Comparisons of benthic invertebrates between riffles and pools

Benthic species assemblages in upstream and downstream ends of riffles and in pools were investigated seasonally in the first five orders of an alluvial gravel stream with distinct pool and riffle channel form. Riffles comprised < 10% of stream area and were separated by pools with extensive bedrock substrate (ca. 15–85% of total surface area) which was scoured during periodic high flow. Virtually all taxa were more abundant in riffles than in pools, except chironomids which were more equally distributed. Inconsistent results were obtained for upstream-downstream comparisons within riffles. Intermittent headwater reaches (orders 1 & 2) which supported half as many taxa retained this pattern during periods of flow, although riffles at these sites were dry from mid-June to mid-November. Pools which contained more gravel, indicating less disturbance during high flow, had a richer assemblage of benthic species than other pools. Many invertebrates in pools may have been there as a result of drift from their preferred riffle habitats, but the presence of gravel in the pools indicates less intense flow disturbance during floods, provides protection from the mild scouring that does occur during floods, and provides refugia from predators.     

Colonization of a headwater stream during three years of seasonal insecticidal applications

We investigated recolonization by insects of a small headwater stream in the southern Appalachian Mountains that was treated along its entire length with an insecticide (methoxychlor). Initial treatment (December 1985) resulted in massive insect drift. Applications continued seasonally for three years, and drift was measured during each treatment. Taxonomic composition of the drift indicated several responses: (1) Some taxa were eliminated. (2) A number of taxa occurred only sporadically following initial treatment. (3) Early instars for some taxa showed seasonal occurrences which closely paralleled known life cycles and flight periods of adults. Groups which provided strong evidence for aerial recolonization included several Ephemeroptera, Plecoptera (Peltoperlidae and Isoperla spp.), and Trichoptera (Parapsyche cardis, Diplectrona modesta, Pycnopsyche spp., and Lepidostoma spp.). (4) Some long-lived taxa survived and exhibited distinct growth through several treatment periods. These include Odonata (Lanthus and Cordulegaster), some Ephemeroptera, and some Diptera (Tipulidae, Ceratopogonidae, and Tanypodinae). (5) Some taxa which were not present at the time of initial treatment appeared during the experiment. Chironomidae dominated the drift in all samples, and the number of genera did not decrease during the three-year treatment period. Of the 27 chironomid genera identified, only Micropsectra decreased in proportional abundance during treatment. In contrast, several genera (Corynoneura, Meropelopia, Parametriocnemus, and Tvetnia) showed little change in relative abundance. Larsia (Tanypodinae) increased in proportional abundance during the treatment period.     

仔鳗生态失调死亡率与肠道微生态系重调整的研究

本文报告,在1989年4月至1991年3月,为考察长江仔鳗资源的开发利用,对仔鳗生态失调死亡率及其防治方法做了一些研究。结果表明,仔鳗溯河性生态失调死亡率为49.8％(可信限为46.3～53.3％);寒冷性生态失调死亡率为48.59％(可信限为43.5～53.5％)。在实验中,应用肝浆(含B族维生素),在早期喂给仔鳗治疗有效(u=2.17>1.96,p<0.05);含抗生素食物喂给无显著性效果。应用由鳗鲡成鱼和黑斑泥鳅体内分离的肠微球菌、贝内克菌和非O-I群弧菌,喂给仔鳗进行肠道微生态系重调整(readjutment of intestinal microecosystem),对提高仔鳗生理功能适应性和降低生态失调死亡率有满意效果(u=2.84>2.58,p<0.01)。     

Ecological release in feeding behaviour: the case of bluegills in Japan

The stomach contents were analyzed monthly for each year-class to elucidate the foraging pattern of bluegills in a small vegetated lake by the frequency occurrence and the points methods. Seasonal dietary changes of the year-classes were considered comparing the monthly fluctuations in abundance of major prey organisms. Though these bluegills are dietary generalists and opportunists like those in North America, their foraging pattern was characterized by a relatively clearer dietary shift during ontogeny and a wider food niche including piscivorous than those of bluegills with congeners in their home land. Therefore this finding provides evidence of the ecological release caused by the absence of congeners.     

Effects of artificial light on the larvae of the firefly Lamprigera sp. in an urban city park,Peninsular Malaysia

Firefly populations are threatened globally by habitat alteration, pesticide use, and anthropogenic sources of light. Lamprigera fireflies were recently reported at an urban city park in Kuala Lumpur, Peninsular Malaysia. Here we report on the responses of Lamprigera larvae to artificial light from street lamps on paved park trails. Larvae were located farther from artificial light sources when street lamps were illuminated than when they were not, and mostly where light intensities were lowest, off park trails. Larvae that were located within the direct field of illumination tended to be immobile, whereas, when street lamps were turned off, they actively travelled paved trails. Larvae positioned directly in the path of downwelling light from street lamps at dusk may therefore experience an effectively longer diurnal period, limited time for active foraging, and greater exposure to pedestrian traffic.