摘要:

An annual energy budget is presented for Bear Brook, a small undisturbed second—order stream in northeastern United States. The ecosystem approach, in which all input and output fluxes of potential energy as organic matter are considered, is used to describe the dynamics of energy flow in a 1,700—m segment of the stream. The annual input of energy to the system is 6,039 Kcal/m2. Over 99% of this is allochthonous, from the surrounding forested watershed or from upstream areas. Autochthonous primary production by mosses accounts for less than 1% of the total energy available to the ecosystem. Algae and vascular hydrophytes are absent from the stream. Meteorologic inputs (litter and throughfall) from the adjacent forest account for 44% of annual energy input. Most of this is in particulate form. The remaining 56% of input enters by geologic vectors (inflowing surface and subsurface waters). Eighty—three per cent of the geologic input and 47% of the total input of energy occur as dissolved organic matter. Approximately 4,730 Kcal/m2of organic detritus, nearly equally divided between leaves and branches, is stored within the system. The size of this detritus reservoir is stable from year to year. The turnover time of the branch compartment is about 4.2 years; of the leaf compartment, about 1 year. Although much of the annual input of energy is in a dissolved state, dissolved organic matter does not tend to accumulate in the system and displays a very rapid rate of turnover. Sixty—six per cent of annual energy input is exported to downstream areas in stream water. The remaining 34% is lost as heat through consumer activity. Bear Brook is a strongly heterotrophic steady—state system in which import and export of organic matter play a significant role. A conceptual scheme is presented by which import, export, photosynthesis, and respiration may be used to describe the functional dynamics and developmental processes of ecosystems.

ISSN:0012-9615    

DOI:10.2307/1942301

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Wizard Island, a ½—square—mile volcanic cinder cone located in Crater Lake, Oregon, was sampled by continuous belt transects. Separation of the one herbaceous and four forested community types, which were mapped as major vegetation units, was remarkably distinct, as 60% of the herbaceous species were found in only one or two communities. Physical factors such as the distribution and stability of substrate materials, temperature extremes, and soil—moisture availability exert the greatest control over plant community structure and development. Biotic factors have reduced effects on the generally sparsely vegetated island. The unstable cinder slope community was dominated by Polygonum newberryi Small., Eriogonum pyrolaefolium Hook. var. coryphaeum T.&G., and Arenaria pumicola Cov.&Leib. Pinus albicaulis Engelm. constituted 55% of the importance value of the crater rim community, but appears to be declining in importance. Pinus contorta is invading the crater area and may slowly replace P. albicaulis. Other characteristic crater rim species were Holodiscus microphyllus Rydb. var. glabrescens (Greenm.) Ley. and Castilleja applegatei Fern. The lower cone and north slope forests were dominated by Abies magnifica Murr. var. shastensis Lemm. and Tsuga mertensian (Bong.) Carr., with Pinus monticola Dougl. the only other important tree species. An importance value of 51% for T. mertensiana in the north slope community as compared with 25% in the lower cone reflects the cooler, moist microclimate and greater community maturity on the north slope. The more tolerant T. mertensiana increases in importance as the stands mature. Characteristic shrub and herb species were Vaccinium membranaceum Dougl. and Luzula glabrata (Hoppe) Desv. in the north slope, and Arctostaphylos nevadensis Gray and Pyrola secunda L. in the lower cone communities, respectively. The lava flow community was largely restricted to recesses between lava ridges where moisture and soil conditions are improved. Tsuga mertensiana was the dominant tree species on the lava flow at 51% importance value, with Sambucus microbotrys Rydb. and Cheilanthes gracillima D. C. Eaton as indicators of the shrub community development was and herb strata. Diversity, total plant density, and herbaceous and shrub community development was greatest in the favorable forest microclimates of the north slope. The north slope, crater rim, lower cone, cinder slope, and lava flow communities had 28, 23, 21, 12, and 10 nonarborescent species, respectively. The reported vascular flora of the island comprises 105 species and varieties. The best forest development occurred in an encircling belt at about 6,400—6,500 ft (1,950—1,980 m) elevation, but tree species characteristic of an elevational range of 2,500 ft (820 m) are telescoped onto the 760—ft—(250—m) high island. Substrate and local climatic diversity and climatic moderation due to lake effects and shielding by the caldera wall permit survival of trees above their usual elevation range. Tree invasion on the upper cone (particularly of Tsuga mertensiana) is slowed more by unstable slopes than by climatic severity. Mat—forming plants, such as Arctostaphylos nevadensis and Penstemon davidsonii Greene, anchor the substrate and serve as nurseries for tree seedlings. Ecesis of tree seedlings on the lava flow occurs only in crevices which exhibit some soil development and microclimatic amelioration. Log density—size class plots gave a straight line relationship for north slope tree species, but all other community types had marked density reductions in some size classes. As such, the north slope community is considered to be in equilibrium at the present level of substrate and microclimatic alteration.

ISSN:0012-9615    

DOI:10.2307/1942302

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Measurements of the abundance of major populations, their metabolism, and the seasonal patterns of total system metabolism throughout a year were used to develop energy—flow diagrams for a New England salt—marsh embayment. The annual ecological energy budget for the embayment indicates that consumption exceeds production, so that the system must depend on inputs of organic detritus from marsh grasses. Gross production ranged from almost zero in winter to about 5 g O2m—2day—1in summer. Respiration values were similar, but slightly higher, with the maximum difference observed in fall. Populations of shrimp and fish were largest in fall, with a much smaller peak in spring. Few animals were present in the embayment from May to July, but fall populations of shrimp ranged from 250 to 800 m—2and fish averaged over 10 m—2. Birds were most abundant in winter and spring. In spite of high numbers, no evidence was found that the marsh embayment exported large amounts of shrimp or fish to the estuary. Production of aboveground emergent grasses on the marsh equaled 840 g m—2for tall Spartina alterniflora, 432 g m—2for short S. alterniflora, and 430 g m—2for S. patens. These values are similar to those for New York marshes, but substantially lower than the southern marsh types. The efficiency of production of marsh grasses in the New England marsh was lower than reported for southern areas. A simulation model based on the laboratory and field metabolism and biomass measurements of parts of the embayment system was developed to predict diurnal patterns of dissolved oxygen in the marsh. The model was verified with field measurements of diurnal oxygen curves. The model indicated the importance of the timing of high tides in determining oxygen levels and was used to explore simulated additions of sewage BOD and increases in temperature.

ISSN:0012-9615    

DOI:10.2307/1942303

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Wild D. pseudoobscura flies were captured, marked, and released in relatively low numbers at nine separate, centrally located sites in each of two Colorado, U.S.A., locations in midsummer 1970. The flies were marked by spraying with micronized dusts which fluoresce in characteristic colors under ultraviolet light. The dusts are harmless, they mark the flies well, and they are not transferred from one fly to another. The trapping design extending out from the central release points contained additional traps on eight evenly spaced radii. Data on the number of captured, unmarked flies and recaptured, marked flies in the central and outlying traps provided maximum likelihood estimates of adult density and dispersion. These data were adjusted for the presence of a sibling species, D. lowei, by means of an accurate morphological technique which permits classification of the two kinds of males. Preliminary analyses indicated that dispersal estimates made during an evening activity period 1 day after release of marked flies pertain mostly to dispersion during the intervening morning activity period, when no traps were exposed. It was necessary to base estimates of both density and dispersion on trapping days following days when only a few or no traps had been exposed in the habitat. The minimum attractive radius of a trap was approximately 46 m. The estimates of density at both locations were similar, averaging 0.38 flies/100 m2. An independent and much simpler estimate of density, based on the number of flies captured at the center trap, gave inconsistent results. This was attributed to accidental interference with normal fly activity. The mean distance (d) of marked flies from the release points after 1 day (presumably after one morning activity period) was 176 and 202 m at the two locations. The mean—squared distance (d2°) was 97 and 146, respectively, in units of 400 m2. The estimates for the first location are more reliable because those data were more homogeneous and extensive. The patterns of the observed dispersion agreed well with Brownian motion expectations on the basis of comparing first— and second—order moments of distance dispersed. This permitted the construction of graphs which depict the spread of released flies with an increasing number of activity periods. An activity parameter °, the standard deviation of dispersed flies along one direction in a two—dimensional environment, was estimated from @ under the assumption of Brownian motion (°b.m.) and without this assumption (°D.F.). These estimates refer only to the observed dispersion. At the first location the values were 141 and 139 m, respectively; at the second they were 162 and 171. Closer inspection of the observed dispersal patterns, accompanied by further analyses of the data, revealed a departure from Brownian motion and probably serious underestimates of the true dispersal rates. A certain proportion of flies dispersed rapidly to points outside the experimental area during the morning activity period following an evening release. Using an estimate of 95.3% daily survival of marked flies, 2—day dispersal data suggested that more than half the flies had moved beyond the experimental area in two morning activity periods. The earlier experiments on density and dispersion of D. pseudoobscura, conducted by Dobzhansky and Wright in California, were re—analyzed by the present methods. Midsummer density of wild flies in Colorado was one—seventeenth that on Mt. San Jacinto in southern California, and three—fifths that at Mather in the Sierra Nevada of central California. Comparison of °d.f. estimates indicated that the wild Colorado flies dispersed at a rate approximately 50% greater than the laboratory flies released in California, even though the latter probably had more opportunity for dispersion. This difference may result partly from an adaptive strategy for greater dispersion of flies in low density habitats, and partly from a fundamentally different behavior of wild and laboratory flies. The large values of °d.f.(which are underestimates due to dispersion beyond the experimental areas) in both Colorado and California suggest that natural populations of D. pseudoobscura are not broken up into a number of very small breeding units within which allelic variation could be stored by genetic drift. Wright's panmictic circle concept yielded estimates of effective population size (Ne) between 1,000 and 10,000 in both Colorado and California. According to existing theory, these values are not large enough to maintain the allelic diversity known to exist for certain enzyme loci. The need for more sophisticated experiments to determine which components of dispersion are most closely associated with distribution of emergence sites of parents and offspring is discussed.

ISSN:0012-9615    

DOI:10.2307/1942304

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Palynological investigations of spring deposits were conducted as part of an interdisciplinary research effort into late Pleistocene archaeology, geology, and paleoecology of the western Missouri Ozarks. The springs, located in the Pomme de Terre River valley in Benton and Hickory Counties, Missouri, lie 400 km south of the maximum extent of the Wisconsin ice sheet on the present Great Plains—Eastern Deciduous Forest border. The valley will soon be flooded by a government impoundment. Two springs were completely excavated and three others sampled, including a spring originally excavated by Albert Koch in 1840. The pollen record, with associated plant macrofossils, is divided into three distinct zones: a lower nonarboreal pollen (NAP) and pine zone, a middle spruce— (Picea) dominated zone, and an upper zone of spruce with deciduous elements. Radiocarbon dates show that the NAP—pine zone was established prior to 40,000 BP and existed until 20,000—25,000 BP; it was deposited during the mid—Wisconsin interstade. The mid—Wisconsin interstadial vegetation of the Ozarks is interpreted as an open pine—parkland. Plant macrofossils of Pinus banksiana in this zone indicate that jack pine was present. Spruce was probably absent as no spruce macrofossils and only traces of spruce pollen were found. The associated mid—Wisconsin fauna is dominated by mastodon (Mammut americanum) with horse (Equus) and musk—ox (Symbos). With the onset of late Wisconsin full—glacial conditions, variously dated at 20,000—25,000 BP, pollen dominance shifts from NAP—pine to spruce. This is interpreted as the replacement of the pine—parkland by boreal spruce forest. Two pollen zones are apparent within the full—glacial: an older zone with up to 92% spruce pollen occurring after the transition from NAP—pine to spruce, and a younger zone with less spruce (38%) and more thermophilous deciduous tree pollen. The change to less spruce and more deciduous tree pollen apparently reflects slightly improved climatic conditions during a late phase of the full—glacial; the zone is radiocarbon dated at 16,500 BP on spruce logs. It contains abundant spruce and larch (Larix) macrofossils associated with the remains of at least 30 mastodons plus giant beaver (Castoroides), ground sloth (Paramylodon), tapir (Tapirus), deer (Odocoileus), and horse (Equus). The western Missouri Ozarks were covered by open pine—parkland from at least 40,000 BP until the start of the full—glacial 20,000—25,000 BP, then boreal spruce forest until at least 13,500 BP. Deciduous elements became more prominent in the spruce forest in its latter phase. The present oak—hickory forest developed after the decline of the spruce and is thus no older than postglacial.

ISSN:0012-9615    

DOI:10.2307/1942305

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY