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1.
    
  1. Long‐term population persistence or population rescue require dispersal from other source populations. Barriers to movement can effectively fragment and isolate populations, reducing persistence and recolonisation. For stream organisms that depend heavily on movement within dendritic networks, research is needed to identify and estimate the effects of such barriers on connectivity.
  2. We used capture–mark–recapture of displaced larval and adult salamanders to estimate return rates across gaps (length 13–85 m) in the riparian canopy and thus to assess the fragmentation of salamander populations within otherwise fully forested catchments.
  3. Relative to salamanders in fully forested reaches, displaced salamanders were 86% less likely to return to their capture location when required to cross gaps in the canopy as short as 13 m, and the likelihood of return declined with increasing gap length. The effects of gaps on return rates were consistent among life stages and for up‐ and downstream movement.
  4. Our study suggests that riparian disturbance can reduce permeability to salamanders, even in the absence of additional land‐use change. Because anthropogenic features, such as roads and powerlines, frequently cross small streams, the accumulation of apparently small land‐cover changes has the potential to reduce continuous populations to small fragments with limited connectivity.
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Larval dispersal can connect distant subpopulations, with important implications for marine population dynamics and persistence, biodiversity conservation and fisheries management. However, different dispersal pathways may affect the final phenotypes, and thus the performance and fitness of individuals that settle into subpopulations. Using otolith microchemical signatures that are indicative of ‘dispersive’ larvae (oceanic signatures) and ‘non-dispersive’ larvae (coastal signatures), we explore the population-level consequences of dispersal-induced variability in phenotypic mixtures for the common triplefin (a small reef fish). We evaluate lipid concentration and otolith microstructure and find that ‘non-dispersive’ larvae (i) have greater and less variable lipid reserves at settlement (and this variability attenuates at a slower rate), (ii) grow faster after settlement, and (iii) experience similar carry-over benefits of lipid reserves on post-settlement growth relative to ‘dispersive’ larvae. We then explore the consequences of phenotypic mixtures in a metapopulation model with two identical subpopulations replenished by variable contributions of ‘dispersive’ and ‘non-dispersive’ larvae and find that the resulting phenotypic mixtures can have profound effects on the size of the metapopulation. We show that, depending upon the patterns of connectivity, phenotypic mixtures can lead to larger metapopulations, suggesting dispersal-induced demographic heterogeneity may facilitate metapopulation persistence.  相似文献   

4.
    
Information on genetic variation and its distribution in tropical plant populations relies mainly on studies of ground‐rooted species, while genetic information of epiphytic plants is still limited. Particularly, the effect of forest successional condition on genetic diversity and structure of epiphytes is scanty in the literature. We evaluated the genetic variation and spatial genetic structure of the epiphytic bromeliad Guzmania monostachia (Bromeliaceae, Tillandsioideae) in montane secondary forest patches in Costa Rica. The sampling design included plants on the same trees (i.e., populations), populations within forest patches and patches within secondary forest at two different successional stages (early vs. mid‐succession). Six microsatellites revealed low levels of population genetic variation (A = 2.06, AE = 1.61, HE = 0.348), a marked deficiency of heterozygotes (HO = 0.031) and high inbreeding (f = 0.908). Genetic differentiation was negligible among populations within the same forest patch, but moderate (GST = 0.123 ± 0.043) among forest patches. Genetic relatedness between individuals was significantly higher for plants located within the same forest patch and separated by <60 m and decreased as distance between plants increased, becoming significantly negative at distances >400 m. An analysis of molecular variance (AMOVA) showed significant genetic variation between forest patches, but non‐significant variation between successional stages. The selfing breeding system and limited seed dispersal capabilities in G. monostachia could explain the observed levels and partitioning of genetic diversity at this geographic scale. However, these results also suggest that forest fragmentation is likely to influence the degree of local genetic structuring of epiphytic plants by limiting gene flow.  相似文献   

5.
    
Kerth G  Petit E 《Molecular ecology》2005,14(13):3943-3950
Metapopulation genetic models consider that colonization and dispersal are distinct behaviours. However, whether colonization and dispersal indeed reflect different biological processes in nature is unclear. One possibility to test this assumption is to assess patterns of autosomal and mitochondrial genetic structure in species with strict female philopatry, such as the communally breeding Bechstein's bat. In this species, mitochondrial DNA can spread only when females establish new colonies, and autosomal DNA is transmitted among colonies only when females mate with solitary males born in foreign colonies. Investigating the genetic structure among 37 colonies, we found that autosomal genes followed an island model on a regional scale and a model of isolation by distance on a larger geographical scale. In contrast, mitochondrial genetic structure revealed no pattern of isolation by distance at a large scale but exhibited an effect of ecological barriers on a regional scale. Our results provide strong empirical evidence that colonization and dispersal do not follow the same behavioural rules in this bat, supporting the assumption of metapopulation genetic models.  相似文献   

6.
Improving the realism of spatially explicit demographic models is important for better inferring the history of past populations and for understanding the genetic bases of adaptation and speciation. One particular type of demographic event to take into account is long-distance dispersal (LDD). The goals of this study are to explore the impact of various levels of LDD on genetic diversity and to show to what extent LDD levels can be correctly inferred from multilocus data sets using an approximate Bayesian computation approach. We therefore incorporated LDD into a 2D stepping stone forward simulation framework coupled to a coalescent backward simulation step to generate genetic diversity at 100 microsatellite markers under various demographic conditions relevant to recent human evolution. Our results confirm that LDD considerably increases genetic diversity within demes and decreases levels of diversity between demes. By controlling the spatial occurrence of LDD, it appears that LDD events occurring during a phase of range expansion into new territories are more important in maintaining genetic diversity than those occurring in the wake of the expansion or when colonization is over. We also show that it is possible to infer whether LDD has occurred during a range expansion, but our results suggest that one can only approximately estimate the extent of LDD based on genetic summary statistics.  相似文献   

7.
Colonization in metapopulations: a review of theory and observations   总被引:1,自引:0,他引:1  
In metapopulation dynamics turnover of populations in isolated patches may be frequent. Regional survival of a species in such a system with frequent extinctions hinges on its colonization ability. Colonization is more than just dispersal; when a propagule reaches a new patch it faces higher extinction probabilities than does an established population. Extinction models as well as empirical data suggest that a large propagule with a potential for rapid increase in a varying environment, or with a low mortality rate in an environment perceived as constant, has a higher probability of successful colonization. Large variation in population size when it is still small increases the risk of failure. Factors introducing such variation are demographic stochasticity and environmental variation. It is hard to single out demographic traits that ensure good colonizing ability, since colonization can be achieved in many different ways, but generalists and species with self-fertilization seem to be superior.  相似文献   

8.
1. Landscape connectivity may greatly influence the distribution of animals when it alters their movements and their ability to reach food patches. Depending on their foraging behaviour, organisms may or may not adapt to anthropogenic changes in landscape connectivity and may eventually undergo local extinctions. 2. Recent studies underlined the need to use indicators of functional landscape connectivity based on the behaviour and movement abilities of studied animals to better link landscape structure to ecological processes in disturbed and fragmented areas. 3. The objectives of this study were: to elaborate an index of functional connectivity for Rhinophylla pumilio, a Neotropical understorey frugivorous bat; to use this index to investigate the possible mechanisms controlling its distribution and sustainability in a fragmented landscape; and to test whether this index could be applied to other species of the same guild. 4. We pursued a 10-year bat mist-net survey, coupled to local estimates of food availability, in a mature forest of French Guiana that was recently fragmented by the completion of a reservoir lake. The 18 sampling sites range from undisturbed continuous forest sites to small remote forest fragments. A connectivity value, based on radio-tracking surveys, was attributed to each site. Connectivity measures mean forest cover within neighbouring landscape units, weighted by the probability that bats would use them, as estimated by frequency distribution of flight distance data. 5. The abundance of R. pumilio was positively correlated with landscape connectivity and not correlated with local food availability. Its foraging strategy has evolved in response to the highly scattered distribution of its fruit resource. In spite of its high mobility, R. pumilio apparently failed to exploit a food resource that is distributed patchily over a low-connective habitat because its foraging movements are not well adapted to habitat disruptions. 6. The connectivity index contributed to explain general tendencies of abundance variations in other understorey frugivorous bats, although the spatial scale we examined was probably too small for these species. We make recommendations to adapt a functional connectivity index to species whose large-scale movements are difficult to survey.  相似文献   

9.
  总被引:1,自引:0,他引:1  
Changes in agricultural practices and forest fragmentation can have a dramatic effect on landscape connectivity and the dispersal of animals, potentially reducing gene flow within populations. In this study, we assessed the influence of woodland connectivity on gene flow in a traditionally forest-dwelling species--the European roe deer--in a fragmented landscape. From a sample of 648 roe deer spatially referenced within a study area of 55 x 40 km, interindividual genetic distances were calculated from genotypes at 12 polymorphic microsatellite loci. We calculated two geographical distances between each pair of individuals: the Euclidean distance (straight line) and the 'least cost distance' (the trajectory that maximizes the use of wooded corridors). We tested the correlation between genetic pairwise distances and the two types of geographical pairwise distance using Mantel tests. The correlation was better using the least cost distance, which takes into account the distribution of wooded patches, especially for females (the correlation was stronger but not significant for males). These results suggest that in a fragmented woodland area roe deer dispersal is strongly linked to wooded structures and hence that gene flow within the roe deer population is influenced by the connectivity of the landscape.  相似文献   

10.
    
Aim Habitat fragmentation is a major driver of biodiversity loss but it is insufficiently known how much its effects vary among species with different life‐history traits; especially in plant communities, the understanding of the role of traits related to species persistence and dispersal in determining dynamics of species communities in fragmented landscapes is still limited. The primary aim of this study was to test how plant traits related to persistence and dispersal and their interactions modify plant species vulnerability to decreasing habitat area and increasing isolation. Location Five regions distributed over four countries in Central and Northern Europe. Methods Our dataset was composed of primary data from studies on the distribution of plant communities in 300 grassland fragments in five regions. The regional datasets were consolidated by standardizing nomenclature and species life‐history traits and by recalculating standardized landscape measures from the original geographical data. We assessed the responses of plant species richness to habitat area, connectivity, plant life‐history traits and their interactions using linear mixed models. Results We found that the negative effect of habitat loss on plant species richness was pervasive across different regions, whereas the effect of habitat isolation on species richness was not evident. This area effect was, however, not equal for all the species, and life‐history traits related to both species persistence and dispersal modified plant sensitivity to habitat loss, indicating that both landscape and local processes determined large‐scale dynamics of plant communities. High competitive ability for light, annual life cycle and animal dispersal emerged as traits enabling species to cope with habitat loss. Main conclusions In highly fragmented rural landscapes in NW Europe, mitigating the spatial isolation of remaining grasslands should be accompanied by restoration measures aimed at improving habitat quality for low competitors, abiotically dispersed and perennial, clonal species.  相似文献   

11.
基于最小费用模型的景观连接度评价   总被引:4,自引:1,他引:4  
作为物种扩散的重要影响因子,景观连接度反映了景观促进或阻碍生物体在资源斑块间运动的程度,它也是区域土地可持续利用和生物保护领域的主要指标.最小费用模型起源于图论,其结合了景观中的详细地理信息和生物体的行为特征,通过费用距离分析可直观形象地描绘出物种在异质景观中的连接度,且可在GIS程序包中实现简便运算和适度的数据需求量,使其在大尺度景观连接度评价中受到广泛关注.本文结合当前的景观连接度研究,详细阐述了最小费用模型评价景观连接度的意义、原理及运算过程,并探讨了该模型应用中存在的问题,以期为进一步开展相关研究及生物多样性保护提供依据.  相似文献   

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13.
  总被引:1,自引:0,他引:1  
  1. Defining functional connectivity between habitats in spatially heterogeneous landscapes is a particular challenge for small‐bodied aquatic species. Traditional approaches (e.g. mark–recapture studies) preclude an assessment of animal movement over the life cycle (birth to reproduction), and movement of individuals may not represent the degree of gene movement for fecund species.
  2. We investigated the degree of habitat connectivity (defined as the exchange of individuals and genes between mainstem and tributary habitats) in a stream brook trout (Salvelinus fontinalis) population using mark–recapture [passive integrated transponder (PIT) tags], stationary PIT‐tag antennae and genetic pedigree data collected over 4 years (3425 marked individuals). We hypothesised that: (i) a combination of these data would reveal higher estimates of animal movement over the life cycle (within a generation), relative to more temporally confined approaches, and (ii) movement estimates of individuals within a generation would differ from between‐generation movement of genes because of spatial variation in reproductive success associated with high fecundity of this species.
  3. Over half of PIT‐tagged fish (juveniles and adults) were recaptured within 20 m during periodic sampling, indicating restricted movement. However, continuous monitoring with stationary PIT‐tag antennae revealed distinct peaks in trout movements in June and October–November, and sibship data inferred post‐emergence movements of young‐of‐year trout that were too small to be tagged physically. A combination of these methods showed that a moderate portion of individuals (28–33%) moved between mainstem and tributary habitats over their life cycle.
  4. Patterns of reproductive success varied spatially and temporally. The importance of tributaries as spawning habitat was discovered by accounting for reproductive history. When individuals born in the mainstem reproduced successfully, over 50% of their surviving offspring were inferred to have been born in tributaries. This high rate of gene movement to tributaries was cryptic, and it would have been missed by estimates based only on movement of individuals.
  5. This study highlighted the importance of characterising animal movement over the life cycle for inferring habitat connectivity accurately. Such movements of individuals can contribute to substantial gene movements in a fecund species characterised by high variation in reproductive success.
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14.
    
Aim To use molecular data to test for dispersal structuring in the immigration history of an amphidromous community on an island. Location The Caribbean island of Puerto Rico. Methods Mitochondrial DNA sequences were obtained from 11 amphidromous species, including shrimps, fish and a gastropod, sampled from throughout the island. The timing of population expansion (TE) in each species was calculated using nucleotide variation and molecular clock dating methods. The order of species accumulation was then reconstructed (oldest to most recent estimate for TE), and groups of species with non‐overlapping estimates for TE were identified. The temporal span and average immigration rate for each group were calculated and compared with expectations of two previously published models of island immigration [the ‘dispersal‐structured model of island recolonization’ ( Whittaker & Jones, Oikos, 1994 , 69 , 524–529), which predicts short phases of rapid immigration followed by extended phases with relatively slow immigration rates; and the ‘colonization window hypothesis’ ( Carine, Taxon, 2005 , 54 , 895–903), which suggests that opportunities for island colonization are temporally constrained to discrete waves of colonization]. Results The molecular data indicated the immigration history of Puerto Rican amphidromous fauna from the late Pleistocene through the Holocene and identified two groups of species with non‐overlapping estimates for TE and one group that overlapped with the other two groups. The temporal span, average immigration rate and lack of discreteness between all three groups indicated a continuum of immigration rather than distinct phases of species arrivals. Main conclusions This study did not support the expectations of the immigration models and suggested that amphidromous species from Puerto Rico comprise a single class of marine‐based dispersers. The immigration sequence we report probably reflects a recolonization chronology in this community, in keeping with the notion of species turnover through time. Four areas of future research into the immigration history of amphidromous species on islands are identified, and indicated the possibility that equilibrium processes govern long‐term community change in amphidromous biota on islands.  相似文献   

15.
    
Habitat fragmentation is among the most important global threats to biodiversity; however, the direct effects of its components including connectivity loss are largely unknown and still mostly inferred based on indirect evidence. Our understanding of these drivers is especially limited in microbial communities. Here, by conducting a 4-month outdoor experiment with artificial pond (mesocosm) metacommunities, we studied the effects of connectivity loss on planktonic microorganisms, primarily focusing on pro- and microeukaryotes. Connectivity loss was simulated by stopping the dispersal among local habitats after an initial period with dispersal. Keeping the habitat amount constant and the abiotic environment homogeneous allowed us to track the direct effects of the process of connectivity loss. We found that connectivity loss led to higher levels of extinction and a decrease in both local and regional diversity in microeukaryotes. In contrast, diversity patterns of prokaryotes remained largely unaffected, with some indications of extinction debt. Connectivity loss also led to lower evenness in microeukaryotes, likely through changes in biotic interactions with zooplankton grazers. Our results imply that connectivity loss can directly translate into species losses in communities and highlight the importance of conserving habitat networks with sufficient dispersal among local habitats.  相似文献   

16.
    
  1. The hyporheic zone of rivers potentially acts as a dispersal corridor for groundwater organisms because it provides a spatially continuous interstitial habitat between isolated aquifers. Yet, the degree to which it can facilitate the movement of organisms has been hypothesized to vary in response to change in sediment regime, which determines channel morphology.
  2. In this study, we used microsatellite markers to test for a relationship between the genetic structure and diversity of the minute interstitial isopod Proasellus walteri and channel morphology along three nearby hyporheic corridors differing widely in their sediment regime. We predicted that genetic diversity would decrease and genetic structuring would increase as sediment supply‐limited channels would become prominent features in the river corridor. The reason is that such channels have fewer and less suitable sedimentary habitats for migration because they lack large depositional bedforms such as gravel bars.
  3. Using genotypic data from seven microsatellite loci for a total of 713 individuals distributed among 25 demes, we found that demes had on average more alleles and were less differentiated in the river showing the most extensive alluvial deposits and shortest length of sediment supply‐limited channels. Population clusters were also of greater size, reaching up to 30 km in length. The longitudinal pattern of genetic differentiation in this sediment‐rich river was best explained by hydrologic distance and the longitudinal pattern of allelic richness was bell‐shaped, as expected under a stepping‐stone model with symmetrical migration.
  4. The length of sediment supply‐channels was more important than hydrologic distance in explaining the longitudinal distribution of genetic differentiation in the two other corridors facing a sediment shortage. Allelic richness decreased monotonically upstream in the most sediment‐poor river. This correlates with the expansion further downstream of sediment supply‐limited channels in this river, which is likely to decrease animal movement and hence gene flow among demes.
  5. This study provides the first evidence that the degree to which the hyporheic zone facilitates the movement of groundwater organisms varies greatly among rivers of contrasted geomorphology. Extending the application of riverscape genetics across a range of interstitial taxa and geomorphic settings holds much promise for assessing the contribution of the hyporheic zone to the dispersal of groundwater organisms.
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17.
    
Natal dispersal has profound consequences for populations through the movement of individuals and genes. Habitat fragmentation reduces structural connectivity by decreasing patch size and increasing isolation, but understanding of how this impacts dispersal and the functional connectivity of landscapes is limited because many studies are constrained by the size of the study areas or sample sizes to accurately capture natal dispersal. We quantified natal dispersal probability and natal dispersal distances in a small migratory shorebird, the Southern Dunlin Calidris alpina schinzii, with data from two extensively monitored endangered metapopulations breeding in Sweden and Finland. In both metapopulations philopatry was strong, with individuals returning to or close to their natal patches more often than expected by chance, consistent with the patchy distribution of their breeding habitat. Dispersal probabilities were lower and dispersal distances were shorter in Sweden. These results provide a plausible explanation for the observed inbreeding and population decline of the Swedish population. The differences between Sweden and Finland were explained by patch‐specific differences. Between‐patch dispersal decreased with increasing natal patch size and distance to other patches. Our results suggest that reduced connectivity reduces movements of the philopatric Dunlin, making it vulnerable to the effects of inbreeding. Increasing connectivity between patches should thus be one of the main goals when planning future management. This may be facilitated by creating a network of suitably sized patches (20–100 ha), no more than 20 km apart from each other, from existing active patches that may work as stepping stones for movement, and by increasing nest success and pre‐fledging survival in small patches.  相似文献   

18.
This review assesses and predicts the impacts that rapid climate change will have on population connectivity in coral reef ecosystems, using fishes as a model group. Increased ocean temperatures are expected to accelerate larval development, potentially leading to reduced pelagic durations and earlier reef-seeking behaviour. Depending on the spatial arrangement of reefs, the expectation would be a reduction in dispersal distances and the spatial scale of connectivity. Small increase in temperature might enhance the number of larvae surviving the pelagic phase, but larger increases are likely to reduce reproductive output and increase larval mortality. Changes to ocean currents could alter the dynamics of larval supply and changes to planktonic productivity could affect how many larvae survive the pelagic stage and their condition at settlement; however, these patterns are likely to vary greatly from place-to-place and projections of how oceanographic features will change in the future lack sufficient certainty and resolution to make robust predictions. Connectivity could also be compromised by the increased fragmentation of reef habitat due to the effects of coral bleaching and ocean acidification. Changes to the spatial and temporal scales of connectivity have implications for the management of coral reef ecosystems, especially the design and placement of marine-protected areas. The size and spacing of protected areas may need to be strategically adjusted if reserve networks are to retain their efficacy in the future.  相似文献   

19.
    
Luis Gimenez 《Ecography》2019,42(4):643-657
Dispersal and migration can be important drivers of species distributions. Because the paths followed by individuals of many species are curvilinear, spatial statistical models based on rectilinear coordinates systems would fail to predict population connectivity or the ecological consequences of migration or species invasions. I propose that we view migration/dispersal as if organisms were moving along curvilinear geometrical objects called smooth manifolds. In that view, the curvilinear pathways become the ‘shortest realised paths’ arising from the necessity to minimise mortality risks and energy costs. One can then define curvilinear coordinate systems on such manifolds. I describe a procedure to incorporate manifolds and define appropriate coordinate systems, with focus on trajectories (1D manifolds), as parts of mechanistic ecological models. I show how a statistical method, known as ‘manifold learning’, enables one to define the manifold and the appropriate coordinate systems needed to calculate population connectivity or study the effects of migrations (e.g. in aquatic invertebrates, fish, insects and birds). This approach may help in the design of networks of protected areas, in studying the consequences of invasion, range expansions, or transfer of parasites/diseases. Overall, a geometrical view to animal movement gives a novel perspective to the understanding of the ecological role of dispersal and migration.  相似文献   

20.
    
One of the most vital and urgent global conservation challenges is to deal with the loss and fragmentation of wildlife habitats, particularly for large-bodied and wide-ranging terrestrial megafauna. The Central Forest Spine Master Plan for Ecological Linkages (CFS) was developed by the Malaysian Federal Government in 2010 to protect biodiversity and ecosystem services by securing landscape connectivity between Peninsular Malaysia's main forest blocks. Here we present an evaluation of the effectiveness of the CFS master plan to promote functional connectivity for Asian elephants, one of its focal species. The specific objectives of our study were to identify the most critical forest patches to maintain connectivity for elephants in Peninsular Malaysia, assess functional connectivity within the CFS ecological linkages, and identify alternative corridors where appropriate to enhance CFS effectiveness. We used the largest animal movement dataset in Peninsular Malaysia (220,000 GPS locations from 53 elephants) to develop models of elephant movement probability and to estimate landscape resistance using step selection functions based on landscape characteristics. According to our evaluation of 28 linkages, 57% of them provided high functional connectivity, 28% provided acceptable connectivity, and 14% provided low to no connectivity. A very important and positive finding is that the CFS linkages with the highest centrality values (i.e., the most important to maintain overall connectivity in Peninsular Malaysia) also score highly in functional connectivity (i.e., they are actually effective corridors for elephant movement). This means that an adequate CFS implementation can lead to high levels of functional connectivity among Peninsular Malaysia's main forest blocks. Based on our assessment, we recommend to conduct some revisions on the CFS plan to ensure its effectiveness.  相似文献   

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