7). Bridge one recorded one occasion where a sugar glider used the bridge. The second bridge recorded 68 sugar glider crossing events and one ringtail possum crossing.
Evaluation of proposed corridor network
Ground-truthing the final modelled corridor pathways was performed for approximately 35% of the corridor network. Permission to access some of the pathways was limited due to private properties or terrain access. Upon evaluation, the species that had the most suitability across all corridor segments was the ringtail possum, followed closely by the sugar glider (Table 2). The least amount of suitability was found for the greater glider, feathertail glider and pygmy possum (Table 2). The segment that performed best in terms of corridor and habitat suitability for all species was segment four, along Woodhill Mountain Road, followed closely by segment one, Beach Road.
Discussion
Our results show a clear trend where generalist species (brown antechinus, sugar gliders, ringtail possums, brushtail possums) had greater connectivity than more specialist species (feathertail gliders, pygmy possums, southern bobucks, and greater gliders). Despite the few species presence records in the fragmented landscape for these specialist species, we have identified areas that with further habitat restoration, are more likely to facilitate the movement of these species.
Species distribution models
Species resistant to human disturbance and considered more generalist, had a greater distribution across the study landscape. Common brushtail possums, ringtail possums, sugar gliders and brown antechinus, all had presence observations spread throughout the entire landscape in both small fragments of habitat and in all the reserves. These species are known to occupy and utilise such habitat despite threats posed in the matrix of cleared land (Laurance and Laurance 1999; van der Ree 2000; Marchesan and Carthew 2008; Malekian et al. 2015; Gracanin et al. 2019; Gracanin and Mikac 2022a). Recent genetic analyses confirmed the ability of sugar gliders to move effectively in our study’s fragmented landscape as they had high gene flow and limited genetic structure (Gracanin et al. 2023). Additionally, we have shown in our other work that sugar gliders are highly mobile (Gracanin and Mikac 2022a) and able to move on the ground (Gracanin et al. 2019).
For more specialist species, predicted distribution was more restricted as observations were limited east of the highway. The southern bobuck was predicted to have higher probability of presence along the Illawarra Escarpment, at higher elevations in forested habitat. Observations of the southern bobuck in this study were restricted to the west of the highway. Despite being highly forest-dependent, other studies have detected bobuck populations in linear road-side remnant vegetation (Martin et al. 2007). Long term monitoring in the study landscape did not detect bobucks in areas west of the highway (Gracanin and Mikac 2022b). However, monitoring of underpass tunnels indicates the possibility of bobucks using the tunnels to cross the highway, and that the species may be present east of the highway. Only two observations were found east of the highway for the eastern pygmy possum and feathertail glider, both at David Berry Memorial Hospital. At this site, the habitat is comprised of Illawarra Lowland Subtropical Rainforest, a critically endangered ecological community. This remnant forest likely represents the type of forest that was historically widespread across most of the study landscape, and that these species are possibly restricted to this site and other wet sclerophyll forest nearby.
Potential connectivity pathways
Dispersal is an important consideration for population dynamics and to maintain viability over time (Doak et al. 1992; Stow et al. 2001; Schtickzelle et al. 2006; Fletcher et al. 2018). Our study found connectivity pathways were numerous and highly conducive to more generalist species, which included the common brushtail possum, ringtail possum, sugar glider and brown antechinus, as these species not only readily move through remnant linear fragments but are also known to reside permanently in such habitat (van der Ree 2000; Wilson et al. 2007; Marchesan and Carthew 2008; Taylor and Rohweder 2013; Molloy and Davis 2017; Gracanin and Mikac 2022a). More specialised and cryptic species, including the feathertail glider, eastern pygmy possum, and greater glider, all had limited connected pathways between focal nodes as both cleared habitat and unsuitable habitat limited the intensity or existence of conductance pathways. It is important to note the limitations of the final models as the friction values manually changed are based on a combination of expert opinion and literature, and thus conductance at barriers (highways and rivers) and linkages (underpasses and rope bridges) may not accurately represent a species capacity for movement at these areas. However, many studies utilise this approach and to overcome these limitations is to conduct field-validation which this study performed on rope bridges and underpasses, as well as conducting habitat assessments of pathways (Sawyer et al. 2011b).
All species corridor
In other studies, the utilisation of an umbrella species, often a threatened species, have priority for conservation planning purposes (Roberge and Angelstam 2004; Mortelliti et al. 2009; Thornton et al. 2016). There were several different pathways for more common, generalist species in our landscape (Fig. 5), however, the all-species corridor created through a least cost path analysis was then constrained by the highly specialised greater glider. This pathway starting from SMBNP, follows medium and large Eucalyptus dominated roadside habitat before utilising less suitable habitat along riparian corridors and a rope bridge for crossing the highway. By using existing connected pathways, and the shortest distance of resistance to movement, targeted restoration efforts can take effect following ground-truthing. One other study into habitat connectivity for greater gliders at SMBNP failed to consider Beach Road (Segment 1; Fig. 6) as a corridor (Vinson et al. 2020b). The study was more hypothetical in their approach by drawing potential corridors, and they recommended the installation of glider poles within the large Coomonderry Swamp as well as reforestation efforts along the boundary of this swamp (Vinson et al. 2020b). However, there are logistical challenges, such as that the swamp and surrounding swamp edge, is subject to regular intense flooding. Furthermore, greater gliders have high site fidelity and dispersal appears to be limited (Suckling 1982; Taylor et al. 2007), and thus are unlikely to use glider poles compared to other, more mobile species (Taylor and Goldingay 2013; Taylor and Rohweder 2020).
Highways present significant barriers for arboreal species, including common, generalist species (Russell et al. 2009, 2013; Soanes et al. 2016; McCall et al. 2017). The all-species corridor modelled identifies one of the rope bridges acting as a pinch point for movement, and through the data collected at these rope bridges, they may provide limited connectivity for all species. Similar to other studies, the sugar glider was readily able to utilise the rope bridge crossing (Goldingay et al. 2013; Soanes et al. 2015, 2017a; Goldingay and Taylor 2017). These studies have also recorded extensive use of these bridges by ringtail possums, brushtail possums and feathertail gliders. There is some evidence of rope bridge usage by a species of pygmy possum, Cercartetus caudatus, however this was for smaller roads and not highways (Weston et al. 2011). There have been no records of greater gliders using rope bridges, though other large gliding species such as the yellow-bellied glider readily use glider poles as steppingstone movement pathways across highways (Taylor and Rohweder 2020).
The greater glider is generally considered a relatively poor disperser, with high site fidelity and has a low reproductive rate (Maloney and Harris 2008). Thus, the species is vulnerable to barriers to movement, however a population viability analysis found that even low dispersal rates could prevent extinctions of populations separated by roads (Taylor and Goldingay 2009). Therefore, through habitat restoration (further discussed below), it is possible that greater gliders could overcome the barrier posed by the highway dissecting the study location.
Management recommendations
Through ground-truthing surveys, limitations in corridors to act as habitat and facilitate movement of species were identified. For all segments surveyed and their surrounding habitat, an increase in hollows is recommended for all species though in particular for the greater glider. This is through both artificial carving of existing hollows in their early stages of formation and nest box installation. A widening of the corridors is needed, through planting a diversity of Eucalyptus sp., though in particular E. pilularis a preferred feed and habitat tree of the greater glider population at Seven Mile Beach National Park (Vinson et al. 2020b). Additional feed trees include Acacia, Banksia and Callistemon species (Lindenmayer 2002). At segment three, a large density of Lantana camara posed a large issue for arboreal mammal usage of the habitat. Removal of weeds in this riparian area is needed, as well as subsequent revegetation with preferred trees.
For all common species, connectivity was apparent, and the least cost path corridor identified the shortest area to target revegetation and habitat restoration efforts. This pathway also utilised a rope bridge over the highway. Though not detected using rope bridges in this study, feathertail gliders have been recorded using artificial structures to cross highways in other areas of Australia (Goldingay et al. 2013, 2018). For the eastern pygmy possums and brown antechinus, further revegetation at underpasses may improve the species propensity to use them, especially for smaller, narrower drainage culverts (between 50 and 100 cm wide) that were not monitored in this study (Yanes et al. 1995; Chen et al. 2021). Unfortunately, of the two underpasses monitored for over a year, cameras from one of the underpasses were stolen. This is a limitation for our interpretations about the usage of the underpasses in this area along the Princes Highway, as other species besides Trichosurus species and brown antechinus, may have used this other underpass.
The endangered population of greater gliders at SMBNP, the focus of the corridor connectivity efforts, is very limited in terms of obtaining functional connectivity in the landscape and is significantly genetically differentiated from other populations (Knipler et al. 2023). A least cost path analysis identifies the shortest, and least costly path, for a wildlife corridor, so that conservation managers can be cost effective with limited funding. For greater gliders, intense reforestation efforts are required to widen linear corridors to at least 100 m wide. If the recommended reforestation efforts and habitat improvements are made along the modelled corridor, the final issue of the highway remains a significant barrier. The gliding threshold for the species is limited by the highway width and the limited ability of greater gliders to use artificial crossing structures (Taylor and Goldingay 2009). However, three scenarios are available to help the greater gliders persist at SMBNP. Firstly, a habitat bridge (wildlife-dedicated land or green bridges; (Plaschke et al. 2021; Corlatti et al. 2009; Taylor and Goldingay 2010; Gužvica et al. 2014) would be the long-term effective solution for overcoming the barrier of the Princes Highway, although the most expensive. Secondly, increasing available habitat accessible to greater gliders east of the highway would allow for the population to increase and be more resilient to stochastic changes (Lande et al. 2003; Reed 2004; Frankham et al. 2010; Ovaskainen and Meerson 2010). In this scenario, segment one of the modelled corridors (Beach Road) presents the best opportunity to allow gliders to disperse into larger fragments of habitat at Hartley Hill Reserve and Moeyan Hill Reserve. Thus, efforts should focus on thickening the habitat on this road and increasing the number of appropriate hollows for the species (Hofman et al. 2022). A third scenario is to translocate greater gliders individuals to SMBNP, to increase genetic diversity of the isolated population (Knipler et al. 2023). However, this requires detailed assessment of genetic data from nearby populations to determine how a program would operate to ensure success (Batson et al. 2015; Weeks et al. 2015; Knipler et al. 2023).
Conclusions
Through a multiple species methodological framework, we identified networks of connected habitat for each species before identifying a final corridor for all species. Spatial models are limited in their ability to capture ecological data, such as hollow availability. Hollow availability was critical for seven of the eight species in this study, as they are reliant on them for denning and for raising young. We found that ground-truthing the all-species corridor was critical to identify actions needed to restore habitat. In addition, artificial structures meant to improve the movement of arboreal mammals over the highway, were found to be limited. Our study exemplifies the importance of ground-truthing in connectivity conservation studies to ensure conservation outcomes are realised.
Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
References
Anitha K, Aneesh A, Raghavan R et al (2013) Identifying habitat connectivity for isolated populations of lion-Tailed Macaque (Macaca silenus) in valparai plateau, Western Ghats, India. Primate Conserv 27:91–97
Batson WG, Gordon IJ, Fletcher DB, Manning AD (2015) Translocation tactics: a framework to support the IUCN guidelines for wildlife translocations and improve the quality of applied methods. J Appl Ecol 52:1598–1607
Beier P, Noss RF (1998) Do habitat corridors provide connectivity? Conserv Biol 12:1241–1252
Braaker S, Moretti M, Boesch R et al (2014) Assessing habitat connectivity for ground-dwelling animals in an urban environment. Ecol Appl 24:1583–1595
Brodie JF, Giordano AJ, Dickson B et al (2015) Evaluating multispecies landscape connectivity in a threatened tropical mammal community. Conserv Biol 29:122–132
Chan BPL, Lo YFP, Hong XJ et al (2020) First use of artificial canopy bridge by the world’s most critically endangered primate the Hainan gibbon Nomascus hainanus. Sci Rep 10:1–9
Chen H-L, Posthumus EE, Koprowski JL (2021) Potential of small culverts as wildlife passages on forest roads. Sustainability 13:7224
Corlatti L, Hackländer K, Frey-Roos F (2009) Ability of wildlife overpasses to provide connectivity and prevent genetic isolation. Conserv Biol 23:548–556
Correa Ayram CA, Mendoza ME, Etter A, Salicrup DRP (2016) Habitat connectivity in biodiversity conservation: a review of recent studies and applications. Prog Phys Geogr 40:7–37
Crooks KR, Sanjayan M (2006) Connectivity conservation. Cambridge University Press, Cambridge
Davey SM (1990) Methods for surveying the abundance and distribution of arboreal marsupials in a south coast forest of new south wales. Wildl Res 17:427–445
DCS Spatial Services (2022) Eastern New South Wales (Zone 56)—Digital Elevation Model
Doak DF, Marino PC, Kareiva PM (1992) Spatial scale mediates the influence of habitat fragmentation on dispersal success: implications for conservation. Theoret Popul Biol 41:315–336
DPIE NSW (2013) NSW Plant Community Type
DPIE NSW (2020) Soil Landscapes of Central and Eastern NSW—v2.1
Elith J, Phillips SJ, Hastie T et al (2011) A statistical explanation of MaxEnt for ecologists. Divers Distrib 17:43–57
Fietz J, Weis-Dootz T (2012) Stranded on an island: consequences of forest fragmentation for body size variations in an arboreal mammal, the edible dormouse (Glis glis). Popul Ecol 54:313–320
Fletcher RJ Jr, Reichert BE, Holmes K (2018) The negative effects of habitat fragmentation operate at the scale of dispersal. Ecology 99:2176–2186
Frankham R, Ballou JD, Briscoe DA (2010) Introduction to conservation genetics, 2nd edn. Cambridge University Press, Cambridge
Garcia FD, Culot L, de Carvalho REWF, Rocha VJ (2022) Functionality of two canopy bridge designs: successful trials for the endangered black lion tamarin and other arboreal species. Eur J Wildl Res 68:20
GER (2021) The Great Eastern Ranges. https://ger.org.au/. Accessed 23 March 2021
Gilpin ME, Soule ME (1986) Minimum viable populations: processes of species extinction. In: Conservation biology: the science of scarcity and diversity
Goldingay RL, Taylor BD (2017) Can field trials improve the design of road-crossing structures for gliding mammals? Ecol Res 32:743–749
Goldingay RL, Rohweder D, Taylor BD (2013) Will arboreal mammals use rope-bridges across a highway in eastern Australia? Aust Mammal 35:30–38
Goldingay RL, Taylor BD, Parkyn JL (2018) Use of tall wooden poles by four species of gliding mammal provides further proof of concept for habitat restoration. Aust Mammal 41:255–261
Gracanin A, Mikac KM (2022a) The use of selfie camera traps to estimate home range and movement patterns of small mammals in a fragmented landscape. Animals 12:912
Gracanin A, Mikac KM (2022b) Camera traps reveal overlap and seasonal variation in the diel activity of arboreal and semi-arboreal mammals. Mammal Biol 102:341–355
Gracanin A, Cappelletti C, Knipler M et al (2019) Exploring new grounds: arboreal sugar gliders frequently observed spending time on the ground as seen on camera traps. Aust Mammal 42:10–13
Gracanin A, Minchinton TE, Mikac KM (2022) Estimating the density of small mammals using the selfie trap is an effective camera trapping method. Mamm Res. https://doi.org/10.1007/s13364-022-00643-5
Gracanin A, Knipler ML, Mikac KM (2023) Informing wildlife corridor creation through population genetics of an arboreal marsupial in a fragmented landscape. Genes 14:349
Gužvica G, Bošnjak I, Bielen A et al (2014) Comparative analysis of three different methods for monitoring the use of green bridges by wildlife. PLoS ONE 9:e106194
Haddad NM, Brudvig LA, Clobert J et al (2015) Habitat fragmentation and its lasting impact on Earth’s ecosystems. Sci Adv 1:e1500052
Haslem A, Avitabile SC, Taylor RS et al (2012) Time-since-fire and inter-fire interval influence hollow availability for fauna in a fire-prone system. Biol Conserv 152:212–221
Hilty JA, Lidicker WZ Jr, Merenlender AM (2012) Corridor ecology: the science and practice of linking landscapes for biodiversity conservation. Island Press, Washington
Hofman M, Gracanin A, Mikac KM (2022) Greater glider (Petauroides volans) den tree and hollow characteristics. Aust Mammal. https://doi.org/10.1071/AM22008
Huang C, Ward S, Lee AK (1987) Comparison of the diets of the feathertail glider, Acrobates pygmaeus, and the eastern pygmy-possum, Cercartetus nanus (Marsupialia: Burramyidae) in sympatry. Aust Mammal 10:47–50
Isaac B, White J, Ierodiaconou D, Cooke R (2014) Simplification of arboreal marsupial assemblages in response to increasing urbanization. PLoS ONE 9:e0091049
Jackson SM, Parsons M, Baseler M, Stanton D (2020) Landscape management of the mahogany glider (Petaurus gracilis) across its distribution: subpopulations and corridor priorities. Aust Mammal 42:152–159
Keinath DA, Doak DF, Hodges KE et al (2017) A global analysis of traits predicting species sensitivity to habitat fragmentation. Glob Ecol Biogeogr 26:115–127
Kilbane S, Weller R, Hobbs R (2019) Beyond ecological modelling: ground-truthing connectivity conservation networks through a design charrette in Western Australia. Landsc Urban Plan 191:103122
Knipler ML, Gracanin A, Mikac KM (2023) Conservation genomics of an endangered arboreal mammal following the 2019–2020 Australian megafire. Sci Rep 13:480
Koprowski JL (2005) The response of tree squirrels to fragmentation: a review and synthesis. Anim Conserv 8:369–376
Lancaster ML, Taylor AC, Cooper SJB, Carthew SM (2011) Limited ecological connectivity of an arboreal marsupial across a forest/plantation landscape despite apparent resilience to fragmentation. Mol Ecol 20:2258–2271
Lande R, Engen S, Saether B-E (2003) Stochastic population dynamics in ecology and conservation. Oxford University Press on Demand
Laurance SG, Laurance WF (1999) Tropical wildlife corridors: use of linear rainforest remnants by arboreal mammals. Biol Conserv 91:231–239
Lees AC, Peres CA (2008) Conservation value of remnant riparian forest corridors of varying quality for Amazonian birds and mammals. Conserv Biol 22:439–449
Lindenmayer D (2002) Gliders of Australia: a natural history. UNSW Press, Kensington
Mackey B, Watson J, Worboys G of AEPL 2010 (2010) Connectivity conservation and the Great Eastern Ranges corridor, an independent report to the Interstate Agency Working Group (Alps to Atherton Connectivity Conservation Working Group) convened under the Environment Heritage and Protection Council/Natural
Malekian M, Cooper SJBB, Saint KM et al (2015) Effects of landscape matrix on population connectivity of an arboreal mammal, Petaurus breviceps. Ecol Evol 5:3939–3953
Maloney KS, Harris JM (2008) Early natural history of the greater glider, Petauroides volans (Kerr, 1792). Proc Linnean Soc NSW 129:39–55
Marchesan D, Carthew SM (2008) Use of space by the yellow-footed antechinus, Antechinus flavipes, in a fragmented landscape in South Australia. Landsc Ecol 23:741–752
Martin JK, Handasyde KA, Taylor AC (2007) Linear roadside remnants: their influence on den-use, home range and mating system in bobucks (Trichosurus cunninghami). Austral Ecol 32:686–696
McCall SC, Cesarini S, van der Ree R et al (2017) Evidence that a highway reduces apparent survival rates of squirrel gliders. Ecol Soc 15:e27
McRae BH, Kavanagh DM (2022) Linkage mapper connectivity analysis. Computer Software Program Produced by the Nature Conservancy in Seattle, WA, US. https://linkagemapper.org/. Accessed 16 June 2022b
McRae BH, Shah VB (2009) Circuitscape user’s guide. The University of California, Santa Barbara
McRae BH, Dickson BG, Keitt TH, Shah VB (2008) Using circuit theory to model connectivity in ecology, evolution, and conservation. Ecology 89:2712–2724
Mella VSA, McArthur C, Krockenberger MB et al (2019) Needing a drink: Rainfall and temperature drive the use of free water by a threatened arboreal folivore. PLoS ONE 14:1–15
Miranda L de S, Awade M, Jaffé R, et al (2021) Combining connectivity and species distribution modeling to define conservation and restoration priorities for multiple species: a case study in the eastern Amazon. Biol Conserv 257:109148
Molloy SW, Davis RA (2017) Resilience to agricultural habitat fragmentation in an arboreal marsupial. Aust Mammal 39:185–196
Monsimet J, Devineau O, Pétillon J, Lafage D (2020) Explicit integration of dispersal-related metrics improves predictions of SDM in predatory arthropods. Sci Rep 10:1–12
Mortelliti A, Santulli Sanzo G, Boitani L (2009) Species’ surrogacy for conservation planning: caveats from comparing the response of three arboreal rodents to habitat loss and fragmentation. Biodivers Conserv 18:1131–1145
Naidoo R, Kilian JW, Du Preez P et al (2018) Evaluating the effectiveness of local- and regional-scale wildlife corridors using quantitative metrics of functional connectivity. Biol Conserv 217:96–103
NSW Government (2022) Environment & Heritage|NSW BioNet. https://www.environment.nsw.gov.au/atlaspublicapp/UI_Modules/ATLAS_/AtlasSearch.aspx. Accessed 16 June 2022
NSW Scientific Committee (2016) Greater Glider population at Seven Mile Beach National Park Endangered population listing. Final Determination to list an endangered ecological community under the Threatened Species Conservation Act 1995
Ovaskainen O, Meerson B (2010) Stochastic models of population extinction. Trends Ecol Evol 25:643–652
Pe’er G, Henle K, Dislich C, Frank K (2011) Breaking functional connectivity into components: a novel approach using an individual-based model, and first outcomes. PLoS ONE 6:e0022355
Petsas P, Tsavdaridou AI, Mazaris AD (2020) A multispecies approach for assessing landscape connectivity in data-poor regions. Landsc Ecol 35:561–576
Phillips SJ, Anderson RP, Dudík M et al (2017) Opening the black box: an open-source release of Maxent. Ecography 40:887–893
Plaschke M, Bhardwaj M, König HJ et al (2021) Green bridges in a re-colonizing landscape: wolves (Canis lupus) in Brandenburg, Germany. Conserv Sci Pract 3:1–12
Pliscoff P, Simonetti JA, Grez AA et al (2020) Defining corridors for movement of multiple species in a forest-plantation landscape. Glob Ecol Conserv 23:e01108
Powers RP, Jetz W (2019) Global habitat loss and extinction risk of terrestrial vertebrates under future land-use-change scenarios. Nat Clim Chang 9:323–329
Reed DH (2004) Extinction risk in fragmented habitats. Anim Conserv 7:181–191
Roberge J-M, Angelstam PER (2004) Usefulness of the Umbrella species concept as a conservation tool. Conserv Biol 18:76–85
Russell TC, Herbert CA, Kohen JL (2009) High possum mortality on urban roads: Implications for the population viability of the common brushtail and the common ringtail possum. Aust J Zool 57:391–397
Russell TC, Herbert CA, Kohen JL, Cooper D (2013) The incidence of road-killed possums in the Ku-ring-gai area of Sydney. Aust J Zool 61:87–94
Saura S, Torné J (2009) Conefor Sensinode 2.2: a software package for quantifying the importance of habitat patches for landscape connectivity. Environ Model Softw 24:135–139
Sawyer SC, Epps CW, Brashares JS (2011a) Placing linkages among fragmented habitats: do least-cost models reflect how animals use landscapes? J Appl Ecol 48:668–678
Sawyer SC, Epps CW, Brashares JS (2011b) Placing linkages among fragmented habitats: do least-cost models reflect how animals use landscapes? J Appl Ecol 48:668–678
Schipper J, Chanson JS, Chiozza F et al (2008) The status of the world’s land and marine mammals: diversity, threat, and knowledge. Science 322:225–230
Schtickzelle N, Mennechez G, Baguette M (2006) Dispersal depression with habitat fragmentation in the bog fritillary butterfly. Ecology 87:1057–1065
Soanes K, Vesk PA, van der Ree R (2015) Monitoring the use of road-crossing structures by arboreal marsupials: insights gained from motion-triggered cameras and passive integrated transponder (PIT) tags. Wildl Res 42:241
Soanes K, Lobo MC, Van Der Ree R (2016) Radio-collared squirrel glider (Petaurus norfolcensis) struck by vehicle and transported 500km along freeway. Aust Mammal 38:127–129
Soanes K, Mitchell B, Van Der Ree R (2017a) Quantifying predation attempts on arboreal marsupials using wildlife crossing structures above a major road. Aust Mammal 39:254–257
Soanes K, Taylor AC, Sunnucks P et al (2017b) Evaluating the success of wildlife crossing structures using genetic approaches and an experimental design: lessons from a gliding mammal. J Appl Ecol 55:129–138
Stow AJ, Sunnucks P, Briscoe DA, Gardner MG (2001) The impact of habitat fragmentation on dispersal of Cunningham’s skink (Egernia cunninghami): evidence from allelic and genotypic analyses of microsatellites. Mol Ecol 10:867–878
Suckling GC (1982) Value of reserved habitat for mammal conservation in plantations. Aust For 45:19–27
Tasker EM, Dickman CR (2001) A review of elliott trapping methods for small mammals in Australia. Aust Mammal 23:77–87
Taylor BD, Goldingay RL (2009) Can road-crossing structures improve population viability of an urban gliding mammal? Ecol Soc 14:140213
Taylor BD, Goldingay RL (2010) Roads and wildlife: impacts, mitigation and implications for wildlife management in Australia. Wildl Res 37:320–331
Taylor BD, Goldingay RL (2013) Squirrel gliders use roadside glide poles to cross a road gap. Aust Mammal 35:119–122
Taylor BD, Rohweder D (2013) Radio-tracking three Sugar Gliders using forested highway median strips at Bongil Bongil National Park, north-east New South Wales. Ecol Manag Restor 14:228–230
Taylor BD, Rohweder DA (2020) Yellow-bellied gliders use glide poles to cross the Pacific Highway at Halfway Creek, north-east New South Wales. Aust Mammal 42:385–387
Taylor AC, Tyndale-Biscoe H, Lindenmayer DB (2007) Unexpected persistence on habitat islands: genetic signatures reveal dispersal of a eucalypt-dependent marsupial through a hostile pine matrix. Mol Ecol 16:2655–2666
Teixeira FZ, Printes RC, Fagundes JCG et al (2013) Canopy bridges as road overpasses for wildlife in urban fragmented landscapes. Biota Neotrop 13:117–123
Thornton D, Zeller K, Rondinini C et al (2016) Assessing the umbrella value of a range-wide conservation network for jaguars (Panthera onca). Ecol Appl 26:1112–1124
van der Ree R (2000) Ecology of arboreal marsupials in a network of remnant linear habitats. 1–232
Vinson SG, Johnson AP, Mikac KM (2020a) Thermal cameras as a survey method for Australian arboreal mammals: a focus on the greater glider. Aust Mammal 42:367–374
Vinson SG, Johnson AP, Mikac KM (2020b) Current estimates and vegetation preferences of an endangered population of the vulnerable greater glider at Seven Mile Beach National Park. Austral Ecol 46:303–314
Weeks AR, Moro D, Thavornkanlapachai R et al (2015) Conserving and enhancing genetic diversity in translocation programs. Adv Reintroduction Biol Aust N Z Fauna 127–140
Weston N, Goosem M, Marsh H et al (2011) Using canopy bridges to link habitat for arboreal mammals: successful trials in the Wet Tropics of Queensland. Aust Mammal 33:93–105
Williams-Guillén K, McCann C, Martínez Sánchez JC, Koontz F (2006) Resource availability and habitat use by mantled howling monkeys in a Nicaraguan coffee plantation: Can agroforests serve as core habitat for a forest mammal? Anim Conserv 9:331–338
Wilson RF, Marsh H, Winter J (2007) Importance of canopy connectivity for home range and movements of the rainforest arboreal ringtail possum (Hemibelideus lemuroides). Wildl Res 34:177–184
Wilson MC, Chen XY, Corlett RT et al (2016) Habitat fragmentation and biodiversity conservation: key findings and future challenges. Landsc Ecol 31:219–227
Wintle BA, Kavanagh RP, Mccarthy MA, Burgman MA (2006) Estimating and dealing with detectability in occupancy surveys for forest owls and Arboreal Marsupials. J Wildl Manag 69:905–917
Yanes M, Velasco JM, Suárez F (1995) Permeability of roads and railways to vertebrates: the importance of culverts. Biol Conserv 71:217–222
Yokochi K, Bencini R (2015) A remarkably quick habituation and high use of a rope bridge by an endangered marsupial, the western ringtail possum. Nat Conserv 11:79–94
Zeller KA, McGarigal K, Whiteley AR (2012) Estimating landscape resistance to movement: a review. Landsc Ecol 27:777–797
Acknowledgements
We acknowledge the Dharawal people, the traditional custodians of the land, and pay our respects to elders past, present and emerging. Special thanks to the following artists for allowing the usage of their illustrations in this paper: Rocco Russo, Tracy MacVean, Elizabeth Ann Francis, Kevin Stead, NSW NPWS, Sarah Hardy (for Blue Roo Inc) and Lizzie Harper www.lizzieharper.co.uk.
Funding
Open Access funding enabled and organized by CAUL and its Member Institutions. Funding was provided by the SMAH Partnership grant with National Parks Association and Berry Wildlife Corridor (NSW Environment Trust) and an Enhancement Grant from the Centre for Sustainable Ecosystem Solutions, University of Wollongong. We thank Transport for NSW for in-kind support in assisting in the installation of cameras up rope bridges over the Princes Highway.
Author information
Authors and Affiliations
Contributions
AG and KM conceived the ideas; AG designed the methodology; AG collected the data; AG analysed the data; AG led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.
Corresponding authors
Ethics declarations
Conflict of interest
The authors declare no conflicts of interest.
Ethical approval
This work was conducted under NSW DPIE Scientific Licence 101968 and UOW Animal Ethics protocol AE1902.
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Information
Below is the link to the electronic supplementary material.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Gracanin, A., Mikac, K.M. Evaluating modelled wildlife corridors for the movement of multiple arboreal species in a fragmented landscape. Landsc Ecol 38, 1321–1337 (2023). https://doi.org/10.1007/s10980-023-01628-8
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10980-023-01628-8