bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Simple Cave Communities: Niche Separation and Species Packing
Authors: Culver David C.
Published: May 2006

This paper considers various ecological relationships of three gammarid amphipods (Gammarus minus, Stygonectes emarginatus, and Stygonectes spinatus) and one asellid isopod (Asellus holsingeri) in cave streams of the Greenbrier Valley in West Virginia. Two clear—cut cases of reduction of realized niche due to the presence of other species were found: S. emarginatus is limited to small trickles of water when G. minus is present in the stream and A. holsingeri is limited to gravel—bottomed pools when G minus is present in riffles. S. spinatus prefers smaller rocks than do the larger amphipod species. All four species maintained weight equally well on rotting leaves or mud, so feeding differences appear to be minimal. Using Levins' matrix of competition coefficients as a framework, interference and exploitation competition were quantified and separated. From these data, it is indicated that the community is closed to immigration by similar species into the microhabitats occupied by the four crustacean species. Field evidence supports this. Some unused microhabitats may be available, but the aquatic insects that might potentially use them are not present.
Spatial and Temporal Structure in a Temperate Intertidal Community, with Special Emphasis on Gemma Gemma (Pelecypoda: Mollusca)
Authors: Green Roger H. , Hobson Katharine D.
Published: May 2006

In the region of Barnstable Harbor, Massachusetts, 67 species of larger invertebrates were found in 3 faunal associations characteristic of different tide levels. The number of species per sample was highest at the intermediate tide level. Temperatures of sediments and densities of several species were followed for a year at two intertidal levels (60 cm and 90 cm above mean low water). Temperature variation was lower at the 60—cm level than at the 90—cm level at all times of the year, and at both levels was higher in spring than at any other time of the year. In three of the four species studied, spatial variation in density and rate of density change was significantly higher at the 60—cm location than at the 90—cm location. The mortality rate for adult G. gemma was higher at 60 cm (where density was lower) than at 90 cm, while the reverse was true for young—of—year. Release of young began sooner in the spring at 90 cm than at 60 cm. The growth rate of G. gemma at Barnstable Harbor was much lower than that reported at Union Beach, New Jersey, although at both places virtually all growth took place in summer. At Barnstable Harbor the maintenance requirements were 20—30 times higher in summer than in early spring. The Q10 within the temperature range 5—20°C was 4.1. G. gemma at 90 cm had less time to feed than at 60 cm, but had higher requirements for population maintenance because of an older age structure and a higher density. The growth rate of G. gemma was higher at 90 cm than at 60 cm.
Ecotypic Differentiation in Koeleria Cristata (L.) Pers. from Colorado and Related Area
Authors: Robertson Philip A. , Ward Richard T.
Published: May 2006

The phenological and morphological response of populations of Koeleria cristata (L.) Pers. from Colorado and related areas in a transplant garden at Ft. Collins indicated marked heritable differences. Most significantly, and contrary to what would be predicted on the basis of other such studies involving elevational gradients, the highest collections from Colorado (about 2,850 m) were latest in development. The moisture regime of the native habitats was a more important selection force than the length of the growing season. Plants from the northern plains were similar in phenology and morphology to plants from the plains—foothills region of eastern Colorado. Two, and possibly three, regional relationships are suggested for the Colorado populations.
Small Mammals and Regeneration of White Spruce Forests in Western Alberta
Authors: Radvanyi Andrew
Published: May 2006

The fate of 7,800 pesticide—treated and radiotagged white spruce seeds (Picea glauca (Moench) Voss var. albertiana (S. Brown) Sarg.) was studied under field conditions near Hinton, Alberta, Canada, from 1962 to 1967. Approximately 50% of spring—placed seeds were destroyed by small mammals within 4 months, whereas only 19% or less of winter—placed seeds were lost within a year. From five to six times more seeds germinated following the winter seeding operations than after the first spring seeding test. Calcualted ground seed—eating small—mammal populations varied from 2.0 to 7.4 (average 4.5) animals per acre in spring and from 4.9 to 12.2 (average 8.1) in the fall. Percentages of seeds destroyed were more directly related to time of seeding than to the number of animals present.
Interspecific Competition Between Drosophila Melanogaster and Drosophila Simulans: Effects of Larval Density on Viability, Developmental Period and Adult Body Weight
Authors: Barker J. S. F. , Podger R. N.
Published: May 2006

In interspecific competition between various strains of Drosophila melanogaster and a vermilion mutant strain of D. simulans in continuous populations, heterogeneity among replicate populations and among generations within populations has been observed when the fitness of the melanogaster strain was apparently similar to that of simulans vermilion. Larval and adult numbers vary widely among generations, so that differential effects of population density on fitness components of the two species could be an important factor contributing to the observed heterogeneity. The effects of variation in larval density and in proportions of the two species on viability, sex ratio, developmental period and adult body weight have been determined for the Oregon—R—C wild type strain of melanogaster and the standard vermilion strain of simulans. Thirty treatment combinations of larval density (six levels) and species proportions (five levels–two single species, three mixed) were repeated three times at intervals of 1 week. This variable of time had highly significant effects on all components. Results observed in mixed cultures generally were not predictable from results in single species cultures, particularly at high densities. The general effects of density on both species were similar, but there were significant differences between the species that would cause differences in competitive outcome at different densities. Further, the different components showed different responses to density. Species frequency also had significant effects on each component, but these effects were often different for the two species and were different for each component. As the outcome of competition within a generation was both density and frequency dependent, and given as well the significant effects of time, variation among populations and among generation within populations can be expected. The dynamics of interspecific competition in continuous populations will not be simply predictable.
Population Ecology of Desert Rodent Communities: Body Size and Seed‐Husking as Bases for Heteromyid Coexistence
Authors: Rosenzweig Michael L. , Sterner Philip W.
Published: May 2006

Seven species of heteromyid rodents varying in size from 8 to 114 g were studied in the laboratory. Starved rodents husked four kinds of large seeds (spinach, sunflower, squash and pumpkin) and were timed at the task. Geometric mean husking times varied from 3.1 to 70.1 seconds, depending on the seed and the rodent. Husking time was inversely proportional to an animal's body size. However, despite their slowness, smaller animals appear to be more efficient at dealing with these large seeds because they have a smaller metabolic drain. This conclusion is based on the assumption that gross caloric need increases linearly with (body weight).75. The authors defend the assumption and thus believe that smaller animals have a competitive advantage while husking seeds. These rodents might engage in a limited amount of habitat and resource selection based on their relative seed—husking abilities. However, the order in which the various species should prefer these seeds is quite similar, so resource allocation based on husking speed differences would seem of little potential importance in maintaining competing heteromyids in a state of coexistence. Previous investigators have shown that seed selection occurs in some cases, but many cases are also known in which little or no selection is practiced.
Ecology of Eastern White Pine Seed Caches made by Small Forest Mammals
Authors: Abbott Herschel G. , Quink Thomas F.
Published: May 2006

Typical seed caches made in the fall of the year by white—footed mice (Peromyscus leucopus) and red—backed voles (Clethrionomys gapperi) contained 20—30 pine seeds, buried beneath the litter of pine needles and in contact with mineral soil. Many caches were revisited by the mice and their contents destroyed before winter. Most caches not decimated in the fall were invaded the following spring. However, some of them escaped complete destruction and their unconsumed seeds germinated and produced seedlings. Although mice make their caches in micro—environments highly favorable to germination, their subsequent feedings on the stored seeds, both before snowfall and before and during the spring germination period, greatly deplete the number of potential germinants. Therefore, the contribution to forest regeneration of seeds stored by these small forest mammals is probably of minor significance except when bumper seed crops are produced and large numbers of caches are created. Under these circumstances, stored seeds may be of sufficient quantity to exceed food requirements of the mice. If pirating by other animals is low, then a surplus of seeds is left to help regenerate the forest.
Correlation, Regression, and Density Dependence
Authors: Eberhardt L. L.
Published: May 2006

Several examples are given to illustrate the dangers of inferring the existence of density—dependent population regulation on the basis of correlation analyses. Alternate models based on a series of random number (or random selections from some other frequency distribution) have expected correlation coefficients very close to those cited as demonstrating density dependence. A "Morris plot" can also be generated from a series of random numbers.
Calcium and Strontium Discrimination by Aquatic Plants
Authors: Ophel I. L. , Fraser C. D.
Published: May 2006

Sr/Ca ratios are given for 22 species of aquatic plants from Perch Lake, Ontario. When compared with the lake water, 16 species are found to discriminate against calcium relative to strontium. Consequently, these species introduce a strontium enrichment step into any food chain in which they participate. One species (Nymphaea odorata) however, shows a remarkable discrimination against strontium.
Modulated Reproductive Periodicity in Chelonia
Authors: Carr Archie , Carr Marjorie H.
Published: May 2006

After 15 yr tagging at the nesting ground of Chelonia mydas at Tortuguero, Costa Rica, 447 remigration returns have been recorded. These confirm previous indications that some Tortuguero females return to nest every 2 yr and some every 3 yr, with the latter being the more frequent cycle. Returns after absences of 4 yr are so frequent that it seems probable that a regular cycle of this magnitude also exists. Longer absences recorded (up to 9 yr) probably can be attributed to missed encounters or to weak site tenacity by the returning turtles. A growing list of two—time and three—time returns shows that although an individual usually maintains a constant cycle, modulation of this may occur, and that the change may be either from 3 to 2 yr, or vice versa. It is suggested that the modulation reflects ecological conditions on the feeding ground. A sudden extensive shift to a 2—yr cycle, by turtles that had been nesting on a 3—yr cycle, probably contributed to the heavy nesting that occurred in 1969, after several previous weak seasons.
Habitat Selection by Birds Following a Forest Fire
Authors: Emlen John T.
Published: May 2006

In the light of current opinion that habitat selection by birds is determined largely by gross visual aspects of the vegetational physiognomy (Hilden 1965), one might intuitively expect that drastic alteration of the ground and shrub strata of a forest would modify the composition and numerical status of resident bird populations. However, counts in a burned pine stand in southern Florida during the first few months after burning were essentially no different than counts in an immediately adjacent unburned stand. The lack of response to this habitat alteration may be attributed behaviorally to individual home range attachments by the resident birds. Its occurrence in this situation may be associated with the relatively brief during of these habitat disruptions and the frequency of forest fires as a normal feature of slash pine ecology.
The Number of Bird Species in Some Tropical Forests
Authors: Orians Gordon H.
Published: May 2006

Resident birds were censused in seven plots in Costa Rica ranging from 0 to 6 months dry season and from sea level to 2,380 m in elevation. Included were one highland and two lowland sites that were dominated by one or two species of trees. All stands were tall, undisturbed forests, but some were surrounded by agricultural land. The number of species of birds recorded was not measurably affected by the tree species diversity or the length of the dry season. However, a larger proportion (about 90%) of the total forest species known to occur in the region as a whole was found in the drier areas, whereas only about 50% were recorded in the wetter areas. This suggests that "between—habitat" diversity" may be greater in the areas with less severe dry seasons. The highland sites and markedly fewer species than the lowland sites, and a greater percentage of the species foraged by moving actively than was the case in the lowland sites. The large number of tropical lowland forest species that hunt by sitting and waiting for prey to move can probably be attributed to lack of wind, larger leaf size, larger biomass and higher recruitment rates of insects, more large nocturnal insects and more arboreal reptiles and amphibians. Many species of birds were limited to narrow vertical ranges in the forests, but the great increase in numbers of species in the tropics is only in small part accounted for by finer vertical subdivision of the forest. The greatest contribution is made by the addition of species with no temperate counterparts, suggesting that the greater range of resource types permanently above threshold values in tropical forests is the major cause of increased bird species diversity.
A Method for Determination of Infrared Emittance of Leaves
Authors: Idso S. B. , Jackson R. D. , Ehrler W. L. , Mitchell S. T.
Published: May 2006

A relatively simple method for determining the infrared emittances of leaves gives reproducible results that are in good agreement with two other methods currently used to determine infrared emittances of soils. Measurements on a wide variety of plants indicate that significant differences exist among the various species. Emittances determined by infrared thermometers of different spectral sensitivity are not uniquely related, thereby emphasizing the importance of the emittance measurement.
Ecosystem Trophic Complexity and Densities of the Willamette Mite, Eotetranychus Willamettei Ewing (Acarina: Tetranychidae)
Authors: Flaherty Donald L.
Published: May 2006

Metaseiulus occidentalis (Nesbitt), a predatory mite, is better able to regulate low densities of willamette mites, Eotetranychus willamettei Ewing, in more complex communities. Willamette mite populations fluctuate more widely in amplitude in simple communities or where monoculture is practiced. Weedy grasses associated with grapevines increase chances for reliable and stable spider mite population control because potentially capable predators are maintained well dispersed in the community by the presence of alternate prey.
The Light Threshold Contolling the Vertical Migration of Chaoborus Punctipennis in a Georgia Impoundment
Authors: Chaston I.
Published: May 2006

The light threshold controlling the migration of Chaoborus punctipennis from the sediments into the water column of a NE Georgia impoundment in the evening was found to be 2.44 lux in the winter. The threshold changed in the spring. This was the result of the seasonal change in light period affecting the animals. Laboratory experiments gave a mean threshold value of 7.44 lux, and showed that the animals were most stimulated by light between 500 and 600 m@m.
Distributional Patterns of Malayan Freshwater Fish
Authors: Johnson D. S.
Published: May 2006

A survey is made of the overall pattern of distribution of freshwater fish within Malaya and also of the associations found in the three important habitat types. The lack of east—west differentiation indicates that geographical barriers are not important in determining the distributional pattern. A marked north—south differentiation probably reflects edaphic and climatic factors. Analyses based on constancy are given for the fish associations of blackwaters, ordinary streams in tree country, and riceland habitats. Each has a distinctive fish association with a relatively small number of frequent species. Blackwater associations can be divided into subassociations corresponding to different types of blackwaters. Tree country and riceland associations show some regional differentiation. The tree country association is remarkably diversified and appears to be a true association, not a fortuitous assemblage of species with similar tolerances. Adverse factors such as low oxygen and low pH probably restrict the associations found in blackwaters and ricelands. These contain both specialist and generally tolerant species, the latter becoming more important the more extreme the habitat. The riceland fauna is depauperate as compared with neighboring countries, and there are possibly vacant ecological niches.
Vital Statistics of the Pacific Sardine (Sardinops Caerulea) and the Population Consequences
Authors: Murphy Garth I.
Published: May 2006

The population parameters of the Pacific sardine are estimated from growth, mortality, and fecundity data, together with the increase per generation Ro estimated by fitting the Ricker equation. Ro is 4.01, rm is .388 and generation, T, is 401 yr. The estimation of these parameters for a large natural population (equilibrium level about 2.4 x 106 tons) was possible because of a well—documented fisher. The environmentally induced, density independent variation in reproductive success is in the order of eight times. In theory, an organism can better tolerate widely variable reproductive success if there is repeated reproduction. Exploitation of the Pacific sardine reduced the number of reproductions, setting the stage for the population to collapse following two consecutive, unsuccessful spawnings. The Ricker function generates a population growth curve not unlike the logistic at low values of rm. Even if fishing were stopped, the recovery of the population would require more than a decade. It will likely be even slower, as a species of with similar ecological requirements (the northern anchovy) has increased by a factor of five following the decline of the sardine, undoubtedly preempting resources once available to the sardine.
Survival of Winter Annuals in the Northern Mojave Desert
Authors: Beatley Janice C.
Published: May 2006

Following early autumn germination in Mojave Desert winter annual populations (53 taxa) sampled on 13 plots (total sample size, 16.4 m2) in three drainage basins in southern Nevada, 1963—64, there was 38% survival to maturity (plot range 10—63%). Death occurred in early spring, at the time of shift from the slow vegetative growth of winter to the beginning of stem elongation. Despite no marked precipitation deficiencies during the 7— to 8—month growing season, mortality apparently resulted from inadequate soil moisture to meet the demands of seedlings at the point in the life cycle of a manyfold increase in plant volume. Mean percentage survival to maturity of seedlings (58 taxa), sampled on 62 plots (total sample size, 62 m2) in sevean drainage basins, following spring germination after rains of 3—5.5 inches in March—April 1965, was 60% (range by basin, 44—83%). Mortality in these populations, whose life cycles were completed in 6—10 weeks, could not be attributed to inadequate moisture levels. In most seasons, regardless of precipitation regimes, the majority of seedlings of desert annuals probably do not survive to maturity.
A Floristic Study of Forests and Bog Vegetation, Northwestern Minnesota
Authors: Janssen C. R.
Published: May 2006

Single vegetation plots in forests and bogs in the deciduous and coniferous—hardwood formation in northwestern Minnesota were studied according to the field methods of the Zurich—Montpellier system. Plots and species were arranged so that the greatest coincidence of occurrences was obtained. Species that show approximately similar amplitudes were united in sociological groups. Plant communities typified by these groups were placed in a hierarchy. The plant communities appear to intergrade but are not completely continuous. Definite concentrations of occurrences remain present in the ordination. Fourteen main types of vegetation are recognized. Their relations to the environment are discussed, and their relations to vegetation in other regions are indicated. Thirteen main types of vegetation (alliances) are recognized in the Itasca State Park region. Lowland vegetation has been divided into five alliances. In three of them the pathway of lake filling, starting in a eutrophic sedge mat and proceeding towards a mesotropic Picea mariana bog forest, is depicted. The two remaining lowland types represent eutrophic swamp forest of Fraxinus nigra and Ulmus americana on shallow peat or young alluvial soils. Upland forests havebeen divided into three "rich" deciduous types and five "poor" coniferous types.The rich types are represented by Tilia americana forests, Acer saccharum forests, Quercus rubra forests, and Populus tremuloides—Quercus sp. forests, allshowing representatives of the rich flora of the mesic Tilia—Acer forest. The coniferous forest types are represented by Popuus tremuloides—Quercus sp. forests and closely related Pinus resinosa—Pinus banksiana forests, Pinus banksiana forests on sandy outwash soils, and Abies balsamea forests in a young stage of development. Of these types the Pinus banksiana forest is floristically the best defined.
Habitat Relationships of Four Species of Mice in Vigo County, Indiana
Authors: Whitaker John O.
Published: May 2006

Information on the interrelationships of Mus musculus, Peromyscus leucopus, Peromyscus maniculatus bairid, and Microtus ochrogaster was accumulated during the study of 429 25x25 m randomly selected plots in Vigo County, Indiana. P. leucopus apparently inhibited Mus musculus when the two occurred together. This may be the factor that limits Mus to cultivated areas, since P. leucopus does not flourish there. Mus and P. m. bairdi reacted in different ways in different habitates. In grassy and weedy fields, and in winter wheat they occurred together about as often as would be expected by chance, but both species were more abundant when together than when alone. In soybeans, cultivated fields, corn, and corn stubble the two occurred together less often than would be expected by chance, and both were less abundant than when alone. Both ecological separation and competitive exclusion appeared to be acting. In wheat stubble P. m bairid occurred at higher rates and Mus at lower rates when the two were together, probably because Mus had to invade and compete with the already established P. m. bairdi. Mus and M. ochrogaster, and P. leucopus and M. ochrogaster occurred together in weedy and grassy fields about as often as expected, and the species concerned were unaffected or were more abundant when together than when alone, apparently indicating similar habitat requirements but different niches. P. m. bairdi and P. leucapus occurred together much less often than would be expected by chance, and average numbers per plot were lower than together, than when either occurred alone. Apparently both ecological and competitive exclusion were occurring. P. m. bairdi and M. ochrogaster were ecologically separated, with M. ochrogaster in better cover, and P. m. bairdi in poorer cover. When together they did not affect each other appreciably.
Responses of Grasses Seeded in an Artemisia Tridentata Habitat in Nevada
Authors: Robertson J. H. , Eckert Richard E. , Bleak A. T.
Published: May 2006

Seventeen grass species and two forbs, planted on a minimal Chestnut soil in northern Nevada, were grown under various degrees of competition in the native shrub, Artemisia tridentata, for 18 years. Grass species included seven native bunchgrasses, six exotic bunchgrasses, one native sodformer, and three exotic sodformers. Forbs gave no persistent stands. Performance of native bunchgrasses was poor. The surviving exotic bunchgrass, Agrophyron desertorum, A. elongatum, and Elymus junceus, rated fair, poor, and good, respectively, after 18 years. These three species produced well for 11 years, after which yields declined sharply. As a group the sodforming agropyrons, Agropyron intermedium, A. trichophorum, and A. smithii, performed better than did the bunchgrasses. The greatest production of Bromus tectorum was on plots that had failed after 5 years or where species were not well adapted to the site. Only scanty B. tectorum grew on plots of A. intermedium and A. trichophorum. When re—invasion by Artemisia tridentata occurred, greatest brush numbers were found on plots of species that failed early in the study and on plots where seeded species failed after 5 years. The sodforming agropyrons were most effective in preventing shrub re—invasion. The ability of Agrophyron intermedium, A. Smithii, and A. trichophorum, especially the latter, to establish readily, to suppress brush and annual grass invasion to produce superior yields, and to spred vegetatively under considerable precipitation fluctuation and brush competition indicates the adaptability, aggressiveness, and competitive strength of these sodformers.
Late‐Wisconsin Pollen and Seed Analysis from the Nebraska Sandhills
Authors: Watts W. A. , Wright H. E.
Published: May 2006

Between two lrge dunes near the northern edge of the grass—covered Nebraska Sandhills on the Rosebud Indian Reservation is an alluviated lowland containing more than 6 m of organic sand and silt. Pollen and seed analyses of the lowest 120 cm of sediment imply that a boreal forest with spruce grew around the site 12,600 c14 years ago and was succeeded abruptly by grassland, with perhaps more pine than exists today (as Pinus ponderosa) in the nearby Niobrara River Valley and the Pine Ridge escarpment of northwestern Nebraska. Pollen analyses of surface samples were used to determine the modern pollen rain at different distances from the modern pine forests of the western plains. The presence of spruce fossils at the Rosebud site, along with similar finds in northeastern South Dakota and southern Minnesota, implies a late—Wisconsin boreal forest over much of the present prairie region. The major disjunction of Picea glauca in the Black Hills, 200 km northwest of the site and 700 km from from the spruce forest of Manitoba, may thus be explained as a relic of a semi—continuous distribution during late—Wisconsin time.
A Radionuclide Tracer Study of Arthropod Food Chains in a Spartina Salt Marsh Ecosystem
Authors: Marples T. G.
Published: May 2006

The arthropods of the Spartina marsh obtain their energy either by grazing on the marsh grass or by eating the microbial—rich organic detritus that is largely derived from the dead Spartina. The two energy sources were labeled with P32 in separate quadrats and the subsequent buildup of radioactivity followed in the arthropod populations. Four species of insects were dominant grazing organisms (one Orthoptera, two Hemiptera and one Homoptera) while two families of Diptera, (Dolichopodidae and Ephydridae) included the important insects associated with the detritus complex. The spiders were the important carnivores and obtained their energy from both the detritus and grazing food chains.
Community Evolution and the Origin of Mammals
Authors: Olson Everett C.
Published: May 2006

The evolutionary course from primitive pelycosaurian reptiles through therapsids to mammals can be profitably studied in relationship to modifications of the structure of the communities in which these reptiles existed. For this purpose the community is defined in very board terms. Three types of communities are recognized upon the basis of the nature of the food chain. Each has an important tetrapod component. Early phases of the evolution that culminated in mammals took place in communities that were strongly tied to water by the structure of the food chain. The physiological bases of the development of mammals appear to have been related to this environmental restriction. In successive pulses, however, the pelycosaur—therapsid communities developed terrestrial reptilian herbivores and thereby broke with the water—based food chain. More strictly terrestrial communities developed concurrently, with the insects, which were a food source for the reptiles, as the principal herbivores. From this sort of community came the terrestrial lepidosaurian—archosaurian reptilian radiation. The terrestrial communities so developed came into competition. In this competition the therapsid lines were temporarily unsuccessful, leaving only small, but very mammal—like, representatives in the late Triassic. After a long period with relatively little adaptive radiation, these remnants provided the basis for the radiations of mammals that led to the great successes of the Cenozoic era.
Egg Cannibalism by Tribolium Larvae
Authors: Ho Frank K. , Dawson Peter S.
Published: May 2006

Synthetic laboratory strains of two species of flour beetles, Tribolium castaneum and T. confusum, were compared in terms of the voracity of larvae for eggs. Significant differences were observed between the species. Tribolium castaneum was much more cannibalistic with the greatest difference observed in 4— to 14—days—old larvae. Older active larvae of both species ate more eggs than did younger larvae. No significant differences were observed in the choice of eggs of both species when they were offered at the same time, but slightly more T. castaneum eggs were consumed than T. confusum eggs when larvae were supplied eggs of a single species. In one experiment a control series was maintained in the same manner as the experimental series, except that the larvae were not given eggs. Fecundity of adult T. castaneum emerging from these larvae was lower than in adults from the experimental series which had fed on eggs during the larval stage. No such difference was observed between experimental and control groups in T. confusum. It is suggested that differences in egg cannibalism by larvae of the two species of flour beetles may account in part for the superiority of T. castaneum in competition with T. confusum under the given conditions (29°C, to to 70% R. H.).
Spatial Relationships in Flocks of Sandhill Cranes (Grus Canadensis)
Authors: Miller Richard S. , Stephen W. J. D.
Published: May 2006

The Clark—Evans model of spatial distribution was applied to aerial photographs of flocks of Sandhill Cranes feeding in cultivated fields. Distance to nearest neighbor for a total of 1,326 individuals in 29 flocks varying in size from 3 to 252 birds had a mean value of 5.79 ± 0.16 ft and was remarkably uniform, regardless of flock size. Departure from random spacing was consistently in the direction of uniform spacing, although the degree of uniformity varied inversely with flock size. A modified model based on flocks occupying circular areas and composed of sub—groups, with a constant individual distance within groups and an additional space factor between groups, seems to provide a reasonable interpretation of dispersion in different—sized flocks of Sandhill Cranes. A conclusion drawn from the correspondence between the theoretical model and the data and observations is that large flocks of Sandhill Cranes are loosely organized assemblages of smaller groups which behave more as coordinated units and are based on a relationship of individual distances.
Studies on Water Relations in North American Termites. II. Water Loss and Cuticular Structures in Eastern Species of the Kalotermitidae (Isoptera)
Authors: Collins Margaret S. , Richards Glenn
Published: May 2006

The rates of water loss from individuals of various species, ages and castes of termites of the family Kalotermitidae have been determined both in the natural condition and after treatment of the individuals with either peanut oil or alumina dust. Special histological methods were used to reveal the cement layer of the cuticle. While the waterproofing barrier may be completely developed at the time of molting to the adult stage, it is so delicate that obtaining completely intact animals is difficult. Greater variability in rates of loss between younger individuals within a caste, and higher sensitivity to rate—increasing effects of peanut oil and alumina dust are reflections of this situation. In older individuals within an instar, the cement layer appears as a discrete heavy layer. This layer could be a significant factor in maintaining the integrity of the transpiration—retarding waxes. Clearly there is a strong positive correlation between resistance to evaporative water loss and the dryness of the natural habitats of the various species. These, in turn, are related to the waterproofing layers of the epicuticle.
Soil‐Plant Relationships in a Eucalyptus Forest on the South Coast of New South Wales
Authors: McColl J. G.
Published: May 2006

The chemical and physical soil characteristics of the Eucalyptus associations in Benandra State Forest are described. Changes in species associations occur over a gradient of increasing moisture and nutrient status of soils from ridge to gully sites. Concentrations of major nutrients in leaves and bark of dominant trees on these sites generally follow the soil gradients. In particular, leaf phosphorus and bark calcium are correlated with the corresponding soil nutrients. Soil calcium and magnesium are also correlated with leaf phosphorus, indicating a possible interaction between these soil nutrients and phosphorus uptake by the trees. Soil magnesium is similarly correlated with bark calcium. Aluminum is the major exchangeable cation in soils of the poorer ridge sites which are the most acid. It is hypothesized that soil aluminum competes with other nutrient cations such as calcium and magnesium for sites of absorption on plant roots. In addition to the effect of soil pH on phosphate solubility, competition between aluminum ions and other cations may inhibit the absorption and uptake of calcium and phosphorus, both of which are important to the growth and nutrition of the Eucalyptus species in the study area.
Photosynthesis in Fluctuating Light
Authors: McCree K. J. , Loomis R. S.
Published: May 2006

Experiments were conducted to test the assumption, always made in models of the productivities of higher plant communities, that photosynthetic rates measured in steady light can be used to predict the rates in fluctuating light. The photosynthetic rates of whole cucumber plants (Cucumis sativus) were measured in light which alternated between high and low levels, at irradiances and frequencies comparable with the fluctuations found in nature (16—220 w/m2 of photosynthetically active radiation, 1012—103 sec at each level). The mean photosynthetic rate in alternating light was always within a few percent of the mean of the two photosynthetic rates in steady light at the two irradiances which were alternated. In a practical test, daily totals of carbon dioxide assimilated in natural fluctuating light caused by clouds were within a few percent of those calculated from the irradiances and the steady—state photosynthetic rate. In both experiments, the plants acted as near—perfect integrators of photosynthate, not of light. The conclusion is that steady—state photosynthetic rates may safely be used to compute the rates in fluctuating light, over the range of light conditions likely to be found in nature, provided that photosynthetic rates, and not irradiances, are integrated.
Productivity of the Water Hyacinth Eichhornia Crassipes (Mart.) Solms
Authors: Bock Jane H.
Published: May 2006

The tropical water hyacinth, Eichhornia crassipes (Mart.) Solms, occurs in some of the sloughs and rivers of northern California's Central Valley, a possible northern limit for its weedy distribution. The growth rates and reproductive rates of these water hyacinths, at least for brief periods each year, were comparable to those of water hyacinths growing in the tropics. Their rapid reproduction and high productivity in the summer months enable the populations to be maintained from year to year in northern California despite a high death rate in winter.
Altitudinal Distribution of Brown Trout and Other Fishes in a Headwater Tributary of the South Platte River, Colorado
Authors: Vincent Robert E. , Miller William H.
Published: May 2006

Upstream distribution of brown trout (Salmo trutta) in the Little South Poudre River drainage stops between the elevations of 2,590 and 2,750 m in five tributaries. As no geomorphic barriers limit distribution, trout distribution may be related to water temperature. Brook trout (Salvelinus fontinalis) is present at higher altitudes in all headwaters. Maximum 5—day water temperature is approximately 13°C at the upper altitudinal distribution of brown trout. Distribution of other species is discussed briefly.
Habitat Specificity in Three Sympatric Species of Ameiva (Reptilia: Teiidae)
Authors: Hillman Peter E.
Published: May 2006

Three sympatric species of Ameiva in Costa Rica (A. quadrilineata, A. festiva, and A. leptophrys) were found in distinct habitats with respect to vegetation cover, a ground isolation, environmental temperatures, surface litter, and activity periods. Ameiva quadrilineata commonly forages in an area of open, low vegetation cover adjacent to bare soil. Its habitat is sunnier and warmer than those occupied by the other two Ameiva. A. festiva usually forages in the open edge of forests are lower where somewhat lower percentages of ground are exposed to direct sunlight and there are lower environmental temperatures than in the habitat of A. quadrilineata. Its peak of foraging activity is later in the morning than is that of A. leptophrys. Adult a. leptophrys forage even deeper into the forest than the other two species where even less of the ground surface is insolated, the ground substrate temperatures are lower, and there is a higher percentage of ground litter. However, this species basks in the same area in which A. festiva forages, but earlier in the morning. Newly hatched A. leptophrys are found in an ecological habitat distinct from that of the adults, but very similar to that of adult A. festiva. There appeared to be no differences in gut contents among the three species with respect to type of food items. However, A quadrilineata contained slightly smaller sized food items than did the other two species. Body temperatures while foraging were very similar in all three species, but were maintained under very different sunlight conditions and microclimatic temperatures.
Some Aspects of Species Diversity Models
Authors: Eberhardt L. L.
Published: May 2006

It is suggested that the sequence of frequency distributions including the Poisson, negative binomial, and logarithmic may serve as useful standards for intercomparing the many measures of diversity in use of proposed. MacArthur's "broken—stick" model is shown to fall essentially into this sequence.
Energetics and Activity Patterns of Short‐Tailed Shrews (Blarina) on Restricted Diets
Authors: Martinsen David L.
Published: May 2006

Several short—tailed shrews were maintained from December 1967 through March 1968 on mealworms in amounts equivalent to one—tenth of their body weight per day. Others lived during the same interval eating only cracked corn. Minimum resting metabolic rates of shrews on restricted diets averaged 2.18 cc )2/g per hr; much less than rates previously reported for this species. Oxygen uptake of shrews while engaged in other behavior patterns was (in cc/g per hr): exploring 4.56; feeding, 6.22; hyperactivity, 11.63. Blarina demonstrated a short, continual activity pattern, and were active for only 16% of each day. The two factors most fundamental to the success of the species in cold—temperate climates are 1) its proclivity to eat almost anything of energy value, and 2) an activity pattern in which the overwhelming majority of time is spent inactive, at low, resting metabolism.
Caloric Value of Wet Tropical Forest Vegetation
Authors: Golley Frank B.
Published: May 2006

Energy values of tropical forest vegetation collected in the Republic of Panama differed significantly depending upon the type of forest and the vegetation part sampled. The pattern of difference was complex, with maximum values varying with the plant part and the forest type. Mangrove generally had higher values than other tropical forests. These observations support the earlier conclusion that tropical vegetation has lower energy values than temperate or alpine vegetation.
Population Dynamics of Daphnia Pulex as Modified by Chronic Radiation Stress
Authors: Marshall J. S.
Published: May 2006

Twenty—five self—regulating populations of Daphnia pulex were exposed to different levels of external 60Co gamma radiation for 18.5 hr per day for 55 weeks. Dose rates ranged from 0 to 516 R/day. Although the population at the 3 highest dose rates became extinct, the remaining 22 populations established quasi—equilibrium densities which decreased with increasing dose rate. The maximum tolerable dose rate was 436 R/day. Average turnover rates increased with dose rate. An approximate inverse relationship between mean population size and mean turnover rate suggested that net production might be unaffected by the radiation. Estimates of yield to decomposers indicated that net production was, indeed, unaffected. Radiation stress became a limiting factor for population size and turnover rate at much lower dose rates than those needed to limit net production. Within the entire range of indefinitely tolerable dose rates, the population consequences of radiation stress stem almost entirely from effects on individual fertility and survival, whereas individual metabolism is apparently unaffected. Increased individual growth is an indirect effect, due to reduced fecundity at a given food supply per individual or increased food consumption at a given food supply per population.
The Light Composition of Solar and Sky Spectra Available to Plants
Authors: Robertson Geo. W.
Published: May 2006

Using a 5—band spectral light meter the spectral energy of light available to plants was measured under several different environmental conditions including bright sunshine, sky light, twilight, light from cloudy skies, and light within leaf canopies of varying densities. Increased haziness or decreased both the ultraviolet and the blue energy in sky light. A closed crop canopy transmitted a high proportion of far red energy.
Response of Three Grasses to Two Soils and a Water Table Depth Gradient
Authors: Mueller-Dombois D. , Sims H. P.
Published: May 2006

Three grasses–Calamagrostis canadensis, Andropogon gerardi, and Koeleria cristata–were grown for 13 months on two soil slopes in a greenhouse. One slope was composed of sand and the other loamy sand; the water table of each was controlled to create equal catenas with sites ranging from dry to wet. All three grasses were seeded uniformly over each tank. Competition was limited as each grass found its own niche above— and below—ground. Some interspecific competition resulted from shading by Koeleria, while the density of Calamagrostis was reduced by intraspecific competition on the better soil (loamy sand) and where the moisture level was most favorable. The density of Andropogon was greatest on the loamy sand and reached its maximum at a very moist site on both soils. Koeleria produced its maximum shoot weight at a greater depth to water table than either of the other two species. During the final month of the study watering was discontinued and a more natural pattern resulted as Calamagrostis died back to the moist sites while Koeleria was able to survive at drier levels. Roots of each species occupied soil stratum, with Calamagrostis having the least flexible root system and Koeleria exhibiting a very flexible root system which readily adjusted to decreasing moisture supply.
Successional Change in Northern Hardwoods Predicted by Birth and Death Simulation
Authors: Leak William B.
Published: May 2006

Two simulation models were used to predict species changes in three deciduous forest cover types in New England. A fixed—rate simulator, employing differences among species in birth/death rates, was used for stands approaching a steady—state condition. A density—related simulator, using birth and death rates related to both species and population size, was applied to stands in dynamic condition. Predicted and actual changes over a 25—year period were reasonably consistent.
Pinyon and Juniper Invasion in Black Sagebrush Communities in East‐Central Nevada
Authors: Blackburn Wilbert H. , Tueller Paul T.
Published: May 2006

As a means of studying inter— and intrazonal invasion in black sagebrush (Artemisia nova A. Nels) communities six maturity classes were established for pinyon (Pinus monophylla Torr. and Frem.) and juniper (Juniperus osteosperma (Torr.) Little) in east—central Nevada. Pinyon and juniper invade and increase in black sagebrush communities until the understory, except for a few hardy plants, is eliminated. Juniper invades first and tends to be eventually replaced by pinyon. Accelerated invasion by both species started about 1921 and is closely related to overgrazing, fire suppression, and climatic change.
Limitations in Radiotracer Determination of Consumer Trophic Positions
Authors: Shure Donald J.
Published: May 2006

Tropic transfer studies on wild radish (Raphanus raphanistrum) and ragweed (Ambrosia artemisiifolia) both indicated variations in the time of P32 uptake by herbivore species. This variation resulted from rapid temporal changes in plant organ availability with subsequent changes in consumer feeding patterns. Specific trophic positions of major herbivores were determined only by correlating phenological changes in plant organ availability with the uptake curves, abundances and feeding adaptations of consumer species. It was concluded that P32 uptake curves cannot be used alone in determining trophic positions unless a long—term stability in producer—consumer relationships is demonstrated.
Carbon Dioxide Exchange in Saguaro Seedlings
Authors: Despain D. G. , Bliss L. C. , Boyer J. S.
Published: May 2006

Two—year—old saguaro seedlings possess crassipes acid metabolism (CAM). Carbon dioxide uptake occurs at night with release during the light period. With a rise in temperature dark CO2 uptake is significantly reduced. The combination of water—storage tissue and CAM may contribute to the success of these large succulents in the Sonoran Desert.
String Bog in Southern Wisconsin
Authors: Grittinger Thomas F.
Published: May 2006

String bog or "Strangmoor" patterns have been identified in Cedarburg Bog, 25 miles north of Milwaukee, Wisconsin. This is about 200 miles south of the southernmost string bog location previously reported near Seney, Michigan. The string bog consists of slightly elevated ridges and islands with cedar (Thuja occidentalis), tamarack (Larix laricina), bog birch (Betula pumila var. glandulifera), leatherleaf (Chamaedaphne calyculata var. angustifolia), and other woody growth alternating with flat, wet sedge mat areas. This string bog, in common with others in North America and Eurasia, is found on a slightly sloping surface; the alternating ridges and flats are at right angles to the direction of slope or the direction of water flow. Presumably this orientation is indicative of the important role of water movement in pattern formation.