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  • 1
    Electronic Resource
    Electronic Resource
    Effects of single and repeated experimental acid pulses on invertebrates in a high altitude Sierra Nevada stream (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 32 (1994), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. We examined responses of aquatic macroinvertebrates to pulsed acidification experiments in twelve streamside channels located in the Sierra Nevada, California. Experiment 1 consisted of a single 8 h acid addition, and Experiment 2 consisted of two 8 h acid additions administered 2 weeks apart. Replicated treatments (four reps/ treatment) consisted of a control (pH 6.5–6.7) and pH levels of 5.1–5.2 and 4.4–4.6. Invertebrate drift was monitored continuously and benthic densities were determined before and after acid addition.2. Drift responses to pH reduction were: (i) increased drift during acidification in pH 5.2 and pH 4.6 treatment channels, often with depressed post-acidification drift in treatment channels relative to controls (exhibited by Baetis only). Depressed post-acidification drift in treatment channels appeared to be due to low benthic densities because a positive relationship between benthic and drift densities was noted for most common taxa; (ii) increased drift rates during acidification only at pH 4.6 (Epeorus, Drunella, Paraleptophlebia, Zapada, and Simulium); (iii) decreased drift at pH 5.2 and/or pH 4.6 relative to control channels (Rhyacaphila and chironomid larvae); (iv) no significant response to acidification (Ameletus, Amiocentrus, Dixa and Hydroporus).3. A high proportion (45–100%) of acid-induced drift in Baetis, Epeorus, and chironomid larvae could be attributed to dead, drifting individuals.4. Except for chironomids, most common invertebrates (i.e. Baetis and Paraleptophlebia) showed reduced benthic densities in treatment relative to control channels after acidification.5. For sensitive taxa, drift was enhanced and benthic densities reduced by single (Experiment 1) and initial [Experiment 2(a)] acid pulses. Drift responses to a second acid pulse [Experiment 2(b)] were not as pronounced as those to the single or initial acid pulses [Experiments 1 and 2(a)], and the second acid pulse had no additional effect on benthic density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1994.tb00875.x
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  • 2
    Electronic Resource
    Electronic Resource
    Responses of zooplankton and zoobenthos to experimental acidification in a high-elevation lake (Sierra Nevada, California, U.S.A.) (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 23 (1990), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. During the summer of 1987 we conducted an acidification experiment using large enclosure at Emerald Lake, a dilute, high-elevation lake in the Sierra Nevada, California, U.S.A. The experiment was designed to examine the effects of acidification on the zooplankton and zoobenthos assemblages of Sierran lakes.2. Treatments consisted of a control (pH 6.3) and pH levels of 5.8, 5.4, 5.3, 5.0 and 4.7; each treatment was run in triplicate. The experiment lasted 35 days.3. The zooplankton assemblage was sensitive to acidification. Daphnia rosea Sars emend. Richard and Diaptomns signicauda Lilljeborg decreased in abundance below pH 5.5–5.8, and virtually disappeared below pH 5.0. Bosmina longirostris (Müller) and Keratella taurocephala Ahlstrom became more abundant with decreasing pH. although B. longirostris was rare in the pH 4.7 treatment. These species might serve as reliable indicators of early acidification in lakes such as Emerald Lake.4. The elimination of D. rosea in acidified treatments probably allowed the more acid-tolerant taxa to increase in abundance because interspecific competition was reduced. Even slight acidification can therefore alter the structure of the zooplankton assemblage.5. In contrast to the zooplankton, there was no evidence that the zoobenthos in the enclosures was affected by acidification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.1990.tb00296.x
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  • 3
    Electronic Resource
    Electronic Resource
    The relationship between nutrients and trophic-level biomass in turbid tropical ponds (1998)
    Oxford, UK : Blackwell Science Ltd, UK
    Freshwater biology 40 (1998), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The total phosphorus–algal biomass relationship from a set of turbid tropical ponds in Kenya was compared with predictions derived from surveys of temperate and subtropical lakes. Despite high concentrations of total phosphorus (TP) (up to 797 μg L–1) and inorganic turbidity (up to 800 mg L–1), the log–log relationship between algal biomass and TP was steeper than expected.2. No evidence of nitrogen limitation was found at high TP, and total nitrogen (TN):TP ratios were higher than in lakes with similar TP levels studied previously. High TN:TP ratios may be a consequence of excretion by cattle into the ponds, a nutrient source characterized by a high ratio of available N to available P.3. Despite extremely high turbidity, the ratio of mixed layer depth to euphotic depth was generally low because these ponds are shallow (≤ 2 m), and was not related to algal yield. A positive relationship was also found between TP and zooplankton biomass, and between TP and the density of the zooplanktivorous bug, Anisops. In contrast, no relationship was found between fish biomass and TP, algal biomass or zooplankton biomass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1998.00332.x
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of trout on the diel periodicity of drifting in baetid mayflies (1994)
    Springer
    Oecologia 98 (1994), S. 48-56 
    Details
    ISSN: 1432-1939
    Keywords: Predator avoidance ; Diel periodicity ; Phenotypic plasticity ; Streams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Some benthic invertebrates in streams make frequent, short journeys downstream in the water column (=drifting). In most streams there are larger numbers of invertebrates in the drift at night than during the day. We tested the hypothesis that nocturnal drifting is a response to avoid predation from fish that feed in the water column during the day. We surveyed diel patterns of drifting by nymphs of the mayfly Baetis coelestis in several streams containing (n=5) and lacking (n=7) populations of rainbow trout, Oncorhynchus mykiss. Drifting was more nocturnal in the presence of trout (85% of daily drift occurred at night) than in their absence (50% of daily drift occurred at night). This shift in periodicity is due to reduced daytime drifting in streams with trout, because at a given nighttime drift density, the daytime drift density of B. coelestis was lower in streams occupied by trout than in troutless streams. Large size classes of B. coelestis were underrepresented in the daytime drift in trout streams compared to nighttime drift in trout streams, and to both day and night drift in troutless streams. Differences in daytime drift density between streams with and without trout were the result of differences in mayfly drift behaviour among streams because predation rates by trout were too low to significantly reduce densities of drifting B. coelestis. We tested for rapid (over 3 days) phenotypic responses to trout presence by adding trout in cages to three of the troutless streams. Nighttime drifting was unaffected by the addition of trout, but daytime drift densities were reduced by 28% below cages containing trout relative to control cages (lacking trout) placed upstream. Drift responses were measured 15 m downstream of the cages suggesting that mayflies detected trout using chemical cues. Overall, these data support the hypothesis that infrequent daytime drifting is an avoidance response to fish that feed in the water column during the day. Avoidance is more pronounced in large individuals and is, at least partially, a phenotypic response mediated by chemical cues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326089
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of an invertebrate grazer on the spatial arrangement of a benthic microhabitat (1993)
    Springer
    Oecologia 96 (1993), S. 208-218 
    Details
    ISSN: 1432-1939
    Keywords: Filamentous algae ; Geostatistics ; Physella herbivory ; Spatial dependence ; Stream periphyton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We demonstrated the effect of an aquatic herbivore on the spatial arrangement of benthic algal biomass within artificial stream channels. Transects of ceramic tiles were exposed to a gradient of snail (Physella) densities in a 30 d experiment. We observed positive effects of snails on the mean abundance of “overstory” algae (the filamentous chlorophyte Cladophora and associated epiphytes), an important benthic microhabitat in streams. Snails altered several aspects of the spatial arrangement of overstory algae. Snails reduced the strength of downstream gradients in overstory biomass, as well as residual variability around these gradients. Geostatistical analysis revealed that snails also reduced the strength of spatial dependence, and so reduced spatial heterogeneity of the overstory, at small scales (〈40 cm). As a result, organisms inhabiting the overstory might experience a more fragmented habitat landscape at high snail densities. In addition, snails increased the scale of spatial dependence in understory algal biomass (algae remaining on tiles after overstory was removed) from 10 cm to 40 cm. Consumer effects on the spatial arrangement of a microhabitat argue for the inclusion of feedbacks between the biota and the environment in spatially-explicit models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317734
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of physical disturbance on the relative abundances of two filter-feeding insects in a small stream (1983)
    Springer
    Oecologia 58 (1983), S. 378-382 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We examined the importance of disturbance in determining the relative abundances of two lotic filter-feeders, Simulium virgatum and Hydropsyche oslari, in a small, coastal stream in southern California, USA. In most years, winter spates effectively scour substrata in fast-flowing areas, thereby drastically reducing stream insect populations. Newly-opened space in these areas is quickly colonized by simuliids. The abundance of simuliids, however, gradually declines as hydropsychid abundance increases in early summer. To determine if these changes in insect abundance represent seasonal changes or successional changes following disturbance, we performed a field experiment where hard substrates were disturbed at 2 wk, 4 wk, or 8 wk intervals, or were left undisturbed. We found that the numbers of simuliids increased and the numbers of hydropsychids decreased as the frequency of disturbance increased. Although seasonal recruitment patterns and longitudinal position in the strem had important effects on the colonization rates of these insects, time since last disturbance was a prime determinant of the relative abundances of Simulium and Hydropsyche. These results and additional observations suggest that Simulium virgatum is an opportunistic species that quickly colonizes new space, but that it is displaced by the slower-colonizing but competitively superior Hydropsyche oslari. Disturbance promotes the coexistence of these two species by preventing the attainment of a climax state where Hydropsyche monopolizes available space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385239
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  • 7
    Electronic Resource
    Electronic Resource
    The effects of trout on water striders in stream pools (1984)
    Springer
    Oecologia 63 (1984), S. 376-379 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Observations made in Rattlesnake Creek, Santa Barbara County, California, U.S.A. indicate that rainbow trout (Salmo gairdneri) affect the microdistribution of adult water striders (Gerris remigis). Gerrids occupied all areas of stream pools lacking trout but stayed in margins of pools containing trout. To test the hypothesis that the presence of trout controlled the distribution of water striders within pools, trout were removed from some pools and transferred to pools lacking trout. Undistrubed pools with and without trout served as controls for the trout transferrals. The results supported the hypothesis; within one week, gerrids moved to the edge of pools where trout were added and to the middle of pools where trout were removed. Time budgets and gut analyses suggest that local patterns of gerrid distribution were maintained by harrassment of gerrids by trout. At times trout had significant effects on components of gerrid fitness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390668
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of an experimental acid pulse on invertebrates in a high altitude Sierra Nevada stream (1989)
    Springer
    Hydrobiologia 171 (1989), S. 45-58 
    Details
    ISSN: 1573-5117
    Keywords: acid deposition ; stream channels ; drift ; benthos ; Baetis spp. ; Sierra Nevada
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of pulsed acidification on invertebrate densities and drift, and water chemistry, in a high altitude Sierra Nevada stream were measured using artificial stream channels. Water was diverted from the Marble Fork of the Kaweah River, California, U.S.A., through twelve replicate channels; however, low flow in the summer of 1985 eliminated all but four of these channels. Channels were stocked with natural substrates and organisms from the Marble Fork of the Kaweah River. After a three week acclimation period, we simulated a low pH rain event by adding acid (H2SO4 and HNO3) to two of the channels, reducing pH to 5.0 for 6 hours. The other two channels acted as controls (pH 6.4). During acid additions, Baetis spp. drift in acidified channels was ca. 7 times higher than in control channels (F = 39.02, p 〈 0.025; data fourth root transformed, ANOVA), and the percentage of drifting baetids that was dead was significantly higher in acidified than control channels (46% vs. 0%, F = 29.86, p 〈 0.05; arcsine square root transformed data, ANOVA). Other taxa showed no significant drift responses, and benthic densities of all taxa showed no effects two days after acidification, probably owing to rapid recolonization by invertebrate drift in influent waters. Stream chemistry data are presented; heavy metal concentrations did not significantly increase in the 2 m stream channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00005723
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  • 9
    Electronic Resource
    Electronic Resource
    Grazing catfish, fishing birds, and attached algae in a Panamanian stream (1989)
    Springer
    Environmental biology of fishes 26 (1989), S. 285-294 
    Details
    ISSN: 1573-5133
    Keywords: Predator avoidance ; Spatial variation in herbivory ; Tropical stream communities ; Multi-trophic level interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Synopsis In streams where algivorous fishes abound, striking variation of attached algae often develops along depth gradients, with bands of high standing crops in shallow water (〈20 cm) and sparse standing crops on deeper substrates. Experimental results from a stream in central Panama support the hypothesis that vertical variation in algal standing crops arises when grazing fishes avoid predators in shallow water by forgoing food resources that accumulate there. When 38 rocks bearing algae in a stream in central Panama were transferred from shallow (〈20 cm) to deeper (〉20 cm) water, algae were rapidly consumed by grazing catfish. Catfish were removed from three stream pools and left in place in three control pools. Ten days after catfish removal, algal standing crops in deep and shallow areas of removal pools were similar, while algal standing crops were higher in shallow than in deep areas of control pools. Catfish were exposed to fishing birds in open-topped enclosures. In one of three series of these pens, most catfish in shallow pens (10 and 20 cm) disappeared after 14 days, while catfish in deeper pens (30 and 50 cm) did not. Other groups of catfish which were caged 8 days showed differences in behavior depending on whether they had been fed or starved. After their release into their home pool, starved catfish spent more time feeding than did fed catfish. Despite their apparently increased hunger levels, starved catfish did not venture into shallow water to obtain algae. These results support the view that predator induced avoidance by grazers of certain areas can produce spatial pattern in the flora of flowing water communities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00002465
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