bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Measurement of Niche Breadth and Overlap
Authors: Colwell Robert K. , Futuyma Douglas J.
Published: May 2006

Measures of niche breadth and overlap that depend on the distribution of individual among resource states (ecological categories) should be independent of the relative abundance of the species and of the number of resource states considered. Such measures should also take into account the degree of distinctness of the resource states from the point of view of the organisms concerned. An ecoassay of the distinctness of resource states may well be easier and more meaningful than measurements of physical and chemical factors. We propose that the species composition of communities utilizing different resource states may be used to develop weighting factors with which each state may be weighted in proportion to its degree of distinctness. The weighting factors are used in the development of indices of niche breadth and overlap that correct for variation in the range and distinctness of resource states and that suffer less from human subjectivity than do the measures used to date. The use of such indices and the relationship of niche overlap to competition are discussed.
The Nonconcept of Species Diversity: A Critique and Alternative Parameters
Authors: Hurlbert Stuart H.
Published: May 2006

The recent literature on species diversity contains many semantic, conceptual, and technical problems. It is suggested that, as a result of these problems, species diversity has become a meaningless concept, that the term be abandoned, and that ecologists take a more critical approach to species—number relations and rely less on information theoretic and other analogies. As multispecific collections of organisms possess numerous statistical properties which conform to the conventional criteria for diversity indices, such collections are not intrinsically arrangeable in linear order along some diversity scale. Several such properties or "species composition parameters" having straightforward biological interpretations are presented as alternatives to the diversity approach. The two most basic of these are simply ▵1=[n/n—1][1—Σi(N_i/_N)2] =the proportion of potential interindividual encounters which is interspecific (as opposed to intraspecific), assuming every individual in the collection can encounter all other individuals, E(Sn) = Σi [1—(N—Nin)/(Nn)] =the expected number of species in a sample of n individuals selected at random from a collection containing N individuals, S species, and Ni individuals in the ith species.
Selective Egg Cannibalism in Sinella Curviseta (Collembola: Entomobryidae)
Authors: Waldorf Elizabeth
Published: May 2006

Sinella curviseta eggs less than 24 hours of age are smooth; older developing eggs are rough. An experiment was concluded to analyze egg cannibalism in unisexual populations exposed to eggs on both types. This experiment demonstrated that egg consumption (i) averaged .03 eggs per animal per hour, (ii) occurs at a significantly higher rate in females than in males, and (iii) is almost completely (99%) confined to smooth eggs. As smooth eggs include very young eggs and faulty eggs of any age, smooth eggs have a lower probability of reproductive success than rough ones. Animals encounter in a clutch first smooth eggs with less chance of hatching; later, smooth eggs with a still probability of success (as more developing ones have become rough); and finally, during the final 72% of the period of exposure to a clutch, smooth eggs whose probability of hatching is effectively zero. It is efficient resource utilization to ingest these eggs.
Energy Levels of Water in a Community of Plants as Influenced by Soil Moisture
Authors: Cary J. W.
Published: May 2006

Free energy levels of plant water were measured during July and August in two communities of annual plants. One set of plants was irrigated, while the other grew on a silt loam soil that became increasingly drier. The different species of plants had widely varying levels of water potential on both the moist and dry soils. The more drought—tolerant plants on the dry soil had the lowest afternoon plant water potentials even though they had the most vigorous root systems (lamb's quarter, kochia, sugar beets, and sunflower). Some of the more drought—tolerant plants also had low water free energies when growing on moist soil. Most of the plants growing in the dry sea gained enough water during the night to raise their water potentials above that of the soil surrounding the bulk of their roots.
Woody Vegetation in the Black Belt Prairie of Montgomery County, Alabama, in 1845‐46
Authors: Rankin H. Taylor , Davis D. E.
Published: May 2006

The presence of prairies in Alabama's Black Belt as reported by early explorers is further substantiated here by using the field notes and plats of the original land survey of Montgomery County (1845—46). One—third of the approximately 200,000 acres of Black Belt in the county was depicted as prairie on the field plats. A strong correlation was found between rates of low tree density (10 trees or less per acre) as given in the field notes and areas shown as prairies on the plants (one tree per acre equals 2.47 per hectare). Areas of low tree density and prairies, when located on recent soil maps (1957), occurred primarily on upland alkaline soils. Apparently these upland alkaline sites composed the true prairie and were those described as savannahs," plains native fields, and prairies by the early explorers. High tree densities (120 trees or more per acre) were associated primarily with areas outside prairies and were mostly on acid soils. In the field notes examined, oaks, pine, hickory, gum, and ash were recorded as the dominant tree species.
Unsuccessful Breeding by Desert Toads (Bufo Punctatus) at the Limit of Their Ecological Tolerance
Authors: Tevis Lloyd
Published: May 2006

Survival and reproduction of a linear population of Bufo punctatus was studied during 1964 in an often waterless, mile—long section of a canyon of the Colorado Desert of California. Reproduction had been unsuccessful in earlier years of record because of little or no springflow and infrequency of summer flashfloods. In 1964, springflow began on March 23 and retreated rapidly in early May. There was one summer flashflood. Toads did not emerge from underground winter retreats until evening air temperature was around 18°C and did not breed until the weather was some 6 degrees warmer. The relatively few females who oviposited, mainly during April 9 to 6, produced and estimated 34,000 eggs. The lowest downcanyon site of oviposition in the spring was 5,370 ft above the lowest downcanyon site in 1962. Home range up and down the canyon during the breeding season was about 600 ft at the most for males and 1,500 ft more for females. Some trilling males went underground when the stream dried at their sites; others migrated upcreek as much as 2,000 ft to new trilling sites beside water. Many females did not migrate, while others showed a tendency to wander great distances (2,700 ft maximum record) towards or away from water. When the stream dried completely all toads disappeared but emerged after the one flashflood of summer in order to hydrate. Tracks then occurred 1,300 ft farther downcreek than any individual had been seen in spring. Very limited breeding was accomplished by individuals who were different from the spring breeders. Rate of larval development in spring (approximately 2 months to metamorphosis) was retarded by coolness of the water. There were four different stages of larval behavior: 1) egg—site aggregations, when tadpoles massed at sites of oviposition; 2) deepwater aggregations, when the mass moved to deepest available water; 3) feeding dispersal when tadpoles dispersed in search of food; and 4) thermal aggregations, when they congregated in warmest water at margins of pools by day and at bottoms by night. Nearly all tadpoles were killed by desiccation both in spring and summer. Since some toe—marked adults were captured after 4 years, longevity may be a reason for survival of populations in severe habitats where successful reproduction is rare.
Relationship Between the Blue‐Green Alga Trichodesmium Thiebautii and the Copepod Macrosetella Gracilis in the Plankton off Northeastern South America
Authors: Calef George W. , Grice George D.
Published: May 2006

A strong correlation between the abundance of the blue—green alga Trichodesmium thiebautii and the abundance of the harpacticoid copepod Macrosetella gracilis is reported at 34 stations off the northeastern coast of South America. This field observation supports previous laboratory observations that filaments of Trichodesmium are required as a substratum for the development of M. gracilis.
Ecologic Sampler for Soft Sediments
Authors: Prokopovich Nikola P.
Published: May 2006

The sampler consists of an open, rectangular box with a movable, reinforced plastic bottom. It is lowered and advanced into the sediments in an opened condition by pushing with the supporting rods or by its own weight if lowered on a cable. The plastic bottom with a sharp cutting edge is then released to undercut and hold the uppermost 3 to 6 in, of sediments inside the sampler for retrieval. The device was successfully tested in the fall of 1965 and proved to be efficient and easy to operate.
Estimation on Cubic Volume of Shrubs (Corylus Spp.)
Authors: Buckman Robert E.
Published: May 2006

A volume equation was developed to determine the physical mass, growth responses, and wood density of hazel (Corylus spp.) for use in prescribed burning research. The equation should be useful for productivity and fuel studies in shrubs with similar growth habits and form.
Old‐Field Sucession on Hastings Reservation, California
Authors: White Keith L.
Published: May 2006

The groundlayer of an abandoned field was found similar to that in nearby foothill woodland, presumably the original vegetation of the field. By 1965, 27 years after abandonment, the annual species in the field were characteristic of ungrazed ranges. Thirteen perennial herb species were found in the field by 1944, 6 years after abandonment, and 26 were present by 1966. Although some of the perennial herbs were abundant, many required intensive searching to detect their presence. Woody plants were present but not abundant by 1966.
The Topograph, An Instrument for Measuring Microtopography
Authors: Boorman L. A. , Woodell S. R. J.
Published: May 2006

Detecting very small variations in topography is difficult. An apparatus is described, using multiple pins for sensing, which permits measurements of small variations in topography quickly and with minimum effort.
Catastrophic Drift of Insects in a Woodland Stream
Authors: Anderson N. H. , Lehmkuhl D. M.
Published: May 2006

The effect of early fall rains on the downstream drift or displacement of insects was studied for two seasons by collecting the entire streamflow at one point through a drift net. Drift rate increased within 24 hr after the start of each rainy period, with the increase approximately proportional to the increase in stream flow. Freshets due to less than 1 in. (2.5 cm) of rain caused a fourfold increase in numbers and fivefold to eightfold increase in biomass. Major components of the drift were Ephemeroptera, Plecoptera, Diptera and terrestrial insects. Plecoptera and Ephemeroptera retained the day—night periodicity of behavioral drift during freshets, but drift of Chironomidae (Diptera) was attributed to catastrophic and constant drift. Mean weight per individual of several taxa was greater at night than day, in freshet than nonfreshet periods, and in drift compared with benthos samples. Though catastrophic drift due to fall freshets displaced large numbers of individuals, the standing crop of the benthos increased during the fall because of hatching. The drift may be beneficial in dispersing aggregations of young larvae. Removal of allochthonous food by increased water flow could be more detrimental to benthos populations than the direct mortality caused by catastrophic drift.
Control of Community Structure by Mosquito Larvae
Authors: Maguire Bassett , Belk Denton , Wells Glenda
Published: May 2006

Observations of communities living in water held in the bracts of flowers of the wild banana, Heliconia bihai, in Puerto Rico show mosquito larvae to have very great influence in determination of community structure. These larvae quickly eliminate all or nearly all Protozoa and micro—Metazoa (other than arthropods) which, in the absence of mosquito larvae, are abundant in Heliconia—held water. Laboratory experiments support this conclusion.
Self Regulation of Adult Numbers by Cannibalism in Two Laboratory Strains of Flour Beetles (Tribolium Castaneum)
Authors: Lloyd Monte
Published: May 2006

Two strains of flour beetles, though different in reproductive potential, maintain similar equilibrium densities when their populations are confined. A simple mathematical model shows that this result is to be expected in a population system dominated by cannibalism, provided the rates of cannibalism do not differ and the predatory adults do not become satiated.
Acetate in Fresh Water: Natural Substrate Concentrations Determined by Dilution Bioassay
Authors: Allen Harold L.
Published: May 2006

A dilution bioassay has been employed to determine concentrations of acetate in fresh water. The response of the bioassay is presumably due to heterotrophy of bacteria and is analyzed by Michaelis—Menten enzyme kinetics. Concentrations of acetate were found to be within the range 0—6 mg liter—1 in five bioassay measurements. The bioassay may prove applicable in determining concentrations of other organic solutes in lake water.
Self‐Absorption of C(14) Radiation in Freshwater Ostracods
Authors: McGregor Don L. , Wetzel Robert G.
Published: May 2006

Self—absorption coefficients of C14 radiation, determined for six species of freshwater ostracods, varied with differences in size, sex, instar, reproductive state, and among species. Self—absorption is generally higher in ostracods than are comparable values for other microcrustacea and some aquatic insects, obligochaetes, and fish larvae. Where C14 is employed as a tracer in precise investigations on feeding and metabolism, variations in self—absorption of radiation must be considered in detail.
The Variation of Carbon Dioxide Under the Snow in the Arctic
Authors: Kelley J. J. , Weaver D. F. , Smith B. P.
Published: May 2006

Atmospheric carbon dioxide was monitored continously by infrared analysis near Barrow, Alaska, from September, 1965 to July, 1966. The purpose of these measures was to determine the fluctuations of carbon dioxide under the snow cover. Average daily surface values of carbon dioxide as measured at the tundra surface increased a few days after the first snowfall. High and variable values occurred until early December and then decreased to lower, relatively stable concentrations that persisted to early May. At that time, the carbon dioxide concentrations under the snow increased until the snow left the tundra in late June. Tundra surface temperature and wind speed four meters above the ground near the study area were monitored simultaneously with the carbon dioxide measurements. There was a general positive correlation between surface temperature and carbon dioxide, and an inverse relationship with wind speed.
Relationships of Physiography and Microclimate to Fallout Deposition
Authors: Whicker F. Ward , Loveless Charles M.
Published: May 2006

Measurements of fallout concentrations in various media were made on four physiographically contrasting sites within a 2—ha mountainous area. Air concentrations of radioactivity were lowest on the north and west slopes as a possible result of air filtration by foliage and lower dust concentrations. Fallout deposition on vertical gummed surfaces was highest at the south and west sites in apparent relation to higher mean wind velocities. Fallout deposition via rainfall was related to amounts of precipitation, but the monthly variations in both measurements were much higher than site variations. Fallout accumulation in soil was lowest on the timbered north slope. Significant differences in plant concentrations of radioactivity were found among species and sampling dates, but no differences were apparent among the four sites.
Pigment Structure of Some Arctic Tundra Communities
Authors: Tieszen L. L. , Johnson P. L.
Published: May 2006

An analysis of four tundra communities in northern Alaska indicates that the chlorophyll contents (0.32—0.77 g/m2) of these communities are similar to those reported from alpine tundra and from temperate grasslands of similar height. There was a high correlation within each community between chlorophyll content (g/m2) and the dry weight (g/m2) of the plant material. In different communities, however, chlorophyll on a dry weight basis varied from a low of 1.5mg/g in Dry Sedge tundra to a high of 8.8 mg/g in Wet Sedge tundra. The communnities with the lowest amounts of total chlorophyll had the greatest amounts of chlorophyll in the moss and ericaceous components of the vegetation. For example, in Dry Sedge tundra about one—third of the chlorophyll was in the ericaceous component of the vegetation and about one—third was in the moss layer. Wet Sedge tundra, which possessed 0.77 g/m2, included no ericaceous material and only about 2% of the chlorophyll was in the moss layer. The ratios of chlorophyll a:b generally ranged between 1.5 and 2.5 and were lowest in the mosses and usually highest in the non—ericaceous components. The a:b and carotenoid ratios were very similar within each component of the four communities investigated, and the low a:b ratios are interpreted as an adaptation to lower light intensity in the Arctic. The evidence emphasized the importance of a bryophyte synusium in some Arctic communities.
Bioenergetics of Captive Willow Ptarmigan under Natural Conditions
Authors: West George C.
Published: May 2006

Adult willow ptarmigan (Lagopus lagopus) were captured from the Brooks Range of northern Alaska and maintained in captivity out of doors under natural conditions of temperature and photoperiod similar to those prevailing in the southern part of the Brooks Range. Metabolized energy, molt, egg laying, body weight, and gross activity were recorded throughout the year. Maintenance energy did not differ between males and females except during egg laying. The amount of energy required in winter for thermoregulation was only slightly greater than that required by molting birds in summer. Egg—laying females had a higher energy requirement than non—laying but molting females and males. The gross activity of the captive ptarmigan began at the onset of civil twilight each day throughout the year. Therefore, in summer, activity continued for 24 hr. There were generally 2 activity peaks; the major peak occurred in the morning in spring and early summer but in the late afternoon in fall and winter. The total daily activity remained constant throughout the year except during May when males were undergoing courtship and territorial activities. Molt proceeded in the captives in the same sequence as in the wild population, but was slightly prolonged. All of the energy—demanding activities, such as seasonal change in weight, molt, egg laying, themoregulation, and gross activity, occur sequentially with only slight overlaps. Thus the total energy requirement is practically uniform throughout the year in captives. Determination of metabolic rates from crop fill and caloric values of natural diets as predicted from field collections closely approximate the laboratory determined rates.
Growth Rates of the Sea Urchin Strongylocentrotus Purpuratus Related to Food Availability and Spine Abrasion
Authors: Ebert Thomas A.
Published: May 2006

A population of the purple sea urchin Strongylocentrotus purpuratus Stimpson was studied at Sunset Bay, Oregon. Three sub—populations had different size—frequency distributions. Such differences in size resulted from differences in growth rate and ultimate size. Two environmental components were examined as possibly causing the different rates of growth: a component of "weather" which broke spines, and food availability and consumption. These two components are important in determining growth rate and ultimate size of these animals.
The Relationship between Species Diversity and Stability: An Experimental Approach with Protozoa and Bacteria
Authors: Hairston N. G. , Allan J. D. , Colwell R. K. , Futuyma D. J. , Howell J. , Lubin M. D. , Mathias J. , Vandermeer J. H.
Published: May 2006

Small experimental communities of bacteria and Protozoa were designed to test the widely held hypothesis that higher species diversity brings about greater stability. Three species of bacteria, three species of Paramecium and two species of protozoan predators, Didinium and Woodruffia, were used. The communities were maintained by regular additions of the appropriate combinations of species of bacteria. Stability was measured as persistence of all species and as a tendency to maintain evenness of the species abundance distribution. The measures were in essential agreement. Stability at the Paramecium trophic level was increased by increasing diversity at the bacterium level, but three species of Paramecium were less stable than two. An important finding was that one pair of Paramecium species consistently showed greater stability without the third species than with it. This finding indicates that there were significant second—order effects, with two species having an interaction that was detrimental to the third species. We conclude that much more experimental and observational work is necessary before the nature of any functional relationship between diversity and stability can be claimed with confidence.
An Ecological Life History of Tall Bluebell (Mertensia Arizonica var. Leonardi) in Utah
Authors: Matthews Verl B. , Conrad Paul W.
Published: May 2006

Tall bluebell (Mertensia arizonica Greene var. leonardi (Rydb.) Johnston) is a tall perennial forb that is distributed in the aspen and subalpine communities throughout the central chain of mountains in Utah. Stems emerge each year from dormant buds on a fleshy caudex. Stem elongation starts with snowmelt (late May to early June) and stops 8 weeks later. Rate of elongation is most rapid (up to 1.5 inches per day) midway in the growing period, and growth curves have a characteristic sigmoid shape. First flowering starts midway in the period of stem elongation and stops 2 weeks after stem elongation has ended. Seeds fall from plants 18—25 days after flowers are pollinated by insects. Seedlings appear the following June, at densities of 0.1—2.5/ft2, but nearly all seedlings die each year when surface soils dry out at midsummer. Surviving seedlings require a growing period of 2 or 3 years before flowering the first time. Once established, plants develop roots to a depth of 7 ft. Tall bluebell competes successfully with other species and may constitute over two thirds of the total ground cover. It produces up to 3,000 pounds (air—dry weight) of forage per acre. Sheep utilize up to 35% (July) and cattle up to 46% (July) of the herbage yield.
Ecological Importance of Snowbrush Ceanothus Velutinus in the Oregon Cascades
Authors: Zavitkovski J. , Newton M.
Published: May 2006

Twelve stands of snowbrush were selected for a biomass study to estimate nitrogen fixation under field conditions west of the summit of the Oregon Cascades. Total nitrogen in the upper 2 ft of soil was higher under snowbrush than in the open, but the difference may have been caused by loss of nitrogen from open areas rather than by nitrogen fixation. Total nitrogen in the upper 15 cm of soil under snowbrush did not differ from that found under nonfixing shrub species. Various shrub species may increase the total soil nitrogen under their canopies, however, if only by accumulation from sites that lack vegetation. More nitrogen may be tied up in the biomass of mature snowbrush stands than in stands of other shrubs. The difference could be explained by nitrogen fixation, which may range from zero to about 20 kg/ha per year under conditions of this study. Nodulated snowbrush seedlings produced 2.5 times the dry weight that non—nodulated seedlings produced in a nitrogen deficient soil. Sixty—one per cent of the nitrogen in nodulated greenhouse seedlings was fixed. Such fixation rates may be reached on infertile soils in the field, but they seem unlikely on soils of medium or better fertility. This point seems to be substantiated by delay in nodulation of snowbrush in soils with increased levels of organic matter. Bioassay tests using Douglas fir seeds and hemlock seedlings showed that snowbrush did not add to the soil any significant amount of nitrogen by nitrogen fixation. The species contributes to the formation of a new organic layer, however, through large amounts of nitrogen—rich litter.
Rooting Patterns of Forest Understory Species as Determined by Radioiodine Absorption
Authors: Nimlos Thomas J. , Van Meter Wayne P. , Daniels Lewis A.
Published: May 2006

The rooting patterns of understory plants were determined with minimal disturbance of the site by injecting radioiodine into the soil and the beta and gamma activity of the aboveground tissue measured with a Geiger—Mueller detector. Injections were made to 72 inches in clay, stone—free soils. Modifications of the procedure are required for injections to depths greater than 36 inches in stony soils. The procedure was applied to two sites of different moisture regimes. Many of the species studied rooted to 72 inches though the amount of aboveground tissue was only a few grams. Rooting on dry sites was deeper than at the more mesic site.
Effects of Light‐Dark Reversal on the Activity Cycle of Sigmodon Hispidus
Authors: Stevenson Michael , Deatherage Gary , LaVaque T. J.
Published: May 2006

The effects of light—dark reversal on activity cycles were investigated in the cotton rat, Sigmodon hispidus. Results supported previous evidence that the cotton rat is primarily nocturnal. However, after light—dark reversal, the shift in activity into the new dark period occurred more rapidly than the 8—day shift earlier reported by Calhoun (1945). Most of the rats in fact shifted their cycles within 24 to 48 hr.
A Limnological Study of a Mangrove Lagoon in the Galapagos
Authors: Howmiller Richard , Weiner Arthur
Published: May 2006

In a mangrove lagoon on Isabela Islands, Galapagos, there was a pronounced Schlieren effect about 0.5 m from the water surface. The lagoon was strongly stratified with regard to salinity and chlorophyll concentration. The low salinity surface water supported considerable production when incubated for 2 days, indicating that rapid loss of surface water to the sea probably accounted for the low standing crop of chlorophyll.
Intraspecific Variation in Osmotic Abilities of Cyprinodon Variegatus Lacepede from the Texas Coast
Authors: Martin F. Douglas
Published: May 2006

Three populations of Cyprinodon variegatus Lacepede were compared as to their abilities to withstand sudden osmotic shocks. A population from an area having large daily and seasonal changes in salinity showed a much greater tolerance than two populations from more stable environments. This difference in ability seems to be largely due to factors experience during ontogeny and rearing of the individuals tested.
Some Indices of Diversity
Authors: Dickman Mike
Published: May 2006

An index of diversity (H) based on the Shannon—Weaver formula, H = — Σn1Pi log Pi, fails to reflect significant changes in a community's structure because it is only sensitive to changes in relative abundance of a few of the trophic levels of a community. Over two thirds of the species encountered in a typical plankton sample had no significant effect on the index of diversity (H), calculated for that sample. To overcome this, the Shannon—Weaver formula was twice altered by redefining Pi in order to give a new index of community diversity which was sensitive to changes in community structure. Pi defined in terms of relative biomass (Hb) failed to improve the index substantially and Pi was then successfully defined in terms of relative productivity (Hp). An index of community diversity sensitive to changes in relative abundance of all the trophic levels, such as the index Hp, appears to be a necessary prerequisite to comparative community studies.
Microsite Effects on Oleoresin Exudation Pressure of Large Loblolly Pines
Authors: Lorio Peter L. , Hodges John D.
Published: May 2006

Daily average oleoresin exudation pressure (OEP) of 40—year—old loblolly pines was not significantly reduced until severe soil and atmospheric moisture stress occurred from mid—September to mid—October. Under these conditions OEP was reduced more in trees on flat, usually wet sites than in trees on low (0.3—0.6 m) mounds. This response is attributed to a deficient fine root system on flat sites.
Stable Manganese and Fallout Radiomanganese in Animals from Irrigated Ecosystems of the Po Valley
Authors: Cavalloro R. , Merlini Margaret
Published: May 2006

Stable manganese and radioactive manganese (Mn54 from fallout) were determined in samples of snakes, fishes, frogs, tadpoles, insects, worms, and molluscs from five sites in flooded rice fields and/or irrigated meadows of the Po Valley, Italy for a period of 1 year. Animals in the second trophic level generally contained more nuclides than the other organisms. High amounts of both stable and radiomanganese were noted for tadpoles, insects, and molluscs, with large variations in the quantities of nuclides based on the site of collection. Stable and radiomanganese concentrations in frogs and fishes were less and varied little from site to site. Fishes showed a decrease in the amount of the nuclides with a change of season. Tadpoles had consistently higher amounts of both stable and radiomanganese than the frogs, and there was a sharp decrease in nuclide concentration with the onset of metamorphosis. There was a reduction in concentration of both nuclides going through the direct three—step food chain from insects to frogs to the water snake. The various factors involved in stable and radiomanganese accumulation by aquatic organisms are discussed.
Transient Competitive Displacement in Natural Populations of Wirligig Beetles
Authors: Istock Conrad
Published: May 2006

A transient competitive displacement of Dineutes nigrior by D. horni was observed in a northern Michigan pond, and the uniform rate of displacement during one larval generation was estimated. The estimate agreed well with rates obtained in laboratory experiments with the same species. It would be difficult to account for the displacement without assuming competition. These species probably came into competition in Michigan as their ranges extended northward after the last glacial recession. The rate of displacement per generation measured here for Dineutes is larger than estimates from data for Aphytis presented by DeBach and Sundby (1963). Despite lower rates of local displacement there have been very rapid geographical displacements among Aphytis species, presumably because of the simplicity and regularity of the citrus grove communities where these species have been introduced. Competitive displacement and competitive coexistence are simply the results of high and low rates of displacement. However, competitive displacement leads to species sorting in the development of communities, whereas competitive coexistence may contribute to community stability and, if prolonged, leads to finely diversifying evolution.
Native Bunchgrass (Stipa Pulchra) on Hastings Reservation, California
Authors: White Keith L.
Published: May 2006

Species composition, cover, and standing crop were sampled in 13 small patches of the native bunchgrass Stipa pulchra on an area protected from grazing for 27 years. The common species present were representatives of lightly grazed annual grassland. Cover of Stipa, as basal area intercept, averaged 11%. Standing crop of all species averaged 98 g/m2, with Stipa comprising 37% of the total. Comparison of the 13 protected stands with four grazed stands showed differences in species composition, but basal area intercept and standing crop of Stipa were not significantly different. An ordination of all 17 stands using species frequency in quadrats showed a pattern consistently related to percentage slope.
Influence of Fire on South Texas Chaparral Communities
Authors: Box Thadis W. , Powell Jeff , Drawe D. Lynn
Published: May 2006

Experimental fall burning of South Texas chaparral communities significantly reduced canopy of all brush species in untreated areas and in areas previously treated by roller chopping, shredding, and scalping. There was a highly significant (P < .01) reduction in frequency of occurrence of lotebush (Condalia obtusifolia (Hook.) Weberb.), lycium (Lycium berlandieri Dunal.), and creeping mesquite (Prosopis reptans Benth. var. cinerascens (Gray) Burkart). Frequencies of occurrence of brasil (Condalia obovata Hook.) and Mexican persimmon (Diospyros texana Scheele) were significantly reduced (P < .05). There was no sgnificant difference in total amount of grass on burned and unburned areas 1 year following the fire. Filly panic (Panicum filipes Scribn.), buffalograss (Buchloe dactyloides (Nutt.) Engelm.), and meadow dropseed (Sporobolus asper var. hookeri (Trin.) Vasey) were more abundant on burned than on unburned areas. Plains bristlegrass (Setaria leucopila Scribn. and Merr.) was less abundant on burned areas than on unburned areas. Forb production was significantly (P <. 01) less on burned than on unburned areas, mostly because of reduction in western ragweed (Ambrosia psilostachya DC.) and Texas broomweed (Xanthocephlum texanum (DC.) Shinners). Fire could have been responsible for the creation of the brush mottes described by early explorers. The study substantiates the theory that fire suppressed brush on south Texas grasslands.
Niche Specificity of Neohaustorius Schmitzi and Haustorius SP. (Crustacea: Amphipoda) in North Carolina
Authors: Croker Robert A.
Published: May 2006

Neohaustorius schmitzi and the larger Haustorius sp. coexist in the upper intertidal zone of Georgia and North Carolina sand beaches. The kinds and sizes of foods ingested and the morphology, setation, and size ratios of maxillae were examined to determine the contribution of these factors to the niche specificity of these sympatric amphipods in North Carolina. The morphology and setation of the maxillae of both species were quite similar, although maxillae lengths of Haustorius sp. were about x2.3 the size of maxillae of N. schmitzi. Body length differences were about 25% less. Both species ingested materials considerably larger than the internal dimensions of the filter apparatus, although Haustorius sp. ingested interstitial invertebrates and larger plant remains that N. schmitzi did not. Detritus made up much of the volume of the gut contents of both species. Laboratory experiments showed that both species fed for short periods, but at frequent intervals, and produced about 1 fecal pellet/animal/hr in unfiltered sea water. Detrital masses with included microorganisms were identified in sea water, gut contents, and fecal pellets by white— and fluorescent light microscopy. Niche specificity is maintained primarily by a size difference between the species, and this is reflected in the size of the foods despite consierable overlap in the types of foods utilized.
Supercooling of the Saguaro Species Drosophila Nigrospiracula in the Sonoran Desert
Authors: Lowe Charles H. , Heed William B. , Halpern E. Annette
Published: May 2006

Winter—active February adults (vicinity Tuscon, Arizona) were observed to be supercooled during freezing nights in their desert habitat, with 24—hr minimum extremes reaching —5.1°C, and to become active (flying) a few minutes after the warming following sunrise. The LD50 for experimental supercooling of the population sampled was —7.73°C, the LD100 between —9° and —10°C, and the LD0 between —5° and —6°C. The ability to survive winter nocturnal temperature extremes in the supercooled state makes it possible for the species to be surface active and breeding throughout the winter over the geographical distribution of its primary host plant, the saguaro (Cereus giganteus), in Arizona and Sonora, Mexico.
PULL‐UP TRAP: A Quantitiative Device for Sampling Shallow‐Water Animals
Authors: Higer Aaron L. , Kolipinski Milton C.
Published: May 2006

A trap was designed for providing quantitative samples of freeswimming animals in marshes and shallow ponds. The device consists of netting tied to an aluminum frame with attachments for rapidly raising the net and entrapped organisms out of the water. Collections from a series of pull—up traps, operated monthly in Everglades National Park, provide an index of fluctuations in aquatic animal populations.
A Technique for Fitting Nonlinear Models to Biological Data
Authors: Glass Norman R.
Published: May 2006

A technique for determining best parameter values for nonlinear mathematical models by an iterative least—squares method is presented. The process is given in detail to enable nonmathematicians to implement it successfully. The technique is based upon a Taylor series expansion and involves solving for successive corrections to trial parameter values until the best possible parameter values are found. A table is given showing for combinations of scatter in the data and error in estimating initial or trial parameter values the number of iterations required for convergence to best parameter values.
Experimental Catastrophic Selection and Tolerances to Low Oxygen Concentration in Native Arizona Freshwater Fishes
Authors: Lowe C. H. , Hinds D. H. , Halpern E. A.
Published: May 2006

Open— and closed—system experimental designs were used to test comparative tolerance, survival, and potential natural selection in four species subjected to low dissolved oxygen concentration–the desert pupfish (Cyprinodon macularius), long—fin dace (Agosia chrysogaster), speckled dace (Rhinichthys osculus), and Gila sucker (Catostomus clarki). Different rankings of the species resulted for tolerance (closed—air system) and survival (open air system). Open—system experiments were designed that demonstrate mechanisms by which this environmental stressor produces catastrophic selection in nature. During interspecific competition, adaptive behavior and structure as well as physiological tolerance were decisive in survival.
The Importance of Gamete Losses in Measurements of Freshwater Fish Production
Authors: Toetz Dale W.
Published: May 2006

Changes in teh maturity, weight and chemistry of ovaries of bluegills, Leopomis macrochirus, taken from Pewaukee Lake, Wisconsin, were observed during the summer of 1963. In June all ovaries were either in spawning condition or very close to this stage; by September all were completely spent. Between June and September the average ovary of an age—group—II female decreased in wet weight from 8.7 to 1.9 g, a decrease of 6.8 g (2.5 g dry weight). Protein accounted for 1.7 g of the decrease in dry weight whereas fat accounted for about 0.7 g. These losses are comapred with the body weight of the fish and annual growth by individuals. Protein loss as spent ova was calculated to be about 13% of the total somatic protein of a spawning female and about 24% of the somatic protein gained by the fish as annual growth during the previous year. The substantial losses of protein as spent gametes are discussed relative to estimates of production by freshwater fish populations.
Asplanchna, Asplanchna‐Substance, and Posterolateral Spine Length Variation of the Rotifer Brachionus Calyciflorus in a Natural Environment
Authors: Gilbert John J. , Waage Jonathan K.
Published: May 2006

A field investigation during the summer of 1965 in Millstone Pond, New Jersey showed that posterolateral spine lengths of the pala and dorcas varieties of Brachionus calyciflorus were unrelated to water temperature and varied directly both with the density of Asplanchna brightwelli and with the presence of threshold quantities of Asplanchna—substance as determined by laboratory assay. These relationships suggest that the production of Asplanchna—substance in this pond during this period was an important factor in controlling the posterolateral spine lengths of the B. calyciflorus and, therefore, that the effect of Asplanchna on B. calyciflorus observed in the laboratory also occurs in the natural environment. Although this investigation suffers because of some difficulties in the interpretation of data and the rather short period of time during which data were collected, a meaningful correlation between a pattern of posterolateral spine length variation and an environmental variable has been reported.
JOZEF PACZOSKI: Founder of the Science of Phytosociology
Authors: Maycock Paul F.
Published: May 2006

The Polish ecologist Jozef Pacoski pioneered in the development of phytosociology and in the evolution of such concepts as vegetational continuity. Details of his life and a compilation of his ecological contributions are provided.
Seasonal Soil Moisture Patterns in Adjacent Greasewood and Sagebrush Stands
Authors: Rickard W. H.
Published: May 2006

Soil moisture measurements were made over a 2—year period in adjacent greasewood (Sarcobatus vermiculatus) and sagebrush (Artemisia tridentata) stands in the desert steppe region of southeastern Washington. Soil moisture accumulated during fall and winter. The greater accumulation of moisture in the upper 4 dm of the greasewood stand appeared to be the result of decreased evaporation losses and the lack of transpiration from shrub species which are leafless during winter and early spring. The more luxuriant growth of cheatgrass in the greasewood stand was related to winter and spring retention of soil moisture.
Differential Pollen Accumulation in Water‐Tank Sediments and Adjacent Soils
Authors: Potter Loren D.
Published: May 2006

Significant differences were found in pollen composition of sediments at different compass directions within large water—storage tanks. The center and north side were closest to the mean for the entire tank. Tank sediments showed an over—representation of arboreal pollen when compared with surface soil samples adjacent to the tank. The lower percentage of nonarboreal pollen in tanks was due to a lower percentage of Chenopodiaceae, Amaranthus, and Gramineae pollen. Miscellaneous arboreal taxa were present in tank sediments but not in soil samples.
Photon Flux, Chlorophyll Content, and Photosynthesis Under Natural Conditions
Authors: Anderson Margaret C.
Published: May 2006

The photon flux in the photosynthetic region from the sun and sky is calculated for a range of conditions and shown to vary by about 10%. A mean figure of 1.2 x 1019 photons cal—1 (400—700 nm) is assumed. This waveband is taken to include 45% of the total incident short wave radiation. The relation between photon flux and the available photosynthetic machinery, in terms of chlorophyll content, is calculated. It seems that the normal chlorophyll content of leaves is adequate to absorb the available photon flux under most natural conditions, and that the chlorophyll content of plant communities is not, in itself, likely to be a limiting factor in photosynthetic production. High chlorophyll content of plant communities is a concomitant of large leaf area index, increasing radiant energy absorption, and total dry matter production.
Structural Habitat and Time Budget of a Tropical Anolis Lizard
Authors: Andrews Robin M.
Published: May 2006

Structural habitat data generally support the interpretation that competition for food results in habitat partitioning. In this investigation, the importance of ethological factors in determining the structural habitat of Anolis lizards is demonstrated by examining the structural habitat of Anolis polylepis during foraging and social interaction, its two major activities. “Overall” structural habitats show that intraspecific classes use perches of significantly different heights and diameters. Perch heights of adult males and females are also shown to be related to the type of activity in which they are engaged. Overall structural habitat data show a greater difference between the sexes than actually exists in their feeding locations. Ecological differences between insular and continental Anolis potentially affecting the structural habitat are also discussed.
Insecticide Effects on Early Succession in an Old Field Ecosystem
Authors: Shure Donald J.
Published: May 2006

An ecosystem approach was used to assess the effects of soil contamination with an organophosphate insecticide on ecological succession in 3—acre old field on the Piedmont of New Jersey. Diazinon was applied to one—half of the field in May 1967 and again in May 1967 and again in May 1968 at a rate of 12 lbs of active ingredient per acre. A latin square experimental design was used to analyze the effects of the insecticide on the density, diversity, and production of vegetation; the density and diversity of herb—stratum arthropods; and the trophic relationships that developed on treated and untreated areas. In 1967, insecticide contamination produced a significant enrichment in both density and diversity of vegetation as well as a consistent trend toward greater plant biomass on treated areas. The vegetation changes represented a summation of small but consistent differences in major producers common to both treated and untreated areas. Plant differences were believed due to a phytotoxic effect of diazinon on Convolvulus sepium, which was significantly reduced on treated areas. Other plant species normally inhibited by Convolvulus subsequently flourished on treated areas. Herb—stratum arthropod populations were similar on treated and untreated areas in 1967, despite the vegetation differences. Only a trend toward greater insect diversity on treated areas was present. The failure of indirect arthropod differences to develop was due to the similar availability of dominant producers and thus food web bases on treated and untreated areas. Radionuclide tracer studies indicated that ragweed (Ambrosia artemisiifolia) was the major food web base for resident consumers in the latter part of the growing season. The trophic transfer from ragweed was quite similar in treated and untreated areas. The lack of arthropod differences was thus attributed to similar availability of ragweed biomass in both areas. Vegetation differences were absent in 1968 following a second treatment with diazinon. Moisture appeared to be a major factor influencing the impart of the insecticide during the two summers. Vegetation differences developed in June 1967 at a time when rainfall was almost absent. In 1968, however, considerable rainfall occurred during the same period. The increased rainfall stimulated a greater seedling development than in 1967, thus apparently overcoming the effects of the insecticide. Environmental factors such as soil moisture can therefore interact with pollutants and seriously influence the degree of ecosystem modification.
Studies on Some Inland Waters of the Galapogos
Authors: Howmiller Richard
Published: May 2006

Arcturus Lake is a stratified hypersaline lake occupying a caldera near the center of Genovesa Island. It is about 500 m in diameter and has a maximum depth of 30 m. The lake is frequented by large numbers of seabirds and is an outstanding example of guanotrophy. Organic production in the epilimnion was great, and the hypolimnion was anoxic at the time of these studies. The lake is probably stratified during the entire year. There appear to be no fishes in the lake. The invertebrate fauna is dominated by corixids and tanaid shrimps. Tagus Crater Lake on Isabele Island, occupies a crater about 100 m from Tagus Cove. It is about 400 m in diameter and 10 m deep over most of the basin. The lake is saturated salt brine with a bottom of rock salt. The fauna is dominated by corixids and anostracan shrimps. Of three small ponds at Noah's Coves. Isabele, one has low salinity from top to bottom, whereas the other two are markedly stratified with regard to salinity. The upper "fresher" water in the stratified ponds is poor in phytoplankton compared to the underlying high—salinity water. Several species of fish, Odonata, corixids, water striders, and crustacean larvae were living in the ponds at the time of these observations.