摘要:

SUMMARY.1. The chironomid fauna on the spiked water‐milfoilMyriophyllum spicatumwas studied quantitatively for a year in a small lowland stream in eastern England.2. A total of nineteen species, comprising fourteen Orthocladiinae, four Chironominae and one Tanypodinae, was recorded. Population dynamics and life histories of the eight most abundant species were described:Orthocladius (O.)Pe 9,O. (O.)sp. A,Cricotopus (C.) annulator, Rheocricotopus chalybeatus, Tvetenia calvescens, Eukiefferiella ilkleyensis, Thienemanniella majusculaandRheotanytarsus curtistylus.The number of generations per year ranged from one(O. (O.)Pe 9,O. (O.)sp. A,C, (C.) annulator)to five (T. calvescens, T. majuscula).Temporal variation in population density often reflected characteristic patterns of the life cycle of each species.3. Species richness (number of species) for each month ranged between six and fifteen. These observed species richnesses were compared with a null species occurrence model and it was revealed that a significantly higher number of species than expected coexisted in April and May. This may be related to the abundance of diatoms in sprin

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00985.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Measurements of the population density ofTheodoxus jordaniwere made for the period July 1980 until June 1981. Numbers showed a well‐defined pattern of fluctuation and varied between 390 in February and 1804 snails m−2in May after recruitment.2. The population age structure revealed that the snail was semelparous, and that one generation dominated the population for most of the year.3. The breeding season was long. Snails laid eggs from early December to the end of April. Eggs were laid in protective capsules and one snail developed per capsule. Total population natality estimated from field samples was 9813 snails m−2.4. Age specific mortality was high immediately after recruitment, low during the juvenile stages, and increased sharply at the adult stage with the onset of reprodu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00986.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The oxygen consumption of the gastropod snailT. jordaniwas determined at six different temperatures corresponding to those experienced in the field.2. The respiration rate increasing linearly with increasing tissue weight at all temperatures studied. Regression equations describing the respiration rate‐live weight relationship were significantly different (P<0. 001).3. The respiration rate‐temperature relationship was linear for seven weight classes of the population. The extent of change in the respiration rate with increasing temperature differed between the different weight classes. The Q10value was highest (2.5) for the smallest weight class and decreased with increasing size.4. The annual respiratory loss by the whole population was estimated to be 334.75 kJ

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00987.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The tendency of larvae ofChyranda centralisto mark themselves by adding coloured plastic segments to their cases was used to study instream movements of the species. Plastic strips of different colours were placed at measured distances down a small spring stream and larvae cut pieces and incorporated them in their cases.2. Over 50% of the marked population moved upstream into cooler water prior to pupation in an exceptionally dry year. The greatest distance moved upstream by a single larva was 56.9m, In a wet year, when daytime stream temperatures were cooler, 11–28% of the marked population moved upstream. Downstream movement occurred in both years late in the fifth instar.3. Larvae selected yellow in preference to other colours in laboratory tests and they preferred heavy, textured plastic to light, smooth plastic as they neared pupation.4. Upstream movements, found also inDesmana bethula(Trichoptera: Limnephilidae) in the same spring stream, may be an adaptation for avoiding pupation in areas of high temperature, low oxygen concentration, or intermittent flo

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00988.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1.Erpobdella octoculata(L.),Glossiphonia complanata(L.) andHelobdella stagnate(L.) were eaten readily by larval and adult dytiscid beetles, larval caddisflies andSialis, nymphal odonatans and various fish in laboratory experiments.2. A serological technique showed that very few lake‐collected specimens of these predatory taxa, plus triclads, leeches and stone fly nymphs, had been feeding on leeches.3. A literature survey of lake studies on fish diet indicated that usually less than 6% of individuals with gut contents had eaten leeches. Few detailed records of waterfowl feeding on leeches have been documented.4. It is concluded that predation pressure on lake‐dwelling leeches is light, and is more severe from fish than invertebrates, less on populations inhabiting stony shores than in vegetation, and greater on the erpobdellid than the two glossiphoniid spec

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00989.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The annual cycle of the freshwater sponge,Anheteromeyenia ryderi, was studied in a seepage pond in Connecticut. The adult form of the sponge persisted throughout the year, although some specimens at the edge of the pond degenerated by late summer. During the middle of the winter, adult sponges had a simplified tissue morphology with reduced numbers of flagellated chambers.2. Gemmules ofA. ryderiwere also present during all seasons. Gemmule germination occurred during the spring, and some specimens produced new gemmules by late spring.3. The gemmules ofA. ryderiunderwent a protracted diapause which was broken under both natural and laboratory conditions by several months exposure to low temperatures (≤5°C).4. The gemmules ofHeteromeyenia tubispermawere also shown to undergo diapause, but in this case diapause was broken by a relatively short cold treatment (1 mont

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00990.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. A series of laboratory and field experiments was performed to determine if the preference of larvae ofHelicopsyche borealis(Trichoptera: Helicopsychidae) for exposed rock surfaces in streams was related to patchiness of periphyton food.2. At low current velocities in the laboratory larvae preferred food‐saturated as opposed to food‐depleted portions of substrata and drifted off the substratum in response to low food levels.3. When offered a choice of three potential foods—a diatom, a green filamentous or a blue‐green filamentous alga—larvae showed no preference.4. Larval densities on artificial subtrata in field experiments were highest in areas of high algal chlorophylla.5. In laboratory experiments more adults emerged from cultures containing green algae or diatoms than cultures with blue‐green algae or bacteria alone.6. Periphyton quality was not as important as abundance in controllingH. borealismicrodistribution. By selecting exposed surfaces of rocks,H. borealislarvae place themselves in the microhabitat most likely to contain both abundant and high quality f

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00991.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The zoopiankton associations in five crater lakes in Ethiopia were examined in April 1984. The two least alkaline lakes had the most diverse zoopiankton.2. The large diaptomid copepodLovenula africanawas present in the lakes with alkalinities between 10 and 63 meq l−1, but was absent from Lake Chitu (239 meq l−1).3. The contribution of the zoopiankton to the nocturnal deoxygenation of Lake Aranguadi is negligi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00992.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. The distribution of breeding dippers was assessed in 1984 over seventy‐four sites on soft‐water streams throughout mid and north Wales.2. Sites without breeding dippers had significantly higher mean concentrations of filterable aluminium, lower mean pH, fewer trichopteran larvae and ephemeropteran nymphs, and were on rivers with more conifer afforestation on their catchments, than sites where dippers were present.3. We speculate that influences which increase the acidity of soft‐water streams could be detrimental to their populations of dippers, although further data are required on causative mecha

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00993.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARY.1. Tagimaucia crater lake and swamp are located at an altitude of 820m in Taveuni, Fiji (lat. 16°S; long. 179°56'W). Rainfall exceeds evaporation in all seasons and residence time for water in the shallow lake (2.5–5.5 m deep) is only 4 days.2. Dissolved ion concentrations are low (conductivity 14–18μScm−lat 25°C), and the water is slightly acidic (pH 5.0–6.5 at 25°C), Median total phosphorus (0.5 gm−3) and total nitrogen (3.3gm−3) are moderately high and probably represent dissolved and suspended organic matter. Median chlorophyllaconcentrations (2.5 mg−3) were low and indicate low phytoplankton productivity.3. The swamp vegetation is dominated byLepironia articulate(Retz.) Domin and algae which form floating sedge peat islands, andPandanus taveuniensisSt John and other small trees where alluvium and colluvium are infilling the margins of the crater. The surrounding slopes are forested.4. The fauna of the lake and swamp are low in both diversity and abundance. The only aquatic vertebrates observed wereAnguillaeels and cane toads,Bufo marinusL., and the only bird was the swamp harrier,Circus approximans approximatePeale. A variety of aquatic insects were observed but crustaceans and other invertebrate taxa were scarcely recorded.5. Although the swamp and lake are otherwise undisturbed, several recently introduced plants and animals

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1986.tb00994.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY