摘要:

The biology of Australian reef populations of the shark Heterodontus portusjacksoni has been studied underwater with SCUBA. Additional life—history data have been obtained from catch records of adults and juveniles and from observations on captive animals. The mature breeding female H. portusjacksoni lays 10—16 eggs which are deposited in rock fissures on shallow reefs; the young emerge approximately 1 year later. The breeding season on the central coast of New South Wales occurs in late winter and spring. This species appears to segregate by sex into separate juvenile, adolescent, and adult populations. A slow growth rate and protracted immaturity is characteristic. Sexual maturity is reached at 8—10 years for males and 11—14 years for females. Most feeding occurs during darkness over both reefs and soft substrates, gut contents reveal that they feed on a variety of benthic invertebrates. Populations of H. portusjacksoni observed on sublittoral reefs consisted of adult sharks, the majority of which were females. A few specific sites, usually caves in which they shelter during the day, are preferred. Resightings of sharks tagged on a reef at Bondi, Sydney, revealed that animals which formed the local population moved freely to and from the reef and also between the several sites on the reef. Reef densities were highest during the breeding season and were correlated with low water temperatures. Emigration from inshore reefs occurs at the end of the breeding season in late September and October. A number of tagged sharks returned to the same reef in the following year and others after periods of up to 2 years. Recaptures made outside the Sydney area indicate that some sharks may travel several hundred kilometers during their migration.

ISSN:0012-9615    

DOI:10.2307/1948494

出版商:The Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The vertical distribution of phytoplankton standing crop, number of species, and community diversity in five transects across the ecotone of the Antarctic Convergence were studied in relation to physical and chemical habitat variables (light, temperature, salinity, density, relative stability, oxygen, phosphate, nitrate, and silicate) and to bacteria and yeasts. Two distinct phytoplankton communities were observed, one north and one south of the convergence. Within the convergence the southern diatomaceous Antarctic community sinks with the formation of Antarctic Intermediate Water and can be traced underneath the northern dinoflagellate subantarctic community by use of indicator species. Chaetoceros bulbosum, Chaetoceros dichaeta, Dactyliosolen antarctica, and Eucampia zoodiacus were used as indicators of the Antarctic community, and Rhizosolenia delicatula, Amphidinium amphidinoides, Oxytoxum variabile, and Phalacroma pulchellum represented the subantarctic community. Submergence of the Antarctic community is corroborated by the vertical distribution of phytoplankton biomass. South of the convergence in the upwelling system, biomass maxima of the phytoplankton consist of Antarctic species. Within the convergence separate subsurface biomass maxima contain the Antarctic community, and both Antarctic and subantarctic species constitute surface maxima of standing crop. In the upper water of the oceanic system north of the convergence, subantarctic species make up most of the biomass, where as small numbers of Antarctic species were observed in the aphotic zone. Surface layers of the euphotic zone in both systems were dominated by a small number of species. Maxima of species number occurred deeper than those of biomass, possibly reflecting the result of competitive exclusion. A low community diversity was observed in the upper water of each area, and a high ecotonal diversity was found at the convergence. A linear multiple regression analysis showed the relative importance of habitat variables in predicting the vertical distribution of the phytoplankton both within the oceanic and upwelling systems and within their transition zone. Water—mass structure, turbulence, light, silicate, and an index of heterotrophic conditions can be used to predict up to 66% of phytoplankton variation across the convergence. Additional prediction can only be achieved by incorporation of biological rate data and nonlinear expression of variable interaction in simulation models based on the present analysis.

ISSN:0012-9615    

DOI:10.2307/1948495

出版商:The Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The population dynamics and energetics of two populations of Diaptomus gracilis have been studied in two Thames Valley reservoirs. The seasonal changes in the standing crop biomass varied from a low of 0.3 Cal/m2to a high of 7 Cal/m2. Although the population overwintered primarily as adults, reproduction was continuous throughout the year. From the mortality rate the production has been estimated to be 52 and 48 Cal/m2for the Queen Elizabeth II and King George VI reservoirs, respectively. Feeding and respiratory rates of D. gracilis were measured both in the laboratory and in the field simultaneously with the population dynamics in the reservoir. The feeding rate and the rate of assimilation varied with the species of phytoplankton used as food. Filtering rates varied from 0.1 ml copepod—1day—1on bacteria to a high of 2.54 on Diplosphaeria, the latter also having an assimilation efficiency of 78% by D. gracilis. Respiratory rates varied with the season. When the metabolic rate was plotted against body weight, evidence of three regression lines during the year was found, the lowest slope in the winter and the highest in the late spring and early summer. When the regression of oxygen consumption on weight and temperature was calculated, it was necessary to calculate two lines, one for the fall—winter period and one for the spring—summer.

ISSN:0012-9615    

DOI:10.2307/1948496

出版商:The Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

The phenology of marked Hydrophyllum plants in five permanent 1—m2plots in Brownfield Woods near Urbana, Ill., was observed from March 1966 through August 1966 and from June 1967 through July 1968. The first—year plant which appears above the soil surface in early spring persists during the entire summer under the closed canopy with two to four erect, solid—colored, palmately shaped leaves. In autumn, mottled, palmately shaped leaves are formed which then overwinter in the form of a basal rosette. The upright, first—year leaves die back with the advent of heavy frosts. The plants break dormancy in early spring with subsequent formation of a large basal rosette of mottled, pinnately shaped leaves. As the forest canopy closes, solid—colored, palmately shaped leaves and an erect stem are formed. Floral buds soon appear. Flowering and seed set take place under a closed canopy with plant senescence occurring approximately 2 months after canopy closure. Carbohydrates are the major form of food reserves (82% of ovendry weight) in Hydrophyllum seed. At least a year is needed after seed dispersal before germination. Accumulated degree—hours and the floral bud and flowering stages are closely related in Hydrophyllum. Low temperatures are important in rosette formation in both greenhouse and field plants, but photoperiod apparently is not important if temperatures remain moderate. Plants will not flower unless they first develop a basal rosette. Although only a relatively short vernalization period is essential, longer periods of low temperature will decrease the length of time needed to flower after the plants have broken dormancy. Floral buds appeared in photoperiods ranging from less than 12 to over 13.5 hr, but longer photoperiods shortened the time interval between breaking dormancy and floral bud initiation. Hydrophyllum is adapted photosynthetically to canopy closure by producing different types of leaves for different light regimes. Plants with only solid—colored, palmately shaped leaves (first—year stage and seed—set stage) are present only under closed canopy conditions Light—compensation point of these plants is 60—80 ft—c, and light—saturation intensity is approximately 700 ft—c. their maximum net photosynthetic rates are about 2.4 mg CO2/dm2per hour. Mottled, pinnately shaped leaves are present on second—year vegetative plants which grow under an open, spring canopy. These plants have a light—compensation point of 100 ft—c and light—saturation intensity of 2,500 ft—c. Their net photosynthetic rate at light saturation is 8.5 mg CO2/dm2per hour. Flowering plants, which occur under a closed canopy and usually have both types of leaves, have net photosynthetic rates and light—saturation intensities at intermediate levels between the solid—colored and mottled groups of plants. All phenological stages except the seed—set stage demonstrated small but significant decreases in photosynthesis with increasing temperatures in the 15°—27°C range.

ISSN:0012-9615    

DOI:10.2307/1948497

出版商:The Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

An understanding of community structure should be based on evidence that the growth and regulation of the component populations in the community are affected in a predictable manner by natural physical disturbances and by interactions with other species in the community. This study presents an experimental evaluation of the effects of such disturbances and competitive interactions on populations of sessile organisms in the rocky intertidal community, for which space can be demonstrated to be the most important limiting resource. This research was carried out at eight stations on the Washington coastline which have been ranked according to an exposure/desiccation gradient and subjected to comparable manipulation and observation. Physical variables such as wave exposure, battering by drift logs, and desiccation have important effects on the distribution and abundance of many of the sessile species in the community. In particular, wave exposure and desiccation have a major influence on the distribution patterns of all the algae and of the anemone Anthopleura elegantissima. The probability of damage from drift logs is very high in areas where logs have accumulated along the intertidal. Log damage and wave exposure have complementary effects in the provision of free space in a mussel bed, as wave shock enlarges a patch created by log damage by wrenching the mussels from the substratum at the periphery of the bare patch. Competition for primary space results in clear dominance hierarchies, in which barnacles are dominant over algae. Among the barnacles, Balanus cariosus is dominant over both B. glandula and Chthamalus dalli; B. glandula is dominant over C. dalli. The mussel Mytilus californianus requires secondary space (certain algae, barnacles, or byssal threads) for larval settlement, but is capable of growing over all other sessile species and potentially is the competitive dominant of space in the community.

ISSN:0012-9615    

DOI:10.2307/1948498

出版商:The Ecological Society of America    

年代:1971

数据来源: WILEY

ISSN:0012-9615    

DOI:10.2307/1948498a

出版商:The Ecological Society of America    

年代:1971

数据来源: WILEY