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The macroinvertebrate fauna of Ecuadorian highland streams in the wet and dry season
Abstract
The community structure and functional feeding groups of the macroinvertebrate fauna were examined in eight Ecuadorian highland streams in the wet and the dry season. The abiotic environment of the streams was highly unstable with great variability in discharge during the wet season, but relatively constant during the short dry season. Overall, the number of individuals and species were significantly higher in the dry season than in the wet season. In all streams the composition of the fauna differed markedly between the two seasons, but no consistent change in community structure and proportions of functional feeding groups was found for the eight streams. In both seasons Baetidae, Simuliidae, Chironomidae and Elmidae were the four most numerous families. The equitability of the communities was, however, lower in all streams during the dry season. Collector-browsers were the most numerous organisms while filterers, predators and shredders were much less important. Maximum stream temperature was the single environmental parameter that best explained the variability in community structure among the streams. Otherwise the fauna was weakly correlated to site characteristics. The instability of these tropical Andes streams is probably the main feature structuring the invertebrate fauna. The streams may be alternating between a stochastic community structure during the wet season and early successional stages dominated by organisms with a fast growth and high colonisation capacity during the dry season.
... In this study, predators are the scarcest FFG (no presence in very poor ecological conditions). The potential correlation between the distribution of predators and low levels of disturbance, such as deforestation, nutrient inputs, intensive land use and organic effluents, in high-altitude environments is a subject of academic interest [15,101,102]. ...
Simple Summary
High-altitude Andean streams are fragile ecosystems that require urgent actions such as bioassessment for proper environmental management. In the present study, we investigated the distribution and composition of the macroinvertebrate community in relation to the environmental variables in the Antisana river basin (Andean–Ecuadorian region). Macroinvertebrates were sampled at fifteen localities to predicate ecological condition which were expressed by the Biological Monitoring Working Party Colombia (BMWP-Col) index, the Andean Biotic Index (ABI) and the Andean–Amazon Biotic Index (AAMBI), and their main feeding traits as indicators of ecological functionality. Results show that dissolved oxygen saturation and total phosphorus, ammonia and conductivity contributed significantly to the composition of taxa and functional feeding groups (FFGs). Taxa and FFG diversity were most abundant at sites with the best ecological conditions. Shredders were, in general, dominant and especially abundant in the medium-high-quality sites. Predators were almost absent throughout the study, but they were collected from low-quality sites, showing greater tolerance to the presence of human disturbance. The BMWP-Col index seems to be the best fit for this ecosystem, showing a significant difference in FFG between the index classes compared to the other indices evaluated. The results of the present investigation may be regarded as a fundamental starting point and used in the future bioassessment works in other tropical Andean streams, especially where their resilience is threatened by poorly managed human activities.
Abstract
High-elevation tropical streams are under increasing threat from human activities and climate change. Specifically, Ecuadorian Andean streams require priority actions such as bioassessment (e.g., biodiversity and functional ecology of macroinvertebrates) in order to generate adequate environmental management policies. Therefore, we investigated the distribution and composition of the macroinvertebrate taxa and their functional feeding groups in relation to the environmental variables in the Antisana river basin (Andean–Ecuadorian Region). We sampled macroinvertebrates from 15 locations to assess ecological conditions (ECs), expressed as the Biological Monitoring Working Party Colombia (BMWP-Col) classes, the Andean Biotic Index (ABI) and the Andean–Amazon Biotic Index (AAMBI). Results indicate that dissolved oxygen saturation, elevation, nutrient concentration and conductivity contributed significantly to the composition of the taxa and functional feeding groups (FFGs). Taxa diversity and FFGs were more abundant in the best EC sites. Shredders (SH) were, overall, dominant and abundant at sites with medium-high ECs. Scrapers constituted the second most prevalent assemblage, exerting dominance at moderate ecological conditions (high altitude and high oxygen saturation). Collector–gathers (CGs) are less sensitive to contamination than the previous two groups but were equally abundant at medium-high EC sites. Collector–filterers (CFs) and parasites (PAs) were less abundant, although the presence of the former was slightly related to better environmental conditions. Predators (PRs) were almost absent throughout the study, but they were collected from poor EC sites. CGs, PAs and PRs showed more tolerance to the presence of human disturbances (e.g., hydraulic constructions or slope erosion). The BMWP-Col index seems to be the best fit for this ecosystem, showing a significant difference in FFG between the index classes, compared to the other indices evaluated. The results of this investigation may be regarded as a fundamental starting point and used in future bioassessment work in other similar ecosystems, particularly high-altitude tropical Ecuadorian streams.
... Highest abundance values were found for the dry season, mainly in May, July and November. This agrees with Jacobsen and Encalada (1998) and González et al. (2013), who report that the number of organisms is higher in the dry season than in the rainy season. Molina et al. (2008) make a similar observation for rivers in Bolivia during the dry season when low values in hydrological parameters are associated to high densities and an increase in the number of taxa. ...
High Andean wetlands are fragile systems, vulnerable to human activity and climate change. In the Arequipa
region (Peru), there are high Andean lotic and lentic systems currently affected by livestock raising, fish farming, and
dams. The aim of the study was to evaluate the aquatic invertebrate community in the Callalli-Oscollo wetlands and
the possible impact of human activities. Samples were taken from November 2017 to October 2018 at 4 sampling
stations in lotic environments and 2 in lentic environments. Macroinvertebrates were identified to the family level. The
following were determined to evaluate community structure: richness, relative abundance, Shannon-Wiener diversity,
Simpson dominance, Pielou evenness, and true diversity. The indices ABI, BMWP/Bol and nPeBMWP were applied
to evaluate the ecological quality of the environments sampled. Thirty families were recorded in lotic environments,
the most abundant being Chironomidae, Naididae, Limnesiidae, Elmidae, Baetidae and Lumbriculidae. The ecological
quality was good, except at the station associated to the dam, where it was doubtful. Twenty-six families were
recorded in lentic environments, the most abundant being Cyprididae, Naididae and Corixidae. The macroinvertebrate
communities in high Andean environments reflect ecosystem conditions. Environments associated to human activity
have lower ecological quality.
... Highest abundance values were found for the dry season, mainly in May, July and November. This agrees with Jacobsen and Encalada (1998) and González et al. (2013), who report that the number of organisms is higher in the dry season than in the rainy season. Molina et al. (2008) make a similar observation for rivers in Bolivia during the dry season when low values in hydrological parameters are associated to high densities and an increase in the number of taxa. ...
High Andean wetlands are fragile systems, vulnerable to human activity and climate change. In the Arequipa region (Peru), there are high Andean lotic and lentic systems currently affected by livestock raising, fish farming, and dams. The aim of the study was to evaluate the aquatic invertebrate community in the Callalli-Oscollo wetlands and the possible impact of human activities. Samples were taken from November 2017 to October 2018 at 4 sampling stations in lotic environments and 2 in lentic environments. Macroinvertebrates were identified to the family level. The following were determined to evaluate community structure: richness, relative abundance, Shannon-Wiener diversity, Simpson dominance, Pielou evenness, and true diversity. The indices ABI, BMWP/Bol and nPeBMWP were applied to evaluate the ecological quality of the environments sampled. Thirty families were recorded in lotic environments, the most abundant being Chironomidae, Naididae, Limnesiidae, Elmidae, Baetidae and Lumbriculidae. The ecological quality was good, except at the station associated to the dam, where it was doubtful. Twenty-six families were recorded in lentic environments, the most abundant being Cyprididae, Naididae and Corixidae. The macroinvertebrate communities in high Andean environments reflect ecosystem conditions. Environments associated to human activity have lower ecological quality.
... Moreover, in our study % Predators were representative in pristine stream (downstream) in rainy season. These high percentage of predators are potentially linked with season, however, the higher predator diversity and numbers was already reported in Ecuadorian highaltitude upstream during the dry season compared to the rainy season (Jacobsen & Encalada, 1998;Van Echelpoel et al., 2018). Furthermore, according to Van Echelpoel et al. (2018), they illustrated that fluctuations in the macroinvertebrate functional community composition are more likely influenced by ex-situ anthropogenic activities than by natural local habitat conditions. ...
Rapid urbanization in Brazil has been dramatically deteriorating the water quality of streams and threatening aquatic ecosystem health. In this study, we aimed to address the question of how urbanization affects macroinvertebrate distribution patterns and the water quality of a strategic stream that runs from the city to an important conservation area. Environmental variables (spatial and temporal) and macroinvertebrate community (use of community deconstruction) data were collected on rainy and dry seasons of 2019 and 2020 at 10 sampling sites, of which four we categorized as impacted, three as altered and three as pristine, based on environment assessment protocols. We submitted the abundance and taxonomic richness data to a two-way ANOVA, then to a GLMMs. We also performed a nMDS to the macroinvertebrate community, followed by the ANOSIM and SIMPER test, respectively. The results of this study showed that impacted and altered streams had lower total richness and % Odonata, and higher % Chironomidae when compared to pristine streams. As expected Chironomidae had a positive relationship with total coliforms, and taxonomic richness and % EPT had a negative one, and % Odonata had a negative relationship with total dissolved nitrogen. Pristine stream community of benthic macroinvertebrates showed different composition between impacted and altered streams, however, communities of impacted and altered environments were generally similar. Our exploratory data showed that gathering collectors were representative in impacted and altered streams, and predators were representative in pristine areas. Moreover, our results suggest that urbanization resulted in less diverse and more tolerant stream macroinvertebrate assemblages.
... For instance, key theories of modern limnology, such as patch-dynamics in aquatic systems (Pringle et al., 1988) or the control point concept (Bernhardt et al., 2017) were developed by women. Further, many female researchers have contributed to increase the knowledge on taxonomy and aquatic species distribution and their interaction with the environment, standing out studies in South America and Asia (e.g., Fang et al., 2013;Hamada et al., 2002;Jacobsen & Encalada, 1998). Finally, female researchers are leading research on new fields, such as freshwater ecosystem restoration (Palmer et al., 2014;Zedler, 2000), urban ecology (Grimm et al., 2004) and translational ecology (Tank, 2017). ...
Research in limnology is nurtured by the work of many fascinating and passionate women, who have contributed enormously to our understanding of inland waters. Female limnologists have promoted and established the bases of our knowledge about inland waters and fostered the need of protecting the values of those ecosystems. However, on numerous occasions, their contribution to the advancement of limnology has not been duly recognized. Here, we review the presence of women in limnology through the history of the discipline: from the pioneers who contributed to the origins to present day' developments. We aim at visibilizing those scientists and establish them as role models. We also analyze in a simple and illustrative way the current situation of women in limnology, the scientific barriers they must deal with, and their future prospects. Multiple aspects fostering the visibility of a scientist, such as their presence in conferences, awards, or representation in societal or editorial boards show a significant gap, with none of those aspects showing a similar visibility of women and men in limnology.
This article raises awareness of the obstacles that women in limnology faced and still face, and encourages to embrace models of leadership, scientific management, and assessment of research performance far from those commonly established.
... However, the effect of FPOM on Andesiops peruvianus growth was not as pronounced, perhaps because this species complements its diet with other food resources (e.g., periphyton). This type of input energy source has been described in Ecuador's high-elevation streams, especially those with no riparian vegetative cover and high penetration of light in the river channels [122], as was characteristic of our aquatic insect collection site. Although we provided tiles colonized with algae throughout the experiment, the quantity and/or quality of algae could not have been sufficient for Andesiops peruvianus larvae given the temperature increases in the S2 and S3 treatments. ...
Temperatures have increased around the globe, affecting many ecosystems, including high-elevation Andean streams where important aquatic insect species coexist. Depending on the magnitude of change, warming could lead to the mortality of sensitive species, and those tolerant to rising water temperatures may exhibit differences in growth rates and development. Taxon-specific optimal temperature ranges for growth determine how high or low temperatures alter an organism's body size. In this study, we observed the effects of different climate change scenarios (following three scenarios of the 2021 IPCC predictions) in two aquatic insect species distributed in high-elevation streams in Ecuador: the mayfly Andesiops peruvianus (Ephemeroptera: Baetidae) and the caddisfly Anomalocosmoecus illiesi (Trichoptera: Limnephilidae). We assessed how increased water temperatures affect larval growth rates and mortality during a 10-day microcosm experiment. Our results showed that Andesiops peruvianus was more thermally sensitive than Anomalocosmoecus illiesi. Mortality was higher (more than 50% of the individuals) in mayflies than in caddisflies, which presented mortality below 12% at +2.5˚C and +5˚C. Mortality in mayflies was related to lower dissolved oxygen levels in increased temperature chambers. Higher temperatures affected body size and dry mass with a faster growth rate of Andesiops peruvianus larvae at experimentally higher temperatures, suggesting an important response of this hemimetabo-lous species to stream temperatures. For Anomalocosmoecus illiesi, we did not find significant changes in mortality, body size or growth rate in response to temperature changes during our experiment. In situ outcomes of species survival and growth in Andean streams are difficult to predict. Nevertheless, our results suggest that at only +2.5˚C, a water temperature increase affected the two insect taxa differentially, leading to a drastic outcome for one species' larvae while selecting for a more tolerant species. Our study suggests that climate change might produce significant mortality and growth rate effects on ectotherm tropical aquatic insects, especially Andean mayflies, which showed higher sensitivity to increased water temperature scenarios.
Andean streams are becoming increasingly impacted by agricultural activities. However, the potential effects of pesticides on their aquatic biodiversity remain unassessed. In order to address this knowledge gap, we conducted an experiment over 37 days in microcosms to assess the effect of two pesticides commonly used in Ecuador (Engeo and Chlorpyrifos) on the aquatic insect Nectopsyche sp. (Trichoptera: Leptoceridae) at 0, 0.10, 5 and 10 μg L−1 concentra-tions. The highest concentration corresponds to the maximum concentration allowed by the Equatorian legislation. We assessed insect mortality every 24 h, with leaf litter decomposition rates of organic matter determined by deploying Andean alder (Alnus acuminata) dry leaf packs in the microcosms. We found significant mortality of Nectopsyche sp. at high concentrations of Chlorpyrifos, whereas leaf litter was not significantly affected by any of the treatments. We con-clude that the environmental legislation of Ecuador might not be fully protecting aquatic biodi-versity from pesticide pollution. Further studies are needed, especially when considering that the maximum permitted concentration is very likely exceeded in many areas of the country. We also suggest that the maximum permissible values should be reviewed, considering each pesticide individually.
Ecological effects of flooding and drying events are relatively understudied in the Neotropics and less is known about these hydrological extremes in intermittent streams. Neotropical headwater streams in Costa Rica provide opportunities to evaluate the response of macroinvertebrate communities to seasonal changes in flow regime in relatively human undisturbed systems. We quantified the effects of seasonal flow variation on aquatic macroinvertebrate assemblages (i.e., density, richness, and functional traits) within two headwater streams with differing hydrological regimes (i.e., intermittent versus perennial), in the Pacific North of Costa Rica. We sampled macroinvertebrates monthly over a year in riffle and pool habitats. Non-metric multidimensional scaling (NMDS) analyses indicated differences in macroinvertebrate taxonomic richness and density between the two streams and riffle and pool habitats. We found that macroinvertebrates in the intermittent stream riffles had significantly higher richness during the dry season. We also found higher macroinvertebrate functional trait richness in the intermittent stream riffle habitats during the dry season. Our results may be explained by life history traits related to stream velocity preference or tolerance, short life cycles that limit exposure to disturbances, and dispersal capacities and feeding mechanisms that are dependent on water movement.
En Colombia, el Agraz (Vaccinium meridionale, Swartz), por su uso alimenticio, representa una alternativa importante. Como fruta, es rica en antioxidantes, contiene vitamina C y vitaminas del complejo B, potasio, calcio, fósforo y magnesio; proteínas, fibra y un alto contenido de agua. Como uso medicinal, el consumo crudo de los frutos de mortiño ayuda a restablecer los niveles normales de azúcar en la sangre en personas con problemas de hipoglicemia y diabetes. En el presente artículo se realiza un análisis comparativo de las propiedades nutricionales y presupuestales del agraz y el arándano, donde se puede observar los costos del cultivo de Arándano y los costos del cultivo de Agraz, mirando las ventajas de este último como planta nativa de los Andes Colombianos, que se quiere dar a conocer como un potencial producto agroindustrial de exportación y foco de desarrollo de la región
A remarkable body of evidence shows that river ecosystems are fundamental in the energy balance of the hydrographic basin and the maintenance of its biological diversity (Naiman et al., 2005). Thus, the fluctuations between periods of drought and rain are expressed in temporary changes in the volumes of water destined for runoff, flooding and (via percolation) for the maintenance of aquifers. The inundation of riparian zones and flood plains is associated with a considerable contribution of ABSTRACT The basins that drain the eastern coast of Lake Maracaibo in Venezuela are under strong impacts with a pernicious effect on river ecosystems, but it is unknown its state of conservation, which limits the adequate management of regional hydrobiological resources. In the Machango and Misoa tributaries, 16 river sections were characterized according to the dimensions of the channel, the composition of the substrate and the physical-chemical variables of the water, and insect samples were collected. The conservation status of the localities was estimated using environmental indices (IHF: fluvial habitat index; QBR-And: Andean riparian forest quality index; HII: habitat integrity index). Relationships between habitat gradient and indices were explored using multivariate classification and ordination analyses. The aquatic habitat showed a gradient of heterogeneity associated directly and significantly with the height and the state of conservation of riverbeds and riparian zones. All the indices had high scores where there was greater vegetation cover in riparian zones and more heterogeneous substrates; In addition, the indices had proportional and significant correlations with the gradient of the fluvial habitat and the number of families of aquatic insects. A gradient in conservation status was recognized, where a low conservation class was associated with homogeneous and intervened habitats and with lower richness of aquatic insects. The indices used are suitable for estimating the conservation classes of rivers and their biota, and may be useful for monitoring hydrographic basins.
RESUMEN Un notable cuerpo de evi-dencias demuestra que los eco-sistemas fluviales son funda-mentales en el equilibrio ener-gético de la cuenca hidrográfi-ca y el mantenimiento de su diversidad biológica (Naiman et al., 2005). Así, las fluctua-ciones entre los períodos de sequía y lluvias se expresan en cambios temporales de los vo-lúmenes de agua con destino al escurrimiento, la inundación y (vía percolación) al manteni-miento de acuíferos. La inun-dación de zonas de ribera y planicies inundables se asocia con un aporte considerable de RESUMEN Las cuencas que drenan la costa oriental del Lago de Ma-racaibo en Venezuela se encuentran bajo fuertes impactos con efecto pernicioso sobre los ecosistemas fluviales, pero se desconoce su estado de conservación, lo que limita el mane-jo adecuado de los recursos hidrobiológicos regionales. En los tributarios Machango y Misoa se caracterizaron 16 tramos de ríos según las dimensiones del cauce, la composición del sustrato y las variables físico-químicas del agua, y se reco-lectaron muestras de insectos. El estado de conservación de las localidades se estimó mediante índices ambientales (IHF: índice de hábitat fluvial; QBR-And: índice de calidad de bos-ques de ribera andina; HII: índice de integridad de hábitat). Se exploraron las relaciones entre el gradiente del hábitat e índices mediante análisis de clasificación y ordenación multi-variada. El hábitat acuático mostró un gradiente de heteroge-neidad asociado directa y significativamente con la altura y el estado de conservación de cauces y zonas de ribera. Todos los índices tuvieron puntajes elevados donde hubo mayor cobertu-ra vegetal en zonas de ribera y sustratos más heterogéneos; además, los índices tuvieron correlaciones proporcionales y significativas con el gradiente del hábitat fluvial y el número de familias de insectos acuáticos. Se reconoció un gradiente en el estado de conservación, donde una clase de conservación baja se asoció con hábitats homogéneos e intervenidos y con menor riqueza de insectos acuáticos. Los índices empleados son adecuados para estimar las clases de conservación de los ríos y sus biotas, pudiendo ser útiles para el monitoreo de las cuencas hidrográficas.
We define disturbance in stream ecosystems to be: any relatively discrete event in time that is characterized by a frequency, intensity, and severity outside a predictable range, and that disrupts ecosystem, community, or population structure and changes resources or the physical environment. Of the three major hypotheses relating disturbance to lotic community structure, the dynamic equilibrium hypothesis appears to be generally applicable, although specific studies support the intermediate disturbance hypothesis and the equilibrium model. Differences in disturbance frequency between lentic and lotic systems may explain why biotic interactions are more apparent in lakes than in streams. Responses to both natural and anthropogenic disturbances vary regionally, as illustrated by examples from the mid-continent, Pacific northwest, and southeastern United States. Based on a generalized framework of climatic-biogeochemical characteristics, two features are considered to be most significant in choosing streams for comparative studies of disturbance: hydrologic regimes and comparable geomorphology. A method is described for quantifying predictability of the hydrologic regime based on long-term records of monthly maximum and minimum stream flows. Different channel forms (boulder and cobble, alluvial gravelbed, alluvial sandbed) have different responses to hydrologic disturbance from spates. A number of structural and functional components for comparing disturbance effects within regions and across biomes are presented. Experimental approaches to studying disturbance involve spatial-scale considerations, logistic difficulties, and ethical questions. General questions related to disturbance that could be addressed by stream ecologists are proposed.
The physical, chemical and biological features of the Sungai Gombak, West Malaysia, were investigated from September 1969 to July 1970 with a view to comprehensive definition of a Malayan small-river biome in its natural state and description of some effects of anthropic activities on this.
Generic-level diagnoses are provided for adult males, females, and larvae of the longhorned caddisfly genus Nectopsyche Müller (Trichoptera:Leptoceridae). In addition, seven new Costa Rican species in the gemma species group are described and illustrated: N. exophthalma n. sp., N. monticola n. sp., N. onyx n. sp., N. ortizi n. sp., (also known from Argentina, Brazil, Guyana, Mexico, Panama, Peru, Surinam, and Venezuela), N. tapanti n. sp., N. tuanis n. sp., and N. utleyorum n. sp. The new species are compared with two previously described gemma group species also known from Costa Rica, N. argentata Flint and N. gemmoides Flint, and these, too, are diagnosed and illustrated.
We examined total development times for 5 mayfly species, 2 stoneflies, 10 caddisflies, and 18 chironomid midges collected from three streams that flow through tropical evergreen forest in northwestern Costa Rica. Most eggs, larvae, and pupae were reared in the laboratory in a photoperiod of 12:12 LD and at 20°C, which simulated field conditions. Algae, algal detritus, and leaves were provided as food for all species; predators were also given various animal prey. All study species had total development times that were rapid relative to the univoltine life histories observed or assumed for many temperate species. Egg development times ranged from a few days to approximately a week for chironomids and from 10 to 38 days for mayflies, stoneflies, and caddisflies. Most chironomids had short larval/pupal development times: development was completed in 19-29 d by seven species, in 30-40 d by nine species, and in >50 d by two species. Relatively short development times (including the pupal stage when present) w...
The faunas of small, forested streams depended primarily on allochthonous sources of carbon whereas variable utlization of allochthonous and autochthonous materials was shown by species from a grassland stream. Relatively 13C-depleted values obtained for the mayfly, Deleatidium from forested sites suggest that its larvae assimilate algae selectively. A shift to greater dependence on autochthonous energy sources was shown by invertebrates from small, recently clearcut catchments in response to canopy removal and flushing of forest-derived organic materials from the streams.-from Authors
Multivariate analyses were used to examine relationships between each of three biological classifications of mayfly (Ephemeroptera) larvae and environmental variables recorded at 95 river sites encompassing 18 degrees of latitude in northwestern North America. Biological samples, collected by kick net, were classified by family and superfamily, by size, and by morphological/behavioural group. Environmental variables included measures obtained from topographical maps and hydrological features recorded at each site. Results of canonical correlation analyses showed that all three biotic indicators were significantly associated with environmental variables. Morphological/behavioural classification yielded stronger correlations with environmental data than did taxonomic or size classifications. Multivariate curvilinear regression analyses gave equivalent results and showed that, although several relationships were curvilinear, all were monotonic. Environmental variables independently and significantly associated with mayfly relative abundance included river size, velocity, slope, latitude, and conductivity. Use of alternative classification variables can potentially reveal patterns not evident when standard taxonomic units are applied.
Field experiments were conducted to examine the effects of disturbance frequency on invertebrates and periphyton colonizing bricks in a third order Rocky Mountain (USA) stream. After an initial colonization period (30 days), sets of bricks were turned over at intervals of 0, 3, 9, 27, or 54 days. Invertebrate species richness and density were reduced as disturbance frequency increased. These trends were evident for both seasons (summer and fall) and sites (open vs. closed canopy). Invertebrate species diversity (H′) displayed no effect during the fall experiment; however, H′ was reduced at high frequencies of disturbance during the summer experiment. Baetis tricaudatus was the most abundant invertebrate on the substrata at both sites and seasons. Alloperla, Baetis, Cinygmula, Chironomidae, Drunella grandis, Hydropsyche, and Seratella tibialis increased in absolute abundances as disturbance frequency decreased. Four other abundant taxa (Capnia, Cleptelmis, Glossosoma, and Isoperla) displayed no clear response to disturbance in either absolute or relative abundances. Species in low abundance tended to colonize only the less frequently disturbed bricks. During both seasons, periphyton biomass increased as disturbance frequency decreased at the open canopy site, while no trend was apparent at the closed canopy site. Periphyton accumulation monitored over time and among treatments revealed that frequent disturbances maintained low standing crops at an open canopy site. These data suggest that disturbance frequency can directly influence the benthic community at the scale of individual rock "islands" by reducing invertebrate richness, total animal density, and periphyton biomass. The effect of disturbance on species diversity (H′) was seasonal, further emphasizing the importance of considering seasonality in stream field studies.
Patterns are described for small-scale experimental studies using introduced or natural substrates, for large-scale observations of new or rewatered channels, for rivers recovering from pollution, and for unstable rivers with fluctuating discharge. Colonization depends on invertebrate mobility (drift, swimming, crawling, and flight), substrate texture and associated food supplies, competition, and predation. Epilithon-browsers and filter feeders can use the resources of smooth stones; gatherers colonize as fine detritus accumulates; grazers increase as periphyton becomes established; shredders and predators tend to be late arrivals. Propagules for colonization are made more available by asynchronous and aseasonal life cycles, long oviposition periods, and refuges in the streambed or neighbouring waterbodies. Species in frequently disturbed streams benefit from these characteristics. Knowledge of the hydrologic regime, food resources, and dominant taxa can be used to predict the overall resilience of a stream community. -from Author
Ninety-nine taxa of aquatic insects and a total 104 macroinvertebrate taxa were collected in Sycamore Creek, Arizona, from July 1977 to November 1979 The fauna is primarily composed of organisms restricted to the American Southwest, although many widespread Nearctic taxa are also present. Life histories of 17 taxa were examined with emphasis on total developmental time (egg to adult), reproductive period and dormancy Ephemeroptera, small Diptera and the corixid Graptocorixa serrulata developed rapidly (1-3 weeks) and reproduced continuously. Aquatic beetles (Dytiscidae and Hydrophilidae) developed in 4-8 weeks and reproduced only in spring and after summer rains. Two Trichoptera species required 6-7 weeks for development and reproduced continuously Degree-day developmental rates (ca. 1200) were similar for some desert and temperate species. Dormant stages were restricted to stoneflies (egg diapause) and tabanids (larval diapause). Drought and flooding markedly influenced life histories. Adaptations to drought are habitat selection by ovipositing adults and rapid development. Adaptations to floods are behavioral avoidance, rapid development and seasonal reproduction. Floods also contribute to the rarity of dormancy, thus aerial adults become the life stage resistant to disturbance. Floods, which do not occur in temporary lentic systems, are an important selective pressure in temporary lotic systems.
Studies were conducted in four distinct geographic areas (biomes/sites) in northern United States to examine changes in key ecosystem parameter: benthic organic matter (BOM), transported organic matter (TOM), community production and respiration, leaf pack decomposition, and functional feeding-group composition along gradients of increasing stream size. Four stations ranging from headwaters (1st or 2nd order) to midsized rivers (5th to 7th order) were examined at each site using comparable methods. The results for each parameter are presented and discussed in light of the River Continuum Concept of Vannote et al. (1980). The postulated gradual change in a stream ecosystem's structure and function is supported by this study. However, regional and local deviations occur as a result of variations in the influence of: (1) watershed climate and geology, (2) riparian conditions, (3) tributaries, and (4) location-specific lithology and geomorphology. In particular, the continuum framework must be visualized as a sliding scale which is shifted upstream or downstream depending on macroenvironmental forces (1 and 2) or reset following the application of more localized @'micro@'-environmental influences (3 and 4). Analysis of interactions between BOM and TOM permitted evaluation of stream retentiveness for organic matter. Headwaters generally were most retentive and downstream reaches the least. Estimates of organic matter turnover times ranged between 0.2 and 14 yr, and commonly were 1-4 yr. Both turnover times and distances were determined primarily by the interaction between current velocity and stream retention. Biological processes played a secondary role. However, the streams varied considerably in their spiraling of organic matter due to differences in the interplay between retentiveness and biological activity. Differences in the relative importance of retention mechanisms along the continuum suggest that headwater stream ecosystems may be functionally more stable, at least to physical disturbances, than are the r intermediate river counterparts.