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This paper tests the model of Meats (1974) by comparing its simulations with the real data of Milne et al. (1965) and of Laughlin (1967). Simulations are also made for conditions not previously investigated. [ABSTRACT FROM AUTHOR]

In a previous paper (Roff, 1974) a simulation model was presented demonstrating the importance of dispersal in a spatially heterogeneous environment. In the present paper this model is analysed in detail. It is shown that the qualitative properties of the model can be understood within the framework of a more general mathematical model. The effect of dispersal in a heterogeneous environment is to reduce the variance in the environmental fluctuations. How the subpopulations are connected with respect to dispersers may be the primary factor in determining the change in population size with changes in environmental fluctuations. Both the type of dispersal pattern and the number of subpopulations may influence the persistence of a population without affecting the mean subpopulation size. Finally, it is noted that the 'value' of a dispersal pattern changes with changes in parameter values and a shift from one parameter value to another may lead to a qualitative change in the type of dispersal pattern 'favoured'. [ABSTRACT FROM AUTHOR]

Investigations on the age-composition of the carabid beetle Calathus melanocephalus are discussed in a number of papers. The overall aim of this study is to estimate the significance of the variability in the age-composition in time and space of field populations of this species. This variability is thought to contribute to some degree to the stabilization of the fluctuations in animal numbers from year to year by which, for this species, the 'chance to survive' in some area will be increased. In an earlier paper the occurrence of this variability was demonstrated by comparing three populations of this species living in three different localities at Schiermonnikoog, and by comparing one population in three succeeding years. This paper tries to develop a general strategy for investigating the degree of variability in the age-composition of field populations of carabid beetles. Two methods of investigation are discussed, i.e.: [ABSTRACT FROM AUTHOR]

Different species of large tropical butterflies belonging to the genus Morpho vary dramatically in both the amount of blue color on their wings and the associated irridescence (reflectance). This paper discusses how such a morphological properties may be related to both courtship behavior and effective means of reducing predation (especially by birds) in the low density adult populations. Essentially, the hypothesis is advanced that territorial species of Morpho can afford to possess very conspicuous wing coloration that may facilitate courtship interactions, in addition to spacing the territorial male population over the suitable habitat. While territoriality may be favored by natural selection, such behavior can only evolve if the species involved possess effective means of reducing predation, because territoriality in morphos is an extremely predictable form of behavior, toward which predators can easily orient. Two alternate hypotheses are advanced to account for low predation in a territorial morpho, Morpho amathonte, a species in which males are very bright and showy. The first hypothesis, which is more consistent with traditional ideas on the function of bright colors in morpho wings, maintains that predators learn quickly to avoid these butterflies as prey, since they are very difficult to catch. The second hypothesis, suggests that conspicuous territorial male morphos actually employ pursuit-stimuli to invite birds to attack and be subsequently unsuccessful. [ABSTRACT FROM AUTHOR]

The CO exchange response of plants to multiple environmental variables is often difficult to frame for purposes of comparison. In this paper, a nonlinear model relating CO exchange to light and temperature is derived from experimental curves determined in other investigations. Parameter values, determined from a least-squares fit of the model to CO exchange data, are useful for comparing responses to light and temperature in terms of seasonal phenology, population heterogeneity, or species variation. The model was fitted to CO exchange data of a group of 40 Alnus rubra Bong. (red alder) seedlings for steady-state combinations of light and temperature. The average deviation of the data from the model was ±6.7%. This steady-state expression satisfactorily predicted CO exchange for dynamic conditions of light and temperature occurring in a diurnal cycle. [ABSTRACT FROM AUTHOR]

When several species co-exist, the amount by which they overlap in their use of resources is a measure of their similarity to one another. As such, resource overlap does not measure the amount of competition among them. When the resources are not limiting to population growth, patterns of resource use may overlap to any degree. However, when the species are frequently in competition for their resources, natural selection will favor the separation of their requirements, and the amount of resource overlap will be reduced. This paper presents a technique which permits comparison of the amount of resource overlap observed in a given case with that expected for a group of similar species co-existing in the absence of competitive interactions. From this comparison can be evaluated the likelihood of competitive processes being important in the situation under study. [ABSTRACT FROM AUTHOR]

A community model may be considered stable when, in the absence of exogenous variation, all population trajectories encircle or asymptotically approach equilibrium. In this paper, community models in which, in the absence of analytical indications of stability, all populations either A real, though simplified, ecological system consisting of Daphnia galeata and its algal food source in an oligotrophic lake appears to be generally resilient in that changes in the exogenous factors nitrate concentration and temperature of the lake water consistently restrain the departure of predicted population densities from equilibrium. Each population in the community is represented by the Verhulst-Pearl logistic model of population growth augmented to include environmental effects on rate of increase, r; carrying capacity, K; and the effects of predation on population density, N; and therefore the population rate of change, dN/dt. It is suggested that such community submodels and sensitivity analysis represent logical and appropriate amplifications in the use of mathematical models in the management of populations. [ABSTRACT FROM AUTHOR]

A mathematical model of the functional response to prey density involving the hunger effect was constructed in this paper. In that model, the amount of prey captured by predators, y, is assumed to be proportional to the product of the prey density, x, and the degree of hunger. The range of prey density is divided into the following three areas along the x-axis, according to the maximum rate of ingestion and the maximum rate of capture: (i) the area in which the value of y increases convexly with increasing x, (ii) the area in which the value of y increases proportionally to x and (iii) the area in which y reaches the maximum. It is shown that these equations are a generalization of Ivlev's equation, and Holling's disc epuation, that is, both equations hold in special cases in only the first area of x. These equations were applied to several experimental results obtained by using two kinds of wolf spiders and some values of parameters were estimated. [ABSTRACT FROM AUTHOR]

For those systems which are amenable to tracer kinetic incorporation experiments it is possible to determine the pathways of nutrient flux throughout the system and to measure the steady state rates of intercomponent mass transfer through these pathways. In this paper a procedure is developed which allows one to employ incubation experiments to obtain the data required to analyse the flow of nutrients throughout the system. In such experiments a tracer is introduced via a single system component and the total radioactivities of the other system components are measured and recorded as functions of the time elapsed since the introduction of tracer. The resulting time-varying radioactivity curves can be successfully fitted to sums of exponentials by employing a particular mode of data point weighting. A specific mode of weighting the data points is required in typical incubation experiments if the component injected with label is large in comparison with the remaining components of the system. The exponential sums describing the time-varying radioactivities of the system components furnish the information required to determine and measure intercompartment nutrient fluxes; such determinations are made by assembling the coefficients and exponents appearing in the sums, into matrices, then employing a collineatory transformation. An illustrative example of the determination of intercomponent rates of mass transfer from data arising from a simulated incubation experiment is presented. [ABSTRACT FROM AUTHOR]

Although the linear relationships characterizing an ecosystem, e.g., nutrient fluxes and pathways of energy flow, may be obtained experimentally or known a priori, these alone are insufficient to yield a model which behaves realistically; the non-linear relationships between system variables must also be incorporated. However, even though a non-linear relationship between two system variables is suspected there exists no formal approach whereby one might experimentally verify the presence of such a non-linear relation, assess the magnitude of its influence, and formulate the relation in a functional notation suited to incorporation into the system model. In this paper it is shown that for those systems amenable to kinetic tracer incorporation experiments it is possible to estimate a parameter which quantitatively states the effect of a non-linear relationship between the two system variables. The approach requires that some one variable of the system is capable of being maintained at a constant value during the course of a tracer kinetic incorporation experiment; i.e., may be employed as an independent variable. A set of experiments is conducted in which a single component of the system is labelled and the time-varying radioactivities of the remaining system components are measured as are the component values themselves. The experiments differ only in the value at which the independent system variable is maintained. From each experiment, one obtains a set of time-varying curves of component radioactivities which are resolved into sums of exponentials by a global fitting strategy. The component values and the exponents obtained in the set of experiments provide the data required to estimate the non-linear system parameter. To demonstrate the validity of this approach tracer kinetic experiments were simulated for two different cases. The models employed in each of the simulated cases were identical in all respects but one. In one case the model system contained a non-linear relationship in the form of a negative feedback loop. In the other case, the model lacked this non-linearity. The proposed analysis was applied to both cases and yielded the parameter values consistent with each case. Thus the analysis is capable of demonstrating the absence of a non-linear relationship presumed to exist between system components. [ABSTRACT FROM AUTHOR]

This paper attempts to determine the effect on the number of prey eaten by predators of the addition of the component 'avoidance learning by prey' to a computer model of the predation process developed by Holling. Generality was retained by concentrating upon a basic aspect of the prey's behaviour, its distance of reaction to an approaching predator. The zebra danio ( Brachydanio rerio), a small freshwater fish, was used as an analogue of a general vertebrate prey. The predator used was the largemouth bass ( Micropterus salmoides). Previous work (Dill, 1973b) showed that prey reactive distance increased with increasing experience with the predator. In the present study, this increased prey reactive distance is shown to increase predator pursuit time and hypothesized to decrease predator pursuit success. These relationships were expressed mathematically and built into Holling's (1965, 1966) model of the predation process, along with an equation describing the way in which reactive distance increases following an unsuccessful attack. Other changes necessitated in the model by the addition of the avoidance learning component included: a) Modifications of the calculation of search time to remove a previously implicit time spent unsuccessfully pursuing prey, and to correct the density of prey to account for those whose reactive distances exceed that of the predator and are therefore not susceptible to discovery; b) Addition of a new subroutine (CHASE) to calculate pursuit time, unsuccessful pursuit time, pursuit success, and strike success; c) Changes in subroutine ADCOM to assign prey to different classes (with different reactive distances) according to the number of times they have been unsuccessfully attacked; and d) Addition of a stochastic element via random numbers to determine the class to which an attacked prey belongs, the time to refuge, and the predator's strike success. Simulation was used to explore the consequences of these additions. The capability of learning substantially increased the prey's probability of surviving subsequent attack. Addition of an avoidance learning component caused declines in the predator's functional responses to both prey and predator density. The new component was also suggested to decrease the predator's numerical response to prey density and to increase the probability of stability in a predator-prey interaction. [ABSTRACT FROM AUTHOR]

Merremia gangetia Linn. (Cuf) is one of the most important weeds invading cultivated lands of India. Temperature, both high (45° C) and low (15° C) exhibit a definite role in development of the weed, particularly during germination. Higher tempeeratures (45° C) during dry storage appeared to be the main factor in laboratory experiments as well as in nature. Low temperature induced secondary dormancy and its removal by incubation at 35° C helps to explain the ecological mechanism through which the weed endures winter conditions. Germination of buried seeds confirm that the atmospheric conditions were found to be more effective in upper layers of soil. Ecological adaptations of this weed via germination requirements are assessed in the paper. [ABSTRACT FROM AUTHOR]

The present paper deals with the reaction of two closely related species of Argemone L., A. mexicana L. and A. ochroleuca Sweet, to its own density in pure stands and a comparison of this with its reaction to the density of the associated species. The results of the pure culture studies indicate that whilst each of the two species reacted to an increase in its own density by higher mortality and a striking reduction in vegetative and reproductive growth, A. mexicana was more susceptible to intraspecific effect than A. ochroleuca. On the other hand, mixed culture studies indicated that A. mexicana was more successful when in competition with A. ochroleuca. Further, that species which was in a majority in the mixture suffered most compared to the minority species. Such a density dependent differential behaviour in pure stands and frequency dependent differential behaviour in mixed cultures along with the reversal in superiority of the two species in pure and mixed cultures was considered to be responsible for the cohabitation of the two species and their relative population sizes in nature. [ABSTRACT FROM AUTHOR]

The Critical temperatures (defined as the upper and lower limits at which the animal can still right itself) were determined for 29 lizard species (13 genera) and four snake species (four genera) of Southeast Australia. In addition to these Critical temperatures, acclimation of the Critical temperatures and also some lethal temperatures were recorded for several of these species. The mean summer Critical Minimum values ranged between 2.2 and 9.8°C. Thigmotherms (Gekkonidae, Lygosominae, Elapidae) and posturing heliotherms (Agamidae, Scincinae, Varanidae) generally had high Critical Minimum values and the shuttling heliotherms (Lygosominae, Elapidae) had the lowest values. The rate of acclimation of the Critical Minimum of ten lizard species was similar and complete acclimation took place within ten days. Following acclimation the final or ultimate Critical Minimum of some species fell below the body freezing point of-0.52°C and locomotion could occur while the lizard was supercooled. Mean summer Critical Maximum values ranged between 37.0 and 44.8°C. Determination of the Lethal Minimum temperatures by continuously cooling the specimens was complicated by the fact that supercooling occurred followed by nucleation or sudden freezing of the body tissues. The Lethal Minimum was best determined by holding specimens at different constant temperature levels then calculating the body temperature at which the species could survive for an indefinite time period. It is concluded, from the data presented in this paper, that if environmental temperatures were to limit the distribution of reptiles then the Critical Minimum level would have more ecological significance than the Critical Maximum. [ABSTRACT FROM AUTHOR]

This paper describes the results of a study of the factors determining the abundance and distribution of the Cinnabar Moth in Britain. The main part of the study was on a population of the moth at Weeting Heath in Norfolk. This is an area of sandy heath which is heavily overgrazed by rabbits. Here the moth fluctuates violently in number and periodically it completely defoliates its food plant (ragwort, Senecio jacobaea L.) over large areas. This happened in 1960, 1961, 1967, and 1968. Since 1966, the numbers of the moth have been studied in detail and Life Tables are presented for five years. Adult fecundity varies considerably between years. This is due mainly to fluctuations in adult size resulting from changes in larval density. By comparison adult mortality and dispersal have little effect on fecundity; although there is some evidence to suggest that dispersal is density dependent. Because the number of eggs laid in one generation depends on the size of the previous generation, fecundity tends to be acting as a delayed density dependent factor. Mortality is low during the egg stage, but is high amongst young larvae, due mainly to arthropod predation. As the caterpillars grow they become immune from this predation. They are distasteful to vertebrate predators. A larval parasite, Apanteles popularis, kills many of the fully grown larvae. The highest rates of parasitism have coincided with the lowest densities of the moth, however, so that over the five years it has acted as an inverse density dependent factor. In 1967, the population became so large that the ragwort was completely defoliated, and about 20% of the caterpillars died from starvation. In the following year the population was still large and the ragwort plants were small, owing to the effects of defoliation in the previous year. Food ran out early in the season and about 50% of the larvae starved. Because of the overriding effect of starvation, total larval mortality tends to be density dependent. Mortality is high at, or immediately after, pupation and this is thought to be due primarily to predation by moles ( Talpa europaea). Pupal mortality does not appear to be density dependent. The upward growth of the population is limited by food supply. Starvation led to a population crash, so that in 1969 only 62 eggs/150 m were laid compared with 17110 and 16493 in the previous two years. The rate of recovery of the population after this crash was dependent upon the rapid recovery of the ragwort plants. Owing to the wet summer in 1968, plant numbers actually increased after defoliation, due to regeneration from root buds. This was in spite of the fact that no seed was produced in the area in either 1967 or 1968. The only factor which appears to buffer the population against extinction in years when food runs out early in the season, is the heterogeneity within the moth and ragwort populations. The earliest individuals manage to obtain sufficient food in those patches of ragwort which survive longest. Large fluctuations in number only occur in some localities. Other populations of the moth persist at low density and never eat out their food supply. Some data are presented from such a population at Monks Wood. This site is on a heavy clay soil, rabbit grazing is less marked than at Weeting, and ragwort occurs only at a low density. The lusher vegetation supports a very large population of arthropod predators and these take a higher percentage of the young caterpillars than was found at Weeting. Pupal survival is also low due probably to waterlogging of the soil. Pupae can withstand considerable desiccation, but excessive moisture soon leads to their death. The distribution of the moth in Britain and its use for the biological control of ragwort are discussed. [ABSTRACT FROM AUTHOR]

Previous authors have used simple models to investigate the relative importance to population increase of variations in the total and age-specific reproductive rates. But while acknowledging that the latter were the product of the age specific birth and death rates, they have used their models only to investigate changes in total or age-specific birth rates and have not been concerned with variations in death rates. This paper extends the use of Lewontin's (1965) model, to a wide range of values of r, the exponential rate of population increase. It shows how the relative importance of changes in certain life-history features can change with r and be reversed when r is near to zero. It is also shown that variations in mortality rate are not necessarily best expressed in analogous terms to variations in birth rate. If more suitable terms are used it is seen that changes in mortality rate can be of varying importance depending on the existing mortality rate. They can be overwhelmingly important when the mortality rate is high. [ABSTRACT FROM AUTHOR]

Dynamic modeling of ecological phenomena has been greatly facilitated by the recent development of continuous system simulator programs. This paper illustrates the application of one of these programs, S/360 Continuous System Modeling Program (S/360 CSMP), to four systems of graduated complexity. The first is a two species system, with one feeding on the other, using differential equations with constant coefficients. The second and third systems involve two competing plant species in which the coefficients of the differential equations are varying with time. The final example considers the management of a postulated buffalo herd in which the dynamics of the herd population and composition by sex and age is combined with various strategies to control its size and to optimize buffalo production. [ABSTRACT FROM AUTHOR]

The plasticity of phenolic acid concentration in plants under various physiological stress situations raises questions concerning the ecological significance of such behavior. Helianthus annuus L. is remarkably plastic with regard to chlorogenic and ischlorogenic acid concentrations when subjected to nitrogen deficiency, NaCl-stress, short exposures to UV radiation or to combinations of these stresses. Stress due to NaCl has not previously been reported to produce this effect. I propose that chlorogenic acid is representative of a group of chemicals which have originated as regulators of various metabolic systems under stress and have subsequently acquired allelochemic properties against pathogens, herbivores, and competitors. If this hypothesis is correct then specific patterns of distribution with regard to concentrations of phenolic acids should be found. Some such predictions are discussed and means of distinguishing between various selective agents are explored. Generally, if natural environmental stress stimulates phenolic acid concentrations and hence more efficient growth patterns, then for several kinds of variables, higher concentrations should be found in more rather than less stressful habitats. If biological agents are significant agents of natural selection for this group of substances, such a pattern should not occur in some cases. [ABSTRACT FROM AUTHOR]

Plethodon richmondi shenandoah occurs in at least three geographically isolated talus slopes in Shenandoah National Park, Virginia, U.S.A., each surrounded by a continuous population of Plethodon c. cinereus in the soil outside the talus. Distributions are contiguous but largely non-overlapping. The talus presents a much drier habitat than does the surrounding soil. Four experiments were designed to test the responses of the two species to moisture and substrate. Although shenandoah lives in a habitat generally drier than that of cinereus, both species choose the wet end of a moisture gradient and do not differ significantly in moisture preference. When given choices between a substrate of rock or soil, the two species respond similarly: neither expresses a preference when both substrates are moist and both choose soil over rock as the substrates dry, showing that substrate preference is based on moisture content and not texture. A third experiment demonstrates that cinereus suffers significantly greater mortality and loss of body water when subjected to a drying rock substrate than when subjected to a soil substrate, since the latter holds moisture longer. Thus the talus most likely presents a greater stress of dehydration to salamanders than does the soil. A fourth experiment shows that when forced to dehydrate, shenandoah survives longer, loses significantly less body water per hour, and withstands a greater loss of body water before death than does cinereus. The conclusions drawn are that cinereus inhabits areas of deep soil not due to a preference for that substrate but due to the requirement of a moist substrate, and it cannot enter the talus due to the dry conditions there. P. r. shenandoah, on the other hand, neither prefers the rocky nor the dry conditions of the talus and is probably excluded from the soil by the presence of cinereus. The survival of shenandoah in the talus is due, at least in part, to its ability to withstand the stress of dehydration for a longer period than can cinereus. [ABSTRACT FROM AUTHOR]

The distribution and abundance of subtidal meiobenthos were studied monthly from June 1967 through May 1968 at five stations on the Bermuda platform: Two in Castle Harbor, two in Baileys Bay, and one in Harrington Sound. Total number of individuals ranged from 12.2-133.3x10/m and dry weight biomass from 33-259.3 mg/m. Free-living nematodes constituted 72.6% of the total numbers and 71.8% of the biomass and were the most abundant organisms at all but one station. Harpacticoid copepods were second in overall abundance and were the most abundant organism at one station. Polychaetes, ostracods, a kinorhynch and a priapulid were also common. Distinct seasonal patterns were observed. Total population values were highest in late spring, lowest in the winter. Nematodes often reached maximum values in the winter and appear to be correlated with minimum temperatures. Copepod abundance was related to reproductive cycles and changing sediment conditions. Copepods were abundant in the medium to coarse-grained sands, nematodes in the finer sediments. Meiofauna was greatly reduced in the lower layers of sediment; this reduction was attributed to decreased interstitial water and oxygen content. Field and laboratory results indicated specific grain size preferences of the Harpacticoida. Epigrowth feeding nematodes were dominant in sandy sediments, deposit feeders in the muds. Epigrowth dominance was probably related to carbon rich aggregated particles coating the sediments. Three distinct harpacticoid 'parallel level bottom communities' were defined: (1) the Leptastacus macronyx (T. Scott)- Praeleptomesochra africana (Kunz) community in the submerged 'beach sands,' (2) the Stenhelia (D.) bermudensis mihi-Typhlamphiascus lamellifer (Sars) - Cletodes dissimilis Willey community in the silty-sands and (3) the Phyllopodopsyllus hermani mihi community in the medium to coarse-grained sands. Diversity analyses of the harpacticoid communities indicated highly evolved, stable assemblages in those areas of low physical stress and less stable, variable assemblages in areas of high physical stress. [ABSTRACT FROM AUTHOR]

The paper reports a possible allelopathic potential of Aristida adscensionis Linn. on the nodulation of Indigofera cordifolia Heyne ex. Roth., at Rajkot (India). When individual plants of I. cordifolia were excavated from plots where it grows in association with A. adscensionis and where A. adscensionis is absent and the nodule numbers counted, it has been observed that the number of nodules was fewer in plants when it grows in association with A. adscensionis. Statistical analysis of the results has confirmed that the standard error of difference in means is highly significant at 1% probability level. Hence it appears that A. adscensionis has some inhibitory effect on the nodulation of I. cordifolia through some mechanism which is yet to be determined. Further work in this direction is in progress. [ABSTRACT FROM AUTHOR]

In order to better understand the adaptations of Astragalus tennesseensis Gray (Leguminosae) to its summer-dry cedar glade habitat, comparisons were made of the free amino acids and amides in leaves of drought- and nondrought-treated plants. No qualitative differences were detected; 13 free amino acids and 2 amides were identified. However, water stressed plants showed a 115% increase in the total amount of amino acids and amides over nondrought stressed plants. Proline accounted for 30.1% of the increase and aspartic acid 37.1%. Water stress caused an increase in the 2 amides and in 11 of the 13 amino acids; alamine and serine decreased. Upon rewatering, the total amount of amino acids and amides quickly decreased. The ability to accumulate proline and aspartic acid may be of adaptive value to A. tennesseensis during short periods of drought. [ABSTRACT FROM AUTHOR]

Social relations among even-sized male individuals of Odontobutis obscurus, a carnivorous eleotrid goby, were observed in a small experimental population with measurements of individual body size and food intake. [ABSTRACT FROM AUTHOR]

An index is proposed for measuring similarity between sets of biota over space and time. It integrates into a single measure hitherto separate and often incompatible procedures, based on species presence-absence and species composition. The index is demonstrated by a hypothetical set of data. When compared with the more usual indices of similarity, the proposed index is found to demonstrate greater rigor and hence greater powers of discrimination between data sets. The S index is applied to one series of temporally and two series of spatially differentiated data sets, resulting from sampling the intertidal meiofauna subcommunity of Gastrotricha. All collections represent whole-beach transects, taken at low tide. The temporal series is derived from a boreal-silicious beach in Massachusetts, which was sampled 18 times during the period of a year. The two spatial series are derived from 16 borealsilicious beaches in Massachusetts and New York, and from 8 tropical-carbonate beaches in Florida (6) and the American Virgin Islands (2). Per cent composition by species and H′ species diversity values were calculated for data from each site. H′ similarity values based on shared species diversity were determined for permutation pairs of sites. These values then were converted into S indices of similarity. The indices were clustered by an unweighted mean, pair-group method and, finally, similarity dendograms were constructed. Results allow the temporal series to be readily separated from both spatial series, and the boreal-silicious spatial series to be clearly distinguished from the tropical-carbonate spatial series. There is strong, though preliminary, evidence that the tropical-carbonate series does not comprise a single biogeographical unit, but that it is subdivided into a Florida subseries and an island subseries. Dendogram analysis indicates that the island effect is nearly as strong as the latitudinal-substratum effect in reducing shared species diversity between intertidal subcommunities of Gastrotricha. [ABSTRACT FROM AUTHOR]

An electronic computer has been used to simulate the development and sampling of a number of insect populations containing individuals passing through stages (instar I, instar II, etc.). This was done in order to compare five methods for analysing sample stage-frequency data (Richards and Waloff, 1954; Richards et al., 1960; Dempster, 1961; Kiritani and Nakasuji, 1967; Manly, 1974a) under a variety of conditions. The simulation results suggest (i) that the method of Kiritani and Nakasuji should be used to estimate stage-specific survival rates whenever populations are sampled at equal intervals of time until almost all insects are dead, and (ii) that the method of Manly should be used if the sample times do not permit the use of Kiritani and Nakasuji's method or if it is desired to estimate the actual number of insects entering stages. [ABSTRACT FROM AUTHOR]

Coleomegilla maculata flies from its hibernation sites to breeding areas in the spring. Flight behaviour among the hibernating beetles was studied using the tethered flight technique. It was found that there is a successive maturation of flight behaviour in the spring. This process is mainly controlled by temperature acting over an extended period. From a standstill at 15°C the rate of the maturation process increased as the temperature was raised. Short photoperiods exerted a depressing effect on glight development early in the winter, but later this effect disappears. [ABSTRACT FROM AUTHOR]

Temperature dependence of net photosynthesis under conditions of light saturation and maximum air humidity was measured throughout the season in the Central Negev Desert (Israel). Experimental plants were the wild growing Hammada scoparia and Prunus armeniaca cultivated in the runoff farm of Avdat. The optimum temperature for net photosynthesis and the upper temperature compensation point of CO exchange showed a characteristic seasonal variation with low values in spring and fall and high values in mid-summer. This shift was exhibited by plants growing under conditions of normal soil-water stress as well as by irrigated plants. There was no general correlation between the changes in temperature dependence of net photosynthesis of the plants, their maximum photosynthetic capacity under the experimental conditions, their daily photosynthesis maximum under natural conditions, and their rate of dark respiration. The seasonal shift of the photosynthetic response to temperature cannot be explained by changes in the temperature sensitivity of the stomata. It may be caused by seasonal changes of biochemical and/or biophysical properties. A number of observations made on other wild plants also showed, in all cases, seasonal shifts of the upper temperature compensation point, with an amplitude of 6.0°C-13.7°C. [ABSTRACT FROM AUTHOR]

A new technique based upon the dilution of C/ C ratios in structural carbon of root systems during the course of the growing season was used to evaluate belowground turnover or productivity of two cool desert communities in northern Utah, USA. This technique provides a measure of turnover of the root system of established perennial plant communities avoiding many of the disadvantages of other techniques. Adjacent communities dominated by Atriplex confertifolia and Ceratoides lanata both exhibited belowground productivity values exceeding aboveground production by three-fold. The greater belowground turnover of the Atriplex-dominated community may be a factor contributing to the maintenance of a greater quantity of aboveground biomass and prolonged periods of active photosynthesis during the driest portions of the year when Ceratoides becomes largely photosynthetically inactive. [ABSTRACT FROM AUTHOR]

Respiratory metabolism was measured each month for Orthoporus ornatus throughout a year. Respiratory rates were determined at a standard 20°C and at the mean ambient soil temperature at time of collection. No significant differences were noted between respiratory rates of reproductively mature males and females. A size relationship between live body weight and oxygen consumption per unit weight was found. The b values for 20°C and 25°C were-0.28 and-0.24, respectively. Premolt specimens had lower respiratory rates than postmolt individuals. There were significant differences between Q values of animals exposed to temperatures above and below ambient field conditions. Seasonal changes in the use of metabolic reserves by O. ornatus were indicated by corresponding changes in RQ values. A 'best estimate' of annual respiratory metabolism was 1332 cal gyr. Respiratory metabolism closely paralleled changes in ambient field temperature and was at its peak in July when animals were on the soil surface. [ABSTRACT FROM AUTHOR]

Plants of Portulaca oleracea L. were grown in a temperature controlled greenhouse. In one experiment plants received 8 hrs of daylight and during the following 16 hrs ('dark period') they either were grown in darkness or received white, red and far red light of low intensity for various times preceeding the dark period or in the middle or the end of the dark period. In other experiments the plants were grown in photoperiods of 8, 11, 13, 15, 16 hrs and in continuous light. The effect of these treatments on number of leaves until the appearance of the first flower bud and the germination of the seeds collected from these plants were studied. P. oleracea was found to be a photoperiodic facultative or quantitative short day plant. The photoperiodic treatments of the mother plants affect the germinability of their seeds, dependent on the last 8 days of seed maturation on the mother plants. The shorter the daylength the faster the germination. Red or far-red treatments of the mother plant also affect the germinability. But in no case is there dark germination even after 8 days of seed maturation under continuous red light. These results suggest that the influence of the light treatments of the mother plants on the germination of its seeds is not mediated via phytochrome but rather through some other pathway. [ABSTRACT FROM AUTHOR]

The effects of pollination, predispersal seed predation, and plant density upon seed production of Astragalus canadensis L. in a tall-grass prairie were studied by experimental manipulation of plant density. Seed production was greater at high than low plant densities; this was inferred to result from differences in pollination success. Predispersal seed predation was lower at high than low plant densities. The relative seed production of different densities of A. canadensis was predicted based upon pollination success and the host detection ability of the predator. Increased seed production and modification of the environment by high densities of A. canadensis appears to maintain a clumped distribution of this species, while also producing new clumps at a low rate. [ABSTRACT FROM AUTHOR]

Respiration of the interstitial ciliate Tracheloraphis sp. was measured with the Cartesian diver. Ciliate respiration ranged from 2353-7088 μl O/hr/g wet weight, averaging 4477 μl O/hr/g wet weight. These metabolic data on Tracheloraphis expand the known size range-metabolic rate differential of the omnipresent meiofauna. The metabolic-size relationship of meiofauna has been calculated based on data from the literature and this study. Results indicate that these smaller organisms maintain the same proportionality of metabolism to body weight ( b=0.74) as do larger animals. When the ciliate data, and published meio- and macrofauna data, are used to estimate the portion each component plays in total benthic metabolism it is apparent that the metabolic role of each can vary significantly. Only when the ratio of macrofauna to ciliate biomass is 90 or more, or when meiofauna/ciliate biomass is 3 or more do the other components play a more important energetic role than do the ciliates. [ABSTRACT FROM AUTHOR]

A hypothesis originally postulated to explain changes in abundance of sapsucking insects is here extended to an interpretation of changes in abundance of populations of geometrid defoliators. The hypothesis states that most herbivorous insects usually remain at a low level of abundance relative to the apparent abundance of their food because most of them die when very young from a relative shortage of nitrogen in their food. Only occasionally do their food plants become a sufficient source of nitrogen to allow a high proportion of the young insects to survive, and the population to increase to outbreak levels. The plants become a richer source of nitrogen when they are stressed by random fluctuations in the summer and winter rainfall, although other factors such as soil type and topography may contribute to this stress. The hypothesis may well have wider application to population fluctuations of other herbivores-both invertebrate and vertebrate. [ABSTRACT FROM AUTHOR]

In central Tennessee Geranium carolinianum L. behaves as a winter annual. Seed germination occurs in autumn, and seed ripening and dispersal are completed in May. Freshly-matured seeds have hard coats and will not imbibe water unless scarified. Embryos of freshly-matured seeds are conditionally dormant; scarified seeds germinate better in darkness than in light at high temperatures. After a short after-ripening period the embryo is essentially nondormant, and scarified seeds germinate to high percentages over a wide range of temperatures in both light and darkness. About 50% of the nonscarified seeds become germinable after 4.5 months of dry-laboratory storage. In order for the seed coat to become permeable (without scarification), seeds must be kept either dry or alternately wet and dry at relatively high temperatures during the summer dormancy period. The ecological significance of seed dormancy in G. carolinianum in central Tennessee is that it allows this non-drought tolerant species to avoid droughts that frequently occur in its habitat between late spring and early autumn. Conditional dormancy of the embryo of freshly-matured seeds, hard seed coats and the inability of seeds (non-scarified but permeable) to germinate in summer at high summer temperatures all seem to play a role in delaying germination until autumn. [ABSTRACT FROM AUTHOR]

The binding of lead to xylem tissue has been studied using an isolated segmentperfusion technique. The results show that free lead ions bind more readily to xylem tissue than does lead in the form of a lead-glycine complex. A small, but significant proportion of the applied lead moves laterally from wood to bark. Both binding and lateral movement of lead are shown to be time-dependant. The results are discussed in terms of using trees and the chemical analysis of their annual growth rings to date heavy metal pollution histories. [ABSTRACT FROM AUTHOR]

The immigration of carabids into the Lauwerszeepolder (constructed in 1969) was studied in 4 areas. These areas have different types of soil and consequently different vegetations. The carabid fauna was sampled by means of striptraps and window traps. In this way a total number of 116000 specimens was caught. A comparison of the catches shows great differences between the fauna in different study areas in successive years. The data are compared with those of another Dutch polder (IJsselmeer polder). It is shown that about 50% of all species caught are able to fly. Moreover it is demonstrated that relatively more specimens of sparse populations than of dense populations fly. The data, especially those on ovarian development, show that flight occurs mostly in early adult life. Moreover, flight muscle autolysis at the onset of ovarian development is a common feature among carabids. Females fly more readily than males. Whereas the flight of most species covers only short distances, some species fly across the borders of their habitats. The data suggest five categories in carabids with respect to flight. Brachypterous carabids were very rarely found in the polder. It is suggested that changes in the numbers of macropterous specimens in carabid populations outside the polder proper are not due to dispersal. The role of migration in the stabilization of carabid populations is estimated to be very small. [ABSTRACT FROM AUTHOR]

The energetics of a population of a free-living nematode Pelodera sp. that feeds on bacteria were studied in the laboratory. A budget was drawn up for Pelodera feeding on Escherichia coli labelled with C. Measurements were also made of population growth, respiration and feeding rate. In vitro, Pelodera ingested on average 37.0×10 J h mg dry weight, of which 13.7×10 J h mg dry weight were respired, 15.0×10 J h mg dry weight were excreted and 8.3×10 J h mg dry weight were retained in growth. The measurements of feeding rate indicated that the values for the percentage energy flow depended partly on the concentration of bacteria present. These results are discussed and an energy budget is calculated for bacterial-feeding nematodes in bog soil, using published field data. [ABSTRACT FROM AUTHOR]

Published results show that variations in mortality due to factors such as predation, parasitism and disease are overshadowed by variations due to effects of physical factors. Soil temperature and the tension of the soil moisture have a profound effect not only on the survival but also on the growth rate and fertility of the two species considered here. The model is based largely upon known and experimentally quantified relationships of causes and effects and is therefore a practical model which integrates our knowledge so that we can compare its results with reality to see if or where our knowledge is lacking. [ABSTRACT FROM AUTHOR]

Evidence has been obtained for lateral transport of bark applied Pb from bark to wood in a range of tree species. This lateral redistribution was found to be independant of cambial reactivation, Lead being recovered from bark and wood in the same proportions from dormant and non-dormant shoots. The results are discussed in relationship to naturally-occurring uptake of Lead by stems. [ABSTRACT FROM AUTHOR]

Lake George, a shallow lake in western Uganda, supports a permanent and dense crop of phytoplankton, and may be regarded as eutrophic although the ambient concentrations of inorganic nitrogen and phosphorus are low. The figures for the annual nutrient loadings (Viner and Smith, 1973) would suggest, however, a eutrophic lake when analysed on the scheme of eutrophication proposed by Vollenweider (1968). The horizontal distribution of chlorophyll a shows a concentric pattern, with the maximum values occurring towards the center. This horizontal variation is thought to reflect water movements, and a general pattern of water flow is proposed. The majority of the species show no seasonal variation but populations of both Anabaena and Melosira show annual variations. These two species also have a horizontal distribution pattern which is the reverse of other species. This pattern is used to support the proposed movements of water. Phytoplankton generation times are discussed in relation to the diurnal cycle occurring in Lake George. [ABSTRACT FROM AUTHOR]

Male hybrids obtained by crossing Bombina bombina with Bombina v. variegata displayed calling behavior when treated with hormones at the age of about 12 months. The mating calls of the hybrids are intermediate with respect to rate, duration, inter-call interval, and fundamental frequency between the calls of the two purebred species. [ABSTRACT FROM AUTHOR]

Carbon dioxide exchange patterns of prickly-pear cactus ( Opuntia phaeacantha var. discata) were studied throughout the year to determine temperature influences on and seasonal responses of the process. Cacti exhibit CAM which permits nighttime carboxylation of CO to malate and daytime decarboxylation of malate to CO. The gas exchange studies were done on plants harvested near Mesa, Arizona, and placed in an open CO exchange analysis system. Carbon dioxide exchange rates varied with temperature and season. Greatest CO influx rates were at low temperatures while efflux rates were greatest at high temperatures. A shift in season caused a change in CO exchange rates at any one temperature. Equal rates were shown at increasing temperatures as CO analyses progressed from winter to summer showing seasonal temperature acclimation. A comparison of the CO exchange temperature compensation point (the temperature at which the plant shows zero CO exchange usually due to the shift from net influx to net efflux or the opposite) with air temperatures shows the months of November through February to have the greatest potential for a large net CO influx while the summer months may actually exhibit a small net CO loss. This loss is much less than would occur if the cacti did not exhibit temperature acclimation. Thus, with a large net CO influx in the cool months and a small net CO efflux during the warm months, prickly-pear cacti maintain a net CO exchange gain for the year. [ABSTRACT FROM AUTHOR]

The relative abundance of the two crabs from Georgetown, South Carolina, compared to other areas characterizes Polyonyx as a more southernly distributed crab than Pinnixa. However, the zoeae and adults of Polyonyx are less tolerant of high temperatures than either the zoeae or adults of Pinnixa as indicated by both lethal limit and metabolic studies. Adult Polyonyx are also less tolerant of low temperatures than adult Pinnixa. Results indicate that Polyonyx is an obligate commensal of Chaetopterus, and Pinnixa is a facultative one. [ABSTRACT FROM AUTHOR]

A method of analysis is suggested for data obtained by sampling an insect population while the individuals in the population are developing through several stages. The method allows the estimation of (i) the numbers entering each stage, (ii) the mean duration of each stage, and (iii) daily survival rates. A basic assumption made is that the time of entry to a stage follows a normal distribution. The method is illustrated on data from a field population of grasshoppers and a laboratory population of locusts. [ABSTRACT FROM AUTHOR]

Along exposed rocky intertidal shorelines of western North America the mussel Mytilus californianus exists as a characteristic, well-defined band. Measurements at Mukkaw Bay and Tatoosh Island, Washington State, suggest that the upper limit to distribution is constant. The lower limit is also predictably constant, as judged by photographs of the same areas taken up to 9 years apart. The band of mussels is formed by larval recruitment to a variety of substrates, especially the filamentous red alga Endocladia muricata. From the settlement site, if the mussels survive a series of predators including the starfish Pisaster ochraceus and a variety of carnivorous gastropods ( Thais spp.), the mussles may be washed inward or migrate (be pushed) downward. When Pisaster was removed manually, the zonation pattern changed rapidly. Mussels advanced downward at Mukkaw Bay a vertical distance of 0.85 m in 5 years. No movement was observed on 2 adjacent control sites. At Tatoosh Island a maximum displacement of 1.93 m has been observed in 3 years; the slope there is 40°. Again, there was no change at control sites with Pisaster. At Mukkaw Bay over 25 species of invertebrates and benthic algae are excluded from occupancy of the primary substratum by mussels. The ecological dominance of mussels is discussed; predation is shown to enhance coexistence among potential competitors. A survival curve for Pollicipes polymerus indicates that the time course for interspecific competitive exclusion may be long (76 months). The clarity of the biological interrelationships and the constancy of pattern through time provide no support for the contention that intertidal communities are physically-controlled. [ABSTRACT FROM AUTHOR]

Between May 1970 and May 1972 the total standing crop of planktonic crustaceans was highest in summer (288-693 ind. x10·m), whilst winter values varied from 8 to 58 ind. x10·m. The dominant species are Arctodiaptomus spinosus Daday and Diaphanosoma brachyurum Liéven. For Arctodiaptomus 4-5 generations per year were found, resting stages were never present. Diaphanosoma starts its development from the resting eggs at the end of March or at the beginning of April; the first male individuals occur at the end of August or at the beginning of September. Production of resting eggs begins in the middle of September. The biomass of individuals at various stages was determined as dry weight. By multiplying these values with the numerical counts one arrives at a value for biomass in the lake. The daily production has been calculated from the turnover time; the annual mean for Arctodiaptomus was 10.3 mg dry weight·m·day (1970) and 26.8 mg dry weight·m·day (1971), and that for Diaphanosoma was 1.6 mg dry weight·m·day (1970), and 21.7 mg dry weight·m·day (1971). [ABSTRACT FROM AUTHOR]

Aspects of male social hierarchies manifest in confined house mice colonies, of population densities comparable with those observed in natural communities, have been studied. Random processes were found to exert significant influences on the social orders established immediately after founding. In addition to the previously reported effect of orders of arrival at the different localities, relative weights were also found to have significant influences on the initial social order. Several changes in the social orders occurred subsequent to the establishment of the initial hierarchies. Aggressiveness and the degree of previous crowding were both found to exert significant effects on the social orders which were finally stabilised. These results are relevant to models recently proposed by Chitty (1960, 1967, 1970) and Christian (1970) for mechanisms of density regulation in rodent populations. In particular, they are consistent with the postulate of Christian (1970) that social dominance ability and density regulation are largely controlled by the adrenopituitary mediated modification of adult behaviour by the juvenile social environment. The relationship between male social status and relative mating success was also investigated. Only a slight positive association was found. Most previous estimates of effective population size have assumed a very pronounced dependence of mating success on social status. The results of the present study thus suggest that the previous estimates have underestimated the effective population size. [ABSTRACT FROM AUTHOR]