摘要:

The kangaroo rat, Dipodomys merriami, occurs with the pocket mouse, Perognathus penicillatus, in stands of mesquite with little herbaceous cover. The dipo avoids areas that have thick cover between 8 cm and 45 cm. The pocket mouse prefers areas that have considerable cover over 45 cm. Those facts have been established both by previous studies and those reported here. This paper reports the results of altering the vegetation in small patches of land and observing concomitant changes in the land—use patterns of the rodents. The difference between the species appears to be crucial to their coexistence.

ISSN:0012-9658    

DOI:10.2307/1934379

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Dormant one—year—old twigs of about 70 tree species were collected during mid—winter from five tree regions in North America (Rocky and Western Mountain, Northern, Pacific Coast, Southeastern Coast, and Central and Eastern Lowlands). The twigs were artificially hardened in a regime of sub—freezing temperatures between —3 degrees C and —10 degrees C for 24 days to induce maximum freezing resistance. Four Northern species, Populus tremuloides, Populus balsamifera, Betula papyrifera and Larix laricina had the greatest freezing resistance of the species tested. They resisted freezing to —80 degrees C and even immersion in liquid nitrogen (—196 degrees C) following prefreezing to —15 degrees C. Most of the Northern and Rocky and Western Mountain conifers survived freezing between —60 degrees and —80 degrees C while several species from the Pacific and SoutheasternCoast regions, which have relatively mild humid winter climates, were hardy to only among —15 degrees C. The ranges of some Pacific Coast species such as Pseudotsuga menziesii, Thuja plicata and Tsuga heterophylla extend into the mountainous inland. Samples collected from inland sites were found to be much hardier than those from the coast. A similar trend was observed in the various collections of Tsuga heterophylla from northern, central and southern areas along the Pacific Coast. Winter minimal temperatures are among the important factors setting the northern boundaries of the natural ranges of many forest tree species. However, Populus deltoides and Salix nigra from locations with temperate or moderate winter climates survived freezing to at least —50 degrees C irrespective to their native habitats. In these species, winter minimal temperatures do not appear to be the principal factor governing geographic distribution.

ISSN:0012-9658    

DOI:10.2307/1934380

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

The importance of nest location in reducing heat loss by radiation and convection is indicated by a preliminary examination of the nest sites of Broad—tailed and Calliope hummingbirds with regard to chilling nights in the Rocky Mountains. Radiation losses are estimated from surface temperatures. Nest diameter and weight increase as a function of time in the nesting season.

ISSN:0012-9658    

DOI:10.2307/1934381

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Triarthrus eatoni (Hall) was a trilobite common in Late Ordovician marine environments of the Appalachian region. New aspects of its growth, development, and population dynamics are surmised from a rare census fossil assemblage. Its development from protaspis larva (three stages separated by molts) through meraspis juvenile (at least 14 stages) to adult halospis (many stages) was very gradual. Size—frequency distributions reveal that reproduction was seasonal, probably having occurred in a single burst per year. This provides a means of measuring time in the life cycle. The growth curve for overall length is approximately linear. The protaspid period lasted on the order of a week or so, the meraspid period through most of the rest of the first year, and the holaspid period to a maximum longevity of at least 4 years. The survivorship curve is essentially an exponential decay curve; the probability of an individual's survival was between 0.3 and 0.4 per year. Through its earlier juvenile stages, very roughly through the first month of life, the trilobite was a planktonic suspension—feeder. This was probably a dispersal phase in the life cycle, and its long duration helps explain the cosmopolitan distribution of the genus. Afterward, the trilobite settled to live on or near the bottom as an epifaunal deposit—feeder.

ISSN:0012-9658    

DOI:10.2307/1934382

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

The limpets Acmaea scabra and A. digitalis graze on encrusting microalgae in the upper intertidal and splash zones in central California, differing in habitat distribution but with considerable overlap. Controlled field experiments tested for interspecific competition in a habitat where both species were common but where A. scabra was similar than A. digitalis. Removal of A. digitalis from fenced exclosure plots resulted in significant growth increases in A. scraba, correlated with pronounced increases in the algal food supply. A converse effect on A. digitalis occurred in one of three experiments. It is concluded that in the habitat studied, limpet grazing strongly limited algal crop most of the year, and interspecific competition (exploitation type) for food limited growth rates and maximum size in A. scraba.

ISSN:0012-9658    

DOI:10.2307/1934383

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

In mid—August bottomland Quercus agrifolia and Q. lobata trees had low xylem sap tensions, as estimated by a pressure chamber. After a very dry winter, pre—drawn minimum tensions were less than 6 atm, suggesting that these rates were rooted to a water table. Widely spaced Q. lobata trees in upland savannas also had low pre—dawn tensions, presumably due to the lack of woody plant competition. In contrast, all strands of Q. douglasii had high pre—dawn tensions even after a very wet winter. They seem well adapted to dry slopes where the water table is usually unavailable. Quercus douglasii trees appear to drop their leaves when the water supply becomes critical. Trees in some north aspect stands had higher tensions in mid—August than trees in south aspect stands due to soil moisture supply and tree density interactions. During the dry season a size—class effect appeared with tension inversely correlated with crown size and probably root depth.

ISSN:0012-9658    

DOI:10.2307/1934384

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

The predatory behavior of a ladybird, Coccinella, was examined as it preyed upon varying ratios of two aphid species, Acrythosiphon pisum and Aphis fabae. Experiments were done in petri dishes and on bean plants. The ladybirds attacked the two prey species in direct proportion to their relative abundance. There was little variability among predators in a given treatment. Training had no effect on the subsequent diets of the predators, and all treatments provided a very good fit to a simpleno—switching" model. Predation on each species was density independent. This simple type of predation contrasts markedly with the results of earlier experiments on predatory snails in which variability among predators and a strong training effect produce switching.

ISSN:0012-9658    

DOI:10.2307/1934385

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Studies were conducted to determine species response to low—temperature environments. Apical development was found to progress at near—freezing temperatures throughout the winter except when the plants were encased in a solid soil—ice matrix. Claytonia lanceolata and Nemophila breviflora shoots developed above the soil surface, under snow cover. In both species, chlorophyll content was inversely proportional to depth of snow cover. Spectrophotometric analysis of light penetration through snow indicated about 10% penetration through shallow layers (ca. 3.5 cm), and 0.01% through layers of 69 cm. C. lanceolata, Orogenia linearifolia, and Erythronium grandiflorum plants developed complete floral structures during the winter months, these being protected by leaves or an apical sheath (Orogenia).

ISSN:0012-9658    

DOI:10.2307/1934386

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

Trapping and banding of wintering juncos and golden—crowned sparrows was carried out from 1964 to 1968 along the opposite edges of an old field. The juncos ranged freely along the field borders but the golden—crowns were largely restricted to dense willow thickets in one part of the field. An attempt to assess possible competition between the two species by removing juncos in 1966—67 was unsuccessful because of infiltration of new birds from outside the study area. Removal of golden—crowns in 1967—68 reduced their population markedly and resulted in significant increase in use of the willow thickets by juncos. Although juncos are primarily seed eaters in winter, and seeds are a steadily dwindling resource at that season, competition for food between the two species was alleviated because the sparrows subsisted in large part on sprouting annuals, a resource renewed continuously after sprouting started following the fall rains. Further, the green food eaten by the sparrows undoubtedly satisfied their water requirements to a great extent and reduced competition for water sources. The competition demonstrated by removal experiments resulted not from direct competition for the same set of resources but from the proximity of a water trough, an important junco resource, to the heavy cover preferred by the sparrows. Although outnumbered about 5:2, the larger sparrows were able to exclude the juncos from this cover to an appreciable extent.

ISSN:0012-9658    

DOI:10.2307/1934387

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY

摘要:

The electrical conductivity and flow—rate of solution in a forest floor were continuously monitored in the field using a tension—lysimeter system coupled with automated recording instruments. Forest floor temperature was also automatically recorded. The field study site was in a uniform second—growth Douglas—fir forest on a glacial outwash soil in western Washington. Total ion amounts released from the forest floor during the movement of individual wetting fronts resulting from natural precipitation were calculated. These field data, together with data obtained in the laboratory, were used to develop a model of the transport process. Over the temperature range experience in the field, I, which is the total ion amount transport by a given total flow of solution, can be described by the algebraic model: I=M/1 + A exp(— BT), (0 degrees C

ISSN:0012-9658    

DOI:10.2307/1934388

出版商:Ecological Society of America    

年代:1973

数据来源: WILEY