ISSN:0012-9658    

DOI:10.2307/1936178

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

A controlled experiment performed on 8 small mangrove islands constituted an exact test of several biogeographic hypotheses which had rested largely on unsatisfying statistical treatments. The islands were censused for arboreal arthropods; each contained a different subset of a species pool of °500. Sections of the islands were then removed and censuses retaken after a waiting period; this procedure was repeated on four islands a second time. The results were consistent with a model which posits the islands as originally in a state of dynamic equilibrium between immigration and extinction, then re—equilibrating quickly when forced into an oversaturated condition. It was specifically demonstrated that: (1) species number increases with island size alone, independent of habitat diversity; (2) the increase with area is faster on separate islands than on increasing subsections of one island; (3) the area effect and the underlying dynamic equilibrium are not due only to an increased sample of transients and vagrants on larger islands, though there are a number of species which are particularly prone to quick extinction and which contribute disproportionately to the observed high turnover rates; and (4) prediction of the effects of decreased area on species composition can be stochastic at best, not deterministic. The equilibrium theory prediction of higher turnover rate on smaller islands could not be conclusively tested because of small sample size. Several species interactions suggested by the distributional data are so subtle that it is apparent that much more intensive work will be required to demonstrate even the existence of interactions, let alone whether they are important. It is clear that much of the dynamic equilibrium and its associated turnover in this system can be ascribed to individual species characteristics and the effects of a rigorous physical environment.

ISSN:0012-9658    

DOI:10.2307/1936179

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The Little Sioux fire of May 1971 burned most of the mixed coniferous—deciduous forest on the watersheds of Meander and Lamb lakes, two small, low conductivity lakes located in the Boundary Waters Canoe Area (BWCA) of northeastern Minnesota, USA. During 1972, hydrologic and chemical (Ca, Mg, K, Na, and P) budgets were determined for the terrestrial watersheds of Meander and Lamb lakes and for the lakes themselves. Budgets were also measured for Dogfish Lake, a lake physically and chemically similar to Meander Lake but whose watershed was not burned in the Little Sioux fire. These budgets show that the atmosphere supplies a significant fraction of the cations and phosphorus (Ca, 90%; Mg, 35%; K, 95%; Na, 55%; P, 95%) to the BWCA watersheds, with the remainder coming from chemical weathering. The budgets are similar to those reported for other Canadian Shield lakes and watersheds. The impact of the Little Sioux fire on nutrient fluxes was evaluated by comparing the budgets measured at Dogfish Lake with those measured at Meander Lake. This comparison showed that as a result of the burning of Meander Lake watershed, runoff increased 60% and the K and P exports increased 265% and 93%, respectively. The exports of Ca, Mg, and Na did not change significantly. The increase in runoff, probably due to the reduction in vegetative transpiration, is comparable to that measured after the 1970 Entiat fire (western Washington) and to that resulting form clear—felling experiments at Hubbard Brook (New Hampshire) and Coweeta (North Carolina). The increased nutrient losses after fire are less than those observed at Hubbard Brook and Coweeta. There was no indication of a drastic increase in nitrate export such as occurred after the Entiat fire and at Hubbard Brook. The increase in phosphorus loading of Meander Lake due to the fire was 38% (to 25 mg/m2°yr), a value that probably falls within the natural year—to—year variation in supply, and it did not represent a major impact on Meander Lake. Fire is a natural part of the BWCA forest ecosystems. The results of this study indicate that nutrient losses after the Little Sioux fire were minimal, perhaps because it was a spring fire. Fall fires may cause larger nutrient losses because more of the forest—floor material is likely to be consumed and revegetation does not begin until the following spring.

ISSN:0012-9658    

DOI:10.2307/1936180

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Environmental control of algal standing crops in two non—stratified prairie lakes in South Dakota and Minnesota, USA was investigated by season for 3 years. Multiple regression analysis was performed using chlorophyll a concentration and cell counts as dependent variables. In both lakes physical factors (light, temperature, wind stress and rainfall) were more frequently correlated with changes in algal standing crops than were nitrogen and phosphorous. Both lakes indicated occasional positive correlations with nitrogen. The correlations were greater in the deeper lake. Phosphorous was positively correlated during one season in the deeper lake, never in the shallower lake. Multiple regression analyses using concentrations of nitrate, ammonia, and orthophosphate as dependent variables and physical factors, algal abundance and zooplankton abundance as independent variables showed positive correlations between increases in orthophosphate and nitrate and prior rainfall and wind stress. Ammonia showed strongest correlations with wind stress. The correlations between wind stress and nutrient levels are assumed to result from recirculation of nutrients released at the sediment surface by circulation of the water column and by direct stirring of sediments in shallow water by wave action. The more extensive direct stirring of sediments in the shallower lake is assumed to partially account for the much higher levels of nutrients observed. Depth of lake relative to depth of wave action determines to what extent the sediments of a shallow lake are subject to direct stirring.

ISSN:0012-9658    

DOI:10.2307/1936181

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The sex ratio of Dark—eyed Juncos wintering in the eastern and central United States and Canada varies clinally along a latitudinal gradient. The percentage of @V @V among both museum skins and live—caught birds is °70% in the south, 20% in the north. When abundance according to latitude is also considered, an average ♀ appears to winter farther south than an average ♂ and hence probably tends to migrate farther. Latitude alone is an excellent predictor of sex ratio (r2= 85%), and latitude plus 13 other measures of climate explain virtually all the variation (r2= 96.6%). Extreme measures of climate, as compared to mean measures, are equally predictive. Principal component analysis indicates that snowfall, temperature, and latitude are the most important climatic variables associated with sex ratio. Because ♂ ♂ average larger than ♀ ♀ and are concentrated northward, mean wing length increases with latitude and is significantly correlated with climatic measures that vary with latitude. Further, larger birds within each sex may select higher altitudes as wintering sites. Sex ratio does not vary measurably with date in wintering populations. Among possible explanations for clinal variation in sex ratio are sex—associated differences in (1) advantages of early arrival on the breeding or wintering grounds, (2) impacts of inter— and intrasexual competition, and (3) effects of low temperature and intermittent food availability. Comparison of ♂ ♂ and ♀ ♀ with respect to potential fasting endurance, a size—related metabolic parameter, indicates that at 0 degrees C an average ♂ should be able to fast 4% longer (1.6 h) than an average ♀ at standard metabolic rates. An extremely heavy 7 ♂ might endured fasting up to 29% (10.7 h) longer than a very light ♀. These differences may confer greater survival ability upon the ♂ at latitudes where snow cover can often preclude feeding.

ISSN:0012-9658    

DOI:10.2307/1936182

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The aboveground biomass of the herb stratum, including woody species up to 30 cm tall, was determined by harvesting annually over a 4—yr period (1969—72) in aspen, maple—aspen—birch, birch, northern hardwood, and logging road communities. Average aboveground biomass in the respective community types was 117.5, 63.0, 51.0, 37.6, and 80.6 g/m2. Root biomass was determined by harvesting the belowground part on selected plots in 1971. Cumulative solar energy received at the sample points was measured with a chemical integrating light meter (petroleum ether chlorophyll extracts). Phenological observations indicated that net annual production in the four forest types was essentially equal to their end—of—season standing crop biomass. Average root:top ratios ranged from 2.98 to 4.79 and were higher in the dry communities (birch and northern hardwood) than in the other more mesic forest. Except for the logging road, two to five species accounted for most of the biomass in each community. Significant positive correlations were found between incident solar energy and aboveground biomass. Efficiency ranged from 0.82% to 2.19% based on May—October cumulative energy in the visible spectrum and cover adjusted aboveground biomass.

ISSN:0012-9658    

DOI:10.2307/1936183

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Autumn—shed leaves of white oak (Quercus alba) and pignut hickory (Carya glabra) were fastened together and incubated in a third order hardwater stream in south—western Michigan. At biweekly intervals, leaves were removed and the microbial populations assessed. Direct counts of bacteria increased logarithmically with time, but viable counts were generally lower. Flexibacter, Achromobacter, Flavobacteria, Pseudomonas, and Cytophaga were isolated from leaves. No apparent bacterial succession was detected. The mycoflora was assessed in five ways, including direct examination and incubations ranging from environment simulating to particle platings on nutrient medium. Although this last technique suggested that common soil and litter fungi dominated, direct examination and environment—simulating incubations showed that aquatic hyphomycetes, particularly Alatospora acuminata, Flagellospora curvula, and Tetracladium marchalianum were the dominant members of the mycoflora. The successional pattern of these fungi on both leaf species is discussed. It is concluded that the aquatic hyphomycetes are actively growing and completing their life cycle in this environment and that the terrestrial fungi are normally present mainly in a dormant state, growing and sporulating only in greatly enriched conditions. The highest ATP levels observed corresponded to the periods of highest fungal frequencies .

ISSN:0012-9658    

DOI:10.2307/1936184

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

The weight loss and changes in the concentrations of major classes of macro—molecules were assessed in white oak (Quercus alba) and pignut hickory (Carya glabra) during processing in a third order hardwater stream in southwestern Michigan. Oak was processed more slowly than hickory. An initial rapid weight loss in hickory was followed by a linear rate of loss, while oak lost weight at a linear rate over the entire processing period. Losses of soluble reducing sugars and polyphenols were rapid, occurring mainly during the initial 2—wk exposure to the stream. Hemicellulose and cellulose losses were similar in both species and nearly paralleled weight loss. An absolute increase in the lignin fraction was observed in both species during the first 6—12 wk of processing. We consider this to be due to an increase of complexed N containing compounds in the lignin fraction. Lipid loss was intermediate between soluble sugars and polyphenols and the structural components. Of the constituents analyzed, only the concentration of Kjeldahl nitrogen and lipid was significantly higher in hickory than in oak leaves during the entire processing period.

ISSN:0012-9658    

DOI:10.2307/1936185

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Species diversity, microhabitat separation, microhabitat shifts and body size patterns are examined in seven sympatric rodent species. Habitat separation and seasonal shifts are identified by multiple—group discriminate analysis on microhabitat variables representing shrub structure and substrate patchiness. The rodents form two functional groups. Four permanent, year—round residents (Peromyscus eremicus, Neotoma lepida, Neotoma fuscipes, and Dipodomys agilis) show significant separation on habitat structure and some temporal habitat shifts. Three seasonal residents (Peromyscus maniculatus, Peromyscus, and Reithrodontomys megalotis) show no microhabitat shifts and have a greater frequency of microhabitat overlap with one another and with permanent residents. There is no relationship between niche breadth and population density for any given species; however, as a group, seasonal residents show reduced breadth with increased population density. The significance of this pattern is discussed with respect to ecological opportunism of seasonal residents. The pattern of body size differences within the fauna is examined in light of habitat structure. Pairwise differences in habitat structure and body size are positively correlated. The data show that permanent residents are more different from one another in body size and structural habitat than pairs in which at least one species is a seasonal resident. Increased similarity in body size and microhabitat structure may not favor year—round coexistence in some pairs of species. The most similar—sized pair of species are congeneric deer mice (P. eremicus and P. maniculatus), and in addition to seasonal separation, they show niche difference by habitat structure.

ISSN:0012-9658    

DOI:10.2307/1936186

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY

摘要:

Simultaneous measurements of the diel patterns of dissolved O_2, pH—CO_2, dissolved organic nitrogen, ammonia, nitrite, nitrate, dissolved organic phosphorus, phosphate, and silicate were made on four occasions in a shallow salt marsh embayment (Bissel Cove, Narragansett Bay, Rhode Island, USA) that was closed to tidal water exchanges for 24—h periods. In spite of high rates of community photosynthesis and respiration, there appeared to be little diel change in dissolved nutrient concentrations, especially with respect to inorganic nitrogen. During summer and early fall, inorganic nutrients appeared to cycle within the sediment—detritus system of the embayment bottom, rather than being released to the overlying water. This suggests that there would be little export of inorganic nutrients from the marsh during tidal exchanges with the estuary. The behavior of this marsh embayment contrasts with reports from other marsh areas where large net imports or exports of nutrients have been observed. The concentrations of dissolved organic phosphorus and nitrogen were higher than inorganic forms, and showed substantial variation over each diel sampling period. The relationship between photosynthetic or respiratory gas exchange and nutrient cycling in water influenced by benthic community metabolism is subtle and complex, and cannot be adequately approximated by simple models such as the Redfield ratio.

ISSN:0012-9658    

DOI:10.2307/1936187

出版商:Ecological Society of America    

年代:1976

数据来源: WILEY