Nile perch (Lates niloticus,L.) and cichlids (Haplochromis spp.) in Lake Victoria: could prey mortality promote invasion of its predator?

The invasion of Nile perch into Lake Victoria is one of the iconic examples of the destructive effect of an introduced species on an ecosystem but no convincing explanation exists of why Nile perch only increased dramatically after a 25 year lag. Here, we consider this problem using a mathematical model that takes into account interactions between Nile perch and its cichlid prey. We examined competing hypotheses to explain Nile perch invasion and show that suppression of juvenile Nile perch by cichlids may cause the system to have two alternative stable states: one with only cichlids and one with coexistence of cichlids and Nile perch. Without cichlid predation on Nile perch, alternative stable states did not occur. Our analysis indicates that cichlid mortality, for example fishing mortality, may have induced the observed shift between the states.     

Differences in feeding selectivity and efficiency between young-of-the-year European perch (Perca fluviatilis) and roach (Rutilus rutilus) — field observations and laboratory experiments on the importance of prey movement apparency vs. evasiveness

Feeding selectivity and efficiency of young-of-the-year European perch and roach were compared under field and laboratory conditions. In laboratory experiments, the importance of prey evasiveness versus prey movement conspicuousness for fish selectivity was evaluated with respect to changing Cladocera/Copepoda prey ratio. Feeding efficiency was additionally investigated in relation to feeding time (5, 10, 20 min) and prey density (approx. 50, 200, 700 ind. L⁻¹). In Říov Reservoir, the diet of both fish species was nearly exclusively composed of crustacean zooplankton. In roach, diet shifted from rotifers and bosminids in May, towards Daphnia sp. and Leptodora kindtii in June and July. Daphnia contributed almost exclusively to the roach diet since June, composing on average more than 94% of total prey. Cyclopoid copepods, occurred in the roach’s diet only on the first sampling date; later on both cyclopoid and calanoid copepods were completely absent. On the other hand, copepods played an important role in the diet of perch. In early and mid-June when their share in the zooplankton was particularly high, copepods contributed by more than 50% to the diet of perch. Although their contribution dropped with their decline in zooplankton in June/July, by the end of July they again comprised about one third of perch’s diet. In both fish species, the increase in numbers of cladocerans in their diet was related to increase in SL. In roach, the numbers of consumed prey were doubled every twenty days during the investigated period. In perch the increase was not so consistent, but significantly higher efficiency of perch was reported on three out of six sampling dates. In laboratory experiments, roach showed a distinct avoidance for copepods and a preference for cladocerans. Both prey categories were only fed non-selectively when they dominated the prey mixture. Perch selectivity was more diversified. Contrary to roach, perch were fed copepods non-selectively on a balanced prey ratio. Further, with an increasing share of Cladocera, a situation resembling that of roach and Copepoda was avoided. However, when the share of copepods in the prey mixture dropped below ten percent, they were consumed non-selectively and with their ongoing decline in the prey mixture their preference even increased. Feeding efficiency differed significantly between perch and roach when foraging on copepods exclusively or on a prey mixture where copepods predominated. In the short time feeding experiment (5 min) with copepods, perch consumed on average 5.9 times more prey than roach. Although roach increased their success with increasing time it was still 1.7 times greater than for perch in the long time feeding experiment (20 min). Total numbers of prey consumed were positively affected by prey density and feeding time. With increasing feeding time, the consumption rate generally declined. With a fourfold increase in feeding time, the numbers of consumed prey increased on average only two times. Only in roach feeding on copepods did the numbers of prey consumed per minute of feeding increase with increasing feeding time. However, the overall numbers were low. Differences in feeding selectivity and efficiency between perch and roach juveniles were found to be significant both in the field and laboratory experiments. In roach, selectivity was determined solely by prey evasiveness. By contrast, perch’s selectivity was influenced by prey movement conspicuousness; prey escape abilities did not play an important role. Perch were more efficient foragers on evasive prey, but its feeding efficiency for non-evasive prey was not lower than that of roach. According to our observations, we suggest feeding behaviour to be responsible for the roach’s inefficiency in capturing evasive copepods.     

Long-term trends in the timing of breeding and brood size in the Red-Backed Shrike Lanius collurio in the Czech Republic, 1964–2004

Climate change has affected breeding dates and clutch sizes in many bird species. To date, most of the studies aimed at assessing the effects of climate change on these phenological events in birds have been on hole-nesting species and the changes linked either to local climate variation or to some large-scale composite variables, such as the North Atlantic Oscillation (NAO). Relatively less is known about the climate responses of open-nesting birds and on the relative roles of climate variables at different scales. Using bird ringing records covering a time span of 41 years, we documented shifts in the timing of breeding and brood size in a long-distance migrant, the Red-Backed Shrike (Lanius collurio) from a central European population. We found a 3- to 4-day shift towards earlier breeding and an increase in brood size by approximately 0.3 nestlings since 1964. The Red-Backed Shrikes start to breed in May and rear the first nestlings in June. During the period 1964–2004, temperatures in May significantly increased, while the increase in June temperatures was not significant. Simultaneous tests on the influence of local climate variables and the NAO index revealed a better performance of local climate. The increasing temperature in May was positively associated with the advancement of breeding. Similarly, at a local scale, higher May temperatures were followed by larger brood sizes, while a high amount of rainfall had a strong negative effect.     

Seed bank of Littorella uniflora (L.) Asch. in the Czech Republic,Central Europe: does burial depth and sediment type influence seed germination?

Littorella uniflora (Plantaginaceae) is a scarce and declining aquatic plant in Europe. Its population has been strongly reduced by changes in fishpond management (eutrophication) in the Czech Republic since the 1950s. We studied its seed bank in both recent (n = 8) and historical localities (the last found from 1972 to 2000; n = 10) and tested the effects of sediment type and burial depth on seed germination using extracted seeds from two recent populations. The seeds were found in 60% of the historical localities, mostly in low densities (≤6 seeds per 3.75 l of sediment), and also in 100% of the recent localities in various densities (8–1390 seeds per 3.75 l of sediment); however, low germination rates (0–13.3%) were estimated. The seeds germinated best on wet filter paper, followed by nutrient-rich fishpond sediment, but poorly on sand mixed with different substrates. Burial depth significantly affected seed germination. The seeds germinated only on the soil surface and at the depth of 1 cm but no seed germinated at the depth of 3 and 5 cm. Besides low water transparency, both high rate of sediment accumulation and the absence of summer drainage may endanger L. uniflora populations in fishponds.

     

Community structure of Anthomyiidae (Diptera) of six peat-bogs in the ?umava Mts (Czech Republic)

The species composition of the family Anthomyiidae in six peat-bogs in the Šumava Mts is analysed with regards to dominance, constancy, seasonal occurrence and type of distribution of each species. Anthomyiid communities in all sites are compared based on the number of species, species richness, diversity and equitability indices, as well as coefficients of similarity and Principal Components Analysis (PCA). Three collecting methods are compared: yellow pan water traps (439 specimens/43 species), sweeping (93/18) and Malaise traps (97/22). Three species, Pegoplata aestiva (24.17%), Delia platura (14.47%), and Hylemya nigrimana (11.29%) were eudominant, two further species were dominant: Delia cardui (8.74%) and Botanophila fugax (8.27%). Two species, Botanophilia fugax and Delia platura, were found in all study sites. These species, together with those collected in five sites (Delia cardui, Heterostylodes nominabilis and Hylemya vagans), had a constancy rate higher than 75% and belonged to the category of euconstant species.     

Stomatal density distribution patterns in leaves of the Jatobá (Hymenaea courbaril L.)

Stomata are leaf structures that are essential for regulating gas exchange and water balance in terrestrial plants. Accurately quantifying stomatal characteristics is consequently of great importance for understanding the physiological processes of plants under different environmental conditions. The objective of this study was to investigate the spatial distribution pattern of stomata on leaflet surfaces, and the possible mechanisms that influence this pattern, particularly leaf expansion. To achieve this, we used geostatistical tools combined with an analysis of biometric relationships of leaves from Hymenaea courbaril L. Our analysis indicates that stomata show a clear spatial structure in this species: average values of foliar expansion rates (ERs) were different on right and left-hand sides of the primary venation of each leaflet and there was a close relationship between the spatial pattern of stomatal density and leaf expansion rate. Such differences in lateral expansion may therefore be partially responsible for the heterogeneous distribution of stomata documented here and in other studies.     

Ueber die F?rbung desMorphnus guianensis (Daud.) undM. Harpyia (L.)

Ohne Zusammenfassung     

Developing phosphinothricin-resistant transgenic sunflower (Helianthus?annuus L.) plants

Most investigations on genetic transformations of sunflower have used the neomycin transferase (nptII) gene as the selectable marker. We previously reported a PPT-based selection system for sunflower transformation that uses the bialaphos resistance (bar) gene as the selectable marker and 20 mg/l of phosphinothricin (PPT) as the selective agent. Sunflower (Helianthus annuus L.) variety Skorospeliy 87 was genetically transformed via Agrobacterium tumefaciens strain EHA 105 harbouring the binary plasmid vector pBAR. Two-day-old explants from mature embryos competent for direct shooting were used. Southern blot and ELISA experiments confirmed the stability of expression in two generations of transgenic plants. Transformed plants transferred to soil in the greenhouse exhibited resistance to the herbicide Basta^? at 3 l/ha.     

Transformation of androgenic-derived Festulolium plants (Lolium?perenne L.?×?Festuca?pratensis Huds.) by Agrobacterium?tumefaciens

Genetic transformation of androgenic-derived amphidiploid Festulolium plants (Lolium perenne L. × Festuca pratensis Huds., 2n = 4x = 28) by Agrobacterium tumefaciens has been achieved. Anther culture-induced calli of Festulolium “Bx351” were inoculated with Agrobacterium tumefaciens strain LBA4404 carrying pIG121-Hm encoding the hygromycin resistance (hph) and β-glucuronidase (uidA) genes under the control of a CaMV 35S promoter. Twenty-three putative transformants were obtained from the hygromycin selection, 19 of which (82.6%) showed GUS activity. The integration of transgene was detected by using genomic DNA PCR analysis, RT-PCR analysis and Southern blot hybridization, respectively, which revealed that foreign gene was integrated into the genomes of dihaploid transformants (2n = 2x = 14). The haploid embryogenic system offers a stable means of transformation, as the introduced trait can be readily fixed through chromosome doubling. An erratum to this article can be found at     

Enteric helminths of perch (Perca fluviatilis L.) and yellow perch (Perca flavescens Mitchill): stochastic or predictable assemblages?

Component communities of perch (Perca fluviatilis L) in Eurasia and the North American yellow perch (Perca flavescens Mitchill) were examined to determine the nature of their parasite communities. The scale of this investigation is continental and includes data collected across the distribution of each host species. Data were compiled from the literature and from 5 sample sites in North America. Four parasite species were found to occur frequently in the helminth component communities of P. flavescens. The cestodes Bothriocephalus cuspidatus and Proteocephalus pearsei, the digenean Crepidostomum cooperi, and the nematode Dichelyne cotylophora comprised a suite of species of which some or all occurred in most samples. Similarly, a group of 4 predictable parasite species was identified for P. fluviatilis in Eurasia, the digenean Bunodera luciopercae, the nematode Camallanus lacustris, the cestode Proteocephalus percae, and the acanthocephalan Acanthocephalus lucii. Specificity was not a requirement for predictability. Despite geographical isolation for millions of years, and different fish species interactions within and between continents, the predictability of these parasite assemblages indicates they are shaped by a biology, especially feeding patterns, common to both perch species. This is evidence that parasite assemblages comprised of nonhost-specific parasites in freshwater fishes are not merely stochastic assemblages but have key components that are predictable at this broad continental scale.     

What are the reasons for the Prussian carp expansion in the upper Elbe River, Czech Republic?

Fifty five Prussian carp Carassius auratus gibelio were radio‐tracked weekly along the course of the upper Elbe River, for 15 months. In addition, diurnal movements were observed in three different habitat types (main channel, navigation canal and floodplain areas). Fish species composition from 10 fish ladders was regularly analysed in 1996, 2000 and 2001, and patterns of juvenile (0+ year) fish distribution and abundance were collected in 2000 and 2001, to support telemetric data on longitudinal migrations, and habitat preference within the studied stretch. Downstream migrations dominated in all seasons, being most intensive in spring and reaching a maximum distance of 85 km. Migration stopped when specimens found a floodplain area, where they occupied larger home ranges compared to the main channel. Migrations upstream of up to 2 km were rare, and specimens did not enter fish ladders. Spontaneous reproduction only occurred on the floodplain and its success was very low. The results suggested that neither upstream migrations, nor spontaneous reproduction represented the key mechanism for the Prussian carp invasion into the Elbe catchment area of the Czech Republic. It can be assumed that escapes from aquaculture activities are primarily responsible for its expansion.     

Holocene subfossil chironomid stratigraphy (Diptera: Chironomidae) in the sediment of Plešné Lake (the Bohemian Forest,Czech Republic): Palaeoenvironmental implications

A faunal record of chironomid remains was analyzed in the upper 280 cm of a 543 cm long sediment core from Ple?né jezero (Ple?né Lake), the Bohemian Forest (?umava, Böhmerwald), Czech Republic. The chronology of the sediment was established by means of 5 AMS-dated plant macroremains. The resolution of individual 3-cm sediment layers is ～115 years and the analyzed upper 280 cm of the sediment core represent 10.4 cal. ka BP. As the results of DCA show, two marked changes were recorded in the otherwise relatively stable Holocene chironomid composition: (1) at the beginning of the Holocene (ca. 10.4-10.1 cal. ka BP) only oligotrophic and cold-adapted taxa (Diamesa sp., M. insignilobus-type, H. grimshawi-type) were present in the chironomid assemblages, clearly reflecting a cool climate oscillation during the Preboreal period, and (2) during an event dated in the interval 1540–1771 AD, when most taxa vanished entirely and only Zavrelimyia sp. and Procladius sp. were alternately present accompanied by Tanytarsus sp. Although, the age of this event is in agreement with the dating of the Little Ice Age, the most probable reason for the elimination of many chironomid taxa was very low sums recorded in this part of the sediment, rather than cool conditions connected with the LIA. Variations in the chironomid fauna after the Preboreal period were reflected mainly by changes in abundances of dominant taxa rather than by changes in species composition. These variations could be explained by: (1) climatic changes, namely temperature and amount of rainfall resulting in oscillations in lake level, with changes in the occurrence of macrophytes in the littoral and (2) increasingly dense afforestation which led to a considerable input of organic material into the lake and a subsequent increase in the trophic status of the lake water.     

Predictive modeling of the potential natural vegetation pattern in the Podyjí National Park, Czech Republic

The relationships between 10 types of potential natural vegetation and several environmental factors derived from a topographical map (altitude, slope inclination, curvature, potential direct solar irradiation, sky view factor), a geological map and a spring phenological map, were modeled for the Podyjí National Park (Czech Republic). Different vegetation pattern models were made using spatial predictive modeling together with the Bayes formula. Compared with the field-based vegetation map, the model which included geology as a factor and all the factors derived from the topographic map, yielded an overall correspondence (i.e. percentage of grid cells in which vegetation types in the field-based map and in the model matched) of 56.8%. This measure of correspondence, however, is not dependable in areas, such as the Podyjí National Park, where one vegetation type prevails. Therefore, correspondence within vegetation types, i.e. the average of correspondences calculated for each vegetation type separately, was used, thus yielding a value of 39.4%. The most important factors in this model were the sky view factor, representing the differences between the valleys and the gently undulating uplands, and altitude, as a surrogate for the macroclimatic gradient. By replacing altitude and irradiation variables related to the macroclimate and mesoclimate respectively, with the spring phenological map, overall correspondence with the original map was increased to 62.6% and correspondence within vegetation types to 50.5%. This result shows that phenological maps, which are relatively easy to create and provide a surrogate for unavailable local climatic maps, might be a powerful tool for predicting vegetation pattern on landscape scale.     

Beitr?ge zur Zytologie der GattungMarchantia (L.)

Ohne Zusammenfassung

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Mit 44 Textfiguren und Tafel I     

Beitr?ge zur Zytologie der GattungMarchantia (L.)

Ohne ZusammenfassungMit 19 Textfiguren und 1 Tafel     

Analysis of the potential evapotranspiration demands in the Czech Republic between 1961–1990

Dynamics of the evapotranspirational demands in the Czech Republic within three decades from 1961 to 1990 has been studied. The determination of the levels of influence of the respective natural components depends on the regionalized modelling techniques. The project of regionalized modelling is theoretically based on the potential evapotranspiration values (ET ₀) calculated by FAO methodology (eqs. 1, 2) and the series of temperature and rainfall observations obtained by climatologic stations during a 30-year period from 1961 to 1990 and its relation to the absolute altimetric. The DMR-2 military digital elevation model of the Czech Republic relief consisting of a regular network of points with their altitudes specified in meters was used for the purpose of regionalized modelling. One step of the network in the S-42 coordinate system with the Gauss conforms cylindrical projection is equal to 100 meters; this implies that the smallest area for which the data can be processed is 1 hectare. The digital relief model can be linked to both direct (temperature, precipitation) and derived (evapotranspiration) quantities, which is one of the many novelties of regionalized modelling. The climatic data used in regionalized modelling records daily measurements were obtained by 85 climatologic and rainfall-monitoring stations from 1961 to 1990. Our results showed an appreciable decrease of the most drying area (ratio P/ET₀ up to 0.755) in the last decade 1981–90; half as less amounts compared with the previous decade 1971–80 (about 500,000 hectares). On the other hand, an apparent increase (more than 500,000 hectares in comparison with the previous decade 1971–80) of the wettest area (ratio P/ET₀ over 1.508) through the last decade was observed. Both first decades 1961–70 and 1971–80 look similar. The project mentioned in this article has made it possible to create models for the different time intervals which have showed higher reliability for heterogeneous application.     

Long-term changes in numbers and distribution of wintering waterbirds in the Czech Republic, 1966–2008

Capsule?Of 26 species of wintering waterbirds, 18 showed an increase in numbers, five showed a decrease and two showed no change.

Aim?To assess long-term trends in the numbers and distribution of the 26 most abundant wintering waterbird species in the Czech Republic.

Methods?We used International Waterbird Census data from between 48 and 639 wetland sites which had been counted annually in the Czech Republic from 1966 to 2008. From these data long-term changes in numbers and distributions were determined. Log-linear Poisson regression analysis was used to estimate missing data using trim software. The distribution of each species was described as the ratio of the number of sites occupied by that species to the total number of sites investigated.

Results?Increasing trends were found for 18 species, five species were found to be declining, one species was stable and two species were found with uncertain trends. Wintering distributions (the ratio of sites occupied by a given species to the total number of sites counted) increased in 16 species and decreased in two species, broadly correlated with the species changes in numbers.

Conclusion?In most species changes in numbers as well as changes in distribution followed the Western Palearctic population trends. Those species which increased were mainly piscivores and included geese, ducks and gulls. Scarcer species also exhibited an increase in numbers. The changes in numbers (both positive and negative) were more frequent among species associated with running water, whereas species which showed uncertain trends were more frequently recorded on standing water, which is more affected by variable weather conditions.     

Grape skins (Vitis vinifera L.) catalyze the in?vitro enzymatic hydroxylation of p-coumaric acid to caffeic acid

The ability of grape skins to catalyze in vitro conversion of p-coumaric acid to the more potent antioxidant caffeic acid was studied. Addition of different concentrations of p-coumaric to red grape skins (Cabernet Sauvignon) resulted in formation of caffeic acid. This caffeic acid formation (Y) correlated positively and linearly to p-coumaric acid consumption (X): Y = 0.5 X + 9.5; R ² = 0.96, P < 0.0001. The kinetics of caffeic acid formation with time in response to initial p-coumaric acid levels and at different grape skin concentrations, indicated that the grape skins harboured an o-hydroxylation activity, proposedly a monophenol- or a flavonoid 3′-monooxygenase activity (EC 1.14.18.1 or EC 1.14.13.21). The K _m of this crude o-hydroxylation activity in the red grape skin was 0.5 mM with p-coumaric acid.     

The migration of spawning stocks of graylingThymallus thymallus, in Lake Mjøsa, Norway

Synopsis The migration of grayling was studied in Lake Mjøsa and 13 of its tributaries in which grayling spawn. The study demonstrate that grayling spawn in creeks in May/June and leave for Lake Mjøsa shortly after spawning to return the next spring. Once mature, the grayling spawn every year. Grayling mix in the lake and are found at a mean distance of 11.9 km from the estuary of their spawning creek in September. Grayling embryos hatch in June and the juveniles stay in the tributaries until September/October. Grayling spend the winter months in the lake. Out of 1599 grayling tagged in tributaries during the spawning season, 240 of 284 recaptures (84.5%) were made in subsequent spawning seasons in the same tributary in which they were first tagged. Forty-four grayling were recaptured in adjacent tributaries. These results demonstrate that, despite the fact that all grayling leave the tributaries and mix in the lake, there is a high precision of homing. It is suggested that the grayling population in lake Mjøsa is composed of stocks using specific tributaries for spawning.