Habitat Patches Research Articles

Restoring declining species through translocations: A test case using flightless grasshoppers in an urban setting

Abstract Population translocations are used increasingly as a conservation strategy for vertebrates. However, relatively few attempts have been made to translocate invertebrates despite their potential benefits for food webs, and despite the practicality of undertaking such translocations in small areas including urban environments where space is limited. We conducted 36 translocations of 1851 individuals of the generalist flightless grasshopper Vandiemenella viatica across urban Melbourne, where 93% of its original habitat has been lost. We aimed to understand characteristics essential for grasshopper persistence and to investigate detection, occupancy, dispersal and habitat suitability throughout its active period to improve insect translocation success in urban settings using revegetated sites and small remnant habitats. We also measured movement and detection probability after one week in short‐term trials. The one‐week trial indicated that grasshopper sex and colour morph did not influence the probability of detection, and there was no evidence of directional movement by females and males. One year after translocation, V. viatica were found in 28 out of 36 translocation sites. These surveys showed that detection probability changed across survey seasons and was influenced by soil temperature. Also, soil temperature positively affected detection in the winter surveys. Occupancy probability was influenced by graminoid cover, plant species richness and weed cover. We found no evidence of directional movement by females and males in the F1 generation. Abundance and presence/absence data were best explained by graminoid cover and plant species richness. Our findings suggest that wingless grasshopper translocations are feasible in small urban patches of suitable habitat, helping to restore invertebrate biodiversity and ecological services.

Patterns and consequences of invasion of tropical montane forests by Cestrum aurantiacum Lindl. in the Western Ghats

In the montane forest-grassland mosaics of the Western Ghats, land cover conversion to silviculture and agriculture over the last five decades has resulted in both loss of natural habitats and widespread invasion of remnant habitat patches. While invasion of the grassland habitats of the mosaic has been relatively well studied, there have been few attempts to understand the extent to which forest habitats (locally known as sholas) have been affected by the spread of exotic species. Here we examine the patterns and impacts of invasion of shola forest understoreys by Cestrum aurantiacum Lindl., an exotic shrub species. At the landscape scale, we demonstrate that the presence and abundance of this invasive in shola understories is negatively related to distance from tea plantations. Further, the intensity of invasion is higher in areas with greater seasonality of temperature and lower mean annual precipitation. At the patch scale, invasion is greatest at shola edges and away from stream courses. We find that C. aurantiacum abundance has negatively affected the regeneration of native shola tree species as well as the abundance of native shola understorey shrubs. Fifty three percent of invaded plots had no native shrubs present. In plots where both C. aurantiacum and native shrubs were present in large enough numbers, we found evidence of negative spatial dependence between stem locations of C. aurantiacum and native shrubs. Our findings have important implications for the management and conservation of these mosaics.

Open areas associated with traditional agriculture promote functional connectivity among amphibian demes in Mediterranean agrosystems

ContextFunctional connectivity across fragmented habitat patches is essential for the conservation of animal populations in humanized landscapes. Given their low dispersal capacity, amphibians in the Mediterranean region are threatened by habitat fragmentation and loss due to changes in land use, including agricultural intensification.ObjectivesWe assessed patterns of functional connectivity of a Near Threatened Mediterranean amphibian, the sharp ribbed newt (Pleurodeles waltl), in an agricultural landscape matrix in NW Spain subject to different intensification regimes.MethodsWe sampled newts in 17 ponds embedded in a terrestrial habitat matrix dominated by agricultural land uses. Genome-wide molecular markers (1390 SNPs) were used to assess patterns of genetic diversity and gene flow among ponds. We tested the role of landscape features on functional connectivity using isolation by resistance models incorporating information on Normalized Difference Vegetation Index (NDVI) data.ResultsWe found low levels of genetic diversity in all sampled populations. Global FST estimates and cluster analyses revealed shallow but significant genetic structure in the study area, with NDVI-based resistance models showing that open areas (rainfed crops and grasslands) offer lower resistance to gene flow and thus promote functional connectivity among demes.ConclusionsOur study highlights the important role of landscape features, such as open areas resulting from traditional rainfed agriculture, in promoting functional connectivity between amphibian populations in Mediterranean agrosystems. Conservation policies must adopt a functional network strategy and protect groups of inter-connected temporary ponds across the traditional agricultural matrix to efficiently preserve their associated biotic communities.

OPTIMIZED ECOLOGICAL NETWORK APPROACH OF HIGHLY URBANIZED CITIES: THE CASE OF ADANA CITY

Abstract. One of the most significant challenges in urban areas, where the process of rapid urban expansion takes place, is the loss of agricultural lands and natural habitats. The conversion of these areas into residential and commercial zones leads to a decline in urban biodiversity and the progressive loss of vital habitat areas. Analyzing habitat connectivity and conducting landscape measurements provide valuable insights for the development of land use and management strategies, enhancing our understanding of the spatial structure of the landscape, and directing conservation efforts. Incorporating measures such as green corridors and landscape connection networks into urban planning management becomes crucial in order to mitigate the adverse effects of habitat fragmentation and enhance ecosystem resilience within cities. Remote sensing techniques offer opportunities to create habitat connectivity models that enable the quantitative and qualitative identification of fragmented habitat patches. These models serve as tools to evaluate the effectiveness of conservation measures and monitor the potential impacts of future land use changes on habitat networks. Within this context, an optimized approach to habitat connectivity is presented, aiming to contribute to landscape planning and ecological-based studies in a city with undergoing rapid urbanization like Adana. By identifying degraded areas and introducing new habitat patches, a significant improvement in the connectivity of the habitat network has been observed. The findings indicated that the addition of new habitat patches to degraded areas can substantially enhance the city's overall habitat connectivity.

Warmer springs increase potential for temporal reproductive isolation among habitat patches in subalpine flowering plants

Abstract Flowering phenology can vary considerably even at fine spatial scales, potentially leading to temporal reproductive isolation among habitat patches. Climate change could alter flowering synchrony, and hence temporal isolation, if plants in different microhabitats vary in their phenological response to climate change. Despite the importance of temporal isolation in determining patterns of gene flow, and hence population genetic structure and local adaptation, little is known about how changes in climate affect temporal isolation within populations. Here, we use flowering phenology and floral abundance data of 50 subalpine plant species over 44 years to test whether temporal isolation between habitat patches is affected by spring temperature. For each species and year, we analysed temporal separation in peak flowering and flowering overlap between habitat patches separated by 5–950 m. Across our study species, warmer springs were associated with more temporal differentiation in flowering peaks among habitat patches, and less flowering overlap, increasing potential for temporal isolation within populations. Synthesis. By reducing opportunities for mating among plants in nearby habitat patches, our results suggest that warmer springs may reduce opportunities for gene flow within populations, and, consequently, the capacity of plant populations to adapt to environmental changes.

Spatial habitat heterogeneity influences host-pathogen dynamics in a patchy population of Ranchman's tiger moth.

Host-pathogen dynamics are influenced by many factors that vary locally, but models of disease rarely consider dynamics across spatially heterogeneous environments. In addition, theory predicts that dispersal will influence host-pathogen dynamics of populations that are linked, although this has not been examined empirically in natural systems. We examined the spatial dynamics of a patchy population of tiger moths and its baculovirus pathogen, in which habitat type and weather influence dynamics. Theoretical models of host-baculovirus dynamics predict that such variation in dynamics between habitat types could be driven by a range of factors, of which we predict two are likely to be operating in this system: (1) differences in the environmental persistence of pathogens or (2) differences in host intrinsic rates of increase. We used time series models and monitored infection rates of hosts to characterize population and disease dynamics and distinguish between these possibilities. We also examined the role of host dispersal (connectivity) and weather as important contributors to dynamics, using time series models and experiments. We found that the population growth rate was higher, delayed density dependence was weaker, and long-period oscillations had lower amplitudes in high-quality habitat patches. The infection rate was higher on average in high-quality habitat, and this was likely to have been driven by higher mean population densities and no differences in pathogen persistence in different habitats (delayed density dependence). Time series modeling and experiments also showed an interactive effect of temperature and precipitation on moth population growth rates (likely caused by variation in host plant quality and quantity), and an effect of connectivity. Our results showed that spatial heterogeneity, connectivity, climate, and their interactions were important in driving host-baculovirus dynamics. In particular, our study found that connected patches and spatial heterogeneity generated differences in dynamics that only partially aligned with theoretical predictions.

Integrating traditional ecological knowledge into habitat restoration: implications for meeting forest restoration challenges

BackgroundTraditional ecological knowledge (TEK) helps tribal communities adapt to socio-ecological changes, improving the long-term sustainability of their livelihood strategies and fostering social–ecological resilience. TEK provides thorough understanding of ecosystem dynamics, as well as how they relate to societal norms, practices, and resource use patterns. The integrity of TEK is often in jeopardy due to changes in belief systems, regional languages, traditional ways of subsistence, and disruption of traditional social–ecological systems. Landscape restoration has the ability to promote self-determination while safeguarding the livelihoods, beliefs, cultural, and biodiversity of indigenous peoples. However, there is a substantial knowledge gap on how TEK might aid ecosystem restoration, particularly in elephant corridors.MethodsThe current study focused on gathering traditional ecological knowledge on the woody tree species from the Dering-Dibru Saikhowa Elephant Corridor using semi-structured interviews, group discussions, and direct observations. The acquired data were applied to heat map cluster analysis and ordination techniques using R software version 4.0.0.ResultsTraditional usage information of 31 tree species utilized for food, fodder, timber, fuelwood, medicinal, and livelihood by local people was gathered. Most of the species utilized locally belonged to the families Combretaceae and Fabaceae. The species were classified into single, double, or multi-uses based on the extent of utilization. Azadirachta indica, Phyllanthus emblica, and Syzygium cumini (six each) had the highest utilization, while Mesua ferrea had the lowest. Chionanthus ramiflorus, Artocarpus heterophyllus, and Dillenia indica were among the plants valuable to wildlife, providing both forage and habitat for a wide variety of birds and animals. Artocarpus heterophyllus, Averrhoa carambola, Mangifera indica, P. emblica, Psidium guajava, and S. cumini were among the plants important for the livelihoods of the local community. Our findings demonstrated that local people were knowledgeable about the plant species to use as pioneer species, such as Bombax ceiba, Albizia lebbeck, D. indica, S. cumini, P. emblica, Lagerstroemia speciosa, and Alstonia scholaris, for habitat restoration in a diverse habitat. We classified the habitat of the enlisted species into different categories, and two clusters (clusters 1 and 2) were identified based on the similarity of woody species in different habitats. We prioritized multiple tree species for eco-restoration using the information collected through TEK. We planted 95,582 saplings on 150 hectares in the Dering-Dibru Saikhowa Elephant Corridors’ degraded habitat patches, which will serve as future reference site for landscape rehabilitation. Out of total saplings planted, 56% of the species were linked to native communities through ethnobotanical uses, as well as providing connectivity and habitat for elephant movement, 16% of all woody species are pioneer species to colonize a degraded habitat, 15% of all woody species are preferred food and foraging by wildlife, and 13% of the species as a source of livelihood for local people, incorporating social, economic, cultural, and biodiversity benefits into the restoration framework.ConclusionThe current study also provides insights how the TEK can assist with aspects of ecological restoration, from reference ecosystem reconstruction and adaptive management through species selection for restoration, monitoring, and evaluation of restoration effectiveness.

Assessing golden‐winged warbler dispersal habitat in a highly parcelized landscape

AbstractGolden‐winged warblers (Vermivora chrysoptera) are facing population declines in the southern Appalachian Mountains. Breeding habitat loss is considered one of the primary reasons for golden‐winged warbler declines in the region. Expanding breeding habitat availability in a manner that promotes population expansion across an interconnected network of habitat patches is particularly problematic in a landscape dominated by private land ownership. We assessed the connectivity of golden‐winged warbler breeding habitat in a 29,680‐ha landscape with 5,664 ownership parcels between 2 state‐owned game lands in northwestern North Carolina, USA, in fall 2021. We created a connectivity map and provided examples of 3 means of prioritizing parcels for golden‐winged warbler habitat maintenance and management based on dispersal distances of fledglings that could return the following spring with prior familiarity of potential nesting areas. Prioritized parcels can guide land acquisition and conservation easement development as well as active management. Despite being highly parcelized, the area has both well‐connected and disjointed clusters of core habitat patches, but habitat management on privately owned parcels would be needed to connect core habitat patches to enable dispersing golden‐winged warbler fledglings to encounter potential breeding habitat that they could use the following spring.

Effects of landscape structure and patch characteristics on the density of central populations of the eastern green lizard Lacerta viridis.

A better understanding of the impact of habitat loss on population density can be achieved by evaluating effects of both parameters within remnant habitat patches and parameters of the landscape surrounding those patches. The integration of predictors at the patch and landscape level is scarce in animal ecological studies, especially for reptiles. In this study, a patch-landscape approach was applied to evaluate the combined effects of within-patch habitat quality, patch geometry and landscape configuration and composition on the density of remnant populations of the eastern green lizard, Lacerta viridis, in a highly modified landscape in Bulgaria. Landscape composition variables (proportion of different land covers) were measured at different spatial scales surrounding patches. Single-scale models were built to evaluate combined effects of all predictors on density, when including all landscape composition variables at a specific spatial scale. Multi-scale models were applied to analyze combined effects when including landscape composition variables at the scale of their strongest effect (scale of effect, SoE). Results showed that the SoE of proportion of cropland and urban areas was small (50 m), while for proportion of habitat was large (1.5 km). The overall effect of habitat loss was better explained by the multi-scale model. Population density increased with patch area and decreased with patch shape irregularity and with the proportion of three land cover types surrounding patches-cropland, urban areas, and habitat. Combining patch and landscape parameters is important to identify ecological processes that occur simultaneously at different spatial levels and landscape scales, which would imply the application of multi-scale approaches for the protection of wild animal populations. Results are contrasted with what is known about occupancy patterns of the species in the same region and approaches to integrate both occupancy and density, in the field design of animal ecological studies are suggested.

The spatial distribution of insect communities of a mountaintop forest archipelago is not correlated with landscape structure: A multitaxa approach

Abstract Understanding community assembly in habitat patches requires an integrative approach, considering the potential role of local and regional factors and organisms' dispersal abilities among patches. For this, assessing the degree of species overlap between patches (nestedness) can be particularly informative, especially regarding different taxa and distinct patch properties. We assessed the potential role of landscape‐patch structure in shaping the nestedness patterns of five taxonomic groups with distinct dispersal abilities (ants, bees, dung beetles, fruit‐feeding butterflies and aculeate wasps). We collected insects from 11 forest patches in the Espinhaço mountain range in southeast Brazil. We assessed the potential contribution of three forest island attributes (size, distance and shape) to the nestedness of insect communities and then tested if metacommunities were significantly nested with respect to habitat (forest islands). Finally, we evaluated how species of each taxonomic group contribute to metacommunity nestedness. While there was a substantial variation in the contribution to the nested pattern within each taxon, all taxa studied exhibited a significantly nested pattern of species distribution. The landscape‐patch structure and the vagility of the different taxa did not influence the contribution of sites to the metacommunity nested pattern. Our integrative approach provides critical data on the role of different factors in shaping species distribution in natural patches. Species with different dispersal abilities and patches with distinct landscape properties contributed similarly to nestedness, indicating the potential role of the vegetation matrix permeability in shaping the distribution of organisms in the studied forest archipelago.

Constraints on the maintenance of wild Taxus cuspidata populations based on regression conservation.

To clarify the key factors constraining the maintenance of wild Taxus cuspidata populations and to develop conservation strategies and technical links for current populations, we investigated the renewal status and distribution patterns of wild T. cuspidata populations in the main distribution areas of China. We analyzed the effects of stand factors and human disturbance on population renewal and maintenance. The results showed that the overall regeneration of wild T. cuspidata populations was poor. The basal diameter and height class structure of renewed individuals showed an unhealthy state. 19% of the area was well regenerated. There were three types of regeneration, including poor regeneration with few adult trees, poor regeneration with many adult trees, and good regeneration with few adult trees. The communities in which T. cuspidata was found could be classified into Abies nephrolepis + Tilia amurensis forest, spinney forest, and Picea jezoensis var. microsperma + A. nephrolepis forest. The renewal number of A. nephrolepis + T. amurensis forest was significantly higher than that of spinney forest. Increased stand density and moderate human disturbance contributed to the regeneration of T. cuspidata. The regenerating T. cuspidata seedlings increased significantly when stand density increased from low to medium. The number of regenerating populations in moderately disturbed habitats was significantly higher than those in lightly disturbed habitats. Human disturbance and habitat were currently critical constraints to maintaining and regenerating wild T. cuspidata populations. The conservation of T. cuspidata should consider current status of population regeneration in each habitat patch to develop corresponding in situ conservation and regression conservation measures and focus on the influence of critical factors such as disturbances and habitat conditions.

Catchment-based sampling of river eDNA integrates terrestrial and aquatic biodiversity of alpine landscapes

Monitoring of terrestrial and aquatic species assemblages at large spatial scales based on environmental DNA (eDNA) has the potential to enable evidence-based environmental policymaking. The spatial coverage of eDNA-based studies varies substantially, and the ability of eDNA metabarcoding to capture regional biodiversity remains to be assessed; thus, questions about best practices in the sampling design of entire landscapes remain open. We tested the extent to which eDNA sampling can capture the diversity of a region with highly heterogeneous habitat patches across a wide elevation gradient for five days through multiple hydrological catchments of the Swiss Alps. Using peristaltic pumps, we filtered 60 L of water at five sites per catchment for a total volume of 1800 L. Using an eDNA metabarcoding approach focusing on vertebrates and plants, we detected 86 vertebrate taxa spanning 41 families and 263 plant taxa spanning 79 families across ten catchments. For mammals, fishes, amphibians and plants, the detected taxa covered some of the most common species in the region according to long-term records while including a few more rare taxa. We found marked turnover among samples from distinct elevational classes indicating that the biological signal in alpine rivers remains relatively localised and is not aggregated downstream. Accordingly, species compositions differed between catchments and correlated with catchment-level forest and grassland cover. Biomonitoring schemes based on capturing eDNA across rivers within biologically integrated catchments may pave the way toward a spatially comprehensive estimation of biodiversity.

Modeling red deer functional connectivity at a regional scale in a human-dominated landscape

Ecological connectivity is a key attribute of landscapes and indicates how landscapes facilitate or impede movement. It is an essential criterion to consider in the design of green infrastructures (GIs) when landscape planners and managers deal with population viability, which in part depends on the movement capacities of organisms. Our goal is to inform about the conservation value of land parcels to maintain or enhance connectivity. For this, we developed a red deer functional connectivity model at a regional scale. We focused our study on this large mammal species inhabiting the Greater Geneva agglomeration between Switzerland and France. Our study site is dominated by forested mountains and lowlands, which are highly fragmented by human infrastructures and agricultural lands. We used GPS location data from 15 red deer to parameterize the habitat resistances with a multivariate analysis. To predict connectivity at the regional scale, we used local expert knowledge to design a graph-based landscape. Then, we used electric circuit theory with Circuitscape software to detect pinch points and map corridors, using the set of resistances parameterized with experimental data and the putative core areas and links identified with the help of expert knowledge. We obtained a map that highlights suitable regional habitat patches and corridors or connectivity pinch points potentially used by red deer between the mountains and the lowlands, ratifying the importance of the transfrontier collaboration while implementing the GI. The obtained results are used to assist landscape managers and planners in their effort to include functional connectivity in the prioritization of the GI across the region.

No net loss of connectivity: Conserving habitat networks in the context of urban expansion

Increasing urbanisation calls for careful landscape conservation planning to maintain biodiversity in urban areas. Urbanisation not only decreases the amount and quality of habitats, but it also affects habitat connectivity, which is crucial for species’ long-term persistence. The mitigation hierarchy approach of avoiding, reducing and offsetting the negative impacts of development projects is a powerful tool to prevent biodiversity loss. However, this process is typically used at the local scale and on a project-by-project basis, ignoring the cumulated effects of several projects on habitat connectivity. We applied a landscape-level approach to the mitigation hierarchy to achieve no net loss of connectivity during urban planning. Using spatial graphs, we assessed avoidance, reduction and offsetting scenarios for mitigating the impact of ten urban development projects in the city of Jyväskylä, Finland, here focusing on the habitat network of the endangered Siberian flying squirrel (Pteromys volans). We found a negative impact of urban development on network connectivity and prioritised habitat patches and corridors, which should be maintained to avoid and reduce the impacts. The no net loss of connectivity was achieved by adding new habitat patches in locations that maximise connectivity. We also found that the results were highly sensitive to variations in the dispersal distance of the focal species used in the connectivity model. An inadequate reference value for this parameter may lead to underestimation of the impacts of development projects and, therefore, insufficient mitigation actions. With a case study, we showed that spatial graph analysis can support decision-making by identifying and prioritising the actions needed to maintain habitat connectivity in urban landscapes.

Wildlife habitat association over a twelve-year period (2008–2020) in the Greater Mahale Ecosystem, western Tanzania

The Greater Mahale Ecosystem (GME) in western Tanzania hosts high faunal biodiversity, including charismatic species such as elephants and chimpanzees. Across the GME, habitat occurs in differently administered, unprotected and protected areas, including village land, forest reserves, and national parks. Areas of lower protective status are prone to deforestation and land cover changes. These land cover changes influence suitable habitat itself as well as the connectivity between habitat patches, but the impact on different mammal species in this region is unknown. In this study, we investigated changes in habitat availability by creating species distribution models for 11 medium-large mammal species based on species occurrence data collected from 2008 to 2020. We tested habitat associations for each species and evaluated the importance of the static predictor variables elevation, slope, aspect and terrain-ruggedness and the dynamic predictor variables distance to deforestation, percent forest, vegetation intensity, and vegetation variability, retrieved through remotely sensed data analysis. Our models suggest habitat declined for most, but not all species. Whilst elephants and buffalo lost more than 50 % of available habitat during this period, primates exhibited habitat stability. Habitat losses were pronounced in the southeast of the GME. Slope, elevation and median tasseled-cap wetness index (vegetation intensity) and distance to deforestation were the most important predictor variables. Our study presents a spatially and temporally explicit estimation of habitat changes in a critically important, biodiverse region undergoing drastic land cover changes. We call for consideration in land-use planning to foster connectivity and landscape integrity to protect and conserve wildlife across the ecosystem.

Identification of Redundant Patches in Early Urbanized Areas Based on mRMR + SVM

Rapid global urbanization has inevitably led to habitat fragmentation, and much research has focused on responding by building ecological networks and improving connectivity. The construction of such post-event ecological networks is sometimes not effective, and the identification and protection of important patches in the early urbanization period is more significant. Based on the redundancy theory, this paper explores the method of identifying potential critical habitat patches after future urban development. The paper takes the Longxing area of Chongqing city as an example and uses the cumulative current value results of circuit theory model simulations and patch characteristic attribute information as sample data, introduces a combination of the minimal-redundancy-maximal-relevance criterion and a support vector machine (mRMR + SVM) to discriminate the redundancy of patches in ecological networks, and ranks the importance of source patches. The results show that the mRMR criterion can exhibit a more realistic ranking of patch importance, allowing patches with better quality to achieve a higher ranking. Compared to the patch importance determined based on the magnitude of the cumulative current value, 66.34% of the patch importance order changed in the mRMR criterion ranking results. The mRMR + SVM method was effective in identifying individuals with redundancy from the set of source-site patches. The test found that ecological corridors still passed through or occurred near these redundant patches after their removal, demonstrating the substitutability of patches identified as redundant. The results of the study can help improve the knowledge of ecological networks and provide quantitative methodological support and decision-making reference for urban development and ecological conservation.

Effects of Forest Fragmentation on Connectivity and Genetic Diversity in an Endemic and an Invasive Rodent in Northwestern Madagascar.

Habitat loss and fragmentation are of concern to conservation biologists worldwide. However, not all organisms are affected equally by these processes; thus, it is important to study the effects of living in fragmented habitats on species that differ in lifestyle and habitat requirements. In this study, we examined the dispersal and connectivity patterns of rodents, one endemic (Eliurus myoxinus) and one invasive (Rattus rattus), in two landscapes containing forest fragments and adjacent continuous forest patches in northwestern Madagascar. We generated genetic (RADseq) data for 66 E. myoxinus and 81 R. rattus individuals to evaluate differences in genetic diversity as well as inbreeding and connectivity in two landscapes. We found higher levels of inbreeding and lower levels of genetic diversity in E. myoxinus compared with R. rattus. We observed related dyads both within and between habitat patches and positive spatial autocorrelation at lower distance classes for both species, with a stronger pattern of spatial autocorrelation in R. rattus. Across each site, we identified contrasting migration rates for each species, but these did not correspond to habitat-matrix dichotomies. The relatively low genetic diversity in the endemic E. myoxinus suggests ecological constraints that require further investigation.

An integrated approach to model connectivity and identify modules for habitat networks

BackgroundRecent studies show that modularity is a crucial aspect of habitat network connectivity that affects the likelihood of population persistence despite unpredictable perturbations, therefore, modularity should be considered while restoring connectivity in highly fragmented landscapes. However, what methods or models can be applied to an integrated analysis of connectivity and modularity are rarely discussed. ObjectivesAn integrated approach is proposed to model connectivity of habitat networks and identify module structure on the basis of comparing Least Cost Path (LCP) with circuit-theoretic model, Informap with Newman Girvan's modularity score Q method. MethodsTo measure connectivity between habitat patches, dispersal probability based on LCP and effective conductance based on circuit-theoretic model were calculated respectively and compared under different cost-weighted distance thresholds of 150, 500, 1000, 2500, 5000, 10,000. Then, results of six scenarios were compared using Infomap and Newman-Girvan's modularity score Q to demonstrate the utility of the two methods in identifying modular structure. These procedures were carried out in a simulated landscape. ResultsThe results show that (1) compared with effective conductance, dispersal probability is more sensitive to the change of cost-weighted distance thresholds.(2) increasing cost-weighted distance thresholds lead to a decrease in current density of pinch points and resistance distance of corridors between two habitats, but it improves habitat connectivity.(3) the results of modules identified by Newman-Girvan's method differ noticeably from that of Infomap, but Infomap can identify the hierarchical module structure of the habitat network. ConclusionOur approach offers an effective means for characterizing functional structure of habitat networks combining connectivity with modularity. Effective conductance has a wider application in identifying important landscape elements, and Infomap can extract multiple levels of network structure, which likely reflect structures determined by different ecological processes at different scales.

Surrounding landscape, habitat and hybridization dynamics drive population structure and genetic diversity in the Saltmarsh Sparrow

Abstract Determining factors that shape a species’ population genetic structure is beneficial for identifying effective conservation practices. We assessed population structure and genetic diversity for Saltmarsh Sparrow (Ammospiza caudacuta), an imperiled tidal marsh specialist, using 13 microsatellite markers and 964 individuals sampled from 24 marshes across the breeding range. We show that Saltmarsh Sparrow populations are structured regionally by isolation-by-distance, with gene flow occurring among marshes within ~110 to 135 km of one another. Isolation-by-resistance and isolation-by-environment also shape genetic variation; several habitat and landscape features are associated with genetic diversity and genetic divergence among populations. Human development in the surrounding landscape isolates breeding marshes, reducing genetic diversity, and increasing population genetic divergence, while surrounding marshland and patch habitat quality (proportion high marsh and sea-level-rise trend) have the opposite effect. The distance of the breeding marsh to the Atlantic Ocean also influences genetic variation, with marshes farther inland being more divergent than coastal marshes. In northern marshes, hybridization with Nelson’s Sparrow (A. nelsoni) strongly influences Saltmarsh Sparrow genetic variation, by increasing genetic diversity in the population; this has a concomitant effect of increasing genetic differentiation of marshes with high levels of introgression. From a conservation perspective, we found that the majority of population clusters have low effective population sizes, suggesting a lack of resiliency. To conserve the representative breadth of genetic and ecological diversity and to ensure redundancy of populations, it will be important to protect a diversity of marsh types across the latitudinal gradient of the species range, including multiple inland, coastal, and urban populations, which we have shown to exhibit signals of genetic differentiation. It will also require maintaining connectivity at a regional level, by promoting high marsh habitat at the scale of gene flow (~130 km), while also ensuring “stepping stone” populations across the range.

Low genetic diversity and high gene flow in the Aquatic Warbler (Acrocephalus paludicola), a threatened marshland songbird with a fragmented breeding range

Breeding habitat loss and depletion of genetic diversity can have critically negative impacts on species, and especially so for habitat specialists. The Aquatic Warbler Acrocephalus paludicola is a threatened European songbird that breeds in fens, which have been lost and fragmented over centuries. We used microsatellite loci to perform a spatial and longitudinal comparison, comparing samples collected recently (contemporary) with those obtained about two decades earlier (historical) from c. 25% of the breeding range (Biebrza and Polesie) of the Aquatic Warbler. With these data we explored changes in genetic diversity, expansions and reductions of population size, population structure, and gene flow. Allelic richness, expected heterozygosity, the number of effective and private alleles, and effective population size (NE ≈ 200) were low and comparable across time and space. We detected a genetic bottleneck in contemporary Biebrza, and a less certain bottleneck in both historical and contemporary Polesie. Across space, Biebrza and Polesie were not genetically differentiated in either period. All the historical samples clustered together, but in the contemporary samples a small part of Polesie clustered separately (FST = 0.011). Across time, Biebrza and Polesie showed low but significant differentiation (FST = 0.026–0.064), and historical and contemporary groups clustered apart. A principal coordinate analysis on genetic distance detected three groups, which spanned sampling locations. In the temporal comparison, the contemporary group and contemporary Biebrza had elevated mean within‐group pairwise relatedness. We did not recover signals for sex‐biased dispersal, asymmetric gene flow or isolation‐by‐distance using the molecular data. Our results suggest that the studied populations show: (1) impoverished genetic diversity, (2) a change in allele frequencies over the two decades studied and (3) high gene flow between distant breeding sites, implying high resilience to habitat fragmentation that should facilitate the success of recolonising restored habitat patches by Aquatic Warblers.