摘要:

Structural and trophic changes in a benthic macroinvertebrate community downriver from Valparaíso Reservoir (northwestern Spain) were compared before (1986) and after (1990–1991) the creation of that hydropower impoundment. The number of taxonomic groups, total biomass and total density significantly declined under the influence of the new flow regulation, with scrapers (as relative density) being the functional feeding group most adversely affected. The environmental impact decreased with time after the construction of the dam Taxonomic richness and diversity of predators appeared to be the most sensitive biological indicators of the progressive recovery of the macrobenthic community.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663453

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The channel catfishIctalurus punctatusis abundant in Lake Oahe, South Dakota, providing a minor sport fishery. Because of it's population size, channel catfish undoubtedly influence the trophic ecology of Oahe Reservoir. However, little research has been conducted on channel catfish since the years following dam closure. We studied the food habits of channel catfish in Lake Oahe during 1991 and 1992. Food habits were evaluated using the relative importance (RI) index. Channel catfish fed on a variety of prey, but aquatic insects dominated the diet for all sizes of fish sampled. Terrestrial insects, zooplankton, and vertebrates (toads and fish) largely comprised the remainder of the diet.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663454

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We compared the macroinvertebrate communities among vegetation types in Swan Lake, a large prairie marsh in south-central Minnesota. Activity traps and sweep nets were used to sample macroinvertebrates during the summer months of 1992 and 1993. Twenty-four sites on the lake were sampled along six established transects. Each site was located in one of four different habitats, including three major macrophyte communities:Typha angustifolia, Scirpus acutus, Potamogeton spp., and an open water site having little or no vegetation. The diversity, relative abundance, and biomass of the invertebrates collected from each vegetation type were compared to assess which type of vegetation supported the greatest numbers and most diverse invertebrate fauna. A total of 16 orders, 46 families and 93 genera were identified. Results suggest that the open water sites produced the largest number of organisms, whereas theTyphasites produced the greatest total biomass of invertebrates. Nine orders showed significant differences in abundance among vegetation communities, but there were no significant differences in biomass of orders among vegetation types. There were significant differences in the mean diversities among vegetation community types.Typhasites supported the most diverse populations of macroinvertebrates and the open sites produced the least diverse populations. The abundance of six orders was significantly different between years and may be attributed to fluctuating water levels. Our results suggest that the occurrence and abundance of certain macrophyte communities may enhance the quality of a marsh for consumers of macroinvertebrates.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663455

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Zooplankters were sampled from Lake Fayetteville and the Illinois River from March 1992 through March 1993. Zooplankton densities were significantly greater in the lake habitat than in the stream. Mean annual density was 633 ± 86/L in Lake Fayetteville, compared with 9 ± 1/L in the Illinois River. Significant seasonal differences in density were also observed. Maximum density was observed during fall, and minimum density during spring. There was also a significant two way interaction between habitat and season. This interaction indicated a much greater seasonal variation in zooplankton density in Lake Fayetteville than in the Illinois River. Depth distribution also was different between the lake and stream habitats. In Lake Fayetteville zooplankters were most abundant in the upper three meters of the water column, and abundance decreased significantly with water depth. The opposite was true of zooplankton abundance in the Illinois River. Plankters were most abundant nearest the bottom, and plankton density decreased significantly closer to the surface.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663456

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Floating chironomid pupal exuviae were collected throughout the Yakima River (Washington, USA) and tributaries in 1989 and 1990. All samples were taken during the October-November low-flow season and most sites were visited once with a sampling effort of approximately 10 minutes. Sampled stream segments ranged from 3rd to 7th order and elevation ranged from 140–1200 m. The total number of taxa distinguished in 77 samples was 150 with a mean of 24 per site. Species richness was not highly correlated with stream order or elevation. An ecological gradient defined by ordinating the taxa by site data was highly correlated with site elevation (r=.93). Comparison with published attributes of chironomid genera suggested that temperature regime was a dominant environmental variable controlling chironomid distribution in this basin. However, since most measured habitat variables were associated with altitude, their effects could not be separated. Cluster analysis of taxa by site data resulted in groupings that distinguished montane from valley sites and agricultural drains from other valley sites. Differences in species composition between moderately enriched agricultural drains and less-impacted sites were minor compared with the underlying elevation gradient.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663457

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A winter survey of a small upland river system, the Clogh River, Northern Ireland, was conducted to appraise the macroinvertebrate community in light of a reportedly declining fishery. Plecoptera were more abundant at the higher elevation sites; Ephemeroptera were more abundant at lower elevations; and Trichoptera were widely distributed but never abundant. With reference to functional feeding groups, grazers/scrapers and collectors were widely distributed at all elevations, while most shredders were found at higher elevation sites. The transition from dependence on allochthonous to autochthonous energy inputs, based on the composition of the community, appeared to occur approximately at the 1–2 stream order boundary. This is probably due to the sparse riparian vegetation and lack of shading on most stretches of this river.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663458

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Depth, alkalinity, pH, and conductivity distributions; substrate preference; and turbidity tolerance were used to explain species groupings formed by association analysis for 62 species of Wisconsin lake plants. Three out of five plant groups could be largely explained by substrate. Turbidity tolerance helped define differences between hard and soft substrate species. Water chemistries explained species groupings within soft substrate species and among a group of plants that did not commonly associate with other species. The habitat factors and adaptations studied did not successfully explain a group of plants found in “mesic” water chemistries and varying substrate and turbidity conditions.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663459

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The septa lengths of bivalve shells were used to estimate shell lengths of the largest zebra mussels (Dreissena polymorpha) crushed and consumed by freshwater drum (Aplodinotus grunniens) to determine if size limitation could preclude the effectiveness of drum as a biological controller of the zebra mussel. We examined gut samples of drum (273 to 542 mm long) collected from western Lake Erie in 1991, found the largest mussel (shell length = 21.4 mm) in the 11th largest drum (TL = 405 mm), and observed a reduction of mussel size in larger drum. The lack of a relationship between mussel size and drum size for larger specimens suggests that either drum prefer smaller mussels or the gape between the upper and lower pharyngeal teeth restricts drum feeding to zebra mussels of limited size. Although drum may reduce zebra mussel populations, because of the apparent size limitation of prey it is unlikely that drum would be fully effective as a biological controller; thus, this fish should not be introduced beyond its native range for that purpose.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663460

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Community impacts of larval walleye (Stizostedion vitreum vitreum) and nutrient addition were examined in an experimental enclosure study. Larval walleye significantly suppressedDaphnia, DiaptomusandCyclops, but enhanced rotifers. Suppression of zooplankton by larval fish alone did not increase phytoplankton blooms unless fertilizers were added. Nutrient levels (NH3-N, NO3N, and PO4-P) were enhanced in enclosures with fertilizer additions, but were not enhanced in enclosures with both fish and fertilizer additions. Fertilizer applications significantly increased phytoplankton biovolume, pH and dissolved oxygen, but did not increase zooplankton biomass. The highest algal abundance was found in enclosures with both fish and fertilizer additions. This could be due to the release of zooplankton grazing pressure by fish together with nutrient enrichment. Our results suggest that larval fish are important in regulating the zooplankton community, but their effects on phytoplankton depend on nutrient availability.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663461

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Length frequencies and diets of smallmouth bass (Micropterus dolomieui) captured from two small ponds by sport fishing and by electrofishing were compared to determine if fishermen's catches were similar to those acquired by electrofishing. The sport-caught fish (N=79) had a mean total length of 32.5 cm (range = 15.6 to 52.0 cm); the electrofished smallmouth bass (N=134) had a mean length of 26.2 cm (range = 8.0 to 47.1 cm). There was no significant difference in total lengths of smallmouth bass from the two ponds. Sport-caught fish were significantly larger than electrofished fish (p < .001). Of 213 smallmouth bass, 93 had empty stomachs, 113 had only one prey type, either crayfish (Orconectes virilis) or fish (Lepomissp.). There was a highly significant difference in prey items of smallmouth bass captured by sport fishing and by electrofishing (p < .001). Crayfish was the most frequent prey item in angler-caught smallmouth bass while fish (Lepomissp.) was a more frequent prey item among electrofished smallmouth bass.

ISSN:0270-5060    

DOI:10.1080/02705060.1995.9663462

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor