摘要:

This investigation compared the mycofloral populations inhabiting the organic and mineralized soil horizons, and evaluated the effect of castastrophic vegetational disturbances on their species composition, in selected upland forests in northern Wisconsin. Eight forests, part of the conifer—hardwood complex, were included in the study: three of them served as virginal reference stands, four represented secondary succesional communities occupying areas that experienced severe forest fires, and one was a yellow birch forest that became established on a clear—cut area. Sample populations, obtained by the dilution plate method, were isolated from each detectable horizon in each stand. In general, the highly organic large, especially the litter and fermentation horizons, possessed the greatest number of fungal propagules as well as the greatest species diversity. With increasing depth, both the density and diversity decreased rapidly. Although many of the species were present in more than one horizon, most of them exhibited maximum densities and freqencies in only one of them. Thus, the populations colonizing each horizon could be characterized by a somewhat specific combination of prevalent species. The relatively low similarity coefficients derived from comparisons between the populations in the horizons within a stand substantiated the view that there were distinct populations. Ordination of the coefficients suggested that the soil profile could not be visualized as an edaphic cline with elicited a soil microfungal continuum. Since most of the predominant species in any specific horizon differed from those residing in overlying horizons, the establishment of a characteristic mycoflora could not be attributed to differential survival of propagules that percolate from horizons above.

ISSN:0012-9658    

DOI:10.2307/1934613

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Mapping of modern pollen and vegetation data as well as principal component analysis of these data reveals the patterns in the vegetation to be quite evident in the pollen data. The pollen was extracted from the top 2 cm of short cores taken from 64 lakes in lower Michigan, and the vegetation data were derived from Forest Inventory records. Except for pine and poplar, the distribution of pollen values for individual genera parallels the distribution of vegetational values. Principal component analysis shows that the north—south gradient between mixed conifer—hardwood forests in the north and deciduous forests in the south occurs in both sets of data, and differences between the major forest types are also evident.

ISSN:0012-9658    

DOI:10.2307/1934614

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

A heat transfer model of a raccoon (Procyon lotor) in a hollow tree was designed and tested by simulating an overwintering raccoon with a fur—covered, electrically—heated cylinder in a closed den. A comparison was made between predicted and observed fur surface temperatures, and heat losses from the top, side, and bottom. Under these conditions, transfer coefficients derived from engineering relationships can be dependably used in the field; the average difference between predicted and observed fur surface temperatures was 1.6°C, and the sum of the predicted fluxes through the surfaces of the model was within 5% of the measured total. Total heat loss increased approximately linearly as inside wall temperature decreased, but the contribution by convection and radiation to the total changed substantially. As inside wall temperature decreased, convective flux was an increasing percentage of the total, whereas radiation loss decreased to a minimum value of 56% of the total flux at the minimum wall temperature. Twenty—five percent of the total flux was lost from the top, 62% from the side, and 13% from the bottom. More than 65% of the total resistance to heat loss through the model side was in the fur. The air space presented 17%, with the rest in the den wall With respect to heat loss through the base of the den, only 6% of the total resistance was in the compressed fur. But because of the high resistance of the den base, the loss was half that of the top. Small variations in den wall thickness are not a major factor in reducing heat loss since the wall accounts for only about 18% of total heat flow resistance. Energy loss and average monthly weather screen air temperature are correlated.

ISSN:0012-9658    

DOI:10.2307/1934615

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Lonicera X bella is an introduced, aggressive hybrid shrub that occurs in Wisconsin and much of central and eastern North America. Both parent species occur in a wide variety of habitats in their native ranges, as does this hybrid in North America. Ordination, by principal components analysis, indicated that the dimension of maximum morphological variability is that which best separates the parent species. Physiological tests and transplant gardens revealed no evidence of ecotypic differentiation in the populations studied. Selection for heterosis is suggested by certain morphological characteristics of the hybrids, by the high freqency of hybrid individuals that are intermediate to the parents, and by the ecological behavior of this shrub.

ISSN:0012-9658    

DOI:10.2307/1934616

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Calculation of net accumulation rates for microfossils in Frains Lake, Michigan, reveals that (1) Daphnia has been an important competitor most of the time, except during the last 140 years; (2) when Daphnia was rare, Bosmina was abundant, and vice versa; (3) extinction of larger species of Daphnia, reduced abundance of Daphnia, and simultaneous increases in Bosmina and Chydorus, all coincide with forest clearance 140 years ago. Man's activities at that time appear to have caused either directly or indirectly a major increase in the number of planktivorous fish in Frains Lake, and the changes seem associated with the extension of littoral vegetation.

ISSN:0012-9658    

DOI:10.2307/1934617

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

A low—resolution simulation model of transpiration was developed and run, with data from field studies in southwestern Oregon. The output of the model served as a means of relating environmental variables to plant response. This relation was used to define an ordinate which, in conjunction with previously developed ecosystem ordinates, proved helpful for comparing ecosystems, predicting community composition and, in special cases, growth. The data requirements of the model are modest; we deliberately developed a model that can be used on data obtained from field studies where electric power is unavailable and use of sophisticated instrumentation is impossible. The model requires inputs of air and soil temperature, atmospheric humidity, seasonal plant water potential (expressed as plant moisture stress, the absolute value of plant water potential), and a model of stomatal behavior. Where it was impossible to obtain accurate data, stochastic models were used to provide the necessary input. The model simulated both potential and actual transpiration, the ratio of which is the most valuable single index of the seasonal moisture regime. Where no measurable stomatal control was exerted by Douglas—fir, the ratio was 1.0, indicating that adequate water was available to meet the transpiration demand. The ratio approached 0.3 on the drier locations. Significant changes in vegetation and growth were associated with this index.

ISSN:0012-9658    

DOI:10.2307/1934618

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Data consisting of samples of species' presences in association with measurements on a set of environmental variables can be used to determine environmental factors separating the species. It the multiple discriminant model is modified by a covariance extraction of time effects applied to the within—species, and total, deviation squares and cross products matrices prior to the discriminant analysis, then temporally varying environmental parameters can be included. If the distribution of sampling in space is consistent over time, then factors separating the species in time, as well as in space, can be determined; if it is not, then separation in space can still be determined even if the samples were collected at different times. The multiple discriminant model is analogous to the Hutchinsonian niche model; its use is illustrated with artificial data, and it is then applied to data from a benthic stream community to demonstrate heterogeneity of niche sizes, and separation of species' niches in space and in time by different environmental factors related to substrate type and water depth. Trophically similar species are more environmentally separated than are trophically different species; the separation is spatial for herbivore—detritivores, and temporal for carnivores.

ISSN:0012-9658    

DOI:10.2307/1934619

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Life history characteristics of two competing starfish (the large Pisaster ochraceus and the smaller Leptasterias hexactis) are examined with respect to their relevance to the predictions and "correlates" of density—independent and density—dependent, or r— and K—selection, theory. Interspecific comparisons indicate that use of fecundity as an indication of reproductive output is inadequate because there species have evolved radically different reproductive strategies (Pisaster females broadcast many, small eggs; Leptasterias females brood few, large fertilized eggs). Further, since similar proportions of their respective total body weights are allocated to reproduction, this measure of reproductive output is also inadequate. However, the energy content of gonads and the part of the storage organs used during reproduction of the smaller species is higher than that of the larger species, suggesting reproduction is indeed costlier to the former. Intraspecific comparisons between fecundity and energy committed to reproduction by Leptasterias at several areas indicates these characters are not directly altered by interspecific competition but are strongly affected by the density—independent effects of wave action. Interspecific competition affects fecunidity only indirectly by reducing body size of Leptasterias (body size and fecundity are positively correlated). Although density—independent factors are believed to increase fecundity and reproductive efforts, increased severity of wave action apparently decreases them. This evidently results from physical limitations imposed by the smaller species' strategy of brooding its young. The difference in cost of reproduction to each starfish apparently conforms to the notion that species can be ranked along a postulated "r—K continuum." However, fecundity of Leptasterias is reduced by increased density—independent mortality. Although no similar departures from r—K selection theory have been reported, the habit of brooding is fairly common in nature. Hence Leptasterias' response to wave action is probably not unique. These data at least suggest that the generality of r— and K—selection theory should be determined before theoretical elaboration of this theory is safe.

ISSN:0012-9658    

DOI:10.2307/1934620

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

Microarthropod population diversity, distribution, and species composition were studied in three South Carolina old fields with the use of fiberglass—mesh litterbags. Mean total arthropod densities were highest in a 1st—year successional field (abandoned cornfield), lowest in a 12—year broomsedge field, and intermediate in a 12—year lespedeza field. Densities differed significantly with season, field, and litter type within field. Litter moisture content also differed significantly with these factors and changes in moisture were correlated with changes in density or microarthropods. Both species diversity and species composition differed significantly between fields, but litter type had no significant effect. Conclusions were (1) the litter fauna is a transient subset of a larger and possibly more diverse soil fauna, present in the litter only during favorable moisture regimes; (2) species diversity and composition of the litter fauna are determined primarily by the successional stage of the field and are affected little by the introduction of allochthonous litter in the small amounts contained in the decimeter—square litterbags used in this study.

ISSN:0012-9658    

DOI:10.2307/1934621

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY

摘要:

The larval food range of the black swallowtail, Papilio polyxenes, is restricted naturally to plants of the family Umbelliferae. When larvae were reared on celery leaves cultured in solutions of sinigrin (a chemical occurring in various species of Cruciferae), feeding rates were not significantly affected but growth and development were substantially reduced. At concentrations of 0.1% (fresh weight of leaf or higher, sinigrin, caused 100% larval mortality. These findings suggest that the larval feeding niche of P. polyxenes is bounded in part by chemical barriers of a toxicological as well as a behavioral nature. They also provide further evidence that sinigrin and other mustard oil glucosides serve a defensive function in plants of the family Cruciferae.

ISSN:0012-9658    

DOI:10.2307/1934622

出版商:Ecological Society of America    

年代:1974

数据来源: WILEY