摘要:

Dursban, an organophosphorus insecticide, was applied on June 3, June 18, and July 1 to eight shallow (24 cm) experimental ponds near Bakersfield, California. Four ponds were treated at 0.028 kg/ha (=0.025 lb./acre), four were treated at 0.28 kg/ha, and four were kept as controls. Phytoplankton, zooplankton, and insect populations were sampled on 21 dates between May 20 and August 16. Insect larvae and nymphs were more reduced in numbers than were insect adults, reflecting in part the ability of the latter to emigrate and immigrate. Twenty—four—hour posttreatment samples for the second and third, but not first, treatments showed greater reductions of predaceous Notonectidae, Dytiscidae, Coenagrionidae, larval Hydrophilidae) than of "herbivorous" (Corixidae, Baetidae, adult Hydrophilidae) insect populations. Predaceous insect populations generally recovered to control—pond levels more slowly than herbivorous insect populations. Five weeks after the last insecticide treatment, predaceous insects averaged only 45% and 9% as abundant in low dose and high dose ponds, respectively, as they were in control ponds (P<0.02); corresponding figures for herbivorous insects were 108% and 206% (P<0.10). Initially, Cyclops vernalis and Moina micrura were the only crustacean zooplankters present, and both experienced high mortality due to treatments. Recovery in low dose ponds was variable, requiring 1—3 weeks, and in high dose ponds occurred only 3—6 weeks after the final treatment. Populations of Diaptomus pallidus seemed unaffected by the lower rate of treatment, but became large only after Cyclops populations had been reduced by the insecticide or other factors. Ceriodaphnia sp. became abundant in late July or early August in all four control ponds but not in any treated ponds. Herbivorous rotifers, principally in the genera Brachhionus, Polyarthra, Hexarthra, Filinia, and Tripleuchlanis, increased dramatically, often five— to twentyfold, within 1—3 days after Moina and Cyclops populations were decimated by Dursban, but became abundant in control ponds only during the brief absence of Moina in early July. All planktonic rotifers, except Polyarthra, were more abundant in treated than in contro ponds; all benthic—littoral rotifers (e.g., Lecane, Monostyle, Tripleuchlanis, Platyias, Lepadella, Testudinella) were more abundant in control than in treated ponds. The predaceous rotifer Asplanchna brightwelli was 35 times more abundant in treated than in control ponds, feeding primarily on herbivorous rotifers, sometimes on Cyclops, Diaptomus, Moina, and large algae, and rarely on small mayfly (Baetidae) nymphs and chironomid larvae. Asplanchna populations were composed of three morphotypes, ampulliform, cruciform, and campanuliform, the last of which tended to be highly cannibalistic. The "wings" of humps of the cruciform morphotype apparently represent a mechanism for minimizing such cannibalism. The reduction of herbivorous crustaceans by Dursban and the restraint of herbivorous rotifers by Asplanchna predation permitted the rapid increase of phytoplankton populations in treated ponds and, even 6 weeks after the last treatment, the phytoplankton was two and 16 times more abundant in low dose and high dose ponds, respectively, than in control ponds. Blooms of bluegreen algae (Anabaena, Anabaenopsis) developed in three high dose and one low dose pond, and a bloom of the diatom Synedra developed in one low dose pond. The long—spined alga Schroederia setigera seemed favored by high Moina and Diaptomuspopulations and low Cyclops populations. The significance of these results for insect—control programs is discussed.

ISSN:0012-9615    

DOI:10.2307/1942211

出版商:Ecological Society of America    

年代:1972

数据来源: WILEY

摘要:

Pollen analysis of several cores from the Dismal Swamp in southeastern Virginia have indicated that the swamp is a relatively young feature, having begun to develop along drainage lows as recently as the late—glacial. Formation of extensive fresh—water marshes along streams appears to have been brought about by general water—table changes controlled by the post glacial rise of sea level. As the sea continued to rise, marsh development proceeded inland and fine—grained organic sediments began to accumulate. By 6,000 years B.P. approximately 50% of Dismal Swamp area had been mantled by fine—grained peat deposits. From 6,000 to 3,500 B. P. peat accumulation continued, but at an appreciably lower rate. The corresponds both to the hypsithermal interval and to a distinct slackening in the rate of sea—level rise. By 3,500 B.P. peat had mantled virtually all of the interfluves and "islands" within the swamp. The pollen diagrams suggest a gradual change from boreal spruce—pine forests during the full—glacial, to somewhat less boreal pine—spruce during the early late—glacial, to hardwood forests containing many species characteristic of the present northern hardwoods forests during the latter portion of the late—glacial, to hardwood—dominated forests containing species now found in southeastern Virginia during the early postglacial. Although precise vegetational and environmental reconstructions are not possible, this general sequence suggests a unidirectional climatic amelioration from conditions comparable to those in northern New England during the full—glacial to a climate comparable to the present by 8,000 years B.P. The climate may have been warmer and drier during the hypsithermal, but the observed changes could just as easily be a result of a slackening in the rate of sea—level rise. The cypress—gum forests that have characterized the Dismal Swamp for the past 3,500 years have been variable both spatially and temporally. These variations doubtless reflect local differences in water table, peat depth, fires, wind throws, and a variety of human disturbances. The origin of Lake Drummond remains an enigma. It is a young feature of the swamp, apparently originating only 4,000 years ago. It is not the last vestige of an earlier open—water phase of the swamp.

ISSN:0012-9615    

DOI:10.2307/1942212

出版商:Ecological Society of America    

年代:1972

数据来源: WILEY

摘要:

Clutch size and related aspects of breeding biology were investigated in the Lapland Longspur (Calcarius lapponicus) and Snow Bunting (Plectrophenax nivalis) in the North American Arctic, and in allied temperate and subarctic species. Evidence was sought to test Lack's hypothesis that the increase in clutch size with latitude is related to the length of daylight available for the adults to collect food for their young, and that clutch size is ultimately determined by the average maximum number of young for which the parents can find food. The arctic species were studied mainly at 76° N on Devon Island; some additional data were collected elsewhere. Increase in clutch size with latitude was correlated with a decrease in the adults' night rest period from 7 hr at 50° N to 3—5 hr in the Arctic. In the Lapland Longspur in Canada clutches were larger at high latitudes and at localities with early breeding seasons. Clutch size and latitude were not significantly related for those localities where activity of adults attending nestlings is not restricted by daylength. Differences in clutch size were not attributable to geographic or interspecific variation in hatching asynchrony, hatching success, or growth of the young. Hatching of Lapland Longspur and Snow Bunting clutches on Devon Island corresponded closely with the emergence of the adult insects which predominate in the nestlings' diet, but other factors may also influence the timing of the breeding season. The decline in clutch size in these single—brooded species as the season progressed apparently was not related to changes in the environmental food supply. In the multiple—brooded Chestnut—collared Longspur (C. ornatus) in Saskatchewan clutch sizes changes little during the season. Annual differences in clutch size were demonstrated in the Snow Bunting, but their significance is unknown. Although Snow Bunting clutches of seven are rare on Devon Island, more young were fledged from experimental broods of seven than from smaller broods, but the young averaged lighter in weight. Adults feeding large broods made more visits to the nest each day and were lighter in weight than those with small broods, but the visiting rate per young was less in large broods. Much of the variation in clutch size, including the increase with latitude, is related to environmental factors influencing the food—gathering potential of the adults. But this does not mean that clutch size has evolved to a limit set by the environmental food supply, because food—gathering behavior and related morphology have also evolved by natural selection. Clutch size must be determined by the effects that changes in it and other aspects of reproductive strategy have on the probability of survival of both the adults and their offspring.

ISSN:0012-9615    

DOI:10.2307/1942213

出版商:Ecological Society of America    

年代:1972

数据来源: WILEY

摘要:

The relationships between drift rates, population density, production rates, key environmental factors, and movements of adults were studied in two populations of stream insects, the caddisfly Oligophlebodes sigma and the mayfly Baetis bicaudatus. Samples of benthic invertebrates (424 total) were collected every 28 days at four stations on Temple Fork of the Logan River, Utah, from October 1967 to September 1969. Samples of drift invertebrates (181 total) were collected every 14 days at three stations on Temple Fork during the same period. During June—September a day and a night drift sample (681 total) were collected every other day. Drift rates of O. sigma larvae were greatest (5,987 g/year) when biomass in the benthos (2.56 g/m2) and production (4.30 g/m2per year) were greatest. Total production (dry weight) of O. sigma larvae in the stream (bottom area = 29,487 m2) was 89.0 kg in 1968 and 80.8 kg in 1969. Total production of B. bicaudatus nymphs was 41.3 kg in 1968 and 39.8 kg in 1969. Drift rates of O. sigma larvae were related directly to biomass in the benthos over an entire year. Drift rates of O. sigma and B. bicaudatus were not related directly to density expressed as numbers/area in the benthos. Drift rates were correlated positively and significantly (r = 0.78 and 0.55 for day drift of O. sigma and B. bicaudatus, respectively) with density during the months of June—September for both O. sigma larvae and B. bicaudatus nymphs. Discharge, distance below the spring source of Temple Fork, and densities of competing aquatic insects were other factors of significance in the multiple—regression analyses of factors affecting drift rates of the two insects. The 17 or 18 independent variables used in the multiple—regression analyses accounted for 65% and 55% of the variability in day drift rates of O. sigma and B. bicaudatus, respectively. Adult O. sigma (but not B. bicaudatus) undertook a definite upstream migration estimated at 2—3 km. This flight of adults resulted in a concentrated deposition of eggs in the upper reaches of the stream. The advantage of the upstream flight may be that it stores reproductive products in areas where they are relatively safe from effects of anchor ice during winter and of floods in late winter and early spring.

ISSN:0012-9615    

DOI:10.2307/1942214

出版商:Ecological Society of America    

年代:1972

数据来源: WILEY