ISSN:0012-9658    

DOI:10.2307/1933800

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Pigments in soil organic matter layers of an oak forest, a spruce—cedar woodland, and a prairie have been identified and measured quantitatively. In all cases lutein was the dominant carotenoid accompanied by smaller amounts of Beta—carotene. Phenophytin a and chlorophyllide a commonly present in the L and F organic layers. Pigment ratios were examined and compared in all three humus types.

ISSN:0012-9658    

DOI:10.2307/1933801

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

In Central American deciduous forests, most of the seeds of the caesalpinaceous legume tree Cassia grandis are killed by the larvae of two bruchid beetles, Pygiopachymerus lineola and Zabrotes interstitialis. Pygiopachymerus lineola oviposits on the large pods, the first—instar larvae bore into the seeds, and the emerging adults cut large exit holes in the pod wall. Moth larvae gain access through these holes and eat clean much of the sticky pulp around the seeds. Simultaneously, the adults of Z. interstitialis enter through the P. lineola exit holes and oviposit directly on all clean seeds. In heavily disturbed communities where vertebrate dispersal agents are absent, these host—specific bruchids achieve almost 100% predation on the C. grandis seed crop; however, the more rapidly the dispersal agents remove the seed pods, the less seed predation there will be by Z. interstitialis. Since C. grandis bears mature fruit every other year, the size of each seed crop is large enough to surpass the predation abilities of the bruchids that survive the distance in time and space between seed crops. The system may be viewed as an example of predator satiation. The potential for further co—evolution of the bruchid—Cassia interaction is high, but numerous opposing forces in the selective process can be identified.

ISSN:0012-9658    

DOI:10.2307/1933802

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

From laboratory data of flying and resting metabolism and field data on time budgets of territorial male Eulampis jugularis hummingbirds we were able to estimate caloric energy budgets associated with territorial behavior. The relative time and energy expenditures for territorial defense, foraging, and sitting varied in territories with different species of flowers. For example, territories centered around banana flowers had lower foraging costs than those centered around Myrtaceae or Inga—Hibiscus. The costs for flycatching, hovering,and perch changes accounted for relatively little of the time and energy budgets at any of the territorial defense and foraging were expended in sitting on perches within the territory. Territorial defense was of relatively low cost in time and energy because of the inactive defense utilized by Eulampis. Selection will optimize time and/or energy budgets, but the type of budget optimized will depend in large part on the exploitation technique of the species. For birds that do not fly to forage, but exploit food items that require a long search time per calorie, time that can be released for other activities may be more important than major shifts in energy budgeting. For hummingbirds, however, optimizing energy may be more important to insure a positive energy budget.

ISSN:0012-9658    

DOI:10.2307/1933803

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

An observational field study was made on predation by Forster's Tern. The major question asked was whether a seasonal change in hunting success occurred. Models proposed by Watt and by Holling and Griffiths predict a decline in the number of captures by individual predators as their density increases. Laboratory studies on protozoa have shown such declines in rate of predation, but in these organisms the decline is offset by an increase in efficiency. In the terns, the effectiveness of their attacks as measured by the percentage of captures increased seasonally from spring to winter. However, the overall hunting success in weight units of fish per unit hunting time declined steadily over the same period. The causes of this were possibly changes in their prey population and changes in the density and composition of the tern population. The increased attack efficiency was insufficient to counteract an overall decline in hunting success. A secondary objective of the study was to determine the relationship of handling time to size of fish. It was found that handling time increased proportionally as the length of the fish squared and was a satisfactory index of prey size.

ISSN:0012-9658    

DOI:10.2307/1933804

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Nocturnal insect activity was observed through telescopes focused on the moon. Flight direction was computed and methods were developed for estimating height and determining vertical distribution. Total density was correlated with light—trap catches; effective range of a light—trap was about 7 meters. Species identification was impossible but the method was selective for larger and higher—flying insects. Characteristics of insect activity observed during periods of army cutworm abundance indicate that it orients to the west during spring migration. Activity and altitude of flight were modified by wind direction and velocity but flight direction during migration was independent of wind.

ISSN:0012-9658    

DOI:10.2307/1933805

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Clear sky (cloud—free) horizontal plane terrestrial solar radiation spectral fluxes can be computed for any time of day and year, geographic location (latitude and longitude), and elevation upon inputing the optical properties of the atmosphere and reflecting properties of the underlying surface. Consideration is given to the problem of diffuse terrestrial radiation spectra for non—sea level elevations and where the terrestrial atmosphere cannot be regarded as being purely a Rayleigh atmosphere. Computation of terrestrial spectra for "large" zenith angles (Z>or = 72 degrees) is considered along with a discussion of irradiation patterns peculiar to polar zones (i.e., long days and nights). Selected results from the integration of these concepts into a computer program include the computation of total diffuse—to—direct flux ratios for radiation from a Rayleigh atmosphere at any solar zenith angle and selected elevations with typical mean ground albedos. Comparisons of integrated energy predictions with measurements in the literature agree favorably.

ISSN:0012-9658    

DOI:10.2307/1933806

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Net photosynthesis and transpiration of intact leaves of seedlings of five species of forest trees were measured under a range of light intensities and leaf temperatures. Leaf transfer resistances to water—vapor loss and CO_2 uptake were calculated. The species tested included Quercus macrocarpa, Q. velutina, Q. alba, Q. rubra, and Acer saccharum, which occur in southern Wisconsin along an ecological gradient from xeric to mesic. Stomatal resistance and water—use efficiencies, the ratio of water—loss resistance to CO_2—uptake resistance, decreased along the gradient from xerophytic to mesophythic species. Mesophyll resistances showed a corresponding increase. Variations among species in transfer resistances help explain the success of different species at various points along the ecological gradient and appear to be an important factor in determining species ecology.

ISSN:0012-9658    

DOI:10.2307/1933807

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

From 12 to 18 species of desert lizards occur in ecologic sympatry on 10 study areas in the Kalahari desert of southern Africa. The number of species of diurnal lizards is similar to the number in the North American deserts, while the nocturnal component of the saurofauna is more comparable to that occurring in the Australian deserts. The between—habitat component of species density is similar in the American and the Kalahari deserts, but is markedly greater in the Australian desert. A variety of climatic and vegetational statistics are examined for the 10 areas, and correlations with lizard species density are discussed.

ISSN:0012-9658    

DOI:10.2307/1933808

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Forty plant species common in western Washington were investigated for the presence of allelopathic chemicals capable of influencing the distribution of subordinate species. Under laboratory conditions most species contained inhibitory volatile compounds and many contained effective water—soluble compounds. The results of up to 13 bioassays per species were compared with descriptions of the distribution of subordinate species under natural conditions. In several cases, notably Acer circinatum, Arbutus menziesii, and Rhododendron albiflorum, high inhibition values in laboratory experiments were associated with distinct changes in ground—cover composition beneath the canopy of these species. The ratio between inhibition values produced by volatile and water—soluble inhibitors was higher in species from arid regions than in those from humid regions. This finding supports Muller and Whittaker's hypothesis that allelopathic compounds are primarily waste products.

ISSN:0012-9658    

DOI:10.2307/1933809

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY