Fragmentation of Atlantic Forest has not affected gene flow of a widespread seed‐dispersing bat

Habitat loss and resultant fragmentation are major threats to biodiversity, particularly in tropical and subtropical ecosystems. It is increasingly urgent to understand fragmentation effects, which are often complex and vary across taxa, time and space. We determined whether recent fragmentation of Atlantic forest is causing population subdivision in a widespread and important Neotropical seed disperser: Artibeus lituratus (Chiroptera: Phyllostomidae). Genetic structure within highly fragmented forest in Paraguay was compared to that in mostly contiguous forest in neighbouring Misiones, Argentina. Further, observed genetic structure across the fragmented landscape was compared with expected levels of structure for similar time spans in realistic simulated landscapes under different degrees of reduction in gene flow. If fragmentation significantly reduced successful dispersal, greater population differentiation and stronger isolation by distance would be expected in the fragmented than in the continuous landscape, and genetic structure in the fragmented landscape should be similar to structure for simulated landscapes where dispersal had been substantially reduced. Instead, little genetic differentiation was observed, and no significant correlation was found between genetic and geographic distance in fragmented or continuous landscapes. Furthermore, comparison of empirical and simulated landscapes indicated empirical results were consistent with regular long‐distance dispersal and high migration rates. Our results suggest maintenance of high gene flow for this relatively mobile and generalist species, which could be preventing or significantly delaying reduction in population connectivity in fragmented habitat. Our conclusions apply to A. lituratus in Interior Atlantic Forest, and do not contradict broad evidence that habitat fragmentation is contributing to extinction of populations and species, and poses a threat to biodiversity worldwide.     

Landscape structure shapes habitat finding ability in a butterfly

Land-use intensification and habitat fragmentation is predicted to impact on the search strategies animals use to find habitat. We compared the habitat finding ability between populations of the speckled wood butterfly (Pararge aegeria L.) from landscapes that differ in degree of habitat fragmentation. Naïve butterflies reared under standardized laboratory conditions but originating from either fragmented agricultural landscapes or more continuous forested landscapes were released in the field, at fixed distances from a target habitat patch, and their flight paths were recorded. Butterflies originating from fragmented agricultural landscapes were better able to find a woodlot habitat from a distance compared to conspecifics from continuous forested landscapes. To manipulate the access to olfactory information, a subset of individuals from both landscape types were included in an antennae removal experiment. This confirmed the longer perceptual range for butterflies from agricultural landscapes and indicated the significance of both visual and olfactory information for orientation towards habitat. Our results are consistent with selection for increased perceptual range in fragmented landscapes to reduce dispersal costs. An increased perceptual range will alter the functional connectivity and thereby the chances for population persistence for the same level of structural connectivity in a fragmented landscape.     

Spatiotemporal patterns of seed dispersal in a wind-dispersed Mediterranean tree (Acer opalus subsp. granatense): implications for regeneration

Seed dispersal can severely limit the quantity of plant recruits and their spatial distribution. However, our understanding of the role of dispersal in regeneration dynamics is limited by the lack of knowledge of seed deposition patterns in space and time. In this paper, we analyse the spatiotemporal variability of seed dispersal patterns in the Mediterranean maple, Acer opalus subsp. granatense, by monitoring seed rain along two years at a broad spatial scale (2 mountain ranges, 2 populations per range, 4 microhabitats per population). We quantified seed limitation and its components (source and dispersal limitation), and explored dispersal limitation in space by analysing dispersal distances, seed aggregation, and microhabitat seed distribution. Acer opalus subsp. granatense was strongly seed‐limited throughout the gradients explored, being always dispersal limitation much higher than source limitation. The distribution of seeds with distance from adult individuals was leptokurtic and right‐skewed in all populations, being both kurtosis and skewness higher the year of the highest seed production. Dispersal distances were shorter than expected by random in the four populations, which suggests distance‐limited dispersal. Dispersal patterns were highly aggregated and showed a preferential direction around adults. At the microhabitat scale, most seeds accumulated under adult maples. However, there were no more seeds under trees and shrubs other than maple than in open interspaces, implying that established vegetation does not disrupt patterns of seed deposition by physically trapping seeds. When compared with patterns of seedling establishment, limited dispersal ability and inter‐annual spatial concordance in seed rain patterns suggest that several potentially safe sites for recruitment have a very low probability of receiving seeds in most maple populations. These findings are especially relevant for rare species such as Acer opalus subsp. granatense, and illustrate how dispersal studies are not only crucial for our understanding of plant population dynamics but also to provide conservation directions.     

Strongly diverging population genetic patterns of three skipper species: the role of habitat fragmentation and dispersal ability

The fragmentation of landscapes has an important impact on the conservation of biodiversity, and the genetic diversity is an important factor for a populations viability, influenced by the landscape structure. However, different species with differing ecological demands react rather different on the same landscape pattern. To address this feature, we studied three skipper species with differing habitat requirements (Lulworth Skipper Thymelicus acteon: a habitat specialist with low dispersal ability, Small Skipper Thymelicus sylvestris: a habitat generalist with low dispersal ability, Essex Skipper Thymelicus lineola: a habitat generalist with higher dispersal ability). We analysed 18 allozyme loci for 1,063 individuals in our western German study region with adjoining areas in Luxembourg and north-eastern France. The genetic diversity of all three species were intermediate in comparison with other butterfly species. The F _ST was relatively high for T. acteon (5.1%), low for T. sylvestris (1.6%) and not significant for T. lineola. Isolation by distance analyses revealed a significant correlation for T. sylvestris explaining 20.3% of its differentiation, but no such structure was found for the two other species. Most likely, the high dispersal ability of T. lineola in comparison with T. sylvestris leads to a more or less panmictic structure and hence impedes isolation by distance. On the other hand, the isolation of the populations of T. acteon seems to be so strict that the populations develop independently. Although no general genetic impoverishing was observed for the endangered T. acteon, small populations had significantly lower genetic diversities than big populations, and therefore the high degree of isolation among populations might threaten its local and regional survival.     

Applying a continua landscape approach to evaluate plant response to fragmentation: Primula vulgaris in the Cantabrian mountains

Question: Continua landscape approaches conceptualize the effects of habitat fragmentation on the biota by considering fragmented landscapes as continuous gradients, departing from the view of habitat as either suitable (fragment) or unsuitable (matrix). They also consider the ecological gradients or the ‘Umwelt’ (species‐specific perception of the landscape) to represent the processes that ultimately limit organisms' ability to colonize and persist within habitat remnants. Are these approaches suitable for evaluating the response of plant species to fragmentation? Location: Fragmented mid‐elevation temperate forests, Cantabrian range, Spain. Methods: The presence, abundance and demographic structure of populations of the perennial herb Primula vulgaris were sampled across a continuous extent of 100 ha, subdivided into 400 50 m × 50 m sampling units. These variables were related to forest availability, forest subdivision and edge density, topography and the spatial clumpiness of populations (a measure of plant dispersal constraints and, hence, a major surrogate of plant Umwelt). Results: Fragmentation processes, especially habitat loss, negatively affect P. vulgaris, with a stronger effect on presence than on abundance and demography. Despite the importance of habitat availability, P. vulgaris does not occupy all potentially suitable forest habitat, mostly owing to dispersal constraints. A positive effect of slope on plant presence also suggests some effect of habitat quality in determining establishment and occupancy of forest landscape. Conclusions: Within‐habitat dispersal constraints are as important as forest fragmentation in determining the landscape‐scale distribution of P. vulgaris. By assessing the relative role of the diverse fragmentation processes, and of the species' landscape perception, a continua landscape approach proves to be a valuable tool for predicting plant response to landscape change.     

Habitat loss and fragmentation reduce effective gene flow by disrupting seed dispersal in a neotropical palm

Habitat loss and fragmentation often reduce gene flow and genetic diversity in plants by disrupting the movement of pollen and seed. However, direct comparisons of the contributions of pollen vs. seed dispersal to genetic variation in fragmented landscapes are lacking. To address this knowledge gap, we partitioned the genetic diversity contributed by male gametes from pollen sources and female gametes from seed sources within established seedlings of the palm Oenocarpus bataua in forest fragments and continuous forest in northwest Ecuador. This approach allowed us to quantify the separate contributions of each of these two dispersal processes to genetic variation. Compared to continuous forest, fragments had stronger spatial genetic structure, especially among female gametes, and reduced effective population sizes. We found that within and among fragments, allelic diversity was lower and genetic structure higher for female gametes than for male gametes. Moreover, female gametic allelic diversity in fragments decreased with decreasing surrounding forest cover, while male gametic allelic diversity did not. These results indicate that limited seed dispersal within and among fragments restricts genetic diversity and strengthens genetic structure in this system. Although pollen movement may also be impacted by habitat loss and fragmentation, it nonetheless serves to promote gene flow and diversity within and among fragments. Pollen and seed dispersal play distinctive roles in determining patterns of genetic variation in fragmented landscapes, and maintaining the integrity of both dispersal processes will be critical to managing and conserving genetic variation in the face of continuing habitat loss and fragmentation in tropical landscapes.     

片段化景观中壳斗科植物种子捕食和扩散模式

生境片段化伴随的面积效应和边缘效应, 可改变分散贮食动物的竞争强度、觅食行为以及隐蔽条件, 影响种子捕食和扩散模式。阐明生境片段化对多物种种子捕食和扩散的影响, 对理解片段化生境中的植物更新和生物多样性维持十分重要。该研究在浙江省千岛湖地区的岛屿和大陆上开展了针对6种壳斗科植物的种子捕食和扩散实验, 分析了物种、分散贮食动物相对多度、种子产量、岛屿大小和边缘效应如何共同影响种子命运和种子扩散距离。主要结果: (1)种子命运和扩散距离在物种间存在显著差异; (2)大陆比岛屿有更长的种子留存时间, 小岛种子留存时间最短, 岛屿内部比岛屿边缘有更长的种子留存时间; (3)物种和岛屿大小对种子原地取食率存在交互作用, 白栎(Quercus fabri)种子在大岛上有更高的原地取食率; (4)种子在小岛上有最高的扩散率, 分散贮食动物相对多度对种子扩散后贮藏率有负效应。表明在千岛湖地区, 生境片段化改变了种子捕食和扩散模式, 且面积效应对不同物种的种子捕食和扩散模式产生了不同作用, 从而影响森林群落更新和生物多样性维持。     

Distribution and colonisation ability of three parasitoids and their herbivorous host in a fragmented landscape

Habitat fragmentation can disrupt communities of interacting species even if only some of the species are directly affected by fragmentation. For instance, if parasitoids disperse less well than their herbivorous hosts, habitat fragmentation may lead to higher herbivory in isolated plant patches due to the absence of the third trophic level. Community-level studies suggest that parasitoids tend to have limited dispersal abilities, on the order of tens of metres, much smaller than that of their hosts, while species-oriented studies document dispersal by parasitoids on the scale of kilometres. In this study the distribution patterns of three parasitoid species with different life histories and their moth host, Hadena bicruris, a specialist herbivore of Silene latifolia, were compared in a large-scale network of natural fragmented plant patches along the rivers Rhine and Waal in the Netherlands. We examined how patch size and isolation affect the presence of each species. Additionally, experimental plots were used to study the colonisation abilities of the species at different distances from source populations.In the natural plant patches the presence of the herbivore and two of the parasitoids, the gregarious specialist Microplitis tristis and the gregarious generalist Bracon variator were not affected by patch isolation at the scale of the study, while the solitary specialist Eurylabus tristis was. In contrast to the herbivore, the presence of all parasitoid species declined with plant patch size. The colonisation experiment confirmed that the herbivore and M. tristis are good dispersers, able to travel at least 2 km within a season. B. variator showed intermediate colonisation ability and E. tristis showed very limited colonisation ability at this spatial scale. Characteristics of parasitoid species that may contribute to differences in their dispersal abilities are discussed.     

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.     

Microsatellite diversity and genetic structure of fragmented populations of the rare,fire-dependent shrub Grevillea macleayana

Recent habitat loss and fragmentation superimposed upon ancient patterns of population subdivision are likely to have produced low levels of neutral genetic diversity and marked genetic structure in many plant species. The genetic effects of habitat fragmentation may be most pronounced in species that form small populations, are fully self-compatible and have limited seed dispersal. However, long-lived seed banks, mobile pollinators and long adult lifespans may prevent or delay the accumulation of genetic effects. We studied a rare Australian shrub species, Grevillea macleayana (Proteaceae), that occurs in many small populations, is self-compatible and has restricted seed dispersal. However, it has a relatively long adult lifespan (c. 30 years), a long-lived seed bank that germinates after fire and is pollinated by birds that are numerous and highly mobile. These latter characteristics raise the possibility that populations in the past may have been effectively large and genetically homogeneous. Using six microsatellites, we found that G. macleayana may have relatively low within-population diversity (3.2-4.2 alleles/locus; Hexp = 0.420-0.530), significant population differentiation and moderate genetic structure (FST = 0.218) showing isolation by distance, consistent with historically low gene flow. The frequency distribution of allele sizes suggest that this geographical differentiation is being driven by mutation. We found a lack mutation-drift equilibrium in some populations that is indicative of population bottlenecks. Combined with evidence for large spatiotemporal variation of selfing rates, this suggests that fluctuating population sizes characterize the demography in this species, promoting genetic drift. We argue that natural patterns of pollen and seed dispersal, coupled with the patchy, fire-shaped distribution, may have restricted long-distance gene flow in the past.     

Rapid evolution of dispersal‐related traits during range expansion of an invasive vine Mikania micrantha

Rapid range expansion of invasive plants provides a unique opportunity to explore evolutionary changes of dispersal‐related traits during the invasion process. Increasing evidence now suggests that a higher dispersal rate is favored at the invasion front. However, little is known about the role of genetic differentiation and phenotypic plasticity on patterns of dispersal ability during the invasion process. In this study, we combined a field survey and a common garden transplant experiment to test for evidence of genetically based dispersal ability in Mikania micrantha, a highly invasive vine, across its invaded range in southern China. Three dispersal‐related traits, plume loading, seed mass and pappus radius, were measured in both natural and common garden populations. We found that in natural conditions, plume loading and seed mass significantly decreased with expanding distance from the source population, but in controlled conditions, these two traits exhibited a significant humped trend against percent field cover, indicating that dispersal ability of M. micrantha was selected for during range expansion and that the related traits were likely to be under genetic control. Furthermore, rebounding dispersal ability was detected in highly competitive sites in the range core, which suggested that this evolutionary process was likely partially driven by intraspecific competition. Because more and more plant species are under spatial nonequilibirum due to climate change, this study can serve to provide hints at the fate of spatially fluctuant populations.     

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.     

Importance of matrix permeability and quantity of core habitat for persistence of a threatened saltmarsh bird

Species habitat preferences can be obscured when individuals have been recorded in non‐core habitats because of dispersal, spillover effects or spatial errors in observation locations. Disentangling the direct effects of the habitats species are observed in from the effects of proximity to other nearby habitats is especially challenging in fragmented landscapes, as many fragmentation metrics are correlated and it is difficult to prove independent effects. In this paper we addressed this issue by comparing a number of models based on predefined ecological theories. We compared models based on quantity of core habitat surrounding observations, proximity to core habitat, or a combination of the two to explain the observed distribution of the saltmarsh inhabiting white‐fronted chat (Epthianura albifrons) in coastal New South Wales, Australia. Proximity to core habitat was considered as either Euclidean distance or cost distance, and models were assessed using Akaike's information criterion and the area under the receiver operator characteristic curve on 10 random subsets of the data. We found that all models performed similarly, with the combination of cost distance and the quantity of saltmarsh performing better, but not significantly so. We compared the advantages and disadvantages of different models and also present a model averaged result. Our models suggested that the majority of saltmarshes in New South Wales were too small to have a large effect on probability of occurrence. As climate change is expected to further reduce the amount of available saltmarsh through continued mangrove incursion, coastal populations of the white‐fronted chat are expected to come under increasing threat. The conversion of grasslands to urban areas may also increase the effective distance between different populations of the species and reduce gene flow and rescue effects.     

Contemporary habitat loss reduces genetic diversity in an ecologically specialized butterfly

Aim This study investigated the influence of contemporary habitat loss on the genetic diversity and structure of animal species using a common, but ecologically specialized, butterfly, Theclinesthes albocincta (Lepidoptera: Lycaenidae), as a model. Location South Australia. Methods We used amplified fragment length polymorphism (AFLP) and allozyme datasets to investigate the genetic structure and genetic diversity among populations of T. albocincta in a fragmented landscape and compared this diversity and structure with that of populations in two nearby landscapes that have more continuous distributions of butterflies and their habitat. Butterflies were sampled from 15 sites and genotyped, first using 363 informative AFLP bands and then using 17 polymorphic allozyme loci (n = 248 and 254, respectively). We complemented these analyses with phylogeographic information based on mitochondrial DNA (mtDNA) haplotype information derived from a previous study in the same landscapes. Results Both datasets indicated a relatively high level of genetic structuring across the sampling range (AFLP, F_ST = 0.34; allozyme, F_ST = 0.13): structure was greatest among populations in the fragmented landscape (AFLP, F_ST = 0.15; allozyme, F_ST = 0.13). Populations in the fragmented landscape also had significantly lower genetic diversity than populations in the other two landscapes: there were no detectable differences in genetic diversity between the two continuous landscapes. There was also evidence (r² = 0.33) of an isolation by distance effect across the sampled range of the species. Main conclusions The multiple lines of evidence, presented within a phylogeographic context, support the hypothesis that contemporary habitat fragmentation has been a major driver of genetic erosion and differentiation in this species. Theclinesthes albocincta populations in the fragmented landscape are thus likely to be at greater risk of extinction because of reduced genetic diversity, their isolation from conspecific subpopulations in other landscapes, and other extrinsic forces acting on their small population sizes. Our study provides compelling evidence that habitat loss and fragmentation have significant rapid impacts on the genetic diversity and structure of butterfly populations, especially specialist species with particular habitat preferences and poor dispersal abilities.     

Condition-dependent dispersal of a patchily distributed riparian ground beetle in response to disturbance

In common with many habitat elements of riverine landscapes, exposed riverine sediments (ERS) are highly disturbed, naturally patchy and regularly distributed, whose specialists are strongly adapted to flood disturbance and loss of habitat due to succession. Investigations of dispersal in ERS habitats therefore provide an important contrast to the unnaturally fragmented, stable systems usually studied. The present investigation analysed the three interdependent stages of dispersal: (1) emigration, (2) inter-patch movement and (3) immigration of a common ERS specialised beetle, Bembidion atrocaeruleum (Stephens 1828) (Coleoptera, Carabidae), in a relatively unmodified section of river, using mark–resight methods. Dispersal was correlated with estimates of local population size and density, water level and patch quality in order to test for condition-dependent dispersal cues. Flood inundation of habitat was found to increase strongly the overall rate of dispersal, and the rate of emigration was significantly higher from patches that were heavily trampled by cattle. Strongly declining numbers of dispersers with distance suggested low dispersal rates during periods of low water level. Dispersal in response to habitat degradation by cattle trampling would likely lead to a higher overall population fitness than a random dispersal strategy. Dispersal distances were probably adapted to the underlying habitat landscape distribution, high-flow dispersal cues and ready means of long-distance dispersal through hydrochory. Species whose dispersal is adapted to the natural habitat distribution of riverine landscapes are likely to be strongly negatively affected by reduced flood frequency and intensity and habitat fragmentation through flow regulation or channelisation.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Colonisation dynamics during range expansion is poorly predicted by dispersal in the core range

The potential ranges of many species are shifting due to changing ecological conditions. Where populations become patchy towards the range edge, the realised distribution emerges from colonisation–persistence dynamics. Therefore, a greater understanding of the drivers of these processes, and the spatial scales over which they operate, presents an opportunity to improve predictions of species range expansion under environmental change. Species reintroductions offer an ideal opportunity to investigate the drivers and spatial scale of colonisation dynamics at the range edge. To this effect, we performed and monitored experimental translocations of water voles to quantify how colonisation and local persistence were influenced by habitat quality and occupancy. We used a novel statistical method to simultaneously consider effects across a range of spatial scales. Densely occupied neighbourhoods were highly persistent and frequently colonised. Persistence was more likely in high quality habitat, whereas the influence of habitat quality on colonisation was less clear. Colonisation of suitable habitat in distant, sparsely occupied areas was much less frequent than expected from the well documented high dispersal ability of the species. Persistence of these distant populations was also low, which we attribute to the absence of a rescue effect in sparsely populated neighbourhoods. Our results illustrate a mismatch between the spatial scales of colonisation dynamics in the core and edge of a species’ range, suggesting that recolonisation dynamics in established populations may be a poor predictor of colonisation dynamics at the range edge. Such a mismatch leads to predictions of long lags between the emergence and colonisation of new habitat, with detrimental consequences for a species’ realised distribution, conservation status and contribution to ecosystem function. Conservation translocations that also reinforce existing populations at the range edge might stimulate the rescue effect and mitigate lags in expansion.     

Understanding species distribution in dynamic populations: a new approach using spatio‐temporal point process models

Understanding and predicting a species’ distribution across a landscape is of central importance in ecology, biogeography and conservation biology. However, it presents daunting challenges when populations are highly dynamic (i.e. increasing or decreasing their ranges), particularly for small populations where information about ecology and life history traits is lacking. Currently, many modelling approaches fail to distinguish whether a site is unoccupied because the available habitat is unsuitable or because a species expanding its range has not arrived at the site yet. As a result, habitat that is indeed suitable may appear unsuitable. To overcome some of these limitations, we use a statistical modelling approach based on spatio‐temporal log‐Gaussian Cox processes. These model the spatial distribution of the species across available habitat and how this distribution changes over time, relative to covariates. In addition, the model explicitly accounts for spatio‐temporal dynamics that are unaccounted for by covariates through a spatio‐temporal stochastic process. We illustrate the approach by predicting the distribution of a recently established population of Eurasian cranes Grus grus in England, UK, and estimate the effect of a reintroduction in the range expansion of the population. Our models show that wetland extent and perimeter‐to‐area ratio have a positive and negative effect, respectively, in crane colonisation probability. Moreover, we find that cranes are more likely to colonise areas near already occupied wetlands and that the colonisation process is progressing at a low rate. Finally, the reintroduction of cranes in SW England can be considered a human‐assisted long‐distance dispersal event that has increased the dispersal potential of the species along a longitudinal axis in S England. Spatio‐temporal log‐Gaussian Cox process models offer an excellent opportunity for the study of species where information on life history traits is lacking, since these are represented through the spatio‐temporal dynamics reflected in the model.     

Levels of gene flow among populations of a wolf spider in a recently fragmented habitat: current versus historical rates

Gene flow among populations is important for countering the deleterious effects of random genetic drift and inbreeding, as well as spreading beneficial mutations. Wind-driven aerial dispersal is known to occur in numerous plants and invertebrates. Its evolution suggests that historically, suitable habitat patches were dense enough to make such undirected dispersal evolutionarily advantageous. Using microsatellite markers we assessed the population genetic structure of seven populations of a wolf spider (Rabidosa rabida) capable of ballooning. Historically, each spider population received a mean of 1.5 migrants per generation from the other six populations. Over the past several generations the number of migrants reaching a population is only 0.2. This statistically significant reduction in gene flow coincides with high levels of habitat fragmentation and suggests that undirected aerial dispersal is ineffective in this fragmented landscape. Further, individuals within populations showed signficantly elevated levels of homozygosity relative to Hardy–Weinberg expectations, suggesting that cursorial dispersal may be very limited and genetic structure within populations exists. Inbreeding coefficients averaged 0.18 over all seven populations with very little variation among populations (s = 0.02). Fitness was lower in smaller populations relative to larger ones. Altered landscapes pose evolutionary dilemmas for many metapopulations and species that depend on undirected movement for dispersal may be particularly vulnerable to habitat fragmentation.     

Pervasive effects of dispersal limitation on within- and among-community species richness in agricultural landscapes

Aim To determine whether the effect of habitat fragmentation and habitat heterogeneity on species richness at different spatial scales depends on the dispersal ability of the species assemblages and if this results in nested species assemblages. Location Agricultural landscapes distributed over seven temperate Europe countries covering a range from France to Estonia. Methods We sampled 16 local communities in each of 24 agricultural landscapes (16 km²) that differ in the amount and heterogeneity of semi‐natural habitat patches. Carabid beetles were used as model organisms as dispersal ability can easily be assessed on morphological traits. The proximity and heterogeneity of semi‐natural patches within the landscape were related to average local (alpha), between local (beta) and landscape (gamma) species richness and compared among four guilds that differ in dispersal ability. Results For species assemblages with low dispersal ability, local diversity increased as the proximity of semi‐natural habitat increased, while mobile species showed an opposite trend. Beta diversity decreased equally for all dispersal classes in relation to proximity, suggesting a homogenizing effect of increased patch isolation. In contrast, habitat diversity of the semi‐natural patches affected beta diversity positively only for less mobile species, probably due to the low dispersal ability of specialist species. Species with low mobility that persisted in highly fragmented landscapes were consistently present in less fragmented ones, resulting in nested assemblages for this mobility class only. Main conclusions The incorporation of dispersal ability reveals that only local species assemblages with low dispersal ability show a decrease of richness as a result of fragmentation. This local species loss is compensated at least in part by an increase in species with high dispersal ability, which obscures the effect of fragmentation when investigated across dispersal groups. Conversely, fragmentation homogenizes the landscape fauna for all dispersal groups, which indicates the invasion of non‐crop habitats by similar good dispersers across the whole landscape. Given that recolonization of low dispersers is unlikely, depletion of these species in modern agricultural landscapes appears temporally pervasive.