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Impact of hydroclimatic variability on regional-scale landscape connectivity across a dynamic dryland region

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... The integration of conservation approaches in connectivity forecasting has also been narrow in scope, focusing on a single subset of candidate actions or evaluating conservation at coarse scales (Carlson et al., 2019). Ideally, conservation planning would integrate landscape dynamics and longer time horizons and evaluate the outcomes of a suite of feasible conservation alternatives to provide the best defense against biodiversity loss and enhance conservation decisionmaking (Pressey et al., 2007;Bishop-Taylor et al., 2018). As such, the evaluation of landscape connectivity under multiple conservation strategies on a spatiotemporally dynamic landscape represents an important but understudied research need in terrestrial systems, especially when considered over long temporal scales (Zeller et al., 2020). ...
... It incorporates the contribution of patches and links as stepping-stones that support connectivity between other habitat areas (Saura & Rubio, 2010). The area units associated with ECA enable a direct comparison between changes in total habitat area and network spatial configuration to assess how the addition or loss of habitat, whether from land acquisition or landscape dynamics, affects connectivity (Bishop- Taylor et al., 2018;McIntyre et al., 2018). ...
... In addition to ECA, we quantified connectivity for three ECA subcomponents: intrapatch connectivity, the connectivity contributed solely by the area within habitat nodes (ECA intra ); connectivity contributed by connections between neighboring nodes (ECA direct ); and connectivity contributions from intermediate stepping-stones that enabled longer distance dispersal (ECA step) (Saura and Rubio, 2010;Saura et al. 2011;Bishop-Taylor et al., 2018). Evaluating ECA intra, ECA direct, and ECA step provided additional insights into the influence of different aspects of connectivity facilitated by each conservation strategy and among species guilds. ...
Article
Maintaining and enhancing landscape connectivity reduces biodiversity declines due to habitat fragmentation. Uncertainty remains, however, about the effectiveness of conservation for enhancing connectivity for multiple species on dynamic landscapes, especially over long time horizons. Focusing on central North Carolina, we forecast connectivity under four common conservation strategies‐ acquiring the lowest cost land, acquiring land clustered around already established conservation areas, acquiring land with high geodiversity characteristics, and acquiring land opportunistically‐ on a dynamic landscape incorporating forest growth and succession, disturbance, and management from 2020 to 2100. We used graph theoretic metrics to quantify landscape connectivity across these four strategies, evaluating connectivity for four ecologically relevant species guilds, representing endpoints along a spectrum of vagility and habitat specificity: long‐ vs. short‐distance dispersal ability and habitat specialists vs. generalists. Our results indicate that landscape connectivity will improve for specialist species under any conservation strategy employed, although these increases were highly variable across strategies. For generalist species, connectivity improvements were negligible. Overall, clustering the development of new protected areas around land already designated for conservation yielded the largest improvements in connectivity, with increases of several orders of magnitude beyond current landscape connectivity for both long‐ and short‐distance dispersing specialist species. Conserving the lowest cost land showed the smallest contributions to connectivity. Our approach provides insight into the connectivity contributions of a suite of conservation alternatives prior to on‐the‐ground implementation, and therefore can inform connectivity planning to maximize conservation benefit. This article is protected by copyright. All rights reserved
... Jordan et al., 2003;Baum et al., 2004;Pascual-Hortal and Saura, 2007). It has only been recognized recently that connectivity is dynamic (Matisziw and Murray, 2009;Saura et al., 2011;Ruiz et al., 2014;Tulbure et al., 2014;Zeigler and Fagan, 2014;Bishop-Taylor et al., 2015;Bishop-Taylor et al., 2017;Martensen et al., 2017), with a challenge remaining in assessing changes in connectivity in temporally fluctuating habitat networks. Comparing an ecological network to a null model constructed with a similar number of nodes (habitat patches) and node degree distribution (e.g. by using a power law function to generate a neutral model of a scale-free network, or a random/Poisson model) is relatively well-established (e.g. ...
... We used the equivalent connected area (ECA) index to evaluate changes in habitat connectivity compared to changes in habitat amount, i.e., the number of wet playas as well as the area in hectares of open water (Bishop-Taylor et al., 2017;Martensen et al., 2017). Based on the number and size of nodes at a specified proximity, ECA indicates the size of a single habitat patch (node) that would be needed to provide the same probability of connectivity as the observed fragmented network of nodes currently being evaluated. ...
... This line effectively parses the graph space into two section: Values above this line would indicate connectivity higher than expected based on habitat availability, and conversely, values below this line would indicate lower-than-expected connectivity. Because ECA can never assume a value smaller than the size of the largest node in the network, we also calculated the ECA:Area index to provide a scaled assessment of how connectivity may change with habitat area (Bishop-Taylor et al., 2017). A maximally connected network has an index value of 1 (i.e., upper limit is 1); node isolation reduces ECA:Area index values (Bishop-Taylor et al., 2017). ...
... Assessment of the overall trend of spatial connectivity values using statistical analysis Although indicators derived from statistical modelling of the relationship between time and connectivity can accurately assess temporal changes in spatial connectivity in multiple time steps, their use remains rare (Fig. 3b-3). To our knowledge, only two studies have used trend analysis to assess the temporal changes in spatial connectivity (Tulbure et al. 2014;Bishop-Taylor et al. 2018a). Tulbure et al. (2014) analysed global connectivity values of aquatic habitat patches for 278 time steps over a 13-year time series. ...
... Third, and lastly, future research should also keep in mind that the temporal scales of response are hierarchically nested (level of organisation), the temporal response at the individual scale being shorter than that of community scale (Hylander & Ehrlén, 2013). Existing works, even those based on multiple intra-and inter-annual time steps (Tulbure et al. 2014;Bishop-Taylor et al. 2018a), investigated the temporal dynamics of connectivity based on the time steps taken independently. These works hence omit that the shortterm (e.g., intra-annual) temporal dynamics of connectivity are nested in long-term (e.g., inter-annual) dynamics. ...
Article
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ContextLandscape connectivity plays a key role in determining the persistence of species inhabiting fragmented habitat patches. In dynamic landscapes, most studies measure connectivity at multiple time steps, but pay less attention to explicitly quantifying its temporal dynamics to gain insights into its role in biodiversity patterns, thereby enabling more effective operational outcomes.Objectives This article aimed at making an overview of the existing methods for the assessment of the temporal dynamics of connectivity. By analysing their differences and possible applications, we aimed to highlight knowledge gap and future research directions.Methods We conducted a systematic review of literature dealing with the assessment of the temporal dynamics of connectivity and obtained 32 studies.ResultsWe presented two main approaches based on graph theory and compared them from conceptual and operational perspectives. The first widely used approach, accounting only for the spatial dispersal of organisms, quantifies temporal changes in spatial connectivity. Based on two or multiple time steps in the time series, this approach enables assessment of the sense and magnitude of the temporal changes in spatial connectivity. The second recently developed approach quantifies spatio-temporal connectivity, thus accounting for both spatial and temporal dispersal. So far, this holistic assessment of spatio-temporal connectivity only covers two time steps.Conclusion Existing methods for the assessment of the temporal dynamics of connectivity provide indicators to advance our understanding of biodiversity patterns, and to be able to implement measures to conserve and restore connectivity. We propose future directions to develop these methods.
... This comparative research was conducted for species associated with broadleaf forests of the different ecoregions of the Iberian Peninsula. We considered species habitat (Taylor et al. 2013;Bishop-Taylor et al. 2018a), and other factors affecting species habitats. Changes in habitat distribution, amount, and quality may result in species' range shifts (among other responses such as phenological, behavioral, or genetic adaptation) to ensure species persistence (Parmesan and Yohe 2003;Chen et al. 2011;Davidson et al. 2020; Román-Palacios and Wiens 2020). ...
... Some graph-based (Urban et al. 2009) habitat availability metrics were proposed to include irreplaceability in connectivity prioritization: the Probability of Connectivity (PC) (Saura and Pascual-Hortal 2007;Saura and Rubio 2010), and the Equivalent Connected Area (ECA) Santini et al. 2016). These indices proved to be good indicators to monitor landscape changes (Bishop-Taylor et al. 2018a;Poli et al. 2019;Keeley et al. 2021) and very useful for quantifying overall connectivity and identifying critical elements to maintain or enhance it. However, so far, they have been mainly used under a static approach (Dondina et al. 2017;de la Fuente et al. 2018;Cisneros-Araujo et al. 2021) despite their potential to be adapted to different spatial and temporal probabilities of connectivity and to deal with the directionality of the links. ...
Article
Full-text available
Context Climate and land-use changes affect spe- cies ranges and movements. However, these changes are usually overlooked in connectivity studies, and this could have adverse consequences in the definition of effective management measures. Objectives We evaluated two ways to incorporate landscape dynamics: (i) by analyzing connectivity as a fluctuating phenomenon (i.e., time-varying connec- tivity); and (ii) by analyzing species movements from past to current ranges (i.e., spatio-temporal connec- tivity). We also compared these dynamic approaches with traditional static connectivity methods. Methods We compared the overall connectivity val- ues and the prioritization of critical habitat patches according to dynamic and static approaches using habitat availability metrics (Probability of Connectiv- ity and Equivalent Connected Area). This compara- tive research was conducted for species associated with broadleaf forests of the different ecoregions of the Iberian Peninsula. We considered species habitat preferences during movement and a wide range of dispersal abilities to assess functional connectivity. Results Static approaches generated varying overall connectivity values and priority patches depending on the time snapshot considered and different from those generated by dynamic approaches. The two dynamic connectivity approaches resulted in very similar priority conservation patches, indicating their potential to guide enduring conservation measures that enhance connectivity between contemporary habitat patches at multiple time snapshots but also species range shifts in time. Conclusions Connectivity is affected by landscape changes, and only dynamic approaches can overcome the issues associated with these changes and provide valuable information to guide improved and enduring measures in changing landscapes.
... We considered species habitat 1 3 Vol:. (1234567890) (Taylor et al. 2013;Bishop-Taylor et al. 2018a), and other factors affecting species habitats. Changes in habitat distribution, amount, and quality may result in species' range shifts (among other responses such as phenological, behavioral, or genetic adaptation) to ensure species persistence (Parmesan and Yohe 2003;Chen et al. 2011;Davidson et al. 2020; Román-Palacios and Wiens 2020). ...
... Some graph-based (Urban et al. 2009) habitat availability metrics were proposed to include irreplaceability in connectivity prioritization: the Probability of Connectivity (PC) (Saura and Pascual-Hortal 2007;Saura and Rubio 2010), and the Equivalent Connected Area (ECA) Santini et al. 2016). These indices proved to be good indicators to monitor landscape changes (Bishop-Taylor et al. 2018a;Poli et al. 2019;Keeley et al. 2021) and very useful for quantifying overall connectivity and identifying critical elements to maintain or enhance it. However, so far, they have been mainly used under a static approach (Dondina et al. 2017;de la Fuente et al. 2018;Cisneros-Araujo et al. 2021) despite their potential to be adapted to different spatial and temporal probabilities of connectivity and to deal with the directionality of the links. ...
Preprint
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Context Climate and land-use changes affect species ranges and movements. However, these changes are normally overlooked in connectivity studies, and this could have adverse consequences in the definition of effective management measures. Objectives We evaluated two ways to incorporate this dynamism: (i) by acknowledging that connectivity is a fluctuating phenomenon (i.e., time-varying connectivity) and therefore, procuring long-term conservation measures; and (ii) by enhancing species movements to their future ranges (i.e., spatio-temporal connectivity). We further compared these dynamic approaches with traditional static connectivity methods. Methods We compared the overall connectivity values and the prioritization of critical habitat patches according to the dynamic and static approaches. This comparison research was conducted for species associated with broadleaf forests of the different ecoregions of the Iberian Peninsula. We considered species habitat preferences for moving and a wide range of dispersal abilities to assess functional connectivity without focusing on a single species. Results Static approaches generated varying overall connectivity values and priority patches depending on the time snapshot considered and different from those generated by dynamic approaches. The two dynamic connectivity approaches resulted in very similar priority conservation patches, indicating their potential to guide endurable conservation measures that enhance connectivity between contemporaneous habitat patches at multiple time snapshots but also species range shifts in time. Conclusions Connectivity is affected by landscape changes, and only dynamic approaches can overcome the issues associated with these changes and provide valuable information to guide improved and endurable measures in changing landscapes.
... Several studies have highlighted the positional importance of habitats with high network centrality for maintaining and enhancing landscape/riverscape connectivity (Er} os, Schmera & Schick, 2011; Ribeiro et al., 2011;Bishop-Taylor, Tulbure & Broich, 2017a). In this study, the network centrality metric BC was used to evaluate the potential importance of each stream segment within SEQ (Figure 2a). ...
Article
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1. The hydrological variability of intermittent streams means that the spatial distribution of dry-season aquatic refuges within river networks and the temporal dynamics of hydrological connectivity between them are critical for the persistence of aquatic biodiversity. Here, a new approach is demonstrated to identify surface water bodies as priority refuges for efficient conservation management of freshwater biodiversity in intermittent stream networks. 2. Recently developed models of surface water extent and daily streamflow were used to represent spatio-temporal variations in hydrological connectivity and surface water persistence within river networks of eastern Australia over a 107-yr period. Using this information, systematic conservation planning was applied to prioritize aquatic areas for conservation of 25 fish species under two scenarios. One scenario identified priority refuges to complement those already occurring in protected areas, whereas the other did not consider protected area status. 3. The priority networks identified concentrated on the main stems of river catchments where surface water was more likely to be persistent and aquatic refuges were more likely to be connected, but also included headwaters for rare fish species. All three set conservation targets for the 25 fish species can be met in the best solution of priority networks. Although the second scenario achieved the targets with a smaller size of priority network overall, it required more new aquatic refuges and was thus less efficient than the first scenario. 4. The newly developed datasets are useful for freshwater conservation prioritization because they account for hydrological variability of intermittent streams. The systematic prioritization approach applied is transferable to other regions and freshwater taxa to identify aquatic refuges for biodiversity conservation within intermittent stream systems.
... To reflect these spatial differences in anthropogenic modification and hydroclimatic variability, we focused our analysis on the entire MDB, the Paroo region, and two other regions with varying degrees of development: the lower Murray (a southern MDB region containing both natural floodplain wetlands and dryland and irrigated agriculture) and the Riverina (a highly regulated region of the south-east MDB adjacent to the Murray and Murrumbidgee rivers and characterised by extensive irrigated agriculture). These three regions were previously shown to differ substantially in their relationship between surface water habitat availability and landscape connectivity (Bishop-Taylor et al. 2017c). ...
Article
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Context: Despite calls for landscape connectivity research to account for spatiotemporal dynamics, studies have overwhelmingly evaluated the importance of habitats for connectivity at single or limited moments in time. Remote sensing time series represent a promising resource for studying connectivity within dynamic ecosystems. However, there is a critical need to assess how static and dynamic landscape connectivity modelling approaches compare for prioritising habitats for conservation within dynamic environments. Objectives: To assess whether static landscape connectivity analyses can identify similar important areas for connectivity as analyses based on dynamic remotely sensed time series data. Methods: We compared degree and betweenness centrality graph theory metric distributions from four static scenarios against equivalent results from a dynamic 25-year remotely sensed surface-water time series. Metrics were compared at multiple spatial aggregation scales across south-eastern Australia’s 1 million km2 semi-arid Murray–Darling Basin and three sub-regions with varying levels of hydroclimatic variability and development. Results: We revealed large differences between static and dynamic connectivity metric distributions that varied by static scenario, region, spatial scale and hydroclimatic conditions. Static and dynamic metrics showed particularly low overlap within unregulated and spatiotemporally variable regions, although similarities increased at coarse aggregation scales. Conclusions: In regions that exhibit high spatiotemporal variability, static connectivity modelling approaches are unlikely to serve as effective surrogates for more data intensive approaches based on dynamic, remotely sensed data. Although this limitation may be moderated by spatially aggregating static connectivity outputs, our results highlight the value of remotely sensed time series for assessing connectivity in dynamic landscapes.
... Tulbure et al. (2016) was also the only published product with a statistical accuracy assessment that created confidence for its use in follow on applications (e.g. Bishop-Taylor et al., 2015, Bishop-Taylor et al., 2017a, 2017b, Bishop-Taylor et al., 2018Heimhuber et al., 2015Heimhuber et al., , 2017Shendryk et al., 2016b). The statistical accuracy assessment met two key criteria. ...
... Large spatial and temporal scales are recognized to be fundamental for amphibian research because changes to landscape conditions across scales may have important impacts on habitat connectivity and migration (Hazell 2003;Bishop-Taylor et al. 2015). Earth observation satellite data (Bishop-Taylor et al. 2017), expert knowledge (Store and Kangas 2001), and geographical information systems (Store and Jokim€ aki 2003) have been successfully combined for developing HSMs. When such data are not available, HSMs can be developed by aggregating habitat features using expert knowledge (Store and Kangas 2001). ...
Article
Wetlands should not be considered as independent objects but as dynamically connected objects, collectively known as wetlandscapes. We developed a framework that analyzes the influences of wetland suitability and connectivity on amphibian distributions. We defined two indices: a Wetland Suitability Index describing wetland quality and a Movement Permeability Index characterizing wetland connectivity for amphibian population dynamics. These indices were calculated from raster datasets and time‐varying inundation estimates. The indices were used to define a wetlandscape and an amphibian model was used to simulate population dynamics within the wetlandscape. The framework was applied to the Nose Creek watershed, a highly modified wetlandscape in Alberta, Canada. Two amphibian species were selected with different habitat preferences: the Northern Leopard Frog that prefers wet habitats and has high mobility over land, and the Great Plains Toad that prefers terrestrial habitats and has low mobility over land. We found each amphibian species had a “preferred” wetlandscape, reflecting their life cycle traits and migration strategies which in turn were dependent on the hydrological and ecological connections within the wetlandscape. This study highlights the importance of investigating both individual wetlands and the wetlandscape and considering both wetland habitat quality and connectivity as non‐substitutable properties that act jointly, but differently, on population dynamics. Research Impact Statement: Both wetland habitat quality and connectivity act jointly but differently on amphibian population dynamics and should both be considered when managing wetlandscapes.
... The focus is on the aspects of establishment and evaluation of networks. For example, habitat networks were constructed to assess how climatic variability influences potential connectivity for water organisms in the Murray Darling Basin of Australia by Robbi et al. [36]. Andrea et al. [37] proposed one methodology to build a network with the patch's area as the weight index of nodes for landscape planning in the peri-urban and urban areas of the town of Nuoro (Italy). ...
Article
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Archaeological sites are facing serious threats from environmental changes in the background of urban sprawl. More efforts are needed to enhance the cognition of human–environment interactions for better conservation. Under the traditional geomantic view, the environmental preference involved was presented to guide ancient life. In this study, we analyzed the edge effect and network structure of two periods in an ecological transition zone where the ancient sites were located. From the cases of Gouzhang and Yinxian, the separability of edge intensity indicated the different site selection patterns because of the discrepancy of patch fragmentation and ecological structure. Additionally, the different trends of the edge effect were thought to be related to the complexity of the ecological network. Besides that, the ancient cities located in or around the high-centrality terrain in the network of closed space could have provided the convenience of accessing living materials from early ecosystems. In practice, the comprehensive methods based on geomantic and ecological analysis proved effective when used to explore possible areas of the undiscovered archaeological sites. What is more important is that traditional environmental perceptions could be integrated into a scientific system of the ecological landscape and contribute more to archaeological research and the study of ancient culture.
... Research on how wetland dynamics shape ecological processes, such as the ways in which species' life histories adapt to phenological patterns of wetland hydroperiod (Niemuth et al. 2014;Davis et al. 2017), is ham-pered by the absence of wetland time-series data. Other limitations include understanding how environmental fluctuations, such as water availability, drive species assemblages and coexistence mechanisms (Chesson 2000) and structure patterns of connectivity (Bishop-Taylor et al. 2018). Despite the presence of data on species' life histories, demography, distributions, and movement, an absence of data on wetland dynamics precludes rigorous testing of most foundational ecological theories that connect environmental dynamics to ecological patterns and processes. ...
Article
Wetland ecosystems are highly biodiverse, essential to human health and well‐being, and in decline, yet knowledge of the natural dynamics and distributions of wetland systems is lacking globally, hindering conservation efforts. We integrated data generated from novel remote‐sensing techniques and Bayesian hierarchical modeling to estimate the daily surface area of 149 wetlands (vernal pools) over a 20‐year period. We used these data to quantify the proportion of pools found suitable for local threatened and endangered species, and we discuss how to apply these methods to help answer fundamental ecological questions. Our modeling approaches, which can be applied to many kinds of wetlands and other freshwater systems, expand our ability to understand hydrologic dynamics across scales relevant to species, populations, and ecosystems, as well as to human needs, concerns, and decision making.
... Similarly, the importance of incorporating connectivity as a dynamic feature has been identified in freshwater research [51,52], with analyses of longitudinal data suggesting that static approaches to assess connectivity fail to capture key connectivity measures [30]. Given the dynamic processes that govern many aquatic systems-e.g., droughts, floods, intermittent flow-it is not surprising that connectivity metrics have been found to shift by orders of magnitude in response to changing conditions [53]. In wetlands, connectivity across the landscape has also been found to be an emergent and dynamic property [54] and closely tied to climate-driven variation and climate change [55]. ...
Article
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Landscape connectivity is increasingly promoted as a conservation tool to combat the negative effects of habitat loss, fragmentation, and climate change. Given its importance as a key conservation strategy, connectivity science is a rapidly growing discipline. However, most landscape connectivity models consider connectivity for only a single snapshot in time, despite the widespread recognition that landscapes and ecological processes are dynamic. In this paper, we discuss the emergence of dynamic connectivity and the importance of including dynamism in connectivity models and assessments. We outline dynamic processes for both structural and functional connectivity at multiple spatiotemporal scales and provide examples of modeling approaches at each of these scales. We highlight the unique challenges that accompany the adoption of dynamic connectivity for conservation management and planning in the context of traditional conservation prioritization approaches. With the increased availability of time series and species movement data, computational capacity, and an expanding number of empirical examples in the literature, incorporating dynamic processes into connectivity models is more feasible than ever. Here, we articulate how dynamism is an intrinsic component of connectivity and integral to the future of connectivity science.
... Change in habitat patch configuration due to seasonal flooding/drought (ST) [61,[141][142][143]. ...
Article
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The conservation field is experiencing a rapid increase in the amount, variety, and quality of spatial data that can help us understand species movement and landscape connectivity patterns. As interest grows in more dynamic representations of movement potential, modelers are often limited by the capacity of their analytic tools to handle these datasets. Technology developments in software and high-performance computing are rapidly emerging in many fields, but uptake within conservation may lag, as our tools or our choice of computing language can constrain our ability to keep pace. We recently updated Circuitscape, a widely used connectivity analysis tool developed by Brad McRae and Viral Shah, by implementing it in Julia, a high-performance computing language. In this initial re-code (Circuitscape 5.0) and later updates, we improved computational efficiency and parallelism, achieving major speed improvements, and enabling assessments across larger extents or with higher resolution data. Here, we reflect on the benefits to conservation of strengthening collaborations with computer scientists, and extract examples from a collection of 572 Circuitscape applications to illustrate how through a decade of repeated investment in the software, applications have been many, varied, and increasingly dynamic. Beyond empowering continued innovations in dynamic connectivity, we expect that faster run times will play an important role in facilitating co-production of connectivity assessments with stakeholders, increasing the likelihood that connectivity science will be incorporated in land use decisions.
... Future research should also keep in mind that the temporal scales of response are hierarchically nested (level of organisation), the temporal response at the individual-scale being shorter than that of community scale (Hylander & Ehrlén 2013). Existing works, even those based on multiple intra-and inter-annual time steps (Tulbure et al. 2014;Bishop-Taylor et al. 2018), investigated the temporal dynamics of connectivity based on the time steps taken independently, hence omitting the short-term (e.g. intra-annual) temporal dynamics of connectivity are indeed nested in long-term (e.g. ...
Thesis
Maintaining and restoring connectivity are proposed as a key landscape-level strategy to mitigate biodiversity loss in fragmented landscapes. However, there is a limited consensus about its efficiency for plant communities. To deepen and broaden our understanding about the role of connectivity, this PhD thesis aims to determine the effect of connectivity and its temporal dynamics on the taxonomic and the functional structure of plant communities. Carried out in the Zone Atelier Armorique, this study focuses on three dominant habitat types in agricultural landscapes (woodlands, grasslands and winter cereal crops). The connectivity provided by the different habitat types and its temporal dynamics (the magnitude and the variability of the temporal changes in connectivity) do not affect species diversity nor the total abundance of species. Rather, they shape species composition of plant communities, selecting species identity depending on their functional trait values related to seed production and transport, as well as seedling recruitment. Below one kilometre, and over decades, connectivity thus shapes the functional structure of plant communities, thereby affecting agroecosystem functioning. We reveal then new insights into the specific interaction between landscape and plant dispersal. Of note, the connectivity provided by other habitat types can impede or facilitate the dispersal of species of a given habitat type. We also showed that the magnitude and the variability of changes in connectivity over the last seven decades are still shaping current communities. Overall, our results may have far-reaching implications for plant biodiversity in agricultural landscapes, its conservation depending, in part, on the relevance and the effectiveness of the actions deployed under the Green and Blue Belt Network policy.
... By using graph theoretic metrics, several studies have evaluated the fragmentation of habitats, caused either by climate variability or by anthropogenic pressures, and their associated ecological implications (Bishop-Taylor et al., 2018;McIntyre et al., 2014;Søndergaard & Jeppesen, 2007;Wright, 2010). Combined with remote sensing, graph theoretic metrics have also facilitated the measurement of floodplain habitat networks over larger spatial extents (Bishop-Taylor et al., 2017;Ruiz et al., 2014;Wright, 2010). ...
Article
1. Floodplain wetlands provide an important subsidy for riverine food webs as sites of high algal production. However, this subsidy depends on the degree of landscape connectivity during flood pulses, which provides the opportunity for movement of higher order consumers between rivers and floodplains to access these productive habitats. Changes in floodplain inundation extent and dura-tion, due to variable wet season flows or water resource development (WRD), can impact landscape connectivity and ultimately the magnitude of the food web subsidy. 2. We explored landscape connectivity using graph theory and derived four new metrics to measure how different flow scenarios can affect connectivity and algal production. We considered a historic scenario with the present level of water resource development in our study area, the Mitchell River, and a WRD scenario with the inclusion of three new dams in the catchment. We generated 240 unique daily spatial graphs, using surface water inundation maps across 40- day flood events to compare a dry year (2006), an average flow year (2001) and a wet year (2009) with and without a WRD scenario. 3. Drier years and WRD scenario resulted in floodplain fragmentation, potentially constraining the movement of higher order consumers. Changes in connectivity due to WRD resulted in predicted reductions of up to 26% of algal production on the floodplain that was otherwise connected to the main river channels. 4. Synthesis and applications. The approach developed in this study provides new metrics to identify how changes in floodplain surface water extent due to water resource development and climatic variation may impact ecosystem function such as connectivity that facilitates access of higher order consumers to primary production in floodplain wetlands. With a direct link to river flow alteration, these metrics can inform catchment planning and management to ensure that the conservation of floodplain ecosystem functions is adequately considered in water resource management decisions.
... The basin has approximately 30,000 wetlands of significant biodiversity, with 16 protected under the international Ramsar convention and 200 wetlands of national significance (Australian Government Department of Environment and Energy, 2012). These wetlands play a significant role in landscape connectivity (Bishop-Taylor et al., 2018, 2015. The riparian vegetation of the MDB exhibits high variability and change in condition in response to water availability Shendryk et al., 2016) due primarily to intermittent river flows. ...
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Spatiotemporal quantification of surface water and flooding is essential given that floods are among the largest natural hazards. Effective disaster response management requires near real-time information on flood extent. Satellite remote sensing is the only way of monitoring these dynamics across vast areas and over time. Previous water and flood mapping efforts have relied on optical time series, despite cloud contamination. This reliance on optical data is due to the availability of systematically acquired and easily accessible optical data globally for over 40 years. Prior research used either MODIS or Landsat data, trading either high temporal density but lower spatial resolution or lower cadence but higher spatial resolution. Both MODIS and Landsat pose limitations as Landsat can miss ephemeral floods, whereas MODIS misses small floods and inaccurately delineates flood edges. Leveraging high temporal frequency of 3–4 days of the existing Landsat-8 (L8) and two Sentinel-2 (S2) satellites combined, in this research, we assessed whether the increased temporal frequency of the three sensors improves our ability to detect surface water and flooding extent compared to a single sensor (L8 alone). Our study area was Australia’s Murray-Darling Basin, one of the world’s largest dryland basins that experiences ephemeral floods. We applied machine learning to NASA’s Harmonized Landsat Sentinel-2 (HLS) Surface Reflectance Product, which combines L8 and S2 observations, to map surface water and flooding dynamics. Our overall accuracy, estimated from a stratified random sample, was 99%. Our user’s and producer’s accuracy for the water class was 80% (±3.6%, standard error) and 76% (±5.8%). We focused on 2019, one of the most recent years when all three HLS sensors operated at full capacity. Our results show that water area (permanent and flooding) identified with the HLS was greater than that identified by L8, and some short-lived flooding events were detected only by the HLS. Comparison with high resolution (3 m) PlanetScope data identified extensive mixed pixels at the 30 m HLS resolution, highlighting the need for improved spatial resolution in future work. The HLS has been able to detect floods in cases when one sensor (L8) alone was not, despite 2019 being one of the driest years in the area, with few flooding events. The dense optical time-series offered by the HLS data is thus critical for capturing temporally dynamic phenomena (i.e., ephemeral floods in drylands), highlighting the importance of harmonized data such as the HLS.
... Tulbure et al. (2016) was also the only published product with a statistical accuracy assessment that created confidence for its use in follow on applications (e.g. Bishop-Taylor et al., 2015, Bishop-Taylor et al., 2017a, 2017b, Bishop-Taylor et al., 2018Heimhuber et al., 2015Heimhuber et al., , 2017Shendryk et al., 2016b). The statistical accuracy assessment met two key criteria. ...
Article
Australia is a continent subject to high rainfall variability, which has major influences on runoff and vegetation dynamics. However, the resulting spatial-temporal pattern of flooding and its influence on riparian vegetation has not been quantified in a spatially explicit way. Here we focused on the floodplains of the entire Murray-Darling Basin (MDB), an area that covers over 1M km<sup>2</sup>, as a case study. The MDB is the country’s primary agricultural area with scarce water resources subject to competing demands and impacted by climate change and more recently by the Millennium Drought (1999–2009). Riparian vegetation in the MDB floodplain suffered extensive decline providing a dramatic degradation of riparian vegetation. We quantified the spatial-temporal impact of rainfall, temperature and flooding patters on vegetation dynamics at the subcontinental to local scales and across inter to intra-annual time scales based on three decades of Landsat (25k images), Bureau of Meteorology data and one decade of MODIS data. Vegetation response varied in space and time and with vegetation types, densities and location relative to areas frequently flooded. Vegetation degradation trends were observed over riparian forests and woodlands in areas where flooding regimes have changed to less frequent and smaller inundation extents. Conversely, herbaceous vegetation phenology followed primarily a ‘boom’ and ‘bust’ cycle, related to inter-annual rainfall variability. Spatial patters of vegetation degradation changed along the N-S rainfall gradient but flooding regimes and vegetation degradation patterns also varied at finer scale, highlighting the importance of a spatially explicit, internally consistent analysis and setting the stage for investigating further cross-scale relationships. Results are of interest for land and water management decisions. The approach developed here can be applied to other areas globally such as the Nile river basin and Okavango River delta in Africa or the Mekong River Basin in Southeast Asia.
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Unprecedented amounts of analysis‐ready Earth Observation (EO) data, combined with increasing computational power and new algorithms, offer novel opportunities for analysing ecosystem dynamics across large geographic extents, and to support conservation planning and action. Much research effort has gone into developing global EO‐based land‐cover and land‐use datasets, including tree cover, crop types, and surface water dynamics. Yet there are inherent trade‐offs between regional and global EO products pertaining to class legends, availability of training/validation data, and accuracy. Acknowledging and understanding these trade‐offs is paramount for both developing EO products and for answering science questions relevant for ecology or conservation studies based on these data. Here we provide context on the development of global EO‐based land‐cover and land‐use datasets, and outline advantages and disadvantages of both regional and global datasets. We argue that both types of EO‐derived land‐cover datasets can be preferable, with regional data providing the context‐specificity that is often required for policy making and implementation (e.g., land‐use and management, conservation planning, payment schemes for ecosystem services), making use of regional knowledge, particularly important when moving from land cover to actors. Ensuring that global and regional land‐cover and land‐use products derived based on EO data are compatible and nested, both in terms of class legends and accuracy assessment, should be a key consideration when developing such data. Open access high‐quality training and validation data derived as part of such efforts are of utmost importance. Likewise, global efforts to generate sets of essential variables for climate change, biodiversity, or eventually land use, which often require land‐cover maps as inputs, should consider regionalized, hierarchical approaches to not sacrifice regional context. Global change impacts manifest in regions, and so must the policy and planning responses to these challenges. EO data should embrace that regions matter, perhaps more than ever, in an age of global data availability and processing.
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Thesis
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Landscape connectivity – the capacity of organisms to move or disperse through their environment – is increasingly threatened by changing land use and increasing hydroclimatic variability driven by climate change. These impacts are likely to be particularly severe within dynamic dryland environments where many organisms rely on unpredictable flooding events for dispersal between fragmented habitats. In this thesis, I use graph theory network analysis to explore how surface water dynamics (i.e. flooding and drought) affect landscape connectivity through time and across large spatial extents. I focus on Australia’s Murray-Darling Basin (MDB), a globally significant and ecologically threatened river basin subject to extreme spatiotemporal habitat variability. In Chapter 2, I use static habitat data and modelled flooding scenarios for the entire MDB to assess how flooding affects landscape connectivity for two amphibian species. I identify ‘hub’ and ‘stepping stone’ habitats important for local and network-scale connectivity, and reveal that changes in movement conditions associated with flooding can greatly impact connectivity through entire amphibian habitat networks. In Chapter 3, I expand this approach by identifying high-priority targets for future conservation management using an unprecedented 25-year remotely sensed surface water time series. Although important habitats for connectivity exhibited extreme variability over time, I show that more of these habitats were located within protected areas than expected by chance. In Chapter 4, I use advanced habitat availability metrics to assess how periods of extreme hydroclimatic conditions (e.g. the 1999–2009 Millennium Drought and the 2010–2011 La Niña floods) affect connectivity at a sub-continental scale, finding that surface water network structure in the MDB provides resistance to drought. Finally, in Chapter 5 I compare habitat prioritisations based the static approach of Chapter 2 against the dynamic approach of Chapters 3 and 4, revealing that accounting for spatiotemporal habitat dynamics can result in large differences in connectivity estimates that vary by study region, spatial scale and hydroclimatic conditions. The computationally efficient graph theory methodology presented in this thesis is directly applicable to other spatiotemporally dynamic regions globally, enabling landscape connectivity to be assessed consistently across long temporal extents and at regional or subcontinental scales.
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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.
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Vertical hydrological connectivity generally related heterogeneity of soil water and nutrient and the sustainability of vegetation restoration. Both the static and dynamic connectivity of soil have been studied for years, the relationship between them remains unclear, especially for coastal wetlands that greatly influenced by hydrological processes. In this study, static connectivity was defined as water flow paths and quantified by dye tracer experiment, whereas dynamic connectivity refers to the process of water movement and solute transport and described by solute penetration. Relationships between them were analyzed through the nonlinear fitting. Results showed that: 1) static connectivity was construed mainly by cracks in the upper soil layer and by root channels in the deeper soil, and these macropores led to heterogeneous distribution of water and solutes; 2) dynamic connectivity differed between soil columns, and non-equilibrium flow characterized by high infiltration rate and concentration in the initial phase was observed in soil with cracks and root channels; and 3) the static connectivity had significant effects on water movement while had no effects on solute transport. Infiltration rate decreased as dye coverage, fractal dimension, and the number of water pathway logistically increases. These findings highlight the importance of cracks and root channels on vertical hydrological connectivity in soil of S. salsa community, and suggest linking the static structure of water flow paths with soil water dynamic and heterogeneity to understand soil functions.
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In order to investigate the dynamic evolution of the sandy land-lake-vegetation landscape in Songnen Sandy Land (SSL) and its response to climate change and human activities, the distribution pattern, evolution, and driving mechanisms of the landscape were analyzed based on Landsat satellite images and meteorological and socio-economic data during 1980–2020. The results indicate that the area of sandy land exhibited an upward fluctuation during the last 40 yr, with a net increase of 251.75 km2 at an increment rate of 3.80%/10 yr. The lake area also exhibited an upward fluctuation, with a net increase of 1200.95 km2 at an increment rate of 20.42%/10 yr. Vegetation coverage decreased by 2633.30 km2, with areas of low vegetation coverage exhibiting a trend of initial decline and subsequent increase, areas of medium vegetation coverage showed an upward fluctuation, and areas of high vegetation coverage showed a trend of initial increase and subsequent decrease, with overall changes of −0.67%/yr, 1.12%/yr, and 0.17%/yr, respectively. The relationships between sandy land, lakes, and vegetation coverage were significant, with areas of sandy land and low vegetation coverage showing the strongest correlation. The dynamic evolution of landscape is controlled by regional climatic and socio-economic factors, with socio-economic factors as the first principal component contributing up to 59.64%.
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Landscape connectivity is important for the long-term persistence of species inhabiting dryland freshwater ecosystems, with spatiotemporal surface-water dynamics (e.g., flooding) maintaining connectivity by both creating temporary habitats and providing transient opportunities for dispersal. Improving our understanding of how landscape connectivity varies with respect to surface-water dynamics and land use is an important step to maintaining biodiversity in dynamic dryland environments. Using a newly available validated Landsat TM and ETM+ surface-water time series, we modelled landscape connectivity between dynamic surface-water habitats within Australia's 1 million km2 semi-arid Murray Darling Basin across a 25-year period (1987 to 2011). We identified key habitats that serve as well-connected 'hubs', or 'stepping-stones' that allow long-distance movements through surface-water habitat networks. We compared distributions of these habitats for short- and long-distance dispersal species during dry, average and wet seasons, and across land-use types. The distribution of stepping-stones and hubs varied both spatially and temporally, with temporal changes driven by drought and flooding dynamics. Conservation areas and natural environments contained higher than expected proportions of both stepping-stones and hubs throughout the time series; however, highly modified agricultural landscapes increased in importance during wet seasons. Irrigated landscapes contained particularly high proportions of well-connected hubs for long-distance dispersers, but remained relatively disconnected for less vagile organisms. The habitats identified by our study may serve as ideal high-priority targets for land-use specific management aimed at maintaining or improving dispersal between surface-water habitats, potentially providing benefits to biodiversity beyond the immediate site scale. Our results also highlight the importance of accounting for the influence of spatial and temporal surface-water dynamics when studying landscape connectivity within highly variable dryland environments. This article is protected by copyright. All rights reserved.
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Periodically inundated floodplain areas are hot spots of biodiversity and provide a broad range of ecosystem services but have suffered alarming declines in recent history. Despite their importance, their long-term surface water (SW) dynamics and hydroclimatic drivers remain poorly quantified on continental scales. In this study, we used a 26 year time series of Landsat-derived SW maps in combination with river flow data from 68 gauges and spatial time series of rainfall, evapotranspiration and soil moisture to statistically model SW dynamics as a function of key drivers across Australia's Murray-Darling Basin (∼1 million km²). We fitted generalized additive models for 18,521 individual modeling units made up of 10 × 10 km grid cells, each split into floodplain, floodplain-lake, and nonfloodplain area. Average goodness of fit of models was high across floodplains and floodplain-lakes (r²>0.65), which were primarily driven by river flow, and was lower for nonfloodplain areas (r²>0.24), which were primarily driven by rainfall. Local climate conditions were more relevant for SW dynamics in the northern compared to the southern basin and had the highest influence in the least regulated and most extended floodplains. We further applied the models of two contrasting floodplain areas to predict SW extents of cloud-affected time steps in the Landsat series during the large 2010 floods with high validated accuracy (r²>0.97). Our framework is applicable to other complex river basins across the world and enables a more detailed quantification of large floods and drivers of SW dynamics compared to existing methods.
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Connectivity is essential to organisms for dispersal, mate finding, and resource access. Management conflicts may arise if the attempts to maintain connectivity in the face of habitat loss result in opening up dispersal corridors to invasive species and disease vectors to already-threatened native species. Using the mule deer (Odocoileus hemionus) and American bullfrog (Lithobates catesbeianus) as examples in a network of surface waters in the Sonoran Desert, we illustrate and propose a resolution to these conflicts. We used structural and functional metrics from graph and circuit theory to quantify landscape connectivity within a spatially nested framework under current and future climate-based scenarios at regional and local scales to project structural and functional climate impacts for both species. Results indicated that climate impacts may reduce both structural and functional potential connectivity for each species. Mule deer, however, will be impacted to a lesser degree, and the proposed management mitigation of exclusion areas will have a potential lesser impact on this species. From our results, we propose a method to create exclusion areas and site new waters to help mitigate increasing spread of invasive species like the bullfrog while maintaining resource availability and local connectivity for economically important species like the mule deer. The isolation of local clusters from invasive species may be a successful and useful way to reduce management conflicts in the Sonoran Desert isolated waters network and beyond.
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Context Submersed aquatic vegetation (SAV) performs water quality enhancing functions that are critical to the overall health of estuaries such as the Chesapeake Bay. However, eutrophication and sedimentation have decimated the Bay’s SAV population to a fraction of its historical coverage. Understanding the spatial distribution of and connectedness among patches is important for assessing the dynamics and health of the remaining SAV population. Objectives We seek to explore the distribution of SAV patches and patterns of potential connectivity in the Chesapeake Bay through time. Methods We assess critical distances, from complete patch isolation to connection of all patches, in a merged composite coverage map that represents the sum of all probable Vallisneria americana containing patches between 1984 and 2010 and in coverage maps for individual years within that timeframe for which complete survey data are available. Results We have three key findings: First, the amount of SAV coverage in any given year is much smaller than the total recently occupied acreage. Second, the vast majority of patches of SAV that are within the tolerances of V. americana are ephemeral, being observed in only 1 or 2 years out of 26 years. Third, this high patch turnover results in highly variable connectivity from year to year, dependent on dispersal distance and patch arrangement. Conclusions Most of the connectivity thresholds are beyond reasonable dispersal distances for V. americana. If the high turnover in habitat occupancy is due to marginal water quality, relatively small improvements could greatly increase V. americana growth and persistence.
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The usage of time series of Earth observation (EO) data for analyzing and modeling surface water extent (SWE) dynamics across broad geographic regions provides important information for sustainable management and restoration of terrestrial surface water resources, which suffered alarming declines and deterioration globally. The main objective of this research was to model SWE dynamics from a unique, statistically validated Landsat-based time series (1986–2011) continuously through cycles of flooding and drying across a large and heterogeneous river basin, the Murray–Darling Basin (MDB) in Australia. We used dynamic linear regression to model remotely sensed SWE as a function of river flow and spatially explicit time series of soil moisture (SM), evapotranspiration (ET), and rainfall (P). To enable a consistent modeling approach across space, we modeled SWE dynamics separately for hydrologically distinct floodplain, floodplain-lake, and non-floodplain areas within eco-hydrological zones and 10km × 10km grid cells. We applied this spatial modeling framework to three sub-regions of the MDB, for which we quantified independently validated lag times between river gauges and each individual grid cell and identified the local combinations of variables that drive SWE dynamics. Based on these automatically quantified flow lag times and variable combinations, SWE dynamics on 233 (64 %) out of 363 floodplain grid cells were modeled with a coefficient of determination (r2) greater than 0.6. The contribution of P, ET, and SM to the predictive performance of models differed among the three sub-regions, with the highest contributions in the least regulated and most arid sub-region. The spatial modeling framework presented here is suitable for modeling SWE dynamics on finer spatial entities compared to most existing studies and applicable to other large and heterogeneous river basins across the world.
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The usage of time series of earth observation (EO) data for analyzing and modeling surface water dynamics (SWD) across broad geographic regions provides important information for sustainable management and restoration of terrestrial surface water resources, which suffered alarming declines and deterioration globally. The main objective of this research was to model SWD from a unique validated Landsat-based time series (1986–2011) continuously through cycles of flooding and drying across a large and heterogeneous river basin, the Murray–Darling Basin (MDB) in Australia. We used dynamic linear regression to model remotely sensed SWD as a function of river flow and spatially explicit time series of soil moisture (SM), evapotranspiration (ET) and rainfall (P). To enable a consistent modeling approach across space, we modeled SWD separately for hydrologically distinct floodplain, floodplain-lake and non-floodplain areas within eco-hydrological zones and 10 km × 10 km grid cells. We applied this spatial modeling framework (SMF) to three sub-regions of the MDB, for which we quantified independently validated lag times between river gauges and each individual grid cell and identified the local combinations of variables that drive SWD. Based on these automatically quantified flow lag times and variable combinations, SWD on 233 (64 %) out of 363 floodplain grid cells were modeled with r2 ≥ 0.6. The contribution of P, ET and SM to the models' predictive performance differed among the three sub-regions, with the highest contributions in the least regulated and most arid sub-region. The SMF presented here is suitable for modeling SWD on finer spatial entities compared to most existing studies and applicable to other large and heterogeneous river basins across the world.
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Heterogeneous landscapes and fluctuating environmental conditions can affect species dispersal, population genetics, and genetic structure, yet understanding how biotic and abiotic factors affect population dynamics in a fluctuating environment is critical for species management. We evaluated how spatio-temporal habitat connectivity influences dispersal and genetic structure in a population of boreal chorus frogs (Pseudacris maculata) using a landscape genetics approach. We developed gravity models to assess the contribution of various factors to the observed genetic distance as a measure of functional connectivity. We selected (a) wetland (within-site) and (b) landscape matrix (between-site) characteristics; and (c) wetland connectivity metrics using a unique methodology. Specifically, we developed three networks that quantify wetland connectivity based on: (i) P. maculata dispersal ability, (ii) temporal variation in wetland quality, and (iii) contribution of wetland stepping-stones to frog dispersal. We examined 18 wetlands in Colorado, and quantified 12 microsatellite loci from 322 individual frogs. We found that genetic connectivity was related to topographic complexity, within- and between-wetland differences in moisture, and wetland functional connectivity as contributed by stepping-stone wetlands. Our results highlight the role that dynamic environmental factors have on dispersal-limited species and illustrate how complex asynchronous interactions contribute to the structure of spatially-explicit metapopulations.
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Amphibian species persisting in isolated streams and wetlands in desert environments can be susceptible to low connectivity, genetic isolation, and climate changes. We evaluated the past (1900–1930), recent (1981–2010), and future (2071–2100) climate suitability of the arid Great Basin (USA) for the Columbia spotted frog (Rana luteiventris) and assessed whether changes in surface water may affect connectivity for remaining populations. We developed a predictive model of current climate suitability and used it to predict the historic and future distribution of suitable climates. We then modeled changes in surface water availability at each time period. Finally, we quantified connectivity among existing populations on the basis of hydrology and correlated it with interpopulation genetic distance. We found that the area of the Great Basin with suitable climate conditions has declined by approximately 49% over the last century and will likely continue to decline under future climate scenarios. Climate conditions at currently occupied locations have been relatively stable over the last century, which may explain persistence at these sites. However, future climates at these currently occupied locations are predicted to become warmer throughout the year and drier during the frog's activity period (May – September). Fall and winter precipitation may increase, but as rain instead of snow. Earlier runoff and lower summer base flows may reduce connectivity between neighboring populations, which is already limited. Many of these changes could have negative effects on remaining populations over the next 50–80 years, but milder winters, longer growing seasons, and wetter falls might positively affect survival and dispersal. Collectively, however, seasonal shifts in temperature, precipitation, and stream flow patterns could reduce habitat suitability and connectivity for frogs and possibly other aquatic species inhabiting streams in this arid region.
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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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The primary focus of studies examining metapopulation processes in dynamic or disturbance-dependent landscapes has been related to spatiotemporal changes in the habitat patches themselves. However, like the habitat patches, opportunities for movement between patches can also exist intermittently in dynamic landscapes, creating transient connectivity windows - which we define as a period of time during which matrix conditions increase the probability of one or more individuals moving successfully between habitat patches. Far less is known about the implications of dynamic changes in connectivity per se, and, to our knowledge, there are no connectivity metrics or metapopulation models that explicitly consider intermittent changes to connectivity between habitat patches. Consequently, in this paper, we examined the peer-reviewed, published literature up to November 2013 to better understand the consequences of variability in connectivity and to highlight knowledge gaps on this topic. First, we describe how connectivity per se can vary along a temporal gradient, offering examples of ecological systems that fall along this gradient. Second, we examine how temporal variability in connectivity is important for metapopulation dynamics, particularly given likely alterations to disturbance regimes as a result of global change. We conclude our review by briefly discussing key avenues for future connectivity-related research, all of which hinge on the need to perceive connectivity as a transient feature.
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The concept of habitat networks represents an important tool for landscape conservation and management at regional scales. Previous studies simulated degradation of temporally fixed networks but few quantified the change in network connectivity from disintegration of key features that undergo naturally occurring spatiotemporal dynamics. This is particularly of concern for aquatic systems, which typically show high natural spatiotemporal variability. Here we focused on the Swan Coastal Plain, a bioregion that encompasses a global biodiversity hotspot in Australia with over 1500 water bodies of high biodiversity. Using graph theory, we conducted a temporal analysis of water body connectivity over 13 years of variable climate. We derived large networks of surface water bodies using Landsat data (1999–2011). We generated an ensemble of 278 potential networks at three dispersal distances approximating the maximum dispersal distance of different water dependent organisms. We assessed network connectivity through several network topology metrics and quantified the resilience of the network topology during wet and dry phases. We identified 'stepping stone' water bodies across time and compared our networks with theoretical network models with known properties. Results showed a highly dynamic seasonal pattern of variability in network topology metrics. A decline in connectivity over the 13 years was noted with potential negative consequences for species with limited dispersal capacity. The networks described here resemble theoretical scale-free models, also known as 'rich get richer' algorithm. The 'stepping stone' water bodies are located in the area around the Peel-Harvey Estuary, a Ramsar listed site, and some are located in a national park. Our results describe a powerful approach that can be implemented when assessing the connectivity for a particular organism with known dispersal distance. The approach of identifying the surface water bodies that act as 'stepping stone' over time may help prioritize surface water bodies that are essential for maintaining regional scale connectivity.
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Landscape connectivity is considered a priority for ecosystem conservation because it may mitigate the synergistic effects of climate change and habitat loss. Climate change predictions suggest changes in precipitation regimes, which will affect the availability of water resources, with potential consequences for landscape connectivity. The Greater Calakmul Region of the Yucatan Peninsula (Mexico) has experienced a 16% decrease in precipitation over the last 50 years, which we hypothesise has affected water resource connectivity. We used a network model of connectivity, for three large endangered species (Baird's tapir, white-lipped peccary and jaguar), to assess the effect of drought on waterhole availability and connectivity in a forested landscape inside and adjacent to the Calakmul Biosphere Reserve. We used reported travel distances and home ranges for our species to establish movement distances in our model. Specifically, we compared the effects of 10 drought scenarios on the number of waterholes (nodes) and the subsequent changes in network structure and node importance. Our analysis revealed that drought dramatically influenced spatial structure and potential connectivity of the network. Our results show that waterhole connectivity and suitable habitat (area surrounding waterholes) is lost faster inside than outside the reserve for all three study species, an outcome that may drive them outside the reserve boundaries. These results emphasize the need to assess how the variability in the availability of seasonal water resource may affect the viability of animal populations under current climate change inside and outside protected areas.
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The Southern Bell Frog Litoria raniformis has declined dramatically in distribution and abundance in New South Wales, where it is presently considered 'endangered'. However, cultivation of rice through irrigation has created suitable habitat for this species, thus enabling it to colonise some, but not all, rice-growing areas. One such area, the Coleambally Irrigation Area, presently contains a large proportion of the remaining known locations of the species in New South Wales. Within this area this frog is widespread and locally abundant, and it uses flooded rice fields for breeding, though there are other kinds of water bodies that may also be used for breeding. The seasonal flooding regime for the rice mirrors the breeding requirements for this frog species. However, through reduction in flooding of natural habitat areas, diversion of water to rice and other irrigation-based agriculture has probably also contributed to the decline of this frog species and reversal of this through 'environmental flows' along rivers could be to its benefit. Its conservation in New South Wales is therefore likely to depend on the nature and extent of rice-growing in this state.
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We quantified fluctuations in the status of individual patches (wetlands) in supporting connectivity within a network of playas, temporary wetlands of the southern Great Plains of North America that are loci for regional biodiversity. We used remote sensing imagery to delineate the location of surface waters in >8,000 playa basins in a ~31,900 km2 portion of Texas and quantified connectivity in this region from 2007 to 2011. We ranked playas as stepping-stones, cutpoints, and hubs at different levels of environmental conditions (regionally wet, dry, and average periods of precipitation) for dispersal distances ranging from 0.5 to 34 km, representing a range of species’ vagilities, to provide baseline dynamics within an area likely to experience disrupted connectivity due to anthropogenic activities. An individual playa’s status as a stepping-stone, cutpoint, or hub was highly variable over time (only a single playa was a top 20 stepping-stone, cutpoint, or hub in >50 % of all of the dates examined). Coalescence of the inundated playa network usually occurred at ≥10 km dispersal distance and depended on wetland density, indicating that critical thresholds in connectivity arose from synergistic effects of dispersal ability (spatial scale) and wet playa occurrence (a function of precipitation). Organisms with dispersal capabilities limited to <10 km routinely experienced effective isolation during our study. Connectivity is thus a dynamic emergent landscape property, so management to maintain connectivity for wildlife within ephemeral habitats like inundated playas will need to move beyond a patch-based focus to a network focus by including connectivity as a dynamic landscape property.
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AimWe assessed the resistance and resilience of anuran amphibians to an abrupt change in weather conditions in 2010-12 (the Big Wet') following the most pronounced drought in eastern Australia's records (1997-2010, the Big Dry'). LocationFive pairs of landscapes (each of 19.6 km(2)) spread across 30,000 km(2) in temperate, inland Australia. One in each pair was eucalypt woodland while the other was cleared agricultural land; there were eight representative waterbodies in each landscape. Methods We collected data on anuran abundances, species richness and breeding by using aural surveys and visual searches. We surveyed six times during the austral winter-springs of 2006 and 2007 (the Big Dry) and six times in the corresponding seasons of 2011 and 2012 (the Big Wet); our results refer only to species breeding in the winter-spring season. ResultsMean species richness, total numbers of calling males and numbers of the five most common species of anurans increased in the Big Wet compared with the Big Dry, but the least common species did not. Proportions of waterbodies with eggs or tadpoles increased in the Big Wet, but the occurrence of eggs and tadpoles was still low (evidence of presence in <50% of waterbodies). The most common species had relatively high resistance to the first 5 years of the Big Dry, but all declined sharply after a decade of drought. Four of the common species showed some resilience, but reporting rates fell much below the peak values prior to the Big Dry. There were virtually no records for seven other species that had been recorded previously in the region. Main conclusionsThe pressure of drying, warming climates, even when broken by shorter wet periods, seems to be sufficient to induce regional-scale declines even among species that, from global analyses of risk factors, might be expected to be relatively immune from such effects.
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Understanding the impact of natural and anthropogenic landscape features on population connectivity is a major goal in evolutionary ecology and conservation. Discovery of dispersal barriers is important for predicting population responses to landscape and environmental changes, particularly for populations at geographic range margins. We used a landscape genetics approach to quantify the effects of landscape features on gene flow and connectivity of boreal toad (Bufo boreas) populations from two distinct landscapes in south-east Alaska (Admiralty Island, ANM, and the Chilkat River Valley, CRV). We used two common methodologies for calculating resistance distances in landscape genetics studies (resistance based on least-cost paths and circuit theory). We found a strong effect of saltwater on genetic distance of CRV populations, but no landscape effects were found for the ANM populations. Our discordant results show the importance of examining multiple landscapes that differ in the variability of their features, to maximize detectability of underlying processes and allow results to be broadly applicable across regions. Saltwater serves as a physiological barrier to boreal toad gene flow and affects populations on a small geographic scale, yet there appear to be few other barriers to toad dispersal in this intact northern region.
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Inter-wetland connectivity, defined here as the movement of biota among discrete water bodies, can have important population- and community-level consequences in aquatic systems. We examined inter-wetland connectivity in a southeastern Australian national park by intensively monitoring the movements of freshwater turtles (Chelodina longicollis) via capture-mark-recapture over a three-year period, and more sporadically for 25 years. A high percentage (33%) of turtles moved between wetlands, suggesting that single wetlands should not represent the minimum habitat unit harboring a C. longicollis population. Distance was the only structural landscape metric correlated with inter-patch transition probability, with probability declining as inter-wetland distance increased. Movements also appear to be strongly influenced by shifting resource quality gradients between temporary wetlands and permanent lakes according to drought and flood cycles, a pattern more consistent with migration between critical resource patches than occasional interpopulational dispersal. Rare dispersal events of up to 5.2 km were known to occur. Captures at a terrestrial drift fence suggest that small and immature turtles moved between wetlands more frequently than our aquatic sampling indicated. We caution that measures of actual (or functional) connectivity can be biased by sampling methods and the temporal scale of sampling and must also be interpreted in the context of factors that motivate animal movements. This requires some understanding of spatial and temporal variation in intra-patch processes (e.g., quality and extent) and the expected movement responses of animals (e.g., habitat selection) over extended time frames, information that can potentially yield more important insight on connectivity than measures of landscape structural features alone.
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Connectivity among populations and habitats is important for a wide range of ecological processes. Understanding, preserving, and restoring connectivity in complex landscapes requires connectivity models and metrics that are reliable, efficient, and process based. We introduce a new class of ecological connectivity models based in electrical circuit theory. Although they have been applied in other disciplines, circuit-theoretic connectivity models are new to ecology. They offer distinct advantages over common analytic connectivity models, including a theoretical basis in random walk theory and an ability to evaluate contributions of multiple dispersal pathways. Resistance, current, and voltage calculated across graphs or raster grids can be related to ecological processes (such as individual movement and gene flow) that occur across large population networks or landscapes. Efficient algorithms can quickly solve networks with millions of nodes, or landscapes with millions of raster cells. Here we review basic circuit theory, discuss relationships between circuit and random walk theories, and describe applications in ecology, evolution, and conservation. We provide examples of how circuit models can be used to predict movement patterns and fates of random walkers in complex landscapes and to identify important habitat patches and movement corridors for conservation planning.
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In the past few years, the framework of complex networks has provided new insight into the organization and function of biological systems. However, in spite of its potential, spatial ecology has not yet fully incorporated tools and concepts from network theory. In the present study, we identify a large spatial network of temporary ponds, which are used as breeding sites by several amphibian species. We investigate how the structural properties of the spatial network change as a function of the amphibian dispersal distance and the hydric conditions. Our measures of network topology suggest that the observed spatial structure of ponds is robust to drought (compared with similar random structures), allowing the movement of amphibians to and between flooded ponds, and hence, increasing the probability of reproduction even in dry seasons.
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Ecologists are familiar with two data structures commonly used to represent landscapes. Vector-based maps delineate land cover types as polygons, while raster lattices represent the landscape as a grid. Here we adopt a third lattice data structure, the graph. A graph represents a landscape as a set of nodes (e.g., habitat patches) connected to some degree by edges that join pairs of nodes functionally (e.g., via dispersal). Graph theory is well developed in other fields, including geography (transportation networks, routing applications, siting problems) and computer science (circuitry and network optimization). We present an overview of basic elements of graph theory as it might be applied to issues of connectivity in heterogeneous landscapes, focusing especially on applications of metapopulation theory in conservation biology. We develop a general set of analyses using a hypothetical landscape mosaic of habitat patches in a nonhabitat matrix. Our results suggest that a simple graph construct, the minimum spanning tree, can serve as a powerful guide to decisions about the relative importance of individual patches to overall landscape connectivity. We then apply this approach to an actual conservation scenario involving the threatened Mexican Spotted Owl (Strix occidentalis lucida). Simulations with an incidence-function metapopulation model suggest that population persistence can be maintained despite substantial losses of habitat area, so long as the minimum spanning tree is protected. We believe that graph theory has considerable promise for applications concerned with connectivity and ecological flows in general. Because the theory is already well developed in other disciplines, it might be brought to bear immediately on pressing ecological applications in conservation biology and landscape ecology.
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Landscape genetics has seen tremendous advances since its introduction, but parameterization and optimization of resistance surfaces still poses significant challenges. Despite increased availability and resolution of spatial data, few studies have integrated empirical data to directly represent ecological processes as genetic resistance surfaces. In our study, we determine the landscape and ecological factors affecting gene flow in the western slimy salamander (Plethodon albagula). We used field data to derive resistance surfaces representing salamander abundance and rate of water loss through combinations of canopy cover, topographic wetness, topographic position, solar exposure, and distance from ravine. These ecologically-explicit composite surfaces directly represent an ecological process or physiological limitation of our organism. Using generalized linear mixed effects models, we optimized resistance using a non-linear optimization algorithm to minimize model AIC. We found clear support for the resistance surface representing the rate of water loss experienced by adult salamanders in the summer. Resistance was lowest at intermediate levels of water loss and higher when the rate of water loss was predicted to be low or high. This pattern may arise from the compensatory movement behavior of salamanders through suboptimal habitat, but also reflects the physiological limitations of salamanders and their sensitivity to extreme environmental conditions. Our study demonstrates that composite representations of ecologically-explicit processes can provide novel insight and can better explain genetic differentiation than ecologically-implicit landscape resistance surfaces. Additionally, our study underscores the fact that spatial estimates of habitat suitability or abundance may not serve as adequate proxies for describing gene flow, as predicted abundance was a poor predictor of genetic differentiation.This article is protected by copyright. All rights reserved.
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The manner in which patches are delineated in spatially realistic metapopulation models will influence the size, connectivity, and extinction and recolonization dynamics of those patches. Most commonly used patch-definition methods focus on identifying discrete, contiguous patches of habitat from a single temporal observation of species occurrence or from a model of habitat suitability. However, these approaches are not suitable for many metapopulation systems where entire patches may not be fully colonized at a given time. For these metapopulation systems, a single large patch of habitat may actually support multiple, interacting subpopulations. The interactions among these subpopulations will be ignored if the patch is treated as a single unit, a situation we term the "mega-patch problem." Mega-patches are characterized by variable intra-patch synchrony, artificially low inter-patch connectivity, and low extinction rates. One way to detect this problem is by using time series data to calculate demographic synchrony within mega-patches. We present a framework for identifying subpopulations in mega-patches using a combination of spatial autocorrelation and graph theory analyses. We apply our approach to southern California giant kelp (Macrocystis pyrifera) forests using a new, long-term (27 years), satellite-based data set of giant kelp canopy biomass. We define metapopulation patches using our method as well as several other commonly used patch delineation methodologies and examine the colonization and extinction dynamics of the metapopulation under each approach. We find that the relationships between patch characteristics such as area and connectivity and the demographic processes of colonizations and extinctions vary among the different patch-definition methods. Our spatial-analysis/graph-theoretic framework produces results that match theoretical expectations better than the other methods. This approach can be used to identify subpopulations in metapopulations where the distributions of organisms do not always reflect the distribution of suitable habitat.
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River flows in the Murray–Darling Basin, as in many regions in the world, are vulnerable to climate change, anticipated to exacerbate current, substantial losses of freshwater biodiversity. Additional declines in water quantity and quality will have an adverse impact on existing freshwater ecosystems. We critique current river-management programs, including the proposed 2011 Basin Plan for Australia’s Murray–Darling Basin, focusing primarily on implementing environmental flows. River management programs generally ignore other important conservation and adaptation measures, such as strategically located freshwater-protected areas. Whereas most river-basin restoration techniques help build resilience of freshwater ecosystems to climate change impacts, different measures to enhance resilience and reoperate water infrastructure are also required, depending on the degree of disturbance of particular rivers on a spectrum from free-flowing to highly regulated. A crucial step is the conservation of free-flowing river ecosystems where maintenance of ecological processes enhances their capacity to resist climate change impacts, and where adaptation may be maximised. Systematic alteration of the operation of existing water infrastructure may also counter major climate impacts on regulated rivers.
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1. Climate and land-use changes will require species to move large distances following shifts in their suitable habitats, which will frequently involve traversing intensively human-modified landscapes. Practitioners will therefore need to evaluate and act to enhance the degree to which habitat patches scattered throughout the landscape may function as stepping stones facilitating dispersal among otherwise isolated habitat areas. 2. We formulate a new generalized network model of habitat connectivity that accounts for the number of dispersing individuals and for long-distance dispersal processes across generations. By doing so, we bridge the gap between complex dynamic population models, which are generally too data demanding and hence difficult to apply in practical wide-scale decision-making, and simpler static connectivity models that only consider the amount of habitat that can be reached by a single average disperser during its life span. 3. We find that the loss of intermediate and sufficiently large stepping-stone habitat patches can cause a sharp decline in the distance that can be traversed by species (critical spatial thresholds) that cannot be effectively compensated by other factors previously regarded as crucial for long-distance dispersal (fat-tailed dispersal kernels, source population size). 4. We corroborate our findings by showing that our model largely outperforms previous connectivity models in explaining the large-scale range expansion of a forest bird species, the Black Woodpecker Dryocopus martius, over a 20-year period. 5. The capacity of species to exploit the opportunities created by networks of stepping-stone patches largely depends on species-specific life-history traits, suggesting that species assemblages traversing fragmented landscapes may be exposed to a spatial filtering process driving long-term changes in community composition. 6. Synthesis and applications. Previous static connectivity models seriously underestimate the importance of stepping-stone patches in sustaining rare but crucial dispersal events. We provide a conceptually broader model that shows that stepping stones (i) must be of sufficient size to be of conservation value, (ii) are particularly crucial for the spread of species (either native or invasive) or genotypes over long distances and (iii) can effectively reduce the isolation of the largest habitat blocks in reserves, therefore largely contributing to species persistence across wide spatial and temporal scales.
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Connectivity is currently a central issue in landscape management and planning for the conservation of wildlife species occupying scarce habitat patches. In recent years, this issue has increasingly been addressed using methodologies based on spatial network analysis. Here, we propose a hybrid approach based on network analysis tools and empirical habitat suitability models to integrate connectivity on decision-making. The study is focused on a pond system used by the European pond turtle, Emys orbicularis, in a coastal area in southwestern Iberia. The main objective of the study was to illustrate how the output of graph models may be useful to guide habitat management and planning. We assessed ponds according to three complementary structural and functional properties derived from a graph model: (1) pond importance as measured by the sensitivity of the overall connectivity to each pond loss, (2) pond coreness, used to identify the most cohesive pond subsystems and (3) pond betweenness, which measure the importance of ponds as stepping stones. The graph model took into account a resistance-to-movement surface, the maximum traveled distance and a habitat suitability model based on field sampling. Pond importance and coreness were shown to be positively related to occupancy, especially by turtle's youngest age classes, suggesting an important contribution of connectivity attributes for turtle populations. We discuss the ways these pond connectivity-related attributes may be helpful to assist and optimize management efforts for the conservation of the European pond turtle in the study area.
Article
Here we apply theoretical frameworks to understanding the influence of flooding on the ecology of lowland river-floodplain systems in the Murray-Darling Basin. Taking a landscape perspective reveals the vast spatial and temporal variability in flooding. We use iconic taxa of the Murray-Darling Basin-river red gum, waterbirds, and fish-to illustrate three strategies for exploiting variable flooding for breeding: (i) reproduce whenever floods occur, regardless of flood characteristics; (ii) reproduce only during floods that provide suitable conditions; and (iii) ignore floods and associated resources because these are too unreliable. Current policy for environmental watering is caught between maintaining individual, ecologically significant sites and a more integrated approach to the management of the riverine system in toto. Landscape ecology has a central role to play in informing the management strategy for the Murray-Darling system.
Article
Context. While much attention has been paid to the effects of global temperature increases on the geographical ranges and phenologies of plants and animals, less is known about the impacts of climatically driven alteration of water regimes. Aims. To assess how three species of freshwater turtle in Australia’s Murray–Darling Basin have responded to long-term decline in river flow and floodplain inundation due to climatic drying and water diversions. Methods. Turtle populations were sampled in a section of the Murray River and its floodplain in 1976–82 following a wet period and in 2009–11 at the end of the most severe drought on record. Catch per unit effort, proportional abundance in different habitat types and population structure were assessed in both periods. Key results. Catch per unit effort in baited hoop nets declined by 91% for the eastern snake-necked turtle (Chelodina longicollis) and 69% for the Murray turtle (Emydura macquarii), but did not change significantly for the broad-shelled turtle (Chelodina expansa). In addition, total catches from a range of sampling methods revealed a significantly reduced proportion of juvenile C. longicollis and E. macquarii in 2009–11, suggesting a fall in recruitment. Key conclusions. The decline of C. longicollis was likely due mainly to drought-induced loss of critical floodplain habitat in the form of temporary water bodies, and that of E. macquarii to combined effects of drought and predation on recruitment. C. expansa seems to have fared better than the other two species because it is less vulnerable to nest predation than E. macquarii and better able than C. longicollis tofind adequate nutrition in the permanent waters that remain during extended drought. Implications. Declining water availability may be a widespread threat to freshwater turtles given predicted global impacts of climate change and water withdrawals on river flows. Understanding how each species uses particular habitats and how climatic and non-climatic threats interact would facilitate identification of vulnerable populations and planning of conservation actions.
Article
Detailed information on the spatiotemporal dynamic in surface water bodies is important for quantifying the effects of a drying climate, increased water abstraction and rapid urbanization on wetlands. The Swan Coastal Plain (SCP) with over 1500 wetlands is a global biodiversity hotspot located in the southwest of Western Australia, where more than 70% of the wetlands have been lost since European settlement. SCP is located in an area affected by recent climate change that also experiences rapid urban development and ground water abstraction. Landsat TM and ETM+ imagery from 1999 to 2011 has been used to automatically derive a spatially and temporally explicit time-series of surface water body extent on the SCP. A mapping method based on the Landsat data and a decision tree classification algorithm is described. Two generic classifiers were derived for the Landsat 5 and Landsat 7 data. Several landscape metrics were computed to summarize the intra and interannual patterns of surface water dynamic. Top of the atmosphere (TOA) reflectance of band 5 followed by TOA reflectance of bands 4 and 3 were the explanatory variables most important for mapping surface water bodies. Accuracy assessment yielded an overall classification accuracy of 96%, with 89% producer’s accuracy and 93% user’s accuracy of surface water bodies. The number, mean size, and total area of water bodies showed high seasonal variability with highest numbers in winter and lowest numbers in summer. The number of water bodies in winter increased until 2005 after which a decline can be noted. The lowest numbers occurred in 2010 which coincided with one of the years with the lowest rainfall in the area. Understanding the spatiotemporal dynamic of surface water bodies on the SCP constitutes the basis for understanding the effect of rainfall, water abstraction and urban development on water bodies in a spatially explicit way.
Article
Landscape networks and ecosystems worldwide are undergoing changes that may impact in different ways relevant ecological processes such as gene flow, pollination, or wildlife dispersal. A myriad of indices have been developed to characterize landscape patterns, but not all of them are equally suited to evaluate temporal changes in landscape connectivity as is increasingly needed for biodiversity monitoring and operational indicator delivery. Relevant advancements in this direction have been recently proposed based on graph theoretical methods to analyze landscape network connectivity and on the measurement of habitat availability at the landscape scale. Building from these developments, we modify a recent index and present the equivalent connected area (ECA) index, defined as the size of a single patch (maximally connected) that would provide the same probability of connectivity than the actual habitat pattern in the landscape. The temporal changes in ECA can be directly compared with the changes in total habitat area. This allows for additional and straightforward insights on the degree to which the gains or losses in habitat amount can be beneficial or deleterious by affecting landscape elements that uphold connectivity in a wider landscape context. We provide a demonstrative example of application and interpretation of this index and approach to monitor changes in functional landscape connectivity. We focus on the trends in European forests at the province level in the period 1990–2000 from Corine land cover data, considering both changes in the forest spatial pattern and in the average permeability of the landscape matrix. The degree of connectivity was rather stable over most of the study area, with a slight overall increase in forest connectivity in Europe. However, a few countries and regions concentrated remarkably high changes in the analyzed period, particularly those with a low forest cover. The species traits also affected the responses to landscape pattern changes, which were more prominent for those species with limited dispersal abilities. We conclude discussing the potential of this approach for consistent indicator delivery, as well as the limitations and possibilities of application to a variety of situations, for which the required quantitative tools are freely available as open source projects.
Article
Amphibians are frequently characterized as having limited dispersal abilities, strong site fidelity and spatially disjunct breeding habitat. As such, pond-breeding species are often alleged to form metapopulations. Amphibian species worldwide appear to be suffering population level declines caused, at least in part, by the degradation and fragmentation of habitat and the intervening areas between habitat patches. If the simplification of amphibians occupying metapopulations is accurate, then a regionally based conservation strategy, informed by metapopulation theory, is a powerful tool to estimate the isolation and extinction risk of ponds or populations. However, to date no attempt to assess the class-wide generalization of amphibian populations as metapopulations has been made. We reviewed the literature on amphibians as metapopulations (53 journal articles or theses) and amphibian dispersal (166 journal articles or theses for 53 anuran species and 37 salamander species) to evaluate whether the conditions for metapopulation structure had been tested, whether pond isolation was based only on the assumption of limited dispersal, and whether amphibian dispersal was uniformly limited. We found that in the majority of cases (74%) the assumptions of the metapopulation paradigm were not tested. Breeding patch isolation via limited dispersal and/or strong site fidelity was the most frequently implicated or tested metapopulation condition, however we found strong evidence that amphibian dispersal is not as uniformly limited as is often thought. The frequency distribution of maximum movements for anurans and salamanders was well described by an inverse power law. This relationship predicts that distances beneath 11–13 and 8–9 km, respectively, are in a range that they may receive one emigrating individual. Populations isolated by distances approaching this range are perhaps more likely to exhibit metapopulation structure than less isolated populations. Those studies that covered larger areas also tended to report longer maximum movement distances – a pattern with implications for the design of mark-recapture studies. Caution should be exercised in the application of the metapopulation approach to amphibian population conservation. Some amphibian populations are structured as metapopulations – but not all.
Article
Australian floodplain wetlands are sites of high biodiversity that depend on flows from rivers. Dams, diversions and river management have reduced flooding to these wetlands, altering their ecology, and causing the death or poor health of aquatic biota. Four floodplain wetlands (Barmah-Millewa Forest and Moira Marshes, Chowilla floodplain, Macquarie Marshes, Gwydir wetlands) illustrate these effects with successional changes in aquatic vegetation, reduced vegetation health, declining numbers of water-birds and nesting, and declining native fish and invertebrate populations. These effects are likely to be widespread as Australia has at least 446 large dams (>10 m crest height) storing 8.8 × 107 ML (106 L) of water, much of which is diverted upstream of floodplain wetlands. More than 50% of floodplain wetlands on developed rivers may no longer flood. Of all of the river basins in Australia, the Murray-Darling Basin is most affected with dams which can store 103% of annual runoff and 87% of divertible water extracted (1983–84 data). Some floodplain wetlands are now permanent storages. This has changed their biota from one tolerant of a variable flooding regime, to one that withstands permanent flooding. Plans exist to build dams to divert water from many rivers, mainly for irrigation. These plans seldom adequately model subsequent ecological and hydrological impacts to floodplain wetlands. To avoid further loss of wetlands, an improved understanding of the interaction between river flows and floodplain ecology, and investigations into ecological impacts of management practices, is essential.
Article
Graph structures and habitat availability metrics are two recent and complementary approaches for analysing landscape connectivity. They have gained rapid popularity and provided significant conceptual improvements for decision making in conservation planning. We present a further methodological development of the habitat availability concept and metrics by partitioning them into three separate fractions that quantify the different ways in which individual landscape elements can contribute to overall habitat connectivity and availability in the landscape, including stepping stone effects. These fractions are derived from the same concept, are measured in the same units and can be directly compared and combined within a unifying framework. This avoids the problematic and, so far, usual combination of metrics coming from different backgrounds and the arbitrary weighting of connectivity considerations in a broader context of conservation alternatives. We analyse how the relative importance of each fraction varies with species traits. In addition, we show how the critical patches differ for each of the fractions by analysing various forest habitats in the province of Lleida (NE Spain). We discuss the conceptual and conservation implications of this approach, which can be adapted to different degrees of ecological and spatial detail within the graph while still maintaining a coherent framework for the identification of critical elements in the landscape network.
Article
The condition of many wetlands across Australia has deteriorated due to increased water regulation and the expansion and intensification of agriculture and increased urban and industrial expansion. Despite this situation, a comprehensive overview of the distribution and condition of wetlands across Australia is not available. Regional analyses exist and several exemplary mapping and monitoring exercises have been maintained to complement the more general information sets. It is expected that global climate change will exacerbate the pressures on inland wetlands, while sea level rises will adversely affect coastal wetlands. It is also expected that the exacerbation of these pressures will increase the potential for near-irreversible changes in the ecological state of some wetlands. Concerted institutional responses to such pressures have in the past proven difficult to sustain, although there is some evidence that a more balanced approach to water use and agriculture is being developed with the provision of increasing funds to purchase water for environmental flows being one example. We identify examples from around Australia that illustrate the impacts on wetlands of long-term climate change from palaeoecological records (south-eastern Australia); water allocation (Murray-Darling Basin); dryland salinisation (south-western Australia); and coastal salinisation (northern Australia). These are provided to illustrate both the extent of change in wetlands and the complexity of differentiating the specific effects of climate change. An appraisal of the main policy responses by government to climate change is provided as a basis for further considering the opportunities for mitigation and adaptation to climate change. KeywordsClimate change–Water regulation–Salinisation–Mitigation–Adaptation–Carbon emissions
Article
Here we propose an integrated framework for modeling connectivity that can help ecologists, conservation planners and managers to identify patches that, more than others, contribute to uphold species dispersal and other ecological flows in a landscape context. We elaborate, extend and partly integrate recent network-based approaches for modeling and supporting the management of fragmented landscapes. In doing so, experimental patch removal techniques and network analytical approaches are merged into one integrated modeling framework for assessing the role of individual patches as connectivity providers. In particular, we focus the analyses on the habitat availability metrics PC and IIC and on the network metric Betweenness Centrality. The combination and extension of these metrics jointly assess both the immediate connectivity impacts of the loss of a particular patch and the resulting increased vulnerability of the network to subsequent disruptions. In using the framework to analyze the connectivity of two real landscapes in Madagascar and Catalonia (NE Spain), we suggest a procedure that can be used to rank individual habitat patches and show that the combined metrics reveal relevant and non-redundant information valuable to assert and quantify distinctive connectivity aspects of any given patch in the landscape. Hence, we argue that the proposed framework could facilitate more ecologically informed decision-making in managing fragmented landscapes. Finally, we discuss and highlight some of the advantages, limitations and key differences between the considered metrics.
Article
We use focal-species analysis to apply a graph-theoretic approach to landscape connectivity in the Coastal Plain of North Carolina. In doing so we demonstrate the utility of a mathematical graph as an ecological construct with respect to habitat connectivity. Graph theory is a well established mainstay of information technology and is concerned with highly efficient network flow. It employs fast algorithms and compact data structures that are easily adapted to landscape-level focal species analysis. American mink (Mustela vison) and prothonotary warblers (Protonotaria citrea) share the same habitat but have different dispersal capabilities, and therefore provide interesting comparisons on connections in the landscape. We built graphs using GIS coverages to define habitat patches and determined the functional distance between the patches with least-cost path modeling. Using graph operations concerned with edge and node removal we found that the landscape is fundamentally connected for mink and fundamentally unconnected for prothonotary warblers. The advantage of a graph-theoretic approach over other modeling techniques is that it is a heuristic framework which can be applied with very little data and improved from the initial results. We demonstrate the use of graph theory in a metapopulation context, and suggest that graph theory as applied to conservation biology can provide leverage on applications concerned with landscape connectivity.
Article
Maintaining and restoring landscape connectivity is currently a central concern in ecology and biodiversity conservation, and there is an increasing demand of user-driven tools for integrating connectivity in landscape planning. Here we describe the new Conefor Sensinode 2.2 (CS22) software, which quantifies the importance of habitat patches for maintaining or improving functional landscape connectivity and is conceived as a tool for decision-making support in landscape planning and habitat conservation. CS22 is based on graph structures, which have been suggested to possess the greatest benefit to effort ratio for conservation problems regarding landscape connectivity. CS22 includes new connectivity metrics based on the habitat availability concept, which considers a patch itself as a space where connectivity occurs, integrating in a single measure the connected habitat area existing within the patches with the area made available by the connections between different habitat patches. These new metrics have been shown to present improved properties compared to other existing metrics and are particularly suited to the identification of critical landscape elements for connectivity. CS22 is distributed together with GIS extensions that allow for directly generating the required input files from a GIS layer. CS22 and related documentation can be freely downloaded from the World Wide Web.
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Landscape ecology and metapopulation ecology share a common interest in developing measures that describe the structure of heterogeneous landscapes, but the specific aim in metapopulation ecology is to construct measures that help predict the dynamics of species with information about the structure of fragmented landscapes. The amount of habitat that individuals in a metapopulation have access to can be divided into four components, the amount of habitat in the present habitat patch (A(i)), the amount of connected habitat in other patches available via migration (Γ(i)), the amount of preserved habitat in the present patch after time period Δt(A(i)), and the amount of linked habitat in other patches after time period Δt(Γ'(i)). Deterministic threshold conditions for metapopulation persistence in patch networks can be approximated with these quantities. For instance, in a version of the Levins model with extinction risk proportional to the inverse of patch area and colonization probability proportional to patch connectivity, the threshold condition for metapopulation persistence is given by ΓA + Var(ΓA)/ΓA > e/c, where e and c are the species-specific extinction and colonization parameters. I conjecture that with measures A' and Γ' the threshold condition for metapopulation persistence can be extended to dynamic landscapes, in which all or part of population turnover is caused by turnover in the habitat patches themselves. The measures of habitat availability described in this paper can be used to rank dissimilar fragmented landscapes in terms of their capacity to support a viable metapopulation.
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Although habitat networks show promise for conservation planning at regional scales, their spatiotemporal dynamics have not been well studied, especially in climate-sensitive landscapes. Here I use satellite remote sensing to compile wetland habitat networks from the Prairie Pothole Region (PPR) of North America. An ensemble of networks assembled across a hydrologic gradient from deluge to drought and a range of representative dispersal distances exhibits power-law scaling of important topological parameters. Prairie wetland networks are "meso-worlds" with mean topological distance increasing faster with network size than small-world networks, but slower than a regular lattice (or "large world"). This scaling implies rapid dispersal through wetland networks without some of the risks associated with "small worlds" (e.g., extremely rapid propagation of disease or disturbance). Retrospective analysis of wetland networks establishes a climatic envelope for landscape connectivity in the PPR, where I show that a changing climate might severely impact metapopulation viability and restrict long-distance dispersal and range shifts. More generally, this study demonstrates an efficient approach to conservation planning at a level of abstraction addressing key drivers of the global biodiversity crisis: habitat fragmentation and climatic change.