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761.
G. R. Hegde 《Hydrobiologia》1986,134(2):113-115
Collections made in July 1984 in a temporary stream at Londa, Karnataka State, India, contained two new varieties of Desmids
belonging to the genera Micrasterias Agardh ex Ralfs and Staurastrum Meyen ex Ralfs. Four other Desmids showed interesting variations, described in detail. 相似文献
762.
The role of Chironomidae in energy flow of a lotic ecosystem 总被引:1,自引:0,他引:1
Chironomid secondary production was estimated on a species-specific basis for 14 dominant taxa in a third-order woodland stream. Results from this study were used to provide an expalanation for the common observation that benthos secondary production in streams is insufficient to account for levels of fish production,i.e., the ALLEN paradox. Annual chironomid secondary production was 29.7 g dry mass m–2 and accounted for 80% of the total aquatic insect secondary production. A contribution by chironomids this high has not been reported previously from similar streams and indicates that chironomids are an energetically important group available for fish consumption. Most studies examining chironomid secondary production group all taxa at the family level and calculate secondary production for the entire family using the size-frequency method. This approach violates assumptions of the size-frequency method and will result in inaccurate and unpredictable estimates of chironomid secondary production. The species-specific approach to estimate chironomid production used in this study, combined with non-chironomid production, yielded a benthos annual production rate that exceeded consumption necessary to support fish production. 相似文献
763.
1. Patterns in species assemblages are the result of the combined influence of processes acting on different spatial scales. Various studies describe the distribution of macroinvertebrate communities and their relationship with environmental factors at different geographical scales, but only a few of these studies concentrate on Western European lowlands. 2. Using Flanders as representative for the densely populated Western‐European lowlands, the specific aims of this study are: (i) to identify the different trichopteran species assemblages and to characterise them biologically using indicator species; (ii) to determine which environmental gradients most influence the observed species assemblages; and (iii) to analyse the relative importance of different spatial scale variables in constraining the Trichoptera distributions. 3. Assessment of the main environmental gradients suggested that the absence of Trichoptera from certain locations was mainly due to elevated nutrient concentrations and lower oxygen contents, confirming their sensitivity to anthropogenic disturbance. 4. Five Trichoptera species assemblages were distinguished based on Bray–Curtis dissimilarity coefficients. These assemblages did not differ significantly in species richness, but a shift in stream zonation preference was observed. In the ordination analysis 11 variables that were selected using a stepwise model building function manifested themselves as upstream–downstream and size‐related gradients. The Trichoptera assemblages in lowland streams thus appear to follow a longitudinal succession pattern that corresponds with the species‐specific preferences. 5. Partitioning the variance over the different spatial scales indicated that the reach‐scale variables were far more important in explaining the variation in species composition. The study design, which limited the minimum–maximum range of catchment‐scale characteristics, however, may have led to an overestimation of the impact of the local‐scale variables. 相似文献
764.
Genetic differentiation over small spatial scales in the absence of physical barriers in an Australian rainforest stream fish 总被引:1,自引:0,他引:1
P. A. Thuesen B. J. Pusey †‡ D. R. Peck R. Pearson B. C. Congdon 《Journal of fish biology》2008,72(5):1174-1187
This study investigated the genetic population structure of the regionally endemic rainforest fish Cairnsichthys rhombosomoides by analysing sequence variation in the mitochondrial control region. The results indicated that individual populations, even those located in close proximity (5 km), were highly distinct. The pattern of genetic structure cannot be explained by physical barriers to gene flow and was not consistent with models based on separation of populations by distance or any hierarchical structuring within the riverine network. The management implications of the observed genetic structure are discussed. 相似文献
765.
766.
Jordan L. Musetta-Lambert David P. Kreutzweiser Paul K. Sibley 《Freshwater Biology》2020,65(6):1047-1062
- We investigated how compositional differences in riparian leaf litter derived from burned and undisturbed forests influenced leaf breakdown and macroinvertebrate communities using experimental mixed-species leaf packs in boreal headwater streams. Leaf pack mixtures simulating leaf litter from dominant riparian woody-stem species in burned and undisturbed riparian zones were incubated in two references and two fire-disturbed streams for 5 weeks prior to measuring temperature-corrected breakdown rates and macroinvertebrate community composition, richness, and functional metrics associated with decomposers such as shredder abundance and % shredders.
- Leaf litter breakdown rates were higher and had greater variability in streams bordered by reference riparian forests than in streams where riparian forests had been burned during a wildfire. Streams bordered by fire disturbance showed significant effects of litter mixture on decomposition rates, observed as significantly higher decomposition rates of a fire-simulated leaf mixture compared to all other mixtures.
- Variation among sites was higher than variation among litter mixtures, especially for macroinvertebrate community composition. In general, fire-simulated leaf mixtures had greater shredder abundances and proportions, but lower overall macroinvertebrate abundance; however, the shredder abundance trend was not consistent across all leaf mixtures at each stream.
- These results show that disturbance-driven riparian forest condition and resulting composition of leaf subsidies to streams can influence aquatic invertebrate community composition and their function as decomposers. Therefore, if one of the primary goals of modern forest management is to emulate natural disturbance patterns, boreal forest managers should adapt silvicultural practices to promote leaf litter input that would arise post-fire, thereby supporting stream invertebrate communities and their function.
767.
768.
Lise Comte Juan Carvajal‐Quintero Pablo A. Tedesco Xingli Giam Ulrich Brose Tibor Ers Ana F. Filipe Marie‐Jose Fortin Katie Irving Claire Jacquet Stefano Larsen Sapna Sharma Albert Ruhi Fernando G. Becker Lilian Casatti Giuseppe Castaldelli Renato B. Dala‐Corte Stephen R. Davenport Nathan R. Franssen Emili García‐Berthou Anna Gavioli Keith B. Gido Luz Jimenez‐Segura Rafael P. Leito Bill McLarney Jason Meador Marco Milardi David B. Moffatt Thiago V. T. Occhi Paulo S. Pompeu David L. Propst Mark Pyron Gilberto N. Salvador Jerome A. Stefferud Tapio Sutela Christopher Taylor Akira Terui Hirokazu Urabe Teppo Vehanen Jean R. S. Vitule Jaquelini O. Zeni Julian D. Olden 《Global Ecology and Biogeography》2021,30(1):38-50
769.
770.
An evaluation was made of the development of two experimental plots where restoration of dominant riparian plant species was conducted in December 1991 along two semiarid Mediterranean summer‐dry watercourses. An overall comparison was made of the vegetation structure, species cover, floral composition, and species richness of the plots restored using vegetation from nearby undisturbed plots along the same watercourse. The monitoring was performed in October 1993, October 1995, September 1997, and October 1999. In the restored zones previously rooted cuttings of the species most representative of these communities were planted, using the undisturbed zones as vegetation models. Climatological conditions (particularly the rainfall regime during the planting period) substantially favored the success of the planting establishment. The results show that a simple planting technique accompanied by monitoring during the first year is adequate to achieve success in establishment of planting species. It is necessary to take precautions against herbivory of small plants of Chamaerops humilis, Ficus carica, and Retama sphaerocarpa. The planting itself causes some disturbance in the soil that may alter the species composition, giving an advantage to ruderal species over others. More time is needed to attain coverage, frequency, and species composition comparable with that of undisturbed zones. 相似文献