摘要:

1. Survivorship and reproductive parameters of eightDaphniapulicariaclones were evaluated in a life‐table experiment under four dietary regimes ranging from food limitation to complete food deprivation.2.D.pulicariaexhibited both diet‐independent interclonal differences and genotype–environment interactions in life‐span.3. Reproduction ceased entirely or nearly so under the three treatments with lowest food availability. Under life‐long food limitation, differences between clones were evident in clutch sizes and age at first reproduction. Some clones produced ephippia at a markedly higher frequency than others under food‐limiting conditions.4. For most of the life‐history traits evaluated, within‐lake variation among clones exceeded differences between the two lake populations they represented.5. Intraspecific variations in response to periods of food deprivation and to extended quantitative or qualitative food‐limitation could affect the clonal composition ofDaphniapopulations. They are therefore of potential importance in determining the effect of altered phytoplankton assemblages on zoopla

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00470.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. This study presents a new approach to modelling subsurface irradiance using concepts from survival and failure time analysis. The model applies a modified Weibull distribution function to predict downwelling irradiance. Data sets from forty‐seven Norwegian sites show extremely high coefficients of determination, up to 99.99%, when analysed by the Weibull model.2. The uncritical use of a singlekdvalue to model underwater light conditions is likely to result in poor estimates of received irradiance. This error may amount to several hundred per cent. The practice of force‐fitting linear least‐squares regressions to log‐transformed irradiance data inevitably leads to highly biased estimates of the true fraction of incident irradiance entering the water.3. Wave effects causing fluctuations of subsurface irradiance are modelled with synthetic data and compared with field observations. Fluctuations of surface elevation by waves produce skewed frequency distributions of the underwater light field. The result of these effects, which are to reduce the accuracy of estimated model parameters, can be largely eliminated by carefully designing field procedures used for the acquisition of subsurface lig

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00471.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. This paper describes the effects of differences in food quantity and quality on selected life history traits ofCeriodaphnia pulchella. Animals were fed with four concentrations of two green algae,Scenedesmus obliquusandChlamydomonas globosa, given separately as well as in a 1 : 1 mixture.2. In most cases growth, reproduction and condition of the animals and consequently the rate of population increase,r, increased with food concentration. Life history parameters of animals raised onS. obliquuswere lowest, whereas no significant differences were found between animals fed withC. globosaand with the mixture of the two algal species.3. In contrast to the large effects of food quantity and quality found in the laboratory, an analysis of the population dynamics ofC. pulchellain Lake Tjeukemeer showed that the effect of changes in food conditions during the growing season of this species was limited, although overall food levels seemed to be poor throughout the year.4. Changes in the birth rate of the population are mainly governed by changes in temperature, and possibly by changes in the densities of the invertebrate predatorLeptodora kindtii.

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00478.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The effects of resource availability during ontogeny on subsequent feeding performance were investigated in larvae of the small‐mouthed salamander (Ambystoma texanum).2. Salamander larvae were reared individually in either high or low prey density treatments for 7 weeks prior to intermediate prey density foraging trials. Larvae from the low prey density treatment were on average 35% smaller in body size than individuals from the high prey density treatment.3. Resource availability during development influenced larval feeding rates and altered the relationship between body size and three feeding performance measures (attack rates, capture success and feeding rates). Feeding rates in predation trials were also positively correlated with growth rate early in the larval period (until the end of week 5).4. These results suggest that the environment to which developing organisms are exposed can have significant effects on subsequent behaviour, and that small‐mouthed salamander larvae may show state‐dependent changes in feeding behaviour in response to differences in long‐term feeding history. Additionally, differences in feeding performance may influence the probability of survival to the adult stage for organisms that utilize ephemeral h

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00479.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. We examined the behavioural response of stream macroinvertebrates to real and simulated predatory activity by a river bird, the Eurasian dipper,Cinclus cinclusL.2. In the field, we assessed whether invertebrate drift changed in response to live dippers in enclosures; we found no effects on the drift of any of the five families for which individual analyses were possible, either because it was infrequent, or involved distances too short to be detected (<0.5 m).3. In a laboratory stream, we observed prey during encounters with a model dipper which simulated flight, swimming, bill contact with the prey, and stone turning. Invertebrate families varied in their response. Simuliids and hydropsychid caddis lacked effective escape behaviour, consistent with heavy losses through predation by dippers in the wild. Other families either drifted (Baetidae, Gammaridae) or moved away (Heptageniidae, Ephemerellidae, Leuctridae, Perlidae) from the model dipper, but responded only to bill contact or simulated stone turning. Such delayed responses would not protect individuals directly targeted by foraging dippers and partly explain the lack of detectable effects by dippers on drift in the field.4. We suggest why invertebrates do not show more marked escape responses to this important predator.

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.d01-442.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The temporal abundance and composition of the plankton of a continental Antarctic lake (Lake Druzhby) situated in the Vestfold Hills, Eastern Antarctica was investigated from December 1992 to December 1993. The system was dominated by microbial plankton (cyanobacteria, heterotrophic bacteria and protozoans) with few metazoans.2. Chlorophyllaconcentrations ranged between 0.15 and 1.1 μg l–1and showed highest levels from late winter to spring.3. Heterotrophic bacteria ranged between 75 and 250 × 106l–1with highest abundances in late winter/spring. Mean bacterial biovolumes showed considerable seasonal variation (0.05–0.31 μm3). Largest biovolumes occurred in summer and this was the time of highest community biomass.4. Heterotrophic nanoflagellates reached highest abundances in late summer (maximum 14 × 105l–1). Their mean biovolume also exhibited considerable seasonal variation, ranging between 1.77 and 27.0 μm3, with largest size resulting in community biomass peaking in early summer. Ciliated protozoa were poorly represented and sparse. Phototrophic nanoflagellates were sparse in this lake; instead the phototrophic plankton was dominated by a small rod‐shaped cyanobacterium which constituted the largest carbon pool in the system. It was common throughout the year, its biomass peaking in autumn. Its presence is discussed in relation to lake morphometry and light climate.5. Heterotrophic flagellate grazing rates ranged from 6.78 bacteria cell–1day–1at 2 °C to 11.8 bacteria cell–1day–1at 4 °C. They remove around 2% of the bacterial carbon pool per day during summer and winter.6. Nutrient levels were low and recorded in pulses. Dissolved and particulate organic carbon were also low, usually less than 3 mg l–1and 600 μg l–1, respectively. The carbon pools were derived from autochthonous sources. This lake system is driven by bottom‐up forces and lacks top‐down control, which fits into the picture currently see

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00480.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The maximum depth of colonization of aquatic macrophytes (Zc) was investigated in eighteen South Island, New Zealand lakes. The downward attenuation coefficient for photosynthetically active radiation (Kd(PAR)) was calculated and the spectral characteristics of the lakes determined with a spectroradiometer.2. Characean algae dominated the deepest communities in sixteen of the study lakes.3.Zcwas significantly related toKd(PAR) by the relationshipZc= 4.5/Kd– 2.2.4. From measurements of the photosynthetic properties ofChara corallina(Kl. ex Willd., em R.D.W.) and incident radiation over the course of a year we calculated the depth at which daily net photosynthesis would be equal to zero for each day of the year. An annual average of this depth was significantly related toZcwith anr2of 0.86.5. CorrectingKd(PAR) for spectral quality and taking into account the potential absorption spectrum of a characean meadow did not improve the relationships.6. We suggest that relationships established betweenKd(PAR) andZcof characean algae in South Island, New Zealand lakes can be explained to a great extent by light limitation of photosynthesi

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00481.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. Temperature dependence of egg development ofDinocras cephalotes(Curtis) (three German and one Norwegian population) and SlovenianD. megacephala(Klapálek) was studied under a constant 14 : 10 light : dark photoperiod and constant temperature ranges of 4–24 °C and 4–18 °C, respectively.D. cephaloteswas also incubated under seasonal field conditions; natural daylength and fluctuating temperatures had no modifying effect.2. Both species have very similar lower threshold temperatures (4 and 3.5 °C, respectively), thermal demand for development (c.600 degree days) and high dependence of mean incubation period on temperature (exponents of regressions near 1.5). Present data onD. cephalotesagree with the literature on British and Norwegian material of the same species.3. Development occurs only at cue temperatures above the lower threshold. Cue temperatures range from 6 °C (someD. megacephala) to 14 °C (someD. cephalotes) and vary strongly within and between egg masses ofD. cephalotes. Variation is not random, but seems to be genetically determined.4. The variable temperature response renders study of effects of particular experimental regimes, and comparisons between local populations, difficult.5. A latitudinal gradient in cue temperatures for development from 6 °C atc.46 °N to 12 or even 14 °C atc.61 °N seems to reflect reduced diversity at high latitudes.6. Average success of spontaneous hatching exceeded 90% between 12 and 20 °C, but declined towards higher and lower temperatures.7. Unhatched eggs were not dead but in parapause; development at other, higher or lower, temperatures was induced. Spontaneous plus induced hatching success approached 90%. Developing eggs rarely died; most dead eggs were apparently unfertilized.8. Dormant plecopteran eggs are proposed to form a seed bank in stream bed sediments. Highly successful development after up to 220 days of dormancy was ascertained inDinocras, and survival for up to 3 years is reported for other Perloidea.9. Only systellognathan egg morphology provides options for long dormancy; the other plecopteran superfamilies, notably Nemouroidea, follow differ

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.00482.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The larval life spans of twelve species of aseasonal aquatic insects (eight Trichoptera, three Ephemeroptera, one Odonata) were investigated in two tropical streams with near constant water temperatures.2. Life spans were estimated from equations relating larval life span to the ratio between cohort production (estimated from the size–frequency technique) and annual production (estimated from regressions in the literature).3. Life spans varied from 40 to 250 days and were positively correlated with maximum larval dry weight (r= 0.73,P<0.001). Ephemeroptera had the shortest larval life spans (40–110 days), Trichoptera intermediate (95–185 days) and Odonata the longest (250

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.d01-449.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km2Yakima River basin in south‐central Washington, U.S.A.2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small‐scale physical structure.4. Multiple discriminant function analyses indicated that segment‐ and reach‐scale variables discriminated among species‐defined groups better than sample‐scale variables.5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and

ISSN:0046-5070    

DOI:10.1046/j.1365-2427.1996.d01-450.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY