Resource dynamics and detritivore production in an acid stream

1. Life history patterns and production of eight shredder‐detritivore species were studied in relation to the detritus dynamics of a small acidic stream in England. Mean annual detritus inputs (direct and lateral sources combined) were approximately 400 g m^?2 year^?1 and showed significant seasonal and annual variation. 2. Detritus standing stock did not increase significantly during times of high input, reflecting low retention efficiency. However, the mean detritus standing stock was relatively large (108 g m^?2) reflecting a slow decomposition rate typical of acid streams. 3. Four species were univoltine with highly synchronous patterns of emergence and recruitment (Leuctra inermis, Leuctra hippopus, Capnia vidua and Amphinemura sulcicollis). Two species were univoltine with extended patterns of emergence and recruitment (Nemoura cinerea, Potamophylax cingulatus). Leuctra nigra was apparently semivoltine, while Protonemura meyeri showed two successive cohorts in the second year of the study, suggesting either bivoltinism or cohort splitting. 3. Secondary production of the dominant shredders was 1.67 g m^?2 year^?1 in 1997 and 1.99 g m^?2 year^?1 in 1998, which is low compared with other small European streams. This was probably because of an impoverished invertebrate community and poor food quality associated with acid conditions. Food availability probably did not account for the low production as the detritus standing stock far exceeded the estimated shredder ingestion of 42–50 g m^?2 year^?1. 4. Despite low overall shredder production, species‐specific production was high, possibly because of competitive release in this species‐poor acid stream. Periods of high production and growth showed no relationship with detritus availability but were closely related to life history.     

In situ measurements of net primary production in a Colorado mountain stream

Six stations were established on a Colorado mountain stream, and net primary productivity was measured in situ during all seasons. For 24-hour periods the dissolved oxygen and temperature of the water were electronically monitored over an undisturbed 1 x 1 m section of rubble bottom enclosed by a large plastic dome tightly fitted to the substrate. A submerged pump maintained a current within the dome, and the whole apparatus was submerged below the stream level. The bottom community net metabolism varied between heterotrophy and autotrophy with no correlations with altitude, season, light, water chemistry, and temperature. Readings were all very low and ranged from -27.38 to 35.59 grams of carbon fixed per square meter per year. There were no correlations between biomass of the bottom fauna and net community productivity.Contribution No. 71, University of Colorado Limnology Laboratory     

Life cycle and production of Skwala parallela (Frison) (Plecoptera: Perlodidae) in a Colorado montane stream

The life cycle and production of Skwala parallela, a perlodid stonefly, was investigated in a third-order Colorado montane stream. The species exhibited a univoltine life cycle with a distinct cohort. Small nymphs appeared in May. Rapid growth was exhibited throughout summer and autumn. During winter, growth slowed somewhat but was continuous until April. Maximum density of 34 nymphs/m² occurred in July. Based upon the instantaneous growth method, annual production was 395.3 mg/m² or 3.95 kg/ha dry weight with a P/B ratio of 4.4     

Impact of simulated drought on ecosystem biomass production: an experimental test in stream mesocosms

Climate models predict widespread shifts in precipitation patterns and increases in the frequency of extreme events such as droughts, but consequences for key processes in affected ecosystems remains poorly understood. A 2‐year manipulative experiment used a series of stream mesocosms to test the effect of recurrent drought disturbance on the composition and secondary production of macroinvertebrate consumer assemblages and functional groups. On average, secondary production in drought‐disturbed communities (mean 4.5 g m^?2 yr^?1) was less than half of that that in controls (mean 10.4 g m^?2 yr^?1). The effects of the drought differed among functional feeding groups, with substantial declines for detritivore shredders (by 69%) and engulfing predators (by 94%). Contrasting responses were evident among taxa within most functional feeding groups, ranging from extirpation to irruptions in the case of several small midge larvae, but production of most species was suppressed. Taxon‐specific responses were related to body mass and voltinism. The ratio of production to biomass (community P/B) increased under drought, reflecting a shift in production from large long‐lived taxa to smaller taxa with faster life cycles. This research provides some of the first experimental evidence of the profound effects that droughts can have on both the structure and functioning of aquatic ecosystems.     

Production by Hexagenia limbata in a warm-water reservoir and its association with chlorophyll content of the water column

We investigated the productivity of nymphs of the mayfly Hexagenia limbata in Lake Waco, a central Texas reservoir, and assessed its association with chlorophyll content of the water. We hypothesized that food availability measured as chlorophyll content of the water may directly associate with growth of Hexagenia and predict population productivity. To test this, we compared production by mayfly populations at two stations in the same reservoir; a northern station receiving water input with high chlorophyll content, and a southern station receiving water with low chlorophyll content. Both stations had similar substrate type and abundant mayflies. Benthic samples were collected from October 1984 through September 1985, and dissolved oxygen and temperature of the water were monitored.Annual production (size-frequency method) was 1270 mg m^–2 (P/B = 7.5) at the northern station and 1990 mg m^–2 (P/B = 6.1) at the southern station. The mean standing crop was 323 mg m ^{– 2} at the southern station and 169mg m^–2 at the southern station. Densities of mayflies at the two stations were not significantly different.Mean chlorophyll concentration (total mg pigment) during the sampling period was 23.5 mg m^–3 at the northern station and 16.7 mg m ^{– 3} at the southern station. Therefore, the station with lower mean chlorophyll content had higher secondary productivity by Hexagenia. Conversely, the station with higher mean chlorophyll content had lower mayfly productivity. The productivity of the mayfly populations did not positively associate with the chlorophyll content of the water, and chlorophyll content did not predict the success of the population of Hexagenia. Variation in mayfly growth success was associated with differences in temperature and dissolved oxygen. The northern station with higher chlorophyll content and lower productivity had low dissolved oxygen and temperatures higher than optimum for growth.     

Effects of logging on macroinvertebrate production in a sand-bottomed, low-gradient stream

1. Macroinvertebrate production and macrophyte growth were studied in logged and unlogged sections of a sand‐bottomed, low‐gradient, blackwater stream on the Coastal Plain of Virginia, U.S.A. A section of the catchment had been clear‐cut 3 years prior to sampling. No logging occurred in the upstream area of the catchment, which had experienced almost no land disturbance by humans for over 100 years. 2. A primary difference among the logged and unlogged sections of the stream was in the abundance of macrophytes. The combined biomass of Sparganium americanum and of Chara sp. was over 300‐times greater in the logged than the unlogged section. 3. Annual macroinvertebrate production in the sediment was higher in the unlogged section (41 g dry mass m^–2) than in the logged section (25 g m^–2). 4. Annual macroinvertebrate production on Sparganium was higher in the logged section (10 g m^–2 of plant surface area) than in the unlogged section (6 g m^–2). Annual production associated with Chara, which occurred only in the logged section, was 196 g m^–2 of stream bottom covered by this plant. 5. Whole‐stream annual macroinvertebrate production, calculated by summing habitat‐specific production that was weighted by habitat availability, was greater in the logged section (103 g m^–2) than in the unlogged section (41 g m^–2). Sediments supported 99% of the annual production in the unlogged section, whereas macrophytes supported 76% in the logged section. 6. Much of the additional macroinvertebrate production in the logged section was by collector‐filterers living on macrophytes. Production by collector‐gatherers was also greater in the logged section, whereas production by other functional feeding groups changed little with logging. 7. Although logging along high‐gradient, rocky streams also results in increased macroinvertebrate production, that increase often is stimulated by greater periphyton growth rather than the macrophyte growth observed in this low‐gradient stream.     

The response of macroinvertebrate production to a pollution gradient in a headwater stream

1. This study quantified patterns of macroinvertebrate secondary production and stored benthic organic matter along a gradient of pollution and habitat channelisation over a 3‐km reach of Goosefare Brook, a first‐order stream in southern Maine (U.S.A.). 2. Whole‐community invertebrate production decreased from 26.4 g ash‐free dry mass (AFDM) m⁻² year⁻¹ at the reference station to 1.1 g AFDM m⁻² year⁻¹ at stations with the greatest levels of pollution. Production decreased along the pollution gradient for most taxa, although decreases were partly offset by production increases in tolerant taxa. Biomass turnover rates (P/B) were less affected by the stresses than was production. 3. Differences in functional characteristics of the community were evident at stations with channelised habitat, but overall production declined in a linear pattern that mirrored the pollution gradient. Stored organic matter showed a decline along the gradient, but was also lower at channelised stations. Populations of taxa with documented pollution tolerance were more likely to maintain or increase production and P/B. 4. Decreasing biomass because of decreasing stored organic matter and lethal effects of pollutants resulted in shifts in the pathways of energy flow observed at stations exposed to moderate physical or chemical stress, to the loss of most taxa and an extreme (96%) decrease in production at the stations receiving the highest levels of metal pollution. 5. The shifting prominence of different taxa along a continuum of stress in Goosefare Brook shows that describing the nature of an impairment in a functional context requires consideration of chemical stressors, habitat alterations and food resources.     

Life-history strategies and production of Tinodes waeneri (L.) (Trichoptera) in Lake Esrom,Denmark

The life cycle and production of Tinodes waeneri (L.) was examined at five shallow littoral localities in Lake Esrom, Denmark, during 1979/80. Five larval instars were demonstrated. The differences in temporal composition of instars indicated three different life cycles. A bivoltine strategy was shown for the most exposed locality which also had the highest average abundance equal to 11 500 ind. m^–2. A univoltine population was found in the more sheltered NW part of the lake with an average density of 1 500 ind. m^–2. At the three remaining stations the life cycles were partly bivoltine with wintering populations of mixed cohorts and densities between 10 500 and 3 000 ind. m^–3. Two distinct flight periods with maxima in June and August were demonstrated for bi- and partly bivoltine populations. Differences in rates of growth and elimination added to the variability in life cycle. Growth rates peaked in August (5.0–7.4% d^–1) at an average temperature of 20°C. Estimates of production ranged from 1.9 to 17.5 g AFDW m^–2 a^–1 with an average of 8.0 g AFDW m^–2. The P/B ratios, which were within the expected range for uni- and bivoltine populations of trichopterans, were 5.73 for the bivoltine population and 3.31 for the univoltine population.Estimates of consumption revealed that the populations could be sustained by autochthonous epilithic production in the habitats. Variability in the quality and seasonal availability of food were judged to influence the type of life cycle.Lake Esrom Littoral Research Publ. No. 8. Publication No. 385 from the Freshwater Biological Laboratory, University of Copenhagen, 51, Helsingørsgade, DK-3400 Hillerød, Denmark.Lake Esrom Littoral Research Publ. No. 8. Publication No. 385 from the Freshwater Biological Laboratory, University of Copenhagen, 51, Helsingørsgade, DK-3400 Hillerød, Denmark.     

Life history and production of Agapetus quadratus (Trichoptera: Glossosomatidae) in a temporary, spring-fed stream

1. The life history and trophic basis of production of the caddisfly grazer Agapetus quadratus were studied in the torrent Gorg Blau, a spring‐fed stream on the island of Majorca that dries annually during summer. 2. Quantitative random samples were taken every 2–3 weeks during an annual surficial flow period, from November 2000 to mid‐July 2001. Instars of field‐collected larvae were determined by measurements of head width and pronotum length, and the sex of all pupae was determined to study sexual dimorphism and sex ratio. 3. Stage‐frequency histograms suggested a trivoltine population, with an average cohort time of 4 months. Larval development was asynchronous, with continuous growth and overlapping generations. Recruitment peaks were identified in mid‐November, early March and late June, indicative of winter, spring and summer generations. On average, females were larger than males and the mean sex ratio was 2 : 3 (females : males). Population densities and biomasses derived from the field data were used to calculate production and turnover rate. 4. Annual production of A. quadratus in the torrent Gorg Blau (4.80 g dry mass m^?2 year^?1) was the highest ever reported for the genus, being comparable with that estimated for some insects with rapid development and multiple cohorts. 5. Estimates of production of A. quadratus were combined with foregut content analysis to estimate the fraction of total production derived from the principal food sources: algae and organic detritus. Algae supported a major proportion of the production of this grazer. 6. The low density of predators characteristic of many temporary streams, and the small amplitudes in discharge and temperature during most of the wet period that characterise the spring habitats might allow high levels of grazer production in this particular Mediterranean stream.     

The effect of continuous physical disturbance on mayflies of a tropical stream: an experimental approach

Field experiments to examine the effect of continuous physical disturbance on the Ephemeroptera of the Naro Moru River, Kenya, wereundertaken from June 1993 to January 1994. Continuous disturbance wasadministered on a randomly selected subsite of the sediment surface.Artificial physical disturbance within the experimental subsite involvedcontinuous local displacement, shifting and stirring of the streambedsurface substrates (about 10 cm depth) by hand every one minute for 10 or 14min. Three control samples were also taken randomly from the sedimentsurface of an undisturbed stratified area of the study riffle at the startof each disturbance occasion. All samples were collected using a Hesssampler (surface sampling area of 3.142 dm²; meshsize 80μm). Seven mayfly species were particularly abundant and these included Afronurus sp., Afroptilum sudafricanum LESTAGE, Baetis s.l., Baetis(Nigrobaetis) sp. 1, Baetis (Nigrobaetis) sp. 2, Caenis sp. and Choroterpes(Euthraulus) sp. About 83,8% of the total mayfly density and88.1% of the biomass were removed from the streambed surface withinthe first three minutes of continuous physical disturbance. A mayfly biomassof 33.7391 mg dm² and total density of 1357.6 inddm² were collected from the disturbed subsite during the studyduration. Further, a biomass of about 42.8335 mg dm⁻²and total density of 2366 ind dm⁻² were collected fromthe control sites. There was a near-complete depletion of mayflyindividuals from the topmost sediment layer within 14 min of continuousdisturbance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Life histories, production dynamics and resource utilisation of mayflies (Ephemeroptera) in two tropical Asian forest streams

SUMMARY 1. A 2‐year study of the life histories, production dynamics and resource utilisation of five mayfly species was undertaken in two forest streams in Hong Kong [Tai Po Kau Forest Stream (TPKFS) and Shing Mun River (SMR)]. Afronurus sp. and Cinygmina sp. (Heptageniidae), Procloeon sp. and Baetiella pseudofrequenta (Baetidae), and Choroterpes sp. (Leptophlebiidae) were abundant in both streams and contributed more than 50% of the total mayfly populations. 2. All species had asynchronous larval development with recruitment occurring throughout the year. Mean annual production (all mayflies combined) was 3.1 and 2.0 g dry weight m^?2 year^?1 in SMR and TPKFS, respectively – the higher value at SMR reflecting greater mayfly densities – with more than 70% of production occurring during the wet season. Mayfly production varied between years, decreasing by 5% in TPKFS and 43% in SMR during 1996–97, reflecting lower densities of heptageniids relative to 1995–96. Annual biomass turnover rates (P/B) were high in both sites ranging from 27.2 to 94.6 in TPKFS (Cinygmina sp. and Procloeon sp.) and from 31.8 to 109.8 in SMR (Cinygmina sp. and B. pseudofrequenta). 3. Patterns of daily production in both streams showed that Afronurus sp., Cinygmina sp. and Choroterpes sp. were most productive during the wet season, while Procloeon sp. maintained high production levels throughout the year. The highest daily production of B. pseudofrequenta occurred during the wet season in TPKFS, but in the dry season at SMR. Temporal overlap in production and hence resource utilisation in both streams, calculated using the proportional similarity index (PS), ranged from 0.39 to 0.81. It was highest (0.63–0.81) between pairs of species of Heptageniidae and Baetidae, and lowest between Choroterpes sp. and other mayflies (0.39–0.61). No clear temporal segregation was observed among any species. However, when using the fraction of production attributable to each food, lower PS values were obtained for all species in both sites. In SMR, trophic segregation may have occurred between the two species pairs Procloeon sp.–Cinygmina sp. and Procloeon sp.–Choroterpes sp. (PS=0.17 and 0.03, respectively). 4. A combination of production data and information on the stable isotope signature of mayflies revealed that, during both the wet and dry seasons, more than 50% of total mayfly production in TPKFS was derived from autochthonous foods. In SMR, 68% of production was supported by allochthonous foods during the wet season, and 72% by autochthonous sources in the dry season. Considering that more than 70% of the total production occurred in the wet season, the trophic basis of mayfly production in SMR is mostly allochthonous (58%) while in TPKFS it is mainly of autochthonous origin (66%). The year‐round importance of autochthonous foods in shaded streams such as TPKFS is surprising, but the wet season contribution of allochthonous foods (especially in SMR) may have resulted from depletion of algal biomass during spates.     

Life history and production of Caenis luctuosa (Burmeister) (Ephemeroptera, Caenidae) in two nearby reaches along a small stream

Population dynamics and production of C. luctuosa were compared in two reaches of the Agüera stream (northern Spain). This species showed univoltine winter life history in both sites. However, the start of the recruitment period, and the cohort production interval differed in 1 month between reaches. Secondary production of C. luctuosa ranged from 76 mg m^–2 year^–1 (upper site) to 93 mg m^–2 year^–1 (lower site). Although annual production seemed to be mainly influenced by the biomass found at each site, changes in life history may have also been important. The need to have accurate information about life history of the analysed species at the study sites when assessing secondary production is highlighted.     

Use and partition of space and resources by two coexisting Rhyacophila species (Trichoptera) in a high mountain stream

Life history, distribution, drift and food habits of two coexisting Rhyacophila species, Rhyacophila evoluta and Rhyacophila intermedia were studied in a high mountain stream in the Pyrénées.The life histories of both species took two years downstream and three years upstream. Several generations and a large range of larval instars permanently coexisted in the river.Slight temporal segregation of the life histories and differences in size and food habits of the coexisting larvae partially reduced the interspecific competition and allowed an optimal use of space. Instars IV of R. evoluta and V of R. intermedia, which had the most similar biological characteristics had the same microdistribution when they lived alone but used different habitats when they coexisted.     

Drift and settlement of stream insects in a complex hydraulic environment

1. The hydraulic and geomorphic characteristics of stream patches are often associated with distinctive assemblages or densities of stream invertebrates, and it is routinely presumed that these patterns reflect primarily species‐specific habitat requirements. An alternative hypothesis is that such patterns may be influenced by constraints on movement, such as the results of departure and settlement processes. We describe a manipulative experiment that examined how the hydraulic environments created by topographic bedforms influenced the drift behaviour and potential settlement sites for two species of mayfly (Baetis rhodani and Ecdyonurus torrentis). These species are common in the drift and often co‐occur in streams, but differ in their small‐scale distribution patterns, body shape and movement behaviour. 2. Flume experiments were carried out to determine how the hydraulic environments conditioned by a step bedform influence the behaviour of mayflies in the drift (swimming, posturing, tumbling), and the consequences of those behaviours (drift distance and time), compared to drift over a plane bed. The ramped step in the flume mimicked step bedforms that are common in coarse‐grained, high‐gradient streams. In contrast to the plane bed, a zone of recirculating flow was created downstream of the step, above which flow was faster and more turbulent. Uniform flows are used in most flume studies of drift; our approach is novel in recreating a complex hydraulic environment characteristic of stream channels. 3. Both species had some behavioural control over drift, and drift distances and times were shorter for live larvae than for dead larvae over the plane bed. The step had no impact on drift time or distance for live Baetis, but dead larvae were trapped in the flow separation eddy and drift time increased accordingly. Some Ecdyonurus also became trapped in the eddy, but live larvae drifted farther than dead larvae, and farther over the step than the plane bed. 4. Whilst in the drift, larvae altered their behaviour according to the ambient hydraulic environment, but in a species‐specific manner. Over the plane bed, Baetis had occasional swimming bursts, but primarily postured (maintained a stable body orientation), whereas Ecdyonurus spent roughly equal time posturing and swimming. In the more turbulent flows generated by the step, Baetis spent proportionately more time swimming, whereas Ecdyonurus spent more time posturing and often tumbling as body orientation became unstable. 5. In a high‐gradient stream, Baetis was more abundant close to steps than in plane bed patches with less complex flow, whereas the opposite pattern held for Ecdyonurus. Thus, the small‐scale distribution patterns of these species within streams correspond to their drift behaviours and ability to access various hydraulic patch types in our flume. These results are consistent with the hypothesis that constraints on movement and settlement may be important driver of distribution patterns within streams.     

Community structure of Trichoptera in a mountain stream: spatial patterns of production and functional organization

SUMMARY. 1. Annual production was estimated for Trichoptera occurring in each of three distinct habitats of a mountain stream: bedrock-outcrops, riffles and pools. Production was greatest on bedrock-outcrops (2608 mg ash-free dry weight m^?2), followed by riffles (1038) and pools (950). 2. Annual production in bedrock-outcrops and pools was dominated by single functional groups, with collector-filterers and shredders contributing 73% and 75% of the annual production, respectively. Production in riffles was due primarily to shredders (46%), followed by collector-filterers (27%). 3. Taking account of the amount of stream area occupied by each habitat type, total annual production was estimated at 1336 mg AFDW m^?2. 53% of this production was attributable to four taxa: Parapsyche cardis Ross (25%), Pycnopsyche gentilis (MacLachlan) (10%), Neophylax mitchelli Carpenter (9%) and Rhyacophila nigrita Banks (9%). 4. Habitat-weighted production was distributed among functional groups as follows: collector-filterers (41%), shredders (29%), engulfing-predators (15%), scrapers (13%) and collector-gatherers (2%). 5. The distinct taxonomic and functional structures of trichopteran sub-communities were shaped by the distinct physical characteristics of their principal habitats. Bedrock-outcrops were characterized by low roughness and high current and were sites of low deposition or organic matter; thus the predominance of collector-filterers. In contrast, the other habitats of greater roughness (riffles) and/or lower current (pools) were sites of deposition of food (e.g. leaf litter) and greatest shredder production. 6. By distinguishing discrete mesoscale habitats, each with a functionally distinct caddisfly sub-community, we speculate that small mountain streams provided the diverse physical templates essential for the evolution of the major feeding tactics (e.g. scraping, shredding, filter-feeding) of the. Trichoptera.     

Relationship between benthic insects (Ephemeroptera, Plecoptera, Coleoptera, Trichoptera) and temperature in small and medium-sized streams in Germany: A multivariate study

Benthic insect communities (Ephemeroptera, Plecoptera, Coleoptera, Trichoptera) were studied together with water temperature and environmental parameters in streams between June 2000 and June 2001. The sampling area consisted of 20 sites in small and medium-sized streams located in the lower mountainous area of Central Europe. Temperature was recorded nearly continuously and several physicochemical and environmental variables were assessed. Macroinvertebrates were sampled both in spring and summer. Data-sets of species abundance and occurrence were analysed using multivariate techniques and were correlated to the thermal and environmental conditions of the streams. The temperature preferences of the species were compared to published data-sets on their autecological characteristics. Up to 29% of the variability in the Ephemeroptera, Plecoptera, Trichoptera and Coleoptera community was explained by summer temperature variation in the data-sets for both small and medium-sized streams. A smaller, but significant part of the variability in species distribution was explained by conductivity, substratum type, and the percent coverage of local riparian forest. Compared to small streams, temperature was less important for the macroinvertebrate composition in medium-sized streams. This result is likely due to the more tolerant, eurythermic species composition in larger streams. A total of 33 Ephemeroptera, Plecoptera, Coleoptera and Trichoptera taxa were positively correlated and 28 taxa were negatively correlated to summer temperature patterns. The temperature preferences of taxa considered in this study were related to species traits, such as egg dormancies and life cycle plasticity.     

Conversion of leaf litter to secondary production by a shredding caddis-fly

Summary 1. The aim of this study was to estimate the amount of leaf litter ingested by the shredder caddis‐fly Sericostoma vittatum in a small stream in central Portugal. The study combined field data on population dynamics and laboratory experiments to determine the effect of temperature (9, 12, 15 and 18 °C), leaf species (Alnus glutinosa, Castanea sativa, Populus × canadensis and Quercus andegavensis) and animal mass on growth and consumption rates of the larvae. 2. Sericostoma vittatum had two overlapping cohorts, each of which needed about 1 year to complete development. Mean annual density and biomass were 115 individuals m^?2 and 83 mg m^?2, respectively. Secondary production was 0.44 g m^?2 year^?1 and production/biomass ratio was 4.9–5 year^?1. 3. Consumption rates of larvae increased with temperature up to the optimal temperature for growth which varied between 13.7 and 16.7 °C depending on the diet. 4. Consumption rate was positively related to larval mass but growth rate was negatively related with larval mass. Larvae fed on A. glutinosa and P. × canadensis had higher consumption and growth rates than those fed on C. sativa or Q. andegavensis. 5. Annual leaf litter consumption by S. vittatum was estimated as 14–22 g m^?2 depending on the diet. No relationship was observed between the amount of detritus consumed by the population of this caddis‐fly in the field and either water temperature, the stock of detritus on the stream bottom, or larval abundance. Instead, the temporal dynamics of leaf litter consumption by S. vittatum were controlled by its life history. 6. This study highlights the influence of factors such as animal size and water temperature on the invertebrate energetics. Models explaining how these variables affect invertebrate production efficiency may be very important for obtaining accurate estimates of the role of shredders in the energy flow across stream ecosystems.     

Life history of a lowland burrowing mayfly, Ephemera orientalis (Ephemeroptera: Ephemeridae), in a Korean stream

Life history aspects of Ephemera orientalis, a common lowland burrowing mayfly that resides in temperate East Asia, were studied in terms of voltinism, secondary production, and accumulated degree days for larval development. From March 1998 to June 1999, larvae were sampled monthly (weekly or biweekly during the emergence period) from a lower reach of the Gapyeong stream in Korea, a stream typical of temperate East Asia, using a Surber sampler (0.25 m², mesh 0.25 mm). As a result, the mean density of E. orientalis was 47.21 ± 13.58 indiv. m⁻² during the study period. Very small larvae less than 2 mm in body length were sampled on three separate occasions, and emergence was observed between late April and early October, except during late May. Based on the larval body length distribution and emergence time, two different developmental groups could be distinguished: the slow developmental group (S-group) and the fast developmental group (F-group). The F-group completed its life cycle within 4 months, whereas the S-group had a one-year life cycle. The S-group could be divided into two subgroups, dubbed the S1 and S2-groups, based on larval development. The developmental groups alternate their life cycles in the order: S1→F→S2→S1. Estimated annual production of the larvae was 68.81 mg DW m⁻² y⁻¹; mean biomass was 8.43 mg DW m⁻²; the annual production to mean biomass ratio was 8.16. The annual mean water temperature of the study year was 14.76 ± 6.63°C. The total accumulated degree days for larval development was 1396°C for the F-group, 2,055°C for the S1-group, and 1,975°C for the S2-group. Two different adult body size groups were distinguished (P < 0.001 by t-test): larger adults, which belonged to the S-group, were present throughout the emergence period, whereas smaller adults, which belonged to the F-group, were mainly present later in the emergence period (August–October). The difference in the accumulated degree days between the developmental groups may explain the size differences of adults.