Showing papers in "Ecology in 1964"

A Comparison of Some Species-Individuals Diversity Indices Applied to Samples of Field Insects

Abstract: A comparison was made of several cumulative species/cumulative individuals indices using a statistical distribution corresponding to the species of insects in a sample from the herb stratum of a lespedeza field. Criteria used in comparison were that the indices be intensive for a given universe regardless of sample size and that the indices differentiate between universes having different numbers of species for a given number of individuals. Species/log individuals, species–1/natural log of individuals, log species/log individuals, and species/square root of individuals were examined. Only the index of species/square root of individual met both of the criteria.

An Experimental Approach to the Dynamics of a Natural Population of Daphnia Galeata Mendotae

Abstract: In general, populations have been studied either in the laboratory under experimental conditions with environmental variables controlled, or in their natural habitat where variables are uncontrolled. In laboratory investigations the analyses are often powerful and yield knowledge of the fundamentals of population growth but are limited to specific conditions seldom found in nature. In field studies, analyses are limited to correlations of population phenomena with environmental variables and frequently involve large errors in estimates of the inferred rates. The apparent paradox of many field and laboratory population studies can be reconciled in part by manipulating laboratory populations in such a manner that information appropriate to an analysis of the natural population is obtained. To manipulate experimental populations properly, some a priori knowledge of influential variables in the natural population is necessary. This study is directed to combining an experimental approach with a field description. The purpose of such an analysis is to predict natural population growth of Daphnia, and, consequently, to focus attention on the factors which control it. Because of the difficulties encountered in determining population rate processes and the role of underlying environmental variables, predictive models of population growth have been limited to controlled laboratory populations or unusual natural situations with relatively constant environmental conditions. Predictive schemes applied to natural populations are more likely to succeed the more information they utilize; but such models become hopelessly complicated, requiring vast amounts of empirical information. It is not yet clear whether simple models, requiring relatively little information, can adequately predict population growth in natural situations. However, comparison of a model with the observed population growth focuses attention upon the kinds and amounts of information absolutely essential for prediction. Inappropriate models may prove valuable by emphasizing the effect of disregarding important variables. Few investigations of this sort have been attempted on plankton populations. Elster (1954) in studying the population dynamics of the copepod, Eudiaptomus gracilis, utilized the ratio of eggs-to-females to obtain a reproductive index for the population. By determining the developmental rate of eggs at different temperatures he was able to estimate the increase of the population. Edmondson (1960) applied the experimental-field approach to several rotifer populations, placing great emphasis on the eggs-to-female ratio as a useful tool for determining the birth rates of populations. A model based on birth alone was then used to predict population growth and size. Although not concerned with zooplankton populations, 2 other studies are pertinent because the approaches are similar. Reynoldson (1961) made a quantitative population study of the triclad, Dugesia lugubris. Laboratory experiments allowed Reynoldson to assess the effects of temperature and food on the reproduction of Dugesia, and to conclude that population growth was often foodlimited. Subsequent field experiments strengthened his conclusion. Morris (1959) in a study of 2 spruce-defoliating insects constructed a predictive model based on a single key factor. The incidence of parasitism in a larval stage of a given generation of defoliators could be used to predict

Interspecific Territories of Birds

Abstract: Territories of birds, usually defended against conspecific individuals, are sometimes defended against individuals of other species. Since such behavior is demanding both of time and energy, natural selection should favor ecological should favor ecological divergence, the establishment of overlapping territories, and the reduction of aggression. Lack of divergence in modes of exploitation could mean that insufficient time has elapsed for the changes to be completed or that the environment imposes some limitation preventing the evolution of the required degree of divergence. Such environmental limitation can be predicted in (a) structurally simple environments, (b) when feeding sites are strongly stratified in structurally complex vegetation, or (c) when the presence of other species in the environment prevents divergence in certain directions. The known cases of interspecific territoriality in birds are analyzed and shown to be largely in accordance with these predictions, although several cases of overlapping territories in situations where interspecific territoriality has been predicted provide relationships worthy of further study. We suggest that Darwinian selection at the level of the individual permits an understanding of the known structure of avian communities and that there is no need at present to invoke new selective mechanisms at the level of the community or ecosystem.

Ecological Distribution in Anoline Lizards of Puerto Rico

Abstract: The eight species of lizards of the genus Anolis in Puerto Rico can be divided into four morphological similarities. One, Anolis curvieri, is very different from the rest and has not been discussed here. The other seven species fall into three groups. Each of these groups occupies a different structural habitat which can be defined in terms of perch height and perch diameter. Within each of these three groups the species have very similar but not indential structural habitats but differ very widely in climatic habitat defined in terms of shade. Shade preferences seem to result from the temperature preferences of the species involved. In each group there is one species with high shade preference which is essentially restricted to the mountains. Each group also has a species with a lower shade preference which occurs in the lowlands and extends up into the mountains in exposed or sunny situations. One of the three groups has an additional species which is restricted to the hot and southwest corner of Puerto Rico. When one compares the temperature preferences or eccritic temperatures of the various species, one finds in each group that the highland species has a lower eccritic temperature than does the lowland species. There is little temperature difference between the lowland species and arid southwest species in the group where this additional third species is present. The species within each structural habitat show many morphological similarities which may be the result of their being closely related or may be the result of adaptation to similar environments. The differences in microhabitat between the Puerto Rican anoles separate them spatially though not completely. In species occupying different structural habitats in the same area the overlap may involve part of the home range of most of the individuals in the area. In species occupying the same structural but different climatic habitats the overlap may involve all of the home range of some individuals but of only a small fraction of the individuals in the total population. The spatial separation among Puerto Rican Anolis can be suggested to be of ecological significance because it reduces interspecific competition and because it allows the various species to adapt more precisely to different parts of the available habitat. Thus members of a genus may exploit the habitat more efficiently.

Viability of Crustacean Eggs Recovered From Ducks

Abstract: A wide variety of viable crustacean eggs has been recovered from the lower digestive tract of both domesticated and wild ducks These have been hatched and raised to maturity This would appear to be one of the most effective means for the dispersal of many fresh—water Crustacea See full-text article at JSTOR

Ecology and Distribution of Pocket Gophers (Geomyidae) in Colorado

Abstract: The general distribution of the family geomyidae in North America is limited only by suitable soils, although a particular species may be also be limited by climatic or other factors associated with altitude and latitude and by interspecies competition. A study was made of the factors affecting the distributions of the pocket gophers Thomomys bottae, T. talpoides, Geomys bursarius, and Cratogeomys castanops in Colorado. The most critical factors in the relationships among pocket gophers are soil tolerance and competition. All four species in Colorado prefer deep light soils,but their ranges of tolerance vary, with the result that interspecies competition consists of the fundamental niche of one species being a proper subset of another. In each combination of competitive and is able to displace the other speices to less favorable habitats. The relationship among the four species in competitive ability is G. bursarius > C. castanops > T. bottae > T. talpoides. Possible mechanisms of competition are discussed in relation to body size, territory, aggression, and dispersal.

Inverse Relationship Between Temperature and Shyness in the Lizard Anolis Lineatopus

Abstract: An increase in flight distance with a decrease in body temperature in 32 male Anolis lineatopus at Mona, Jamaica, supports more casual field observations that these lizards are shier when they are cold than when they are warm. It is suggested that this increased shyness compensates for the slowing effects of lower temperatures on biological processes and so helps protect these arboreal lizards from warm—blooded predators. See full-text article at JSTOR

Ash and Calorie Determinations of Sponge and Opisthobranch Tissues

Abstract: Studies on the caloric value of sponge and opisthobranch tissue have been used to indicate 2 actual sources of error in determining an organism's cal/ash—free g value. If the skeleton is hydrated, this water is not removed at normal drying temperatures (100°C) when the skeletal material is CaCO3, and is only partly removed from SiO2 skeletons. The cal/ash—free g value is seriously underestimated in these cases. In addition, if the per cent of ash is determined by weight difference in the calorimeter, or at too great a temperature in a muffle furnace, the value may again be underestimated. Appropriate corrections for these errors bring values for some opisthobranches, which would otherwise be inexplicably low, into general agreement with other published values. See full-text article at JSTOR

Division Rates of Salt Marsh Diatoms in Relation to Salinity and Cell Size

Abstract: Fourteen species of motile pennate diatoms obtained from a Georgia salt marsh were cultured under uniform conditions (19°—20°C, 16,000—23,000 lux) in soil—water medium at salinities between 1 and 68 %. All species grew well over at least the range of 10 to 30%; several species grew well over the entire salinity range. At 20 % the division rate was either maximal or close to maximal. Diatom preconditioned to particular salinities in general divided at the same rate as those not preconditioned. Maximum rates for the 14 species ranged from 0.6 to 3.2 divisions/day. These maximum rates had highly significant correlations with both the logarithm of the cell volume and the square root of cell area/cell volume. Least squares regressions were computed for these relationships with volume expressed in μ3 and area in μ2. Maximum number of divisions per day = 3.75 — 0.7 (log volume) =—0.01 + 1.64 (area/volume)½ See full-text article at JSTOR

An Analysis of Background Color‐Matching in Amphibians and Reptiles

Abstract: The colors of living amphibians and reptiles have been studied, using a General Electric recording reflectance spectrophotometer. The animals were brought to activity tempera- ture levels and the appropriate surface pressed over the reflectance port of the machine while a color record was taken. Background samples from the localities at which the animals were taken were also recorded. Reptiles and amphibians living on backgrounds of relatively uniform color tend to matcl that background through superposition with considerable fidelity. The animal's color curve is superimposed over that of the background. Ventral color in most forms tested was lighter than the dorsal surfaces of the same animal. It was darker only in some forest-dwelling salamanders and in desert lava-dwelling species. The difference results primarily from the highly reflective ventral surfaces of these forms. The ventral surfaces of white-bellied amphibia show clear oxyhaemoglobin absorption peaks, as do the dorsal surfaces of some amphibia. These effects are entirely absent in curves recorded from reptiles. It is concluded that the degree of background color-matching is related to: (a) the degree of color uniformity of the animal's background, (b) the degree of exposure of the color-matched species to predators, (c) the illumination level prevalent in the habitat, (d) the size range of the color-matched species, (e) the ecological restriction of the species, (f) the qualities of the visual apparatus of predators upon the species, and (g) the adaptive compromise struck by the species. The size of a color-matched animal, or the size of the part of its body that is normally exposed, is related to the point at which such color-matching breaks down. This point of just noticeable difference between animal and background is also determined by the wave-length discrimination curves of the predators, the closeness of the match involved, the uniformity of the background color and its texture, and the presence or absence of concealing patterns. Back- ground color-matching varies greatly in its degree of perfection. This variation is the result of adaptive compromise and balance between this adaptive characteristic and many others that in one way or another affect its complete expression.

Shallow-Water Marine Climates and Molluscan Provinces

Abstract: Definitions of shallow—water marine climatic zones that equate the northern limit of climatic zones with minimum temperatures are shown to be not critical. The critical factor that probably determines the limits of marine shallow—water climates is the number of consecutive days or months that shallow sea water is at temperatures required for reproduction and early growth. The relations that appear to exist between duration of marine water temperature or climate and molluscan provinces are: (1) Inner tropical includes molluscan species that live in water that is 20 C or nearly 20 C for 6 or more months, and with no months cooler than 18 C. (2) Outer tropical includes those species that live in water 20 C. For only 4 months, in water that is 18 C for approximately 6 months, and for no months cooler than 10 C. (3) Warm temperate includes species that live in water approximately 15 or 18 C for almost 4 continuous and in water no colder than 10 C. (4) Mild temperate contains species living in marine water that...

Use of Life Tables in a Bioclimatic Study of an Experimental Aphid-Braconid Wasp Host-Parasite System

Abstract: to environmental extremes of drought and flash floods. 2. The natural life span for most Rhinichthys oscults in the Chiricahua Mountains is less than 3 years. None was found to reach 4 years. 3. High mortality rates during summer drought must be interpreted, in part, as an acceleration of death among older fish since most fish are expected to die before they are 3 years old. Among younger fish, drought directly elevates the mortality rate. 4. Mortalities during a drought are caused directly by the disappearance of water and indirectly by starvation of the fish which are crowded into reduced habitat with inadequate food. 5. Flash floods are an important cause of mortality among fish of the year if they occur while the fish are very small. The greatest potential loss of fish of the year occurs in late summer when the initial flash flood induces major reproduction and is then followed by another flash flood. 6. Flash floods are not a significant cause of mortality among older fish. 7. Temporary waters may persist in some sections through a period of wet years. The populations of fish inhabiting them are derived from upstream sections during a flash flood. All fish that were located in downstream temporary sections in the spring of 1960, were one-year-olds. 8. Temperatures do not rise to lethal levels in any of the flowing streams. In exposed shallow isolated pools, the temperatures may become lethal for oldcr fish, but not for fish of the year. 9. Predators play a minor role. Only one, the garter snake, Thamnophtis cyrtopsis, is common and apparently important. 10. Although fish populations are greatly reduced by a year of drought, there is no immediate threat of their local extinction.

Granite Outcrop Communities of the Piedmont Plateau in Georgia

Abstract: Communities in depressions, occurring as islands surrounded by naturally exposed granitic rock, were classified by the correlated of maximum soil depth and characteristic vegetation cover into: diamorpha communities, 2—6 cm; lichen—annual herb communities 16—39 cm; and herb—shrub communities, 40—50 cm. The total flora of the 40 island communities, included 76 species, but only 39 of these occurred in five or more communities and were considered characteristic. The extreme environmental conditions of high light intensity and low soil moisture content were indicated by the fact that of the 20 plants present in over 50% of the communities, 18 were lichens, mosses, and flowering annuals and only two were perennial flowering plants. The flora of the island communities is distinct from that of border vegetation. Only three endemics are among the 39 characteristics plants. Seasonal aspects of the outcrop vegetation are striking. During the winter months, November through February, mosses and lichens are most con...

Bioenergetics of the Southern Harvester Ant, Pogonomyrmex Badius

Abstract: The bioenergetics of the southern harvester ant were studied on the Savannah River Project, Aiken, South Carolina. Excavation of hills revealed that density of ants ranged from 4,000 to 6,000 per hill. Labeling ants with p32 indicated that only 10% of the ants in a colony were active above ground during any 2-week period (the limit of recognition of the label) * thus, short-term marking recapture estimates based on above-ground individuals greatly underestimate the size of the colony. There were 27 hills per hectare on the study area. The consumption of oxygen of workers at various temperatures was determined in a simple respirometer, and the temperature at which the ants were living in the field was determined during a year's observation at mounds. The energy expense of heat production was calculated from the oxygen consumption and activity- temperature records. Total energy flow (heat production plus tissue growth) was highest in summer and lowest in winter. The annual range was from 14 to 48 kgcal/m2/yr. Tissue growth was estimated to amount to only 0.09 kgcal/m2/yr. Energy flow in this species was higher than that of 2 vertebrate granivores studied in the same field, the old-field mouse and the savannah sparrow.

A Possible Ecological Relation Between Soil Disturbance, Light-Flash, and Seed Germination

Abstract: A connection is suggested between two well—known but hitherto unrelated phenomena: germination under field conditions of certain seeds following soil disturbance and germination in laboratory experiments of certain seeds following brief exposures to light. A light—flash mechanism for breaking dormancy is proposed as a possible adaptation aiding pioneer plants in exploitation of disturbed habitats. See full-text article at JSTOR

Root Development of Native Plants Under Three Grazing Intensities

Abstract: The purpose of this study was to determine the effects of various intensities of grazing upon roots and root systems of plants native to the ponderosa pine zone of the Colorado Front Range. It was designed to ascertain the root characteristics of certain species of the plant community and any changes in root distribution induced by 17 years of moderate and heavy grazing by cattle. The cumulative effects of such grazing are also illustrated. Most studies concerning the effects of plant defoliation show that any cropping (clipping or grazing) reduces plant growth, especially root growth. The initial root and rhizome response to defoliation is the cessation of elongation (Parker and Sampson 1931, Crider 1955). Subsequent reactions to continued defoliation are reduction in root numbers and branching (Jacques 1937, Albertson, Riegel, and Launchbaugh 1953), root diameter (Biswell and Weaver 1933), and depth of soil penetration (Ruby and Young 1953, Cook, Stoddart, and Kinsinger 1958). The amount of reduction is directly related to the severity and frequency of defoliation (Graber 1931, Albertson et al. 1953, Thaine 1954). In general the degree of defoliation is more detrimental to root growth than frequency of defoliation. Crider (1955) showed that apical growth of grass roots stopped within 24 hr after the removal of 40% or more of the foliage in one operation. The time required for roots to resume growth varied directly with the degree of foliage removal. The consequences of overgrazing are apparently carried over from season to season. WVeaver

Larval Competition in Drosophila Melanogaster and D. Simulans

Abstract: The Gause principle of interspecies competition states that if 2 species are forced to coexist in an undiversified environment, one inevitably becomes extinct, and if 2 species do coexist they must occupy different ecological niches. An extensive literature has been written on the development of this principle and the confusion that has arisen from the problem of competitive exclusion and identical niches (cf. Elton and Miller 1954; Andrewartha and Birch 1954; Hutchinson 1957). Gilbert et al. (1952) and Hardin (1960) have discussed the circularity that is usually involved in attempts to prove or disprove the Gause principle. If one species eliminates another we say the principle is "proved," but if they coexist we conclude that they differ ecologically and occupy different niches. Any meaningful concept of species or ecological niches recognizes that no 2 species are genetically or ecologically identical, so that the "axiom of inequality" provides automatic confirmation of the principle as it is stated. To this extent the principle can neither be proved nor disproved (Hardin 1960).The Gause principle is useful only when it can be applied to a conceptual model which can be tested with empirical data. When we find that a prediction is not verifiable we modify the model, but there is no procedural rule to tell us which element in the model we should abandon or change. Elton and Miller (1954) attempted to resolve certain of the descriptive problems in the niche concept by considering "arenas" of potential competition between species. Hutchinson (1957) has more recently used set theory to provide a more precise definition of an ecological niche and the conditions of interspecies competition. According to Hutchinson's formulation, if we consider the array of environmental variables relative to a species S1, we can define an n-dimensional hypervolume which corresponds to the state of environment which would permit species S1 to exist indefinitely. For any species Si this hypervolume N1 is its "fundamental niche." If N1 and N2 are 2 fundamental niches, they may have points in common which are said to intersect. Thus, N1 . N2 is the subset of points common to both and is referred to as the "intersection subset." An intersection subset, according to H-utchinson's terminology, corresponds to what Elton and Miller (1954) referred to as an "arena of competition" in the overlap of 2 niches. Identity of 2 fundamental niches would imply that N1 N2, or every point of N1 is a member of N2 and every point of N2 is a member of N1. For the reasons mentioned above with regard to the "axiom of inequality," this condition is, as Hutchinson (1957) states, "so unlikely that the case is of no empirical interest." We frequently find among closely related species, however, that the intersection subset of fundamental niches provides a wide range of overlap in ecological requirements. The data provided by Park (1954, 1955) for interactions between the flour beetles Tribolium confusum and T. castaneum are an extremely well-documented example. A detailed analysis of these data by Neyman, Park, and Scott (1958) has shown that the outcome of competition between these 2 species is predictable in certain environments and "indeterminate" in others. In other words, within the intersection subset for confusun and castaneum there are points at which the ecological requirements and increase potentials of the 2 species are so similar that the outcome of competition is a statistical probability rather than a predictable certainty. The genus Drosophila is a particularly good source of material for the study of competition among closely related species. The genus contains more than 700 recognized species and is well represented in all zoogeographical regions of the world (Patterson and Stone 1952) ; investigations of the genetics and ecology of Drosophila. have shown that remarkable similarity exists among various sibling species which coexist in nature, in apparent contradiction to the Gause principle. Merrell (1951) studied competition in cage populations of Drosophila funebris and D, melanogaster which coexisted in the laboratory for almost 2 years. Analysis showed that a fresh yeast medium was more suitable for melanogaster whereas funebris was able to maintain itself in older food, so that periodic renewal of the food and medium induced environmental fluctuations which alternately favored one species and then the other. Moore (1952) obtained somewhat similar results with cage populations of the more closely related species Drosophila melanogaster and D. simulans. He concluded that melanogaster is superior to simulans in competition at 25?C and simulans

Arctostaphylos Myrtifolia, Its Biology and Relationship to the Problem of Endemism

Abstract: Arctostaphylos myrtifolia is a California endemic plant limited to only certain outcrops of an Eocene laterite in the Sierra Nevada foothills near Ione and to a kaolin—altered rhyolite and an acid sericitic schist eastward at higher altitudes of 500 m. Taxonomically the diploid species is isolated. Morphologically it resembles a low, sclerophyllous heath. The plants are killed by fire, but seedlings are favored by the ensuing bare areas. It flowers in late winter or very early spring. The climate where A. myrtifolia occurs is dry in summer, wet in winter. Frosts are infrequent and slight, but summer heat is severe. Only some 350 mm of actual evapotranspiration of water is calculated to take place in these environments, but leaching may amount to 200 mm at lower elevations and to 400 mm at higher. The stations for A. myrtifolia do not differ greatly in climate from surrounding areas where the plant does not occur, but they have a somewhat more maritime temperature regime. The soils at these stations are acid and presumably so low in nutrients as to exclude the normal, zonal, climax vegetation. The endemic plant thus is presumed to be a better competitor on the nonzonal sites of acid soil parent material. Many cases of similarly disjunct plant distribution can be related to regionally peculiar soil parent materials whose evident effect is to exclude the regionally climax vegetation. With competition by zonal vegetation thus weakened, disjunct plants can and do occur. The vegetation associated with A. myrtifolia is poor, therophytic, and adapted to acid, seasonally wet sites. Its shows similarities to the Cisto—Lavanduletea of the Mediterranean region. Historical factors of some kind, and not the contemporaneously acting ecologicalfactors alone, are assumed to help account for the limited distribution of the species.

Studies of Warning Coloration and Mimicry. IV. A. Mathematical Model of Model-Mimic Frequencies

Abstract: One of the principal tenets of the Batesian theory of mimicry is that the effectiveness of pseudaposematic coloration is reduced as the incidence of models decreases in relation to that of the mimics. This is to be expected since learning efficiency of predators will be reduced if models become scarce. Field studies (Carpenter 1932, 1949; Ford 1936) have shown that mimicry is, indeed, less effective where the frequency of models is low. Unfortunately, the following generalization is often assumed: if the model outnumbers the mimic, the pseudaposematic coloration is effective, whereas if the mimic outnumbers the model, the system breaks down. Sometimes the principle is stated qualitatively: the mimic must be rare with respect to the model. However, as pointed out by Sheppard (1959) and. Brower (1960), there is nothing unique about the 50-50% ratio. In studies by Brower using caged starlings as predators and meal worms as artificial models and mimics, it was found that the effectiveness of mimicry in a population containing 60% mimics was of the same order of magnitude as that of one containing only 30%. The effectiveness of aposematic and pseudaposematic coloration depends upon a number of variables in addition to model frequency. One is the ability of the predator to remember the aposematic signal. This in turn depends upon the inherent ability of the predator to learn, the nature of the warning signal, and the intensity of the stimulus that the predator receives upon sampling the model. Sheppard (1958) has called attention to the last factor: "An animal sufficiently obnoxious to make predators avoid its colour pattern, even when having encountered only one, could give protection to a mimetic form as common as, or commoner than, the model." In addition, the effectiveness of pseudaposematic coloration depends on the degree of similarity of the model and mimic. Other variables such as hunger, although influencing behavior strongly, may be considered relatively unimportant since their effects would be averaged out over a large sample. It would be advantageous if a mathematical model could be used to describe the situation obtaining between a model and a mimic. Although it should be possible to construct such a model employing all of the variables mentioned above, a simplified model is less cumbersome to handle, and at our present state of knowledge appears entirely adequate. As more data accumulate, it may become desirable to elaborate the simple model presented here. The following assumptions are made: (1) The effectiveness of the mimic pattern is 100%, i.e., the mimic cannot be distinguished visually from the model. This is patently untrue except in the case of artificial models and mimics analyzed below, but it must be admitted that in many cases of known mimicry this condition is approached closely. (2) The strength of the model's stimulus and the ability of the predator to remember it can be expressed in terms of a single parameter, n. This parameter corresponds to the total number of individuals (including the original model) protected by the predator rejecting the model, remembering the stimulus received from it, and thus avoiding both models and mimics until it forgets and renews sampling.

Fecundity, Reproductive Rates, and Innate Capacity for Increase of Three Parasites of Therioaphis Maculata (Buckton)

Abstract: Three species of hymenopterous parasites of the spotted alfalfa aphid were reared over a range of constant temperatures At each thermal level, life—table data were obtained for each species These data were used in computing certain statistics concerning reproduction and rates of potential population increase which are valuable in assaying the effectiveness of each species as an aphid parasite The temperatures studied ranged from 10 to 35°C, and the relative humidity was held as constant as possible between 40 and 60% Artificial illumination and photoperiods were identical in all studies The studies showed that the braconid, Trioxys utilis Muesebeck, generally has the highest mean total fecundity of the three species, although the aphelinid, Aphelinus semiflavus Howard, produced more eggs in the temperature range of 18 to 22°C The gross reproductive rate and net reproductive rate of T utilis were also higher than the other parasites throughout most of the temperature range studied, although again A semiflavus showed higher reproductive rates between 24 and 27°C The innate capacity for increase, rm, of T utilis was decidedly the highest of the three parasites at all temperatures The braconid, Praon palitans Muesebeck, was inferior tot he other two parasites in nearly all phases of these life—table statistics Its inclination to enter a facultative hibernal diapause at relatively mild temperatures, plus its intolerance of higher temperatures, which the other two species endured, limited its thermal range of effectiveness Statistics such as total fecundity, gross reproduction, rate, net reproduction rate, and innate capacity for increase are discussed relative to their value in indicating the potential effectiveness parasites can be expected to possess in the field

Relative abundance of species and macarthur's model

Abstract: MacArthur's model was derived to predict the relative abundance of species in adequately sampled sympatric associations in which niches are contiguous and nonoverlapping, the species are comparable in size and physiology and are maintained in equilibrium so that relative abundances are constant. The model is applicable only to homogeneously diverse biotopes in which the range of the environmental mosaic is small in relation to the require- ments of the inhabitant species. These factors require that the niche arrangement be the out- come of competitive exclusion. Data are presented on the adequacy of the MacArthur model in describing the relative abundance of fish, ophiuroids, gastropods, pagurid crabs, and ciliates. In addition, summaries of previously reported tests are included. By comparing groups which are adequately and inadequately described by the MacArthur model, it is possible to examine the characteristics which may establish the equilibrium. It is hypothesized that characteristics of importance are length of life cycle, duration and frequency of reproduction, and relative (to generation time) constancy of environmental conditions. It is shown that when fish or gastropod species are tested, the goodness-of-fit to the model's predictions is related to the taxonomic affinity of the group being tested. Stable associations of species with high taxonomic affinity must be highly organized. A high degree of organiza- tion is required to maintain the random distribution of abundances. Density dependent com- petition for food is the most likely basis of this organization.

Possible Relationships Between Plankton‐Diatom Species Numbers and Water‐Quality Estimates

Abstract: Semimonthly samples from 103 scattered stations on the major rivers and Great Lakes of the United States reveal differences in kinds and numbers of dominating planktonic organisms. Diatoms dominate at these stations. A counting of 250 to 300 individuals per sample of diatoms using special hyrax mounts gives an adequate proportional representation of the four most abundant species of the population. Samples with high representation of individuals in the four most abundant species reliably indicate low species diversity, which in most situations is an indication of enrichment or eutrophication. Samples with high standing crops (productivity) usually show low species diversity. A study of the four most abundant species of diatoms and the six most abundant genera of algae demonstrated, with few exceptiosn, that the most frequent dominants have the highest standing crops. Dominating diatom species with highest frequency and composing 50% of the total abundance of diatoms for each of 2 years were calculated for...

Fossil Pine Pollen and Full-Glacial Vegetation in Southeastern North Carolina

Abstract: A reassessment of the difficulties inherent in size—frequency identification of pollen indicates that the reliability of the method is of low order. Accurate identifications assume: (1) Adequate data on size variation for all relevant extant species; (2) a standardized method of preparation for all modern samples; (3) use of mounting medium in which size is stabilized (not glycerine or glycerine—jelly); (4) preparation of all samples from a given fossil profile by an identical technique (not necessarily the same as that employed for modern material); (5)cognizance of the fact that size of modern and fossil grains cannot be compared directly and that the size changes may occur as a function of sediment type within a profile; and (6) presentation of size—frequency curves for the fossil material. New Pollen size measurements for the 13 eastern pines indicate that no single species can be identified on a size—frequency basis. The mode for small pine grains described by Frey from the full—glacial portion (M Zone) of the Singletary Lake profile could have been contributed to by either jack pine or red pine (or both). These data and new pollen analyses from the M Zone sediments suggest that the dominant full—glacial forest type in the region consisted of widely spaced pines (jack and/or red pine) associated with heliophytic herbs and shrubs (Artemisia, Polygonella, Plantago, Ambrosia, caryophylls, and chenopods). Boreal elements (Picea, Abies, Schizeae pusilla, Sanguisorba canadensis, Lycopodium annotinum, L. lucidulum) may have occurred on more mesic sites surrounding the lakes or on the poorly drained inter—Bay regions.

Long-Term Effects of Defoliation of Aspen by the Forest Tent Caterpillar

Abstract: A second study of the effect of aspen of defoliation by the forest tent caterpillar in Minnesota was conducted 6 years after the conclusion of an initial comprehensive investigation Results indicate increasing mortality in other than suppressed trees with increasing defoliation intensity Hypoxylon, Nectria, and insect incidence increased with defoliation intensity Growth is significantly reduced 1 year beyond the cessation of defoliation in stands where three successive heavy defoliations have occurred Growth of the dominants increases significantly, however, the third year after defoliation in such stands See full-text article at JSTOR

The Ecology of Spanish Moss (Tillandsia Usneoides): Its Growth and Distribution

Abstract: The growth pattern of Spanish moss is one of alternately dominant dichotomous forking (scorpioid dichotomy). The non—dominant branch at each fork is a leaflike branch. The flowers, which are terminal on the pendant plants, are produced in South Georgia from the middle of April to the first of June. The subsequently formed capsule remains closed for 6 months and its remnants remain in the same position for a year. Spanish moss has a positive geotropic response when oriented in a horizontal position. The formation of several vertical plants on old horizontal stems is a means of vegetative reproduction. An almost direct relationship is evident between terminal growth and the percentage of solar radiation. Atmospheric moisture alone will not support growth; experimental plants die in 3—4 months with natural humidity but no rain. Rate of growth could not be correlated with moisture or temperature, but it was adversely affected by shade. Although Spanish moss does not appear to favor any one host, it is not often found on pines. Possible explanations for this scarcity are that pines are self—pruning, the dense leaves are a formidable barrier to wind—blown entry, and the proportion of intercepted rainfall is greater in pines than in broad—leaved species. The distribution of Spanish moss in the United States, limited to the Coastal Plain of the southeastern states, ranging from Texas to Virginia, may be related to major storm paths which arise to Mexico or cross other storm paths which arise there and move laterally over the Coastal Plain. Some of the plants may have been carried into Florida by storms from the islands in the Caribbean Sea. Spanish moss is able to survive and produce viable seeds outside the Coastal Plain, and ability of the species to survive in habitats completely dissimilar to those of the Coastal Plain areas is shown by its distribution in various physiographic regions of South America. The close relationship between Spanish moss and ponds in Georgia appears to be the result of unfavorable conditions elsewhere (such as fire and lumbering which remove suitable substrates), rather than conditions provided by the ponds.