Strong genetic exchange among populations of a specialist bee, <Emphasis Type="Italic">Andrena vaga</Emphasis> (Hymenoptera: Andrenidae)

Habitat fragmentation is believed to be a key threat to biodiversity, with habitat specialists being stronger affected than generalists. However, pioneer species might be less affected by fragmentation, as their high colonization potential should increase gene flow. Here, we present an analysis of the genetic structure of populations of the solitary bee Andrena vaga, which naturally occurs in sandy habitats and is specialized on willow (Salix) pollen as larval food and sandy soils as nesting sites. While the species is widespread in the young sandy landscapes of our main study area (Emsland, northwestern Germany), it occurs less frequently in the Lower Rhine valley. Our analyses of six polymorphic microsatellites show that the populations are only slightly differentiated, suggesting a relatively strong gene flow. No genetic structure corresponding to the geographic origin was found as the variability within populations accounted for the major proportion of variation. F_ST values were higher and allelic richness was lower in the Lower Rhine valley, supporting the hypothesis that habitat availability affects the degree of genetic exchange between populations. Inbreeding coefficients were generally high and nearly all populations had a heterozygote deficiency, which could be explained by the breeding strategy of A. vaga, which nests in aggregations.     

How can river-estuarine planktonic copepods survive river floods?

Distribution of brackish-water zooplankton was surveyed in the Chikugo River estuary, Japan, at 3-h intervals for 24h, including several hours when the river was heavily flooded because of rainfall and discharge from an upstream dam. The populations of the dominant copepods Pseudodiaptomus inopinus and Sinocalanus sinensis were concentrated in the mixing zone of the salt wedge before river flooding. During the period of flooding, they were almost completely swept out from the river, but examination of water trapped by a sediment grab sampler revealed that adults of Pseudodiaptomus inopinus were aggregated immediately above the bottom of the submerged channel outside the river mouth. After the flood, aggregations of both species appeared again in the river together with the salt wedge, and the proportion of adults in the aggregations became significantly higher than before. These results suggest that immature copepods suffer population losses through river flooding, but that the copepods can survive such flooding by means of both behavioral and reproductive mechanisms; that is, adult copepods maintain their position on the bottom of submerged channels outside the river mouth during a river flood and replace the population loss through reproduction after the flood. Channels outside river mouths are thus regarded as important topographic refuges for river-estuarine zooplankton to survive a flood.     

Population dynamics of the solitary digger bee<Emphasis Type="Italic"> Andrena vaga</Emphasis> Panzer (Hymenoptera,Andrenidae) studied using mark-recapture and nest counts

The population size of the solitary digger bee Andrena vaga was documented using mark-recapture methods during 4 consecutive years (1996–1999). Additionally, the numbers of the parasitoids Nomada lathburiana and Bombylius major were estimated. For calculations of the daily population size, the Jolly-Seber model for open populations with time-dependent survival and capture rates was used. The mean daily population size corresponded well to the number of nests marked in the aggregation of A. vaga. The method of mark-recapture achieved the most accurate data when the number of sampling periods and the capture probability was high. The results document a decrease in population size of the investigated A. vaga aggregation during 4 successive years. A population increase of its parasitoids B. major is considered to be one reason for the population decline of A. vaga in 1999. The sex ratio of A. vaga was biased toward females, contrary to the expected higher number of males. Results of the mark-recapture studies showed that up to 50% of females left the aggregation or died at the beginning of the season. The females probably colonized new aggregations at distances further than 200 m away from their birth aggregation, as no marked females were observed in the environs of the study area. This behavior is interpreted as a parasite avoidance strategy. The bee populations in the study area form a web of interconnected aggregations. Apparently a flux of extinction and recolonization exists between the different aggregations.     

How Big of an Effect Do Small Dams Have? Using Geomorphological Footprints to Quantify Spatial Impact of Low-Head Dams and Identify Patterns of Across-Dam Variation

Longitudinal connectivity is a fundamental characteristic of rivers that can be disrupted by natural and anthropogenic processes. Dams are significant disruptions to streams. Over 2,000,000 low-head dams (<7.6 m high) fragment United States rivers. Despite potential adverse impacts of these ubiquitous disturbances, the spatial impacts of low-head dams on geomorphology and ecology are largely untested. Progress for research and conservation is impaired by not knowing the magnitude of low-head dam impacts. Based on the geomorphic literature, we refined a methodology that allowed us to quantify the spatial extent of low-head dam impacts (herein dam footprint), assessed variation in dam footprints across low-head dams within a river network, and identified select aspects of the context of this variation. Wetted width, depth, and substrate size distributions upstream and downstream of six low-head dams within the Upper Neosho River, Kansas, United States of America were measured. Total dam footprints averaged 7.9 km (3.0–15.3 km) or 287 wetted widths (136–437 wetted widths). Estimates included both upstream (mean: 6.7 km or 243 wetted widths) and downstream footprints (mean: 1.2 km or 44 wetted widths). Altogether the six low-head dams impacted 47.3 km (about 17%) of the mainstem in the river network. Despite differences in age, size, location, and primary function, the sizes of geomorphic footprints of individual low-head dams in the Upper Neosho river network were relatively similar. The number of upstream dams and distance to upstream dams, but not dam height, affected the spatial extent of dam footprints. In summary, ubiquitous low-head dams individually and cumulatively altered lotic ecosystems. Both characteristics of individual dams and the context of neighboring dams affected low-head dam impacts within the river network. For these reasons, low-head dams require a different, more integrative, approach for research and management than the individualistic approach that has been applied to larger dams.     

Nitrate elimination by denitrification in hardwood forest soils of the Upper Rhine floodplain – correlation with redox potential and organic matter

Denitrification in floodplains is a major issue for river- and groundwater quality. In the Upper Rhine valley, floodplain forests are about to be restored to serve as flood retention areas (polders). Besides flood attenuation in downstream areas, improvement of water quality became recently a major goal for polder construction. Redox potential monitoring was suggested as a means to support assessment of nitrogen elimination in future floodplains by denitrification during controlled flooding. To elucidate the relationship between redox potential and denitrification, experiments with floodplain soils and in situ measurements were done. Floodplain soil of two depth profiles from a hardwood forest of the Upper Rhine valley was incubated anaerobically with continuous nitrate supply. Reduction of nitrate was followed and compared with redox potential and organic matter content. The redox potential under denitrifying conditions ranged from 10 to 300 mV. Redox potential values decreased with increasing nitrate reduction rates and increasing organic matter content. Furthermore, a narrow correlation between organic matter and nitrate reduction was observed. Experiments were intended to help interpreting redox potentials generated under in situ conditions as exemplified by in situ observations for the year 1999. Results obtained by experiments and in situ observations showed that monitoring of redox potential could support management of the flooding regime to optimize nitrogen retention by denitrification in future flood retention areas.     

Variation in life-cycle between three rare and endangered floodplain violets in two regions: implications for population viability and conservation

We studied the demography of Viola elatior, V. pumila, and V. stagnina, three rare and endangered Central European floodplain species, to (i) analyse variation in life-cycles among congeners and between regions (Dyje-Morava floodplains, Czech Republic; Upper Rhine, Germany), (ii) to define sensitive stages in the life-cycles, and (iii) to identify possible threats for population viability and species conservation. Matrix models were based on the fate of marked individuals from a total of 27 populations over two years. We analysed population growth rate (λ), stage distribution, net reproductive rate (R ₀), generation time, age at first reproduction, and elasticity and calculated a life table response experiment (LTRE). Most populations were declining and λ did not differ between species or regions during the observed interval. Despite higher probabilities for survival and flowering in the Dyje populations, R ₀ was higher in the Rhine populations. Also other demographic traits showed consistent differences between regions and/or species. Complex life-cycles and large variation in λ precluded unequivocal identification of sensitive stages or vital rates for conservation. Variation between regions may be a consequence of differences in habitat quality. Our results suggest that deterministic processes such as reduced management, succession, habitat destruction, and lack of disturbance through reduced or eliminated flooding present the strongest threat for the viability and persistence of populations of the three floodplain violets as compared with stochastic processes. However, the persistent seed bank of the species may buffer populations against environmental variation and represents a reservoir for recovery after resumption of suitable land-use management.     

Ecological impacts of dams,water diversions and river management on floodplain wetlands in Australia

Australian floodplain wetlands are sites of high biodiversity that depend on flows from rivers. Dams, diversions and river management have reduced flooding to these wetlands, altering their ecology, and causing the death or poor health of aquatic biota. Four floodplain wetlands (Barmah‐Millewa Forest and Moira Marshes, Chowilla floodplain, Macquarie Marshes, Gwydir wetlands) illustrate these effects with successional changes in aquatic vegetation, reduced vegetation health, declining numbers of water‐birds and nesting, and declining native fish and invertebrate populations. These effects are likely to be widespread as Australia has at least 446 large dams (>10 m crest height) storing 8.8 × 10⁷ ML (10⁶ L) of water, much of which is diverted upstream of floodplain wetlands. More than 50% of floodplain wetlands on developed rivers may no longer flood. Of all of the river basins in Australia, the Murray‐Darling Basin is most affected with dams which can store 103% of annual runoff and 87% of divertible water extracted (1983–84 data). Some floodplain wetlands are now permanent storages. This has changed their biota from one tolerant of a variable flooding regime, to one that withstands permanent flooding. Plans exist to build dams to divert water from many rivers, mainly for irrigation. These plans seldom adequately model subsequent ecological and hydrological impacts to floodplain wetlands. To avoid further loss of wetlands, an improved understanding of the interaction between river flows and floodplain ecology, and investigations into ecological impacts of management practices, is essential.     

Damming interacts with the flood pulse to alter zooplankton communities in an Amazonian river

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Decomposition of Cynodon dactylon (L.) Pers. in the seasonally flooded areas of the Pongolo river floodplain: pattern and significance of dry matter and nutrient loss

Cynodon dactylon meadows occupying seasonally inundated areas of the Pongolo river floodplain, South Africa, decompose during periods of submergence. The loss of dry matter and nutrients from both fresh and dried material enclosed in litter bags was studied. The pattern of loss of dry matter was diphasic. Loss was more rapid from dried than from fresh material, half the mass being lost in 18 and 28 days respectively. Nutrient loss followed an exponential pattern. Nitrogen, phosphorus and magnesium were lost more rapidly from dried than from fresh material whilst rates of loss of sodium, potassium and calcium were similar. The significance of Cynodon decomposition in the functioning of the floodplain is assessed from estimates of the above- and below-ground standing crop around one small lake before and after submergence. It is concluded that decomposition of plants growing in seasonally inundated areas of the floodplain may contribute significantly to the productivity of the system, but that the extent of the contribution can be greatly influenced by the flooding regime. The completion of the Pongolapoort dam upstream of the floodplain will alter the natural flooding pattern, effecting a reduction in floodplain productivity, unless a programme for flood release can be initiated.     

An assessment of the importance of water stress in seasonally floodedC. dactylon on the Pongolo River floodplain in the formulation of guidelines for controlled flooding

Daily variation in water potential was measured inCynodon dactylon in seasonally flooded areas of the Pongolo river floodplain. Soil moisture declined during the dry winter season when the plants were exposed, causing them to experience increasing water stress. Fog and mist appeared to relieve stress but it is concluded that water stress is sufficient to reduce production during exposure. The results are discussed in relation to the timing of flood releases from the upstream Pongolapoort dam and it is concluded that the period of exposure is of less significance than the duration and frequency of inundation in the formulation of guidelines for flood releases from the dam.     

Dams and canyons disrupt gene flow among populations of a threatened riparian plant

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Geographical patterns of flow-regime alteration by flood-control dams in Japan

Natural variability in water flow is an inherent feature of river ecosystems, but many rivers in the world have been dammed, altering the flow regime and leading to ecosystem degradation. Dam reoperation to maintain environmental flows has been proposed for ecosystem and biodiversity improvement. Reoperation requires an understanding of flow alteration due to dam operations. However, knowledge of natural flow regimes and their degree of alteration remain poor in Japan. The Japanese islands extend from the sub-Arctic to the subtropics with four seasons and thus are considered to show high spatial and temporal variation in flow regime and alterations caused by those variations. We examined the spatial and temporal dependency of flow alteration by flood-control dams in Japan. We confirmed that flood-control dams reduced the rate of change in discharge and peak discharge and that such dams fulfilled their primary role of preventing flood disaster by reducing and delaying flooding. However, other flow characteristics, such as high- and low-flow frequency and duration, were also altered. We demonstrated that the magnitude, frequency, duration, and seasonality of high and low flows in undammed flow regimes differed with latitude and that discharge alteration was spatially and temporally dependent, presumably because dam operation responded to the inherent differences in seasonal flow variability at different latitudes.     

Erhaltung und Wiederansiedlung des Kleinen Rohrkolbens (Typha minima) – Vegetationsaufnahmen, Monitoring und genetische Herkunftsanalysen

Galeuchet D. J. and Holderegger R. 2005. Conservation and re-introduction of Dwarf Bulrush (Typha minima) – vegetation surveys, monitoring and genetic analysis of origin. Bot. Helv. 115: 15–32.Typha minima was formerly widespread along fast flowing alpine rivers but is now red-listed as critically endangered. To assess its conservation perspectives, we surveyed the few remaining natural populations along the alpine part of the River Rhine from 1997 to 2002 and determined their genetic diversity using isozyme electrophoresis. Six of the populations became extinct or extremely small, probably due to shading by taller plants and trampling, while six other populations remained stable or increased, partly due to habitat restoration measures. The largest populations, with areas of more than 10000 m², are found in secondary habitats which are regularly disturbed due to water regime management. Of the 19 investigated isozyme loci, only six were polymorphic. Allelic diversity (1.4–1.8) was low in all populations, and the number of multilocus genotpyes (1–18) was low for 11 of 13 investigated populations. Genetic diversity was also studied for ex-situ cultivations of T. minima in Swiss botanical gardens and reintroduced stands.These artificial populations (each with 1–3 multilocus genotypes) were genetically similar to natural populations (average genetic distance 0.094). For two ex-situ cultivations with unknown origin, the likely origin could genetically be defined. Hybridisation between two ex-situ cultivations of different origin (i.e. a potential risk of genetic introgression) was detected in one botanical garden. It is concluded that the long-term conservation of T. minima requires both the restoration of regularly disturbed, sparsely vegetated river margins and the re-introduction of plants from ex-situ cultivations with appropriate origin.Manuskript angenommen am 2. Februar 2005     

The impact of flooding regime on the soil seed bank of flood‐meadows

Abstract. We assessed the significance of flooding for the floristic composition of seed banks in flood‐meadows of the northern valley of the Upper Rhine. We compared three hydrological compartments of the alluvial plain, consisting of the regularly flooded land between the river and low summer dykes (functional flood‐plain), the occasionally flooded land between summer dykes and high winter dykes (hybrid floodplain) and the land behind the winter dykes, which is now only submerged by ascending groundwater (fossil flood‐plain). Due to their different flooding regime, the three compartments should differ with respect to the prevailing conditions of diaspore input. The seed density of soil samples increased with the duration of flooding in the three compartments, while species richness and the proportion of species not occurring in the vegetation was constant. The increase in seed density can be largely attributed to an increase of disturbance indicators, which are present in the above‐ground vegetation and capable of forming a long‐term persistent seed bank. No effects of flooding on the composition of seed banks in the three flood‐plain compartments were found. The differences in seed bank composition can be largely explained by corresponding differences in above‐ground vegetation and former and present‐day meadow management. Seeds of species absent from above‐ground vegetation can be attributed to the local species pool present in the immediate vicinity of the study plots. We discuss consequences of the results for the restoration of species‐rich flood‐plain meadows.     

Der Buntsandstein. Eine lebensfeindliche Wüste oder doch mehr?

A hostile desert – or still more? The Bunter During the time span of the Bunter a continental, semiarid to arid climate with high temperatures prevailed in the “Germanic Basin”. The sediments deposited are often “coloured” – mostly red – because of the oxidizing conditions. They mostly represent braided river systems and large flood plains. In the Upper Bunter a connection to the Tethys sea existed. The evaporation of salt water led to the formation of thick layers of hydrogenetic rocks in the Early Upper Bunter. Palynomorphs and the famous fossil communities found are providing evidence of life and climate during the Bunter period.     

The filtration rate of the zebra mussel Dreissena polymorpha used for water quality assessment in Dutch rivers

The effects of contaminated river water on the filtration rate of zebra mussels from a clean reference site were studied. After a 48-h exposure period to filtered water from the rivers Rhine, Meuse and Amstel (The Netherlands), the filtration rate was measured. It was demonstrated that water from contaminated locations inhibited the filtration rate. Inhibition was higher during low water levels in the rivers Rhine and Meuse than during high water levels, suggesting that contaminants are diluted during high water levels. It is concluded that the shortterm filtration assay with D. polymorpha can be used for assessing water quality.     

Phylogeography of <Emphasis Type="Italic">Ceriops tagal</Emphasis> (Rhizophoraceae) in Southeast Asia: the land barrier of the Malay Peninsula has caused population differentiation between the Indian Ocean and South China Sea

The genetic structure of mangrove species is greatly affected by their geographic history. Nine natural populations of Ceriops tagal were collected from Borneo, the Malay Peninsula, and India for this phylogeographic study. Completely different haplotype compositions on the east versus west coasts of the Malay Peninsula were revealed using the atpB-rbcL and trnL-trnF spacers of chloroplast DNA. The average haplotype diversity (Hd) of the total population was 0.549, nucleotide diversity (θ) was 0.030, and nucleotide difference (π) was 0.0074. The cladogram constructed by the index of population differentiation (G _ST) clearly separated the South China Sea populations from the Indian Ocean populations. In the analysis of the minimum spanning network, the Indian Ocean haplotypes were all derived from South China Sea haplotypes, suggesting a dispersal route of C. tagal from Southeast Asia to South Asia. The Sunda Land river system and surface currents might be accountable for the gene flow directions in the South China Sea and Bay of Bengal, respectively. The historical geography not only affected the present genotype distribution but also the evolution of C. tagal. These processes result in the genetic differentiation and the differentiated populations that should be considered as Management Units (MUs) for conservation measurements instead of random forestation, which might lead to gene mixing and reduction of genetic variability of mangrove species. According to this phylogeographic study, populations in Borneo, and east and west Malay Peninsula that have unique genotypes should be considered as distinct MUs, and any activities resulting in gene mixing with each other ought to be prevented.     

Morphological and molecular characterization of the Landes honey bee (<Emphasis Type="Italic">Apis mellifera</Emphasis> L.) ecotype for genetic conservation

A population of honey bees (Apis mellifera mellifera L.) with an annual colony brood cycle adapted to a locally abundant floral source in the Landes region of Southwest France is the subject of genetic conservation efforts. This population is maintained by local beekeepers in an area that experiences both an annual seasonal influx of non-local colonies and the permanent culture of imported stock. However, some colonies native to the Landes do not have the adapted brood cycle and their status as ecotypic are in question. The present study used morphology, mitochondrial DNA and microsatellites to characterize the endemic population and suggests further genetic conservation strategies. These methods yielded different degrees of discrimination of native and imported colonies and provided a powerful suite of tools for local resource managers. Colonies from the Landes could be differentiated from non-local French A. m. mellifera populations using morphometric analysis, and from non-native and reference populations using mtDNA and microsatellites. Seven morphological characters were identified by discriminant analysis as informative for delineating the Landes ecotype from other A. m. mellifera populations. Mitochondrial haplotypes for the population were characterized and five microsatellite loci were found to be informative in characterizing the Landes population. Asymmetric gene flow detected with microsatellite alleles was observed to be 5.5–5.9% from imported to native stocks of honey bees while introgression of native microsatellite alleles into imported colonies was 21.6%.     

Spatio-temporal genetic structuring of brown trout (Salmo trutta L.) populations within the River Luga, northwest Russia

The brown trout populations of the Baltic Sea region have been drastically affected by various human activities during the past century. Due to their propensity to home to their natal site to spawn and their tendency to evolve local adaptations, populations may be genetically differentiated in water systems where no physical barriers preventing interbreeding exist. Consequently, identification of management units, a prerequisite for appropriate conservation and management planning, cannot necessarily be deduced from the physical properties of the habitat. In this study, microsatellite markers were employed to assess the spatio-temporal genetic structuring of inter-connected brown trout populations from a river-system in Northwest Russia. Populations were found to be genetically differentiated from each other (global F _ST 0.06) and the genetic structuring within the river to follow an isolation by distance pattern. Indications of temporal stability were found in some populations, however others appeared to be temporally unstable suggesting differences in the demographic forces affecting the populations. Based on the observed isolation by distance pattern of genetic differentiation, preserving several breeding sites spaced evenly throughout the river-system would appear to be more appropriate than focussing conservation effort on any single stretch of the river. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Comparing the fish assemblages and food‐web structures of large floodplain rivers

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