摘要:

The classicaldegree day approach to plant phenological stage—of—growth prediction is combined with the recentstress degree day approach to plant H_2O stress determination to yield a new tool for more accurate assessment of physiological time scales in plants.

ISSN:0012-9658    

DOI:10.2307/1936570

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Surface root mats on oxisols and spodosols near San Carlos de Rio Negro, Venezuela, were sprayed with(45)Ca and(32)P to simulate the addition of nutrients to the soil surface through leaching of decomposing litter, and through precipitation and throughfall. Collections from lysimeters placed below the root mat and humus layer showed that in all but 1 case,<0.1% of the radiotracers leached past the root–organic mat, and leaching stopped completely after 1 to 2 months. Through analysis of root mat samples, the radioisotopes were found to have been taken up and translocated by living roots. This is the first evidence supporting the ability of the root map on the surface of poor, depleted tropical soils to efficiently take up dissolved nutrients before they percolate down to mineral soil. Other studies have shown up that one of the uptake mechanisms is mycorrhizal fungi.

ISSN:0012-9658    

DOI:10.2307/1936571

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Associations of 41 species of fungi isolated form 858 samples (feathers, nests, pellets, and droppings) of free—living birds were evaluated using Jaccard's coefficient and a "half—linkage" clustering method. Eleven clusters of the fungi was established, 3 of which were singletons. Representative species of the individual groups were Alternaria alternata with Cladosporium herbarum; Chaetomium funicolum with Chaetomium globosum; Arthroderma ciferrii with Scopulariopsis brevicaulis; Aphanoascus fulvescens with Chrysosporium keratinophilum; Penicillium chrysogenum with Trichoderma viride; Arthroderma curreyi; Gliocladium roseum with Trichothecium roseum, Mucor pusillus, Aspergillus flavus, Gymnoascus reessii, and Rhizopus nigricans.

ISSN:0012-9658    

DOI:10.2307/1936572

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The life—history characteristics of the biennial herb Pastinaca sativa (Umbelliferae) influenced its within—patch structure in size and growth form which, in turn, influenced availability of plants to a specialized herbivore, Depressaria pastinacella (Lepidoptera: Oecophoridae). Of 115 plants tagged in October, 1975, only rosettes with root weights of at least 0.7 g and a total weight of at least 1.1 g flowered the next spring. Plants that grew larger as rosettes produced larger flowering individuals that set more seed. In 4 patches studied in 1976, plants in the interior were significantly smaller (in terms of biomass) and closer to conspecifics than those on the periphery. Larger plants were more susceptible to attack by Depressaria larvae, because unopened umbels, necessary for successful oviposition, were available on these plants over a longer period of time. Pattern of attack within a patch could be predicted from knowledge of plant basal stem diameter, a reliable estimator of availability of unopened umbels. Attack on more isolated plants (no conspecifics within 3 metres) was also significantly related to basal stem diameter. Within a size class, however, plants in patches were more susceptible to attack than isolated plants. The major factor governing dispersion of larvae among isolated plants and within patches was the dispersion of host plants of various sizes and growth forms. Depressaria larvae significantly reduced seed output in size classes in which comparisons were possible. Within—patch dynamics in Pastinaca appears to be governed by life history characteristics, individual plant plasticity and the pattern of attack by Depressaria.

ISSN:0012-9658    

DOI:10.2307/1936573

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

A mutualistic association of the type namedant—garden by Ule (1901) between Crematogaster longispina, an arboreal, carton—building ant, and Codonanthe crassifolia, an epiphytic vine, is found in northeastern Costa Rican lowland rain forest. Both species gain an increase in food resources by participating in the association. The plant produces floral and extrafloral nectar and fruit with pulp and seed arils that are eaten by the ants. In turn, the ants place the seeds of the plant in the walls of their carton nests. The seeds germinate and the plants grow and obtain nutrients from the detritus with which the ants construct their nests. The growth rate of plants which are not on ant nests is significantly less than the growth rate of plants on ant nests.

ISSN:0012-9658    

DOI:10.2307/1936574

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

In this paper we derive versions of Fisher's Fundamental Theorem of natural selection for the case of a single density—regulated population, and for the case of 2 species engaged in standard ecological interactions. Selection is assumed to be weak and the selective values of genotypes to depend only on the total densities of species in the ecosystems, not on the densities of specific genotypes. Our results enable us to draw some general conclusions about the way in which natural selection, of the type we consider, affects the densities of species in an ecosystem. Evolution within a single species tends to increase the density of individuals in the age—group to which density—dependent factors respond. For a pair of competing species, we conclude that often, but not invariably, the densities of both species will be increased by selection. In an exploiter—victim system, the exploiter tends to increase in density whereas the victim will increase only if the exploiter is strongly self—regulating. It will otherwise remain stationary or even decrease.

ISSN:0012-9658    

DOI:10.2307/1936575

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

In order to develop a general model of litter decomposition rates suitable for the prediction of regional variations in decay rates, and to determine the relative control by macroclimate and litter quality on decomposition rates, data were selected from 5 locations ranging in climate from subpolar to warm temperate. Actual evapotranspiration (AET) was selected as an index of the climatic (energy and moisture) forcing function of the specialized decomposers which is superior to temperature and precipitation. Lignin concentration was selected as an index of litter quality and may be treated as a mediator of climatically (AET) regulated decay rates. In a stepwise, multiple linear correlation—regression, using AET, lignin concentration (%) and AET/lignin concentration (interaction), AET alone accounted for 51% of the variance in observed decay rates, AET/lignin concentration (interaction) added 19% and lignin concentration added 2% of the total (72%) variance accounted. Simple correlation of the five locations between lignin concentration and decomposition rate ranged from r = .32 to r = .95, however, the regression lines for each of the 5 locations indicated that these slopes progressively declined with AET. Moreover, the slope decline was not parallel, indicating a climatically variable control by lignin concentration on decay rates. In low—AET (not arid) climates, litter with high and low lignin, will decay at more nearly similar rates, but as the AET environment increases, the difference in decay rates becomes progressively greater than the increase in AET alone would seem to warrant. A general model of the interaction control by AET and lignin concentration on decomposition rates was formulated which overcomes the restraints of the multiple regression model. At the scale of subpolar to warm—temperate climates, the climate as indicated by AET is several orders of magnitude more important as a predictor of decay rate than is litter quality. This importance is evident in spite of the fact that the data on lignin concentration used in this analysis had a 12—fold range while the AET values had a 2.3—fold range.

ISSN:0012-9658    

DOI:10.2307/1936576

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Plant species richness and other variables were analyzed on 41 islands and 2 mainland plots. The species—area coefficient was .30, but was higher (.73) for strictly terrestrial and lower (0.13) for shore species. In a stepwise multiple regression analysis, 85% of the variation in species richness was accounted for by logesurface area, percent of the ground covered by stones, and foliage, respectively. The average height of the trees correlated positively with the number of strictly terrestrial species but negatively with shore species. The difference between the number of strictly terrestrial species, predicted from the multiple regression equation, and that observed was proportionally larger on smaller islands. There was evidence that plant species carried by animals dispersed less efficiently to the islands. The flora contained proportionally fewer of these species with decreasing island area. The converse was true for water—dispersed species and some wind—dispersed (those with pappi). These observations are consistent with the hypothesis of higher extinction rates on small islands. A dynamic equilibrium in species number does not necessitate an equilibrium in the proportions of species in different dispersal categories.

ISSN:0012-9658    

DOI:10.2307/1936577

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Aquatic microecosystems of 3 litres were established in replicate for the 8 combinations of high or low physical heterogeneity, high or low plant nutrient levels and stable or unstable temperature. Plankton succession from a pond water inoculum was observed for 5 mo. Microcrustacea, periphyton and benthic organisms were sampled only at the end of the study. Final species diversity (H') was higher for low—nutrient and for most high physical—heterogeneity systems. Stability of temperature did not affect species diversity. Numerous interactions of the 3 variables occurred, so that the diversity of the systems could not be predicted from the combined effects of single variables. The significance of this observation for theoretical analyses of species diversity is discussed.

ISSN:0012-9658    

DOI:10.2307/1936578

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The distribution of nutrients in plants, litter, and soil were studied before and after a prescribed burn in southern California chaparral. Total N, P, K, Na, Mg, and Ca were measured. The various nutrients were distributed differently in the plant parts and the litter before fire and this affected their redistribution by fire. Measurable losses of only 2 nutrients occurred–N (146 kg/ha) and K (49 kg/ha). Erosional losses of nutrients during the first rainy season after fire are also reported.

ISSN:0012-9658    

DOI:10.2307/1936579

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY