ISSN:0012-9658    

DOI:10.2307/1936887

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The herbivorous gastropod Tegula funebralis is not highly ranked in a food preference hierarchy of its major predator, the starfish Pisaster ochraceus, and exhibits a persistent broad overlap with it in the rocky intertidal zone at Mukkaw Bay, Washington. Observations on Tegula over a 5—yr period indicate that it settles high intertidally, lives there for 5—6 yr, and then tends to migrate lower into contact with Pisaster. Tegula lays down an annual growth line permitting it to be aged and a growth curve constructed. Analysis of relative growth and reproduction indicates that beyond a certain size (16 mm) large individuals perform less well in the upper than those in the lower intertidal zone. Pisaster consumes 25—28% of the adult Tegula per year in the area of spatial overlap, based on analysis of the age structure of 6—17 yr old Tegula, and by direct estimates of the percentage of the standing crop consumed annually. The relationship between Pisaster and sex ratio, relative energy limitation and reproductive output (fitness) of Tegula is discussed for three subpopulations. It is suggested that the implied results of the interaction is typical of that between a major predator and one of its less preferred prey. The prominent zonation exhibited by preferred prey, the observed intimacy of association of predator and less preferred prey, and the zoogeographic homogeneity of the Pacific rocky coastline community are discussed in relation to three intermeshing ecological processes.

ISSN:0012-9658    

DOI:10.2307/1936888

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Monthly samples of nutrients, phytoplankton and zooplankton were taken in the Columbia River estuary over a period of 16 months in order to determine distribution with season and salinity, and interrelationships between plankton and nutrients. Nitrate and phosphate levels in the river water entering the estuary are high in the winter and show depletion during the summer. Silicate levels are high in the river water at all seasons. During the summer up—welling season nitrate and phosphate levels in the entering ocean water are high. Although nutrient levels in the estuary generally show a linear relationship with salinity, nutrients tend to be enriched in the bottom waters of the central part of the estuary. The estuarine phytoplankton is primarily composed of freshwater species, and probably represents a downstream extension of the river flora. Linear regression analysis indicates a strong correlation between phytoplankton abundance and solar radiation. The estuary zooplankton is composed of fresh water, oligohaline and polyhaline forms. Eurytemora affinis, an oligohaline form, is the major zooplankter, reaching population densities of 100,000/m3or more. Regression analysis indicates a strong correlation between abundance of freshwater zooplankter and river temperature. Regression analysis indicates close correlation between phosphate levels and Eurytemora abundance. This indicates a strong potential for zooplankton regeneration of phosphate necessary for phytoplankton growth.

ISSN:0012-9658    

DOI:10.2307/1936889

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The distribution of I131among the biota of Fern Lake, Washington, was compared in aquarium and field experiments. The samples for study in the laboratory were isolated in containers so that the water solution, and not food, was the major source of the radionuclide. The field experiment related the uptake of I131by organisms isolated in containers to the accumulation by those with access to their usual sources of food. In the aquarium, the initial concentration of I131was 8,000 times the average concentration calculated for the lake experiment. Maximum concentration factors ranged from 1.7 and 2.6 for the muscle of trout and crayfish, respectively, to 280 for the "thyroid" of trout, 380 for Nitella, and 600 for an amphipod. I131was not detected in a number of samples collected from the lake, but accumulation factors were as high as 1,400 for Nitella clumps and 12,000 for the "thyroid" of trout. Young microcrustaceans, which are able to accumulate iodine directly from water, were an important source of I131for trout.

ISSN:0012-9658    

DOI:10.2307/1936890

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The feasibility of using the Ca, Mg, and Sr content of freshwater clamshells as indicators of paleohydrologic conditions has been investigated. The Sr/Ca ratio varies with the discharge of Mill Creek, Iowa. The Sr/Ca ratios of clamshells excavated from American Indian midden sites near the Big Sioux River in Plymouth County, Iowa (Kimball Site 13 PM 4), and the Phipps site (13 CK 21) located near Mill Creek in Cherokee County, Iowa, show significant changes that can be related to changes in climate in the period 900 to 1400 A. D. Based on the results of this investigation, the alkaline earth composition of freshwater clams probably can be used as an indicator of paleohydrologic conditions.

ISSN:0012-9658    

DOI:10.2307/1936891

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

This was a study of seasonal distribution of dominant benthic macroinvertebrates in Pickerel Slough, a Mississippi River floodplain lake in Minnesota. The lake was shallow–0.75 m deep during the summer–and had a relatively uniform benthic habitat with no rooted aquatic plants. The total number of benthic macroinvertebrates was greatest in the late fall and winter; they decreased rapidly in the spring owing to emergence of dipterans and decrease in number of oligochaetes. Congeneric species demonstrated three patterns of life cycle interrelationships. Complete seasonal replacement was found for Tanypus: T. stellatus produced two summer generations and probably overwintered as eggs, whereas T. neopunctipennis overwintered as larvae. Overlapping seasonal replacement was shown by Procladius: the largest P. culiciformis preceded P. bellus in both emergence and larval growth. Although both populations were present in the sediments at the same time, they always maintained larval size difference. Overlapping seasonal replacement combined with annual substitution was demonstrated by Chironomus. The largest species, C. plumosus, was the first to have growing larvae in the fall, and this was followed by the growth of the two smaller species: C. near staegeri, and C. decorus. C. plumosus and C. decorus predominated in alternate years. There was a population of growing dipteran larvae at all times during the year. The dominant populations (Chaoborus punctipennis, Chironomus spp., Procladius spp., and Tanypus stellatus) had the growing larval stages of their life cycles spaced so that they did not overlap, thus reducing the competition between them.

ISSN:0012-9658    

DOI:10.2307/1936892

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Seven species of congeneric lizards (Ctenotus) frequently occur in ecologic sympatry in the Australian desert. The ecologies of these and seven other species are described and compared, with particular reference to niche differences. Adult Ctenotus range from 45 to 118 mm in snout—vent length. Larger species take larger prey items than smaller ones. Six species do most of their foraging in the open spaces between plants, while six others forage mostly within the dense tussocks of porcupine grass (Triodea). The former have proportionately longer hindlegs than the latter. It is demonstrated that hindleg and head proportions are good morphological indicators of the place niche and the food niche, respectively, and that body temperature reflects the time niche in a useful way. Lizards with higher body temperatures are usually active later in the day than those with lower body temperatures. Whereas the species which forage in the open show a poor correlation between air temperature and body temperature, those that forage in shady places within vegetation have body temperatures closely correlated with ambient air temperatures. The former are dependent upon direct solar and/or substrate heat, while the latter appear not to substantially exploit these heat sources. After analyzing the ways in which the lizards subdivide habitat space and environmental resources, it is concluded that there are at least three dimensions to the Ctenotus niche: place, food, and time. An analysis is presented which demonstrates that Ctenotus are ecologically rather tightly "packed," and it is suggested that the overall differences between pairs may represent minimal ecologic distances.

ISSN:0012-9658    

DOI:10.2307/1936893

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

The rate of growth in body weight of birds is not correlated with nestling mortality, but rather is a function of the adult body size of the species and the mode of development of the young. To examine the adaptive basis of growth rates, models are formulated which incorporate the mortality of the young, their energy requirement and their rate of growth into a function which determines the productivity of offspring. This function is maximized when growth rate occurs as rapidly as possible, at the expense of brood size. Optimally, one young should be raised which grows as rapidly as the parents are able to supply food. Because this is not observed in nature, and because of other inefficiencies due to the form of the growth curve, it is postulated that physiological constraints, based on the functional organization of the body plan, limit growth rate. This may occur either through bottlenecks placed on the rate at which food can be processed and utilized, or by problems of allocation of energy and tissues among mature and embryonic functions.

ISSN:0012-9658    

DOI:10.2307/1936894

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

Homing to overwintering sites, spring emergence, and structure and density of a population of the Manitoba toad, Bufo hemiophrys, were studied in northwestern Minnesota from 1960 to 1967. Data were obtained on 15,837 individuals as they emerged from their wintering sites. Toads generally returned to the same Mima—type mound each fall, although individuals from various mounds were mixed in the breeding choruses and at the pond margins during summer. The high percentages of toads which homed to the wintering site correctly, ranging from 88 to 95%, indicate remarkable orientation capabilities. Toads committing an error when homing are much more likely to select a mound near their "home" mound, rather than a more distant one. Error rates were 10.2% for toads released as year—old juveniles and 2.9% for adults. Emergence occurs during a 5—6 week period, generally starting during the last few days of April. In general adult males emerged before adult females with juveniles emerging last. Deep frost in the soil delays the period of emergence. Population structure and density were determined mainly from toads wintering in four mounds. Yearly trends in juvenile numbers have been unanimously reflected by all four mounds. The 1966 population size, estimated by the Lincoln index, was 510 males, 1,276 females and 2,415 juveniles. Adult sex ratios varied from 33 to 38% males. The best estimate of the age structure of the total population at the time of breeding varied from 1.47 to 14.06 juveniles per adult. Survival of all toads from year to year ranged from 23.9% in 1963 to 44.4% in 1965. Juveniles had lower survival rates than adults, with the greatest mortality occurring in 1963 as the result of light snow and subsequent deep frost.

ISSN:0012-9658    

DOI:10.2307/1936895

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY

摘要:

This study analyzes ecological factors determining numbers of adults produced in pure and mixed larval populations of two strains of houseflies, Orlando No. 1 (OL) and green—eye (ge), at low and high density. In pure and mixed cultures at low density, survival of OL was greater than that of ge. However mixtures significantly facilitated survival of ge, while lowering their mean dry weights. The interaction in mixtures resulted from 1) higher mortality in late hatching, smaller larvae; 2) more such in ge than in OL; 3) lack of a substance in ge, produced in OL, that enhances yeast growth. These factors lead to fewer deaths of small ge larvae in mixtures, resulting in increased mean survival while lowering mean adult weight. In pure cultures at high density, performance of ge was greater than that of OL because lower egg hatching in ge made more food available per individual. In mixtures OL is superior to ge owing to a faster feeding and growth rate relative to a constant critical weight for completing development.

ISSN:0012-9658    

DOI:10.2307/1936896

出版商:Ecological Society of America    

年代:1969

数据来源: WILEY