bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of Density from a Sample of Joint Point and Nearest‐Neighbor Distances
Authors: Batcheler C. L.
Published: May 2006

Distances are measured from sample points to the nearest member of a population, from that member to its nearest neighbor, and from that neighbor to its nearest neighbor. The point—to—nearest member is used to obtain an estimate of density, which is characteristically unbiased if the population is random, but biased if the population is uniformly or contagiously distributed. The bias is corrected by an exponential function of the sum of the point distances divided by the sum of either the nearest— or second—nearest—neighbor distances. The distances also provide an index of departure from randomness.
Factors Controlling the Productivity of Drosophila Melanogaster and D. Simulans
Authors: Sameoto D. D. , Miller Richard S.
Published: May 2006

The ecology of selected populations of the siblings species Drosophila melanogaster and D. simulans was studied. Single females of both species had sigmoid—shaped productivity curves during 10 days of oviposition with D. simulans producing the largest offspring population. Keeping oviposition time constant and increasing the density of females resulted in second—degree productivity curves for both species with D. melanogaster producing more offspring at each density. Changes in fecundity with time, and density of females of both species were examined. A linear increase in the offspring of D. melanogaster with increases in oviposition area was found. D. simulans had a greater pupal mortality and D. melanogaster a greater larval mortality at high larval densities. The importance of these factors in determining the population size is discussed.
The Metabolism of Fossorial Rodents: A Study of Convergence
Authors: McNab Brian K.
Published: May 2006

Temperature regulation and rate of metabolism were studied in five species of fossorial rodents: Geomys pinetis, Spalax leucodon, Tachyoryctes splendens, Heliophobius kapeti, and Heterocephalus glaber. The burrows of these rodents are in well—drained soils of poor water—holding capacity. Burrow atmospheres have an oxygen concentration of 15 to 20%, a carbon dioxide concentration of 0.5 to 2.0%, and limited temperature fluctuations; they are saturated with water vapor. Body temperature are somewhat low (35 to 37°C) in four species; temperature regulation is good in these species at ambient temperature down to 5 or 10°C. Heterocephalus, however, has a much lower body temperature (about 32°C) and the poorest capacity for thermoregulation of any known mammal. Fossorial rodents have low basal rates of metabolism, high conductances, and high ranges of thermoneutrality. Lethal ambient temperatures are inversely proportional to the normal levels of body temperature. Analysis of basal rates of metabolism (M), conductances (C), and body temperature suggests that the first two are determined in relation to environmental characteristics, and that body temperature, "goodness" of thermoregulation, midpoint of thermoneutrality, and lethal ambient temperature are dependent upon the ratio M/C. It is concluded that the lowest body temperature in homoiotherms compatible with good thermoregulation is about 35°C. A comparison of Heterocephalus and lizards illustrates the energetic similarities and differences between endotherms and ectotherms. The reduction of M and the increase of C in fossorial rodents are directly related to the mean burrow temperatures. These modifications reduce the probability of overheating in an environment where evaporative and convective cooling are greatly reduced. Tachyoryctes and Heliophobius use forced evaporative cooling for emergency thermoregulation, in spite of the saturated burrow atmosphere. Heterocephalus facilitates heat loss during heat stress by increasing peripheral circulation over its naked body; Geomys does this by increasing the circulation to its naked tail and, possibly, naked feet. Geomys may lose up to 30% of its heat production via its tail. As a result of these modifications, the lethal ambient temperature is proportional to the mean burrow temperature. Geomys responds to geographic variation in heat loading either by a decrease in body size or by an increase in tail length. The smaller size of nonpregnant, female gophers helps to maintain their heat production during pregnancy below the limits established by the environment for males. Gopher distribution appears to be limited to soils with high rates of gas exchange. Interaction among species of gophers has, to some extent, a physiological basis. It is suggested that the physiological characters concerned with energetics are readily modified, in an evolutionary sense, to conform to the requirements imposed by the environment.
Effects of Population Density on Growth Rates of Animal Populations
Authors: Tanner James T.
Published: May 2006

The growth rate of a population at time t is defined as the change in numbers per unit population at that time period (rt = dn/Ntd). The rate usually changes with time as the population increases or decreases. The objective of this study was determine whether the growth rate of animal populations is or is not a function of the population density. In most mathematical models of populations whose changes resemble those of actual populations, the growth rate is a decreasing function of density, meaning that as the population increases the growth rate decreases and vice versa. Records of actual populations can be used to test the relation between growth rate and density by calculating correlation coefficients for these two characteristics. The methods of doing this are described and the limitations on the data are explained. The records of 111 different populations representing 71 species were analyzed by these methods. Of the 71 species, 7 were eliminated from further analysis because their census records were not significantly different from a series of random numbers, 47 had correlation coefficients that were negative and significantly different from zero, 16 had coefficients not significantly different from zero (all but one of these estimated coefficients were negative), and one, the world's human population, had a positive coefficient significantly different from zero. There were no differences between taxonomic groups (insects other invertebrates, fish, birds, mammals). The primary conclusion is that in most animal species a population's growth rate is a decreasing function of density. The explains the relative stability of animal populations, which never continue to increase at rates their fertility would allow, and rarely decrease to extinction. Tentative conclusions are presented regarding the processes regulating population numbers. Populations of herbivorous insects at low and moderate levels are regulated by disease, parasites, and predators causing mortality that is an increasing function of density. Favorable conditions may allow an increase in insect numbers so rapid that the population temporarily escapes regulation by its enemies. Nonterritorial species of vertebrates are normally controlled by predation and, when that fails, by competition; in both cases juvenile individuals are most affected. In territorial vertebrates competition for suitable territories determines the size of the breeding population. Populations of vertebrate species (expecting man) are in general regulated by the production of adult individuals being a decreasing function of population density.
Ecological and Competitive Relations Among Three Species of Frogs (Genus Rana)
Authors: Inger Robert F. , Greenberg Bernard
Published: May 2006

Interspecific competition is often advanced as an explanation for replacement of species by ecological counterparts. Where environments are stable, as in controlled laboratory experiments, interspecific competition usually leads to the extinction of one species. In a complex natural environment, fluctuations in physical and biotic factors may long delay competitive exclusion. The existence of three related species of frogs (genus Rama) confined to stream in tropical rain forest provided an opportunity to manipulate natural populations and thus to study the relation between overlap in niches and interspecific competition. A rain forest area was chosen because it lacks significant seasonal variation in rainfall, temperature, and photo—period and consequently prevents seasonal specialization of the fauna. These three species, R. blythi, R. ibanorum, and R. macrodon, proved to be very similar in habits. Rana blythi is larger than the other two and usually was found farther from the stream bed. Rana macrodon reaches sexual maturity faster than the others and R. ibanorum lays fewer eggs. Nonetheless it is clear that their niches overlap extensively. Populations of these frogs were studied on surveyed portions of three streams by mark and release techniques. Populations of R. blythi on one stream (Sungei Ensurai) and R. ibanorum on another (Sungei Sekentut) were initially much smaller than the respective populations on the other streams. Following removal of R. blythi from Sungei Sekentut and of R. ibanorum from Sungei Ensurai, leaving the populations on Sungei Serbong as controls, R. blythi on Sungei Ensurai appeared almost to double in numbers and to reach the population levels originally found on the other streams. Population estimates of R. ibanourm on Sungei Sekentut fluctuated, being larger at midyear; statistical support for this variation is weak. Rana macrodon seemed to quadruple its numbers on Sunge Sekentut. There is evidence that macrodon is in the process of invading this part of Borneo and may be doing so at the expense of R. ibanorum. Maximum population levels for the blythi and ibanorum may be fixed by intraspecific competition, which in turn may be responsible for maintaining the coexistence of these related species.
Daily Vertical Migration of Lucifer, Planktonic Numbers in Relation to Solar and Tidal Cycles
Authors: Woodmansee Robert A.
Published: May 2006

The daily variation in planktonic numbers of mature and juvenile Lucifer faxoni Borradaile has been determined for two neritic locations in the northern Gulf of Mexico. The planktonic numbers are apparently related to both solar and tidal cycles. There are more Lucifer in the sampled water column during the night than during the day and more during the flooding tide than during the ebbing tide. The flood to ebb ratios are higher than the nocturnal to diurnal ratios at both locations. It is suggested that the daily vertical migration of Lucifer at these locations is being modified to achieve landward transport by the tendency of Lucifer to swim up into, or remain up in, the water column during a flooding tide and to drop out of the water column during an ebbing tide.
Some Characteristics of a Second‐Growth Northern Hardwood Stand
Authors: Piussi Pietro
Published: May 2006

A stand of northern hardwoods located in the Adirondacks Mountains (N.Y.) was studied in regards to structure, composition, and development. The stand has been exploited in the past by selection cutting but during the last 40 years has remained practically undisturbed. Eighteen tree species contribute to the composition of the stand within the 4 acres studied; the most abundant are Fagus grandifolia, Acer saccharum, and Tsuga canadensis. The forest mixture is made up of single trees of small groups of trees of the same species. Stand structure is typically uneven—aged even in small areas, showing characteristics of selectively cut forests, though the frequency—dbh distribution examined separately for Quercus borealis, Betual lenta, and Betula papyrifera is of the even—aged type. There is abundant regeneration of Fagus gradifolia, Ostrya virginiana, and Acer saccharum, and the forest is slowly changing to an increasing predominance of tolerant species. Good correlation between diameter and age exists for Fagus grandifolia, Tsuga canadensis, and Acer saccharum.
Species Diversity and Longitudinal Succession in Stream Fishes
Authors: Sheldon Andrew L.
Published: May 2006

A quantitative survey was made of the distribution and abundance of fishes in Owego Creek, New York. Four of the five headwaters species occurred throughout the area and two of these species dominated the fauna in all areas. Thirty—one species were found in the area. Succession took the form of additions to the headwaters assemblage and replacement was of minor importance. Regression analyses show that the number of species in any area was correlated most strongly with stream depth although an effect of position was also significant. Species diversity (information theoretic) was independent of position and depended on depth alone. Behavioral observations support the importance of the depth factor.
Influence of Water Balance and Microclimate on the Local Distribution of the Redback Vole and White‐Footed Mouse
Authors: Getz Lowell L.
Published: May 2006

A comparison was made of the importance of water balance, as influenced by microclimate, upon the local distribution of the white—footed mouse, Peromyscus leucopus, and the redback vole, Clethrionomys gapperi. The characteristic habjtats of the two species in southern New England are dry upland woods and low swamps, respectively. Temperature and relative humidity in the habitats of the two species differed only from 0800 to 1600 on clear days; at other times they were the same. Daytime relative humidities averaged 75 to 85 and 70 to 80% in swamp and upland sites, respectively. There was no consistent difference in the absolute humidities between the swamp and upland at any season. Air temperatures during the summer were 2 and 3oC lower in the swamp than in the upland; during the winter they were the same in both. Water turn—over rate of C. gapperi is appriximately 2.2 times that of P. leucopus (10.46 and 4.82 g/day, respectively). The difference results primarily from a more dilute urine from C. gapperi; the urine of P. leucopus is 2.2 times as concentrated as that of C. gapperi. Restriction of C. gapperi to low, wet areas in southern New England is correlated with the availability of standing water or an accessible water table, not with micorclimate. Evaporative water losses of C. gapperi are significantly greater than those of P. leucopus at absolute humidities of 6.0—12.8 mg/l; they were essentially the same at 16.3 mg/l. C. gapperi is only slightly diurnal; living in the drier uplands would increase its water requirements by only 0.02 g/day. The low water requirement for kidney function of P. leucopus permits it to live in drier upland wooded situations where free water is normally restricted to that available in food (fruits and insects). P. leucopus is strictly nocturnal; mcroclimates in swamps and uplands are similar at these times and would not be a factor in the water balance or local distribution of this species.
Environmental Relationships of the Structural Types of Australian Rain Forest Vegetation
Authors: Webb L. J.
Published: May 2006

The physiognomic—structural features used to classify Australian rain forest vegetation into 20 structural types vary along different gradients. The high correlation demonstrated between the structural types and the climatic and edaphic factors enables the identificatin of habitat types which are defined by limits of mean annual temperature and rainfall, and soil mineral status and soil drainage. The physiognomic—structural features are arranged in a hierarchical table. The primary division into vine, fern, and moss forests corresponds with tropical—subtropical, warm temperate (submontane), and cool temperate (montane) thermal regions, respectively. The temperate forms are strictly evergreen. Further subdivision of the vine forests into evergreen (including associated sclerophyll forests) and raingreen (more of less deciduous) types is correlated with differences in soil mineral status as inferred from topography, depth of soil, and parent materials. The tropical forms are differentiated from the sub—tropical forms by a higher proportion of mesophyll than notophyll leaf sizes. Further differentiation of vine forests with complex, mixed, and simple structure is correlated with inferred soil nutrient status defined as eutrophic, mesotrophic, and enriched obligotrophic. Obligotrophic soils do not support rain forest vegetation. Climatic and topographic factors tend to outweigh soil nutrient availibility at the climate extremes of the monsoonal and cool temperate regions. The structure types are finally differentiated by differences in height of canopy closure, nature of emergents, or proportion of deciduous species, and are further correlated with variations in soil moisture availability and drainage, or local exposure in montane situations. A field key to the habitat types associated with the different structural types is given. The inter—relationships thus established enable the prediction of either the type of vegetation, climate, or soil once any two of these are known. Deviations from the inferred distribution of rain forest are related to the past influence of wildfires which favor the regeneration of eucalypts and other scle sclerophylls after the destruction of the mostly fire—sensitive rain forest species. Destruction by surface fires in the tropical—subtropical region, or by running—crown fires of the mass—ignition type in the temperate regiion results respectively in abrupt ecotones, or diffuse ecotones and the virtual absence of climax rain forest vegetation. The practical implications of the ecological relationships established are briefly discussed in relation to land use and conservation.
Microhabitats, Abundance and Food of Conus on Atoll Reefs in the Maldive and Chagos Islands
Authors: Kohn Alan J.
Published: May 2006

Assemblages of up to 17 species and averaging 13 species of Conus were found on topographically complex subtidal coral reefs (Type III habitat) in the Maldive and Chagos Islands, Indian Ocean. Topographically simpler intertidal smooth limestone benches (Type II habitat) supported eight species. At a station with intermediate habitat, 12 species were present. Only two species were found in extensive areas of sand substrate (Type I habitat). Although most of the commoner species occurred in habitat Types II and III, their relative abundances differed strikingly. Species characteristic of the physically harsher, topographically simpler Type II environment are smaller, sometimes occur in dense populations of up to 1 individual/m2, and are quite specialized predators on herbivorous errant polychaetes. Species characteristic of the more equable but topographically diverse Type III environment are larger, have lower population densities of 0.03—0.15 individual/m2, and are somewhat more generalized predators on deposit—feeding sedentary polychaetes. Detailed analysis of diets supports the conclusion of prior studies that most species of Conus are primary carnivores. The 13 most abundant species of Conus in the Maldive and Chagos Islands feed almost exclusively on polychaetes, which comprised 96% of all food items identified. Species that eat gastropods and fishes were present but uncommon. The nature of the food of eight species was determined for the first time. Calculations of amount of food eaten, based on rather crude data for five species, gave a mean of about 10% of body weight eaten per day, but some of the estimates seemed unreasonably high. Species with more specialized diets are larger numbers of prey items than generalists, but the larger ratio of prey size to body size of the latter probably compensates, so that specialists are not more successful predators than generalists. In the habitats studied, Conus species are not more specialized predators where larger numbers of congeners co—occur. The topographic uniformity and less patchy nature of Type II habitat probably favor both increased density of the prey and mobility of Conus, thus making appropriate food more abundant and accessible than in Type III habitat. Conus diets are correspondingly more specialized in Type II than Type III habitat. These opposite feeding strategies foster increased feeding efficiency in the two topographically contrasting habitats. It is proposed that topographically simpler, more uniform, intertidal bench habitats favor lower species diversity, specialization, smaller body size, and higher population density, while topographically more complex, patchier, slightly subtidal coral reef habitats favor higher species diversity, somewhat more generalized habits, larger size, and lower population density.
The Effect of Grazing by Tadpoles on the Structure of a Periphyton Community
Authors: Dickman Mike
Published: May 2006

The species composition and standing crop of the algal epiphytes on the walls of experimental cages in a small lake were greatly altered following the emergence of frog tadpoles from eggs laid in the cages. The results support the hypothesis that tadpoles may be a major cause of the massive spring reduction in standing crop of filamentous green algae in the lake.
Breaking Seed Dormancy of Kalmia Hirsuta with High Temperatures
Authors: Jaynes Richard A.
Published: May 2006

Kalmia hirsuta exhibits a kind of seed dormancy not previously known for Ericaceous plants or other small—seeded species. Dormancy was most effectively broken by treating the seed under humid conditions for 10 min to 19 hr at temperatures between 60° and 90°C, the higher the temperature the shorter the treatment period required. The dormancy requirement may have evolved as a mechanism for survival in an area subject to recurrent ground fires.
Radial Mat Growth on Cedar Creek Bog, Minnesota
Authors: Buell Murray F. , Buell Helen F. , Reiners W. A.
Published: May 2006

A bog mat surveyed in 1934, and at irregular intervals since, was reexamined in 1967. After 33 years the position of the margin of the mat was essentially unchanged, but the width of the zones had changed. The Decodon on the aquatic margin had increased slightly, and the larch—shrub zone had expanded outward, greatly reducing the sedge mat. The indications are that the concentric zones surrounding open water expand and contract under changing conditions, principally fluctuating water levels.
"Sun Leaves" and "Shade Leaves": Differences in Convective Heat Dissipation
Authors: Vogel Steven
Published: May 2006

Temperatures of radiantly heated sun and shade leaves of white oak (Quercus alba L.) were measured in a low—speed wind tunnel. In either still air or a gentle updraft the difference between ambient and leaf temperature is about 20% less for the sum leaves than for the shade leaves. Consequently the former are more effective heat dissipaters.
Precipitation from Fog Moisture in the Green Mountains of Vermont
Authors: Vogelmann H. W. , Siccama Thomas , Leedy Dwight , Ovitt Dwight C.
Published: May 2006

Fog and low—lying clouds occur frequently on the higher slopes in the Green Mountains of Vermont. To determine the amount of precipitation contributed from cloud moisture, rain gauges were equipped with screen coils to intercept and collect cloud droplets. Screened gauges were paired with unscreened gauges and set out in forest openings along a mountain slope at 1,800, 2,800, and 3,600 ft. After 8 weeks the screened rain gauge at 1,800 ft collected slightly less water than the unscreened gauge. But at 3,600 ft, where clouds and fog are frequent, the screened gauge collected 66.8% more water than the unscreened gauge.
On the Distribution and Ecology of Cyclops Scutifer Sars in New England (Copepoda, Crustacea)
Authors: Elgmork K.
Published: May 2006

Cyclops scutifer Sars was found to be common in lakes in the Rangeley Lake area in Maine, and present in a few lakes in the northwestern corner of Connecticut. The species was found in deeper lakes in Connecticut than in Maine, which may be related to a dependence upon cold water, as in the warm season it occurs in cold, deeper layers of water.
Dispersal in Vertebrates
Authors: Murray Bertram G.
Published: May 2006

A hypothetical population is considered in order to gain insight into the factors that may be responsible for the skewed distributions of dispersal distances that have been reported in vertebrates. In this population the most effective factor is the relative dominance of the indivduals in procuring breeding sites. If this is true of natural populations, dispersal permits each individual to maximize its chance to reproduce. Earlier explanations that selection for genotypes that are advantageous to the species but disadvantageous to individuals are not necessary to explain the skewed distributions of dispersal distances in vertebrate populations.
A Statistical Method for Determining Quadrat Size and Adequacy of Sampling
Authors: Rice Elroy L.
Published: May 2006

A procedure is suggested to eliminate dependency on the species—area curve, based on the view that the most important fact of plant distribution is the distribution of quantity of material as indicated by cover, either areal (projective) or basal area. The first step in the procedure (applicable to density data also) is to determine the proper quadrat size to give a reasonably normal distribution of the desired data for the various species for which quantitative results are desired. The next step would be to determine how many quadrats of the determined size would be necessary to give reproducible data. It is suggested that the most satisfactory procedure to determine adequacy of sampling would be to obtain confidence limits for the mean from the sample estimates of the mean and standard error. If it is decided that the confidence interval for the mean based on a given number of qudrats is too broad, a larger sample is indicated.
Reproductive Cycles of Three Species of Anoline Lizards from the Isthmus of Panama
Authors: Sexton Owen J. , Ortleb Edward P. , Hathaway Loline M. , Ballinger Royce E. , Licht Paul
Published: May 2006

A study of the reproductive cycle of three species of lizards, a forest form, Anolis limifrons, a forest edge species, A. tropidogaster, and a grassland species, A. auratus, was carried out in the Isthmus of Panama from November 1965 until September 1969. The collecting sites were: Pacific side for all three species, mid—Isthmus for A. limifrons and A. auratus and Caribbean side for A. limifrons. Females of all three species of all sites were reproductively active during the wet season (May through December). For A. tropidogaster and A. auratus egg production almost ceases during the dry season. In A. limifrons egg production essentially ceases at the drier Pacific site and is reduced at the other two wetter ones during the same January—to—April period. The testes of males of all three species have mature spermatozoa during the dry season but mean testis weight declines from wet season highs. The male changes occur before the corresponding ones in their females so that the cycles of the two sexes may be controlled by different factors. Lipid levels of adults from the mid—Isthmus site show high values in the late dry season and lower ones throughout much of the wet season. Precipitation, food level, temperature, photoperiod, soil and leaf litter, wind, and evaporation are considered as cues influencing the cycle. The most likely candidate for the female cycle is precipitation with certain limitations. The flexible reproductive system of A. limifrons enables it to reproduce at low rates in some areas where the other two species must cease reproduction during dry periods.
The Foraging of Warblers Isolated on Small Island
Authors: Morse Douglass H.
Published: May 2006

In this paper I attempt to answer the question, What (if any) differences occur in the foraging of isolated wood warblers (Parulidae) and ones in large multispecies populations? Parula (Parula americana), Myrtle (Dendroica coronata), and Black‐throated Green (D. virens) Warblers were studied on seven small spruce‐clad islands off the coast of Maine, each island supporting one pair of one to three of these species. Data obtained were compared with earlier studies of these species in large adjacent populations. Though seasonally isolated, all individuals belonged to the large gene pools of the appropriate species on the adjoining mainland. While the insular forests resemble those of the mainland, they are in general shorter and more open. When only one species was present, it was always the Parula Warbler; when two species were present, they were always the Parula and Myrtle. Black‐throated Green Warblers only occurred in the presence of the latter two species. diversity increased as the size of forest and proportion of foliage in tree crowns grew. Parula and Myrtle Warblers experienced greater nesting success than Black‐throated Green Warblers. Black‐throated Green Warblers foraged much as they did in large populations; however, Myrtle and Parula Warblers demonstrated considerably more plasticity in foraging. When Black‐throated Green Warblers were absent, the two other species tended to modify their foraging. On the one island studied in detail where only Parula Warblers occurred, they appeared to expand their foraging range farther than where Myrtle Warblers were present. Overlap in foraging usually decreased as species compositions became more depauperate. Though variability occurred among individuals of each species, variability of an individual in two different years appeared as great. Black‐throated Green Warblers dominate the other two species socially, and the implications of this situation upon distributions in larger populations and on small islands are discussed. I hypothesize that the stereotypy of the Black‐throated Green Warbler represents an adaptation to the extremely high density it experiences in large populations, which make up the major part of the gene pool. The higher degree of plasticity seen in Parula and Myrtle Warblers may be appropriate to their subordinate roles.
Regulation of the Annual Testis Cycle by Photoperiod and Temperature in the Lizard Anolis Carolinensis
Authors: Licht Paul
Published: May 2006

Males of the lizard Anolis carolinensis are potentially continuous breeders but an annual testicular cycle is induced by seasonal climatic changes. Both photoperiod and temperature are involved as proximate factors in the regulation of testes activity but the importance of each varies with the phase of the cycle. The regenerative phase of spermatogenesis between late fall and spring is controlled primarily by temperature, whereas, the maintenance and eventual regression of the testis in late summer depends primarily on photoperiod. The male reproductive system shows a discrete period of photosensitivity; in nature the lizard shows photo—sexual responses only between late June and mid—October. It is the reduction in day length below about 13.5 hours (the critical day length) in August that induces gonadal regression. The onset and rate of regression is slightly retarded by high temperatures (32 degrees C). The critical day length and temperature dependence of these photoperiodic responses gradually change during the 4—month photosensitive period; and some photorefractoriness is evident early in this period. The factors that determine the onset of the photosensitive phase are poorly understood; short day lengths appear to be important for the termination of this phase. Photoperiod may also affect appetite and growth but these photoperiodic responses differ in several respects from the photo—sexual responses. The two types of photoperiodic responses have different seasonalities, critical day lengths and temperature dependencies. Analysis of the photo—thermal relations of testis activity in A. carolinensis in light of phenological and experimental data for testis cycles in other species indicates that considerable interspecific variation exists in saurian physiological adaptations.
Dispersal: Population Consequences and Evolution
Authors: Gadgil Madhav
Published: May 2006

Most animal and plant populations are divided into a number of local populations with some dispersal of individuals from one site to another. A theoretical investigation of the phenomenon of dispersal suggests the following consequences: Isolated and poorly accessible sites will tend to become less crowded than an average site as a result of dispersal. An episode of dispersal will result in uneven crowding at the various sites. Variation in the degree of crowding resulting from dispersal will depress the total population size of a species over its entire range. Variation in the carrying capacity with time will lead to an analogous depression of the mean population size. Spatial variation in the carrying capacities of the sites will favor a sensitive response leading to a rapid increase in the emigration rate with crowding, while variation with time will disfavor a response very sensitive to crowding. Variation in space will favor the emigration of a small fraction of the population, while variation in time will favor the emigration of a larger fraction.
Energy Budgets of Four Ponds in Northwestern Florida
Authors: Walsh Gerald E.
Published: May 2006

The annual energy budgets of four small ponds in northwestern Florida were calculated from the amounts of 1) solar radiation, 2) atmospheric long—wave radiation, 3) back radiation, 4) evaporative energy, 5) conducted energy, and 6) sensible heat which entered or was lost from the wager. Long—wave radiation constituted between 62.1 and 63.9% of the total incoming radiative energy and 80.8 to 85.0% of the total energy loss. Evaporative loss was between 14.6 and 18.3% of the total. Between 370,498 and 631,970 kcal m(—2)yr(—1) (37,050 — 63,197 cal cm(—2)y(—1)) were stored. Atmospheric radiation counteracts a portion of the radiative loss from water, thus reducing loss of stored solar energy.
Effects of Time of Day and Weather on Spider Catches with a Sweep Net
Authors: Lowrie Donald C.
Published: May 2006

The effects of time of day, season, trampling by the collector, cattle grazing, wetness of vegetation, and air temperature are analyzed for the size of sample catches of four species of oxyopid spiders living in a long—leafed pine community of northern Florida. All of these factors modify the sizes of sample catches although there are only slight changes, if any, in the population size. Therefore, changes due to these variables can cause erroneous population size estimates and judgments on the effects of ecological factors. Night collecting, warm winter weather, periods of heavy dew, and lack of cattle grazing contribute to greater catches of Oxyopes. Sweeping as a population sampling device may be inaccurate due to the inconsistency of these factors. Sampling must be supplemented with observation of spider activities (and the same probably applies to other inhabitants of the vegetation) to evaluate properly the results of sweepings and the causes of variation in catch sizes.
Fat Cycles and Condition Factors of Altamaha River Shad
Authors: Perkins Richard J. , Dahlberg Michael D.
Published: May 2006

The fat content and condition factor of American shad (Alosa sapidissima) and hickory shad (A. mediocris) in the Altamaha River drainage in Georgia are analyzed. The fat content of these anadromous species ranged from 5.1 to 17.8% for American shad and from 3.0 to 12.9% for hickory shad. In contrast to Pacific salmon (Oncorhynchus), fat content did not decrease with distance upstream, probably because of he relatively short and easy passage. The likely decrease in fat content with spawning was not statistically demonstrable because of the small number of spent individuals analyzed. Condition factor was not consistently related to fat content.
An Experiment to Determine Substrate Preference of the Fingernail Clam, Sphaerium Transversum (SAY)
Authors: Gale William F.
Published: May 2006

In substrate preference experiments, the fingernail clam, Sphaerium transverum, preferred mud (about 90% clay and slit). Sandy mud and sand ranked second and third, respectively. Clam movement during experimentation appeared random, with no detected differences due to current or innate dispersal tendencies. Experiments were conducted by using a circular substrate apparatus and a novel application of Latin—square statistical design.
Competition in the Semidesert Grass‐shrub Type as Influneced by Root Systems, Growth Habits, and Soil Moisture Extraction
Authors: Cable Dwight R.
Published: May 2006

Measurements of phenological development, herbage production, basal area, and density of annual and perennial grasses and of the half—shrub burroweed (Aplopappus tenuisectus (Greene) Blake), over a 4—year period show that production of each class of plant was affected to some extent by each of the others, except that annual grasses had no effect on burroweed crown area. Production of Arizona cottontop (Trichachne californica (Benth.) Chase), the dominant perennial grass, was restricted about 25% on plots with annual grass or burroweed competition and 46% by both together. Annual grass production averaged 18% lower with burroweed competition and 44—54% lower with perennial grass competition. Burroweed crown area increased 220% on plots with no perennial grass, but only 111% on plots with perennial grass competition. Presence of burrowed reduced perennial grass yield only moderately, because the root systems of burroweed and grass do not overlap greatly, and their main growth periods are at different seasons. High evaporation rates during the summer growing season masked most differences in moisture extraction between species. During the winter—spring growing period, on the other hand, burroweed depleted the available soil water rapidly, while water loss on perennial grass plots was little more than from bare soil.
A Laboratory Study of the Interaction Between the Predatory Rotifer Asplanchna and Paramecium
Authors: Maly Edward J.
Published: May 2006

The interaction between Asplanchna, predator, and Paramecium, prey, was studied in the laboratory using many experiments of short duration to insure maintenance of a uniform environment over a wide range of population densities. The results of the experiments were used to construct a vector map describing population changes. Regions of uniform vector direction were delineated to produce the isoclines of a graphical model formulated by Rosenzweig and MacArthur (1963). These isoclines were used to predict successfully the instability of this experimental interaction. The effect of time lag in predator response to changed food conditions was incorporated into the model. Time lag increases the instability of this interaction. The relationships between predator and prey and their physiologies determine the shapes of the isoclines. This analysis may be used to help explain other experimental results and naturally occuring situations.
Selection and Host Overlap in Two Desert Papilio Butterflies
Authors: Emmel Thomas C. , Emmel John F.
Published: May 2006

The two California desert Papilio (Lepidoptera: Papilionidae) species, P. indra fordi Comstock & Martin and P. rudkini Comstock, are frequently sympatric in range but mutually exclusive in host plant source. In 1966, optimal rainfall conditions led to a large simultaneous emergence of the adults of both species, synchronizing the growth of the resulting larvae, and larvae of both species switched to feeding on both foodplants wherever defoliation of the usual foodplant had already occurred from earlier larval feeding. By feeding on different foodplants in years of normal population levels, larval competition is avoided and many host plants remain unused. But apparently when population peaks are reached simultaneously, the selective advantage of separate hosts breaks down and direct competition through foodplant overlap occurs.
Population Structure in Overwintering Larval Odonata in North Carolina in Relation to Adult Flight Season
Authors: Paulson Dennis R. , Jenner Charles E.
Published: May 2006

The hypothesis that North Temperate Odonata can be categorized into spring or summer species by the predominant overwintering instars and the position and duration of the adult flight season was tested for 55 species in North Carolina. Over 3,000 larvae of these species, collected at a time of stable instar distribution (winter), were examined and the population structure determined for each species. The composition of the wintering populations varied from a single instar to (probably) the entire spread of instars, known for the species. The peak occurred in any one of the last four instars, depending upon the species. The spring vs. summer species classification is valid at high latitudes but breaks down at the latitude of North Carolina, where there is a continuum of variance from one type of life history to another.
Breeding Habits and Embryonic Thermal Requirements of the Frogs, Rana Aurora Aurora and Rana Pretiosa Pretiosa, in the Pacific Northwest
Authors: Licht Lawrence E.
Published: May 2006

Embryonic thermal adaptations of the frogs, Rana aurora aurora and Rana pretiosa pretiosa from the Pacific Northwest, are described. Limits of temperature tolerance of young R. aurora embryos are about 4—21 degrees C, both the upper and lower lethals being the lowest for any North American ranid frog. For R. pretiosa, the lethal thermal limits of young embryos are approximately 6—28 degrees C. The tolerance limits broaden as embryos become older, and embryos of both species can survive short—term exposure to normally lethal chronic cold temperatures. The developmental rates for embryos of both species at a wide range of constant temperatures are given. Egg masses of both species are compact and globular. The ova of R. aurora average 3.03 mm, those of R. pretiosa 2.31 mm. R. aurora embryos hatch at stage 21, and R. pretiosa embryos hatch at stage 19, a difference that may reflect the O2 needs of the hatching embryos. The O2 consumption by R. aurora embryos between developmental stages 12—15 at 18.5 degrees C averaged 0.59 cmm O2/egg per hour. R. pretiosa embryos at the same stage and temperature averaged 0.57 cmm O2/egg per hour. Field observations of breeding frogs indicate a correlation between breeding habits–such as initiation of breeding season, time of daily sexual activity, male calling behavior, and spawning site–and embryonic thermal requirements. High mortality of R. pretiosa embryos in the field often results from freezing temperatures at night and desiccation of egg masses. These factors do not greatly affect R. aurora embryos. These thermal adaptations of the two western species of Rana are compared with those of species from eastern North America, as an aid in broadening our understanding of the evolutionary strategies within the genus in North America.
Root Distribution of a Plantation‐Grown Red Pine in an Outwash Soil
Authors: Leaf Albert L. , Leonard Raymond E. , Berglund John V.
Published: May 2006

Root distribution and mass of a single dominant sample tree (17 m high, 20 cm diameter) in a 39—year—old Pinus resinosa Ait. plantation supported by a deep, stratified, outwash sandy soil were related to soil horizonation characteristics and aboveground tree components (foilage, branches, bolebark, and bolewood). All roots were excavated by hand in the A_p and B horizons and by 0.3—m depths in the C strata, were separated into five size classes, cleaned, dried, and weighed. Root—depth penetration terminated in a great number of fine roots in a thick, very fine sandy—silty stratum below the coarser textured solum at 2.7 m. Lateral root distribution was extremely variable; the maximum radial extent was approximately 9 m from the stump. Total root weight was approximately twice the total needle weight.
Modern Vegetation and Pollen Rain in Bladen County, North Carolina
Authors: Whitehead Donald R. , Tan Kiat W.
Published: May 2006

The different vegetation types within Bladen County, in order of areal dominance, are pine and hardwoods, mixed hardwoods, pocosin, mixed pine, and long—leaf pine. Basal area data from Continuous Forest Inventory (CFI) plots indicate that the most abundant trees, in order of frequency, are Pinus taeda, Liquidambar, Acer rubrum, Pinus serotina, Pinus australis, "bay" shrubs (Gordonia, Magnolia, Persea), Quercus spp., Liriodendron, Nyssa, Taxodium, and Chamaecyparis. The surface pollen spectra from the four lakes studied are extremely similar. The dominant pollen types are, in order of frequency, Pinus, Quercus, Cupressacaea–Taxodium, Nyssa, Liquidambar, Ambrosia, Carya, Corylus, Ericaceae, and Belta. Comparison of vegetation and pollen data indicates that Quercus is only sightly over—represented and Pinus more or less proportionately represented. This is in distinct contrast to findings in other areas. Among those types over—represented are Taxodium, Carya, Betula, Ulmus, Alnus, and Nyssa; those proportionately represented include Fagus, Juglans, Castanea, Populus, Salix, and Itea; those under—represented include Liquidambar, Ilex, Acer, Gordonia, Ericaceae, Cyrilla, Magnolia, and Liriodendron. The size of the lake may influence the character of the pollen rain, and the marginal vegetation mat (bay vegetation) may filter out pollen derived from xerophytes on the bay rims.
Experimental Zoogeography of Islands: Defaunation and Monitoring Techniques
Authors: Wilson Edward O. , Simberloff Daniel S.
Published: May 2006

In order to facilitate experiments on colonization, a technique was developed that permits the removal of the faunas of very small islands. The islands are covered by a tent and fumigated with methyl bromide at concentrations that are lethal to arthropods but not to the plants. Seven islands in Florida Bay, of varying distance and direction from immigrant sources, were censused exhaustively. The small size (diameter 11—18 m) and ecological simplicity of these islands, which consist solely of red mangrove trees (Rhizophora mangle) with no supratidal ground, allowed the location and identification of all resident species. The terrestrial fauna of these islands is composed almost exclusively of arboreal arthropods, with 20—50 species usually present at any given moment. Surveys of these taxa throughout the Florida Keys, with emphasis on the inhabitants of mangrove forests, were made during 1967 in order to estimate the size and composition of the "species pool." The seven experimental islands were defaunated in late 1966 and early 1967, and the colonists were monitored for 17—20 man—hours every 18 days. Precautions were taken to avoid artificial introductions during the monitoring periods.
Bird Mortality Following DDT Spray for Dutch Elm Disease
Authors: Wurster Doris H. , Wurster Charles F. , Strickland Walter N.
Published: May 2006

Avian populations in Hanover, N. H., a town that has sprayed its elms with DDT for many years in an attempt to control Dutch elm disease, were compared with those in Norwich, Vt., a town 1 mile (1.6 km) west of Hanover that has never sprayed. Hanover applied 109 lb DDT/acre (2.1 kg/hectare) in April 1963, then used Methoxychlor in April 1964. Population surveys were taken regularly during spring and early summer of these years, dead birds were collected in both towns, and 106 birds were analyzed for DDT, DDE, and DDD. Severe mortality of both resident and migrant birds occurred in Hanover during spring 1963, and the evidence implicates DDT as its cause. Robin loss was estimated at 70% of the resident population, or 350 to 400 individuals, but mortality among other species of widely varied feeding habits was also substantial. Feeding habits suggest that some birds acquired the toxicant by eating living insects carrying DDT, presenting the paradox of survival of the intended DDT victims, and death, instead, of insectivorous birds. Organ and whole bird analyses are presented and criteria for establishing cause of death are discussed. Most of the DDT had been converted to DDE and DDD, and residues were found in all organs analyzed. Robin mortality was reduced, but not eliminated following Methoxychlor application in 1964; these losses were believed caused by residual DDT in the soil. There was no evidence DDT poisoning among other species in 1964, though the dead birds collected were not analyzed.