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.     

Delayed dispersal and prolonged brood care in a family‐living beetle

Delayed juvenile dispersal is an important prerequisite for the evolution of family‐based social systems, such as cooperative breeding and eusociality. In general, young adults forego dispersal if there are substantial benefits to remaining in the natal nest and/or the likelihood of dispersing and breeding successfully is low. We investigate some general factors thought to drive delayed juvenile dispersal in the horned passalus beetle, a family‐living beetle in which young adults remain with their families in their natal nest for several months before dispersing. Fine‐scale population genetic structure indicated high gene flow between nest sites, suggesting that constraints on mobility are unlikely to explain philopatry. Young adults do not breed in their natal log and likely disperse before reaching breeding age, suggesting that they do not gain direct reproductive benefits from delayed dispersal. We also examined several ways in which parents might incentivize delayed dispersal by providing prolonged care to adult offspring. Although adult beetles inhibit fungal growth in the colony by manipulating both the nest site and deceased conspecifics, this is unlikely to be a major explanation for family living as both parents and adult offspring seem capable of controlling fungal growth. Adult offspring that stayed with their family groups also neither gained more mass nor experienced faster exoskeleton development than those experimentally removed from their families. The results of these experiments suggest that our current understanding of the factors underlying prolonged family living may be insufficient to explain delayed dispersal in at least some taxa, particularly insects.     

Genetic effects of landscape,habitat preference and demography on three co‐occurring turtle species

Expanding the scope of landscape genetics beyond the level of single species can help to reveal how species traits influence responses to environmental change. Multispecies studies are particularly valuable in highly threatened taxa, such as turtles, in which the impacts of anthropogenic change are strongly influenced by interspecific differences in life history strategies, habitat preferences and mobility. We sampled approximately 1500 individuals of three co‐occurring turtle species across a gradient of habitat change (including varying loss of wetlands and agricultural conversion of upland habitats) in the Midwestern USA. We used genetic clustering and multiple regression methods to identify associations between genetic structure and permanent landscape features, past landscape composition and landscape change in each species. Two aquatic generalists (the painted turtle, Chrysemys picta, and the snapping turtle Chelydra serpentina) both exhibited population genetic structure consistent with isolation by distance, modulated by aquatic landscape features. Genetic divergence for the more terrestrial Blanding's turtle (Emydoidea blandingii), on the other hand, was not strongly associated with geographic distance or aquatic features, and Bayesian clustering analysis indicated that many Emydoidea populations were genetically isolated. Despite long generation times, all three species exhibited associations between genetic structure and postsettlement habitat change, indicating that long generation times may not be sufficient to delay genetic drift resulting from recent habitat fragmentation. The concordances in genetic structure observed between aquatic species, as well as isolation in the endangered, long‐lived Emydoidea, reinforce the need to consider both landscape composition and demographic factors in assessing differential responses to habitat change in co‐occurring species.     

Contrasting microsatellite variation between subalpine and western larch, two closely related species with different distribution patterns

Subalpine larch (Larix lyallii Parl.) and western larch (Larix occidentalis Nutt.) represent two closely related species with contrasting abundance and distribution patterns in Western North America. Genetic diversity at seven informative microsatellite loci was determined for 19 populations of subalpine larch and nine populations of western larch. Contrasting genetic diversity and patterns of population differentiation were observed between the two species. The overall within-population genetic diversity parameters were lower in subalpine larch (A = 3.2; A(P) = 3.6; H(E) = 0.418) than in western larch (A(P) = 5.51; H(E) = 0.580), a pattern that is likely related to historical or demographic factors. No evidence of interspecific hybridization was observed. Significantly more population differentiation (theta = 0.15; R(ST) = 0.07), consistent with more restricted gene flow, was observed for subalpine larch as compared to western larch (theta = 0.05; R(ST) = 0.04). Under the assumption of an infinite allele mutation model, 12 of the 19 subalpine larch populations showed signs of deviation from the mutation-drift equilibrium, which suggests Holocene population bottlenecks and fluctuations in effective population size for this species. None of the western larch populations deviated significantly from the mutation-drift equilibrium. For both species, Mantel's test revealed a significant positive relationship between geographical and genetic distances indicative of isolation by distance. A similar geographical structure was detected in both species, suggesting at least two genetically distinct glacial populations in each species. The various implications for gene conservation are discussed.     

Closing the gaps for animal seed dispersal: Separating the effects of habitat loss on dispersal distances and seed aggregation

Habitat loss can alter animal movements and disrupt animal seed dispersal mutualisms; however, its effects on spatial patterns of seed dispersal are not well understood. To explore the effects of habitat loss on seed dispersal distances and seed dispersion (aggregation), we created a spatially explicit, individual‐based model of an animal dispersing seeds (SEADS—Spatially Explicit Animal Dispersal of Seeds) in a theoretical landscape of 0%–90% habitat loss based on three animal traits: movement distance, gut retention time, and time between movements. Our model design had three objectives: to determine the effects of (1) animal traits and (2) habitat loss on seed dispersal distances and dispersion and (3) determine how animal traits could mitigate the negative effects of habitat loss on these variables. SEADS results revealed a complex interaction involving all animal traits and habitat loss on dispersal distances and dispersion, driven by a novel underlying mechanism of fragment entrapment. Unexpectedly, intermediate habitat loss could increase dispersal distances and dispersion relative to low and high habitat loss for some combinations of animal traits. At intermediate habitat loss, movement between patches was common, and increased dispersal distances and dispersion compared to continuous habitats because animals did not stop in spaces between fragments. However, movement between patches was reduced at higher habitat loss as animals became trapped in fragments, often near the parent plant, and dispersed seeds in aggregated patterns. As movement distance increased, low time between movements and high gut retention time combinations permitted more movement to adjacent patches than other combinations of animal traits. Because habitat loss affects movement in a nonlinear fashion under some conditions, future empirical tests would benefit from comparisons across landscapes with more than two levels of fragmentation.     

Genetic diversity,population structure and sex‐biased dispersal in three co‐evolving species

Genetic diversity and spatial structure of populations are important for antagonistic coevolution. We investigated genetic variation and population structure of three closely related European ant species: the social parasite Harpagoxenus sublaevis and its two host species Leptothorax acervorum and Leptothorax muscorum. We sampled populations in 12 countries and analysed eight microsatellite loci and an mtDNA sequence. We found high levels of genetic variation in all three species, only slightly less variation in the host L. muscorum. Using a newly introduced measure of differentiation (Jost’s D_est ), we detected strong population structuring in all species and less male‐biased dispersal than previously thought. We found no phylogeographic patterns that could give information on post‐glacial colonization routes – northern populations are as variable as more southern populations. We conclude that conditions for Thompson’s geographic mosaic of coevolution are ideal in this system: all three species show ample genetic variation and strong population structure.     

Dispersal ability and habitat requirements determine landscape‐level genetic patterns in desert aquatic insects

Species occupying the same geographic range can exhibit remarkably different population structures across the landscape, ranging from highly diversified to panmictic. Given limitations on collecting population‐level data for large numbers of species, ecologists seek to identify proximate organismal traits—such as dispersal ability, habitat preference and life history—that are strong predictors of realized population structure. We examined how dispersal ability and habitat structure affect the regional balance of gene flow and genetic drift within three aquatic insects that represent the range of dispersal abilities and habitat requirements observed in desert stream insect communities. For each species, we tested for linear relationships between genetic distances and geographic distances using Euclidean and landscape‐based metrics of resistance. We found that the moderate‐disperser Mesocapnia arizonensis (Plecoptera: Capniidae) has a strong isolation‐by‐distance pattern, suggesting migration–drift equilibrium. By contrast, population structure in the flightless Abedus herberti (Hemiptera: Belostomatidae) is influenced by genetic drift, while gene flow is the dominant force in the strong‐flying Boreonectes aequinoctialis (Coleoptera: Dytiscidae). The best‐fitting landscape model for M. arizonensis was based on Euclidean distance. Analyses also identified a strong spatial scale‐dependence, where landscape genetic methods only performed well for species that were intermediate in dispersal ability. Our results highlight the fact that when either gene flow or genetic drift dominates in shaping population structure, no detectable relationship between genetic and geographic distances is expected at certain spatial scales. This study provides insight into how gene flow and drift interact at the regional scale for these insects as well as the organisms that share similar habitats and dispersal abilities.     

Genetic evidence for spatio‐temporal changes in the dispersal patterns of two sympatric African colobine monkeys

Western black‐and‐white colobus and Temmink's red colobus are two forest‐dependent African primates with similar ecological requirements, often found in sympatry. Their most striking difference lies in their social system: black‐and‐white colobus live in small groups with mainly male‐mediated dispersal but where females can also disperse, whereas red colobus live in larger groups with males described as philopatric. To investigate whether genetic evidence supports the reported patterns of dispersal based on observational data, we examined eight black‐and‐white and six red colobus social groups from Cantanhez National Park, Guinea‐Bissau. Microsatellite markers revealed a lack of sex‐biased dispersal for black‐and‐white colobus. Gene flow, mainly mediated by females, better explained the genetic patterns found in red colobus, with some evidence for less extensive male dispersal. In contrast to the microsatellite data, low mitochondrial diversity for the black‐and‐white colobus suggests that historical and/or long‐range male‐mediated gene flow might have been favored. In red colobus, the co‐existence of three divergent mitochondrial haplogroups suggests that the Cantanhez population contains a secondary contact zone between divergent lineages that evolved in allopatry. Female‐biased dispersal in this species may be a major factor contributing to the colonization by such differentiated mitochondrial lineages in the region. Overall, we find evidence for a spatio‐temporal change in the dispersal patterns of the colobus monkeys of Cantanhez, with mitochondrial DNA indicating dispersal by mainly a single sex and microsatellite data suggesting that recently both sexes appear to be dispersing within the population. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.     

Male‐biased dispersal and the potential impact of human‐induced habitat modifications on the Neotropical bat Trachops cirrhosus

Gene flow, maintained through natal dispersal and subsequent mating events, is one of the most important processes in both ecology and population genetics. Among mammalian populations, gene flow is strongly affected by a variety of factors, including the species’ ability to disperse, and the composition of the environment which can limit dispersal. Information on dispersal patterns is thus crucial both for conservation management and for understanding the social system of a species. We used 16 polymorphic nuclear microsatellite loci in addition to mitochondrial DNA sequences (1.61 kbp) to analyse the population structure and the sex‐specific pattern of natal dispersal in the frog‐eating fringe‐lipped bat, Trachops cirrhosus, in Central Panama. Our study revealed that—unlike most of the few other investigated Neotropical bats—gene flow in this species is mostly male‐mediated. Nevertheless, distinct genetic clusters occur in both sexes. In particular, the presence of genetic differentiation in the dataset only consisting of the dispersing sex (males) indicates that gene flow is impeded within our study area. Our data are in line with the Panama Canal in connection with the widening of the Río Chagres during the canal construction acting as a recent barrier to gene flow. The sensitivity of T. cirrhosus to human‐induced habitat modifications is further indicated by an extremely low capture success in highly fragmented areas. Taken together, our genetic and capture data provide evidence for this species to be classified as less mobile and thus vulnerable to habitat change, information that is important for conservation management.     

Contrasting habitat use of morphologically similar bat species with differing conservation status in south‐eastern Australia

The east‐coast free‐tailed bat Mormopterus norfolkensis Gray, 1839 is a threatened insectivorous bat that is poorly known and as such conservation management strategies are only broadly prescribed. Insectivorous bats that use human‐modified landscapes are often adapted to foraging in open microhabitats. However, few studies have explored whether open‐adapted bats select landscapes with more of these microhabitat features. We compared three morphologically similar and sympatric, molossid bats (genus Mormopterus) with different conservation status in terms of their association with vegetation, climate, landform and land‐use attributes at landscape and local habitat element scales. We predicted that these species would use similar landscape types, with semi‐cleared and low density urban landscapes used more than forested and heavily cleared landscapes. Additionally, we explored which environmental variables best explained the occurrence of each species by constructing post‐hoc models and habitat suitability maps. Contrary to predictions, we found that the three species varied in their habitat use with no one landscape type used more extensively than other types. Overall, M. norfolkensis was more likely to occur in low‐lying, non‐urban, riparian habitats with little vegetation cover. Mormopterus species 2 occupied similar habitats, but was more tolerant of urban landscapes. In contrast, Mormopterus species 4 occurred more often in cleared than forested landscapes, particularly dry landscapes with little vegetation cover. The extensive use of coastal floodplains by the threatened M. norfolkensis is significant because these habitats are under increasing pressure from human land‐uses and the predicted increase in urbanization is likely to further reduce the amount of suitable habitat.     

Using isolation‐by‐distance‐based approaches to assess the barrier effect of linear landscape elements on badger (Meles meles) dispersal

As the European badger (Meles meles) can be of conservation or management concern, it is important to have a good understanding of the species’ dispersal ability. In particular, knowledge of landscape elements that affect dispersal can contribute to devising effective management strategies. However, the standard approach of using Bayesian clustering methods to correlate genetic discontinuities with landscape elements cannot easily be applied to this problem, as badger populations are often characterized by a strong confounding isolation‐by‐distance (IBD) pattern. We therefore developed a two‐step method that compares the location of pairs of related badgers relative to a putative barrier and utilizes the expected spatial genetic structure characterized by IBD as a null model to test for the presence of a barrier. If a linear feature disrupts dispersal, the IBD pattern characterising pairs of individuals located on different sides of a putative barrier should differ significantly from the pattern obtained with pairs of individuals located on the same side. We used our new approach to assess the impact of rivers and roads of different sizes on badger dispersal in western England. We show that a large, wide river represented a barrier to badger dispersal and found evidence that a motorway may also restrict badger movement. Conversely, we did not find any evidence for small rivers and roads interfering with badger movement. One of the advantages of our approach is that potentially it can detect features that disrupt gene flow locally, without necessarily creating distinct identifiable genetic units.     

Multi‐scale effects of habitat structure and landscape context on a vertebrate with limited dispersal ability (the brown‐throated sloth,Bradypus variegatus)

As human population, food consumption, and demand for forest products continue to rise over the next century, the pressures of land‐use change on biodiversity are projected to intensify. In tropical regions, countryside habitats that retain abundant tree cover and structurally complex canopies may complement protected areas by providing suitable habitats and landscape connectivity for a significant portion of the native biota. Species with low dispersal capabilities are among the most at risk of extinction as a consequence of land‐use change. We assessed how the spatial distribution of the brown‐throated sloth (Bradypus variegatus), a model species for a vertebrate with limited dispersal ability, is shaped by differences in habitat structure and landscape patterns of countryside habitats in north‐central Costa Rica using a multi‐scale framework. We quantified the influence of local habitat characteristics and landscape context on sloth occurrence using mixed‐effects logistic regression models. We recorded 27 sloths within countryside habitats and found that both local and landscape factors significantly influenced their spatial distribution. Locally, sloths favored structurally complex habitats, with greater canopy cover and variation in tree height and basal area. At the landscape scale, sloths demonstrated a preference for habitats with high proportions of forest and nearby large tracts of forest. Although mixed‐use areas and tree plantations are not substitutes for protected forests, our results suggest they provide important supplemental habitats for sloths. To promote the conservation and long‐term viability of sloth populations in the tropical countryside, we recommend that land managers retain structurally complex vegetation and large patches of native habitat.     

The effects of species pool,dispersal and competition on the diversity–productivity relationship

Aim The diversity–productivity relationship is a controversial issue in ecology. Diversity is sometimes seen to increase with productivity but a unimodal relationship has often been reported. Competitive exclusion was cited initially to account for the decrease of diversity at high productivity. Subsequently, the roles of evolutionary history (species pool size) and dispersal rate have been acknowledged. We explore how the effects of species pool, dispersal and competition combine to produce different diversity–productivity relationships. Methods We use a series of simulations with a spatially explicit, individual‐based model. Following empirical expectations, we used four scenarios to characterize species pool size along the productivity gradient (uniformly low and high, linear increase and unimodal). Similarly, the dispersal rate varied along the productivity gradient (uniformly low and high, and unimodal). We considered both neutral communities and communities with competitive exclusion. Results and main conclusions Our model predicts that competitive interactions will result in unimodal diversity–productivity relationships. The model often predicts unimodal patterns in neutral communities as well, although the decline in richness at high productivity is less than in competing communities. A positive diversity–productivity relationship is simulated for neutral communities when the species pool size increases with productivity and the dispersal rate is high. This scenario is probably more widespread in nature than the others since positive diversity–productivity relationships have been observed more frequently than previously expected, especially in the tropics and for woody species. Our simulated effects of species pool, dispersal and competition on diversity patterns can be linked to empirical observations to uncover mechanisms behind the diversity–productivity relationship.     

Uncovering the drivers of host‐associated microbiota with joint species distribution modelling

In addition to the processes structuring free‐living communities, host‐associated microbiota are directly or indirectly shaped by the host. Therefore, microbiota data have a hierarchical structure where samples are nested under one or several variables representing host‐specific factors, often spanning multiple levels of biological organization. Current statistical methods do not accommodate this hierarchical data structure and therefore cannot explicitly account for the effect of the host in structuring the microbiota. We introduce a novel extension of joint species distribution models (JSDMs) which can straightforwardly accommodate and discern between effects such as host phylogeny and traits, recorded covariates such as diet and collection site, among other ecological processes. Our proposed methodology includes powerful yet familiar outputs seen in community ecology overall, including (a) model‐based ordination to visualize and quantify the main patterns in the data; (b) variance partitioning to assess how influential the included host‐specific factors are in structuring the microbiota; and (c) co‐occurrence networks to visualize microbe‐to‐microbe associations.     

Evaluating the influence of life‐history characteristics on genetic structure: a comparison of small mammals inhabiting complex agricultural landscapes

Conversion of formerly continuous native habitats into highly fragmented landscapes can lead to numerous negative demographic and genetic impacts on native taxa that ultimately reduce population viability. In response to concerns over biodiversity loss, numerous investigators have proposed that traits such as body size and ecological specialization influence the sensitivity of species to habitat fragmentation. In this study, we examined how differences in body size and ecological specialization of two rodents (eastern chipmunk; Tamias striatus and white‐footed mouse; Peromyscus leucopus) impact their genetic connectivity within the highly fragmented landscape of the Upper Wabash River Basin (UWB), Indiana, and evaluated whether landscape configuration and complexity influenced patterns of genetic structure similarly between these two species. The more specialized chipmunk exhibited dramatically more genetic structure across the UWB than white‐footed mice, with genetic differentiation being correlated with geographic distance, configuration of intervening habitats, and complexity of forested habitats within sampling sites. In contrast, the generalist white‐footed mouse resembled a panmictic population across the UWB, and no landscape factors were found to influence gene flow. Despite the extensive previous work in abundance and occupancy within the UWB, no landscape factor that influenced occupancy or abundance was correlated with genetic differentiation in either species. The difference in predictors of occupancy, abundance, and gene flow suggests that species‐specific responses to fragmentation are scale dependent.     

Long‐distance geneflow and habitat specificity of the rock‐dwelling coppertail skink,Ctenotus taeniolatus

Rock boulders or ‘bush‐rocks’ provide essential habitat for many organisms and there has been interest in rehabilitating areas denuded of rock with artificial substitutes. We examine whether the density and size of bush rock influences the density of the coppertail skink (Ctenotus taeniolatus). The success of habitat rehabilitation is contingent on dispersal of rock‐dwelling organisms into areas that have been remediated. To gauge the likelihood of this we characterize geneflow of coppertail skinks among discrete patches of rocky habitat associated with ridge tops. We genotyped 154 individuals from seven localities at six microsatellite DNA loci and from a subset of these individuals we obtained sequence data from the mitochondrial ND4 region. Our field survey established that lizard density was positively associated with the availability of suitably sized bush‐rock (P < 0.001), highlighting the importance of maintaining this habitat element, or replacing it where it has been lost. Despite the presence of habitat features that might be presumed as barriers to dispersal for coppertail skinks, such as intervening gullies and dense vegetation, our genetic data demonstrated high levels of geneflow among rocky ridge tops. Levels of partitioning estimated by global F_ST were significant but low for both microsatellite (F_ST = 0.020) and mitochondrial data (F_ST = 0.113). Spatial autocorrelation of genotypic similarity supports our conclusion of regular longer‐distance geneflow, and we infer lower levels of dispersal in juveniles than in adults. This study suggests that dispersal of coppertail skinks can be sufficient to naturally colonize areas of restored habitat.     

Paddock‐scale patterns of seed production and dispersal in the invasive shrub Acacia nilotica (Mimosaceae) in northern Australian rangelands

Paddock‐scale Acacia nilotica L. Willd. ex Del. (prickly acacia) spatial distribution, seed production and dispersal patterns were investigated in the Astrebla (Mitchell) grasslands of northern Australia as a step toward predicting future patterns of invasion. A number of hypotheses were tested based on what we know of this species in both Australia and regions where it is native, for example South Africa. It was hypothesized that most A. nilotica seeds would be produced by trees in riparian habitats with access to permanent water. In addition, we predicted that seeds would be dispersed throughout the Astrebla grassland landscape by cattle, following observations that cattle readily ingest and pass seeds and that cattle have access to all areas within paddock boundary fences. Tree density, seed production and seed dispersal by cattle were measured along a series of transects from permanent watering points to paddock boundary fences. Trees associated with permanent watering points produced more seeds per unit area and occurred at higher density than their non‐riparian counterparts. The importance of riparian trees decreased in years with high rainfall and in paddocks with only small areas of riparian habitat. Cattle spread dung and seeds throughout paddocks, with peaks of deposition adjacent to permanent watering points. These results suggest that invasion patterns are likely to be uneven across the landscape and may be reactive to climate. High seedling recruitment and possible thicket formation is expected adjacent to permanent watering points and wherever cattle congregate. Patterns of recruitment in non‐riparian areas are likely to be relatively sparse. The importance of post‐dispersal factors in determining recruitment patterns is discussed.