ISSN:0012-9658    

DOI:10.2307/1935487

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The grass shrimp, Palaemonetes pugio, is a dominant species uniquely adapted to a highly stressed tidal marsh embayment. Monthly sampling of length and dry weight revealed that its life cycle was a single year, with spawning in May, June, and July and most rapid growth in late summer and fall. Mark and recapture estimates conducted quarterly and quadrat net estimates calculated monthly indicated that shrimp were present throughout the year and that densities peaked in the fall (over 1.2 million in 0.01 km2 in October). Production of biomass (growth) equated loss to predation (including decomposition) over the annual cycle, averaging 0.2 kcal°m—2°day—1. Respiration averaged 1.1 kcal 1.1 kcal°m—2°day—1. Average daily production per square meter of total consumables (fecal pellets = 0.8 kcal, dissolved organic matter [DOM] = 0.7 kcal, biomass = 0.2 kcal) was 60% of total ingestion (2.9 kcal); production of feces and DOM thus outweighed biomass production 15:2. Microcosm studies and observations by scanning electron microscope revealed that shrimp macerated detritus into a heterogeneous assortment of uneaten particles by plucking away the cellular matrix from surfaces of large detrital fragments. This action provided cavities that became heavily invaded by pennate diatoms, and particles that became suspended in the water column and populated by bacteria. Nutrient analyses indicated the shrimp excreted large quantities of ammonia and phosphate which together with DOM release was presumably responsible for heavy growth of microflora and increased protein fraction in both feces and large and small uneaten detrital fragments. Palaemonetes pugio, while supporting its own trophic requirements, accelerated breakdown of detritus, preventing blockages or accumulations that might have occurred from pulses of emergent grass and macroalgal detritus in the embayment. This repackaging into feces, heterogeneous fragments, DOM, and shrimp biomass made detrital energy available at a variety of trophic levels, smoothing out organic pulses over time and space, and raising the efficiency of transfer to the food web. The special adaptation of P. pugio to the low—oxygen environment of the decomposer system appeared to limit predation and competition, allowing the shrimp to develop large populations necessary to carry out its role effectively.

ISSN:0012-9658    

DOI:10.2307/1935488

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Vegetation studies in the Red Lake peatland, a patterned fen studded with forested islands, resulted in the recognition and description of plant communities typical of the following environments: Menyanthes pools, furrows, sedge—strings, forested tussocks, and forest hollows. Pollen analyses of 15 surface samples taken along a transect in the same area separated two distinct local pollen assemblages. The Larix forest assemblage corresponds to the forest tussock and forest hollow communities, and the sedge fen pollen assemblage corresponds to the Menyanthes pool, the furrow, and the sedge—string communities.

ISSN:0012-9658    

DOI:10.2307/1935489

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

A simulation model developed in the Grassland Biome Program of the US/IBP is applied to data gathered in the Coniferous Forest Biome Program to estimate the magnitudes and patterns of energy flow in breeding bird populations in Northwestern coniferous forests. Six stands along a moisture—temperature gradient in the central Oregon Cascades supported breeding avifaunus of 7—15 species, with standing crops of 223—526 g/ha. Total energy flow through these avifaunas during the April—October breeding season was estimated at roughly 10 kcal m—2season—1in the low—elevation, moderately xeric stands; 12 kcal m—2season—1in the high—elevation stands; 17 kcal m—2season—2in a mesic floodplain stand; and 21 kcal m—2season—1in a midelevationtransitional stand. About 1% of the seasonal energy flow was channeled into production, while reproduction—related processes accounted for 15%—16% of the total energy intake. Thermoregulation required 13%—19% of the seasonal total, with the higher relative costs associated with the cooler, higher elevation stands. Foiliage—gleaning bird species accounted for the greatest proportion of the energy intake at most stands, but within thisguild the importance of granivorousopportunistic species generally increased through the stand sequence as the growing season became shorter and environmental conditions more severe.

ISSN:0012-9658    

DOI:10.2307/1935490

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The object of our study was to compare the distributions of bird species common to two Andean localities in order to improve our understanding of the factors involved as primary causes in imposing distributional limits. A previous paper (Terborgh 1971) had evaluated the importance of three mechanisms in the avifauna of a control locality: (1) factors that vary continuously and in parallel with the elevational gradient, (2) competitive exclusion, and (3) ecotones. As was discussed in that paper, the method, when applied to a single transect, leads to a systematic underestimation of the incidence of competition—mediated limits and to an overestimation of ecotone effects. By studying appropriately selected test localities, we could overcome many of these deficiencies and obtain results that are several steps closer to expressing reality. The control locality, the Cordillera Vilcabamba, is a sector of the Cordillera Oriental, or eastern chain of the main body of the Peruvian Andes. It carries what may be regarded as a complete avifauna, as the transect sliced through a continuous belt of forested terrain which, at any elevation, is exposed to invasion by appropriately adapted species from above and below as well as laterally. It differs in this respect from the test locality (Cerros del Sira), which is an isolated massif that rises out of the Amazonian plain some 100 km east of the main Andes. Because of this isolation, the upper portions of the Sira are exposed to invasion principally from below. An estimated 80%—82% of the species that would have occupied the summit zone of the Sira, had it been a portion of the main body of the Andes, were missing. Such a species deficit provides an ideal test of the efficacy of competition in limiting distributions, because it invites whatever species are available as colonists (in this case, those lower on the mountain) to invade until the community is effectively filled. Of the species that had the opportunity to expand their elevational ranges in the absence of high—elevation congeners that apparently excluded them on the control transect, a minimum of 71% did so, confirming the original assignments of these as competition—limited species in the control locality. In addition, a majority (58%) of the species that had no high—elevation congener on the control transect (assigned to the gradient mechanism), and that had the opportunity to expand into the species—deficit zone of the Sira, were found to do so. This reveals that diffuse competition (as distinguished from the directly observable exclusion of congeners) was really the primary limiting mechanism for most of the species that had been assigned to the gradient mechanism in the control study. Instead of accounting for approximately a third of all distributional limits, as was concluded in the earlier report, it now appears that competition, both direct and diffuse, accounts for something more than two—thirds of the distributional limits of Andean birds whose ranges end somewhere between the lowland plain and tree line.

ISSN:0012-9658    

DOI:10.2307/1935491

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

In this paper variations in life history data among local populations of Atlantic salmon have been examined. The following patterns emerge: (1) The mean age of first spawning increases with the difficulty of upstream migration as estimated by the distance the fish ascend into freshwater. Other indices of river harshness yield similar results. (2) The effect of commercial fishing has been to eliminate larger and older fish from the run. Available evidence suggests that this has selected for an early age of first return on the Miramichi River and that the frequencies of genes coding for different ages of first spawning have been altered. (3) The mean age of first spawning is positively correlated with marine growth rates after the grilse stage. Rapid growth at sea subsequent to the grilse stage is associated with delayed reproduction; slower growth with an earlier age of first breeding. This result suggests different paths of high—seas migration. (4) The variability about the mean age of first spawning first increases and then decreases as one moves north over the salmon's range from Maine to Ungava. In addition, we have observed that these results are in accord with predictions made by recent theoretical analyses of the optimal reproductive response to differing environmental conditions. We, therefore, conclude that the observed patterns of variation in life history are adaptive. We further take the agreement between theory and nature as a validation of the hypothesis that populations will in general differ from each other in the manner of their respective optima.

ISSN:0012-9658    

DOI:10.2307/1935492

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Macroinvertebrates were identified from seven (0.2—2.7) minerotrophic peatlands (fens) in the Sagehen Creek basin, northern California, at 1,943—m elevation. Mean peat depth was 17.3—87.4 cm. Aquatic oligochaetes, certain species typical of oligotrophic lake benthos, dominated the fauna. Kincaidiana freidris (Lumbriculidae) and Mesenchytraeus sp. (Enchytraidae) were the most abundant species. Annual production of major groups was estimated by the Hynes and Coleman method. Oligochaete production ranged from 7.4 to 58 g°m—2yr—1and was positively correlated (r = 0.951) with mean peat depth of the seven fens. Production of ceratopogonids, chironomids, and nematodes was much less than that of oligochaetes (0.05—1.0 g°m—2yr—1). Annual turnover ratios averaged 6.7 oligochaets, 6.1 for ceratopognids, and 7.0 for chironomids.

ISSN:0012-9658    

DOI:10.2307/1935493

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Allelopathy seems to be the mechanism that allows Sassafras albidum to maintain itself in relatively pure stands through many stages of old—field succession. Field studies revealed that 10 species consistently occurred exclusively outside of clump canopies and 7 other species predominated beneath the sassafras canopy. We suggest that annual herbs are being effectively excluded from the understory flora. 2—pinene, α—phellandrene, eugenol, safrole, citral, and d—camphor were isolated were within and outside of sassafras stands from leaves, litter, soil, and roots. Germinating seeds watered with aqueous leachates of leaves, litter, and canopy washings showed varying degrees of radicle reduction during germination. Germination on soil discs from beneath sassafras stands was significantly lower in four of the test species; in seeds overwintered in sassafras litter it was significantly lower in all species. There was a positive correlation between α—phellandrene concentration and reduction in radicle growth in Acer negundo and Ulmus americana. Sufficient incoming and buried seeds were available to support a richer and more abundant understory flora than was found in the vegetational survey. The different modes of sassafras for releasing phytotoxins into the environment at different times of the year operate to continually influence its surroundings.

ISSN:0012-9658    

DOI:10.2307/1935494

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Similarity among avifaunas is calculated for both historical and current distributions of resident land birds of the Galapagos Islands. Multiple regression analysis indicates the variation in avifaunal similarity is accounted for primarily by variation in the similarity in composition of island floras and, to a much smaller degree, by isolation among islands. Thus, plant similarity and interisland distance seem the principal identifiable factors influencing avifaunal resemblance. Similarities among islands based on numbers of plant species, area, and elevation do not have a detectable effect. Variation in plant similarity among the Islands is explained largely by isolation, with area and elevation having a reduced, but significant, influence. Close to half of the variation in avifaunal similarity is unaccounted for by plant similarity and isolation. Characteristics of islands with avifaunas that deviate most from the predicted relationship suggest that small, outlying islands in a zone of infrequent and irregular rainfall may have populations of birds prone to extinction. This would have the effect of reducing similarity with most other islands. Compounding this, islands that are upwind most of the year in the prevailing trade winds of the region probably do not receive as many colonizers from other islands as do islands that are downwind. Average avifaunal similarity among congeners is less than among noncongeners. This would be expected if ecological incompatibility exists among congeneric species of the Galapagos, or if there is differentation owing, in part, to geographic isolation.

ISSN:0012-9658    

DOI:10.2307/1935495

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Dark uptake of35SO4was investigated as a possible method for estimating bacterial production rates in Castle Lake, California. Assuming a fixed cellular sulfur; carbon ratio, bacterial productivities determined in this manner ranged from 2.5 to 28 mg C°m.—3°day—1in 48 in situ measurements in the summer of 1972. Average production rates increased throughout the sampling period and corresponded in part to increasing levels of dissolved organic carbon. Production rates were stimulated by addition of NH4Cl and vitamin B12to water samples, but not by thiamine, biotin, SO4, NO3, PO4or a trace metal mix. Further studies on the sulfur content of bacteria and the role of phytoplankton in SO4uptake are required before dark35SO4uptake is used for routine field measurements.

ISSN:0012-9658    

DOI:10.2307/1935496

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY