摘要:

An improved light sensor with a spectral response based on photon absorption between 400 and 700 nm was developed for both field and environmental chamber use. The indicated sensor response was selected because it approximates the photosynthetic response of plants for which data are available. A silicon photo cell with high response in the visible range was used as a sensor. The spectral response was controlled by use of a Kodak Gelatin Wratten Filter. A visible bandpass interference filter produced a sharp cutoff at 700 nm. Heat—absorbing glass eliminated transmission beyond 1,000 nm, and a diffusing plastic and filters were mounted in a miniaturized cosine—corrected head that was fitted with a collimating system to eliminate spectral shifts which arise when light enters the interference filter at oblique angles. Error calculations indicate that under sun—and—sky radiation and various artificial light sources the errors are smaller than those associated with available standard calibration lamps. The device also includes a battery—operated meter circuit suitable for making measurements over a wide range of intensities.

ISSN:0012-9658    

DOI:10.2307/1934743

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

If a predator eats more prey at higher prey densities, grows more as a consequence, and then kills more prey because of its larger size, this produces a developmental response to prey density. In its functional response a predator sea shore snail caused a decreasing percentage mortality as prey (barnacle) density increased (type 2 response). This causes instability in prey numbers. However, when account was taken of the developmental response in a hypothetical pseudosnail, the prey mortality caused over a year by a single—predator as a function of prey density, was different from that expected on the basis of the functional response alone. There is a tendency for the mortality to be a fairly constant percentage of prey density over a rather large range of prey densities. This results in the reduction of the destabilizing effect. Problems of integrating these responses with the numerical response and of generalizing the results are discussed.

ISSN:0012-9658    

DOI:10.2307/1934744

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

A description is given of a field experiment from winter through fall in which excess artificial food was provided in some areas with Peromyscus maniculatus, but not in others. Population size and production of young increases, and adult but not juvenile survival improves slightly with additional food; hence the hypothesis that no differences in breeding and survival would exist between experimental and control areas is rejected in part. The numbers of adult males in experimental and control situations are similar, suggesting that the male portion of the breeding population may, as hypothesized by Sadleir (1965) and Healey (1967), be held relatively constant during breeding by behavioral mechanisms. Attention is drawn to the different numerical responses of males and females, and the possibility of different regulating mechanisms for the sexes.

ISSN:0012-9658    

DOI:10.2307/1934745

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

From a simple model, we have calculated with a digital computer the standing crop, the gains in weight (secondary production), and the transfer of biomass by death (potential food for predators) on a monthly basis for all age and sex categories of the Isle Royale moose, a population unhunted by man and in equilibrium with its predator, the timber wolf. These estimates provide a more accurate and detailed picture than available before of biomass dynamics in a wild ungulate population. For this single—prey—single—predator system, results demonstrate that the accumulation of biomass in the prey population permits a steady flow of food to the predator, although production of food for the prey (woody and aquatic vegetation) is seasonally highly cyclic. The storage of biomass is examined in terms of the year classes of moose. Further uses of the model are discussed.

ISSN:0012-9658    

DOI:10.2307/1934746

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Root distribution and mass of a single dominant sample tree (17 m high, 20 cm diameter) in a 39—year—old Pinus resinosa Ait. plantation supported by a deep, stratified, outwash sandy soil were related to soil horizonation characteristics and aboveground tree components (foilage, branches, bolebark, and bolewood). All roots were excavated by hand in the A_p and B horizons and by 0.3—m depths in the C strata, were separated into five size classes, cleaned, dried, and weighed. Root—depth penetration terminated in a great number of fine roots in a thick, very fine sandy—silty stratum below the coarser textured solum at 2.7 m. Lateral root distribution was extremely variable; the maximum radial extent was approximately 9 m from the stump. Total root weight was approximately twice the total needle weight.

ISSN:0012-9658    

DOI:10.2307/1934747

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The reproductive cycle of a neotropical sphaerodactylid lizard, Gonatodes albogularis, was studied at Ancon, Panama Canal Zone, from September 1968, until October 1969. Counts of eggs oviposited at seven selected sites were made biweekly over this period; adults were collected monthly to provide information about reproductive condition. The maximum number of ovipositioned eggs was made just before the height of the rainy season and the minimal one during mid—dry season. The apparent reproductive condition of the adults did not reflect the decline in number of oviposited eggs during the end of the wet season.

ISSN:0012-9658    

DOI:10.2307/1934748

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

A modification of the standard technique of rearing Drosophila in bottles (with paper supports for pupation) allows one to obtain rather stable populations and to control, to some extent, their age distribution. It consists in transferring, at constant time intervals, appropriate fractions of adults, pupae and larvae to new bottles. A number of combinations of such fractions, the number and size of bottles and different quantities of medium have been tried.

ISSN:0012-9658    

DOI:10.2307/1934749

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Data from a single subarctic locality are used to test Ricklef's general conclusions regarding patters of nesting mortality in arctic birds. They provide additional evidence that hatching success is greater among arctic than among Temperate Zone passerines. However, they do not indicate important differences in hatching success between ground—nesting birds with precocial young and those with altricial young, nor do they confirm that predator—induced nesting losses are density dependent in arctic regions. Predation may be a more important cause of nesting failure than Ricklefs acknowledged. Differences in our findings in part from differences in sampling methods. further analyses of nesting morality should combine data from studies of selected species with those from regional studies.

ISSN:0012-9658    

DOI:10.2307/1934750

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

A random walk model for insect dispersal leads to the diffusion equation. Diffusivity is a suitable parameter to characterize the rate of dispersal. The methods by which diffusivity may be computed using data from the most common types of dispersal experiments are discussed. Some of the implications and limitations of the model are mentioned. The probability that an insect will move more than a certain distance in a certain time in proposed as a useful statistic. Dispersal data from adult Pantorhytes weevils in a dense canopy of cacao are presented and successfully interpreted in terms of the diffusion analysis. The diffusivity found was 0.75 m2day(—1). It is calculated that there is a probability of 0.01 that any beetle will move more than 20 m in 1 month.

ISSN:0012-9658    

DOI:10.2307/1934751

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The movement of adult apterous cacao weevils, Pantorhytes szentivanyi Mshl. (Coleoptera: Brachyderinae) marked with scandium—46 was studied in cacao plantations with open or closed canopies. A diffusion model of dispersal was used to calculate diffusivities (D). These were higher in a closed canopy (D = 0.75 m2/day) than in open canopy (D = 0.16 m2/day). This reflects the more rapid dispersal occurring when the branches of adjacent trees are touching. In a closed canopy plantation, the calculated probable distance moved by any individual in a month was 14—25 m (P = 0.1 — 0.001).

ISSN:0012-9658    

DOI:10.2307/1934752

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY