Showing papers in "Ecology in 1967"

An Index of Diversity and the Relation of Certain Concepts to Diversity

Abstract: The uses in ecology of the terms richness, diversity, homogeneity, and similarity are considered in the context of recent studies of plant and animal communities. Various uses of divesity are reviewed and an index of diversity derived from the distance measure of similarity is suggested. This index is Σi=1n2i where S equals the number of species and n equals the number of individuals in each species. This index is compared with other indices of diversity. The principal problem of measuring diversity is the assessment of the homogeneity or similarity of the sample or samples being studied. An advantage of the proposed index is that it derives from a measure of similarity of which it is a special case, and it is a special case, and it is a more natural and familiar representation of points in a coordinate system. See full-text article at JSTOR

Role of Allochthonous Detritus in the Trophic Structure of a Woodland Springbrook Community

Abstract: The community trophic structure of Morgan's Creek, Meade County, Kentucky was analyzed through regular measurement of standing crops of the chief potential sources of plant materials available to the animals (suspended particulate, attached particulate, and allochthonous leaf materials) and an examination of their gut contents. The most important food was allochthonous leaf materials, which occurred as suspended material in the water, as a component of materials attached to the streambed, and as whole leaves and fragments. Diatoms were the only other important source of plant materials and constituted the greatest proportion of the attached organic fraction. Mean standing crop measurements of potential foods for five sampling stations ranged from 0.6 to 1.0 kcal/m3 for suspended particulate organic matter; 12 to 19 kcal/m2 for attached particulate organic matter; and 4.7 to 13 kcal/m2 for allochthonous leaf materials. Comparison of standing crop data with previous findings indicates that the values generally are within the known ranges for flowing waters. Analysis of gut contents and determination of the principal pathways of energy flow in the stream indicate that imported organic matter in the form of allochthonous leaf materials provides the main source of energy for the primary consumers and, indirectly, for the entire benthic community of Morgan's Creek. Of the 37 taxa of animals studied, 24 were herbivores, 5 omnivores, and 8 carnivores. In general, detritus made up from 50 to 100% of all the materials ingested by both the herbivores and omnivores. The total number of benthic animals was comprised of 14% herbivores, 83% omnivores, and 3% carnivores. Gammarus minus was the single most important member of the fauna. It contributed 81% of the total number of invertebrates, and well over 90% of its diet consisted of allochthonous leaf detritus.

A New Model For Age-Size Structure of a Population

Abstract: An equation describing the dynamics of single species populations is derived. The model allows for variations in the physiological characteristics of animals of different ages and sizes. An analytical solution which holds under certain specific conditions is found. It is shown that Von Foerster's equation, the logistic equation and other prior models are special cases of the new model. See full-text article at JSTOR

On Lizard Species Diversity: North American Flatland Deserts

Abstract: Eight potential mechanisms for the determination of species diversity are described and discussed, and data relevant to each are presented for a particular diversity gradient: namely that of the flat land desert lizards of western North America. It is concluded that ecological time, spatial heterogeneity, length of growing season, and amount of warm season productivity are all factors which determine the total number of lizard species occurring on an area, but that the most important single factor is the spatial heterogeneity (mainly vegetative) of the environment. It is suggested that climatic variability allows the coexistence of many different plant life forms, the variety of which in turn controls the number of lizard species.

The Calcium, Magnesium, Potassium, and Sodium Budgets for a Small Forested Ecosystem.

Abstract: Six West Thornton, New Hampshire watersheds are characterized by a near climax, northern hardwoods ecosystem, humid continental climate, and acid metamorphic rock. Concentration of Ca/sup + +/, Mg/sup + +/, K/sup +/, and Na/sup +/ in weekly precipitation samples was variable. The annual weighted average values (mg/liter) were; 1973-74, Ca 0.26, mg. 0.06, K 0.21, Na 0.09; 1964-65, Ca 0.30, Mg 0.12, K 0.19, Na 0.22. Differences were not related to elevation. The contribution of cations from dry fallout was negligible. Cation content of stream water was relatively very low. The weighted average content for the entire area (mg/liter) was Ca 1.18, Mg 0.38, K 0.26, Na 0.87 during 1963-64; and Ca 0.80, Mg 0.38, K 0.22, Na 0.91 during 1964-65. In general, the cationic concentrations in drainage water were constant although discharge of water varied greatly. Statistically, the relationship between concentration and discharge was not significant for Ca/sup + +/ and Mg/sup + +/ in any of the watersheds, but was inversely significant for Na/sup +/, and was possibly direct for K/sup +/ in a few instances. The budget for dissolved cations was calculated from determinations of input (cation concentration times volume of precipitation) and output (cation concentration timesmore » volume of runoff.) During 1963-64 the average inputs in kg/ha were 3.0 Ca/sup + +/, 0.7 Mg/sup + +/, 2.5 K/sup +/, and 1.0 Na/sup +/, while the output averaged 8.0 Ca/sup + +/, 2.6 Mg/sup + +/, 1.8 K/sup +/, and 5.9 Na+. During 1964-65 the values were: input, 2.8 Ca/sup + +/, 1.1 Mg/sup + +/, 1.8 K/sup +/, and 2.1 Na/sup +/; and output, 3.9 Ca/sup + +/, 11.8 Mg/sup + +/, 1.1 K/sup +/, and 4.5 Na/sup +/. Assuming that the vegetation is near synamic equilibrium, the net losses of Ca/sup + +/, Mg/sup + +/, and Na/sup +/ represent conservative measurements of geochemical weathering in the system. The K/sup +/ budget is probably near balance.« less

Ecology of Vervet Monkeys (Cercopithecus Aethiops) in The Masai-Amboseli Game Reserve, Kenya

Abstract: Aspects of the ecology of vervet monkeys (Cercopithecus aethiops) are de- scribed on the basis of a 21 month field study in East Africa. Analysis of home range utilization demonstrated differences between 4 groups. The smallest group distributed its time over a greater area than did the other groups. For 3 of the groups there appeared to be a strong relationship between group size and the amount of optimal habitat defended. The smallest group defended more optimal habitat than expected. However, this same group spent only 60% of its time in this habitat, whereas the other groups all spent more than 95% of their time in it. The smallest group may have avoided the optimal habitat of its territory as an area of frequent intergroup aggression, and as a result utilized a larger and less pro- ductive area. Sleeping-tree preferences of groups and individuals are described and discussed. The minimal distance traveled each day by vervet groups varied from 148 to 2,797 yd. In comparing the mean daily distance covered by 2 groups of equal size it was found that one moved significantly further than the other. More trips were made to permanent water holes between 1300 and 1500 hr and during the dry season than at other times. The frequency of group progressions was greatest at 0700 to 1000 and 1600 to 1900 hr. Study of food habits shows that they were opportunistic omnivores. Elephants were the greatest food competitors of the vervets. The monkeys had at least 16 potential predators. Outside of parks and reserves the greatest predator was the European commercial trapper. Ecological characteristics of vervets and their niche separation from baboons are discussed.

Aggression and Self-Regulation of Population Size in Deermice

Abstract: Sadleir (1965) proposes that seasonal changes in the survival of juvenile deermice are determined by seasonal changes in the aggressiveness of the adult population. The purpose of the study is to examine some of the consequences of Sadleir's hypothesis experimentally. Laboratory studies confirmed Sadleir's observations on seasonal changes in the aggressiveness of male deermice. Similarly, in the laboratory, juvenile deermice grew poorly when competing with adults in their home cage. Further analysis showed that only aggressive males are capable of inhibiting juvenile growth. In order to avoid the crowded conditions and confinement implicit in the laboratory experiments, the relations between adult aggressiveness and juvenile growth and survival was reexamined in field experiments. Artificial populations or docile male deermice were established in field plots. Juveniles were then released onto the plots, and their growth and survival followed. Juveniles again grew poorly when competing with aggressive adults, but in the field juveniles also disappeared rapidly from the experimental plots when the adult population was aggressive. The success of immigrants onto trapped out plots and plots with a resident population was examined as well. Immigrants were more successful in establishing themselves on trapped out plots. All the data collected support Sadleir's hypothesis, and it is concluded that the correlation he drew between adult aggressiveness and juvenile survival is real. The data also provide some clues to the organization of deermouse populations. An organization is proposed in which the social units is an animal and its immediate neighbours. Within the social unit mutual antagonism is reduced. But the members of the unit remain highly aggressive, and are intolerant of any stranger that wanders into their home ranges. The system proposed prevents immigrants from settling, the helps to regulate population size, while conserving energy by reducing antagonism between familiar animals.

Dispersal in Vertebrates

Abstract: A hypothetical population is considered in order to gain insight into the factors that may be responsible for the skewed distributions of dispersal distances that have been reported in vertebrates. In this population the most effective factor is the relative dominance of the indivduals in procuring breeding sites. If this is true of natural populations, dispersal permits each individual to maximize its chance to reproduce. Earlier explanations that selection for genotypes that are advantageous to the species but disadvantageous to individuals are not necessary to explain the skewed distributions of dispersal distances in vertebrate populations. See full-text article at JSTOR

Population Ecology of Feral House Mice

Abstract: Demographic changes which occurred during population fluctuations in the field were studied by live—trapping six populations during a two—year period. An attempt was made to determine the factors which prevent unlimited population increase. Four major population declines were observed. Epidemic disease caused mortality in one. A second population declined in the fall when insufficient food caused cessation of reproduction. The addition of supplemental food on two experimental grids, however, was sufficient to support both high growth rates and high recruitment of young during the winter, but supplemental food was not sufficient to maintain breeding indefinitely. These populations declined during the usual breeding season in the presence of supplemental and natural food, abundant cover, and few predators. It therefore seemed probable that these two populations were not limited by external factors, but by some intrinsic mechanism. Increased emigration and mortality, primarily of juveniles and subadults, occurred during the latter part of the population increase, but the decline of these populations was primarily caused by a large reduction in the number of weaned young per lactating female, and finally by cessation of breeding conditions in females. Several general characteristics of these populations were established. Body growth rates were highest during the late spring and early summer and lowest during the winter. Home ranges were first established by juveniles or subadults, and were rarely shifted unless the animal left the population. Similarly, the mean length of daily movement by any weight group did not vary greatly, even with a change in breeding activity or population density. Both mortality and dispersal, however, were affected by the breeding condition of the population. In breeding populations, mortality and dispersal of juveniles and subadults increased markedly as density increased, whereas during the nonbreeding season, those parameters were not affected by the weight of an animal, density, or supplemental food.

Meditteranean Ecosystems and Vegetation Types in California and Israel

Abstract: A comparison of climate, soils, vegetation, and biotic history of mediterranean ecosystems revealed closest ecological equivalence between the blue oak grassland in California and the vallonea oak grassland in Israel, both mediterranean oak savannas in which overall environmental resemblance seems closest. Ecological amplitude and syndynamics in most other comparable types are similar, but the chamise chaparral on non-calcic brown upland and lithosols differs from its maqui counterpart by its one-layered structure and by its adverse influence on the ecosystem. Annual grasslands in California foothills are comparable to seral batha dwarfshrub and grassland in Israel as human-induced degradation stages of chaparral and maqui. For such ecological comparisons a holistic ecosystem approach seems more suit- able than any preconceived phytoclimatic and climax concepts.

Dispersal of Aquatic Organisms: Viability of Disseminules Recovered From the Intestinal Tract of Captive Killdeer

Abstract: Earlier studies have shown that viable disseminules of a variety of aquatic, organisms my be recovered from the feces of birds. The present report is concerned primarily with the maximum length of time that vegetative cells and spores of algae, various crustacean eggs, and living adult ostracods can be retained within the divestive tracts of Killdeer (Charadrius vociferus) and, to a lesser extent, Mallard Ducks (Anas platyrhynchos). Some disseminules survived only rapid passage while others were still viable after being retained within the intestional tract for 12—24 hr. Eggs of Artemia salina and oospores of Chara zeylanica were retained for the longest periods. Viable disseminules were retained for much longer periods by Killdeer than by ducks. The results suggest that Killdeer and similar shore birds may be important agents of transport for many kinds of aquatic organisms. Smaller numbers of disseminules area carried by individual shore birds than by ducks, but they can be retained for longer periods, ...

Food, Age, and the Dynamics of a Laboratory Population of Rotifers

Abstract: Two clones of the rotifer Euchlanis dilatata were derived from a single parent by parthenogenesis so that in succeeding generations the individuals of one clone (the young orthoclone) were always derived from young parents and those of the other (the old orthoclone) from old parents. These clones were fed four different food concentrations (1.6, 4.9, 16.4, and 49.2 mg/ml) of three different algal species (Chlamydomonas reinhardti, Euglena gracilis, and E. geniculata). Rates of increase, birth, death, survivorship, net reproduction, and generation time were measured for all combinations of these variables. Growth rates of individual animals depend on food concentration and not age or food species. Although population growth rates in mass culture are related to both food species and food concentration, the ultimate density of the population depends only on food concentration. Individuals of the young orthoclone have higher rates of population increase than those of the old orthoclone. When Euchlanis fees upon Chlamydomonas the rates of increase are higher than when Euglena gracilis serves as food. E. gracilis, in turn, leads to higher rates than E. genicultata. The rate of population increase is directly related to the density of food for concentrations up to 16.4 mg/ml, but a further increase in food concentration does not result in a corresponding increase in the rate of population growth. These different rates of increase result more from corresponding differences in net reproduction (number of eggs laid by the average female in her lifetime) than from the schedule of egg laying of survivorship. The different rates of population growth can not be explained by differences in the rate of food intake and must result from either differences in assimilation or chemical differences in the foods themselves.

Population Growth in Micro‐Organisms Limited by Food Supply

Abstract: It is suggested that an hyperbolic equation of the form (1/n) (dn/dt) = rb/(b + A) where n is the population density, b the concentration of limiting food supply and A and r are constants, is widely applicable as a density-dependent growth model. An attempt is madse to state explicitly the conditions under which it would apply. A consideration of the kinetics of food uptake leads to the interpretation of the constant A as representing a ratio of two rate constants, k3 /k1 where k1 is the rate constant associated with first step in food uptake and k3 is associated with the second step which results in the freeing of the adsorption site. The constant r represents a composite expression, k3 co /(qn) where co /n is the number of adsorption sites per individual, and q is the amount of food required to produce a new individual. Density dependent population growth models must always include a second equation which describes the effect of population growth on the environment (in this case food supply). The failure of the logistic equation to provide the necessary generality for this effect is pointed out. The applicability of this model for a number of different bacterial populations using a variety of both energetic and substantive food as the growth-limiting factor has been established for several years. Data are presented to show that it is also applicable to the unicellular alga, Isochrysis galbana, growing under limiting nitrate concentration and to several species of phytoplankton growing under limiting light intensity. The quantitative effects of preconditioning light intensity on chlorophyll per cell (co /n) and on k3 are noted as examples of the usefulness of this more detailed consideration of the growth constants, r and A.

The Energy Budget of a Lizard on a Tree Trunk

Abstract: Lizard and environmental properties which determine the exchange of energy between a lizard and its environment are described and related analytically in the equilibrium state to the lizard temperature. Absorptivities, surface areas, body temperatures, and convection coefficients were determined; metabolic and evaporative energy exchanges estimated for a representative Sceloporus occidentialis. The environmental properties of a particular tree trunk habitat are estimated for a June 21 day and the behavior of S. occidentialis predicted in terms of the positions lizards could assume and maintain their body temperatures within the range characteristic of the population in that habitat. The predictions are compared with field observations. See full-text article at JSTOR

Flowering and Fruiting in the White Oaks. Pistillate Flowering, Acorn Development, Weather, and Yields

Abstract: Female flowering and acorn development in three species of which oaks were studied in Pennsylvania from April 1949 through August 1962 with emphasis on the effect of weather on floral development and acorn production. Pistillate flowers emerge in late April or early May, 5—10 days after the appearance of staminate flowers. After pollination and fertilization, developemnt of acorn forms begins, and filled acorns mature late in August. Spring air temperatures strongly affect acorn yields. Good white oak acorn crops were obtained in years when a warm 10—day period occurred late in April, with average night temperatures 55—60°F, followed by cooler periods (45—50°F) for 13—20 days early in May. During years when April remained cool and was followed by warm days and nights in May, acorn production was poor. Wind, precipitation, relative humidity, and vapor pressure deficits did not significantly influence acorn yields. While some individual trees were inherently copious acorn producers, others in the same stand produced none or a light crop throughout the 14—year period.

Tropical Savanna Vegetation of the Llanos of Colombia

Abstract: The Llanos Orientales of Colombia are between 3? and 70 lat N, extending as a level plain between 600 and 200 m above sea level, east of the Andes Mountains. The hot trop- ical climate shows a seasonal pattern of rainfall, divided between one rainy season and one dry season. In the survey of a 45,000-square-mile study area within this llanos region, 10 savanna types were recognized and classified on a floristic basis. Three of these types were floristically distinct, but with the homologous factor of all having relict forests. The other seven savanna types intergraded along a gradient of increasing humidity, and for convenience were divided into dry, humid, and inundable savannas. A great number of species were shared by these last seven types, their distinction being based on the relative dominance of species in the different types. The various theories on the origins of tropical savanna are discussed in the light of this new information on vegetation and that found in a concurrent soil survey. No single factor is believed responsible for savanna formation, but deflection from forest development is considered the result of several adverse factors, with savanna formation accelerated once the. process has started.

Effect of Shade on Leaf Structure of Deciduous Tree Species

Abstract: Sun and shade leaves of 21 deciduous tree species were measured and tissue development compared. Species considered tolerant of shade had normally thinner sun leaves and less reduction in thickness in shade than did species considered intolerant. Sun—leaf/shade leaf ratios in the palisade layer were 1.22, 1.32, and 2.36 for the tolerant, intermediate, and intolerant classes respectively, while for the mesophyll the equivalent ratios were 1.9, 1.27, and 1.51. Thickness of both palisade and spongy tissue was highly correlated with blade thickness in both sun— and shade—grown leaves. Druse and prismatic crystals were prevalent in the mesophyll and vascular tissues of 14 species. See full-text article at JSTOR

Survival of Winter Annuals in the Northern Mojave Desert.

Abstract: Following early autumn germination in Mojave Desert winter annual populations (53 taxa) sampled on 13 plots (total sample size, 16.4 m2 ) in three drainage basins in southern Nevada, 1963-64, there was 38% survival to maturity (plot range 10-63%). Death occurred in early spring, at the time of shift from the slow vegetative growth of winter to the beginning of stem elongation. Despite no marked precipitation deficiencies during the 7- to 8-month growing season, mortality apparently resulted from inadequate soil moisture to meet the demands of seedlings at the point in the life cycle of a manyfold increase in plant volume. Mean percentage survival to maturity of seedlings (58 taxa), sampled on 62 plots (total sample size, 62 m2 ) in sevean drainage basins, following spring germination after rains of 3-5.5 inches in March-April 1965, was 60% (range by basin, 44-83%). Mortality in these populations, whose life cycles were completed in 6-10 weeks, could not be attributed to inadequate moisture levels. In most seasons, regardless of precipitation regimes, the majority of seedlings of desert annuals probably do not survive to maturity.

Growth Inhibition in Crowded Tadpoles: Intraspecific and Interspecific Effects.

Abstract: Tadpoles are inhibited in growth when raised in water previously crowded by other larger tadpoles. The `alga—like' cells described in earlier crowding studies were found in the fecal material and intestinal tracts of inhibited tadpoles. Results of 38 crowding experiments using 17 species of tadpoles show that the effects of the inhibitory cell are nonspecific. Water (with cell—laden fecal matter) from crowded tadpoles of one suborder can inhibit the growth of assay tadpoles of a different suborder. There is no decreasing level of inhibition with phylogenetic distance. Bufo woodhouse is the only one of 17 anuran species tested that seems immune to these inhibitory effects. Tests with Bufo woodhouse indicated the existence of a possible intraspecific growth—promoting substance. The substance may also inhibit some species, and not affect others. Metamorphosing tadpoles may release a nonspecific growth—stimulating substance (thyroxine?) into the water, which may alleviate the effect of inhibitory substances. ...

Total net productivity and turnover on an energy basis for tallgrass prairie

Abstract: The energy equivalent of total net productivity including foliage and roots on unburned prairie in 1962 was 4.351 X 106 cal/m2, representing 992 g of biomass. The root system provided slightly over 50% of the annual increment. For 1963 the total growth was 1,133 g/m2. The average energy for these years was equivalent to 1.21% of the incident radiation received during the growing season for the 400—700 μm portion of the light spectrum. The maximum energy budget including current increment, roots of previous years, and litter was equal to 2.6 turnovers. In years with favorable rainfall, fire approximately doubled the aboveground yield. During drought, productivity increases of fire plots over control plots were curtailed sharply. On a dry matter basis, the total aboveground biomass at the end of the growing season was approximately twice that of the standing crop. During the April—September period for 3 years of observation, the loss in dry weight of the aboveground material ranged from 57% to 65%. For the remiander of the year the decrease was 31—39%. These values indicate a fluctuating but generally balanced annual system of growth and decay. For aboveground biomass, the turnover estimate was 2 years, and for root biomass, 4 years. The decay time of a standing crop or root increment as determined from isolated litter samples and carbon—14—labeled roots in the field indicated that the annual turnover was comprised of a series of increments of different ages, decreasing in caloric content with time on a dry weight basis (uncorrected for ash). On an ash—free basis, litter 4 years old showed some increase in caloric content, suggesting changing composition of the residual fraction. The tallgrass prairie is seen as a relatively efficient ecosystem when compared to the worldwide terrestrial average. The stimulus of fire to dry matter production in the humid prairie indicates a more efficient use of solar energy; however, the long—term effects of sustained burning require observation.

Salinity Tolerances of Five Marine Spermatophytes of Redfish Bay, Texas

Abstract: Thalassia testudinum Konig and Sims and Halophila engelmanni Aschers. (Hydrocharitaceae); Diplanthera wrightii (Aschers.) Aschers., Ruppia maritima L., and Syringodium filiforme Kutzing (Potamogetonaceae) are the major plants of the highly productive estuaries along the Texas coast. When transplanted to outdoor ponds and to controlled growth rooms, the greatest tolerance to increasing salinity was shown by Diplanthera. Lesser salinity tolerance was shown by Thalassia and Ruppia. Although survival was not complete under all transplant conditions for Syringodium, it showed least tolerance of high salinity. Halophila survived sporadically in the study but showed active growth at high salinity. The distributional patterns of these species in Redfish Bay are partially correlated with their salinity tolerances. See full-text article at JSTOR

Temperature and Development of the Wood Frog, Rana Sylvatica, in Alaska

Abstract: Wood frogs breed in a variety of ponds and lakes in central Alaska. Dates of first appearance of frogs ranged from 24 April to 22 May. Egg laying began 4—6 days later. Egg laying was completed in a pond 4—8 days after the first egg mass appeared. Wood frogs tend to lay their egg masses at the same spot. The average number of eggs per mass was 778 with an egg diameter of 1.6 mm. Development of eggs was directly related to water temperature and occured at the same rate as that shown for wood frogs from New York. Temperature limits that permit at least 50% survival of eggs through hatching were 6°—24°C. Temperature tolerance of eggs and tadpoles varied with age and acclimatization. Temperature preference of tadpoles followed a normal curve and ranged from 9° to 29°C. Development in the field varied among different ponds and different years. Rapid growth occured once the larvae were free swimming. Average maximum weight ranged from 2.15 to 2.85 g; maximum length varied from 5.5 to 6.0 cm. Time to metamorephosis ranged from 53 to 78 days. Two periods of development are distinguished: In period I, fertilization to free—living stage, growth rate is determined by water temperature. This period occupies one—third of the development time but has a higher mortality rate than period II. The later period includes the free—swimming stage until climax metamorphosis, and development rate is determined by environmental factors such as food and population density, as well as temperature.

Changes in Internal Atmosphere of Submersed Vascular Hydrophytes in Relation to Photosynthesis

Abstract: Gases were extracted from the internal atmosphere of Elodea canadensis and Ceratophyllum demersum in a closed system under reduced pressure. The volume of extractable gases varied throughout the daily period. Gases separated and quantitatively measured by gas chromatography included CO2, O2, N2, and CH4. Results from diurnal studies showed a lag between peak values for dissolved oxygen in the surrounding water and oxygen in the internal atmosphere. Lags were also observed in the CO2 values. As a result photosynthetic activity by these plants is not immediately reflected by changes in dissolved oxygen content of the surrounding water. The lacunal system apparently functions as a reservoir for metabolic gases. Experiments in whcih light intensity was controlled by floating screens indicated that at low intensities evidence of oxygen production in E. canadensis may be obtained only by observing the changes which occur within the internal atmosphere. At these intensities no increase in dissolved oxygen can be detected in the surrounding water although internal oxygen concentrations may increase slightly. Confirmation that carbon was being fixed by the plants under these conditions has been obtained by carbon—14 uptake studies using gas phase counting procedures. The observations cast furthur doubt on the reliability of using changes in dissolved oxygen as a sole measure of photosynthetic activity in aquatic ecosystems where submersed vascular plants are dominant.

Species Diversity in Chydorid (Cladocera) Communities

Abstract: Microfossil remains from surficial sediments of 20 Danish and 14 northern Indiana Jakes were counted, and their relative percentages calculated. Using the function H = — Σp°ilog2°° species diversity was calculated for each lake. Indices of diversity for each lake and data on primary production and transparency were subsequently ranked and Spearman's rank correlation coefficient was determined between species diversity and production, and species diversity and transparency. Interpretation of results within the framework of information theory was not satisfactory. It is sugested that species diversity of chydorids is controlled primarily by complexity of the thier habitat, the rooted aquatic macrophytes of lakes. See full-text article at JSTOR

Relationship Between Standing Crop and Primary Productivity Along a Hot Spring Thermal Gradient

Abstract: Quantitative measurements of photosynthesis (by carbon—14) and chlorophyll were made for algal mats which had developed at a series of stations along the thermal gradient formed by the outflow channel of a hot spring at Yellowstone National Park. The temperature range studied was from 30°—70°. Comparisons were made of photosynthetic efficiency, which had been measured and calculated in different ways. There was no simple correlation between standing crop (as measured by chlorophyll, protein or RNA per unit area) and photosynthesis. Animal grazers on the algal mats occur only at temperatures below 50°; the low standing crop at the lower temperatures may be due to the comsumption of algae and bacteria by these animals. At a temperature of 58oC, very thick mats are found, composed mostly of filamentous bacteria with a surface layer of algae. It is suggested that the organic carbon originating from the algae is assimilated by these bacteria and is not released because of the absence of grazers. At temperatures close to the upper limit for algal growth, standing crop is low although photosynthetic efficiency is high, and the algae are optimally adapted to the temperatures at which they are living. Some physiological factor other than photosynthesis may limit the growth of algae at these highest temperatures. The value of hot springs as models to study aspects of ecosystem trophodynamics is shown by this work.

Zonation of Nearshore Mysids

Abstract: Between the shore and 17 m depth, over sand bottom on the open coast of southern California, five species of hypopelagic mysids and four species of benthic mysids occurred in bathymetric zones roughly parallel with the shore. The possible causes and function of zonation of the numerically dominant pelagic species were examined. The information suggests that the zonation may have developed as observed mainly in response to the pattern of availability of food that was imposed by the nearshore circulation system, and that competitive exclusion of other pelagic specied occurred. The zonation may provide a situation wherein population control can be effected by changes in reproduction rate. See full-text article at JSTOR

Systems Analysis of 134Cesium Kinetics in Terrestrial Microcosms.

Abstract: Laboratory experiments were conducted to determine patterns and rates of 1 34Cs exchange in microecosystems composed of different combinations of radioactive leaf litter, soil, microflora, millipedes, and aqueous leachate. Rate constants were determined by fitting models to data with an analog computer. Simulations with the models permitted comparisons of different microcosms in terms of time to radiocesium equilibrium, steady state concentrations, concentration factors, input and output fluxes, turnover rates, and stability. Rate constants varied with different compartment combinations, indicating both qualitative and quantitative differences in the cesium exchange patterns within different systems. This result is generalized: transfers of energy and matter in ecosystems are functions of networks which define intercompartmental interactions; internal coupling should be considered a significant variable in investigation of ecosystems processes. Points of particular interest derived from the computer simulations are (i) organism concentration factors for a material may vary in different systems, depending upon how the organism is coupled to other compartments; (ii) total flux of a material in a steady state system may vary considerably from that in another system which receives identical input; (iii) material turnover within compartments and in the system as a whole tends to increase as more compartments are added; and (iv) stability of material concentration does not appear to increase with system complexity.

Ecology of Zooplankton, Benthos and Fishes in the Columbia River Estuary

Abstract: Fauna of the Columbia River estuary were sampled regularly for 21 months. Analyses of plankton samples indicated that three distinct populations existed in the estuary: a freshwater group, a marine group, and an indigenous estaurine group. The latter consisted principally of a large population of Eurytemora hirundoides. Changes in the salinity of the estuary were reflected in the composition of the plankton. The majority of the fish and benthic invertebrates found in the estuary are euryhaline. The largest numbers of fish species, as well as the largest numbers of individuals, occupy the slightly brackish waters of the central portion of the estuary. the major plankton blooms also occur in this area. Starry flounder (Platichthys stellatus) and sand shrimp (Crangon franciscorum) use the upper estuary as a nursery ground. Extensive analyses of fish stomach contents confirm that food habits of fishes generally reflect the availability of prey. See full-text article at JSTOR

Evidence that Drift of Stream Benthos is Density Related

Abstract: The abundance of bottom fauna and of fauna in drift was studied in streams treated with DDT at various times in the past Recovery of the bottom fauna was found to be rapid, but that of drift was delayed The relationship of quantity of drift to the increasing bottom standing crop during recovery from spray effects was found to be curvilinear This suggested that drift is a density—related process Possible mechanisms to explain drift are discussed, and the conclusions of earlier reports on recovery of streams following insecticidal treatment are questioned See full-text article at JSTOR