摘要:

SUMMARY.1. The mayflyEphemerella ignitadoes not occur in upland streams of the River Duddon catchment which have waters with low pH values of 4.8‐5.2, negative alkalinities and low ionic contents. However, it does occur in lowland streams of the catchment which have waters with higher pH values of 6.6 and above, large positive alkalinities and high ionic contents. This study addresses the question of whether the absence of the animal in the acid water streams is due directly to the water chemistry or to the absence of suitable food.2. In comparative experiments using unfed animals of several species it was shown thatE. ignitahas a considerable tolerance of low pH, low ion water. In this it is similar toAmphinemura sulcicollis(Plecoptera), a stonefly which occurs in the acid water streams of the River Duddon catchment.3. Growth rates in laboratory experiments withE. ignitawere equally good whether the food supplied was that available in the low pH water streams (bryophyteNardia compressaplus filamentous algaHormidium subtile)or typical of that available in high pH water streams (mossRhynchostegium riparioideswith the epiphytic diatomCocconeis placentula).However, a consideration of the natural habits of the animal suggests that it is the inaccessibility of theH. subtilealgal food, rather than its unsuitability, which is relevant to the exclusion ofE. ignitafrom the low pH streams. In addition, the very limited diversity of other algae in the low pH water streams, in the summer season, may well be influential in inhibiting the establishment ofE. ignita.4. The comparative experiments using unfed animals suggested that, contrary to the findings forE. ignita, the mayfliesBaetis muticusandBeatis rhodaniare probably excluded from the acid water streams of the Upper Duddon because of water chemistr

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00337.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The vulnerability of six species of freshwater snails to the leechNephelopsis obscurawas determined in laboratory predation experiments.2.Nephelopsiswas unable to prey on prosobranch snails with an operculum, but did consume certain pulmonate species though predation rates were low, ranging from one to two snails per leech per night at 20°C. Apparently,Nephelopsisdoes not actively select prey, but merely consumes those species most easily handled.3. Among pulmonates, leeches captured species in the following order:Physa gyrina(Say),Helisoma anceps(Menke).Lymnaea emarginata(Say) andHelisoma trivolvis(Say). Susceptibihty of size classes varied among snail species.4. Neither environmental structure, such as cobble or macrophytes, nor gastropod escape behaviors, such as clamping to substrates or vertical migration away from bottom‐feeding leeches, lowered capture rates byNephelopsis.5. In 2 years sampling, only one of seven lakes, however, had appreciable abundances ofNephelopsis.It is therefore suggested that the rarity, low feeding rates, and lack of strong gastropod preference limit the effect ofNephelopsison field gastropod distributio

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00338.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The behavioural responses of six species of British freshwater gastropods to chemical gradients of short chain carboxylic acids (C‐2 to C‐5, C‐8) and maltose were investigated by means of diffusion olfactometers.2. The species were ranked as follows on the basis of the number of significant behavioural responses to the test chemicals:Lymnaea peregra>Planorbis contortus>Physa fontinalis>Planorbis planorbis>Bithynia tentaculata>Planorbis vortex.These differences were not a result of differences in activity but reflect real differences in ehemoreception.3. Propanoate (C‐3) was a significant attractant or arrestant to five snail species, C‐4, C‐8 and maltose to four species and C‐5 to three species. Acetate (C‐2) was a significant attractant toL. peregraandP. fontinalisbut it was the only acid to act as a repellent, toP. planorbisandB. tentaculata.4.Lymnaea peregracontinued to respond to repeated butanoate application. Response levels could be enhanced by increasing concentration (minimum thresholds 10‐4M to 10−5M), pH (above 6) and food deprivation.5. The ecological relevance of the results are discussed with particular reference to the distributional patterns of the chemicals and snails and the feeding n

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00339.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The distribution of softwater and acid tarns and streams in central Cumbria is briefly summarized and compared for the periods 1983‐85 and 1949‐56.2. Fifty‐three upland tarns (altitude>350m) and forty lowland tarns (altitude7.0. Thirty‐one of the sixty tarns had mean Alk<100μequiv. I−1in summer (May‐September); sixteen became temporarily acid (negative Alk) for varying periods in winter. Acid episodes also occurred in the tarns in 1949‐56.3. Acid and very low alkalinity tarns and streams commonly occur on the high western, central and northern fells. Few occur on the high eastern felts, where there are veins of calcite in exposed rocks.4. Seventy‐five lowland tarns were sampled on Silurian Slates in southern Lakeland. On these bedrocks, tarns and streams are not highly sensitive to further acidification. Only six tarns had summer mean Alk<100μequiv. 1−1. No permanently acid tarns or streams were found.5. Over a mean span of about 30 years. Eel Tarn appears to have become slightly more acid and Harrop Tarn slightly less acid. The remainder of all tarns surveyed in 1983‐85 have altered little, although there is a heavy load of acidic deposition on to the catchments and some tarns contain very low concentrations of Alk. Rapid acidification in recent years has been prevented by the neutralizing capacity of volcanic and sedimentary rocks. These rocks produce relatively high concentrations of Alk, up to 650μequiv.l−1in some spring‐fed streams on the central fells and even more at lowe

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00340.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Food availability during instar F‐3 affected duration of instar F‐3 of larvalIschnura vertiealis(Say) maintained in the laboratory but did not affect the increase in head width at the moult to instar F‐2.2. Food availability during instar F‐2 altered both duration in instar F‐2 and weight per unit head width of newly moulted F‐l larvae, but not the increase in head width at the moult to instar F‐1.3. Food availability during instar F‐3 had no effect on instar duration, weight per unit head width, or increase in head width of F‐2 larvae at the moult to instar F‐l.4. Survival of larvalCoenagrion resolution(Hagen) reared in the laboratory was dependent on mean number ofDaphniaoffered per day. In addition, larvae fed less frequently, but on the same mean number ofDaphniaper day. had lower survival rates than larvae

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00341.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The toxicity of cadmium to matureGammarus pulexat different stages in the moult cycle is described.2. Immediate post‐moult animals are significantly more sensitive than intermoult specimens at cadmium concentrations between 1.0 and 0.1 mg 1−1but not at 0.03 or 0.01 mg Cd 1−1.3. At a calcium concentration of 40mgl−1, post‐moult animals undergo recalcification within 7 days and thereafter there is little variation in their response to cadmium.4. External calcium concentrations of 40 and 115mg 1−1do not affect cadmium toxicity but at 180 mg Ca1−1the sensitivity of immediate post‐moult specimens is significantly reduced.5. The results are discussed with regard to the protection ofG. pulexby present water qu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00342.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The life cycle of a predatory insect, Protohermes grandis (Megaloptera: Corydalidae), was compared in four streams in central Japan. The effects of annual temperature regime and prey availability on life history characteristics were also assessed.2. The larval period was 2 years and small adults emerged in the Morito River, where summer water temperature was high and large prey scarce.3. In the Nagura River, rich in large prey, the larval period was also 2 years in spite of slightly lower temperature, and the adult size was largest among the streams.4. In Anado Fork with a low summer temperature, the larval development took 3 years, and large adults emerged. Large prey were abundant in this stream.5. Seasonal abundance of large prey also affected the time large larvae left the stream to pupate. Larvae emigrated earlier in streams where the density of large prey sharply decreased after spring, than in streams where large prey were available throughout the year.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00343.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Modern diatom samples, for which physical and chemical environmental conditions were recorded, were collected from forty‐seven sites across Central Mexico2. The results of the diatom counts were analysed using the clustering program TWINSPAN and the ordination program DECORANA.3. Results from ‘Laguna Zacapu and associated sites’ showed that where water chemistry varies little between sample sites the effects of habitat are emphasized. This data set highlighted the problems of looking for modern analogues where anthropogenic disturbance is great.4. TWINSPAN results from the ‘Other Sites’ data set suggested possible changes in diatom assemblages with chemical composition. The DECORANA analyses, however, again seemed to emphasize habitat.5. In the context of this study, bottom sediment samples appeared to provide the most useful picture of ‘average’ conditions and to be the best source of analogues for the interpretation of fossi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00344.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. The toxicity to the freshwater amphipodGammarus pulex(L.) of soft water (pH6.0) with three concentrations of XAD‐extracted aquatic humus was treated in the laboratory.2. Exposure to pH6.0 water without humus added resulted in 92% mortality after 3 weeks. Humus, added at concentrations of 7 and 20 g Cm3, decreased the mortality to 80% and 64% in the same period.3. Surviving animals kept at pH6.0 had a lower growth rate, lower food conversion efficiency and higher body water content than animals kept at pH 7.3.4. Humus had no significant effects on growth, food conversion or body composition ofG. pulexkept at pH 6.0. However, there was a tendency for growth and food conversion to increase, and for body water content to decrease with increased humus concentration. The effects of humus on growth and food conversion ofG. pulexobserved in this study do not support the contention that humus acts as a free coupler to lower metabolic efficiency. On the contrary, humus tended to benefit food conversion.5. It is suggested that low concentrations of humus can be directly beneficial to organisms in acidified water in ways other than by complexing toxic metal

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00345.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY.1. Differential use of food resources by instars I‐1V ofChaoborus punctipenniswas examined in a mesotrophic New Hampshire lake during midsummer when all instars coexisted. Diet composition and prey preference were quantified first, at night when all instars were feeding at the same depth, and second, during the day when the early instars (I‐II) and instar III were segregated by depth. Relative abundance, per cent biomass, and per cent frequency of occurrence of soft and hard‐bodied rotifers, flagellated phytoplankton, protozoans, and crustaceans inC. punctipennisdiets were quantified using crop content analyses.2. All four instars ingested large, flagellated phytoplankton (mainlyDinobryonandCeratium). This unexpected result suggests that the effects of phytoplankton onChaoborusgrowth and survival should be investigated. All instars also consumed rotifers (mainlyKellicottia, Gastropus, Polyarthra), but only instars III and IV fed upon crustaceans (mainlyDaphnia, BosminaandDiaphanosoma). Small rotifers (Gastropusspp.,Keratella cochlearis, Trichocerca similis) occurred more frequently and were more abundant in early instar diets than late instar (III and IV) diets, whereas large rotifers (Asplanchna priodontaandKeratella crassa) were eaten only by instars III and IV. Zooplankton with gelatinous sheaths (e.g.Ascomorpha, CollothecaandHolopedium) were rarely ingested.3. Developmental increase in gape diameter ofC. punctipennisseemed to be the major proximate mechanism causing dietary differences among instars. Body widths of hard‐bodied prey inC. punctipenniscrops were always less than gape diameter. The relationship between prey body width andChaoborusgape diameter, coupled with knowledge of prey escape behaviour, should be useful for predicting the presence of hard‐bodied prey taxa in diets of otherChaoborusspecies.4. All four instars ofC. punctipennisselected soft‐bodied, or weakly loricate, rotifer prey over crustaceans and phytoplankton. Early instars preferred the small rotiferT. similisand the protozoanDifflugiasp. to other rotifers and phytoplankton when feeding in the epilimnion or thermocline during the day or night. Late instars positively selected the rotifer,Asplanchna.Prey value (prey weight ingested per u

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb00346.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY