Gene flow and genetic structure of the aquatic macrophyte Sparganium emersum in a linear unidirectional river

1. River systems offer special environments for the dispersal of aquatic plants because of the unidirectional (downstream) flow and linear arrangement of suitable habitats.
2. To examine the effect of this flow on microevolutionary processes in the unbranched bur-reed ( Sparganium emersum ) we studied the genetic variation within and among nine (sub)populations along a 103 km stretch of the Niers River (Germany–The Netherlands), using amplified fragment length polymorphisms.
3. Genetic diversity in S. emersum populations increased significantly downstream, suggesting an effect of flow on the pattern of intrapopulation genetic diversity.
4. Gene flow in the Niers River is asymmetrically bidirectional, with gene flow being approximately 3.5 times higher in a downstream direction. The observed asymmetry is probably caused by frequent hydrochoric dispersal towards downstream locations on the one hand, and sporadic zoochoric dispersal in an upstream direction on the other. The spread of vegetative propagules (leaf and stem fragments) is probably not an important mode of dispersal for S. emersum , suggesting that gene flow is mainly via seed dispersal. Realized dispersal distances exceeded 60 km, revealing a potential for long-distance dispersal in S. emersum .
5. There was no correlation between geographical and genetic distances among the nine S. emersum populations (i.e. no isolation by distance), which may be due to the occurrence of long-distance dispersal and/or colonization and extinction dynamics in the Niers River.
6. Overall, the genetic population structure and regional dispersal patterns of S. emersum in the Niers River are best explained by a linear metapopulation model. Our study shows that flow can exert a strong influence on population genetic processes of plants inhabiting stream systems.     

Genetic diversity and dispersal of Phragmites australis in a small river system

Even though the reed, Phragmites australis, is an extensively studied wetland species, little is known about reproduction and dispersal modes within and among reed populations at the scale of small river systems. Using microsatellite analysis of 189 individuals from three adjacent river catchments in the Czech Republic, we elucidated the role of the river corridors in the dispersal of P. australis. Using Bayesian clustering of individuals, we found that 19% of clusters were distributed only along one river, which implied dispersal by water (or by wind) along river corridors, whereas 38% of clusters were widely distributed and were likely the product of wind long-distance dispersal among rivers. Intensive exchange of propagules among river systems is further demonstrated by only 6% of total variance being attributed to the variance among rivers in the AMOVA-analysis. Spatial autocorrelation analysis revealed a decreasing pattern up to 5–10 km and no clear pattern over longer distances. This gives an evidence for pollen and seed dispersal at short distances (up to 1 km), whereas most likely only seed dispersal at longer distances up to 10 km. We found five multilocus genotypes distributed in two different populations. The distances between populations with the same genotype ranged from 0.5 to 10.8 km. This can be interpreted as long-distance vegetative dispersal.     

Population genetics suggests effectiveness of habitat connectivity measures for the European tree frog in Switzerland

1.  Governmental authorities in many countries financially support the implementation of habitat connectivity measures to enhance the exchange of individuals among fragmented populations. The evaluation of the effectiveness of such measures is crucial for future management directions and can be accomplished by using genetic methods.
2.  We retraced the population history of the European tree frog in two Swiss river valleys (Reuss and Thur), performed comprehensive population sampling to infer the genetic structure at 11 microsatellite markers, and used first-generation migrant assignment tests to evaluate the contemporary exchange of individuals.
3.  Compared with the Thur valley, the Reuss valley has lost almost double the number of breeding sites and exhibited a more pronounced genetic grouping. However, similar numbers of contemporary migrants were detected in both valleys. In the Reuss valley, 81% of the migration events occurred within the identified genetic groups, whereas in the Thur valley migration patterns were diffuse.
4.  Our results show that the connectivity measures implemented in the Reuss valley facilitated effective tree frog migration among breeding sites within distances up to 4 km. Nevertheless, the Reuss valley exhibited high genetic differentiation, which reflected the impact of barriers to tree frog movement such as the River Reuss. By contrast in the Thur valley, a larger number of breeding sites have been preserved and high admixture indicated exchange of individuals at distances up to 16 km.
5.   Synthesis and applications . We show that genetic methods can substantiate the effectiveness of connectivity measures taken in conservation management at the landscape scale. We urge responsible authorities from both river valleys to continue implementing connectivity measures and to create a dense network of breeding sites, as spatial gaps of 8 km are rarely traversed by tree frogs.     

Correlations between observed dispersal capabilities and patterns of genetic differentiation in populations of four aquatic insect species from the Arizona White Mountains, U.S.A.

SUMMARY 1. Dispersal ability is an important ecological factor that can influence population structure. In an attempt to determine the extent that the pattern of genetic differentiation is correlated with dispersal ability in stream-dwelling aquatic insects, we used the amplified fragment length polymorphism (AFLP) technique to characterise genetic variation in four aquatic insect species: Gumaga griseola (Trichoptera: Sericostomatidae), Helicopsyche mexicana (Trichoptera: Helicopsychidae), Psephenus montanus (Coleoptera: Psephenidae) and Ambrysus thermarum (Hemiptera: Naucoridae). Individuals were sampled from several sites within two adjacent catchments in the Arizona White Mountains. In addition to the genetic analyses, a 20-week-long trapping study was used to determine the relative dispersal ability of adults of the four species examined.
2. We obtained hierarchical indicators of genetic differentiation for catchments, sites within catchments and sites across the region examined. Overall, average estimators of genetic differentiation ( F -statistics) were consistent with direct observations of organismal movement, although it was our direct observations on adult insect flight that permitted us to interpret our results correctly. This was because of the fact that a lack of genetic differentiation across watersheds can be interpreted in two ways.
3. In contrast to F -statistics, patterns of genetic isolation by distance for each species more clearly reflected dispersal ability, suggesting that such analytical approaches provide less ambiguous information about the importance of gene flow in the hierarchical partitioning of genetic variation in stream organisms.     

Reproductive strategy, clonal structure and genetic diversity in populations of the aquatic macrophyte Sparganium emersum in river systems

Many aquatic and riparian plant species are characterized by the ability to reproduce both sexually and asexually. Yet, little is known about how spatial variation in sexual and asexual reproduction affects the genotypic diversity within populations of aquatic and riparian plants. We used six polymorphic microsatellites to examine the genetic diversity within and differentiation among 17 populations (606 individuals) of Sparganium emersum, in two Dutch-German rivers. Our study revealed a striking difference between rivers in the mode of reproduction (sexual vs. asexual) within S. emersum populations. The mode of reproduction was strongly related to locally reigning hydrodynamic conditions. Sexually reproducing populations exhibited a greater number of multilocus genotypes compared to asexual populations. The regional population structure suggested higher levels of gene flow among sexually reproducing populations compared to clonal populations. Gene flow was mainly mediated via hydrochoric dispersal of generative propagules (seeds), impeding genetic differentiation among populations even over river distances up to 50 km. Although evidence for hydrochoric dispersal of vegetative propagules (clonal plant fragments) was found, this mechanism appeared to be relatively less important. Bayesian-based assignment procedures revealed a number of immigrants, originating from outside our study area, suggesting intercatchment plant dispersal, possibly the result of waterfowl-mediated seed dispersal. This study demonstrates how variation in local environmental conditions in river systems, resulting in shifting balances of sexual vs. asexual reproduction within populations, will affect the genotypic diversity within populations. This study furthermore cautions against generalizations about dispersal of riparian plant species in river systems.     

Patterns of genetic structure in the endangered aquatic gastropod Valvata utahensis (Mollusca: Valvatidae) at small and large spatial scales

1. The aquatic snail Valvata utahensis (Gastropoda: Valvatidae) is a federally endangered aquatic mollusk known only from the Snake River in southern Idaho, U.S.A. The Snake River, like many other large river systems in the western United States, has undergone substantial anthropogenic modifications in recent history that have altered water flows, changed physicochemical attributes of the water and produced an overall spatially fragmented aquatic system. 2. Because little is currently known about the basic biology and life history of V. utahensis, we conducted a detailed genetic analysis of amplified fragment length polymorphism (AFLP) and mitochondrial DNA sequence variation in this species from six locations along the Snake River. This study was designed to discern (i) levels of within‐location genetic diversity, (ii) patterns of genetic structure at small spatial scales (i.e. within sampling locations) and (iii) patterns of genetic structure at large spatial scales (among sampling locations). 3. We show that comparable levels of nuclear genetic variation exist within each of the six locations examined. However, reduced mitochondrial sequence diversity was observed at Thousand Springs compared with the other locations examined. 4. We further illustrate that V. utahensis shows no genetic structure within locations over relatively small physical distances up to approximately 3 km. We suggest that active dispersal of individuals via crawling and passive dispersal because of downstream displacement or floating behaviours may have produced this pattern. However, at large spatial scales genetic structure generally followed an isolation‐by‐distance pattern. This pattern was not directly correlated with the connectivity of locations through the river corridor and suggested the possible role of episodic passive dispersal via avian waterfowl or the effects of historical floods throughout the Snake River c. 14 000 years ago.     

Allozyme diversity and population genetic structure of the caddisfly Orthopsyche fimbriata and the mayfly Acanthophlebia cruentata in New Zealand streams

1. Allozymes were used to measure genetic variation within and among regional populations of the caddisfly Orthopsyche fimbriata and the mayfly Acanthophlebia cruentata in North Island New Zealand streams.
2. High levels of genetic differentiation were recorded in populations of O. fimbriata within and among catchments separated by more than 100 km, but little or no differentiation in populations separated by around 10 km. The Auckland isthmus appears to be a major barrier to north–south gene flow, with nearly fixed allelic differences at one locus. Genotype frequencies conformed to Hardy–Weinberg equilibrium.
3.  Acanthophlebia cruentata had low levels of genetic variation; the results are unexpected given that O. fimbriata apparently has greater potential for dispersal. The limited genetic data for A. cruentata provided evidence for genetic differentiation among populations separated by around 100 km, or more, within catchments and some differentiation between catchment populations separated by only 25 km.     

Inferring long-distance dispersal and topographic barriers during post-glacial colonization from the genetic structure of red maple (Acer rubrum L.) in New England

Aim  This study aims to assess the role of long-distance seed dispersal and topographic barriers in the post-glacial colonization of red maple ( Acer rubrum L.) using chloroplast DNA (cpDNA) variation, and to understand whether this explains the relatively higher northern diversity found in eastern North American tree species compared with that in Europe.
Location  North-eastern United States.
Methods  The distribution of intraspecific cpDNA variation in temperate tree populations has been used to identify aspects of post-glacial population spread, including topographic barriers to population expansion and spread by long-distance seed dispersal. We sequenced c.  370 cpDNA base pairs from 221 individuals in 100 populations throughout the north-eastern United States, and analysed spatial patterns of diversity and differentiation.
Results  Red maple has high genetic diversity near its northern range limit, but this diversity is not partitioned by topographic barriers, suggesting that the northern Appalachian Mountains were not a barrier to the colonization of red maple. We also found no evidence of the patchy genetic structure that has been associated with spread by rare long-distance seed dispersal in previous studies.
Main conclusions  Constraints on post-glacial colonization in eastern North America seem to have been less stringent than those in northern Europe, where bottlenecks arising from long-distance colonization and topographic barriers appear to have strongly reduced genetic diversity. In eastern North America, high northern genetic diversity may have been maintained by a combination of frequent long-distance dispersal, minor topographic obstacles and diffuse northern refugia near the ice sheet.     

Genetic and ecological data provide incongruent interpretations of population structure and dispersal in naturally subdivided populations of white-tailed ptarmigan (Lagopus leucura)

The dispersal of individuals among populations affects the demographic and adaptive trajectories of animal populations and is fundamental to understanding population dynamics. White-tailed ptarmigan (Lagopus leucura) are a high elevation grouse species that live year-round in patchily distributed alpine areas in western North America. We investigated the patterns of dispersal and identified barriers to gene flow for a threatened subspecies (L. l. saxatilis) endemic to Vancouver Island, Canada. Connectivity among seven sites was examined using nine microsatellite loci (n = 133 individuals, H(O) = 0.62, mean number of alleles = 10) and direct movement observations using radio-telemetry (n = 118 individuals). Average movement distances of individuals measured by radio-telemetry were 0.63-3.23 km and considerably less than the shortest distance between sampling sites (18 km). Furthermore, despite extensive radio-telemetry data, movement was never observed between any of the seven sampling sites. In contrast, genetic results (STRUCTURE, TESS) showed connectivity among most of the seven sampling sites and suggested that genetic variation is best explained by two clusters of individuals which separated the South sampling site from all other areas of Vancouver Island. Analysis of molecular data also showed a generally consistent pattern of isolation by distance (Mantel test r = 0.11, P < 0.01) with large areas of unsuitable low elevation habitat possibly acting as barriers to gene flow. Despite the naturally subdivided distribution of populations, white-tailed ptarmigan do not fit well into any common definition of a metapopulation. We conclude the incongruities between the genetic and radio-telemetry data are best explained by episodic dispersal patterns. In this study, we demonstrated the importance of combining genetic and ecological data in understanding patterns of dispersal and population structure.     

Population spatial structuring on the feeding grounds in North Atlantic humpback whales (Megaptera novaeangliae)

Population spatial structuring among North Atlantic humpback whales Megaptera novaeangliae on the summer feeding grounds was investigated using movement patterns of identified individuals. We analysed the results from an intensive 2-year ocean-basin-scale investigation resulting in 1658 individuals identified by natural markings and 751 individuals by genetic markers supplemented with data from a long-term collaborative study with 3063 individuals identified by natural markings. Re-sighting distances ranged from <1 km to >2200 km. The frequencies ( F ) of re-sighting distances ( D ) observed in consecutive years were best modelled by an inverse allometric function ( F =6631 D ^−1.24, r ²=0.984), reflecting high levels of site fidelity (median re-sighting distance <40 km) with occasional long-distance movement (5% of re-sightings >550 km). The distribution of re-sighting distances differed east and west of 45°W, with more long-distance movement in the east. This difference is consistent with regional patterns of prey distribution and predictability. Four feeding aggregations were identified: the Gulf of Maine, eastern Canada, West Greenland and the eastern North Atlantic. There was an exchange rate of 0.98% between the western feeding aggregations. The prevalence of long-distance movement in the east made delineation of possible additional feeding aggregations less clear. Limited exchange between sites separated by as little as tens of kilometres produced lower-level structuring within all feeding aggregations. Regional and temporal differences in movement patterns reflected similar foraging responses to varying patterns of prey availability and predictability. A negative relationship was shown between relative abundance of herring and sand lance in the Gulf of Maine and humpback whale movement from the Gulf of Maine to eastern Canada.     

Molecular approaches reveal weak sibship aggregation and a high dispersal propensity in a non‐native fish parasite

Inferring parameters related to the aggregation pattern of parasites and to their dispersal propensity are important for predicting their ecological consequences and evolutionary potential. Nonetheless, it is notoriously difficult to infer these parameters from wildlife parasites given the difficulty in tracking these organisms. Molecular‐based inferences constitute a promising approach that has yet rarely been applied in the wild. Here, we combined several population genetic analyses including sibship reconstruction to document the genetic structure, patterns of sibship aggregation, and the dispersal dynamics of a non‐native parasite of fish, the freshwater copepod ectoparasite Tracheliastes polycolpus. We collected parasites according to a hierarchical sampling design, with the sampling of all parasites from all host individuals captured in eight sites spread along an upstream–downstream river gradient. Individual multilocus genotypes were obtained from 14 microsatellite markers, and used to assign parasites to full‐sib families and to investigate the genetic structure of T. polycolpus among both hosts and sampling sites. The distribution of full‐sibs obtained among the sampling sites was used to estimate individual dispersal distances within families. Our results showed that T. polycolpus sibs tend to be aggregated within sites but not within host individuals. We detected important upstream‐to‐downstream dispersal events of T. polycolpus between sites (modal distance: 25.4 km; 95% CI [22.9, 27.7]), becoming scarcer as the geographic distance from their family core location increases. Such a dispersal pattern likely contributes to the strong isolation‐by‐distance observed at the river scale. We also detected some downstream‐to‐upstream dispersal events (modal distance: 2.6 km; 95% CI [2.2–23.3]) that likely result from movements of infected hosts. Within each site, the dispersal of free‐living infective larvae among hosts likely contributes to increasing genetic diversity on hosts, possibly fostering the evolutionary potential of T. polycolpus.     

Migratory behaviour of ide: a comparison between the lowland rivers Elbe, Germany, and Vecht, The Netherlands

Individual movement patterns of adult ide Leuciscus idus , a Eurasian river‐dwelling cyprinid, in two lowland rivers were measured all year‐round during 1997–2000 to assess migratory behaviour and variation between and within these populations. In the River Elbe, a 1091 km long lowland river with a free flowing stretch of 590 km, 24 ide were implanted with radio transmitters. Fish were hand‐tracked all year‐round once a week in the main study area (75 km), and once per 6 weeks in a larger area (321 km). In the River Vecht, a 190 km long highly regulated river with six weirs and fishways in the Dutch section, 25 ide were implanted with transponders. An array of three automatic detection stations covering the entire river width, registered each individual passage continuously. Within population variation in year‐round movement patterns was very high. In both rivers a similar continuum was found from individuals using a river stretch of only a few km for spawning, feeding and wintering, to individuals migrating >100 km. The populations in the two rivers differed, however, in spawning site fidelity. In the River Vecht spawning site fidelity was observed in all individuals and appeared much stronger than in the River Elbe, where individuals moving downstream >60–90 km tended to adopt new spawning sites in the next year. Moreover, some ide in the River Vecht migrated upstream to wintering habitats in autumn, whereas this was not observed in the River Elbe. The results suggest that ide is a flexible species capable of using a wide variety of movement patterns and scales.     

Inland dispersal of adult aquatic insects

1. Adult caddisflies (Trichoptera) and mayflies (Ephemeroptera) were light-trapped on summer evenings along the Detroit River and Lake St. Clair, near Windsor, Ontario, Canada. Light traps were located at the shore and at increasing distances inland up to 5 km, and were operated simultaneously for 2 h following sunset. Catches of five species of caddisflies of the family Hydropsychidae ( Cheumatopsyche campyla , Cheumatopsyche speciosa , Hydropsyche hageni , Hydropsyche phalerata , Macrostemum zebratum ) and the mayfly Hexagenia (Ephemeridae) were used to examine inland distribution.
2. Inland dispersal was limited: catches of caddisflies declined at a greater than exponential rate with increasing distance from shore. Mean dispersal distance from the shoreline ranged from 650 to 1845 m. Smaller caddisfly species dispersed shorter distances than larger caddisflies and Hexagenia .
3. Inland distribution of adult caddisflies exhibited considerable interspecific variation: distribution was inconsistent among trials for Hexagenia , possibly owing to timing of collections in relation to periods of peak emergence.
4. Sex ratios of caddisflies were female biased at most sites. No consistent bias was observed for Hexagenia . Different inland distribution patterns were observed for males and females. The differences appeared to reflect species-specific reproductive strategies.     

Inland dispersal of adult aquatic insects

1. Adult caddisflies (Trichoptera) and mayflies (Ephemeroptera) were light-trapped on summer evenings along the Detroit River and Lake St. Clair, near Windsor, Ontario, Canada. Light traps were located at the shore and at increasing distances inland up to 5 km, and were operated simultaneously for 2 h following sunset. Catches of five species of caddisflies of the family Hydropsychidae ( Cheumatopsyche campyla , Cheumatopsyche speciosa , Hydropsyche hageni , Hydropsyche phalerata , Macrostemum zebratum ) and the mayfly Hexagenia (Ephemeridae) were used to examine inland distribution.
2. Inland dispersal was limited: catches of caddisflies declined at a greater than exponential rate with increasing distance from shore. Mean dispersal distance from the shoreline ranged from 650 to 1845 m. Smaller caddisfly species dispersed shorter distances than larger caddisflies and Hexagenia .
3. Inland distribution of adult caddisflies exhibited considerable interspecific variation: distribution was inconsistent among trials for Hexagenia , possibly owing to timing of collections in relation to periods of peak emergence.
4. Sex ratios of caddisflies were female biased at most sites. No consistent bias was observed for Hexagenia . Different inland distribution patterns were observed for males and females. The differences appeared to reflect species-specific reproductive strategies.     

Dispersal and recruitment of Tasiagma ciliata (Trichoptera: Tasimiidae) in rainforest streams, south-eastern Australia

1. This study examined genetic variation within and among populations of the caddis fly Tasiagma ciliata (Tasimiidae: Trichoptera) from rainforest streams in south-east Queensland, Australia.
2. Very low levels of genetic differentiation at large spatial scales, between subcatchments and between catchments, indicated that dispersal by the winged adults is widespread. However, significant genetic differentiation at the smallest spatial scale examined, within reaches in a single stream, suggested limited movement by larvae within streams.
3. A patchy distribution of deviations from Hardy–Weinberg equilibrium and differences in patterns among allozyme loci suggested that populations in particular reaches were the result of only a few matings.
4. These results are surprising, given the large numbers of larvae present within a single reach. We suggest that stochastic effects of recruitment may underlie much of the spatial and temporal variation in population numbers in these rainforest streams.     

Deciphering ecological barriers to North American river otter (Lontra canadensis) gene flow in the Louisiana landscape

For North American river otters (Lontra canadensis) in Louisiana, statewide distribution, availability of aquatic habitats, and the absence of physical barriers to dispersal might suggest that they exist as a large, panmictic population. However, the wide variety of habitat types in this region, and the dynamic nature of these habitats over time, could potentially structure river otter populations in accordance with cryptic landscape features. Recently developed landscape genetic models offer a spatially explicit approach that could be useful in identifying potential barriers to the movement of river otters through the dynamic aquatic landscape of Louisiana. We used georeferenced multilocus microsatellite genotypes in spatially implicit (STRUCTURE) and spatially explicit (GENELAND) models to characterize patterns of landscape genetic structure. All models identified 3 subpopulations of river otters in Louisiana, corresponding to Inland, Atchafalaya River, and Mississippi River regions. Variation in breeding seasonality, brought about by variation in prey abundance between inland and coastal populations, may have contributed to genetic differentiation among populations. It is also possible that the genetic discontinuities we observed indicate a correlation between otter distribution and access to freshwater. Regardless of the mechanism, it is likely that any genetic differentiation among subpopulations is exacerbated by relatively poor dispersal.     

Genetic spatial autocorrelation can readily detect sex-biased dispersal

Sex-biased dispersal is expected to generate differences in the fine-scale genetic structure of males and females. Therefore, spatial analyses of multilocus genotypes may offer a powerful approach for detecting sex-biased dispersal in natural populations. However, the effects of sex-biased dispersal on fine-scale genetic structure have not been explored. We used simulations and multilocus spatial autocorrelation analysis to investigate how sex-biased dispersal influences fine-scale genetic structure. We evaluated three statistical tests for detecting sex-biased dispersal: bootstrap confidence intervals about autocorrelation r values and recently developed heterogeneity tests at the distance class and whole correlogram levels. Even modest sex bias in dispersal resulted in significantly different fine-scale spatial autocorrelation patterns between the sexes. This was particularly evident when dispersal was strongly restricted in the less-dispersing sex (mean distance <200 m), when differences between the sexes were readily detected over short distances. All tests had high power to detect sex-biased dispersal with large sample sizes (n ≥ 250). However, there was variation in type I error rates among the tests, for which we offer specific recommendations. We found congruence between simulation predictions and empirical data from the agile antechinus, a species that exhibits male-biased dispersal, confirming the power of individual-based genetic analysis to provide insights into asymmetries in male and female dispersal. Our key recommendations for using multilocus spatial autocorrelation analyses to test for sex-biased dispersal are: (i) maximize sample size, not locus number; (ii) concentrate sampling within the scale of positive structure; (iii) evaluate several distance class sizes; (iv) use appropriate methods when combining data from multiple populations; (v) compare the appropriate groups of individuals.     

Availability of and access to critical habitats in regulated rivers: effects of low-head barriers on threatened lampreys

1.  Conservation of freshwater animal populations requires their access to, as well as sufficient availability of, critical habitats, such as those for reproduction. Abundant small-scale barriers may cause extensive fragmentation of freshwater habitat but, by comparison to larger structures their effects are rarely considered by catchment managers. The relationship between the distribution of, and access to, spawning habitat in a regulated river, characterized by abundant small barriers, was examined for river lamprey Lampetra fluviatilis , a threatened migratory fish.
2.  Telemetry of adult lamprey in the River Derwent, North East England was used to quantify upriver migration and access to spawning habitat, together with surveys of spawning habitat availability and spawning activity between 2002 and 2007.
3.  Access in to the Derwent appeared severely restricted by a tidal barrage, beyond which lamprey migrated rapidly in unobstructed reaches. Of all lamprey tagged in the lower 4 km of river, or ascending the barrage, 64% and 17% passed the first and second weirs respectively, with high flows crucial for this. Although over 98% of lamprey spawning habitat occurred more than 51 km upstream, on average just 1.8% of river lamprey spawners were recorded there.
4.  In order to protect or rehabilitate species or species assemblages, greater attention needs to be paid to the relative spatial distribution of low-head barriers and the resultant availability of key habitats within individual catchments. This is particularly important given the renewed emphasis internationally on low-head hydropower solutions as a source of renewable energy, and the rapid growth in numbers of low-head barriers in many catchments.     

Local population genetic structure of the montane caddisfly Drusus discolor is driven by overland dispersal and spatial scaling

相似文献   

Macroinvertebrate diversity in headwater streams: a review

1. Headwater streams are ubiquitous in the landscape and are important sources of water, sediments and biota for downstream reaches. They are critical sites for organic matter processing and nutrient cycling, and may be vital for maintaining the 'health' of whole river networks.
2. Macroinvertebrates are an important component of biodiversity in stream ecosystems and studies of macroinvertebrate diversity in headwater streams have mostly viewed stream systems as linear reaches rather than as networks, although the latter may be more appropriate to the study of diversity patterns in headwater systems.
3. Studies of macroinvertebrate diversity in headwater streams from around the world illustrated that taxonomic richness is highly variable among continents and regions, and studies addressing longitudinal changes in taxonomic richness of macroinvertebrates generally found highest richness in mid-order streams.
4. When stream systems are viewed as networks at the landscape-scale, α-diversity may be low in individual headwater streams but high β-diversity among headwater streams within catchments and among catchments may generate high γ-diversity.
5. Differing ability and opportunity for dispersal of macroinvertebrates, great physical habitat heterogeneity in headwater streams, and a wide range in local environmental conditions may all contribute to high β-diversity among headwater streams both within and among catchments.
6. Moving beyond linear conceptual models of stream ecosystems to consider the role that spatial structure of river networks might play in determining diversity patterns at the landscape scale is a promising avenue for future research.