摘要:

SUMMARY1. The objective was to compare variations in egg hatching between the two species (interspecific variations) and between populations of the same species (intraspecific variations). There were significant interspecific, but not intraspecific, differences in female size, adult life‐span, egg production, hatching success, incubation periods and hatching periods.2. The optimum temperature for hatching success within the range 3.8–22.1°C in the laboratory and the range over which at least 50% of the eggs hatched were lower for Chloroperia tripunctata (Scopoli) (8.5°C, 4.2–17.3°C) than forSiphonoperla torrentium(Pictet) (12.8°C, 6.1–19.4°C). Few eggs hatched at 22.r°C.3. The relationship between incubation period (d days) and water temperature (T°C) was given by: d=1219/T1.368for S.torrentium, d=253/T0.459for C.tripunctata. Both equations successfully predicted incubation periods for eggs placed in a stream. The period over which eggs hatched was much longer for C.tripunctatathan for S. torrentium at all temperatures.4. The shorter incubation period (at r>5.6°C) and shorter hatching period for S.torrentiumensure that larvae of this species are already growing when eggs of C.tripunctatastart to hatch, but the prolonged hatching period of the latter species ensures a long period of larval recruitment to the population. These differences in egg hatching may reduce competition between the two closely

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01712.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. Prey selection by the dobsonfly larva,Protohermes grandis(Thunberg), was studied in stony riffles of the Yataro River, central Japan. The density, size distribution and taxonomic composition of available prey were assessed for 2 years. In order to know the encounter rate between prey and this ambush predator, prey mobility was also estimated from patterns of colonization of experimentally detiuded stones.2. Foregut analyses revealed that maximum size of prey eaten increased with larval size, and large larvae did not take the smallest prey in spite of high availability in all seasons.3. Charnov's (1976) optimal diet model quantitatively predicted such size‐selective feeding under seasonally fluctuating conditions of water temperature and prey availability. Larvae maximized the feeding rate by selecting prey.4. Maximum width of prey eaten coincided approximately with larval mandible length. Mandible size seemed to play an important role in the selection of prey in the optimal size rang

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01713.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. Two taxonomically unrelated species, the ciliated protozoanScyphidiasp. and the chironomidEpoicocladius flavens(Malloch), share a commensal mode of life on nymphs of the burrowing mayflyEphemera danicaMüller in a small river in eastern England.2. Both commensals were present all through the year, with an average level of infestation of 25.1% and 54.7% forScyphidiasp. andE. flavens, respectively, of the totalE. danicapopulation.3.Scyphidiasp. occurred more frequently on younger, smaller nymphs ofE. danicaand was totally absent from hosts of more than 10 mm in length. In contrast,E. flavenspreferred hosts of larger body size, usually more than 10 mm. Change in dominance of infestation between the two commensals occurred in the host size range of 6–8 mm and this pattern of habitat partitioning on the basis of host size was consistent throughout the study period.4. AmongstE. danicaindividuals colonized byE. flavens, larger hosts supported heavier commensal load. A similar trend, though weak, was also observed among hosts harbouringSchyphidiasp.5. Both commensals are considered to benefit from the association withE. danicain that they gain enhanced mobility and security in otherwise inhospitable habitats. Although plausible on an evolutionary time scale, competition alone cannot constitute a proximate cause for the clear partitioning of habitat observed in the two commensal speci

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01714.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. We measured biomass and light/dark bottle productivity of macrophytes in a Wisconsin stream throughout one growing season. Except for a brief period in early spring when aCladophora glomerata‐filamentous algal community was dominant,Potamogeton pectinatuswas the dominant macrophyte species in Badfish Creek.2. Maximum community biomass was 710 g DW m−2, with a maximum above ground biomass of 620 g DW m−2and a maximum below ground biomass of 120 g DW m−2. Annual productivity was estimated at 1435 g DW m−2year−1, with a calculated P/B of 2.01.3.In situnet production averaged 2.83g C g AFDW−1h−1Net positive carbon gain by theP. pectinatuscommunity occurred when water temperatures were above 15°C, and daylength at least 12h. This is correlated to the onset of tuber germination in spring, and the point of maximal biomass d

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01715.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. The planktonic ciliate communities of eleven organically coloured north and central Florida lakes representing a variety of trophic conditions were examined during 1979–80. The total abundance and biomass of ciliates were not significantly different from comparable clearwater lakes and only minor taxonomic replacements were noted at the order level.2. Timing of population peaks of oligotrophic lakes was dissimilar to clearwater lakes of the same trophic state, but seasonality in meso‐trophic and eutrophic lakes resembled patterns described for comparable clearwater lakes.3. Various ciliate components were strongly correlated with chlorophyllaconcentrations, but only moderately correlated to dominant phytoplankton groups. No significant correlations were found between ciliate components and bacterial abundance.4. Myxotrophic taxa numerically dominated oligotrophic systems, particularly during midsummer, and accounted for a large percentage of the total ciliate biomass. Estimates of the ciliate contribution to total autotrophic biomass indicate that these zoochlorellae‐bearing protozoa may account for much of the autotrophic biomass during midsummer periods in coloured lakes, and thus may lead to an overestimation of phytoplankton standing crops available to zooplankton grazers if chlorophyllais used as a surrogate measure of algal bi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01716.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. The study presents adaptive and acclimatory changes observed inCyprinus carpio communisL with respect to ovarian cycle and serum levels of electrolytes, calcium, total proteins and albumin as a consequence of wide temperature and sunshine variation in the natural environment of Dal lake in Srinagar, Kashmir (India).2. The atmospheric temperatures in Srinagar show well‐defined seasonal and diurnal variations. During the period of study, the mean monthly average temperature in summer (June‐August) was 24°C whereas in winter (December‐February) it fell to 3.6°C. The total hours of sunshine during the winter months were about half of those found in summer.3. Under local thermal and photo conditions the fish was found to spawn once a year compared to biannual spawning in tropical chmates.4. A significant decrease was found in serum sodium, potassium and chloride concentrations during the months of January and February when the mean minimum atmospheric temperatures reached −2.5°C and −l.2°C respectively.5. The serum calcium levels showed a marked increase during the period corresponding to ovarian maturity and spawning of fish.6. A significant rise in total serum protein concentration was induced by decreased environmental temperatures. Serum albumin levels were found to exhibit a sharp fall coinciding with the sp

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01717.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. Two populations ofDaphnia pulex, one from a permanent pond and one from a temporary pond, and two temporary pond populations ofDaphnia obtusain the East Midlands of Britain were examined by enzyme electrophoresis. The three temporary pond populations showed good fits to Hardy‐Weinberg expectations, suggestive of cyclic parthenogenesis, while the permanent pond population showed deviations bordering on statistical significance.2. Laboratory characterization of the ephippiai offspring of heterozy‐gous mothers from each population showed normal Mendelian segregation and males were produced. This indicates that in both species ephippiai egg production was a sexual process, and confirms that these populations reproduce by cyclic, rather than obligate, parthenogene

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01718.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. Life history parameters of two species of Chydoridae (Leydigia leydigiandDisparalona rostrata) were studied in the field and in the laboratory.2. For both species the number of juvenile instars was variable and tentatively related to initial size of neonate. Egg volume increased with increasing parent length and with decreasing temperature; possible advantages gained by the offspring are discussed in relation to invertebrate predation.3. The life history strategy employed by the littoral Chydoridae is compared to that of large and small planktonic cladocerans. Small planktonic cladocerans and the Chydoridae (except the Eurycercinae and the Saycinae) produce large young relative to their size at maturity and mature early. However, unlike the small planktonic cladocerans, growth in the Chydoridae is curtailed after the onset of reproduction and in this they resemble the large planktonic cladocerans. This strategy may be related to vertebrate predation and the presence of vegetation in the habitat.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01719.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. Predatory, net‐spinning larvae of the caddisPlectrocne‐mia conspersa(Curtis) were abundant in the acid headwaters of some southern English streams where fish were absent, but were scarce or absent downstream where brown trout (Salmo trutta L.) occurred.2. Field enclosure experiments showed that both underyearling and older brown trout reduced the density ofP. conspersa. However, whereas small trout affected the overall density of caddis, older fish reduced that of large larvae only.3. AlthoughP. conspersais itself an important invertebrate predator there was little evidence of an indirect effect of brown trout on the prey ofP. conspersa. Perhaps the diets of brown trout andP. conspersaare so similar that fish simply replaced the caddis as top preda

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01720.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARY1. Historical and recent data on the occurrence of macrophytes in twenty‐eight lentic soft waters in The Netherlands are summarized. These waters were, and a few still are, characterized by a submerged vegetation of isoetid plants. Changes in the species composition of macrophytes are visualized by means of multivariate analysis and by shifts in species‐spectra.2. Ordination of the available data shows that the pH, alkalinity, acidity, contents of heavy metals, dissolved organic matter and some important salts and nutrients in water and interstitial water are strongly related to the recent distribution of aquatic plants in waters, which were originally of low alkalinity. In addition, the available inorganic carbon and the redox potential in the sediment are also important environmental parameters in explaining differences in aquatic vegetation.3. The recorded changes in the macrophyte species composition can be attributed to the effects of acidification and eutrophication. The most important, overall change is a reduction of the number of species.4. Hydrology proves to be important in controlling the sensitivity of a body of water for acidifying deposit

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1988.tb01721.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY