摘要:

SUMMARY1 The combined effects of fish predation, substrate complexity and flow on benthic macroinvertebrates inhabiting riffles was investigated in a Hong Kong stream. Predation was manipulated using fish inclusion/exclusion cages containing complex (= many refuges) or simple (= few refuges) substrates. Experiments were undertaken during the winter dry season, when disturbance due to flow events was minimal, and repeated during the summer monsoon, when the stream experienced spates of varying intensity and duration.2 Predation by the fish,Oreonectes platycephalus, significantly reduced the abundance of macroinvertebrates, especially chironomids and mayflies. Because chironomids (mostly Chironominae) were the dominant cage colonists, there was also a reduction in total macroinvertebrate density.3 Predator impacts were significantly lessened during the wet season, when macroinvertebrate densities increased considerably, but significant reductions in the densities of vulnerable taxa and total macroinvertebrate abundance were nevertheless apparent.4 Substrate complexity (the presence of prey refuges) had no significant effect on the ability of predators to reduce prey abundance.5 Detritus accumulated in cages during the latter part of the study, and densities of most taxa were correlated with detrital standing stocks.6 The results of this experiment indicate that biotic interactions such as predation may be suppressed during periods of spate‐induced disturbance, although they can still influence benthic communities significantly. However, the effects of predation are highly taxon specific and may vary among streams in response to changes in predator and prey species composition, or the severity and durat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00801.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 This study attempts to determine the mechanisms by which the downstream displacement of lotic invertebrates is compensated by the upstream movements of immatures and adults. To this end, submerged and aerial traps were set up at three sites, each 100 m apart on a small mountain stream (Yr Ogof) in North Wales and operated for 12 months.2 At Site 1 (the source), 19.3% of the benthic invertebrates lost as drift were replaced by the upstream movement of aquatic stages. At Site 2, the average upstream compensation was 51.1% (although there was a marked difference between the two traps at the site). At downstream Site 3 the average compensation was 55.4%. The net loss of benthos downstream over 1 year was estimated to be 261920 individuals from Site 1, 41891 from Site 2, and 40470 from Site 3.3 At Sites 1 and 2, the numbers of invertebrates drifting were positively correlated with both current speed and water depth. At Sites 2 and 3, the numbers moving upstream were positively correlated with water temperature. At all three sites, the numbers of animals drifting were positively correlated with the numbers moving upstream, under water.4 In none of the eight common species of stoneffy did females show a strong overall upstream flight preference—however, two species,Leuctra nigraandNemoura erratica, showed a significant downstream preference.5 As with the stonefly nymphs, most of the caddisfly larvae showed a longitudinal distribution.Agapetus fuscipeslarvae were most abundant at Site 1, yet females showed no preferred flight direction—this would seem to be inappropriate for maintaining this larval distribution pattern. However, females caught moving upstream at Site 2 were bigger and contained twice as many eggs, which were also larger, than females moving upstream at Site 1. The flight patterns of the other Trichoptera also seemed inappropriate for maintaining their respective larval distributions. Immature insects moved upstream at certain sites and times, but trends were not consistent. There was no correlation between female flight direction and local wind speed and direction.6 Downstream displacement of the most abundant non‐insect species,Gammarus pulex, was quite considerable at all three sites. However, at several times during the year the numbers moving upstream approached or exceeded those drifting. Maintenance of benthic population densities in this species is thought to be through a combination of upstream movement (which was highly correlated with benthic density at Sites 1 and 3) and production of young over a long (10 month) reproductive period. Maintenance of the benthic populations of the immature stages of the majority of insect species in Yr Ogof is thought to be through oviposition by females in the vicinity of thei

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00802.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 To test the hypothesis that the variability in hatching response of the sexual eggs ofDaphniahas a genetic component, hatching after a standardized decapsulation technique was studied in different D.magnafamilies, resulting from intra‐ as well as interclonal crosses.2 There were significant differences in hatching response between families. Average hatching rates ranged from 0.0% to 81.9%, depending on the family under study.3 Offspring‐on‐parent regressions indicate that the hatching rate‐of sexual eggs is to a large extent determined by the genotype of the mother (maternal inheritance).4 Our results suggest that there is ample generic variation on a microgeographic scale for characteristics related to hatching of sexual

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00803.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 We examined the effect of age on the hatching response ofDaphnia magnasexual eggs of specific families. For old eggs (>2 years), hatching characteristics were compared at two storage temperatures (4°C and 20°C). Also, the hatching response after a second dark incubation and subsequent incubation under conditions favourable for hatching was compared with that after the first stimulus.2 Daphniasexual eggs were found to remain viable for several (at least 4.5) years. The effect of age on the hatching rate was family dependent. At least in some families, hatching rate was higher for old (>2 years) than for young (<5 months) eggs. Low temperature (4°C) during dark incubation resulted in a higher hatching rate compared with incubation at 20°C.3 The application of a second hatching stimulus resulted in a renewed hatching response. The overall hatching rate after the second stimulus was, however, lower than that of the first stimulus.4 More than 80% of the hatchlings of young eggs appeared on Day 3 or 4, with minor between‐family differences in time distribution of hatching. The timing of the response to hatching stimuli was more variable in old than in young eggs, with the average time at hatching being 6.4 instead of 4.0 days. The response to the application of hatching stimuli was also slower after the second stimulus compared with the f

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00804.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 A simple water sampler and an incubation chamber are presented. The water sampler is simpler in construction than the Ruttner sampler and other comparable devices. In addition to enclosure of water at a discrete depth, the incubation chamber releases a radioisotope or other substance of experimental interest into the sample.2 Tests of performance are presented, demonstrating efficiency in enclosure of water from discrete depths, and time course of mixing of a tracer into the sample after activation of the release mechan

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00805.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The larval chironomid community of the sediment surface and the hyporheic inters titial was investigated in two longitudinal transects of an alpine gravel stream between September 1984 and August 1985. Eighty larval species and species groups were identified, most of which belonged to the subfamily Orthocladiinae. Of all larval individuals 51.1% inhabited the first 10cm of the bed sediments, and 93.2% occurred between the surface and 40cm depth.2 The spatial species turnover showed marked variations between horizontally adjacent sampling sites in each of the four sediment depth layers. In both transects the species composition showed a significantly lower turnover in the upper 10cm of the bed sediments than in the deeper layers.3 Spatial community stability showed an oscillating pattern between all sampling sites due to density shifts of larvae between depth layers. Temporal differences in resilience (local stability) were significantly and positively related to changes in the cumulative discharge pattern in the gravel brook, thus indicating the apparent ability of the community to recover quickly following disturbances.4 The five abundant species,Corynoneura lobata, Synorthocladius semivirens, Tvetenia calvescens, Micropsectra atrofasciataandRheotanytarsus nigricauda, exhibited significant differences in their sediment depth distribution, with density maxima shifting between depth layers. Spatial autocorrelations suggest that these larvae form patches between neighbouring sampling sites with varying sizes and inter‐patch distances in each of four sediment layers. A simulation test, in which individuals of each species were randomly permuted between microhabitats of each depth layer separately, indicated that the patches might have arisen by chance.5 To evaluate the significance of observed spatial resource overlap values amongst these five chironomid species, neutral models were developed based on 300 randomizations of each possible species pair‐wise association of individuals and patches of species. The spatial organization of a larval chironomid assemblage in the stream Oberer Seebach seemed to be governed by coexistence due to random patch formation and dispersal patterns within the interstitial habitats, which reduce the probability of strong competitive

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 Experiments on the influence of temperature (5–25°C) on morphology, life history and growth rate ofFilinia terminalisandF. cf.pejleriwere performed in replicated individual cultures withOocystissp. as food.2 Some morphological characteristics previously used for the identification of both species were found to be affected by temperature and also by life cycle stage. However, numbers of unci teeth were not affected.3 Body and setal lengths, life spans, all stages of development, and growth rates of both species decreased with increasing temperature.4 Offspring number per female of both rotifers was highest at 20°C. Maximum growth rate ofF. terminaliswas at 25°C, whereas that ofF. cf.pejler

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The potential importance of phytoplankton to the nutrition of adultCyclops vicinuswas studied.2 The flagellateChlamydomonas reinhardiiwas ingested and digested at a higher rate than the coccale green algaMonoraphidium minutum.3 The predation rate on the rotiferBrachionus rubensdecreased if C.reinhardiiwas also available as food. No significant reduction of predation was found whenM. minutumwas offered together withB. rubens.4 The species of available phytoplankton influenced egg production. Females which were allowed to feed onB. rubensandC. reinhardiiproduced more eggs than females which fed on rotifers only or a diet containing rotifers and M.minutum. Egg production was also possible when rotifers were absent from the diet.5 Production efficiency was higher whenC. reinhardiiwas the only food resource than on a diet containing roti

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00808.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 In reservoirs of the south‐eastern United States,Daphniatypically decline in abundance during the summer months. Current understanding suggests that adult shad (Dorosomaspp.), the dominant planktivore in these reservoirs, plays a limited role inDaphniamidsummer declines. The impact of shad larvae is beginning to be documented.2 To examine the impact of larval shad onDaphniaseasonal dynamics, larval dynamics were studied over two seasons and stomach contents were analysed during one season.3 InitialDaphnia panwladeclines correlated with abundance of shad larvae. During the decline, shad stomach contents consisted of 97—100%D. parvula. After D.parvuladeclined,BosminaandDiaphanosomaaccounted for up to 97% of larval diets. When shad diets included other cladocerans,D. parvulaabundance increased in the reservoir.4 When this predation pattern was incorporated into a predictive model, larval shad predation accounted for an initial, temporary decline in D.parvulaabundance. However, when other crustaceans were incorporated into the shad diet,D. parvulapopulations increased.5 These results suggest that larval shad have a temporary, strong influence on the structure and abundance ofD. parvulapopulations in south‐eastern reservoirs of th

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00809.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 This study compares small‐scale (i.e. neighbourhood) associations among distributions of phytoplankton, zooplankton, and zooplankton grazing rates using a combination of correlations and analyses of spatial patchiness.2 All zooplankton and phytoplankton populations had patchy distributions. On average, individuals experienced members of their same taxon at a density that was 42% greater than the mean sample density.3 The various zooplankton taxa experienced different average neighbourhoods, even within the same stratum of the lake. For example,Daphnia galeata mendotae(Birge) experienced phytoplankton concentrations that were nearly 50% greater than those experienced byDaphnia pulicaria(Forbes) at the same depth.4 The distributions of the various phytoplankton taxa were positively correlated with each other, but the distributions of zooplankton were negatively correlated, or more often, unrelated to each other.5 Phytoplankton abundance was negatively correlated with zooplankton grazing rates.6 We hypothesize that while phytoplankton distributions are driven by common external factors, the factors that determine horizontal distributions of zooplankton are species specific. In addition, zooplankton grazing appears at least partially responsible for the generation of patchiness in the distribution of

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00810.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY