bluuebunny/crossref_metadata_2025 huggingface dataset:
Diurnal Torpor and Its Relation to Food Consumption and Weight Changes in the California Pocket Mouse Perognathus Californicus
Authors: Tucker Vance A.
Published: May 2006

Perognathus californicus is a nocturnal, burrowing rodent and in the mountains of southern California is locally distributed in association with the edge of grasslands. The thermal environment of P. Californicus is moderate. Temperatures on the surface of the ground at night range from 0 to 25°C in summer. P. Californicus undergoes a daily period of torpor if its food supply is reduced below its ad libitum consumption. At an ambient temperature of 15°C, 17 g of bird seed per 100 g body weight is required each day to maintain weight in the absence of torpor. If this food ration is reduced, mice on a 12—hr photoperiod with lights on from 0600 to 1800 hr enter torpor between 2000 and 0500 hr and allow their body temperatures to drop to about 16°C. The earlier times of entry into torpor are associated with smaller food rations. Since the mean time of arousal is between 1100 and 1330 hr on all food rations, the duration of the torpor period increases as the food ration decreases. The torpor period in the laboratory may encroach on the nightly activity period and decrease the total activity of mice on rationed food. A linear relation exists between daily food ration, time in torpor, and weight loss. This relation can be explained theoretically and measures the food requirement for weight maintenance in the absence of torpor, the food savings associated with torpor, and the influence of food ration on the rate of weight loss. This information, together with data on population dynamics, could be used to estimate the population energetics of P. californicus.
A Modified Piche Evaporimeter
Authors: Waring Richard H. , Hermann Richard K.
Published: May 2006

A Piche evaporimeter is described that has only one evaporative surface, is constructed from inexpensive plastic tubing, and from which water loss is measured gravimetrically. Such instruments were calibrated in the laboratory by controlling vapor pressure deficits, and their precision was found adequate for many laboratory experiments. Field use for 30 days or longer is possible with the large reservoir capacity.
Distribution of C‐14 in Products of Photosynthesis and Its Relationship to Phytoplankton Composition and Rate of Photosynthesis
Authors: Olive John H. , Benton Duane M. , Kishler Jack
Published: May 2006

Relationships among the phytoplankton standing crop, rate of photosynthesis, and the distribution of C—14 in primary products of photosynthesis were investigated in western Lake Erie from July to August 1965. Sixty species of phytoplankton were noted during the study, but only four species, Coscinodiscus sp, Ceratium hirundinella (O.F.M.) Schrank, Aphanizomenon flos—aquae (L) Ralfs, and Microcystis aeruginosa Kutz accounted for over 98% of the total cell volume. Cell volumes ranged from 10 to 282 mm3 liter—1. Total photosynthesis (mgC m—3 day—1) in the upper photic zone averaged 566, ranging from 55 to 1690. Relative photosynthesis (mgC day—1 mm—3) ranged from 1.6 to 332. Ethanol—soluble C—14 fractions (mostly carbohydrate and lipids) of the phytoplankton accounted for 25—60% of the total C—14 assimilated. Insoluble C—14 fractions (mostly proteins) accounted for 20—48% of the total C—14 uptake. Large carbohydrate and small protein fractions occurred in Coscinodiscus standing crops under moderate illumination and in steady—state Alphanizomenon—Microcystis standing crops under high illumination. C—14 labeled protein fractions exceeded carbohydrate fractions in rapidly growing Aphanizomenon—Microcystis standing crops under moderate illumination and at the peak of a blue—green algae bloom under low illumination.
Physiological and Ecological Tolerances of Eucalyptus Incrassata and E. Socialis to Edaphic Factors
Authors: Parsons R. F.
Published: May 2006

The relative distribution of the mallee eucalypts E. incrassata and E. socialis seems to be controlled by slight soil differences, with E. incrassata usually on soils both lower in nutrients and with a higher water—supplying capacity. Seedling monocultures in soils naturally supporting either species or both showed that the two species had closely comparable physiological tolerance to a wide range of macronutrients. In mixed cultures, F. incrassata had a competitive advantage in all soils at optimal water levels, but this was greatly reduced in a drought treatment. E. socialis seems to have superior drought avoidance related to higher root: shoot ratio and possibly to slower growth in competition. Drought susceptibility is shown to be positively correlated with soil fertility. E. incrassata may succumb to drought on the dry, fertile soils carrying E. socialis, whereas E. socialis may be out—competed by E. incrassata on wetter, less fertile sites.
The Behavior and Life History of a Sand‐Beach Isopod, Tylos Punctatus
Authors: Hamner W. M. , Smyth Michael , Mulford E. D.
Published: May 2006

Tylos punctatus is an abundant oniscoid isopod on sheltered sandy beaches in southern California and in Baja California. It is strictly nocturnal, being buried in the sand or under wrack by day. During the winter it does not emerge onto the surface, remaining buried in the sand high up on the beach, the adults up to a meter deep and the juveniles shallower. From March to late October or November, however, it emerges at night to feed on stranded seaweeds and dead animals. When the high tide is early in the evening, T. punctatus emerges onto the surface only after the tide has begun to ebb from over the sand in which it is buried. Tylos moves seawards at first, but this strict seaward tendency diminishes the further down the beach it has walked. It apparently navigates by beach slope. Later in the night, having fed, Tylos moves back up the beach to bury itself at the previous night's high—water mark. T. punctatus is extremely abundant on El Estero Beach. Its reproductive rate is very low compared with that of other oniscoid isopods. Females breed once a year in summer. They incubate with that of other oniscoid isopods. Females breed once a year in summer. They incubate the embryos in their brood pouches in the sand above the high—tide line for about 9 weeks and produce an average of 13.6 young each. Larger females tend to produce more young. Very few if any females breed before they are 3 years old and most, if not all, die soon after. Some males, however, live for at least 4 years. T. punctatus only grows during a 5—month period in the summer. There is no significant difference between mean sizes or growth rates of males and females. Growth rate declines with age.
An Orthokinetic Response to Rates of Salinity Change in Two Estuarine Fishes
Authors: Perez Kenneth T.
Published: May 2006

The average swimming speed of two estuarine fishes, spot (Leiostomus xanthurus) and croaker (Micropogon undulatus), was determined in the laboratory under a constant and a changing salinity regime. It was found that croaker moved faster under 5 and 10% salinity change hr—1 as compared to the fixed salinity regime. Spot increased its speed of movement only under the 10% change hr—1 condition. These results suggest that (1) those portions of the estuary possessing similar salinity changes may be avoided by spot and croaker and that (2) possibly the rate of change in salinity rather than the actual salt concentration limits the distribution of these species.
Equitability Indices: Dependence on the Species Count
Authors: Sheldon Andrew L.
Published: May 2006

Three measures of equitability or relative diversity are shown to be dependent on the species count component of total diversity. This dependence limits the use of equitability indices as comparative statistics.
Ant Communities of the High‐Altitude Appennine Grasslands
Authors: Baroni‐Urbani Cesare
Published: May 2006

High—altitude Appennine grassland ant communities were studied by sampling two stations with very different exposures and plant associations. In spite of these differences, the distribution of the ant population is very similar in the two stations, and it is probable that the situation found on Monte Terminillo also exists on most of the high altitude grasslands of the central Appennines. Two species, Lasius alienus and Tetramorium caespitum, predominate; and a few others are quantitatively of lesser importance. The dominant species, which have similar alimentary regimes, and whose colonies are randomly distributed, forage at somewhat different hours.
The Visible Albedo of Surfaces in Central Minnesota
Authors: Bray J. R. , Sanger J. E. , Archer A. L.
Published: May 2006

Incident and reflected visible radiation under clear skies was measured in summer 1960 over surfaces in central Minnesota. Measurements were made with Weston photometers, model 756, on the ground, from ladders, and from a Bell 47—G2 helicopter. Percent albedo over natural upland surfaces at 60—65° solar altitude decrease from 12.0 for inorganic sand to 6.1 for organic sand, to 5.3 for short grassland, and to 2.2 for forest; lowland surfaces decreased from 4.0 for water to 2.3 for forest. Albedo decreased with an increasing chlorophyll a + b content of vegetation, but the decrease was negligible above a chlorophyll content of around 1.0g/m2. Urban surfaces were more reflective than agricultural surfaces, which had a higher mean albedo than natural vegetation. The mean albedo of an aerial transect from Bethel to St. Paul was 6.5% and was estimated to have increased around 15% the settlement of the area by European man. Percent albedo over a Quercus forest increase from 2.4 at 65—70° solar altitude of 11.6 at 8—10° and the decreased to 3.8 at 0° altitude. A similar albedo pattern was found for a pioneer (short) grassland which increased from 5.2 to 13.2 and then decreased to 4.6%. Changes in albedo with solar were attributed to changing proportions of diffuse and direct radiation and to Fresnel's Law. Light penetration into the Quercus forest decreased most rapidly in the lower tree canopy layer and decreased with increasing solar altitude. Albedo within the Quercus forest increased with increasing forest depth and with increasing solar altitude, reaching a maximum of 12.7% at a forestheight of 0—3 m and a solar altitude of >60°.
Ecological Status of Introduced Brome Grasses (Bromus Spp.) in Desert Vegetation of Southern Nevada
Authors: Beatley Janice C.
Published: May 2006

Of the plant species introduced on the Nevada Test site, Nye County, Nevada, Bromus rubens and B. tectorum are well established in the present vegetation mosaic. B. rubens is frequently the dominant winter species in Colegyne (blackbrush) communities at 4,000—5,000 ft. Relative density (or absence) of populations is a site characteristic, as indicated by quantitative data from 18 study sites in Yucca Flat in the Years 1963—65. Like the native species, it occurs in higher densities on disturbed sites of areas where it is already established in the undisturbed vegetation. Its success is in part due to a growth regime and environmental requirements unlike those of the native winter annuals, and perhaps to higher percentage survival to maturity as in the 1963—64 season. It is not aggressive in the region today. B. tectorum is confined to disturbed sites at the higher elevations (5,000—7,500 ft) where vegetation is Artemisi (sagebrush) or Armenisia—Pinyon—Juniper. It is numerically and really increasing with an increase in disturbed sites at these elevations. Fire is promoted by both species, but the contribution of B. rubens is much greater, either directly or indirectly, because it is identified with Coleoptera vegetation, the shrub type in the region most susceptible to fire.
Spectral Distribution of Light in the Forest
Authors: Federer C. A. , Tanner C. B.
Published: May 2006

Spectral distributions of shade light between 400 and 740 mm were measured under corn, sugar maple, oaks, pines, and spruce with a portable recording spectrophotometer. Differences were found between hardwoods and softwoods and between clear cloudy days. An energy maximum at 550 nm, a minimum at 670 to 680 nm, and a very high maximum in the near infrared occurred under all species. Four components of light within a plant canopy can be distinguished: both beam solar radiation and diffused sky radiation are transmitted both directly and indirectly (reflected and scattered). Separate consideration of each of these components leads to great understanding of similarities and differences between light regimes in different stands.
Rate of Weight Loss of Tree Frogs at Various Temperatures and Humidities
Authors: Jameson David L.
Published: May 2006

Sixteen Hyla regilla, four each from four localities, were desiccated at each of four temperatures (10, 15, 20, 25°C); each animal was weighed five time in 23 hr. Three of the frogs maintained at 25°C died after a loss of approximately 36 to 52% of body weight during 23 hr; none died at lower temperatures. The rate of weight loss was significantly higher at high temperatures than at low temperatures and increase logarithmically with temperature. The total difference between localities was not statistically significant. Fifteen combinations of temperature (5,10, 15, 20, 25°C) and humidity (35 to 40, 50 to 55, 60 to 80% R.H.) were successively established in a plant growth chamber. The mean rate of weight loss of 6 Hyla regilla from each of 11 localities and 6 H. californiae from 1 locality was obtained at each set of conditions. The effect on rate of weight loss of a given increase in temperature is greater at low humidities than at high humidities. The rate of weight loss was adjusted by initial weight and by eigenvector values from principal component of morphological values. The adjusted rates were than analyzed by split—plot design analysis of variance. The sample means were found to differ significantly with respect to temperature, humidity and locality. The interaction of locality and temperature of humidity was not significant; temperature and humidity did have a significant interaction. Multivariate discriminant analysis separated the population into three groups. One group consisted of frogs from southern California desert and Baja California localities. The second group consisted of frogs from southern Carolina coast and mountains, and frogs from Yosemite. The third consisted of frogs from the northern part of the range. The rate of weight loss of different localities demonstrates a relation between latitude and some linear function of the first two discriminant axes. The data were reanalyzed after removal of the 25°C conditions. The split—plot design analysis of variance then indicated that the rate of weight loss of the frogs from the different localities were not significantly different. The discriminant analysis did not show a grouping as discrete as before, but the general pattern was about the same. The grand means for each locality of all frogs for all conditions were obtained and compared. A single sample (Lee's Camp) differed greatly from all samples, more than Hyla regilla differs from H. californiae. No relation between available environmental moisture and rate of weight loss was discerned. The linear arrangement of the discriminant values of the northern populations suggests some relation to the "ecogegrophical rules." This relationship is not shown in the discriminant values of the rates from southern localities.
Ecology of the Vegetation of a Second‐Growth Sequoia Forest
Authors: Biswell H. H. , Buchanan H. , Gibbens R. P.
Published: May 2006

Studies were made of an 80—acre tract of big tree forest which was logged about 1875 for sugar pine, ponderosa pine, and big tree. Disturbances related to logging created conditions ideal for establishment of trees, and a dense second—growth forest has developed. Incense—cedar and white fir are the most abundant trees, but the rapidly growing big trees now dominate in the early successional stages, but now the many species of shrubs and herbaceous plants present occur in low frequency.
Analysis of Spatial Pattern in Epiphytes
Authors: Hazen William E.
Published: May 2006

A method is described for transposing the position of epiphytes on a branch to a single straight line segment. Assuming a random pattern after the transposition, when there are N. Intervals along L units of line, the rth shortest interval between neighboring epiphytes is given by L/N Sri=1/ 1/N—i + 1. This theory of the distribution of interval length is applied to a population of bromeliads in a tree, and the result compared to a Poisson distribution. The methods agree in leading to the conclusion that the pattern is random. The assumptions made in the model, the conditions under which it is applicable, and the factors leading to different patterns are discussed.
Interspecific Competition and the Foraging Behavior of Plain‐Brown Woodcreepers
Authors: Willis Edwin O.
Published: May 2006

When Plain—brown Woodcreepers (Dendrocincla fuliginosa) follow swarms of army ants on Barro Colorado Island, Panama Canal Zone, they forage in the zone near the ground more frequently when Ocellated Antthrushes (Phaenostictus mcleannani) are absent. The ground—foraging ant thrushes regularly supplant the smaller woodcreepers, which then move to higher or to peripheral and less productive zones. This seems a clear example of competitive exclusion by dominance. On Trinidad, where competing low—foraging antbirds are nearly always absent, fuliginosa forages near the ground at swarms. In British Guiana, where several small antibirds saturate the lower levels over the ants, fuliginosa again forages high in the undergrowth. Instead of following Svardson's hypothesis that increasing interspecific competition restricts the habitat of a species, fuliginosa restricts the foraging—zone dimension of its habitat when interspecific competition is low. Both on Barro Colorado and on Trinidad the species gravitates to a narrow but more productive zone when interspecific competition is low; it seems to leave the upper zones unoccupied at such times. This failure to fill zones occupied under conditions of more stringent interspecific competition, as well as the inability of antthrushes to completely exclude fuliginosa from the lower levels of Barro Colorado, may be explained by the "irregularity principle": available food supplies are frequently left by biological or physical irregularities in time or space, since exploitation of food always lag behind its appearance. The principle suggests that superabundance of food may be frequent rather than exceptional. In the case of the woodcreeper and the antthrush, periodic low numbers of swarms may limit the numbers of antithrushes, leaving superabundant food supplies which the woodcreepers quickly exploit. The failure of fuliginosa to occupy the upper part of its foraging beat on Trinidad may, however, reflect absence of prey in that zone. Comparison of foraging zones of populations of a species are made difficult by differences in environment and heredity of organisms in different areas even thought this study shows that results of interspecific competition in one area are similar to results for different areas for Dendrocincla fuliginosa.
The Behavior of Sponge Larvae
Authors: Warburton Frederick E.
Published: May 2006

Larvae of Cliona celata and Microciona prolifera swim constantly upward, or at the surface, until 20 to 30 hr old, then always swim vertically downward. This behavior is not oriented by chemical of thermal gradients and is independent of light.
Habitat Preferences of Five Sympatric Species of Long‐Tailed Sherws
Authors: Spencer Albert W. , Pettus David
Published: May 2006

Long—tailed shrews of 5 species were captured throughout four years at a single 60—acre at 9,700 ft elevation in western Larimer County, Colorado. Interspecific differences in the proportions of captures in 3 main habitats, sedge marsh, subalpine forest, and clear—cut forest were significant. All species except one, Sorex palustris, were captured in all three types however. S. palustris was taken only adjacent to bodies of water. Sorex cinereus and Sorex vagrans were captured with the greatest relative frequency in marsh situations. The frequency of captures of the former species in the clear—cur habitat was proportionally lower than for the latter species. Sorex nanus and Microsorex hoyi were taken with high frequency in the forest. S. nanus was taken with the greatest frequency of any species in the clear—cut area and also at the greatest mean distance from permanent surface water. M. hoyi was captured more frequently than any other species at sites intermediate in character between marsh and forest. It was captured much less frequently in the clear—cut area and more frequently in the marsh than S. nanus but less frequently in the marsh than either S. cinereus or S. vagrans. Indices of relative abundance of S. cinereus and S. vagrans synchronously declined sharply in 1963 from high points in 1962 but increased again in 1964. Indices for S. nanus and M. hoyi remained approximately uniform throughout the four years.
Factors Affecting Interaction and Distribution of Haplopappus Divaricatus and Conyza Canadensis in North Carolina Old Fields
Authors: Shontz John P. , Oosting H. J.
Published: May 2006

Haplopappus divaricatus and Conyza canadensis commonly appear in first—year old fields of North Carolina. Haplopappus is very rare in fields of the North Carolina Piedmont, but occurs in varying densities on the coastal plain (0—83.8% relative density in 26 coastal plain old fields). Within the coastal plain, there is no east—west or north—south trend in the distribution of Haplopappus, and no correlation with the most recent grown crop is found. Fields disturbed in fall or winter, and fields with deep sandy soils and soils with low clay content, low moisture retention, and low available nutrients had high densities of Haplopappus and correspondingly low densities of Conyza. Haplopappus plants transplanted from the coastal plain to the Piedmont survived and produced large numbers of viable seeds, but no seedlings grew the following year around these transplants. Transplants from greenhouse to coastal plain and Piedmont fields survived and grew, but those in the coastal plain had greater dry weights. Haplopappus seeds planted in three plots in the Piedmont produced only one plant which set viable seeds. In greenhouse experiments both species were more affected by competition in sandy soil than in heavy soil. Haplopappus was more sensitive to interspecific competition, but decreased nutrients reduced the competitive ability to Conyza plants more than that of Haplopappus. Drought stress, which did not affect old or young Conyza plants, reduced the growth of young Haplopappus plants. Haplopappus showed less sensitivity to specific nutrient deficiencies than did Conyza. In the field and in greenhouse flats Haplopappus seeds did not germinate in heavy soil. The presence of added organic matter in sand reduced the germination percentage of Haplopappus, as did decay products of Conyza shoots. Haplopappus seeds in petri dishes on a temperature—gradient bar germinated at lower temperatures than did Conyza seeds. Germination percentages of Haplopappus were also greater when less water was available in the substrate. It is concluded that fall and winter disturbance of old fields kills many Conyza seedlings and opens bare soil. Because Haplopappus seeds germinate at low temperatures and in bare soil, this species is able to invade these areas. If no such disturbance occurs, few Haplopappus plants will mature, because Conyza plants are better competitors. Haplopappus apparently is prevented from becoming established in the Piedmont by the inability of its seeds to germinate in heavy soil and by the superior competitive ability to Conyza plants in the richer Piedmont soils.
Microbial and Ecological Investigations of Recent Cinder Cones, Deception Island, Antarctica‐‐A Preliminary Report
Authors: Cameron Roy E. , Benoit Robert E.
Published: May 2006

Cinder cones that arose December 1967 within Telefon Bay, Deception Island, Antarctica, were investigated 1 year later to determine the establishment of microorganisms and cryptogams. Culture media were inoculated to determine the presence and abundance of algae, fungi, heteorotrophic and chemoautotrophic, aerobic, microaerophilic, and anaerobic bacteria. No mosses or lichens had become established on the cones. Algae, fungi, and bacteria were generally most abundant around fumaroles emitting moisture and CO2. Several samples contained few or no culturable microorganisms. "Soil" properties of coarse—textured, relatively unweathered acid volcanic materials were unfavorable for growth, despite the presence of moisture. Microorganisms were identified from the cinder cones and included primarily soil diphtheroids and Bacillus spp., Chlorococcum humicola, and Penicillium spp. Most of the bacteria could grow at 2°C as well as at 20°C.
Further Study of Conifer Seed Survival in a Western Oregon Clearcut
Authors: Gashwiler Jay S.
Published: May 2006

The survival of naturally disseminated, filled, seed of Douglas—fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and western redcedar (Thuja plicata) was studied from 1960 to 1967. Ten per cent of the Douglas—fir seed survived from the start of seed fall until the end of germination the following year. Mice and shrews, mostly deer mice (Peromyscus maniculatus), destroyed an estimated 41% of the seed; birds and chipmunks (mostly birds) took 24% and other factors (nonviability of filled seeds, invertebrates, disease, and others) accounted for 25%. Western hemlock seed survival was 22%. Mice and shrews (mostly deer mice) destroyed an estimated 22% of the seed, birds and chipmunks (mostly birds) 3% and other agents 53%. The sample of western redcedar seed was too small to be reliable. Douglas—fir seeds were preferred by ground—feeding birds and small mammals–less than half as many hemlock were taken. Most Douglas—fir and hemlock seed mortality occurred before the start of germination.
Interspecific Competition Between Drosophila Melanogaster and Drosophila Simulans. Effects of Larval Density and Short‐Term Adult Starvation on Fecundity, Egg Hatchability and Adult Viability
Authors: Barker J. S. F. , Podger R. N.
Published: May 2006

The effects of variation in larval density and variation in proportions of the two species during development on the fitness components of fecundity, hatchability and adult viability were studied using the Oregon—R—C wild type strain of D. melanogaster and a vermilion mutant strain of D. simulans. In addition, the effects on these fitness components of a restricted period of starvation immediately following eclosion were studied. Thirty—two treatment combinations of species, species frequency, larval density and adult feeding were set up on each of two occasions, 14 days apart. Hatchability data were obtained only for the second time. This variable of time had significant effect on fecundity, which would contribute to the heterogeneity between generations in interspecific competition populations. Significant effects of larval density of fecundity were probably mediated through effects on adult body weight. D. melanogaster females raised in mixed species cultures were less fecund than those from pure cultures, while D. simulans showed the reverse effect. Therefore results in competition cultures cannot be predicted from those in pure species cultures. There were significant differences between the species for hatchability and viability, but these components of fitness showed relative few effects of the imposed treatments. The short—term adult starvation treatment was not as severe as that which occurs in at least some generations in interspecific competition populations. The effects of this and other environmental differences between this experiment and competition populations are discussed.
The Distribution of Carpenter Ant Colonies in the Spruce‐Fir Forests of Northwestern Ontario
Authors: Sanders C. J.
Published: May 2006

Colonies and underground tunnel systems of carpenter ants (Camponotus spp.) were mapped in three 1—acre plots (0.4 hectares), respectively of successional stages of the spruce—fir forest in northwestern Ontario. The youngest stand with the most intensively tunneled and contained the most colonies and the highest worker population. This was attributed to the greater abundance of stumps and logs for nesting sites than in the more mature stands. However, such sites lacked permanence and many colonies were decadent. It is postulated that carpenter ants reproduced more successfully in the mature stands where large living trees provide more permanent nesting sites.
The Biodemography of an Intertidal Snail Population
Authors: Frank Peter W.
Published: May 2006

Numbers, deaths and growth rates were observed for three years in a delimited population of Acmaea digitalis whose members had been individually marked. The zone of vertical distribution of the species is determined by the behavior of these snails. In the fall and winter they ascend in the intertidal, and descend a smaller distance in the spring. This leads to a differential distribution of size classes. The oldest and largest animals are found highest in the intertidal zone. That the vertical movements are adaptive is suggested by death rates which are highest in the upper portions in summer, but rise in the lowest zone in winter. Probability of survival improves with age. Growth rate was remarkably consistent during the period of observation. It was fastest in the fall and winter months. During the month of July, and in part of June and August growth ceased, at least as measured by a change in shell length. Crowding decreased growth slightly but significantly. Growth rates in different areas suggest that time available for feeding may be a significant variable. Experimental manipulation of density indicates that emigration rates are density—dependent. The mechanism of density regulation is postulated as operating even at low overall densities because of the behavior pattern of the species.
Microarthropod Ecology of a Porcupine‐Inhabited Cave in Nova Scotia
Authors: Calder Dale R. , Bleakney J. Sherman
Published: May 2006

The most important source of organic detritus in Nova Scotia caves is feces of the porcupine, Erethizon dorsatum. The high organic content of this cave detritus supports a numerically rich microarthropod fauna, composed of epigean species preadapted to a troglic environment. The fauna is of recent, postglacial origin, and no troglobites were identified. Three distinct stages in detritus decomposition presented three stages in ecological succession, each with a characteristic fauna. The majority of the cave Collembola were eyeless and unpigmented. The Isotomidae accounted for 83.5% of the cave fauna. All families of Collembola were represented except the Poduridae. Recognizable trophic levels and food web patterns exist in the cave biotic community. The fauna is active all year, since deep in the cave temperatures remain above freezing during the winter.
Chronic Exposure of Blue Crabs, Callinectes Sapidus, To Sublethal Concentrations of DDT
Authors: Lowe Jack I.
Published: May 2006

Juvenile blue crabs, Callinectes capidus, were reared in flowing seawater contraining sublethal concentrations of DDT. Crabs fed, molted, and grew for 9 months in seawater containing 0.25 ppb (micrograms/liter) DDT but could survive only a few days in water containing DDT in excess of 0.5 ppb.
Seasonal Changes in Oak Leaf Tannins and Nutrients as a Cause of Spring Feeding by Winter Moth Caterpillars
Authors: Feeny Paul
Published: May 2006

Concentration in the spring of feeding by caterpillars of the winter moth, Operophtera brumata L., and other species of Lepidoptera on oak trees in England is believed to be related to seasonal changes in the texture and chemical composition of the leaves. Increasing leaf toughness is a proximate, though probably not ultimate, factor preventing late larval feeding by the winter moth, the commonest spring species on oak. Early feeding coincides with maximum leaf protein content and mimum leaf sugar content, with suggests that availability of nitrogen, rather than of carbohydrate, may be a limiting factor for spring—feeding larvae. The content of oak leaf tannins, which inhibit the growth of winter moth larvae, increases during the summer and may render leaves less suitable for insect growth by further reducing the availability of nitrogen and perhaps also by influencing leaf palatability. Oak trees are extensively damaged by insect attack, and it is likely that leaf tannins have a defensive function against insects as well as against other herbivores and against pathogens.
Age Specificity and Ecological Theory
Authors: Emlen J. Merritt
Published: May 2006

This paper attempts first to deal with the question of aging as a byproduct of natural selection, drawing on the theories of Medawar, Williams and Hamilton, and second, to apply the conclusions to considerations of population and behavioral ecology. It is concluded that: (1) Age—specific mortality should drop to a minimum prior to earliest reproductive age and then rise with age. (2) Age—specific fecundity should rise with age to a peak, which may occur at almost any age depending on the sort of organism considered, and then fall. (3) A sudden increase in mortality at a given age will result in natural selection favoring higher relative mortality at immediately preceding and following ages, and lowered fecundity immediately after that age. (4) A sudden increase in fecundity at a given age will result in natural selection favoring relative higher mortality in early life and immediately after that age, as well as relaxed selection for increased fecundity, especially at middle and late ages. (5) Selection acts to make increasingly steep the survivorship curve of a population declining or fluctuating due to changes in mortality. (6) Selection acts to postpone reproductive effort in populations declining or fluctuating due to changes in fecundity. (7) If mortality is very low, animals, as they age, should ideally take greater risks to secure reproductive success. (8) The nature of altruistic behavior may be age specific, with older individual more characteristically altruistic and younger individuals more characteristically pampered. (9) Intergroup hostilities should be largely directed toward certain age groups.
Distribution of Cs 134 in Andropogon Scoparius Michx. Clones in Two Native Habitats
Authors: Dodd J. D. , Van Amburg G. L.
Published: May 2006

Cesium—134 distribution in native Andropogon scoparius clones and in single tillers indicates that each clone consists of a group of tillers each acting as individual plants. Two zones of concentration occur: the upper 5 cm of the roots and the inflorescence, including the florets. Cesium transport from the foliage to the upper portion of the roots occurs with fall dormancy. With the initiation of spring growth the mineral is exported from the roots to the expanding leaf blades. Cesium activity within the plants growing on the Heiden—Hunt clay soil decreases more with time than in plants growing on Tabor fine sandy loam.
Total Energy Balance in Salt Marsh Grasses
Authors: Teal John M. , Kanwisher John W.
Published: May 2006

Leaf temperature in Spartina alternifolia and S. patens varies little from the ambient air temperature. Spartina leaves lose from 70 to 460 molecules of water for every molecule of CO2 taken out of the air. This loss of water is consistent with the hypothesis that gases move between the air and the leaf by simple diffusion. There is evidence of a lowered water potential at the evaporating surface within the leaf.
Water‐Repellent Soils, Fire, and Annual Plant Cover in a Desert Scrub Community of Southeastern California
Authors: Adams Susan , Strain B. R. , Adams M. S.
Published: May 2006

Surveys relating soil wettability and the establishment of annual plants were conducted on soil hummocks under burned and unburned shrubs and trees in a desert scrub community 4 years following a fire. Hummocks under burned and unburned individuals of Larrea divaricata, Prosopis juliflora, and Cercidium floridum were nearly devoid of established annual vegetation, whereas the surrounding soil was densely populated with several species of annual plants, predominately Sphaeralcea emoryi. Hydrophobic (water—repellent) layers of soil were found at various depths in the barren hummocks. In general, the layers were further below the soil surface under burned shrubs or trees, and the degree of water repellency was greater. The soil surrounding the hummocks did not contain hydrophobic layers. The mosaic of annuals in the desert scrub vegetation is probably the result of a reduction of available soil moisture due to the formation of water—repellent soils under the shrubs. The effect was more pronounced following fire.
The Role of Behavior in the Nature Regulation of Numbers in the Gekkonid Lizard Gehyra Variegata
Authors: Bustard H. Robert
Published: May 2006

There is a definite limit to the number of female geckos which can inhabit a stump with the single male. This number, a result of social behavior between the females, was usually constant for any particular experiment. The intensity of behavioral interaction between the resident female(s) and introduced female(s) varies seasonally. The number of females which inhabited a stump did not vary with food supply. Under conditions of abundant food and total starvation the limit was reached with the same number of females present on the stump. These experiments, together with previous work indicate the key role behavior can play in the natural regulation of animal numbers quite independent of food supply. Social behavior can set an upper limit on population size. In nature, food shortage will not occur for this gecko since behavioral regulation takes place long before food becomes limiting.
Why Don't Boblinks Breed in Brazil?
Authors: Hamner William M. , Stocking John
Published: May 2006

The Bobolink, Dolichonyx oryzivorus, experiences two sets of "long" and "short" days each year during the transequatorial migration between North and South America. Increasing daylength normally stimulates gametogenesis in birds, and thus it is perplexing that Bobolinks do not also respond to the southern summer and attempt to breed in Brazil. Previous hypotheses regarding transequatorial migration are discussed; four experiments relating to these hypotheses are presented and evaluated. The testis cycle, moult pattern, body weight fluctuations, and beak color of male birds were followed on simulated natural daylength cycles for 15 months at 20—day intervals. Body weight and testis cycles appeared normal on this simulated natural cycle; beak color patterns and moult desynchronized. Absolute insensitivity to light terminates by late October; thereafter the birds are sensitive to "long days" for 6 months, yet they do not respond to an increasing daylength cycle comparable to 20° S latitude. Birds were also exposed to 17 months of continuous bright light: body weight cycles were regular for 6 months, then desynchronized; the testes regressed but spontaneous recrudescence was observed in 3 of 13 birds; recrudescence was not synchronous. Bobolinks did not respond to the 6L—30D lighting cycle that indicates a circadian control mechanism in other birds. A summarization of the photoperiodic responses of the Bobolink is included.
Wind as a Factor in the Local Distribution of Small Mammals
Authors: Vose Rory N. , Dunlap Donald G.
Published: May 2006

The purpose of this study was to investigate the effect of wind on the distribution of small mammals within a large field. The field was uniform in all gross environmental factors other than a gradient in the velocity of the prevailing winds produced by a large windbreak on one side of the field. Animals were trapped at three distances from the windbreak; one where there was a large degree of shelter from the wind, another where there was no sheltering influence, and the third intermediate to these. The trapping results showed a statistically significant difference in animal distribution in these three areas, with more animals being found in the area of greatest shelter. Subsnow maximum—minimum temperature measurements showed no marked differences among the three distances from the windbreak, so this was discarded as a possible factor causing the observed distribution. The occurrence of deeper litter and snow accumulation in the more sheltered area, together with the fact that this provides shelter from weather and predators, led to the conclusion that these accumulations were the primary factors responsible for the observed distribution of small mammals within the study area. Since these accumulations are secondary effects of wind, it is proposed that wind can be a major factor in the local distribution of small mammals.
Changes in Cryptozoan Numbers Due to Systematic Variation of Covering Boards
Authors: Jensen Paul
Published: May 2006

The area beneath small square boards and the boards themselves were varied in a systematic factorial experiment placed in a quasi—Latin square on a patch of prairie near Northfield, Minnesota, in the summer of 1961. As compared to small boards (8 x 8 in.), large boards (12 x 12 in.) had per board 5 more animals, one more kind, .5 more of a collembolan, .5 more Entomobrya color (collembola), 1.8 more Lasius niger (ant) and .9 more common crickets. White boards as compared with black boards had per board one more kind and 4.6 more Gastrocopta armifera (snail). The number of animals under boards on peaks was less per board than the number under boards on depressions by 1 spider, 1 lycosid, .25 orobatid mites, 1 beetle, 1.6 crickets, 2.3 Lasius niger and –.5 kinds. Redistribution of E. bicolor beneath the boards had no discernible effect on the numbers of this or any other species. Soaking of the underboard area was also without effect. Diversity (Margalef index) was significantly greater on peaks than on depressions. Regression analysis showed that numbers of collembola were significantly predicted by diversity and were correlated with numbers of kinds of other animals and the number of other animals. Few interactions of factors were observed.
Description and Analysis of Breeding Habitats of the Chickadees, Parus Atricapillus and P. Rufescens
Authors: Sturman William A.
Published: May 2006

The breeding habitats of Parus rufescens and P. atricapillus are largely nonoverlapping. A multiple regression analysis was used to describe carefully their breeding habitats and to analyze the extent of their coexistence. The abundance of P. rufescens is most highly correlated with the percent of the upper story canopy volume which is coniferous and the average height of the upper story conifers; taken together, these 2 variables account for more than 90% of the variability in the observed abundances. For P. atricapillus, the canopy volume of all trees, all bushes, and middle story trees together most accurately predict its abundance; the regression of these 3 variables on abundance accounts for over 90% of the variability in the observed abundances of P. articapillus on the study areas. Evidence is presented which supports the view that it is these features of the habitat to which the chickadees respond in selecting a breeding habitat. On the San Juan Islands, from which P. atricapillus is absent, P. rufescens was seen to breed in a broadleafed area. On the mainland it was not seen to breed in a comparable situation. However, P. rufescens appears to be more abundant on the island, and this greater abundance may have caused some individuals to select the "vacant" broadleafed area instead of the preferred conifers. Further observations in the broadleafed trees on Vancouver Island are needed to test further the idea that the absence of P. Atricapillus from it and the San Juan Islands has led to a modification in the habitat selection mechanism of P. rufescens on these islands.
Carbon Dioxide Evolution from the Floor of Three Minnesota Forests
Authors: Reiners W. A.
Published: May 2006

Carbon dioxide evolution rates from forest floors, measured approximately weekly for 54 weeks in oak forest, marginal fen, and cedar swamp, were closely related to soil temperature and secondarily to moisture conditions. As a result, microclimatic and drainage characteristics of the three forests produced seasonal differences in carbon release. However, compensatory factors produced nearly equal cumulative annual totals of CO2 evolution. Total CO2 evolution was over three times higher than expected from an equivalent amount of carbon release from annual litter fall. Respiration by tree roots was suspected as the major contributor to this disparity although methodological problems related to flow rate are still open to question.
The Estimation of Density Dependence
Authors: Green Roger H.
Published: May 2006

Andrewartha (1963) and Watt (1964) state that the correlation of the ratios of successive population densities (Nt+1/Nt) with initial densities (Nt) will show a negative correlation in the absence of true density dependent mortality and fecundity because Nt+1/Nt and Nt are not independent variables. For the common situation where population densities after successive time intervals are not independent of initial densities, this correlation would in fact be zero, and, in addition, the use of random numbers as a model for the null hypothesis of density dependence is not valid.
Shrinkage Thresholds in Freshwater Triclads
Authors: Reynoldson T. B.
Published: May 2006

Several species of triclad have the ability to shrink to an extremely small size before succumbing to starvation. In the laboratory, size and age (up to 12 months) per se do not appear to influence the threshold length at which mortality occurs in Dugesia lugubris when starved. But in those individuals which have bred, the threshold is increased from 1.0mm to 1.8mm. It appears unlikely that this contrast is important in nature because other factors cause mortality before such thresholds are reached.
A Multivariate Statistical Approach to the Hutchinsonian Niche: Bivalve Molluscs of Central Canada
Authors: Green Roger H.
Published: May 2006

The use of multiple discriminant analysis to identify the significant and independent ecological factors separating species distributions is proposed and discussed. Such an analysis was performed on 345 samples, containing a total of 10 bivalve mollusc species, from 32 lakes in Manitoba, Ontario, and Saskatchewan. Measurements of nine ecological parameters were associated with each sample. Five discriminant functions account for 95% of the among species variance, and 4 of the 5 are ecologically interpretable. Three of these, accounting for 80% of the among—species variance, are interpreted as bases of trophic, rather than physical or chemical, separation. There is separation of species on each discriminant function. The use of dissatisfied scores to classify lakes with maximum relevance to species distributions is demonstrated and discussed. A generally applicable measure of environmental heterogeneity based upon this type of analysis is proposed. The value of this type of analysis in quantifying ecological concepts derived from the Hutchinsonian niche model is discussed. An example is given of a reduced available niche resulting in the loss of two species, smaller realized niches for the remaining species, and greater niche overlap.