摘要:

Freezing resistance studies were carried out on Salix sachalinensis (northern Japan), S. Sieboldiana (southwestern Japan), S. babylonica (Japan proper and Hachijo Island), S. caerulea (Lahore, Pakistan), S. tetrasperma (Singapore and Quetta, Pakistan), S. bonplandiana (Mexico City), and S. safsaf (Cairo). Twigs of the tenderest willows (S. Sieboldiana) wintering in the southwestern part of Japan resisted freezing to about —15°C, but when hardened at —3°C for 14 days in Sapporo, they resisted freezing at °50°C. After growing in Sapporo (northern Japan) for 1 year, these twigs survived immersion in liquid nitrogen (—196°C) following prefreezing at —20°C in winter. Cuttings from willows native to the tropics, when grown outdoors in Sapporo for 1 year, produced twigs which resisted freezing to about —30°C for 16 hr. A genetic potential to withstand freezing to very low temperatures is apparently present even in tropical willows. The temperatures most effective in producing maximum freezing resistance were nearly the same for both northern and subtropical willows irrespective of their native habitats, and the degree of freezing resistance in winter of any species of willow differed considerably and depended on air temperature in the localities at which plants were wintering.

ISSN:0012-9658    

DOI:10.2307/1935383

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Inhibitors localized at the micropyle and interacting with gibberellin impose dormancy on seeds of both Luzula spicata and L. parviflora from the Colorado Front Range. Removal of the inhibition by precise scarfication elicits germination in both species. Luzula spicata seeds lacking precise scarification were found germinated in tundra soil. Germination was experimentally induced in L. spicata by random scarification, which may be accomplished by repeated freeze—thaw cycles, followed by stratification for 2—3 months. The inhibitor in L. parviflora was inactivated by after—ripening. Germination requirements of L. spicata may represent adaptions to fall freeze—thaw cycles followed by extended chilling under accumulated snow in its tundra habitat. Luzula parviflora, a subalpine and montane species, lacks these adaptations.

ISSN:0012-9658    

DOI:10.2307/1935384

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Regulation is defined as the return of a population to equilibrium density. An operational definition of regulation is convergence to a single density by subpopulations which have been manipulated previously to different densities. The equilibrium density may be fixed or variable. If the equilibrium is variable then regulation may produce instability (numerical inconstancy) and non—density—dependence. Population inertia is the tendency for a population to resist changes away from its current density. If speed of regulation is defined as |s|, the speed of convergence to equilibrium, then inertia is 1/|s|. The evolution of mechanisms of inertia involves changes in the demographic functions, mediated through physiology or behavior, which keep the rate of numerical change low. It is not clear if populations are control systems or non—control systems, which makes the convergence experiment difficult to interpret theorectically. Experiments and observations are needed which will try to distinguish, among stable populations, between those with tight regulation and those with high inertia.

ISSN:0012-9658    

DOI:10.2307/1935385

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Equations describing biological phenomena frequently have parameters entering nonlinearly. A highly efficient method for determining the values of parameters in such equations that will give the best least—squares fit to a set of data is Marquardt's algorithm. A step—by—step derivation of the algorithm is given in terms that require only a knowledge of elementary calculus and matrix algebra. As an example, the method is used to fit the logistic equation to a set of data.

ISSN:0012-9658    

DOI:10.2307/1935386

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

A general model is formulated relating the outcome of a series of events such as the capture or escape of a prey item to the probability, time and outcome of each kind of event. Application of the model and its derivation are demonstrated for predator hunting behavior and the nesting biology of birds.

ISSN:0012-9658    

DOI:10.2307/1935387

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

A population of the isopod Tylos punctatus on a California beach was sampled by simultaneous coring and pitfall trapping. The traps showed a statistically significant bias against females, particularly gravid ones, and against juvenile isopods when compared to the cores. It is concluded that, for studying the population structure of this species, and perhaps others as well, pitfall traps produce samples that are too inaccurate to be useful.

ISSN:0012-9658    

DOI:10.2307/1935388

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Large cyclic fluctuations in the densities of laboratory populations of both bacteria and Protozoa were produced by adding sterile nutrient solutions to the cultures at long intervals. The fluctuations were greatly reduced, and they were no longer cyclic when the nutrient solution was added at shorter intervals. Experimentally, the major form of interaction between bacteria and Protozoa was predation of the Protozoa upon the bacteria. Both the population density of the Protozoa and the population density of the bacteria were reduced by decreasing the amount of nutrient solution added to the cultures.

ISSN:0012-9658    

DOI:10.2307/1935389

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

The iron—constantan thermocouple contact thermometer here described is mounted on spring clamp and can be quickly attached to the leaf; a large number of determinations can be made in a short time. The thermocouple junction equilibrates very rapidly (1.5 sec), has a low heat capacity, and is spring loaded. The performance of the contact thermometer compares well with that of a thermocouple inserted within the leaf mesohyll and with measurements made with an infrared radiation thermometer.

ISSN:0012-9658    

DOI:10.2307/1935390

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

The influences of seed—nursery environment upon genecological characteristics of 20 medusahead strains was studied. Environmentally induced variation was observed in germination, early height development, and winter survival. Small, but significant, variation in dates of spike emergence and anthesis, caused by differences in seed—nursery environment, were observed. Results suggest that the common practice of attaching genecological significance to wild—grown seed may be subject to error, especially in germination and early phenological stages following germination.

ISSN:0012-9658    

DOI:10.2307/1935391

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY

摘要:

Rapidly elongating Bromus tectorum and Taeniatherum asperum roots penetrated the soil ahead of Agropyron spicatum roots and used available moisture. In contrast, Agropyron desertorum roots penetrated the soil almost as rapidly as B. tectorum and T. asperum and remained in favorable moisture. These differences in root penetration resulted in lower leaf water potentials and poorer survival in A. desertorum. The results suggest that in areas where root growth occurs at low temperatures and where lands are infested with B. tectorum and T. asperum, seedlings of A. desertorum would be more successful than seedlings of A. spicatum.

ISSN:0012-9658    

DOI:10.2307/1935392

出版商:Ecological Society of America    

年代:1970

数据来源: WILEY