Variation of a floral polymorphism at different spatial scales in the Mediterranean geophyte Narcissus assoanus

Aims Habitat fragmentation impacts the spatial extent and isolation of local populations and communities. Although the biological consequences of these impacts have been well studied at the site level, effects directly related to changes in the spatial configuration of populations in the landscape remain less clear. The objective of this study is to examine how changes in the spatial-scale configuration of populations are associated with variability in morph rations in the floral polymorphic Mediterranean geophyte Narcissus assoanus .Methods We performed a nested analysis of morph ratio variation at three spatial scales: a 50×50 km regional scale in SE France, in fourteen 1×1 km landscapes located in the same region, and within 12 spatially extensive population patches. We also quantified variation in the behaviour of pollinators in population patches of contrasting spatial configuration.Important findings At a regional scale, morph ratios show a geographic pattern of increasing isoplethy (1:1 morph ratio) away from centres of human population development and in upland pastures. At the landscape scale, isoplethy of local population patches is more correlated with decreased isolation among patches than with patch size. Finally, within local isoplethic populations, small patches can show significantly biased morph ratios. In small isolated patches, pollinators perform shorter flight distances among consecutive flower visits than in spatially extensive patches. This study of variation in a genetic polymorphism at multiple spatial scales provides new insights into the scale-dependent effects of habitat fragmentation and the potential occurrence of metapopulation dynamics in natural plant populations.     

Anthropogenic landscape change promotes asymmetric dispersal and limits regional patch occupancy in a spatially structured bird population

1. Local extinctions in habitat patches and asymmetric dispersal between patches are key processes structuring animal populations in heterogeneous environments. Effective landscape conservation requires an understanding of how habitat loss and fragmentation influence demographic processes within populations and movement between populations. 2. We used patch occupancy surveys and molecular data for a rainforest bird, the logrunner (Orthonyx temminckii), to determine (i) the effects of landscape change and patch structure on local extinction; (ii) the asymmetry of emigration and immigration rates; (iii) the relative influence of local and between-population landscapes on asymmetric emigration and immigration; and (iv) the relative contributions of habitat loss and habitat fragmentation to asymmetric emigration and immigration. 3. Whether or not a patch was occupied by logrunners was primarily determined by the isolation of that patch. After controlling for patch isolation, patch occupancy declined in landscapes experiencing high levels of rainforest loss over the last 100 years. Habitat loss and fragmentation over the last century was more important than the current pattern of patch isolation alone, which suggested that immigration from neighbouring patches was unable to prevent local extinction in highly modified landscapes. 4. We discovered that dispersal between logrunner populations is highly asymmetric. Emigration rates were 39% lower when local landscapes were fragmented, but emigration was not limited by the structure of the between-population landscapes. In contrast, immigration was 37% greater when local landscapes were fragmented and was lower when the between-population landscapes were fragmented. Rainforest fragmentation influenced asymmetric dispersal to a greater extent than did rainforest loss, and a 60% reduction in mean patch area was capable of switching a population from being a net exporter to a net importer of dispersing logrunners. 5. The synergistic effects of landscape change on species occurrence and asymmetric dispersal have important implications for conservation. Conservation measures that maintain large patch sizes in the landscape may promote asymmetric dispersal from intact to fragmented landscapes and allow rainforest bird populations to persist in fragmented and degraded landscapes. These sink populations could form the kernel of source populations given sufficient habitat restoration. However, the success of this rescue effect will depend on the quality of the between-population landscapes.     

Habitat quality of source patches and connectivity in fragmented landscapes

Because spatial connectivity is critical to dispersal success and persistence of species in highly fragmented landscapes, the way that we envision and measure connectivity is consequential for biodiversity conservation. Connectivity metrics used for predictive modeling of spatial turnover and patch occupancy for metapopulations, such as with Incidence Function Models (IFM), incorporate distances to and sizes of possible source populations. Here, our focus is on whether habitat quality of source patches also is considered in these connectivity metrics. We propose that effective areas (weighted by habitat quality) of source patches should be better surrogates for population size and dispersal potential compared to unadjusted patch areas. Our review of a representative sample of the literature revealed that only 12.5% of studies incorporated habitat quality of source patches into IFM-type connectivity metrics. Quality of source patches generally was not taken into account in studies even if habitat quality of focal patches was included in analyses. We provide an empirical example for a metapopulation of a rare wetland species, the round-tailed muskrat (Neofiber alleni), demonstrating that a connectivity metric based on effective areas of source patches better predicts patch colonization and occupancy than a metric that used simple patch areas. The ongoing integration of landscape ecology and metapopulation dynamics could be hastened by incorporating habitat quality of source patches into spatial connectivity metrics applied to species conservation in fragmented landscapes.     

Evidence based conservation of butterflies

Few results of research aimed at solving questions arising from butterfly conservation are rigorously tested by manipulating populations and habitats in the field. Some factors common to successful conservation projects are analysed. In most non-migratory species, population density may vary by up to two orders of magnitude between sites or over time, and is primarily determined by the extent to which a subset of each species’ foodplant (or ant host) exists in the optimum growth-form or micro-habitat preferred by its larvae. Successful conservation projects have identified the optimum subset of each species’ larval resource before managing sites to increase its representation. In contrast, short-term fluctuations around a site’s carrying capacity or equilibrium level are mainly attributable to variation in weather, and are generally two orders of magnitude smaller than that attributable to larval habitat quality. There is little evidence that changing the abundance of adult resources, apart from shelter, influences population size or trends. The main constraint of the adult stage is the inability of many species to track the generation of new habitat patches that arise across modern landscapes. Within-patch larval habitat quality is again critical at the meta-population scale, explaining slightly more examples of patch occupancy than site isolation. This is because the higher density populations supported by optimum habitat are less likely to go extinct, and immigrants to new high-quality patches have a higher probability of founding new populations. Such patches may also generate up to a hundred times more emigrants per hectare than low-quality source patches.     

Potential metapopulation structure and the effects of habitat quality on population size of the endangered False Ringlet butterfly

The False Ringlet (Coenonympha oedippus) is a European butterfly species, endangered due to the severe loss and fragmentation of its habitat. In Hungary, two remaining populations of the butterfly occur in lowland Purple Moorgrass meadows. We studied a metapopulation occupying twelve habitat patches in Central Hungary. Our aim was to reveal what measures of habitat quality affect population size and density of this metapopulation, estimate dispersal parameters and describe phenology of subpopulations. Local population sizes and dispersal parameters were estimated from an extensive mark–release–recapture dataset, while habitat quality was characterized by groundwater level, cover of grass tussocks, bush cover, height of vegetation and grass litter at each habitat patch. The estimated size of the metapopulation was more than 3,000 individuals. We estimated a low dispersal capacity, especially for females, indicating a very low probability of (re)colonization. Butterfly abundance and density in local populations increased with higher grass litter, lower groundwater level and larger area covered by tussocks. We suppose that these environmental factors affect butterfly abundance by determining the microclimatic conditions for both larvae and adult butterflies. Our results suggest that the long-term preservation of the studied metapopulation needs the maintenance of high quality habitat patches by appropriate mowing regime and water regulation. Management also should facilitate dispersal to strengthen metapopulation structure with creating stepping-stones or gradually increase habitat quality in present matrix.     

Using connectivity metrics in conservation planning – when does habitat quality matter?

Aim The objective of conservation planning is often to prioritize patches based on their estimated contribution to metapopulation or metacommunity viability. The contribution that an individual patch makes will depend on its intrinsic characteristics, such as habitat quality, as well as its location relative to other patches, its connectivity. Here we systematically evaluate five patch value metrics to determine the importance of including an estimate of habitat quality into the metrics. Location We tested the metrics in landscapes designed to represent different degrees of variability in patch quality and different levels of patch aggregation. Methods In each landscape, we simulated population dynamics using a spatially explicit, continuous time metapopulation model linked to within patch logistic growth models. We tested five metrics that are used to estimate the contribution that a patch makes to metapopulation viability: two versions of the probability of connectivity index, two versions of patch centrality (a graph theory metric) and the metapopulation capacity metric. Results All metrics performed best in environments where patch quality was very variable and high quality patches were aggregated. Metrics that incorporated some measure of patch quality did better in all environments, but did particularly well in environments with high variance of patch quality and spatial aggregation of good quality patches. Main conclusions Including an estimate of patch quality significantly increased the ability of a given connectivity metric to rank correctly habitat patches according to their contribution to metapopulation viability. Incorporating patch quality is particularly important in landscapes where habitat quality is highly variable and good quality patches are spatially aggregated. However, caution should be used when applying patch metrics to homogeneous landscapes, even if good estimates of patch quality are available. Our results demonstrate that landscape structure and the degree of variability in patch quality need to be assessed prior to selecting a suitable method for estimating patch value.     

Effects of patch characteristics and isolation on relative abundance of the scarce heath butterfly <Emphasis Type="Italic">Coenonympha hero</Emphasis> (Nymphalidae)

The scarce heath (Coenonympha hero) is an internationally threatened butterfly in Western Europe, where it occurs primarily on hay fields and abandoned arable land in a small-scale agricultural landscape of south-central Scandinavia. Due to afforestation, this habitat is becoming increasingly fragmented in Sweden, and it can be expected that the scarce heath will decline abruptly when threshold conditions for metapopulation persistence are no longer met. We used stepwise polychotomous logistic regression to compare habitat characteristics and isolation measures for patches that harbour large, small or no populations, respectively, in an area of south-western Sweden. We found that patch area, distance to the nearest large population and amount of Galium spp. explained a significant part of the variation in relative abundance among patches. Distance to nearest large population resulted in a better model to predict occupancy than both distance to the nearest inhabited patch and connectivity, which suggests that primarily large populations act as sources for small satellite populations. Today, sites of three of the eight larger populations in the study area have been planted with spruce or pine and will disappear within 20 years. We argue that the disappearance of these patches may very well lead to rapid extinction of the whole metapopulation system.     

Exploring the legacy of goat grazing: signatures of habitat fragmentation on genetic patterns of endemic weevil populations in Northern Isabela Island,Galápagos (Ecuador)

Together with reduction in habitat area and quality, reduction in habitat connectivity is one of the major factors influencing species’ persistence in fragmented landscapes. We explore the consequences of recent habitat fragmentation on volcanoes across Isabela Island, Galápagos by analyzing genetic patterns of populations of endemic weevils whose host plants have been depleted by indiscriminate goat grazing. We predicted that if grazing on the weevils’ host plants has caused habitat fragmentation on the weevils populations themselves, then the effects on the genetic architecture of populations should be more severe on Galapaganus conwayensis populations from volcanoes on Northern Isabela than on those from Santa Cruz or Pinta islands where vegetation destruction was not as extensive. We used mitochondrial sequences to reveal historical colonization patterns and microsatellite variation to understand more contemporary genetic changes. We found significantly lower microsatellite genetic diversity and population size within localities and increased genetic differentiation at a small geographic scale with a stronger isolation by distance pattern and larger numbers of genetic clusters on Isabela. In the absence of long-standing mitochondrial structure within each volcano, we interpret the microsatellite results as suggesting that recent host plant habitat fragmentation may indeed influence the genetic patterns of plant feeding insects and highlight the importance of controlling the spread of introduced herbivores in the Galápagos Islands.     

Toward ecologically scaled landscape indices

Nature conservation is increasingly based on a landscape approach rather than a species approach. Landscape planning that includes nature conservation goals requires integrated ecological tools. However, species differ widely in their response to landscape change. We propose a framework of ecologically scaled landscape indices that takes into account this variation. Our approach is based on a combination of field studies of spatially structured populations (metapopulations) and model simulations in artificial landscapes. From these, we seek generalities in the relationship among species features, landscape indices, and metapopulation viability. The concept of ecological species profiles is used to group species according to characteristics that are important in metapopulations' response to landscape change: individual area requirements as the dominant characteristic of extinction risk in landscape patches and dispersal distance as the main determinant of the ability to colonize patches. The ecological profiles and landscape indices are then integrated into two ecologically scaled landscape indices (ESLI): average patch carrying capacity and average patch connectivity. The field data show that the fraction of occupied habitat patches is correlated with the two ESLI. To put the ESLI into a perspective of metapopulation persistence, we determine the viability for six ecological profiles at different degrees of habitat fragmentation using a metapopulation model and computer-generated landscapes. The model results show that the fraction of occupied patches is a good indicator for metapopulation viability. We discuss how ecological profiles, ESLI, and the viability threshold can be applied for landscape planning and design in nature conservation.     

The influence of patch demographics on metapopulations, with particular reference to successional landscapes

The classical view of metapopulations relates the regional abundance of a species to the balance between the extinction and colonization dynamics of identical local populations. Species in successional landscapes may represent the most appropriate examples of classical metapopulations. However, Levins‐type metapopulation models do not explicitly separate population loss due to successional habitat change from other causes of extinction. A further complication is that the chance of population loss due to successional habitat change may be related to the age of a patch. I developed simple patch occupancy models to include succession and included consideration of patch age structure to address two related questions: what are the implications of changes in patch demographic rates and when is a move to a structured patch occupancy model justified? Age‐related variation in patch demography could increase or decrease the equilibrium fraction of the available habitat occupied by a species when compared to the predictions of an unstructured model. Metapopulation persistence was enhanced when the age class of patches with the highest species occupancy suffered relatively low losses to habitat succession. Conversely, when the age class of patches with the highest species occupancy also had relatively high successional loss rates, extinction thresholds were higher that would be predicted by a simple unstructured model. Hence age‐related variation in patch successional rate introduces biases into the predictions of simple unstructured models. Such biases can be detected from field surveys of the fraction of occupied and unoccupied patches in each age class. Where a bias is demonstrated, unstructured models will not be adequate for making predictions about the effects of changing parameters on metapopulation size. Thinking in successional terms emphasizes how landscapes might be managed to enhance or reduce the patch occupancy by any particular metapopulation     

Drivers of local densities of endangered Lycaena helle butterflies in a fragmented landscape

Due to their specialised habitat requirements, butterflies are particularly vulnerable to habitat loss and fragmentation. Understanding the drivers of local abundances of species is essential for their effective conservation in fragmented landscapes. We investigated factors affecting population densities of an endangered European butterfly, the Violet Copper (Lycaena helle), occurring in a small metapopulation near the city of Kraków, southern Poland. The environmental parameters tested as predictors of the local densities of the species included both the variables associated with spatial structure of habitats such as patch sizes, their isolation and fragmentation as well as those potentially reflecting habitat quality. Patch area and vegetation height turned out to be the only factors significantly influencing L. helle densities, both having a positive effect. The positive impact of patch area is a bit surprising, since its relationship with population densities is typically negative in butterflies. In our study system it is likely to derive from source-sink dynamics as the smaller habitat patches are apparently too small to sustain viable local populations. In turn, the positive influence of vegetation height implies that the ongoing succession does not deteriorate the quality of the recently abandoned meadows yet, whereas higher turf may provide better sheltering places. The loss of almost half of L. helle habitat patches in the study area in recent years is alarming. However, its inclusion into the Natura 2000 system should help to conserve the species as long as this act is followed by proper management of its habitats.     

Metapopulation dynamics for spatially extended predator–prey interactions

Traditional metapopulation theory classifies a metapopulation as a spatially homogeneous population that persists on neighboring habitat patches. The fate of each population on a habitat patch is a function of a balance between births and deaths via establishment of new populations through migration to neighboring patches. In this study, we expand upon traditional metapopulation models by incorporating spatial heterogeneity into a previously studied two-patch nonlinear ordinary differential equation metapopulation model, in which the growth of a general prey species is logistic and growth of a general predator species displays a Holling type II functional response. The model described in this work assumes that migration by generalist predator and prey populations between habitat patches occurs via a migratory corridor. Thus, persistence of species is a function of local population dynamics and migration between spatially heterogeneous habitat patches. Numerical results generated by our model demonstrate that population densities exhibit periodic plane-wave phenomena, which appear to be functions of differences in migration rates between generalist predator and prey populations. We compare results generated from our model to results generated by similar, but less ecologically realistic work, and to observed population dynamics in natural metapopulations.     

Metapopulation processes and persistence in remnant water vole populations

We examined the spatial distribution of water vole populations in four consecutive years and investigated whether the regional population processes of extinction, recolonisation and migration influence distribution and persistence. We examined how such regional processes are influenced by spatial variation in habitat quality. In addition, we assessed the relevance of metapopulation concepts for understanding the dynamics of species that deviate from classical metapopulation assumptions and developing conservation measures for them. Populations were patchy and discrete, and the patchy distribution was not static between years. Population turnover occurred even in the absence of predatory mink, which only influenced the network of populations at the end of the study. Most populations were clustered close together in the upper tributaries. Local population persistence was predominantly influenced by population size: large populations were more persistent. Recolonisation rates were influenced by isolation and habitat quality. The isolation estimates which best explained the distribution of water vole populations incorporated straight‐line distances, suggesting water voles disperse overland. The distribution of recolonised sites indicated that dispersing voles actively selected habitat on the basis of its quality. Water voles depart from some of the assumptions made by frequently used metapopulation models. In particular there is no clear binary distinction between suitable and non‐suitable habitat. Accounting for variation in habitat quality before investigating temporal changes in population distribution allowed us to demonstrate that the key metapopulation processes were important. The significance of regional population processes relative to local population processes may have increased in declining, fragmented populations compared to pristine regional populations. We hypothesise that although mink predation is likely to eventually cause regional extinction in many areas, metapopulation processes have delayed this decline. Consequently, conservation measures should take into account mink predation rates and regional population processes, before considering aspects of habitat quality.     

Patch occupancy of two hemipterans sharing a common host plant

Aim Two hemipteran species were chosen as a study system for the comparative analysis of patch occupancy and spatial population structure of insects sharing a common host plant. This study tested whether (1) the incidence in the host plant patches differed between the two species, and (2) the two species exhibited a different spatial population structure, i.e. were they affected differentially by isolation and area of the host plant patches. Location The porphyry landscape north of Halle (Saale) in Germany comprising 506 patches of the host plant Brachypodium pinnatum. Methods The host plant patches were surveyed for the two hemipterans. To assess the influence of patch quality on species occurrence the patches were characterized by mean cover abundance of B. pinnatum, type of subsoil, slope, exposure, and shading. The spatial configuration of the patches was considered by patch area and isolation. The influence of the habitat factors and the spatial configuration on the occupancy of the two species was analysed by logistic regression. Results Adarrus multinotatus was found in 441 patches, while Neophilaenus albipennis was found in only 90 patches. While A. multinotatus showed virtually no relationship to the habitat factors, the occupancy of N. albipennis was influenced by subsoil type, cover abundance, and shading. The effects of area and isolation on occupancy of the patches also differed between the two species. The occupancy of N. albipennis was determined largely by area and isolation, whereas in A. multinotatus no considerable effect of spatial configuration was found. Main conclusions The study revealed a marked difference between the two hemipteran species in respect of spatial population structure. Adarrus multinotatus built up a ‘patchy population’, whereas N. albipennis showed a ‘metapopulation’ structure within the same set of patches in the same landscape. Spatial population structure was found to be not only a function of spatial configuration of habitat patches, but population structure differed between the habitat generalist A. multinotatus and the habitat specialist N. albipennis.     

Experimental beetle metapopulations respond positively to dynamic landscapes and reduced connectivity

Interactive effects of multiple environmental factors on metapopulation dynamics have received scant attention. We designed a laboratory study to test hypotheses regarding interactive effects of factors affecting the metapopulation dynamics of red flour beetle, Tribolium castaneum. Within a four-patch landscape we modified resource level (constant and diminishing), patch connectivity (high and low) and patch configuration (static and dynamic) to conduct a 2(3) factorial experiment, consisting of 8 metapopulations, each with 3 replicates. For comparison, two control populations consisting of isolated and static subpopulations were provided with resources at constant or diminishing levels. Longitudinal data from 22 tri-weekly counts of beetle abundance were analyzed using bayesian Poisson generalized linear mixed models to estimate additive and interactive effects of factors affecting abundance. Constant resource levels, low connectivity and dynamic patches yielded greater levels of adult beetle abundance. For a given resource level, frequency of colonization exceeded extinction in landscapes with dynamic patches when connectivity was low, thereby promoting greater patch occupancy. Negative density dependence of pupae on adults occurred and was stronger in landscapes with low connectivity and constant resources; these metapopulations also demonstrated greatest stability. Metapopulations in control landscapes went extinct quickly, denoting lower persistence than comparable landscapes with low connectivity. When landscape carrying capacity was constant, habitat destruction coupled with low connectivity created asynchronous local dynamics and refugia within which cannibalism of pupae was reduced. Increasing connectivity may be counter-productive and habitat destruction/recreation may be beneficial to species in some contexts.     

Area-dependent migration by ringlet butterflies generates a mixture of patchy population and metapopulation attributes

Interpretation of spatially structured population systems is critically dependent on levels of migration between habitat patches. If there is considerable movement, with each individual visiting several patches, there is one ”patchy population”; if there is intermediate movement, with most individuals staying within their natal patch, there is a metapopulation; and if (virtually) no movement occurs, then the populations are separate (Harrison 1991, 1994). These population types actually represent points along a continuum of much to no mobility in relation to patch structure. Therefore, interpretation of the effects of spatial structure on the dynamics of a population system must be accompanied by information on mobility. We use empirical data on movements by ringlet butterflies, Aphantopus hyperantus, to investigate two key issues that need to be resolved in spatially-structured population systems. First, do local habitat patches contain largely independent local populations (the unit of a metapopulation), or merely aggregations of adult butterflies (as in patchy populations)? Second, what are the effects of patch area on migration in and out of the patches, since patch area varies considerably within most real population systems, and because human landscape modification usually results in changes in habitat patch sizes? Mark-release-recapture (MRR) data from two spatially structured study systems showed that 63% and 79% of recaptures remained in the same patch, and thus it seems reasonable to call both systems metapopulations, with some capacity for separate local dynamics to take place in different local patches. Per capita immigration and emigration rates declined with increasing patch area, while the resident fraction increased. Actual numbers of emigrants either stayed the same or increased with area. The effect of patch area on movement of individuals in the system are exactly what we would have expected if A. hyperantus were responding to habitat geometry. Large patches acted as local populations (metapopulation units) and small patches simply as locations with aggregations (units of patchy populations), all within 0.5 km². Perhaps not unusually, our study system appears to contain a mixture of metapopulation and patchy-population attributes.     

Population Dynamics of the Andean Lizard Anolis heterodermus: Fast‐slow Demographic Strategies in Fragmented Scrubland Landscapes

Habitat fragmentation and loss affect population stability and demographic processes, increasing the extinction risk of species. We studied Anolis heterodermus populations inhabiting large and small Andean scrubland patches in three fragmented landscapes in the Sabana de Bogotá (Colombia) to determine the effect of habitat fragmentation and loss on population dynamics. We used the capture‐mark‐recapture method and multistate models to estimate vital rates for each population. We estimated growth population rate and the most important processes that affect λ by elasticity analysis of vital rates. We tested the effects of habitat fragmentation and loss on vital rates of lizard populations. All six isolated populations showed a positive or an equilibrium growth rate (λ = 1), and the most important demographic process affecting λ was the growth to first reproduction. Populations from landscapes with less scrubland natural cover showed higher stasis of young adults. Populations in highly fragmented landscapes showed highest juvenile survival and growth population rates. Independent of the landscape's habitat configuration and connectivity, populations from larger scrubland patches showed low adult survivorship, but high transition rates. Populations varied from a slow strategy with low growth and delayed maturation in smaller patches to a fast strategy with high growth and early maturation in large patches. This variation was congruent with the fast‐slow continuum hypothesis and has serious implications for Andean lizard conservation and management strategies. We suggest that more stable lizard populations will be maintained if different management strategies are adopted according to patch area and habitat structure.     

Dispersal-induced desynchronization: from metapopulations to metacommunities

The conceptualization of fragmented populations in terms of metapopulation theory has become standard over the last three decades. It is well known that increases in between‐patch migration rates cause more synchronous population fluctuations and that this coherence increases the risk of global metapopulation extinction. Because species’ migration rates and the probability of individuals surviving migration events depend on the effective distance between patches, the benefit of improving conservation corridors or the matrix between habitat patches has been questioned. As populations occur in the context of larger communities, moving from a metapopulation to a metacommunity model framework is a natural extension to address the generality of these conclusions. We show how considering a metacommunity can modify the conclusion that decreasing the effective distance between habitat patches (via improving matrix quality or other measures) necessarily increases the degree of metapopulation synchrony. We show that decreases in effective between‐patch distance may deter population synchrony because of the simultaneous effect this change has on the migration patterns of other species. These results indicate that species interactions need to be considered when the effect of conservation measures on population synchrony, and ultimately persistence, is addressed.     

A candidate locus for variation in dispersal rate in a butterfly metapopulation

Frequent extinctions of local populations in metapopulations create opportunities for migrant females to establish new populations. In a metapopulation of the Glanville fritillary butterfly (Melitaea cinxia), more mobile individuals are more likely to establish new populations, especially in habitat patches that are poorly connected to existing populations. Here we show that flight metabolic rate and the frequency of a specific allele of the metabolic enzyme phosphoglucose isomerase (pgi) were both highest in newly established, isolated populations. Furthermore, genotypes with this pgi allele had elevated flight metabolic rates. These results suggest that genetic variation in pgi or a closely linked locus has a direct effect on flight metabolism, dispersal rate, and thereby on metapopulation dynamics in this species. These results also contribute to an emerging understanding of the mechanisms by which population turnover in heterogeneous landscapes may maintain genetic and phenotypic variation across populations.     

Metapopulation Persistence in Random Fragmented Landscapes

Habitat destruction and land use change are making the world in which natural populations live increasingly fragmented, often leading to local extinctions. Although local populations might undergo extinction, a metapopulation may still be viable as long as patches of suitable habitat are connected by dispersal, so that empty patches can be recolonized. Thus far, metapopulations models have either taken a mean-field approach, or have modeled empirically-based, realistic landscapes. Here we show that an intermediate level of complexity between these two extremes is to consider random landscapes, in which the patches of suitable habitat are randomly arranged in an area (or volume). Using methods borrowed from the mathematics of Random Geometric Graphs and Euclidean Random Matrices, we derive a simple, analytic criterion for the persistence of the metapopulation in random fragmented landscapes. Our results show how the density of patches, the variability in their value, the shape of the dispersal kernel, and the dimensionality of the landscape all contribute to determining the fate of the metapopulation. Using this framework, we derive sufficient conditions for the population to be spatially localized, such that spatially confined clusters of patches act as a source of dispersal for the whole landscape. Finally, we show that a regular arrangement of the patches is always detrimental for persistence, compared to the random arrangement of the patches. Given the strong parallel between metapopulation models and contact processes, our results are also applicable to models of disease spread on spatial networks.