Multiple events determine the distribution of fishes' early life stages in the Abrolhos Bank, Southwestern Atlantic

Fluctuations in reef fish settlement and recruitment significantly impact local population dynamics and adult population size. We use light traps to evaluate reef fish settlement in inshore and offshore reefs in the Abrolhos Bank, in addition to the spatio-temporal distribution patterns, and environmental variables' influence. Data were collected from inshore and offshore reefs, and statistical analyses, including GLMs, PERMANOVA and nMDS, aimed to understand spatial-temporal species distribution patterns and the relationship between environmental variables. Results indicate greater species abundance and diversity offshore, influenced by winds, tides, and distance from shore, explaining 50% of larval patterns and highlighting the importance of spatial-temporal variations in early-life reef fish assemblages. However, several factors, including habitat type, quality, complexity, seascape configuration, and MPA location, may influence these patterns. Additionally, we provide evidence that commercially important species like Lutjanids use Abrolhos reef areas as nursery grounds.

White-Toothed Shrews (Genus Crocidura): Potential Reservoirs for Zoonotic Leptospira spp. and Arthropod-Borne Pathogens?

Three species of white-toothed shrews of the order Eulipotyphla are present in central Europe: the bicolored (Crocidura leucodon), greater (Crocidura russula) and lesser (Crocidura suaveolens) white-toothed shrews. Their precise distribution in Germany is ill-defined and little is known about them as reservoirs for zoonotic pathogens (Leptospira spp., Coxiella burnetii, Brucella spp., Anaplasma phagocytophilum, Babesia spp., Neoehrlichia mikurensis and Bartonella spp.). We investigated 372 Crocidura spp. from Germany (n = 341), Austria (n = 18), Luxembourg (n = 2) and Slovakia (n = 11). West European hedgehogs (Erinaceus europaeus) were added to compare the presence of pathogens in co-occurring insectivores. Crocidura russula were distributed mainly in western and C. suaveolens mainly in north-eastern Germany. Crocidura leucodon occurred in overlapping ranges with the other shrews. Leptospira spp. DNA was detected in 28/227 C. russula and 2/78 C. leucodon samples. Further characterization revealed that Leptospira kirschneri had a sequence type (ST) 100. Neoehrlichia mikurensis DNA was detected in spleen tissue from 2/213 C. russula samples. Hedgehogs carried DNA from L. kirschneri (ST 100), L. interrogans (ST 24), A. phagocytophilum and two Bartonella species. This study improves the knowledge of the current distribution of Crocidura shrews and identifies C. russula as carrier of Leptospira kirschneri. However, shrews seem to play little-to-no role in the circulation of the arthropod-borne pathogens investigated.

Assessing the Effects of Landscape Change on the Occupancy Dynamics of the Greater White-Toothed Shrew Crocidura russula

Land-use change is the main driver of biodiversity loss in the Mediterranean basin. New socio-economic conditions produced a rewilding process so that cultural landscapes are being invaded by more natural habitats. We analyze the effects of landscape change on the demography and the spatial distribution of Crocidura russula in six protected areas of the western Mediterranean basin. The study was conducted in the period 2008–2020 on 19 live trapping plots representing the three main natural habitats of the area (scrubland, pinewood, and holm oak woodland). We used a multiscale approach to ensure that the scale of response matched landscape structure (from plot to landscape) using either vegetation profiles (LiDAR) and land use data obtained from years 2007 and 2017. Statistical models (multiple-season single-species occupancy models) showed that C. russula populations were strongly associated to habitat features at the plot level. These models were used to predict occupancy at sampling units for the whole study area (850 km²), showing contrasting trends that shifted at relatively small spatial scales (expansions and retractions of species ranges). Parks showing extreme scrubland encroachment (−8% of area) and afforestation (+6%) significantly reduced habitat suitability for shrews and reductions in occupancy (−5%). Results would indicate faster changes in the spatial distribution of the target species than previously expected on the basis of climate change, driven by fast landscape changes.

When ecological marginality is not geographically peripheral: exploring genetic predictions of the centre-periphery hypothesis in the endemic plant Lilium pomponium

Background

Quantifying variation of genetic traits over the geographical range of species is crucial for understanding the factors driving their range dynamics. The center-periphery hypothesis postulates, and many studies support, the idea that genetic diversity decreases and genetic differentiation increases toward the geographical periphery due to population isolation. The effects of environmental marginality on genetic variation has however received much less attention.

Methods

We tested the concordance between geographical and environmental gradients and the genetic predictions of center-periphery hypothesis for endemic Lilium pomponium in the southern Alps.

Results

We found little evidence for concordance between genetic variation and both geographical and environmental gradients. Although the prediction of increased differentiation at range limits is met, genetic diversity does not decrease towards the geographical periphery. Increased differentiation among peripheral populations, that are not ecologically marginal, may be explained by a decrease in habitat availability that reduces population connectivity. In contrast, a decrease of genetic diversity along environmental but not geographical gradients may be due to the presence of low quality habitats in the different parts of the range of a species that reduce effective population size or increase environmental constraints. As a result, environmental factors may affect population dynamics irrespective of distance from the geographical center of the range. In such situations of discordance between geographical and environmental gradients, the predictions of decreasing genetic diversity and increasing differentiation toward the geographical periphery may not be respected.

Population dynamics of small endotherms under global change: Greater white-toothed shrews Crocidura russula in Mediterranean habitats

Small endotherms would be especially exposed to main global change drivers (habitat and climate changes) but would also be able to withstand them by adjusting population dynamics locally to changing climate- and habitat-driven food and predation conditions. We analyse the relative importance of changes in climate (mean and variability, including relevant time-lags) and habitat conditions on the abundance, age structure and growth rate of Mediterranean populations of a small endotherm, the greater white-toothed shrew Crocidura russula, along a 10-year period (2008-2017). Habitat type and season were the key factors shaping shrew population dynamics, which showed consistent peak numbers in open habitats in autumn, after the spring-summer reproductive period. Significant increases in aridity (increasing temperature and decreasing rainfall) along the study period did not explain variation in shrew numbers, although short-term variations in abundance were negatively related to relative air humidity and temperature over three last months prior to the surveys. Overall, ongoing climate change have not yet affected shrew population dynamics in its core areas of the Mediterranean region, in spite of expectations based on climate change rate in this region and small endotherm sensitivity to these changes. Reliance on open habitats with lower predation pressure would explain the resilience of shrew populations to climate change. However, current trends of land use change (land abandonment and afforestation) threaten Mediterranean open habitats, so that resilience would not last for long if these trends are not counteracted.

Spatial ecology of the quokka (Setonix brachyurus) in the southern forests of Western Australia: implications for the maintenance, or restoration, of functional metapopulations

We used radio-telemetry to investigate the home-range size and movement patterns of the quokka (Setonix brachyurus) in the southern forests of Western Australia to assess the ability of animals to move between increasingly segregated habitat patches and to identify implications for metapopulation function. We found that quokkas in this region have a much larger home range (71 ± 5.8 ha) and move larger distances (up to 10 km per night) than previously reported for this species in other regions. Temporal and sex variations in home-range size, overlap and movement patterns provided insights into the social structure, reproductive strategies and resource availability for the species in this part of its range. Quokkas moved up to 14 km between habitat patches, where these patches were connected by dense riparian vegetation. While riparian vegetation was used exclusively for movement between habitat patches, quokkas spent only 40% of their time in this ecotype. The current management paradigm of protecting linear riparian vegetation as habitat for quokkas is important for maintaining habitat connectivity, but is unlikely to meet broader habitat and spatial requirements. Management of preferred habitat as well as riparian corridors is necessary for the maintenance of a functional metapopulation.

Hierarchical habitat-use by an endangered steppe bird in fragmented landscapes is associated with large connected patches and high food availability

Multidimensional approaches must be employed when addressing habitat use patterns. In this study, we aim to elucidate the hierarchical nature of space use by species inhabiting fragmented landscapes, using the threatened Dupont’s lark (Chersophilus duponti). The intensity of space use by Dupont’s lark was estimated using the Kernel Density Function on territory locations in 2015. We measured descriptors of habitat quality at metapopulation (connectivity and patch size), landscape (land-use types and anthropogenic disturbance) and microhabitat-scale (plant structure and composition, herbivore abundance and food availability) at 37 sampling stations. We fitted a Partial Least Squares Regression (PLSR) which yielded two components, accounting for 81% of total variance. Metapopulation-scale factors had the greatest explanatory power (32%), followed by microhabitat (17%) landscape (10%) and spatial predictors (3.6%). Connectivity and patch size were key factors explaining habitat use, and wind farms had a negative effect. At microhabitat-scale, space use was positively associated with Coleoptera, Orthoptera, Araneae and Diptera biomass, but negatively with Formicidae and Blattodea biomass, the cover of Stipa spp, Koeleria vallesiana and moss. This research highlights the hierarchical nature of habitat use in fragmented landscapes. Therefore, conservation measures should ensure connectivity, guarantee a minimum patch size, and improve habitat quality within patches.

Stressful living in lower-quality habitats? Body mass, feeding behavior and physiological stress levels in wild wood mouse populations

Wild populations are continuously subjected to changes in environmental factors that pose different challenges. Body condition and hormones have been commonly used as health indicators due to their potential correlation with fitness. In the present study, we analyzed whether habitats of different quality influenced body mass, food intake and physiological stress levels in wild wood mice (Apodemus sylvaticus). Field work was seasonally carried out in Holm oak woods and pine forests in central Spain. A total of 93 wood mice from 4 different populations (2 per habitat type) were live-trapped. From each captured individual we noted body mass and food intake, measured as the amount of bait remaining in each trap. The physiological stress levels were measured non-invasively in collected fresh feces by quantifying fecal corticosterone metabolites (FCM) with a 5a-pregnane-3ß,11ß, 21-triol-20-one enzyme immunoassay. Wood mice abundances decreased from spring to summer, were higher in Holm oak woods than in pine forests and also resulted in different age-class distribution between both habitats. Individuals inhabiting pine forests showed a lower body mass and increased food intake, probably because of the comparatively lower food quality and availability in this habitat. Furthermore, these individuals showed increased physiological stress levels, likely due to the lower quality habitat in relation to both food and vegetation cover availability. Overall, besides affecting local wood mouse abundance, our study underscores the effect of habitat quality on body mass, food intake and the endocrine stress response. Considering the wood mouse's pivotal position in ecosystems, these results could help in the understanding of environmental traits hampering the viability of wild populations.

Influence of local and landscape factors on distributional dynamics: a species-centred, fitness-based approach

In spatially structured populations, distributional dynamics are driven by the quantity, connectivity and quality of habitat. Because these drivers are rarely measured directly and simultaneously at relevant scales, information on their relative importance remains unclear. I assessed the influence of both direct and indirect measures of local habitat quality, and of landscape habitat amount and connectivity on long-term territory occupancy dynamics of non-migratory pygmy owls. Direct measures of local habitat quality based on territory-specific reproductive output had greater effects on distribution than landscape factors, but only when spatio-temporal fluxes in performance linked to environmental stochasticity and intraspecific competition were considered. When habitat quality was measured indirectly based on habitat structure, however, landscape factors had greater effects. Although all landscape factors were important, measures of landscape connectivity that were uncorrelated with habitat amount and based on attributes of matrix structure and habitat configuration that influence dispersal movements had greater effects than habitat effective area (amount weighted by quality). Moreover, the influence of connectivity (but not habitat effective area) depended on local habitat quality. Such results suggest the relative importance of local habitat quality in driving distribution has been underestimated and that conservation strategies should vary spatially depending on both local and landscape contexts.

Variability in primary productivity determines metapopulation dynamics

Temporal variability in primary productivity can change habitat quality for consumer species by affecting the energy levels available as food resources. However, it remains unclear how habitat-quality fluctuations may determine the dynamics of spatially structured populations, where the effects of habitat size, quality and isolation have been customarily assessed assuming static habitats. We present the first empirical evaluation on the effects of stochastic fluctuations in primary productivity—a major outcome of ecosystem functions—on the metapopulation dynamics of a primary consumer. A unique 13-year dataset from an herbivore rodent was used to test the hypothesis that inter-annual variations in primary productivity determine spatiotemporal habitat occupancy patterns and colonization and extinction processes. Inter-annual variability in productivity and in the growing season phenology significantly influenced habitat colonization patterns and occupancy dynamics. These effects lead to changes in connectivity to other potentially occupied habitat patches, which then feed back into occupancy dynamics. According to the results, the dynamics of primary productivity accounted for more than 50% of the variation in occupancy probability, depending on patch size and landscape configuration. Evidence connecting primary productivity dynamics and spatiotemporal population processes has broad implications for metapopulation persistence in fluctuating and changing environments.

Invading and expanding: range dynamics and ecological consequences of the greater white-toothed shrew (Crocidura russula) invasion in Ireland

Establishing how invasive species impact upon pre-existing species is a fundamental question in ecology and conservation biology. The greater white-toothed shrew (Crocidura russula) is an invasive species in Ireland that was first recorded in 2007 and which, according to initial data, may be limiting the abundance/distribution of the pygmy shrew (Sorex minutus), previously Ireland's only shrew species. Because of these concerns, we undertook an intensive live-trapping survey (and used other data from live-trapping, sightings and bird of prey pellets/nest inspections collected between 2006 and 2013) to model the distribution and expansion of C. russula in Ireland and its impacts on Ireland's small mammal community. The main distribution range of C. russula was found to be approximately 7,600 km² in 2013, with established outlier populations suggesting that the species is dispersing with human assistance within the island. The species is expanding rapidly for a small mammal, with a radial expansion rate of 5.5 km/yr overall (2008–2013), and independent estimates from live-trapping in 2012–2013 showing rates of 2.4–14.1 km/yr, 0.5–7.1 km/yr and 0–5.6 km/yr depending on the landscape features present. S. minutus is negatively associated with C. russula. S. minutus is completely absent at sites where C. russula is established and is only present at sites at the edge of and beyond the invasion range of C. russula. The speed of this invasion and the homogenous nature of the Irish landscape may mean that S. minutus has not had sufficient time to adapt to the sudden appearance of C. russula. This may mean the continued decline/disappearance of S. minutus as C. russula spreads throughout the island.

Recolonisation of rabbit warrens following coordinated ripping programs in Victoria, south-eastern Australia

Context Warren ripping has been demonstrated to be an effective tool for controlling rabbit populations. However, few studies have examined factors influencing the rate at which ripped warrens are likely to be recolonised (i.e. be re-opened). Aims To examine factors influencing the recolonisation of ripped warrens by rabbits by using data collected on 555 warrens for up to 15 years following coordinated ripping programs at 12 sites in Victoria, south-eastern Australia. Methods Warren-monitoring data (number of active and inactive warren entrances) were analysed using discrete-time survival analysis to determine the effects of warren-level and site-level covariates on the recolonisation of ripped warrens. Key results Warren recolonisation was related to the distance between the ripped warren and the nearest active warren, the number of active entrances in the nearest warren, the initial number of active entrances in the ripped warren and the rabbit spotlight abundance index at the site. The probability of warren recolonisation was highest for ripped warrens within 1 km of an active warren and negligible beyond 3 km. The probability of warren recolonisation also increased by 22% for every increase in the rabbit spotlight count at the site by 10 rabbits km–1. Conclusions The recolonisation of ripped warrens was highly influenced by both the distance to, and size of, neighbouring active warrens. Larger warrens also appear to be preferentially recolonised compared with smaller warrens, suggesting that recolonisation of ripped areas may be related to habitat quality. The present results are consistent with ideas from classical metapopulation theory predicting that the rates of colonisation of vacant patches are dependent on both the proximity and size of the source population as well as the quality of habitat patches. Implications Although coordinated warren ripping programs are effective at achieving long-term control of rabbits, their efficiency at maintaining low rabbit populations can be increased by adopting an adaptive monitoring program that incorporates warren size and the spatial relationships among warrens, and using this information to better target maintenance-control activities.

Matrix matters: differences of grand skink metapopulation parameters in native tussock grasslands and exotic pasture grasslands

Modelling metapopulation dynamics is a potentially very powerful tool for conservation biologists. In recent years, scientists have broadened the range of variables incorporated into metapopulation modelling from using almost exclusively habitat patch size and isolation, to the inclusion of attributes of the matrix and habitat patch quality. We investigated the influence of habitat patch and matrix characteristics on the metapopulation parameters of a highly endangered lizard species, the New Zealand endemic grand skink (Oligosoma grande) taking into account incomplete detectability. The predictive ability of the developed zxmetapopulation model was assessed through cross-validation of the data and with an independent data-set. Grand skinks occur on scattered rock-outcrops surrounded by indigenous tussock (bunch) and pasture grasslands therefore implying a metapopulation structure. We found that the type of matrix surrounding the habitat patch was equally as important as the size of habitat patch for estimating occupancy, colonisation and extinction probabilities. Additionally, the type of matrix was more important than the physical distance between habitat patches for colonisation probabilities. Detection probability differed between habitat patches in the two matrix types and between habitat patches with different attributes such as habitat patch composition and abundance of vegetation on the outcrop. The developed metapopulation models can now be used for management decisions on area protection, monitoring, and the selection of translocation sites for the grand skink. Our study showed that it is important to incorporate not only habitat patch size and distance between habitat patches, but also those matrix type and habitat patch attributes which are vital in the ecology of the target species.

Determinants of extinction-colonization dynamics in Mediterranean butterflies: the role of landscape, climate and local habitat features

Many species are found today in the form of fragmented populations occupying patches of remnant habitat in human-altered landscapes. The persistence of these population networks requires a balance between extinction and colonization events assumed to be primarily related to patch area and isolation, but the contribution of factors such as the characteristics of patch and matrix habitats, the species' traits (habitat specialization and dispersal capabilities) and variation in climatic conditions have seldom been evaluated simultaneously. The identification of environmental variables associated with patch occupancy and turnover may be especially useful to enhance the persistence of multiple species under current global change. However, for robust inference on occupancy and related parameters, we must account for detection errors, a commonly overlooked problem that leads to biased estimates and misleading conclusions about population dynamics. Here, we provide direct empirical evidence of the effects of different environmental variables on the extinction and colonization rates of a rich butterfly community in the western Mediterranean. The analysis was based on a 17-year data set containing detection/nondetection data on 73 butterfly species for 26 sites in north-eastern Spain. Using multiseason occupancy models, which take into account species' detectability, we were able to obtain robust estimates of local extinction and colonization probabilities for each species and test the potential effects of site covariates such as the area of suitable habitat, topographic variability, landscape permeability around the site and climatic variability in aridity conditions. Results revealed a general pattern across species with local habitat composition and landscape features as stronger predictors of occupancy dynamics compared with topography and local aridity. Increasing area of suitable habitat in a site strongly decreased local extinction risks and, for a number of species, both higher amounts of suitable habitat and more permeable landscapes increased colonization rates. Nevertheless, increased topographic variability decreased the extinction risk of bad dispersers, a group of species with significantly lower colonization rates. Our models predicted higher sensitivity of the butterfly assemblages to deterministic changes in habitat features rather than to stochastic weather patterns, with some relationships being clearly dependent on the species' traits.

Conservation of the patchily distributed and declining purple-crowned fairy-wren (Malurus coronatus coronatus) across a vast landscape: the need for a collaborative landscape-scale approach

Conservation of species that are patchily distributed must consider processes that influence both the occurrence of individuals within patches, and the persistence of populations across multiple habitat patches within the landscape. Here we present a rare regional assessment of the population size and distribution of a patchily distributed, threatened species, the purple-crowned fairy-wren (Malurus coronatus coronatus), across a vast landscape. We used data from aerial vegetation mapping of waterways, with on-ground bird surveys to predict the occurrence of suitable habitat for M. c. coronatus across 14 catchments in the Kimberley region of Western Australia. Suitable habitat was extremely limited (305 km of riparian vegetation) and fragmented (342 patches) along the 2700 km of waterway surveyed within catchments where the species occurs. Populations were predicted to be large on the Fitzroy, Durack and Drysdale catchments, and small on the Isdell and northern Pentecost catchments, and a total population of 2834 to 4878 individuals could be supported. The sub-populations spanned numerous patches of habitat across multiple properties of varying tenure. Therefore, a landscape-scale approach to conservation management, across multiple tenures, is critical to safe-guard connectivity within populations. The greatest benefit may be achieved by a combination of broad-scale actions to reduce the impact of ubiquitous threatening processes, and fine-scale targeted effort in areas where populations are most vulnerable. Controlling access of stock to waterways and management of fire are most important to conserve suitable habitat. Such a landscape-scale approach to conservation may be of benefit to other patchily distributed species.

Effects of culling on mesopredator population dynamics

Anthropogenic changes in land use and the extirpation of apex predators have facilitated explosive growth of mesopredator populations. Consequently, many species have been subjected to extensive control throughout portions of their range due to their integral role as generalist predators and reservoirs of zoonotic disease. Yet, few studies have monitored the effects of landscape composition or configuration on the demographic or behavioral response of mesopredators to population manipulation. During 2007 we removed 382 raccoons (Procyon lotor) from 30 forest patches throughout a fragmented agricultural ecosystem to test hypotheses regarding the effects of habitat isolation on population recovery and role of range expansion and dispersal in patch colonization of mesopredators in heterogeneous landscapes. Patches were allowed to recolonize naturally and demographic restructuring of patches was monitored from 2008-2010 using mark-recapture. An additional 25 control patches were monitored as a baseline measure of demography. After 3 years only 40% of experimental patches had returned to pre-removal densities. This stagnant recovery was driven by low colonization rates of females, resulting in little to no within-patch recruitment. Colonizing raccoons were predominantly young males, suggesting that dispersal, rather than range expansion, was the primary mechanism driving population recovery. Contrary to our prediction, neither landscape connectivity nor measured local habitat attributes influenced colonization rates, likely due to the high dispersal capability of raccoons and limited role of range expansion in patch colonization. Although culling is commonly used to control local populations of many mesopredators, we demonstrate that such practices create severe disruptions in population demography that may be counterproductive to disease management in fragmented landscapes due to an influx of dispersing males into depopulated areas. However, given the slow repopulation rates observed in our study, localized depopulation may be effective at reducing negative ecological impacts of mesopredators in fragmented landscapes at limited spatial and temporal scales.

Dispersing Siberian flying squirrels (Pteromys volans) locate preferred habitats in fragmented landscapes

In fragmented landscapes, dispersal abilities determine the potential of a species to colonize temporally unoccupied habitats. For example in territorial species, even the high-quality sites will be temporally unoccupied between the death of residents and recolonization by dispersers. This has implications for conservation management, because whether or not unoccupied habitats are worthy of protecting depends on likelihood that these sites will be recolonized in the near future. We analysed the ability of dispersing Siberian flying squirrels ( Pteromys volans (L., 1758)) to locate the preferred habitats. Dispersers encountered many patches of preferred habitat and, in the end, a majority of them successfully settled in these patches. The dispersal distance increased with increasing distance between patches, but settlement in preferred patches and short-term mortality were independent of dispersal distance or distance between available patches. We conclude that dispersers were effective in locating the preferred habitat in fragmented landscapes. Indeed, large interpatch distances partly explain that dispersal distances are longer in flying squirrels than usually observed in similar-sized mammals. For conservation management, our findings encourage managers to protect temporally unoccupied, high-quality habitats in addition to occupied habitats to promote a sustainable habitat network in space and time.

Density-dependent population dynamics and dispersal in heterogeneous metapopulations

1. Metapopulation microcosms were constructed to test the effect of four different types of habitat heterogeneity on the dynamics and dispersal in spatially extended systems; homogeneity, spatial heterogeneity, temporal heterogeneity and spatio-temporal heterogeneity. Resources were distributed across discrete habitat patches in bruchid beetle (Callosobruchus maculatus) metapopulations, and long-term time series were recorded. 2. Mathematical models were fitted to the long-term time series from the experimental systems using a maximum likelihood approach. Models were composed of separate birth, death, emigration and immigration terms all of which incorporated stochasticity drawn from different probability distributions. Models with density-dependent and density-independent birth, death and emigration terms were investigated and, in each case, the model that best described the empirical data was identified. 3. At the local scale, population sizes differed between patches depending on the type of heterogeneity. Larger populations were associated with higher resource availabilities. As a result of this, the variation between local population sizes was greatest when there was spatial heterogeneity in which mean resource abundance varied from patch to patch. Variation in population sizes within patches was largest when there was temporal heterogeneity. 4. Density-dependent processes leading to the regulation of local population dynamics in our experimental systems were strongest in homogeneity or temporal heterogeneity treatments. Associated with this, we found that these systems were best described using mathematical models with density dependence acting on mortality. In contrast, spatial and spatio-temporal time series were adequately described using density-independent population processes. 5. Experimental metapopulations showed varying degrees of density-dependent dispersal. Local net dispersal each week was primarily driven by the local population size and secondarily affected by neighbourhood population density. Mathematical population models illustrated the importance of explicit description of density-dependent dispersal in all systems except the homogeneous metapopulations.