Catches of invertebrate drift by pump and net

Catches of invertebrate drift by pump and surface net were compared. Faunal composition was similar in the two methods but pump catches of drifting benthos, micro-crustaceans and suspended solids were significantly greater than those by nets.     

Seasonal fluctuations of macroinvertebrate drift in a South Carolina Piedmont stream

The seasonal fluctuations of larval macroinvertebrate drift, exuvial drift and larval benthic density were quantitatively examined over a 1-year period in a fourth order, spring-fed stream in the Piedmont area of South Carolina. The drift was dominated by the mayfly Baetis spp. and by two species of blackfly (Prosimulium mixtum and Simulium jenningsi). Peak drift densities were noted during early spring and especially late summer. Strong correlations were noted between larval drift densities and exuvial drift, indicating a relationship between drift and seasonal growth and emergence patterns. Seasonal trends in drift and benthic densities, though less strongly correlated, were also generally similar.     

Incorporating invertebrate predators into theory regarding the timing of invertebrate drift

Theory concerning the timing of lotic invertebrate drift suggests that daytime-feeding fish cause invertebrates to restrict their drift behavior to the nighttime. However, there is growing evidence that the nighttime foraging of invertebrate predators also contributes to the nocturnal timing of drift, though it is unclear whether the nocturnal behavior of invertebrate predators is innate or proximately caused by fish. In two experiments, one conducted in a fish-bearing stream and a second in a fishless stream, we compared the drift patterns of Baetidae (Ephemeroptera) from channels with and without benthic invertebrate predators. We tested whether invertebrate predators affect the timing of drift, either as a proximate cause of nocturnal drift in the fishless stream (diel periodicity) or as a proximate cause of a pre-dawn peak in drift in the fish-bearing stream (nocturnal periodicity). In the fish-bearing stream experiment, a pre-dawn increase of baetid drift occurred independently of invertebrate predators, indicating that invertebrate predators were not the proximate cause of nocturnal periodicity in the stream. In the fishless stream experiment, invertebrate predators caused more baetid drift at night than during the day, indicating that invertebrate predators caused the nocturnal drift pattern we observed in the stream, and that invertebrate predators can influence drift timing independently of fish. Therefore, we suggest that both visually feeding fish and nocturnally foraging benthic predators, when present, affect the timing of invertebrate drift; visually feeding fish by reducing daytime drift, and benthic predators by increasing nighttime drift.     

The effect of patch disturbance on stream invertebrate community structure: the influence of disturbance history

The effect of disturbance history on the recovery of benthic invertebrate communities following disturbance was investigated in four streams in the Southern Alps of New Zealand. Two of the streams had a history of fluctuating discharge and temperature while the others did not. Recovery from disturbance was tested experimentally using baskets of cobbles, a third of which were disturbed every week for 9 weeks, a further third every 3 weeks and the final third left undisturbed. Algal biiomass, number of invertebrate taxa and total number of invertebrates all declined in baskets disturbed more frequently. Although the relative abundance of some taxa declined with time since the last disturbance, no taxa showed a significant decline in absolute abundance. However, several taxa showed marked increases in relative abundance in the less disturbed treatments particularly at the more stable sites. In contrast to the predictions of ecological theory, numbers of taxa and total invertebrates appeared to recover more quickly in the more complex communities at the stable sites. However, if these communities are considered to represent only stable communities, they do support the view that more complex communities will be more resilient. Community structure at the stable sites was also more similar between baskets in the undisturbed treatment than at the unstable sites, suggesting communities had reached a constant state more quickly. The more rapid recovery of communities measured at the stable sites may have been a consequence of experimental scale; disturbed patches were only 0.045 m² in area and the higher densities of invertebrates at the stable sites meant a larger pool of colonists was available following each experimental disturbance. Nevertheless, ideas of stability in ecological theory and the scale of most spate events suggest this is the appropriate scale for examining community recovery. Furthermore, the larger pool of available colonists could not explain all the differences in community response, as patterns of change in community structure at the stable sites differed considerably more from those expected by purely random colonisation processes than at the unstable sites.     

Stream corridor restoration research: a long and winding road

Stream corridor restoration research and practice is presented as an example of the application of ecology and engineering to solve a class of environmental problems. Interest and public investment in stream corridor restoration has increased sharply in developed nations over the last two decades, as evidenced by the volume of technical and refereed literature. However, real progress at the regional and national scale depends on successful research outcomes. Research addressing problems associated with stream corridor ecosystem restoration is beset by numerous problems. First, terms referring to restoration are loosely defined. Secondly, stream ecosystems are not amenable to rigorous experimental design because they are governed by a host of independent variables that are heterogeneous in time and space, they are not scalable, and their response times are often too long for human attention spans. These problems lead to poorly controlled or uncontrolled experiments with outcomes that are not reproducible. Extension of results to other sites or regions is uncertain. Social factors further complicate research and practice—riparian landowners may or may not cooperate with the experiment, and application of findings normally occurs through a process of suboptimal compromise. Economic issues, namely assigning costs for present and future ecosystem services that provide off-site benefits, further impede progress. Clearly, the situation calls for a hybrid approach between the rigor of the ecologist and the judgment and pragmatism of the engineer. This hybrid approach can be used to develop creative, low-cost approaches to address key factors limiting recovery.     

Persistence, spread and the drift paradox

We derive conditions for persistence and spread of a population where individuals are either immobile or dispersing by advection and diffusion through a one-dimensional medium with a unidirectional flow. Reproduction occurs only in the stationary phase. Examples of such systems are found in rivers and streams, marine currents, and areas with prevalent wind direction. In streams, a long-standing question, dubbed 'the drift paradox', asks why aquatic insects faced with downstream drift are able to persist in upper stream reaches. For our two-phase model, persistence of the population is guaranteed if, at low population densities, the local growth rate of the stationary component of the population exceeds the rate of entry of individuals into the drift. Otherwise the persistence condition involves all the model parameters, and persistence requires a critical (minimum) domain size. We calculate the rate at which invasion fronts propagate up- and downstream, and show that persistence and ability to spread are closely connected: if the population cannot advance upstream against the flow, it also cannot persist on any finite spatial domain. By studying two limiting cases of our model, we show that residence in the immobile state always enhances population persistence. We use our findings to evaluate a number of mechanisms previously proposed in the ecological literature as resolutions of the drift paradox.     

Stream drift,size-specific predation,and the evolution of ovum size in an amphibian

Summary A stream-breeding race of small-mouthed salamanders (Ambystoma texanum) in central Kentucky produces ova that are twice as large as those of a pond-breeding race found nearby. Embryos of stream-breeders also hatch at a more advanced developmental stage than those of pond-breeders. Morphological evidence indicates that stream-breeders were derived from pond-breeding stock. Assuming that differences between stream and pond-breeders reflect evolutionary change, and that the ancestral pond stock that invaded streams was similar to extant pond-breeders, we examined three hypotheses that might explain changes in ovum size and stage at hatching following the invasion of streams. (1) Larger ovum size evolved indirectly as a consequence of selection for rapid development which minimizes mortality risk from stream drying. (2) Increased ovum (hatchling) size and stage at hatching of stream-breeders are adaptations to resist stream current. (3) Increased ovum (hatchling) size and stage at hatching are adaptations to reduce predation on hatchlings from stream invertebrates. The results of field and laboratory studies only support hypotheses (2) and (3). Hatchlings that were relatively large or at a more advanced developmental stage had slower drift rates and were less vulnerable to predation by Phagocata gracilis, a flatworm abundant in streams in central Kentucky. Developmental and growth parameters were not correlated significantly with ovum size in populations of either geographic race. Differences in degree of parental care among races also cannot explain variation in ovum size since both races abandon their eggs immediately after oviposition.     

Species traits and channel architecture mediate flow disturbance impacts on invertebrate drift

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Psychiatric disturbance as a consequence of abnormal periodic cardiac variation

Abstract

The relationship between cardiac rate variation, resting sinus rhythm heart rate in beats per minute, and mental state is reviewed. A small series of 12 psychiatric patients in whom these variables were studied both before and after appropriate psychiatric treatment is reported. Comparison with the periodicity of cardiac rate variation in a normal group of subjects showed that the setting of the biological clock governing cardiac rate variation in psychiatric patients is abnormal, and in these cases running at a slower frequency than that of mental health. Appropriate psychiatric therapy re‐sets this clock in patients responding to treatment, but fails to do so in those patients who remain unimproved. Resting mean sinus rhythm heart rate in beats per minute does not show this relationship.     

Stream hydraulics as a major determinant of benthic invertebrate zonation patterns

SUMMARY. 1. Studies on the zonation of benthic fauna in fourteen streams situated in a variety of latitudes from Alaska to New Zealand have been evaluated.
2. We suggest that physical characteristics of flow ('stream hydraulics') are the most important environmental factor governing the zonation of stream benthos on a world-wide scale.
3. From the source to the mouth of a stream, zones of transition in stream hydraulics' occur, to which the general pattern of stream invertebrate assemblages can be related. In these zones benthic community stability and resilience must be different from those upstream and downstream of the hydraulic transition zones.     

Annual production by a stream brook charr population and by its principal invertebrate food

Synopsis Annual production by the brook charr (Salvelinus fontinalis) population in Valley Creek, Minnesota, over the five-year period 1968–1972, was closely correlated to production by its main invertebrate food, Gammarus pseudolimnaeus, which had been reduced by siltation. Annual production was 163–191 kg ha^–1 (wet weight) in 1968–1969, respectively, and then dropped to a mininum of 79 kg ha^–1 in 1971, the year most seriously affected by decreased invertebrate production and siltation; year-class strength, standing stock, and total year-class (cohort) production followed approximately the same pattern. Total year-class production was highest for the 1968–1969 year classes at 211–178 kg ha^–1, respectively, and lowest for the 1971 year class at 76 kg ha^–1. Annual P/B ratios ranged from 1.0 to 1.9; cohort P/B ratios, for the 1968–1972 year classes, ranged from 5.6 to 7.2.Paper No. 11,384, Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul, Minnesota 55108, U.S.A.     

Aquatic insect drift through a final-cut strip mine pit,with emphasis on drift distances

Drift samples were taken upstream and at the outlet of a final-cut strip mine pit through which a portion of the Tongue River, Wyoming, USA, was rerouted. All prominent rheophilic insect species (except cased Trichoptera) were found capable of drifting the length of the pit (> 500 m). However, drift densities leaving the pit were reduced in comparison to those entering it. Pit inhabitants such as burrowing mayflies, Chaoborus flavicans, and several species of Chironomidae were also collected at the pit outlet. Under the physical conditions created by rerouting the river through a strip mine pit, the observed maximum behavioral and background drift distances (> 500 m) were significantly greater than those reported in the past (< 100 m).     

Reservoir manipulations and benthic macroinvertebrates in a Prairie River

Samples were taken on the Tongue River, Montana, USA, during 1974 and 1975 to determine the distributions and abundances of the benthic fauna after various reservoir manipulations. The upper cold water section, influenced by hypolimnial discharge from the Tongue River Reservoir, was impoverished in insect fauna and dominated by the molluscs Physa and Sphaerium. The lower warm water sections of the river contained two communities determined primarily by turbidity and periphyton cover. The upper warm water area was dominated by Strophopteryx and hydropsychid caddis larvae. The lower river was dominated by Cheumatopsyche. The summer fauna, in the warm water area, was dominated by short-lived mayfly species. During the summer, 1975, the cold water section was invaded by many insects due to warming of the area when no hypolimnion was formed in the reservoir. Invasion was apparently due to increased thermal fluctuations which caused diapause eggs to hatch and influenced the upstream migration of older nymphs and larvae.Results of drift and distributional samples after closure of the Tongue River Reservoir Dam for repairs showed that massive drift of all invertebrates began at a discharge of 130 c.f.s. (3.68 m³/sec), a drop from 190 c.f.s. (3.38 m³/sec) over a period of three days. Community composition was radically altered by reduced discharge.     

Zooplankton community structure driven by vertebrate and invertebrate predators

Summary A zooplankton community was established in outdoor experimental ponds, into which a vertebrate predator (topmouth gudgeon: Pseudorasbora parva) and/or an invertebrate predator (phantom midge larva: Chaoborus flavicans) were introduced and their predation effects on the zooplankton community structure were evaluated. In the ponds which had Chaoborus but not fish, small- and medium-sized cladocerans and calanoid copepods were eliminated while rotifers became abundant. A large-sized cladoceran Daphnia longispina, whose juveniles had high helmets and long tailspines as anti-predator devices, escaped from Chaoborus predation and increased. In the ponds which had fish but not Chaoborus, the large-sized Daphnia was selectively predated by the fish while small-and medium-sized cladocerans and calanoid copepods predominated. In the ponds containing both Chaoborus and fish, the fish reduced the late instar larvae (III and IV) of Chaoborus but increased the early instar larvae (I and II). Small- and large-sized cladocerans were scarcely found. The former might have been eliminated by predation of the early instar larvae of Chaoborus, while the latter was probably predated by fish. Consequently, the medium-sized cladocerans, which may have succeeded in escaping from both types of predator, appeared abundantly. The results suggest that various combinations of vertebrate and invertebrate predators are able to drive various kinds of zooplankton community structure.     

Ecology of invertebrate predators in a Coastal Plain stream

1. The spatial and temporal abundance patterns, production and feeding habits of invertebrate predators were determined in a sand-bottomed, headwater stream in Virginia, U.S.A. 2. Annual mean density and biomass of predators in debris dams were 3897 individuals m^?2 and 2.5 g dry mass m^?2, respectively, but only 711 individuals m^?2 and 0.2 gm^?2 on the sediment. Predator production was 8.36 gm^?2yr^?1 in debris dams compared to 1.52 gm^?2yr^?1 on the sediment. Annual predator production, weighted by habitat availability, was 1.73gm^?2yr^?1. 3. The predominant taxa in terms of production were the chironomids Thienemannimyia spp, complex, Ablabesmyia parajanta, Zavrelimyia sp., and the odonate Cordulegaster maculata. Chironomidae and Odonata together comprised 77% of the production of the predator guild. 4. Based on gut content analysis and calculations of the trophic basis of production, estimated predator production was supported mostly by Chironomidae (38%), detritus (20%), unidentifiable insects (14%), and Ephemeroptera (11%). Total food ingestion by predators was 9.8 gm^?2yr^?1, 63% of which was detritus and 37% of which was animal material on an areal basis. The predator guild consumed an estimated 94% of primary invertebrate consumer production on the channel surface of the stream.     

Interaction of a biotic factor (predator presence) and an abiotic factor (low oxygen) as an influence on benthic invertebrate communities

We examined the response of benthic invertebrates to hypoxia and predation risk in bioassay and behavioral experiments. In the bioassay, four invertebrate species differed widely in their tolerance of hypoxia. The mayfly, Callibaetis montanus, and the beetle larva, Hydaticus modestus, exhibited a low tolerance of hypoxia, the amphipod, Gammarus lacustris, was intermediate in its response and the caddisfly, Hesperophylax occidentalis, showed high tolerance of hypoxia. In the behavioral experiments, we observed the response of these benthic invertebrates, which differ in locomotor abilities, to vertical oxygen and temperature gradients similar to those in an ice-covered pond. With adequate oxygen, invertebrates typically remained on the bottom substrate. As benthic oxygen declined in the absence of fish, all taxa moved above the benthic refuge to areas with higher oxygen concentrations. In the presence of fish mayflies increased activity whereas all other taxa decreased activity in response to hypoxia. Mayflies and amphipods remained in the benthic refuge longer and endured lower oxygen concentrations whereas the vertical distribution of caddisflies and beetle larvae was not influenced by the presence of fish. As benthic oxygen declined in the presence of fish, all but the beetle larva reduced activity over all oxygen concentrations compared to when fish were absent. As benthic oxygen continued to decline, mayflies and amphipods moved above the benthic refuge and were preyed upon by fish. Thus, highly mobile taxa unable to tolerate hypoxia (mayflies and amphipods) responded behaviorally to declining oxygen concentrations by migrating upward in the water column. Taxa that were less mobile (beetle larvae) or hypoxia-tolerant (caddisflies) showed less of a response. Taxa most vulnerable to fish predation (mayflies and amphipods) showed a stronger behavioral response to predator presence than those less vulnerable (caddisflies and beetle larvae). Because invertebrates differ in their ability to withstand hypoxia, episodes of winter hypoxia could have long-lasting effects on benthic invertebrate communities either by direct mortality or selective predation on less tolerant taxa.     

Predation by invertebrate predators on the colonial rotifer Sinantherina socialis

Abstract. Colonies of the freshwater colonial rotifer Sinantherina socialis (Monogononta, Flosculariidae) have been shown to be unpalatable to a variety of small-mouthed, zooplanktivorous fishes. To test whether invertebrate predators ingest the rotifer S. socialis , we conducted two types of experiments: (1) Microcosm experiments—in separate experiments, four invertebrate predators (i.e., dragonfly nymphs, damselfly nymphs, notonectids, and Hydra ) were offered prey either singly or in combination. Prey were comprised of S. socialis; Epiphanes senta , a solitary, free-swimming rotifer; and Daphnia magna , a microcrustacean. In each experiment, the percent of prey surviving after 12, 18, and 24 h was recorded. (2) Paired-feeding experiments—in separate experiments, predators were offered prey in a pairwise fashion, in which members of D. magna were alternated with a rotifer, either S. socialis or E. senta. The results of the microcosm experiments showed that, after 24 h, 60–100% prey items of S. socialis survived the predators, but significantly fewer individuals of E. senta (6–89%) and D. magna (<25%) survived. When offered rotifers and individuals of D. magna simultaneously, predators tested consistently consumed more specimens of Daphnia. However, predators significantly reduced percent survival in E. senta but not in S. socialis. Predators, given a choice between the two rotifer species, all consumed significantly more specimens of E. senta than S. socialis after 24 h. In the paired-feeding experiments, three of the four predators captured members of S. socialis , but these colonies were frequently released rather than ingested, although in some cases colony structure was seriously disrupted. Our results suggest that the unpalatable nature of members of S. socialis to certain fishes extends to several invertebrate predators, but the nature of the putative factor(s) responsible for this remains unknown.     

Stream invertebrate communities of Campbell Island

Invertebrates at 20 sites on 19 Campbell Island streams were sampled over the Austral summer of 1996/97. Twelve of the 16 benthic invertebrate taxa known from the island were collected. The most abundant group was the Crustacea, which included an isopod (Notidotea lacustris) and two amphipods, one belonging to the family Eusiridae and one to the suborder Gammaridea. Five species of Diptera were found (three chironomids; Orthocladiinae sp., Chironominae sp. and Maoridiamesa insularis, as well as an empidid and a simuliid Austrosimulium campbellense). One trichopteran, the hydroptilid caddis Oxyethira albiceps and two plecopteran species Rungaperla campbelli and R. longicauda and unidentified Oligochaetes were also collected. In general, Campbell Island streams are stable, deeply incised, have unusually high salinity from wind-blown sea spray and a unique benthic invertebrate fauna. With the exception of high altitude streams with large boulders which had invertebrate communities dominated by Crustacea and the endemic stonefly of the genus Rungaperla, none of the measured environmental variables or geographic location could explain the distinctive communities found. The species-poor stream fauna and the absence of many invertebrate families commonly found on mainland New Zealand appears to be related to the extreme isolation and geological history of the island.     

A rapid technique for analysing diets of invertebrate predators by electrophoresis

A technique has been developed for the rapid determination of some species of prey consumed by mites and insects. The method detects prey enzymes within the gut of a predator by polyacrylamide gradient gel electrophoresis and subsequent staining for esterase activity. It is sufficiently sensitive to detect fruit tree red spider mite (Panonychus ulmi) esterases within the gut of a single predacious mite (Typhlodromus pyri) for at least 31 h after feeding. The method has been used to demonstrate feeding relationships among a range of insect and mite predator and prey species in the laboratory and in the field.     

Habitat-specific predation susceptibilities of a littoral rotifer to two invertebrate predators

The rotifer Euchlanis dilatata lives associated with submerged vegetation in the littoral zone of freshwater lakes and ponds. I assessed habitat-specific predation susceptibilities for this rotifer in the presence of three aquatic macrophytes (Myriophyllum exalbescens, Elodea canadensis, and Ceratophyllum demersum) and two predators (damselfly nymphs — Enallagma carunculata; and cnidarians — Hydra). Rotifer survival was greatest on Myriophyllum in the presence of both predators. Conversely, the presence of the other macrophyte species actually increase rotifer suspectibility to predation by damselfly nymphs. I also manipulated plant structural complexity. As predicted, decreasing the relative complexity of each plant resulted in lower rotifer survival.