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Surface water network structure, landscape resistance to movement and flooding vital for maintaining ecological connectivity across Australia’s largest river basin
Abstract and Figures
Context: Landscape-scale research quantifying ecological connectivity is required to maintain the viability of populations in dynamic environments increasingly impacted by anthropogenic modification and environmental change.
Objective: To evaluate how surface water network structure, landscape resistance to movement, and flooding affect the connectivity of amphibian habitats within the Murray–Darling Basin (MDB), a highly modified but ecologically significant region of south-eastern Australia.
Methods: We evaluated potential connectivity network graphs based on circuit theory, Euclidean and least-cost path distances for two amphibian species with different dispersal abilities, and used graph theory metrics to compare regional- and patch-scale connectivity across a range of flooding scenarios.
Results: Circuit theory graphs were more connected than Euclidean and least-cost equivalents in floodplain environments, and less connected in highly modified or semi-arid regions. Habitat networks were highly fragmented for both species, with flooding playing a crucial role in facilitating landscape-scale connectivity. Both formally and informally protected habitats were more likely to form important connectivity “hubs” or “stepping stones” compared to non-protected habitats, and increased in importance with flooding.
Conclusions: Surface water network structure and the quality of the intervening landscape matrix combine to affect the connectivity of MDB amphibian habitats in ways which vary spatially and in response to flooding. Our findings highlight the importance of utilising organism-relevant connectivity models which incorporate landscape resistance to movement, and accounting for dynamic landscape-scale processes such as flooding when quantifying connectivity to inform the conservation of dynamic and highly modified environments.
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... Using Circuitscape 4.0 software, this study selected the pairwise mode and all-toone mode to simulate and analyze the connectivity characteristics between ecological source areas and the relative importance of ecological corridors [29,30]. To better identify the functional ecological network of the green space, combined with relevant research results [32,33], the current study selected the top 30% grid pixels of the pairwise mode current density values as important functional connectivity corridors in combination with the zoning model. The top 20% of grid pixels of the all-to-one mode current density were regarded as important patches that functioned as stepping stones in the landscape [29,34]. ...
Strengthening and optimizing the spatial structure and functional connectivity of green space ecological networks can not only relieve the tight urban space and provide biodiversity protection but also promote the virtuous cycle of the urban ecosystem and provide a new method for the resilient development of the urban landscape. In this study, the central area of Chengdu was taken as the study area; Morphological Spatial Pattern Analysis (MSPA) with landscape metrics were combined to determine the optimal distance threshold and identify the ecological sources. Graph theory and circuit theory were applied to construct and optimize the green space ecological network with structural or functional connectivity, respectively. Based on the coupling effect, the optimization of the ecological network was put forward, and the network analysis method was used to evaluate the connectivity of three different types of ecological networks. The results were as follows: (1) The ecological network with structural connectivity was composed of 74 stepping stones, 43 protective sources, and 315 ecological corridors. The connectivity of green space structures gradually decreased from west to east and from periphery to center. (2) In the optimal ecological network with functional connectivity, 176 important ecological corridors were protected, and 40 pinch points and 48 protective sources were identified. The number of important corridors in the east and south was the largest, and the network structure was relatively complex. The barriers were divided into three different levels of ecological restoration areas. (3) The green ecological network with structural and functional connectivity has the best network connectivity. A green space ring network optimization pattern of one center, two belts, multi-points, multi-corridors, and multi-zones connected in a series was proposed. It was suggested to build a multi-level forest ecosystem in Longquan Mountain, develop eco-fruit agriculture and eco-tourism, enrich the biodiversity of the ecological source, and improve its anti-interference ability to the external environment. It is also important to increase ecological strategic points and stepping stones to strengthen the links between different ecological restoration areas, properly handle the use of cultivated land in different regions, strictly observe the red line of cultivated land, and maintain the integrity and diversity of ecological sources. Therefore, the optimization method of the green space ecological network in this study provides technical support for the effective determination of ecological protection areas, the accurate implementation of green space ecological networks, and a scientific planning strategy for decision-makers.
... On the one hand, the rivers are considered efficient natural ecological corridors (Bishop-Taylor et al., 2015;Guo & Liu, 2017;May, 2006). These characteristics are the ideal place to focus an urban defragmentation scenario (Wang et al., 2022;Wang et al., 2021). ...
Ecological sustainability has recently risen to prominence in scientific research and management applications. Approaches to measuring ecological connectivity and their application to optimize ecological network (EN) design are powerful tools against landscape fragmentation and biodiversity loss. We focused on building an EN by identifying the most sensitive areas for ecological connectivity within the Reggio Calabria (Italy) metropolitan area. We also proposed a defragmentation scenario to improve the obtained EN. The CORINE Land Cover and the Urban Atlas 2018 were used to obtain a fine-scale representation of the study area. Ten terrestrial mammal species were used to model connectivity following a multi-species approach. Dispersal distance, patch size, and resistance to species movement were used to identify patches and corridors. Vegetational fractional coverage based on three years time series of Sentinel-2 red-edge normalized difference vegetation index was used to discriminate areas with higher naturalness. We used graph theory and connectivity metrics to test the EN's robustness and identify locations for restoration in a defragmentation scenario. The obtained EN, formed by three separate components, was composed of 724 arcs and 300 nodes with an average patch area of 27.04 ha. After the defragmentation hypothesis, the EN, formed by only one component, was composed of 771 arcs and 328 nodes with an average patch area of 26.82 ha. It was possible to analyze an EN's connectivity and evaluate the impact of a scenario intended to enhance multi-species connectivity. By comparing several connectivity metrics, we highlighted the potential of land interventions as a planning tool to enhance future ecological sustainability and biodiversity conservation.
... It is influenced by ecological resistance factors in the process of energy and information transfer, and the resistance surface constructed by ecological resistance factors reflects the trend and pattern of ecological flow in the ecosystem. Referring to relevant literature [31][32][33], six ecological resistance factors ( Figure 3) are selected including land use, roughness, NDVI, road network density, water network density, and soil organic matter. Using the natural breakpoints in the ArcGIS reclassification tool, each factor resistance is classified into 5 levels, and then, the resistance factors are summed and calculated by the raster calculator to obtain the resistance coefficients. ...
Forest and grass ecological space is the key component of the ecosystem and plays a vital role in regulating the carbon, water, and energy cycle. The long-term exploitation of forest and grass ecological space and huge population pressure have gradually degraded the function of China’s ecosystem. Therefore, forest and grass ecological space plays an important role in maintaining the stability of the ecosystem. The relationship between forest and grass ecospatial network structure and ecosystem service has been the focus of research. In this study, the forest and grass ecospatial network is constructed based on the minimum cumulative resistance (MCR) model. Then, the topological indicators (degree, weight clustering coefficient, node weight, unit weight, weight distribution difference, betweenness, PageRank) of the forest and grass ecospatial network were calculated by combining the complex network theory to analyze the relationship between these topological indicators and the three ecosystems (water retention, soil conservation, carbon storage). Based on the ecological significance of topological indicators, we identified ecologically fragile areas and proposed areas and directions for optimizing the ecospatial structure. Results show that the spatial distribution of the three ecosystem services in the southeast region of China is higher than that in the northwest region of China and shows a gradual decrease from the east to the west. The degree, node weight, unit weight, PageRank, and betweenness were highly significant and positively correlated with the three ecosystem services, among which PageRank had the highest correlation with water retention (p < 0.01, R2 = 0.835). Based on the spatial distribution characteristics of the different topological indicators, the quantitative relationship between the structural characteristics of the forest and grass ecospatial network and ecosystem services is clarified, revealing the intrinsic connection between ecological processes and ecosystem services. Through rational optimization of the forest and grass ecospatial network, ecosystem services can be effectively improved and ecosystem stability can be enhanced.
... A way in which our work advances graph theory applications for freshwater ecology and conservation is through the use of hubs, which in our case were major lake nodes that disproportionately influenced freshwater network structure. The concept of hubs in freshwater ecology (Bishop-Taylor et al., 2015;Muirhead & MacIsaac, 2005) or general landscape ecology (Minor & Urban, 2008) as highly connected nodes is not new, but our characterization using multiple axes of lake-stream network analysis allows for a unified definition across all freshwater networks in the conterminous United States and could be similarly applied elsewhere. Critical nodes, T A B L E 3 Protection status of networks and hub lakes in the conterminous United States for high-scoring networks. ...
Maintaining regional‐scale freshwater connectivity is challenging due to the dendritic, easily fragmented structure of freshwater networks, but is essential for promoting ecological resilience under climate change. Although the importance of stream network connectivity has been recognized, lake‐stream network connectivity has largely been ignored. Furthermore, protected areas are generally not designed to maintain or encompass entire freshwater networks. We applied a coarse‐filter approach to identify potential freshwater corridors for diverse taxa by calculating connectivity scores for 385 lake‐stream networks across the conterminous United States based on network size, structure, resistance to fragmentation, and dam prevalence. We also identified 2080 disproportionately important lakes for maintaining intact networks (i.e., hubs; 2% of all network lakes) and analyzed the protection status of hubs and potential freshwater corridors. Just 3% of networks received high connectivity scores based on their large size and structure (medians of 1303 lakes, 498.6 km north–south stream distance), but these also contained a median of 454 dams. In contrast, undammed networks (17% of networks) were considerably smaller (medians of six lakes, 7.2 km north–south stream distance), indicating that the functional connectivity of the largest potential freshwater corridors in the conterminous United States currently may be diminished compared with smaller, undammed networks. Network lakes and hubs were protected at similar rates nationally across different levels of protection (8%–18% and 6%–20%, respectively), but were generally more protected in the western United States. Our results indicate that conterminous United States protection of major freshwater corridors and the hubs that maintain them generally fell short of the international conservation goal of protecting an ecologically representative, well‐connected set of fresh waters (≥17%) by 2020 (Aichi Target 11). Conservation planning efforts might consider focusing on restoring natural hydrologic connectivity at or near hubs, particularly in larger networks, less protected, or biodiverse regions, to support freshwater biodiversity conservation under climate change.
... The increase in chorusing duration in Limnodynastes tasmaniensis after inundation from river flows is consistent with previous findings (Heard et al., 2015;McGinness et al., 2014). The negative effect of arrival of flow on Limnodynastes fletcheri was surprising and one possible explanation is that Limnodynastes fletcheri has good dispersal ability and calling males can move to nearby low-laying vegetated shallow waterbodies which allowed them to disperse beyond the recorders in response to inundation of nearby habitats (Bishop-Taylor et al., 2015;Ocock et al., 2014). Future acoustic sampling would benefit from pairing trail cameras with acoustic recorders to allow researchers to gauge the specific spatial layout of inundation at the site. ...
Globally, river regulation has degraded wetlands, including parts of the Murray-Darling Basin (MDB), an ecologically significant basin in Australia. Frogs in a floodplain environment largely depend on habitats created by river flows, but little is known about how frogs in the northern MDB are impacted by river regulation. We tested how wetland inundation affected frogs in a catchment of the northern MDB. We surveyed frogs between 2015 and 2019 to determine long-term changes in the community composition associated with wetland inun-dation from river flows. Additionally, we recorded nightly soundscapes for four days before and after the arrival of river flows between 2019 and 2020. The abundance and richness of frog species increased during larger inundation events leading to altered community composition (beta diversity). Warmer temperatures increased frog species richness, and frog community dominance decreased with decreasing vegetation cover (i.e., the relative abundance became more even across species). The abundance of five frog species (Limnodynastes tas-maniensis, Limnodynastes fletcheri, Crinia parinsignifera, Litoria peronii, and Litoria latopalmata) was higher in response to increased inundation extent. The total species richness of chorusing frogs increased after the arrival of river flows; six species chorused over the four nights preceding flow, whereas eight species chorused following the flow arrival, but the responses varied among species and sites. Frog species richness increased at three sites after flows, but not at others. After inundation, the choruses of Limnodynastes tasmaniensis increased whereas Limnodynastes fletcheri decreased. Our findings indicate that wetland inundation is beneficial for frog communities and suggest that chorusing behaviour varied in response to river flows inundating floodplain wetlands.
... On Sado Island, a major river improvement project was carried out in the 1970s, and the frequent flooding that had previously occurred in the central region has been significantly reduced (Uchida 1991). Since flooding plays a major role in the movement of frogs, the dramatic reduction of flood events in the central region might have had an adverse impact on the functional connectivity between the local populations (Ocock et al. 2014;Bishop-Taylor et al. 2015). ...
The Sado wrinkled frog (Glandirana susurra) is a recently described threatened amphibian species found only on Sado Island, a small island located off the north coast of Honshu, Japan. We conducted an extensive field survey and genetic analysis of G. susurra to identify its (1) large-scale distribution patterns, (2) remaining levels of genetic diversity, (3) major genetic groups (i.e., regional populations), and (4) levels of genetic differentiation and gene flow within and between its populations on the island. G. susurra was most prevalent in the central part of the island but was also observed in some areas to the east and west. We found a strong, hierarchical genetic structure that includes three genetically distinct groups of populations (‘eastern’, ‘central’ and ‘western’). The eastern and western regional populations had significantly lower genetic diversity than the central population. We found, however, that many local populations in the central population had experienced several recent bottleneck events. Conservation recommendations for G. susurra include (1) considering the three major groups of G. susurra populations as separate units for purposes of conservation planning, (2) increasing the population sizes of the eastern and western populations which showed relatively lower genetic diversity, and (3) increasing habitat connectivity to facilitate gene flow among local populations in the central part of the island.
Context Both anthropogenic change and environmental variability cause spatiotemporal fluctuations in the availability of habitat on a landscape. Land acquisition and restoration for conservation also facilitates dynamic habitat accessibility. Accounting for these spatiotemporal dynamics is critical to the success of conservation planning to increase landscape connectivity.
Objectives We aimed to forecast the individual and interactive effects of anthropogenic change, environmental variability, and conservation action on landscape connectivity over time. In doing so, we sought to evaluate the capacity of conservation actions intended to enhance connectivity to keep pace with global change.
Methods We used a landscape change model to simulate strategies for the expansion of protected area networks on a ~1.5 million ha landscape in North Carolina. We forecasted spatiotemporal changes (2020-2100) to complex habitat networks across multiple scenarios of climate and land-use change, using graph theory to assess the variance in connectivity between conservation strategies and among global change futures.
Results Both climate and land-use change reduced the influence of conservation on landscape connectivity, but through different mechanisms. Climate change increased available longleaf pine habitat, improving overall landscape connectivity and camouflaging connectivity improvements from conservation. Land-use change reduced the connectivity improvements facilitated by conservation as the cost of movement between habitat patches increased.
Conclusion Rather than acting synergistically with land-use change, climate change negated the connectivity declines from land-use change in the study area. More broadly, our approach to forecast landscape-level responses to climate change, land-use change, and management can support the identification of conservation strategies that are more robust to global change, better enhancing landscape connectivity.
China’s Ecological Conservation Redline (ECR) program ensures the coordination and sustainability of natural and economic development while maintaining regional ecological security. Current research focuses on the ecosystem services within ECR areas but ignores cross-boundary ecological flow and the interactions between the internal and external ecological effects of ECR areas. In addition, the ecological background has spatial continuity that is not limited by boundaries, and the radiation effect areas extending beyond ECR areas have not been quantified. In this study, the Beijing ECR areas and ecological security network were integrated in order to connect the ecological process and landscape pattern to the ECR through the circulation path of ecological corridors, and cross-boundary effects between patches were examined. The field spread model was used to quantify the radiation influence range of ECR areas. Additionally, 972.46 km of ecological corridors were identified in Beijing, and abundant corridors effectively linked the ECR areas and maintained the material cycle. In the surrounding areas, ecological corridors were spread radially, with a total length of 941.85 km, promoting cross-boundary ecological flow between the ECR and surrounding source areas. This study used 25 ecological nodes to constitute the cross-boundary ecological security network system. The total radiation area based on the ECR source was 9572.16 km ² . These results provide support for the radiation effect of ECR and cross-boundary ecological flows and suggest a useful model for sustainable ecological development and cross-boundary management.
Graph theory (GT) is extensively applied in the ecological network analysis. This review study aimed to examine GT in the field of ecological network analysis based on the following questions: In what areas are the articles focused?, what indexes or graph-based indicators have been thus far utilized in ecological network analysis?, and what aspects of ecological network analysis have been less considered in terms of the use of the GT indicators? To address these questions, a systematic literature review was conducted and the results showed that most of the articles in this field had been fulfilled in China, the United States, and France. This theory could have implications for more research on plants and mammals. In addition, 118 indicators were identified in the field of GT in the ecological network analysis. Among these indicators, the probability of connectivity (PC) and an integral index of connectivity (IIC) had been consistently exploited in most articles. Moreover, the results revealed the increasing trend of introducing the new indicators of GT to ecological network analysis, suggesting the applicability of GT in this context. Despite the importance of ecological network resilience, it has been less reflected from the GT perspective while it can be useful and efficient in analyzing the sustainability of ecological networks within this framework. The current trend of exploiting the GT indicators delineates three future lines of development, viz. (1) the GT use more widely in ecological network analysis, (2) emerging new and more precise indexes, and (3) new concerns mainly examining ecological network resilience.
The development of road networks over the years has caused serious damage to biodiversity. However, few studies have explored the impact of different road grades on ecological network connectivity, especially at multiple levels and at different dispersal distances. Here, we propose an analytical framework based on the integrated graph theory and the circuit theory method, in order to model the ecological network of virtual species, to evaluate connectivity at the landscape, patch, and corridor levels, and to identify the key patches and key corridors that contribute the most to the maintenance of connectivity. The empirical analysis in this study was performed on six scenarios, which were designed by successively integrating different road grades into the landscape. On this basis, the impact of different road grades on the connectivity, key patches, and key corridors in Wuhan, China, were explored. The results showed that: (1) High-grade roads have a significant impact on landscape-patch-corridor connectivity, while medium-grade roads have a similar degree of impact on patch-level connectivity as high-grade roads do. (2) Species with long dispersal ability (25 km) are susceptible to roads at the landscape and corridor levels; species with low and medium dispersal abilities (10, 15 and 20 km) are vulnerable to roads at the patch levels. (3) The importance of key patches and the resistance of key corridors are significantly increased by the influence of roads, while their spatial distribution changes slightly. This integrated framework contributes to an evaluation of the impacts of different grades road on ecological processes, so as to better provide targeted suggestions for biodiversity conservation and transportation planning.
Models of metapopulations have focused on the effects of extinction and colonization rate upon metapopulation persistence and dynamics, assuming static landscapes wherein patches are neither created nor go extinct. However, for species living in ephemeral (patchy) habitats, landscapes are highly dynamic rather than static. In this article, we develop a lattice metapopulation model, of the patch occupancy type, based on interacting particle systems that incorporate explicitly both metapopulation and patch dynamics. Under this scenario, we study the effects of different regimes of patch dynamics upon metapopulation persistence. We analyze the lattice behavior by numerical simulations and a mean field approximation (MF). We show that metapopulation persistence and extinction are strongly influenced by the rate at which the landscape changes, in addition to the amount of habitat destroyed. We derive MF analytical expressions for extinction thresholds related to landscape properties such as habitat suitability and patch average lifetime. Using numerical simulations, we also show how these thresholds are quantitatively overestimated by the MF equations, although the qualitative behavior of the spatial model is well explained by the MF when the array of habitat patches is dynamic or static but connected in space and time. The implications for conservation are also discussed.
The R package gdistance provides classes and functions to calculate various distance measures and routes in heterogeneous geographic spaces represented as grids. Least-cost distances as well as more complex distances based on (constrained) random walks can be calculated. Also the corresponding routes or probabilities of passing each cell can be determined. The package implements classes to store the data about the probability or cost of transitioning from one cell to another on a grid in a memory-efficient sparse format. These classes make it possible to manipulate the values of cell-to-cell movement directly, which offers flexibility and the possibility to use asymmetric values. The novel distances implemented in the package are used in geographical genetics (applying circuit theory), but also have applications in other fields of geospatial analysis.
