Salinisation reduces biodiversity in neighbouring freshwater patches in experimental metacommunities

1. Aquatic ecosystems are biodiversity hot spots across many landscapes; therefore, the degradation of these habitats can lead to decreases in biodiversity across multiple scales. Salinisation is a global issue that threatens freshwater ecosystems by reducing water quality and local biodiversity. The effects of salinity on local processes have been studied extensively; however, the effects of salinisation or similar environmental stressors within a metacommunity (a dispersal network of several distinct communities) have not been explored.
2. We tested how the spatial heterogeneity and the environmental contrast between freshwater and saline habitat patches influenced cladoceran biodiversity and species composition at local and regional scales in a metacommunity mesocosm experiment. We defined spatial heterogeneity as the proportion of freshwater to saltwater patches within the metacommunity, ranging from a freshwater-dominated metacommunity to a saltwater-dominated metacommunity. Environmental contrast was defined as the environmental distance between habitat patches along the salinity gradient in which low-contrast metacommunities consisted of freshwater and low-salinity patches and high-contrast metacommunities consisted of freshwater and high-salinity patches.
3. We hypothesised that the α-richness of freshwater patches and metacommunity γ-richness would decrease as freshwater patches became less abundant along the spatial heterogeneity gradient in both low- and high-contrast metacommunities, because there would be fewer freshwater patches that could serve as source populations for declining populations. We hypothesised that low-contrast metacommunities would support more species across the spatial heterogeneity gradient than high-contrast metacommunities, because, via dispersal, low-salinity patches can support halotolerant freshwater species that can mitigate population declines in neighbouring freshwater patches, whereas` high-salinity patches will mostly support halophilic species, providing fewer potential colonisers to freshwater patches.
4. We found that α-richness of freshwater mesocosms and metacommunity γ-richness declined in saline-dominated metacommunities regardless of the environmental contrast between the freshwater and saline mesocosms. We found that environmental contrast influenced freshwater and saline community composition in low-contrast metacommunities by increasing the abundances of species that could tolerate low-salinity environments through dispersal, whereas freshwater and high-salinity communities showed limited interactions through dispersal.
5. Freshwater mesocosms had a disproportionate effect on the local and regional biodiversity in these experimental metacommunities, indicating that habitat identity may be more important than habitat diversity for maintaining biodiversity in some metacommunities. This study further emphasises the importance in maintaining multiple species-rich habitat patches across landscapes, particularly those experiencing landscape-wide habitat degradation.

     

Effects of local and landscape factors on the abundance of an endangered multivoltine butterfly at riverbanks

Plebejus argyrognomon is one of the grassland‐dwelling butterflies undergoing rapid decline in recent decades. Grassland habitats for butterflies are generally threatened by fragmentation and invasive species, hence are among the most vulnerable ecosystems. We studied the seasonal abundance of P. argyrognomon at habitat patches along the banks of the Kinugawa River in eastern Japan, to identify environmental factors suitable for population persistence of this species, including habitat patch connectivity. Results showed that the patch's host plant cover had a positive effect on abundance in all three seasons, while the shading of the host plants by surrounding non‐host plants and nearby forested area showed negative effects. Additionally, habitat patch connectivity and nectar richness could be considered as positive factors in autumn and summer, respectively. Analysis of habitat connectivity also showed that the Kinugawa River did not appear to act as a dispersal barrier for P. argyrognomon. Our findings emphasize the importance of understanding environmental factors that may vary among seasons, and such understanding could contribute to habitat management of multivoltine butterflies in fragmented landscapes.     

Landscape configuration determines gene flow and phenotype in a flightless forest-edge ground-dwelling bush-cricket, Pholidoptera griseoaptera

Spatial configuration of habitats influences genetic structure and population fitness whereas it affects mainly species with limited dispersal ability. To reveal how habitat fragmentation determines dispersal and dispersal-related morphology in a ground-dispersing insect species we used a bush-cricket (Pholidoptera griseoaptera) which is associated with forest-edge habitat. We analysed spatial genetic patterns together with variability of the phenotype in two forested landscapes with different levels of fragmentation. While spatial configuration of forest habitats did not negatively affect genetic characteristics related to the fitness of sampled populations, genetic differentiation was found higher among populations from an extensive forest. Compared to an agricultural matrix between forest patches, the matrix of extensive forest had lower permeability and posed barriers for the dispersal of this species. Landscape configuration significantly affected also morphological traits that are supposed to account for species dispersal potential; individuals from fragmented forest patches had longer hind femurs and a higher femur to pronotum ratio. This result suggests that selection pressure act differently on populations from both landscape types since dispersal-related morphology was related to the level of habitat fragmentation. Thus observed patterns may be explained as plastic according to the level of landscape configuration; while anthropogenic fragmentation of habitats for this species can lead to homogenization of spatial genetic structure.     

Habitat patch size alters the importance of dispersal for species diversity in an experimental freshwater community

Increased dispersal of individuals among discrete habitat patches should increase the average number of species present in each local habitat patch. However, experimental studies have found variable effects of dispersal on local species richness. Priority effects, predators, and habitat heterogeneity have been proposed as mechanisms that limit the effect of dispersal on species richness. However, the size of a habitat patch could affect how dispersal regulates the number of species able to persist. We investigated whether habitat size interacted with dispersal rate to affect the number of species present in local habitats. We hypothesized that increased dispersal rates would positively affect local species richness more in small habitats than in large habitats, because rare species would be protected from demographic extinction. To test the interaction between dispersal rate and habitat size, we factorially manipulated the size of experimental ponds and dispersal rates, using a model community of freshwater zooplankton. We found that high‐dispersal rates enhanced local species richness in small experimental ponds, but had no effect in large experimental ponds. Our results suggest that there is a trade‐off between patch connectivity (a mediator of dispersal rates) and patch size, providing context for understanding the variability observed in dispersal effects among natural communities, as well as for developing conservation and management plans in an increasingly fragmented world.     

Spatial Heterogeneity in Habitat Quality and Cross-Scale Interactions in Metapopulations

Abstract Integration of habitat heterogeneity into spatially realistic metapopulation approaches reveals the potential for key cross-scale interactions. Broad-scale environmental gradients and land-use practices can create autocorrelation of habitat quality of suitable patches at intermediate spatial scales. Patch occupancy then depends not only on habitat quality at the patch scale but also on feedbacks from surrounding neighborhoods of autocorrelated patches. Metapopulation dynamics emerge from how demographic and dispersal processes interact with relevant habitat heterogeneity. We provide an empirical example from a metapopulation of round-tailed muskrats (Neofiber alleni) in which habitat quality of suitable patches was spatially autocorrelated most strongly within 1,000 m, which was within the expected dispersal range of the species. After controlling for factors typically considered in metapopulation studies—patch size, local patch quality, patch connectivity—we use a cross-variogram analysis to demonstrate that patch occupancy by muskrats was correlated with habitat quality across scales ≤1,171 m. We also discuss general consequences of spatial heterogeneity of habitat quality for metapopulations related to potential cross-scale interactions. We focus on spatially correlated extinctions and metapopulation persistence, hierarchical scaling of source–sink dynamics, and dispersal decisions by individuals in relation to information constraints.     

Disturbance alters habitat isolation's effect on biodiversity in aquatic microcosms

Isolated habitats generally have fewer species at local spatial scales than more connected habitats. However, over larger spatial scales, the response of species richness to variation in the degree of isolation is variable. Here, we hypothesized that the effects of habitat isolation on patterns of regional level species richness may depend at least in part on the level of disturbances those habitats receive. We tested this hypothesis in a microcosm experiment using an aquatic community consisting of container dwelling protists and rotifers by manipulating disturbance and dispersal to experimental regions factorially. In disturbed regions, regional species richness was lower in regions with isolated patches compared to regions where patches were experimentally connected by dispersal. A likely mechanism for this result is that dispersal from adjacent undisturbed local patches allowed disturbance-intolerant species a temporary refugia, thereby allowing regional coexistence of disturbance-tolerant and intolerant species. In contrast, without disturbances (and thus no temporal heterogeneity) it is likely that dispersal homogenized communities, leading to overall lower richness with higher dispersal. Our results emphasize the importance of simultaneously considering multiple limiting factors, disturbance and dispersal in this case, as well as the spatial scale of the response, in order to fully understand factors that control biodiversity.     

Metacommunity,mainland‐island system or island communities? Assessing the regional dynamics of plant communities in a fragmented landscape

Understanding the regional dynamics of plant communities is crucial for predicting the response of plant diversity to habitat fragmentation. However, for fragmented landscapes the importance of regional processes, such as seed dispersal among isolated habitat patches, has been controversially debated. Due to the stochasticity and rarity of among‐patch dispersal and colonization events, we still lack a quantitative understanding of the consequences of these processes at the landscape‐scale. In this study, we used extensive field data from a fragmented, semi‐arid landscape in Israel to parameterize a multi‐species incidence‐function model. This model simulates species occupancy pattern based on patch areas and habitat configuration and explicitly considers the locations and the shapes of habitat patches for the derivation of patch connectivity. We implemented an approximate Bayesian computation approach for parameter inference and uncertainty assessment. We tested which of the three types of regional dynamics – the metacommunity, the mainland‐island, or the island communities type – best represents the community dynamics in the study area and applied the simulation model to estimate the extinction debt in the investigated landscape. We found that the regional dynamics in the patch‐matrix study landscape is best represented as a system of highly isolated ‘island’ communities with low rates of propagule exchange among habitat patches and consequently low colonization rates in local communities. Accordingly, the extinction rates in the local communities are the main drivers of community dynamics. Our findings indicate that the landscape carries a significant extinction debt and in model projections 33–60% of all species went extinct within 1000 yr. Our study demonstrates that the combination of dynamic simulation models with field data provides a promising approach for understanding regional community dynamics and for projecting community responses to habitat fragmentation. The approach bears the potential for efficient tests of conservation activities aimed at mitigating future losses of biodiversity.     

The effects of spatially correlated perturbations and habitat configuration on metapopulation persistence

All natural populations are confronted with the temporal variability of their environment, and most of them occur in fragmented habitats. I use spatially explicit modeling to examine the interactive effects of habitat configuration, habitat deterioration and spatially correlated environmental perturbations on the viability of fragmented populations. When considering a fixed amount of habitat, viability is maximized for an intermediate (optimal) density of habitat patches, allowing effective dispersal without strong environmental correlation among patches. Starting from this optimal density, I show that the scale of habitat change (density reduction vs range contraction) interacts with the direction of change (reduction vs improvement of habitat availability). An improvement in habitat availability is always more beneficial if occurring through an increase of the species range, while a reduction in habitat availability is always more critical if occurring through a reduction of patch density (even in the presence of environmental correlation). In the context of the 'single large or several small' debate in reserve design, results indicate that a large number of small patches may be optimal to long-term species persistence if the species range increases with the number of patches.     

Is the matrix a sea? Habitat specificity in a naturally fragmented landscape

Abstract.  1. Metapopulation and island biogeography theory assume that landscapes consist of habitat patches set in a matrix of non-habitat. If only a small proportion of species conform to the patch–matrix assumptions then metapopulation theory may only describe special cases rather than being of more general ecological importance.
2. As an initial step towards understanding the prevalence of metapopulation dynamics in a naturally fragmented landscape, the distribution of beetle species in three replicates of three habitat types was examined, including rainforest and eucalypt forest (the habitat patches), and buttongrass sedgeland (the matrix), in south-west Tasmania, Australia.
3. Ordination methods indicated that the buttongrass fauna was extremely divergent from the fauna of forested habitats. Permutation tests showed that the abundance of 13 of 17 commonly captured species varied significantly among habitats, with eight species confined to eucalypts or rainforest, and three species found only in buttongrass. Approximately 60% of species were confined to forested habitat implying that metapopulation theory has the potential to be very important in the forest–buttongrass landscape.
4. Although floristically the rainforest and eucalypts were extremely distinct, the beetle faunas from eucalypts and rainforests overlapped substantially. Therefore rainforest patches connected by eucalypt forest represent continuous habitat for most species.
5. Other studies report a wide range of values for the proportion of patch-specific species in fragmented landscapes. Understanding the environmental or historical conditions under which a high proportion of species become patch specialists would help to identify where spatial dynamic theory may be especially applicable, and where habitat loss and fragmentation poses the greatest threat to biodiversity.     

Home Range,Movement, and Distribution Patterns of the Threatened Dragonfly Sympetrum depressiusculum (Odonata: Libellulidae): A Thousand Times Greater Territory to Protect?

Dragonflies are good indicators of environmental health and biodiversity. Most studies addressing dragonfly ecology have focused on the importance of aquatic habitats, while the value of surrounding terrestrial habitats has often been overlooked. However, species associated with temporary aquatic habitats must persist in terrestrial environments for long periods. Little is known about the importance of terrestrial habitat patches for dragonflies, or about other factors that initiate or influence dispersal behaviour. The aim of this study was to reveal the relationship between population dynamics of the threatened dragonfly species Sympetrum depressiusculum at its natal site and its dispersal behaviour or routine movements within its terrestrial home range. We used a mark–release–recapture method (marking 2,881 adults) and exuviae collection with the Jolly–Seber model and generalized linear models to analyse seasonal and spatial patterns of routine movement in a heterogeneous Central European landscape. Our results show that utilisation of terrestrial habitat patches by adult dragonflies is not random and may be relatively long term (approximately 3 mo). Adult dragonflies were present only in areas with dense vegetation that provided sufficient resources; the insects were absent from active agricultural patches (p = 0.019). These findings demonstrate that even a species tightly linked to its natal site utilises an area that is several orders of magnitude larger than the natal site. Therefore, negative trends in the occurrence of various dragonfly species may be associated not only with disturbances to their aquatic habitats, but also with changes in the surrounding terrestrial landscape.     

Identifying refugia and corridors under climate change conditions for the Sichuan snub‐nosed monkey (Rhinopithecus roxellana) in Hubei Province,China

Using a case study of an isolated management unit of Sichuan snub‐nosed monkey (Rhinopithecus roxellana), we assess the extent that climate change will impact the species’ habitat distribution in the current period and projected into the 2050s. We identify refugia that could maintain the population under climate change and determine dispersal paths for movement of the population to future suitable habitats. Hubei Province, China. We identified climate refugia and potential movements by integrating bioclimatic models with circuit theory and least‐cost model for the current period (1960–1990) and the 2050s (2041–2060). We coupled a maximum entropy algorithm to predict suitable habitat for the current and projected future periods. Suitable habitat areas that were identified during both time periods and that also satisfied home range and dispersal distance conditions were delineated as refugia. We mapped potential movements measured as current flow and linked current and future habitats using least‐cost corridors. Our results indicate up to 1,119 km² of currently suitable habitat within the study range. Based on our projections, a habitat loss of 67.2% due to climate change may occur by the 2050s, resulting in a reduced suitable habitat area of 406 km² and very little new habitat. The refugia areas amounted to 286 km² and were located in Shennongjia National Park and Badong Natural Reserve. Several connecting corridors between the current and future habitats, which are important for potential movements, were identified. Our assessment of the species predicted a trajectory of habitat loss following anticipated future climate change. We believe conservation efforts should focus on refugia and corridors when planning for future species management. This study will assist conservationists in determining high‐priority regions for effective maintenance of the endangered population under climate change and will encourage increased habitat connectivity.     

Contrasting demographic and genetic estimates of dispersal in the endangered Coahuilan box turtle: a contemporary approach to conservation

The evolutionary viability of an endangered species depends upon gene flow among subpopulations and the degree of habitat patch connectivity. Contrasting population connectivity over ecological and evolutionary timescales may provide novel insight into what maintains genetic diversity within threatened species. We employed this integrative approach to evaluating dispersal in the critically endangered Coahuilan box turtle (Terrapene coahuila) that inhabits isolated wetlands in the desert‐spring ecosystem of Cuatro Ciénegas, Mexico. Recent wetland habitat loss has altered the spatial distribution and connectivity of habitat patches; and we therefore predicted that T. coahuila would exhibit limited movement relative to estimates of historic gene flow. To evaluate contemporary dispersal patterns, we employed mark–recapture techniques at both local (wetland complex) and regional (intercomplex) spatial scales. Gene flow estimates were obtained by surveying genetic variation at nine microsatellite loci in seven subpopulations located across the species’ geographical range. The mark–recapture results at the local spatial scale reveal frequent movement among wetlands that was unaffected by interwetland distance. At the regional spatial scale, dispersal events were relatively less frequent between wetland complexes. The complementary analysis of population genetic substructure indicates strong historic gene flow (global F_ST = 0.01). However, a relationship of genetic isolation by distance across the geographical range suggests that dispersal limitation exists at the regional scale. Our approach of contrasting direct and indirect estimates of dispersal at multiple spatial scales in T. coahuila conveys a sustainable evolutionary trajectory of the species pending preservation of threatened wetland habitats and a range‐wide network of corridors.     

Characterizing the importance of habitat patches in maintaining landscape connectivity for Tibetan antelope in the Altun Mountain National Nature Reserve,China

Connectivity of habitat patches is crucial for wildlife dispersal and survival, and identifying patches with high importance for maintaining connectivity can aid effective wildlife management. Knowledge of the habitat distribution of the Tibetan antelope in the Altun Mountain National Nature Reserve, which is essential for connectivity analysis, remains limited. We analyzed potential habitat distribution and priority patches using GIS-based habitat suitability modeling with three weighting factors and evaluated the connectivity of habitat patches under four dispersal distance scenarios. Patches with high habitat suitability covered 25.39 % of the total area, and these patches were selected for connectivity analysis as resource patches. Connectivity analysis indicated that, although the overall probability of connectivity (PC) showed an upward trend with increasing dispersal distance, the importance of each patch varied considerably under different dispersal distance scenarios. Transfer analysis of patch numbers between different importance levels revealed that the number of patches becoming less important was higher than the number of patches becoming more important when dispersal distance increased. In addition, nine patches covering 38.49 % of the suitable habitat area were identified as priority patches, in particular the patches near the Kardun and the Karchuka inspection stations. We also found that the habitat distribution of the Tibetan antelope obtained from the suitability model matched the population distribution determined by a field survey. Correlation analysis between patch area and the percentage of PC index value loss (dPC) revealed that the larger patches in this region were more likely to be important for maintaining connectivity.     

Identifying potential conservation areas in the Cuitzeo Lake basin,Mexico by multitemporal analysis of landscape connectivity

Lake Cuitzeo basin is an important ecological area subjected to strong human pressure on forest covers that are key elements for the long-term support of biodiversity. We studied landscape connectivity changes for the years 1975, 1996, 2000, 2003 and 2008 to identify potential conservation areas in the basin. We modeled potential distributions of the Mexican bobcat (Lynx rufus escuinapae) and the ringtail (Bassariscus astutus) – two terrestrial mammal focal species with contrasting dispersal capacities – and we determined their habitat availability and suitability in the basin. We then identified their optimal habitat patches and produced landscape cumulative resistance maps, estimated least-cost paths (graph theory approach), and elaborated current flow maps (circuit theory approach). For evaluation of landscape connectivity, we applied an integral index of connectivity (IIC) to each study period, and determined individual habitat patch contribution to the overall landscape connectivity. The IIC index had very low values associated with reduced availability of focal species habitat. However, our study showed the conservation importance of the surface of optimal habitat patch areas. The combined application of a graph-based approach and current flow mapping were useful, and complementary both in terms of estimating potential dispersal corridors and identifying high probability dispersal areas. This indicated that landscape connectivity analysis is a useful tool for identification of potential conservation areas and for local landscape planning.     

The future distribution of river fish: The complex interplay of climate and land use changes,species dispersal and movement barriers

The future distribution of river fishes will be jointly affected by climate and land use changes forcing species to move in space. However, little is known whether fish species will be able to keep pace with predicted climate and land use‐driven habitat shifts, in particular in fragmented river networks. In this study, we coupled species distribution models (stepwise boosted regression trees) of 17 fish species with species‐specific models of their dispersal (fish dispersal model FIDIMO) in the European River Elbe catchment. We quantified (i) the extent and direction (up‐ vs. downstream) of predicted habitat shifts under coupled “moderate” and “severe” climate and land use change scenarios for 2050, and (ii) the dispersal abilities of fishes to track predicted habitat shifts while explicitly considering movement barriers (e.g., weirs, dams). Our results revealed median net losses of suitable habitats of 24 and 94 river kilometers per species for the moderate and severe future scenarios, respectively. Predicted habitat gains and losses and the direction of habitat shifts were highly variable among species. Habitat gains were negatively related to fish body size, i.e., suitable habitats were projected to expand for smaller‐bodied fishes and to contract for larger‐bodied fishes. Moreover, habitats of lowland fish species were predicted to shift downstream, whereas those of headwater species showed upstream shifts. The dispersal model indicated that suitable habitats are likely to shift faster than species might disperse. In particular, smaller‐bodied fish (<200 mm) seem most vulnerable and least able to track future environmental change as their habitat shifted most and they are typically weaker dispersers. Furthermore, fishes and particularly larger‐bodied species might substantially be restricted by movement barriers to respond to predicted climate and land use changes, while smaller‐bodied species are rather restricted by their specific dispersal ability.     

Models of Regional Habitat Quality and Connectivity for Pumas (Puma concolor) in the Southwestern United States

The impact of landscape changes on the quality and connectivity of habitats for multiple wildlife species is of global conservation concern. In the southwestern United States, pumas (Puma concolor) are a well distributed and wide-ranging large carnivore that are sensitive to loss of habitat and to the disruption of pathways that connect their populations. We used an expert-based approach to define and derive variables hypothesized to influence the quality, location, and permeability of habitat for pumas within an area encompassing the entire states of Arizona and New Mexico. Survey results indicated that the presence of woodland and forest cover types, rugged terrain, and canyon bottom and ridgeline topography were expected to be important predictors of both high quality habitat and heightened permeability. As road density, distance to water, or human population density increased, the quality and permeability of habitats were predicted to decline. Using these results, we identified 67 high quality patches across the study area, and applied concepts from electronic circuit theory to estimate regional patterns of connectivity among these patches. Maps of current flow among individual pairs of patches highlighted possible pinch points along two major interstate highways. Current flow summed across all pairs of patches highlighted areas important for keeping the entire network connected, regardless of patch size. Cumulative current flow was highest in Arizona north of the Colorado River and around Grand Canyon National Park, and in the Sky Islands region owing to the many small habitat patches present. Our outputs present a first approximation of habitat quality and connectivity for dispersing pumas in the southwestern United States. Map results can be used to help target finer-scaled analyses in support of planning efforts concerned with the maintenance of puma metapopulation structure, as well as the protection of landscape features that facilitate the dispersal process.     

Clustered or scattered? The impact of habitat quality clustering on establishment and early spread

The match between the environmental conditions of an introduction area and the preferences of an introduced species is the first prerequisite for establishment. Yet, introduction areas are usually landscapes, i.e. heterogeneous sets of habitats that are more or less favourable to the introduced species. Because individuals are able to disperse after their introduction, the quality of the habitat surrounding the introduction site is as critical to the persistence of introduced populations as the quality of the introduction site itself. Moreover, demographic mechanisms such as Allee effects or dispersal mortality can hamper dispersal and affect spread across the landscape, in interaction with the spatial distribution of favourable habitat patches. In this study, we investigate the impact of the spatial distribution of heterogeneous quality habitats on establishment and early spread. First, we simulated introductions in one‐dimensional landscapes for different dispersal rates and either dispersal mortality or Allee effects. The landscapes differed by the distribution of favourable and less favourable habitats, which were either clustered into few large aggregates of the same quality or scattered into multiple smaller ones. Second, we tested the predictions of simulations by performing experimental introductions of hymenopteran parasitoids (Trichogramma chilonis) in ‘clustered’ and ‘scattered’ microcosm landscapes. Results highlighted two impacts of the clustering of favourable habitat: by decreasing the risks of dispersal from the introduction site to unfavourable habitat early during the invasion, it increased establishment success. However, by increasing the distance between favourable habitat patches, it also hindered the subsequent spread of introduced species over larger areas.     

The genetic structure of populations of Metrioptera bicolor in a spatially structured landscape: effects of dispersal barriers and geographic distance

The stability and long-term survival of animal populations in fragmented landscapes largely depends on the colonisation of habitat patches and the exchange of individuals between patches. The degree of inter-patch dispersal, in turn, depends on the dispersal abilities of species and the landscape structure (i.e. the nature of the landscape matrix and habitat distribution). Here, we investigated the genetic structure of populations of Metrioptera bicolor, a wing-dimorphic bush cricket, in a spatially structured landscape with patches of suitable habitat distributed within a diverse matrix of different habitat types. Using six microsatellite markers, we assessed the effects of geographic distance and different matrix types on the extent of genetic differentiation among 24 sampling sites. We found that forest and a river running through the study area both impede inter-patch dispersal. The presence of these two matrix types was positively correlated with the extent of genetic differentiation between sites. In addition, we found a significant positive correlation between pairwise genetic and geographic distances for a subsample of sites which were separated only by arable land or settlements. For the complete data set, this correlation could not be found. This is most probably because the adverse effect of forest and river on gene flow dominates the effect of geographic distance in our limited set of patches. Our analyses clearly emphasize the differential resistance of different habitat types on dispersal and the importance of a more detailed view on matrix “quality” in metapopulation studies.     

Single large AND several small habitat patches: A community perspective on their importance for biodiversity

The debate whether single large or several small (SLOSS) patches benefit biodiversity has existed for decades, but recent literature provides increasing evidence for the importance of small habitats. Possible beneficial mechanisms include reduced presence of predators and competitors in small habitat areas or specific functions such as stepping stones for dispersal. Given the increasing amount of studies highlighting individual behavioral differences that may influence these functions, we hypothesize that the advantage of small versus large habitat patches not only depends on patch functionality but also on the presence of animal personalities (i.e., risk-tolerant vs. risk-averse). Using an individual-based, spatially-explicit community model, we analyzed the diversity of mammal communities in landscapes consisting of a few large habitat islands interspersed with different amounts and sizes of small habitat patches. Within these heterogeneous environments, individuals compete for resources and form home-ranges, with only risk-tolerant individuals using habitat edges. Results show that when risk-tolerant individuals exist, small patches increase species diversity. A strong peak occurs at approximately 20% habitat cover in small patches when those small habitats are only used for foraging but not for breeding and home-range core position. Additional usage as stepping stones for juvenile dispersal further increases species persistence. Overall, our results reveal that a combination of a few large and several small habitat patches promotes biodiversity by enhancing landscape heterogeneity. Here, heterogeneity is created by pronounced differences in habitat functionality, increasing edge density, and variability in habitat use by different behavioral types. The finding that a combination of single large AND several small (SLASS) patches is needed for effective biodiversity preservation has implications for advancing landscape conservation. Particularly in structurally poor agricultural areas, modern technology enables precise management with the opportunity to create small foraging habitats by excluding less profitable agricultural land from cultivation.