Structure Of Fragmented Populations Research Articles

Estimating the abundance of the Hector’s dolphins (Cephalorhynchus hectori hectori) that use Porpoise Bay, New Zealand

ABSTRACT Hector’s dolphin, an endangered species endemic to the coastal waters of Aotearoa New Zealand, has a highly fragmented population structure. Low abundance of some local subpopulations, coupled with a stepping-stone mode of gene flow, suggests that these are at high risk of extinction. During the austral summer, dolphins from the small, genetically distinct subpopulation found along the South Island’s south-east coast frequently use Porpoise Bay, an important foraging and calving area. The estimate of abundance of dolphins using the bay has not been updated since the introduction of protection measures in 2008 intended to mitigate bycatch in fisheries. Photo-ID surveys, including random photography to estimate mark rate, were conducted during summer 2020. Using Chapman’s version of the Lincoln-Petersen estimator, it was estimated that 63 Hector’s dolphins (95% CI = 46–79), including three new calves, used Porpoise Bay during the study period. While regression analyses showed no evidence of change since previous abundance estimates in 1996–97, 2002–03, and 2008, the very low estimated abundance validates fears for the long-term persistence of this subpopulation. In this context, potential threats need to be managed within a precautionary framework, with a clear goal of facilitating recovery.

Kinship and Breeding Site Philopatry Drive Fine-Scale Genetic Structure in Fragmented Populations of the Gopher Frog (Rana capito) in North Carolina

The Gopher Frog (Rana capito) is a threatened species native to the southeastern longleaf pine ecosystem. Although once much more widespread across the southeastern United States, they now occur in North Carolina at only a handful of disjunct sites in the Coastal Plain and Sandhills regions of the state. The long-term persistence of these populations is thus a concern, as is a loss of genetic variation over time. We used mitochondrial and microsatellite markers to better understand the spatial structure of genetic variation and levels of genetic variability across these remaining populations in order to inform conservation and management decisions. Eight unique mitochondrial haplotypes were found, but these were all genetically similar to one another. Levels of genetic diversity based on the microsatellite analyses were similar across populations, but inbreeding coefficients in two populations were significant, suggesting a potential vulnerability to inbreeding depression. All disjunct populations showed significant genetic differentiation, which was not related to geographic distance. Conversely, within populations, the genetic relatedness of individuals between ponds decreased as distance between ponds increased. This kinship pattern is likely driven by strong breeding philopatry (individuals returning to the same ponds across years) and indicates that conservation actions at the scale of <1 km would primarily affect kin groups of Gopher Frogs, whereas conservation actions at scales ‡1.5 km would be needed to capture more distantly related individuals. Management efforts should thus focus on local metapopulation dynamics by maintaining multiple breeding ponds at each location, and by enhancing connectivity between these breeding ponds.

Gene Flow and Recruitment Patterns among Disjunct Populations of Allocasuarina verticillata (Lam.) L.A.S. Johnson

Allocasuarina verticillata (Lam.) L.A.S. Johnson is a widespread species in south-eastern Australia providing vegetation cover, protecting fragile soils and providing food for birds. Understanding the effects of gene flow on the recruitment patterns, genetic differentiation and structure of fragmented populations provides fundamental guidelines to underpin plant conservation strategies and activities. In this study, four spatially disjunct populations of A. verticillata were sampled to explore the effects of population size, reproductive patterns and pollen and seed dispersal on among-population genetic diversity, genetic differentiation and structure, using field survey and microsatellite marker techniques. It was found that stands of A. verticillata were predominantly sexually reproductive, but asexual reproduction through root suckering was an additional mode of reproduction. The reproductive success of A. verticillata is positively correlated with the effective population size rather than actual population size. The reduction in effective population size and increment of spatial isolation resulted in lower genetic diversity and higher inbreeding coefficient of progenies. Moderate pairwise genetic differentiation and weak genetic structure were identified. The results suggest that exogenous, wind-mediated pollen flow provides some maintenance of genetic diversity in the isolated stands. Seed dispersal appears mainly to be over short distances (i.e., within populations), but the infrequent transport of seeds between disjunct locations cannot be ruled out as another factor that may help maintain genetic diversity.

Evolution of cooperation on temporal networks

Population structure is a key determinant in fostering cooperation among naturally self-interested individuals in microbial populations, social insect groups, and human societies. Traditional research has focused on static structures, and yet most real interactions are finite in duration and changing in time, forming a temporal network. This raises the question of whether cooperation can emerge and persist despite an intrinsically fragmented population structure. Here we develop a framework to study the evolution of cooperation on temporal networks. Surprisingly, we find that network temporality actually enhances the evolution of cooperation relative to comparable static networks, despite the fact that bursty interaction patterns generally impede cooperation. We resolve this tension by proposing a measure to quantify the amount of temporality in a network, revealing an intermediate level that maximally boosts cooperation. Our results open a new avenue for investigating the evolution of cooperation and other emergent behaviours in more realistic structured populations.

Diversity and structure of fragmented populations of a threatened endemic cyprinodontid (Aphanius sophiae) inferred from genetics and otolith morphology: Implications for conservation and management

Diversity and structure of fragmented populations of a threatened endemic cyprinodontid (<i>Aphanius sophiae</i>) inferred from genetics and otolith morphology: Implications for conservation and management

No evidence for early inbreeding depression in planted seedlings of Eucalyptus caesia, an anciently fragmented tree endemic on granite outcrops

Selection against inbred progeny is a well-documented phenomenon in natural and experimental populations of trees with mixed mating systems. This inbreeding depression can be expressed at multiple life stages, including early seedling development. Eucalyptus caesia, a long-lived tree that is endemic to granite outcrops in south-west Australia, has an anciently fragmented population structure, low levels of heterozygosity and limited genetic interconnection between stands and small population sizes. To test whether purging of genetic load may have facilitated the persistence of E. caesia on its granite rock habitat, we assessed the early growth and survivorship of seedlings in a common garden trial. A total of 120 seedlings from eight maternal trees were planted in four plots at the study site. Seedling growth rate and survivorship were assessed over 26 months against familial background and level of individual heterozygosity. We found no significant variation in the early growth or survivorship of selfed or outcrossed seedlings, or between seedlings with low or high levels of individual heterozygosity. These results support the hypothesis that purging of genetic load may have reduced the negative impacts of inbreeding in seedlings of E. caesia.

Genetic diversity and structure of Populus nigra populations in two highly fragmented river ecosystems from Turkey

European black poplar (Populus nigra L.) is an important tree species in terms of social, economic, and ecological interest in Turkey. Although large poplar plantations meet the needs of the economy, natural genetic resources of the species have been highly degraded due to anthropogenic effects such as overexploitation and habitat fragmentations. To assess genetic diversity and structure of fragmented populations, 124 naturally distributed European black poplar trees from two major rivers (Kizilirmak and Goksu) in Turkey were sampled and screened by using 20 nuclear microsatellite DNA loci. To detect the possibility of natural hybridization, 10 reference Populus deltoids L. trees were studied with six microsatellite loci. Out of 124, five trees were determined as F2 hybrids with diagnostic and informative alleles. Studied populations appear to have experienced a recent bottleneck event which is likely to cause to reduction in allelic diversity and to increase heterozygosity (mean Ho = 0.80). Four populations representing upstream, middle and downstream parts of the Kizilirmak River were found to be differentiated from Goksu river population, evidenced by genetic differentiation (FST = 0.06), geographical distances in principal coordinate analysis and clustering pattern in structure analysis. Traditional management of European black poplar coupled with bottleneck and hybridization events has played an important role in reduced genetic diversity and degradation of the genetic resources of the species in two river systems. The study has provided invaluable information to prevent further genetic degradation, to maintain existing genetic diversity of the species in its natural habitats, and to implement efficient conservation strategies and breeding programs for future generations.

RETRACTED ARTICLE: Comparison of traditional and new generation DNA markers declares high genetic diversity and differentiated population structure of wild almond species

Wild almond species as sources of genetic variation may have crucial importance in breeding. A total of 389 accessions of 18 species have been analysed using inter-retrotransposon amplified polymorphism (IRAP), retrotransposon-microsatellite amplified polymorphism (REMAP), sequence-specific amplification polymorphism (S-SAP), amplified fragment length polymorphism (AFLP), inter simple sequence repeat (ISSR) and simple sequence repeats (SSR). Retrotransposon markers indicated the presence and movement of some Ty3-gypsy and Ty1-copia-elements in almond genome. Since transposable elements are associated with large-scale genome alterations, REMAP produced more reliable phylogenetic inferences than AFLP where homoplasy may affect clustering. In addition, high resolution melting (HRM) analysis was developed to detect SNPs. HRM analysis revealed 1:189 bp frequency of SNPs in exon positions, and the transition-to-transversion proportion was 1.84:1. The low transition bias suggests low methylation levels in almond genome. The polymorphic information content (PIC) was the highest for SSR markers, while SNPs had an average PIC of 0.59, which is close to the values of the rest of the markers. Huge genetic diversity, fragmented population structure and footprints of human selection was confirmed by merging information from all marker strategies. Considering time, cost and performance HRM can be a marker of choice in future studies of Prunus diversity.

Population genetic structure and adaptation of malaria parasites on the edge of endemic distribution.

To determine whether the major human malaria parasite Plasmodium falciparum exhibits fragmented population structure or local adaptation at the northern limit of its African distribution where the dry Sahel zone meets the Sahara, samples were collected from diverse locations within Mauritania over a range of ~1000 km. Microsatellite genotypes were obtained for 203 clinical infection samples from eight locations, and Illumina paired‐end sequences were obtained to yield high coverage genomewide single nucleotide polymorphism (SNP) data for 65 clinical infection samples from four locations. Most infections contained single parasite genotypes, reflecting low rates of transmission and superinfection locally, in contrast to the situation seen in population samples from countries further south. A minority of infections shared related or identical genotypes locally, indicating some repeated transmission of parasite clones without recombination. This caused some multilocus linkage disequilibrium and local divergence, but aside from the effect of repeated genotypes there was minimal differentiation between locations. Several chromosomal regions had elevated integrated haplotype scores (|iHS|) indicating recent selection, including those containing drug resistance genes. A genomewide FST scan comparison with previous sequence data from an area in West Africa with higher infection endemicity indicates that regional gene flow prevents genetic isolation, but revealed allele frequency differentiation at three drug resistance loci and an erythrocyte invasion ligand gene. Contrast of extended haplotype signatures revealed none to be unique to Mauritania. Discrete foci of infection on the edge of the Sahara are genetically highly connected to the wider continental parasite population, and local elimination would be difficult to achieve without very substantial reduction in malaria throughout the region.

Multiple reversals of chirality in the land snail genus Albinaria (Gastropoda, Clausiliidae)

Reversed chirality has frequently evolved in snails, although the vast majority coils dextrally. However, there are often sinistral species within a dextral genus or almost exclusively sinistral families, such as the Clausiliidae. Some populations of the predominantly sinistral clausiliid genus Albinaria, in the southern Greek mainland, coil dextrally. The origin, evolution and distribution of the dextral Albinaria are puzzling, and as there is no reliable phylogenetic reconstruction for this speciose genus, it remains unclear how many times a shift in chirality has really occurred. In this study, our aim was to elucidate the evolutionary pathways of dextrality in Albinaria. We undertook a molecular phylogenetic analysis of two mtDNA (16S and COI) and one nDNA marker (ITS1) and included dextral and sinistral representatives found in syntopy or not. Both mtDNA and nDNA tree topologies imply that dextrals did not evolve as a monophyletic lineage. Instead, dextral lineages have evolved from sinistral ancestors multiple times independently. The fragmented population structure in Albinaria facilitates genetic drift and contributes to fixation of the opposite chirality and overcoming of the mating disadvantage of left–right reversal. Stochastic phenomena and biogeographical barriers have trapped those reversals in a limited geographical area.

Gene flow and population structure of a solitary top carnivore in a human-dominated landscape.

While African leopard populations are considered to be continuous as demonstrated by their high genetic variation, the southernmost leopard population exists in the Eastern and Western Cape, South Africa, where anthropogenic activities may be affecting this population's structure. Little is known about the elusive, last free-roaming top predator in the region and this study is the first to report on leopard population structuring using nuclear DNA. By analyzing 14 microsatellite markers from 40 leopard tissue samples, we aimed to understand the populations' structure, genetic distance, and gene flow (Nm). Our results, based on spatially explicit analysis with Bayesian methods, indicate that leopards in the region exist in a fragmented population structure with lower than expected genetic diversity. Three population groups were identified, between which low to moderate levels of gene flow were observed (Nm 0.5 to 3.6). One subpopulation exhibited low genetic differentiation, suggesting a continuous population structure, while the remaining two appear to be less connected, with low emigration and immigration between these populations. Therefore, genetic barriers are present between the subpopulations, and while leopards in the study region may function as a metapopulation, anthropogenic activities threaten to decrease habitat and movement further. Our results indicate that the leopard population may become isolated within a few generations and suggest that management actions should aim to increase habitat connectivity and reduce human–carnivore conflict. Understanding genetic diversity and connectivity of populations has important conservation implications that can highlight management of priority populations to reverse the effects of human-caused extinctions.

Fragmented population structure of Plasmodium falciparum in Papua New Guinea: Implications for malaria control

Malaria is being controlled in Papua New Guinea (PNG) where the epidemiology of the disease ranges from highly endemic in low-lying regions to epidemics in the highlands. Analyses of microsatellite haplotypes have revealed that populations of Plasmodium falciparum on the north coast of PNG are genetically isolated. If this fragmented population structure is found throughout PNG it will provide a unique opportunity for planning malaria control strategies and focusing efforts on regions where they are likely to have the greatest impact. We are working towards defining a high-resolution population genomic map of parasite networks and migration patterns throughout PNG using single nucleotide polymorphisms. Our approach, preliminary data and the practical implications of this research will be discussed in context with the national malaria control program.

Mind the gap: genetic distance increases with habitat gap size in Florida scrub jays

Habitat gap size has been negatively linked to movement probability in several species occupying fragmented landscapes. How these effects on movement behaviour in turn affect the genetic structure of fragmented populations at local scales is less well known. We tested, and confirmed, the hypothesis that genetic differentiation among adjacent populations of Florida scrub jays--an endangered bird species with poor dispersal abilities and a high degree of habitat specialization--increases with the width of habitat gaps separating them. This relationship was not an artefact of simple isolation-by-distance, as genetic distance was not correlated with the Euclidean distance between geographical centroids of the adjacent populations. Our results suggest that gap size affects movement behaviour even at remarkably local spatial scales, producing direct consequences on the genetic structure of fragmented populations. This finding shows that conserving genetic continuity for specialist species within fragmented habitat requires maintenance or restoration of preserve networks in which habitat gaps do not exceed a species-specific threshold distance.

Genetic structure in fragmented populations of Solanum lycocarpum A. St.-Hil. with distinct anthropogenic histories in a Cerrado region of Brazil

Solanum lycocarpum is a woody tree widely distributed in the Cerrado that reaches high population densities in disturbed environments. We examined the genetic diversity and population differentiation of six S. lycocarpum populations with different degrees of human disturbance in order to determine if they are negatively affected by anthropogenic activity. Three populations located in southern and three located in southeastern regions of Goiás State, Central Brazil, were genotyped with five microsatellite markers. The population located in a protected area had higher number of alleles (26) than the remaining populations (19 to 21 alleles). It indicates that extensive and continuous areas of preserved native vegetation contribute positively to the conservation of genetic diversity, even with S. lycocarpum that easily adapts to disturbed environments. The three southeastern populations, although fragmented, had preserved native vegetation and were not significantly different from each other (θp = 0.002). All other population pairs compared were significantly divergent (θp varied from 0.03 to 0.11 between pairs, P < 0.05). We found three distinct sets of allele frequencies. The three southeastern populations shared similar gene pools, as well as the two disturbed southern populations, which are secondary vegetation. The southern population located in protected area had the most dissimilar gene pool. In conclusion, populations showing a higher degree of human disturbance tends to show a larger population differentiation than expected from the isolation by distance model, which in the current scenario of the Cerrado destruction points out to a threat to the long-term conservation of the species.

Islands beneath islands: phylogeography of a groundwater amphipod crustacean in the Balearic archipelago

BackgroundMetacrangonyctidae (Amphipoda, Crustacea) is an enigmatic continental subterranean water family of marine origin (thalassoid). One of the species in the genus, Metacrangonyx longipes, is endemic to the Balearic islands of Mallorca and Menorca (W Mediterranean). It has been suggested that the origin and distribution of thalassoid crustaceans could be explained by one of two alternative hypotheses: (1) active colonization of inland freshwater aquifers by a marine ancestor, followed by an adaptative shift; or (2) passive colonization by stranding of ancestral marine populations in coastal aquifers during marine regressions. A comparison of phylogenies, phylogeographic patterns and age estimations of clades should discriminate in favour of one of these two proposals.ResultsPhylogenetic relationships within M. longipes based on three mitochondrial DNA (mtDNA) and one nuclear marker revealed five genetically divergent and geographically structured clades. Analyses of cytochrome oxidase subunit 1 (cox1) mtDNA data showed the occurrence of a high geographic population subdivision in both islands, with current gene flow occurring exclusively between sites located in close proximity. Molecular-clock estimations dated the origin of M. longipes previous to about 6 Ma, whereas major cladogenetic events within the species took place between 4.2 and 2.0 Ma.ConclusionsM. longipes displayed a surprisingly old and highly fragmented population structure, with major episodes of cladogenesis within the species roughly correlating with some of the major marine transgression-regression episodes that affected the region during the last 6 Ma. Eustatic changes (vicariant events) -not active range expansion of marine littoral ancestors colonizing desalinated habitats-explain the phylogeographic pattern observed in M. longipes.

Genetic structure in fragmented populations of Hippophae rhamnoides ssp. sinensis in China investigated by ISSR and cpSSR markers

Hippophae rhamnoides ssp. sinensis is an ecologically and economically important species that has been widely used as a pioneer plant in China. In this study, we employed both nuclear ISSR and maternal cpSSR markers to survey the genetic diversity and structure of populations of ssp. sinensis representing three different landscapes, the northwestern desert and grassland region, the alpine vegetation region of the Qinghai-Tibetan Plateau, and the northeastern humid forest region. In all, 12 natural populations with a scattered distribution in the area were studied. The genetic diversities of populations were found to be uneven, and the total genetic diversity was low on the basis of both types of marker. Mantel tests based on both individual Euclidean distance matrices and population genetic distance (measured by Φpt) matrices showed that the two marker systems detected similar trends with respect to genetic distances between populations. The analysis of molecular variance (AMOVA) revealed significant differentiation among populations and among regions for both types of marker. Although the detected pattern of isolation-by-distance among all sampled populations confirmed the earlier colonization pathway, the low level of gene flow and the lack of isolation by distance within each region suggested the presence of an additional dispersal barrier. UPGMA dendrograms and PCA plots also revealed clear clustering and significant regional differentiation. Our results indicate that the genetic structure of ssp. sinensis has been affected by habitat fragmentation and restricted population sizes. We propose that the biology of reproduction and ecology have played determinant roles in the development of the regional structure of populations. The genetic information obtained will help to establish conservation strategies and programs for sustainable management of H. rhamnoides ssp. sinensis.

Assessing genetic diversity and structure of fragmented populations of eastern white pine (Pinus strobus) and western white pine (P. monticola) for conservation management

Aims Many pine populations in Canada have fragmented distributions resulting from the effects of glaciations, overharvesting and white pine blister rust infections. Forest fragmentation can modify gene flow and reduce genetic diversity. Selective logging can reduce the density of trees, thereby altering mating patterns and increasing inbreeding. The hypothesis of the present study is that forest fragmentation will not increase inbreeding and will have no effect on genetic diversity parameters in the Canadian Pinus moniticola and P. strobus populations targeted because of (i) the long life span of the pine species, (ii) outbreeding and self-incompatibility of P. monticola and P. strobus and (iii) wind pollination resulting in high gene flow among populations. We studied the genetic diversity of P. strobus across its range in Canada, and we completed a detailed analysis of the genetic structure of P. monticola populations from western Canada using microsatellites genetic markers. Methods Seed samples from 10 P. monticola populations and 10 P. strobus populations were collected from western and eastern Canada, respectively. The mother trees included in seed lots were representative of each stand. Genomic DNA extracted from each sample was amplified with microsatellite primers. The intra- and interpopulation genetic diversity parameters were assessed using Popgene and Genepop softwares and the genetic distances among populations within each species using the PowerMarker software. Important findings Pinus monticola and P. strobus exhibited moderate to high genetic diversity. Also, both species showed low levels of inbreeding despite the geographic isolation and small stand size. Gene flow estimates were high and population differentiation values were relatively low for these fragmented forest sites.

A conflict of morphological and genetic patterns in the Australian anostracan Branchinella longirostris

Branchinella longirostris is a fairy shrimp endemic to ephemeral pools on granite outcrops in southwestern Australia. The patchy nature of its habitat is thought to result in a high degree of subdivision among populations, potentially promoting speciation. We combined traditional taxonomy with a molecular phylogeny of cytochrome c oxidase I (COI) to test whether B. longirostris could be a species complex and whether the frontal appendage on the second antennae of males is a suitable character to differentiate new species. We also used nested clade analysis to assess the population structure and demographic factors explaining the geographical distributions of the mt DNA haplotypes. The results show that shapes of frontal appendages are not congruent with the mitochondrial genetic structure; however, they are positively correlated with geography. We conclude that the frontal appendage in B. longirostris is either subject to selection or a result of morphological plasticity; thus, its use in taxonomy remains uncertain. The intraspecific divergence in B. longirostris (≤7.7%) was approximately one third as large as the divergence from the outgroup (17.8–20.8%) and well within the ranges of divergence found in other crustaceans with fragmented population structure. There is some association between genetic structure and geography, resulting in the inference of restricted gene flow with isolation by distance and allopatric fragmentation as the most suitable models of the historical population processes. It is likely that the current distribution of haplotypes resulted from the dispersal of resting eggs by stochastic events (wind, birds) rather than from a fragmentation of previously continuous habitat as the estimated evolutionary age of the species (≤6.1 my) is much younger than its habitat (50–100 my). We found some evidence on the genetic level to support the hypothesis that B. longirostris could be a complex of species; however, the lack of correlation between the genetic pattern and the reproductively important frontal appendage lends a support to a view that B. longirostris is a single species with an exceptionally high intraspecific diversity.

Genetic Diversity and Structure in Fragmented Populations of the Tropical Orchid Myrmecophila christinae var christinae1

ABSTRACTIn recent years the coastal dune vegetation of the state of Yucatan, Mexico has become highly fragmented due to clearing for development. We evaluated patterns of genetic differentiation and genetic variability among orchid populations (Myrmecophila christinae var christinae) in eight habitat fragments along a west‐to‐east disturbance gradient in which sites located on the western end began experiencing fragmentation earlier than those in the east. Leaf samples from adult individuals and juvenile plants were collected from all eight populations, and analyzed using starch‐gel electrophoresis in a lithium buffer system. Per population estimates of genetic diversity, proportion of polymorphic loci at 95 percent, mean number of alleles per locus, allelic richness, and population structure were calculated, as well as estimate comparisons between generations. Genetic diversity at the loci analyzed did not show significant differences among the eight populations. Based on the results, the model of isolation by distance does not fit the M. christinae populations under study; in some cases, populations close to one another apparently experienced very little genetic exchange. Thus, we propose that so far, fragmentation has not led to significant genetic differences between populations subject to different historical backgrounds of disturbance (i.e., time since onset of disturbance), as well as between generations within each of the M. christinae study populations. Nevertheless, the genetic characteristics of some remnant populations might change over time due to a future decrease in the opportunities for genetic exchange with other populations.

Sex ratio mediated pollen limitation in the dioecious herb Antennaria dioica

We examined how population structure affects seed set and recruitment in the dioecious plant Antennaria dioica, which is a declining species inhabiting semi-natural grasslands in Sweden. Flowering and sex ratio in A. dioica were studied over 4 y at a local (1.2 km2) scale and over 1 y at a regional (742 km2) scale in southern Sweden. Antennaria dioica was also hand-pollinated during 2 y to examine whether sex ratios, male abundance, and distance to nearest male influence the degree of pollen limitation. Seed-sowing experiments were conducted to assess whether recruitment is limited by seed or microsite availability. There was a considerable spatio-temporal variation in both flowering and sex ratios. The regional scale survey showed that patch size and number of patches per site were positively correlated, and small patches of A. dioica tended to have biased sex ratios. Experimental hand-pollinations showed that the degree of pollen limitation increased with increasingly female-biased sex ratios in the closest vicinity of the experimental plants. Thus, even though A. dioica is pollinated by many different insects, a fragmented population structure has a large influence on reproductive performance of A. dioica. The seed-sowing experiments showed that recruitment is limited by a combination of seed and microsite availability. It is therefore plausible that reduced seed production due to pollen limitation translates into reduced recruitment. The results from the local and the regional scale indicate that a large fraction of local patches and populations of A. dioica have decreased sexual reproduction. The conclusion is that A. dioica is likely to be particularly sensitive to habitat fragmentation.