摘要:

SUMMARY.1. The diet of the Eurasian dipperCinclus cinclus. a riverine bird from a globally widespread genus, was assessed through all stages of its annual cycle using published data and field studies from streams of contrasting chemistry. Time‐activity budgets were also compiled throughout the year and used to estimate annual energy requirements from the stream ecosystem.2. The annual energy requirements for a territorial pair ranged from 148,000 to 158,000 kJ yr−1depending on whether one or two broods were reared. After allowing for assimilation efficiency, these requirements were estimated to represent 10.5–11.0 kg dry mass of fish and invertebrates. Using representative values for territory size (4680–11,250 m2), annual exploitation of secondary production was estimated at 0.93–2.35 g dry mass m−2.3. Several features combined to focus the predatory load on certain organisms over different stages of the annual cycle. These included the availability and selection of alternative prey, the need to provision nestlings with large items such as trichopteran larvae, and the use by females of calcium‐rich prey such as fish prior to egg formation.4. Across their range of territory size, annual exploitation (dry mass) by dippers was estimated at 0.06–0.29 g m−2for Plecoptera. 0.02–0.22 g m−2for Ephemeroptera. 0.59–1.11 g m−2for Trichoptera and 0–0.78 g m−2for fish. Exploitation of Ephemeroptera. I richoptera and fish were all highest in circumneutral streams, but exploitation of Plecoptera was highest in acidic streams because other prey were scarce.5. Cottids dominated the fish component of the diet. Influences on their density could be substantial according to available data on production in Welsh streams. Hydropsychids and limnephilids dominated the trichopteran component, with exploitation again representing potentially substantial amounts of production. Contemporaneous data are required on benthic production and exploitation by the birds.6. The ecological role of birds in rivers particularly, and aquatic ecosystems generally, is currently neglected but worthy of

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00477.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Brown Hill Creck, a small intermittent stream in dry sclernphyll forest in South Australia, flows for about 6 months during winter and spring. When flow ceases the stream dries to isolated pools which receive high summer inputs ofEucalyptus obliqualitter. Decomposition of this material in remnant pools causes extremely dark waters and depressed oxygen concentrations for up to 90 days.2. Only two fully aquatic insect species,Lepntorussa darlingtoniandLectrides varians(Trichoptera: Leptoceridae), persist under these conditions. Both utilize litter as food, but have different feeding strategies. The more abundantL. darlingtoniingests organic and microbial material from leaf surfaces, whereasL. variansis a leaf shredder.3. Larval processing budgets based on laboratory and fleid experiments indicated thatL. varianthas a greater impact on litter decomposition rates thanL. darlingtoni. However, because of low density, low oxygen concentrations in pools during summer, and rapid flushing of litter from pools once flow recommences.L. variauslarvae process a small proportion of the total litter input.

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00478.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. The population dynamics and annual production of the multivoltine. pelagic amphipodHyalella montezumawere studied over a 3‐year period in the thermally constant environment of Montezuma Well. Arizona.2.H. montezumashowed two maxima which coincided with spring and autumn phytoplankton maxima. Juveniles comprised over 85% of the population in the pelagic zone compared to 37% in the littoral vegetation and there were significantly more females in the littoral vegetation. It appears that juvenile and adultH. montezumashow different habitat preferences.3. Total annual mean production forH. montezumacalculated by the size frequency method and adjusted for multiple generations, was 357 kg ha−1yr−1, which is higher than single‐species production estimates reported for most zoobenthic amphipods and multivoltine planktonic crustaceans. Average energy production forH. montezumawas 4640 kJ ha−1yr−1in the pelagic zone and 1072 kJ ha−1yr−1in the littoral vegetation.4. Average cohortP/B̄ ratios forH. montezumawere higher in the pelagic zone (5.5) than in the litttoral vegetation (3.7). Juveniles had higher cohortPB̄ ratios than adults in the pelagic zone, while the reverse relationship was true in the littoral vegetation. We propose that different size‐selective predators may contribute to the differences inPB̄ ratios for juveniles and adults i

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00479.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. During two, 1‐month studies, the abundance of mayfly nymphs,Callibaetis californicusBanks, in small ponds that contained the tadpole shrimp,Triops longicaudatus(LeConte), often was significantly lower than in ponds without tadpole shrimps. Mayfly abundance was either positively correlated or not significantly associated with that of predacious insects.2. Larger mayfly nymphs were a greater fraction of the population in ponds withTriopsthan in ponds without tadpole shrimps. Between 2 and 3 weeks after ponds were flooded, the smallest mayfly nymphs were absent from ponds in whichT. longicaudatusdensities were>5 individuals per square metre during the summer and>15 individuals per square metre during the autumn.3. In prey‐choice trials,T. longicaudatusconsumed predominantly smallC. californicusnymphs (mean headwidth ± 1 SD: 0.44 ± 0.05 mm). After encounters with tadpole shrimps, small mayfly nymphs moved relatively shorl distances, were easily overtaken, and were, consequently, more susceptible to tadpole shrimps than larger‐sized

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00480.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. Threespine stickleback (Gasterosteus aculeatus) andChaoborus(C. punctipennisandC. trivittatus) planktivore populations were sampled from several oligotrophic lakes on the Avalon Peninsula of Newfoundland, Canada. Pelagic zooplankton communities in these lakes consist ofDaphnia catawba, Holopedium gibberum, Eubosmina longispina, Leptodiaptorma minutus, Epischura nordenskioldi, Cyclops scutiferand rotifers (Conochilus unicornis, KeratellaandKellicottiaspp.).2. Comparison of gut contents ofG. aculeatusand crop contents of later instarChaoboruslarvae with lake zooplankton communities indicated that the vertebrate and invertebrate plank tivores show contrasting species and size selectivities in their choice of zooplankton prey. Prey selectivities were quantified by means of the selectivity index α.3.G. aculeatusshowed positive selectivity for larger zooplankton (greater than 0.76 mm in length), typically the cladoceranD. catawba, whileChaoboruslarvae showed positive selectivity for smaller zooplankton (less than 0.50 mm in length), typically the cladoceranE. longispina. While rotifers never featured in the diet of the sticklebacks, these zooplankters were a common component of the chaoborid diet.H. gibberum, with its gelatinous sheath, was rarely found in the gut contents ofG. aculeatusand was never found in the crop contents ofChaoboruslarvae.4. Selective predation by these planklivores in the relatively shallow and well‐mixed oligotrophic Avalon lakes may influence species composition and size structure of the pelagic zooplankton communiti

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00481.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. A soft‐water stream in upland mid‐Wales was dosed with sulphuric acid, aluminium sulphate and limestone slurry to produce a zone of aluminium at low pH. and one of aluminium, low pH and added lime.2. Three episodes of 24‐h duration were induced, each separated by a 12‐h inter‐dosing period, and the responses of the crustaceanGammarus pulexmonitored throughout.3.G. pulexparasitized by the acanthocephalanPomphorhynchus laeviswere significantly more sensitive than unparasitized individuals.4. Liming significantly reduced mortality during dosing but postexposure deaths were greatest for animals which had been exposed in the time zone.5. The disruption of precopulalory behaviour inG. pulexwas rapid and liming did not mitigate this

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00482.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

SUMMARY.1. We assessed substratum effects on lotic biofilm development by placing glass and white pine sampling units in a fourth‐order boreal river, and analysing, at 6‐week intervals, upper‐surface biofilms for ATP, chlorophyll, ergosterol, and the activities of nine exoenzymes.2. All parameters, except chlorophyll standing stock (range 80–320 μg dm−2) and β‐xylosidase activity (range 0.4–4.8 μmol h−1dm−2), were significantly greater for epixylic biofilms than for epilithic ones, but the magnitude of the increases varied from 2 to 5 fold, showing that, even under similar hydrodynamic conditions, epilithic and epixylic biofilms are structurally and functionally distinct. For example, ergosterol concentrations ranged from undetectable to 0.93 μg dm−2for epilithon and from 11–49 μg dm−2for epixylon; corresponding ranges for ATP were 1.6–3.7 (epilithon) and 4.2–7.7 μg dm−2(epixylon), for acid phosphatase activity: 2.3–4.9 and 20–41 μmolh−1dm−2, and for alkaline phosphatase activity: 1.9–8.1 and 29–150 μmol h−1dm−2, respectively.3. The more extensive epixylic development was attributed to utilization of the wood substratum as a supplemental carbon source

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1991.tb00483.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY