摘要:

SUMMARY1. Predator (laboratory‐grownAsplanchna girodiand prey (several field‐collected non‐carnivorous rotifer species) interactions were studied in the laboratory as a function of both predator and prey densities. The clearance rates ofA, girodidecreased with increasing prey density. Predator density had no effect on the feeding ofA. girodi.2.Asplanchna girodiselectively fed onKeratella cochlearis. Its clearance rates forK. cochleariswere much higher than those forPolyarthraandBrachionus. Short‐spined forms (spine length less than 25 μm) showed a significantly higher susceptibility to predation than either the non‐spined or the long‐spined forms.3. LargeAsplanchnaindividuals fed selectively on reproductive females ofK. cochlearis, thereby reducing the fecundity o

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00396.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Fluorescently labelled algae (FLA) were used to measure clearance rates of the rotiferKeratella cochlearis. The freshwater algaeChlorella vulgarisandStichococcus bacillariswere labelled with a fluorescent dye, 5‐(4,6‐dichlorotriazin‐2‐yl) aminofluorescein (DTAF), following a modified staining procedure.2.Keratella cochlearisingested both algal species. Clearance rates on tracer foods varied between 2.4 and 6.9 μl ind−1h−1, which are comparable with those determined using other techniques.3. The main drawback of the FLA technique was that only a little more than one‐third of the total amount of algal cells of bothC, vulgarisandS. bacillariswere well stained with the dye (DTAF), despite the use of a higher concentration of dye and a longer staining period than recommended in the literature.4. The FLA method can be successfully applied in grazing studies involving size selection and competition for food among zooplankton. The method complements existing techniques for measuring the clearance and ingestion rates of

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00397.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Parabolic (power) growth is characteristic of many aquatic poikilothermic animals for certain stages of their development. The parabolic pattern describing growth in weight (or length) under constant ambient conditions can be expressed in the following general form:where Y is growth rate (or specific growth rate), X is animal size, and Ω and τ are coefficients. The constancy of ambient conditions is of cardinal importance in determining τ. The problem of maintaining a constant level of nutrition can be reliably solved only by the presence of food in excess of demand. Data satisfying these requirements have demonstrated that τ does not depend on factors such as temperature, and can be assumed to be independent of ambient conditions. In the growth rate‐weight equation, τ ranges between 0.5 and 0.85 for animals representing a variety of taxonomic groups.2. The coefficient Ω. is affected by ambient conditions (e. g. temperature, amount of food). Its value reflects the ‘level’ of the growth rate‐size relationship under given conditions. For a specific time period, Ω can be computed from the following formula:whereX1andX2are the animal sizes (weights, lengths) at timet1andt2, the beginning and end of the time period. The calculated value of Ω corresponds to the average intensity of the ambient factor (F) affecting the growth during the period between the two observations. If the values of the Ω are calculated for wide range of the factor, the relationship between the Ω. andF, Ω=f(F), can be determined. The function can be then incorporated into the parabolic equation of growth, as3. Dependence of the development rate (1/D, whereDis time interval needed to complete a given stage) on temperature (T), and dependence of Ω onT, are both described by sigmoid‐shape curves. The broad intermediate part of these curves, a range to which animals are adapted in nature, can be approximated by straight line functions. For two groups, pan‐size sockeye salmon (Oncorhynchus nerka) and different species of chironomid larvae, it was shown that an equation combining parabolic growth and linear temperature patterns describes accurately the variability observed in growth rates under experimental

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00398.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Biofilm biomass and metabolism were analysed in La Solana, a calcareous, undisturbed second‐order stream. Measurements were carried out in two Mediterranean climatic extremes, summer and winter. Two on‐site experimental channels were used to study changes following nutrient addition to one of them.2. Algal biomass (chlorophylla), NDPP (net daily primary production), GDPP (gross daily primary production) andR(respiration) increased in the enriched channel, and these increases were greater in summer.3. Photosynthetic capacity (Pmaxchl) decreased during summer, possibly due to enhanced self‐shading accompanying the increase in biomass.4. In winter, Pmaxchlincreased and reached values similar to those in the summer control channel. Because grazing was low, the higher values of Pmaxchlwere attributed to partial substitution of the cyanobacterial assemblage by a green‐algae dominated assemblage with higher photosynthetic capacity as well as the low increase in biomass preventing any significant self

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00399.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Precipitation inputs and outflow stream outputs are presented for 1993 in an upland lake and catchment system on the Antrim Plateau, Northern Ireland.2. Phosphorus, potassium, chloride and possibly sulphate behaved conservatively inputs were approximately balanced by outputs. Combined nitrogen outputs were very much less than inputs, whereas there was a net export of calcium, magnesium, sodium and silica from the catchment.3. Precipitation phosphorus inputs (22 kg P km−2yr−1) are compared with literature data and are shown to be near the median value.4. The phosphorus budget is discussed in relation to the fact that there are few oligotrophic lakes in Northern Ireland. It is suggested this is due to the rainfall inputs, low phosphorus retention by the catchment and rapid flushing rates in the la

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00400.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. We tested the hypothesis that the indirect effects of colonization byHydropsychespp. (Trichoptera: Hydropsychidae) may be greater than direct effects of nutrients on the benthic algal community growth. Two sets of nutrient‐releasing substrates (a total of twenty‐four) were deployed into a small pristine stream in northern Michigan. Each set was composed of four treatments replicated three times: (i) no nutrient enrichment (C), (ii) 0.5 M phosphate‐P enrichment (P), (iii) 0.5 M nitrate‐N enrichment (N) and (iv) 0.5 M phosphate‐P plus 0.5 M nitrate‐N enrichment (P + N). All hydropsychids colonizing on the substrate in one set (twelve substrates) were removed regularly and the other set (twelve substrates) with undisturbed hydropsychids served as the controls.2. Algal biomass and gross primary productivity were estimated as chlorophylla(chla) concentration, algal biovolume, and carbon fixation rate, respectively. There was a significant interactive effect of hydropsychid colonization and P enrichment on algal biomass measured as chlaconcentration. With removal of hydropsychids, chlaconcentration increased 11‐fold in the P enrichment treatments relative to the controls. The effects of P on chlawas, however, not significant in the presence of hydropsychids. Such interactive effects were not observed when algal responses were measured as biovolume and carbon fixation rate (GPP).3. It is recommended that algal responses to nutrient enrichment should be measured as biovolume or carbon fixation rate in small streams where hydropsychids are com

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00401.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Larvae of the sedentary aquatic caterpillarPetrophila confusalis(Walker) construct silken retreats around which they feed; outside these clearly demarcated grazed areas, stream algae are exposed to a variety of mobile grazers. Comparisons of the algal community inside and just outside grazed zones were made for third‐ and fifth‐instarPetrophilain the South Fork of the Eel River, California.2. Densities of both the filamentous macroalgaCladophoraand diatom assemblages were significantly reduced within the grazed areas during both larval instars. Grazing of diatoms was taxonomically non‐selective.3. In spring, the grazed zones were relatively large (mean = 22.7 cm2) and visibly increased epilithic spatial patchiness.4. Per cent composition of diatom assemblages inside and outside the grazed areas differed during the third instar but not during the fifth instar. During the third instar, the grazed zone contained moreSynedra ulna(a common immigrant) and lessGomphonema olivaceum(a late‐successional s

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00402.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. The objective was to determine the thermal limits for feeding and survival in the bullhead,Cottus gobio, using juveniles (total length 20–30 mm, live weight 0.5–1.5 g) from one population and adults (50–70 mm, 3.5–5.5 g) from three populations.2. Fish were acclimated to constant temperatures (3, 7, 10, 15, 20, 25 or 27 °C) and the temperature was then changed at a rate of 1 °C /30 min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1 °C/30 min was the optimum value from preliminary experiments, using nine rates from 0.5 °C/48 h to 18 °C h−1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature.3. Feeding limits increased with acclimation temperature to upper and lower mean values (± 95% CL) of 26.5 ± 0.16 °C and 4.2 ± 0.20 °C for adults, 26.6 ± 0.59 °C and 5.0 ± 0.55 °C for juveniles. Incipient lethal levels defined a tolerance zone within which fish survive indefinitely; upper limits increased with acclimation temperature to a plateau of 27.6 ± 0.22 °C for adults and 27.5 ± 0.47 °C for juveniles, lower limits increased from near 0 °C to 2.5 ± 0.31 °C for adults and 2.7 ± 0.47 °C for juveniles. Ultimate lethal levels increased with acclimation temperature to a plateau of 32.5 ± 0.24 °C for adults and 32.6 ± 0.46 °C for juveniles, whilst the lower limits increased from near 0 to 0.9 ± 0.29 °C. Upper feeding, incipient and ultimate lethal values were significantly lower for juveniles than those for adults at acclimation temperatures<20,<20 and<15 °C, respectively.4. The thermal tolerance of bullheads was slightly lower than that of stone loach, similar to that of juvenile Atlantic salmon and higher than that of brown trout; the thermal limits for feeding were mu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00403.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Periphyton chlorophylla(chla), ash‐free dry mass, taxonomic composition, and cellular and water‐column nutrients were analysed every 4 weeks for a year at sixteen stream sites in New Zealand. The hypothesis was investigated that broad‐scale differences in mean monthly periphyton development are defined primarily by the frequency of flood disturbances and the periphyton's interaction with the nutrients. it us of the streams as determined by catchment geology and land use.2. Overall, mean monthly chlaconcentration declined with increasing flood frequency (r= ‐0.711, P15 yr−1).3. No relationship existed between inorganic nutrient concentrations and catchment geology or land development. However, conductivity declined significantly as a function of the percentage of the catchment underlain by nutrient‐poor, hard rocks (plutonic and fine‐grained metamorphic rocks) (r= ‐0.515, P<0.05), but increased significantly with the percentage of the catchment in intensive agricultural land use (r= 0.799, P<0.001).4. Cellular nutrient concentrations suggested that nitrogen was the nutrient most commonly limiting periphyton production. In turn, cellular N concentrations declined significantly with increasing percentage of the catchment in hard rock (r= ‐0.5M, P<0.05) and increased with percentage of the catchments in intensive agricultlural land use (r= 0.948, P<0.001).5.The sites were classified into three enrichment groups (high, moderate and low) based on their land use and underlying geology. Cellular N concentrations varied significantly among these enrichment groups (ANOVAF= 14.661, P<0.001).6. Log chladecreased significantly with increases in the annual 80th percentile velocity. However, the relationship was significantly different among the enrichment groups.7. A stepwise multiple regression on the full dataset identified that the frequency of floods, proportion of the catchment in high‐intensity agricultural land use and proportion in alkaline rocks were the most significant factors explaining variation in mean monthly chlaamong the sites (r2= 89%).8. Overall, the results showed that flood disturbance and catchment enrichment regimes are probably the principal axes of the habitat template of periphyton among the study streams, and could be used to explain and predict broad‐scale differences in periphyton development among other temper

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00404.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SUMMARY1. Spatial patterns of benthic‐invertebrate communities were examined in the 62 900 km2South Platte River Basin in Colorado, Nebraska and Wyoming, U.S.A., to determine major environmental factors associated with invertebrate distribution. Stable substrates were sampled semiquantitalively for invertebrates from 27 July to 7 August 1992, at twenty‐one sites. Data on physical and chemical variables were collected concurrently at each site.2. Four site groups were identified using derrended correspondence analysis (DCA), one in the mountains and three in the plains (braided channels, tributaries near the confluence with the main stem, and sites affected by effluent from wastewater‐treatment plants). DCA axis 1 separated sites into the two major ecoregions (Southern Rocky Mountains and Western High Plains), and regression of DCA axis 1 with environmental variables indicated significant relationships primarily with slope, water temperature, specific conductance, and concentrations of organic nitrogen + ammonia and total phosphorus in surface water. Regression of DCA axis 2 with environmental variables indicated significant relationships with channel width and concentrations of nitrate + nitrite in surface water.3. Invertebrate community composition and structure varied between ecoregions with greater number of taxa and number of insect families in mountain streams than in plains streams. Within an ecoregion, land use affected the invertebrate community.4. Factors affecting invertebrate community distribution in stream ecosystems are scale depe

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1995.tb00405.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY