bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of Leaf Resistance to Lodgepole Pine Transpiration in Wyoming
Authors: Fetcher Ned
Published: May 2006

Leaf resistance (r_L) of lodgepole pine (Pinus contorta ssp. latifolia [Engelm. ex Wats] Critchfield) was measured with an aspirated porometer at three sites in the Medicine Bow Mountains, Wyoming. In the early part of the growing season all the sites had low leaf resistances (3—5 s/cm) and few significant changes in r_L during the day. Towards the end of the growing season, in August, significant increases in midday leaf resistance occurred at all sites. The greatest increase (to 57 s/cm) was found on the driest site. Smaller increases (to 10—14 s/cm) were measured at a dry—mesic site and a mesic site. The results indicate that stomatal control of transpiration is more important towards the end of the growing season and that the degree of control varies with the soil water regime of the site. The response of r_L to soil H_2O status appears to be nonlinear. When based pressure potential readings were above an upper threshold ( ‐9 bars) r_L did not increase during the day. Below a lower threshold ( ‐17 bars) r_L increased significantly. Between the two thresholds, changes in r_L under high light conditions are explained more readily by the interaction between vapor pressure deficit and soil H_2O status than by either factor alone.
Phytotron Analysis of a Photoperiodic Response in a High Arctic Plant Species
Authors: Teeri J. A.
Published: May 2006

High arctic plants of Saxifraga rivularis require nearly continuous (23 or more h/day) irradiance of ° 0.3 ly/min for induction of floral development in growth chambers. A daily dark period of several hours' duration, or a daily low intensity irradiance period of ° 0.1 ly/min, of similar duration prevents flowering. A series of phytotron experiments showed that the plants produce preformed flower buds under a nonflowering light regime, and that the development of these buds is arrested at a developmental stage corresponding to that of the overwintering flower bud observed in the field. Approximately 7—9 days of continuous irradiance of 0.3 ly/min induces these preformed buds to flower. Both the spectral distribution of radiant energy and the total radiant flux density appear to be involved in the induction of floral development in the growth chambers.
Prey Selectivity and Switching Response of Zetzellia Mali
Authors: Santos Miguel A.
Published: May 2006

The predatory behavior of the mite Zetzellia mali was observed as the proportion of its three prey species changed. The prey were Aculus schlechtendali, Panonychus ulmim, and Tetranychus urticae. The predator preference remained constant as the proportion of he available prey changed. Unsuccessful attempts were made to alter predator preference by training experiments.
Determinants of Local Distribution and Abundance in White‐Footed Mice
Authors: M'Closkey Robert T. , Lajoie Daniel T.
Published: May 2006

To establish plausible explanations of the factors determining patterns of local distribution and abundance of white—footed mice, Peromyscus leucopus, concurrent measures of habitat structure, plant species composition, and mouse density were performed in several seral stages at Point Pelee National Park, southern Ontario. Population density covaries with foliage profile structure among habitats in which P. leucopus occur, whereas floristic composition is unimportant. White—footed mouse distribution and restriction to nongrassland habitats may be due to a significant structural difference between grassland and nongrassland habitats.
Bermudian Ants Revisited: The Status and Interaction of Pheidole Megacephala and Iridomyrmex Humilis
Authors: Lieberburg Ivan , Kranz Peter M. , Seip Anne
Published: May 2006

A survey of the distribution on Bermuda of the ant species Pheidole megacephala and Iridomyrmex humilis was conducted from August 6 to August 16, 1973. Based on 760 data points, Iridomyrmex appears to have established two new foci since 1966, one at Wreck Road and the other on the eastern end of St. Davids's Island, whereas Pheidole recaptured territory in the vicinity of Christ Church Leamington Caves, White Hill and Knapton Hill, the reclamation at the latter two sites begun in 1957 and 1963 respectively. Other than these changes, the overall distribution of the two species, as revealed in our survey, seems to be much more mosaic than seen in previous surveys. These observed changes in distribution suggest a need to reexamine the concept of the Iridomyrmex expansions as unidirectional. The fighting between Pheidole and Iridomyrmex that was occasionally observed probably took place at times when Iridomyrmex was attempting to expand its territory. Iridomyrmex was generally the aggressor and the victor. Baiting experiments were performed, the results of which indicate that Pheidole prefers clumped food resources, while Iridomyrmex prefers dispersed food resources. The potential for a partioning of the food resources suggests that the competition between Pheidole and Iridomyrmex is predominantly spatial. On the basis of our study, we believe an equilibrium between Iridomyrmex and Pheidole might be possible on Bermuda.
Long‐Term Responses of Cistus and Certain Other Introduced Shrubs on Disturbed Wildland Sites in Southern California
Authors: Juhren M. C. , Montgomery Kenneth R.
Published: May 2006

The performance of seven introduced shrubs in four genera planted for erosion control on 12 disturbed sites, was observed over a 10— to 20—yr period. The sites differed widely in elevation, steepness, soils, and climatic factors. Three species of Cistus proved satisfactory on most sites for 3 to 5 yr. On several sites they persisted as useful stands for 10 yr or longer, with promise of permanent self—maintenance in at least five cases. Plantings of Atriplex, Rosmarinus, and Baccharis species generally decline and did not reproduce. The length of the effective life of the Cistus stands depended on (1) water availability, in which the chief factor was sufficiency and timing of the winter rains, and (2) the development of tall native shrubs on the sites. Cistus plantings declined and did not reproduce when overtopped by tall chaparral. This failure is ascribed to lack of light. The need of Cistus seedlings for high light intensities was established experimentally. When low—growing native species invaded a site, Cistus grew compatibly with them. Cistus seedlings competed successfully with forbs and weeds but did not survive in thick grass. They spread aggressively over level areas of thin cover. On the hottest, driest inland sites, the original Cistus bushes became woody and senescent in about 12 yr. Management is recommended to reduce the fuel load in case of fire, and to stimulate growth of new bushes. Limits of cold tolerance were established for C. villosus at 1,790 m and for heat/drought tolerance of C. laurifolius at 930 m. The latter thrived at temperatures far lower than those of a mediterranean climate.
Seasonal Carbon Flow and Decomposer Parameter Relationships in a Semiarid Grassland Soil
Authors: Klein Donald A.
Published: May 2006

The microbial activities of soil cores removed from a semiarid grassland at 3—wk intervals from February to November 1972 were evaluated both with and without nutrient enrichments. Control, wetted, and substrate—treated core O2 utilization rates were measured over the first 3 h of incubation to provide information on seasonal changes in microbial substrate use patterns. Relationships between changes in decomposer parameters also were evaluated on a seasonal basis. Unamended soils showed highest microbial activity in the spring, followed by minimum O2 use and CO2 evolution in the dry summer period, the time when H2O additions caused maximum stimulation of O2 utilization with lower (° 0.7) respiratory quotients. Protein use was strongly correlated with field soil H2O content, followed by increased utilization of amino acids suggesting a sequential breakdown process. Glucose, starch, and cellulose use was independent of short—term changes in soil H2O content and appeared related to seasonal changes in plant root carbohydrage reserves, being minimum in summer and maximum in fall, the only time when marked cellulose use occurred. An all—year correlation showed strong relationships between changes in substrate availability, soil H2O content, respiration, and microbial populations, while on a seasonal basis shifts in the parameters controlling decomposer processes were observed. Respiratory quotients became more positive only during the spring period, a trend which was reflected in seasonal matrix correlations.
Chydorid (Cladocera) Ecology: Seasonal Patterns and Abundance of Populations in Elk Lake, Minnesota
Authors: Whiteside Melbourne C.
Published: May 2006

Population dynamics of chyorids from Elk Lake, Minnesota, were followed from May through October 1971 by means of three collecting methods. Emphasis was placed on data obtained by use of artificial substrate. This method was found to collect most species of chydorids living in the underlying substrate. A second method, funnel trapping, collected animals that migrated 10—20 cm vertically from their substrate into the funnel traps. Funnel trapping was found to be not very efficient at collecting all chydorid species, but to be useful for following overall population trends and for exploring the vertical movements of some species. A third method, called pattern sampling, was tried experimentally. It appears to collect most chydorid species, and also shows the mocro—distributions (or spatial arrangements) associated with population densities. Most chydorid species increase in population numbers during spring and fall, and decrease during midsummer. Chydoris have clumped or contagious patterns that fit the negative binomial distribution. A log/log relationship exists between estimates of the mean and variance over the sampling interval, May–October; this relationship establishes a relatively constant structural arrangement of patterns as reflected by the exponent k of the negative binominal, and by b of Taylor's power law. There are several possible explanations for chydorid clumping–heterogeneous habitat, aggregation about food sources, predation, lack of dispersal, and behavior. Future studies will be directed at evaluating the relationships between spatial patterns and population densities.
Drought‐Stress Avoidance in Three Pioneer Tree Species
Authors: Tobiessen Peter , Kana Tobb M.
Published: May 2006

Leaf resistance to water vapor flow was determined relative to leaf—water potential for white ash, quaking aspen, and bigtooth aspen. Ash leaves were found to close their stomata at approximately —20 bars and bigtooth aspen leaves at approximately —30 bars, whereas quaking aspen maintained low leaf resistance to —60 bars. This lack of control of water loss is suggested as a possible reason for the apparent moist site preference for quaking aspen in the study region. Bigtooth aspen may be able to survive in more xeric habitats than ash because of the latter's high leaf—water potential for stomatal closure.
Overlap, Similarity, and Competition Coefficients
Authors: Lawlor Lawrence R.
Published: May 2006

Several problems arise if niche overlaps are equated with species similarities or interspecific competition coefficients. Niche overlaps based on food types in the diet rely on proportional utilization rates of the different food types. But because proportional utilizations reflect consumer—environment interactions, measures of similarity based on such proportions may reflect similarities between environments rather than similarities between species pairs. Competition coefficients, as derived by MacArthur, weight renewable resources on the basis of their productivity–not their relative abundance. Use of proportional utilization rates intrinsically incorporates relative resource abundance and ignores differences in resource productivity. Thus, equating overlaps based on proportional utilizations with competition coefficients will overestimate the contribution of abundant resources, which will be actually less limiting if they are very productive. These problems are illustrated with the MacArthur—Levin's measure of niche overlap, but the same problems will arise with other measures of overlap. On the other hand, measures of species' similarities which are independent of resource abundance may reflect evolutionary divergence of consumers' resource utilization patterns due to past competitive pressures.
On Calculating Demographic Parameters from Age Frequency Data
Authors: Michod Richard E. , Anderson Wyatt W.
Published: May 2006

Caughley and Birch (1971) showed that the usual method for calculating age—specific longevities from the age distribution of living animals, mammals in particular, has built into it the assumption that r = 0. Consequently a set of li's calculated this way could not in turn be used with a table of fecundities to predict r. We show that when both the frequencies and fecundities of the age classes are known, provided that the fecundities correspond to what Leslie (1945) termed Fi, the assumption that r = 0. is unnecessary. It is a sample matter to calculate not only the li but r as well, assuming only a stable age structure. Formulas for doing so are given and applied, as an example, to data on the grey fox.
An Experimental Analysis of Reproductive Effort and Cost in the Japanese Medaka, Oryzias Latipes
Authors: Hirshfield Michael F.
Published: May 2006

Experiments measured the effects of differences in controlled temperature and food intake on reproduction, growth, and survival of female Japanese medaka, Oryzias latipes, a daily spawning killifish. Maintenance of isolated breeding females at nine different food—temperature treatments allowed the construction of individual energy budgets and hence the measurement of reproductive effort (the proportion of an individual's total energy intake devoted to reproduction). Increased temperature was associated with increased total reproduction and decreased growth at all food levels, although total production (sum of reproduction + growth) was essentially the same at all temperatures. Increased food intake led to higher fecundity at two of the three temperatures, while reproductive effort actually declined with increased food intake at two temperatures. Growth (change in female length, total mass, ovary size, and total energy content) increased with greater food intake at all temperatures. There was no evidence of an increase in reproductive effort with size or age; fecundity declined during the experiments although food intake was constant. Costs of reproduction included reduction in energy content of fish tissue and substantial loss of mass in many fish that nevertheless continued to reproduce at high levels. Reproduction and growth were in general negatively correlated, suggesting that individuals reproducing the most were not able to grow as rapidly as individuals reproducing less. Mortality varied substantially (0—30%) among the treatments and was highest at high temperatures and high levels of reproductive effort.
Three Types of Remote‐Reading Dendrographs
Authors: Phipps Richard L. , Yater Wallace M.
Published: May 2006

Three types of remote—reading dendrographs operate long periods of time in such remote locations as high in trees. They are easy to install, have weatherproof housings, and may be read by any of a variety of resistance—measuring recorders of meters.
Loblolly Pine Rooting Varies with Microrelief on Wet Sites
Authors: Lorio Peter L. , Howe Virgil K. , Martin Carolyn N.
Published: May 2006

Loblolly pine root systems on flat or slightly concave sites had significantly less surface area and dry weight in fine roots (<5 mm) in the top 15 cm of soil than comparable neighbors on low mounds. Surface area of mycorrhizal tips was usually lower on the intermound areas over a 2—year sampling period. Root mapping in soil pits and root washing revealed differences between mound and intermound areas in terms of root numbers, distribution, and condition that indicated the eventual development of deficient root systems and intermittent severe moisture stress on flat sites. These conditions probably contribute to premature tree decline and tree susceptibility to bark beetle attack on such areas.
The Adaptive Nature of Seed Germination in Nemophila Menziesii Aggr.
Authors: Cruden Robert William
Published: May 2006

Nemophila menziesii aggr, includes three closely—related winter annual plants found in many communities in cismontane California and Oregon. The germination response is adapted to the Mediterranean climate that characterizes the region, i.e., wet winters and dry summers. The seeds germinate in late fall or early winter and are inhibited from germinating during late spring, summer, and early fall by high temperatures, long photoperiods, and low available moisture. Temperature and photoinhibition are proportional to the length of the inhibitory period and, in the case of photoinhibition, to light intensity. In combination these factors interact synergistically to inhibit the germination response. Seeds of all ages are able to germinate but germination of young seed is inhibited at temperatures that do not affect mature seed. Seed maturation is a function of high summer temperatures and aging. Populations from more northern and/or higher—elevation communities require more water and lower temperatures to germinate than more southern and/or lowest—elevation communities. These adaptations reflect the greater precipitation and cooler temperatures of the former sites as compared to the latter sites. The ecological parameters and germination responses change gradually both latitudinally and elevationally; hence the adaptations are ecoclinal in nature.
The Estimation of Population Size with Equal and Unequal Risks of Capture
Authors: Wilbur Henry M. , Landwehr James M.
Published: May 2006

Behavioral characteristics and microhabitat distributions of individuals may cause heterogeneity in their risk of capture in field studies of the dynamics of natural populations. The number of recaptures of marked individuals can be used to test for equicatchability by their fit to a Poisson distribution. If the null hypothesis of equal risk of capture is rejected the number of captures per individual may follow a negative binomial distribution. The use of truncated distributions to estimate the number of transients in the population, or the number of animals never caught is found to be of very limited value. These methods are applied to an original set of capture histories from a study of a population of the painted turtle, Chrysemys picta.
A Method for Detecting Migration of Forest Vegetation
Authors: Leak W. B. , Graber R. E.
Published: May 2006

A theoretical method is described for detecting and estimating the rate of tree— and shrub—species migration based upon measurements of maximum and minimum age along a transect. Age data from Mt. Washington indicate that the method does detect migration trends under field conditions, although appreciable variation is encountered.
A Model Explaining Successional Change in Standing Crop of Thermal Blue‐Green Algae
Authors: Fraleigh Peter C. , Wiegert Richard G.
Published: May 2006

The gross productivity and changes in the standing crop of both biomass and chlorophyll @a were measured during ecological succession in thermal blue—green algal community. The rate of gross production (Pg) in gC°m—2°h‐1 was directly related to the chlorophyll α (Chl) in mg°m—2 and independent of light intensity (Pg = 0.018 chl0,51). In turn we found a log—log relationship of chlorophyll α (mg°m—2) to biomass (x) in g°m—2 (Chl = 0.59 x1,40). The respiration rate (R) in gC°m—2°day—1 of the algal mat was directly proportional to the biomass (R = 0.0164 x). The increasing concentration of chlorophyll α per unit biomass as succession proceeded in these thermal ecosystems contrasted with the decreasing chlorophyll concentration noted in other ecosystems. The equations were combined into a nonlinear model, and algal growth during succession was predicted on the basis of algal density, free CO2 concentrations in the water, and day length. These predictions agreed closely with field data on biomass increase during succession.
Physiological Ecology of Three Codominant Successional Annuals
Authors: Wieland N. K. , Bazzaz F. A.
Published: May 2006

Setaria faberii, Abutilon theophrastii, and Polygonum pensylvanicum growing together in a 1—yr successional field exhibit differing daily patterns of leaf water potential; S. faberii develops and maintains more negative water potentials than A. theophrasti, and P. pensylvanicum maintains much less negative water potential than either species. Setaria faberii and P. pensylvanicum do not light—saturate at 1.1 x 105 lx irradiance while A. theophrasti approaches light saturation at 8 x 104 lx, indicating that the species are adapted to high light intensities of the open field. In the field, leaf temperatures are maintained appreciably below air temperatures and are in the range of temperatures consistent with near—maximal photosynthetic rates. Under optimal conditions the rates of photosynthesis are 38, 24, and 18 mg CO2°dm—2°h—2 respectively for S. faberii, A. theophrasti, and P. pensylvanicum. Setaria faberii maintains near—maximum photosynthesis down to water potential of —12 bars, photosynthesizes at 30% of maximum at —24 bars, and recovers from potentials of —50 bars. In A. theophrasti photosynthesis remains unchanged to —10 bars, and becomes negligible at °—26 bars. In P. pensylvanicum photosynthesis begins to decline sharply at potentials of —6 bars; it becomes negligible at —18 bars; and the plants die at —20 bars. The root systems of the three species grow in different parts of the soil resource; the root system of S. faberii is fibrous and shallow; the tap root of A. theophrasti is sparsely branched and extends to intermediate depths; the tap root system of P. pensylvanicum is moderately branched in the upper soil layers and proliferates mostly below the rooting zone of the other two species. The three species have evolved differing intercompenstory mechanisms for habitat exploitation. One apparent niche difference among the species that allows for their coexistence is the exploitation of various levels of the soil and consequently different moisture resources.
Parasite‐Induced Alterations in Host Reproduction and Survival
Authors: Lanciani C. A.
Published: May 2006

The effects of a parasitic water mite, Hydryphantes tenuabilis, on the reproduction and survival of its aquatic insect host, Hydrometra myrae, were determined through laboratory rearing experiments. The parasite attaches to any of the five immature instars of the host but uses these stages only as an indirect route to the parasitism of the adult, the only stage from which the parasite extracts appreciable amounts of nutrient. Accordingly, the parasite had no effect on the immature stages of the host but changed the reproductive and survival characteristics of adult ♀ ♀. Highly significant differences between parasitized and unparasitized female hosts were shown in survivorship and age at which oviposition began. Once oviposition began, formerly parasitized ♀ ♀ laid as many egges as formerly unparasitized ♀ ♀ in the earlier segments of their respective m(x) distributions. The results suggest that parasitic water mites in loads observed in natural populations should reduce the rate of population increase of the host. Approximate values of the instantaneous rates of increase of each experimental and control host group were calculated, and the rates of the control (unparasitized) groups were found to be higher at all food levels offered to the host. Adjusting the rates of increase by assuming that survivorship was perfect for all hosts and that oviposition of experimental hosts began on the same day as the controls produced a high level of convergence in the rates of increase of all host groups within any food level and emphasized the importance of parasite—induced alterations in survivorship and age of first oviposition in determining rates of population growing of the host.
A Computer Program for Fitting Tracer Kinetic and Other Differential Equations to Data
Authors: Marten Gerald G. , Kleiber Pierre M. , Reid J. A. Keith
Published: May 2006

A computer program is available for fitting any linear or nonlinear ordinary differential equations to data, and for estimating transfer rates and/or compartment sizes from time—series tracer data in a compartmental system. The program is easy to use because compartment problems are specified simply in terms of the geometry of the components and transfers between them. The program generates confidence limits for the estimates, a feature that can be used to examine in advance the effectiveness of proposed tracer experiments.
Biogeography of the Puerto Rican Bank: Introduction of Species onto Palominitos Island
Authors: Levins Richard , Heatwole Harold
Published: May 2006

Frogs, snails, and a rainforest Drosophila introduced to a small sandy cay became locally extinct almost immediately, probably because microhabitats suitable for avoiding the extremes of physical environnemt were lacking. Two introduced species of lizards and one ant species, all three of which have been known from habitats similar to that of Palominitos, survived for from several weeks to about 1 year. Their eventual extinction was probably due to biotic factors: absence of a suitable habitat in which the introduced species had an advantage over its native competitors, predation (between lizard species), and a general advantage of established populations (mature ant colonies, lizards with territories) over an immigrant propagule. An argument is presented that if the rigors of the physical habitat reduced life expectancy by less that 60% below that of a species' optimum habitat this will not be sufficient to prevent its establishment, but a reduction of over 90% is almost certainly enough to exclude it.
The Effects of Hurricane Camille on the Marshes of the Mississippi River Delta
Authors: Chabreck Robert H. , Palmisano A. W.
Published: May 2006

The active delta of the Mississippi River was sampled in August 1968 to determine plant species composition, plant coverage, and soil and water chemistry. Hurricane Camille struck this area in August 1969, with winds in excess of 200 km/h and tides raging upward to 5.2 m above MSL. The delta was resampled 2 weeks following the hurricane to evaluate the immediate effects on vegetation, soil, and water, and again 1 year after the hurricane to determine the recovery rate of vegetation. The hurricane resulted in a drastic reduction of vegetation. Regrowth was rapid in the delta marshes and after 1 year plant coverage approached pre—hurricane levels of abudance; however, recovery was slower in ponds and lakes. The loss of vegetation was mainly a result of the sweeping action of wind and water, and plants were either uprooted or ripped apart and carried away by the current. Water salinity increased with the hurricane but declined by the following year and appeared to have only slight effect on marsh vegetation. Plant species caried in their response to the hurricane. Bacopa monnieri showed practically no effect, and Phragmites communis and Spartina alterniflora were reduced only slightly. Myriophyllum spicatum, Panicum repens, and Alternanthera philoxeroides were greatly reduced by the storm: and after 1 year, only Alternanthera philoxeroides showed significant recovery.
Social Influences on Trap Response of the Cotton Rat, Sigmodon Hispidus
Authors: Summerlin Carl T. , Wolfe James L.
Published: May 2006

The role of social rank in heterogeneous trap response by cotton rats (Sigmodon hispidus) was investigated. Data from field and laboratory trapping indicate that dominant animals are more trap prone than are subordinates. Social subordination appears to inhibit trap response in several ways. Subordinate animals exhibit less exploratory activity and a neophobic response not shown by domnants. Low—ranking animals also tend to avoid traps treated with conspecific scent, whereas dominant animals do not.
Ecological Energetics of a Homeothermic Predator, The Short‐Tailed Shrew
Authors: Randloph J. Collier
Published: May 2006

A detailed examination of the thermal and chemical energy fluxes of an individual predator is used in estimating seasonal energy transfer from prey populations to predator populations. The short—tailed shrew, Blarina brevicauda, was selected as the predator because it is a homeotherm that is active during the entire year. Blarina has a combination of metabolic, insulative, and behavioral adaptations permitting survival through a wider range of environmental temperatures than usually occur in its typical habitat. Both insulative and metabolic modifications occur seasonally. Within the range of 0 degrees to 25 degrees C, Blarina metabolism is inversely porportional to ambient temperature. At any given ambient temperature heat loss is lower from winter shrews than from summer shrews. Winter shrews at winter temperatures have a higher metabolic rate than do summer shrews at summer temperatures. Blarina has a digestive efficiency of about 0.90, which is not affected by seasonal temperature changes. Changes in the thermal environnemt have a more pronounced effect on a shrew's energy requirement than do changes in the daily level of locomotor activity. Blarina's metabolic rate during normal exploring locomotor activity is approximately double that during sleep. Existing models of assimilation and heat transfer in animals were used as subsystem components in a deterministic model. The model estimated that the winter food requirement of the predator population is about 43% higher than the summer food requirement. A population of 20 Blarina in a 6.47—acre deciduous woodlot near Manotick, Ontario, would require only about 3% of the total prey energy base during the summer and about 37% of the prey energy base during the winter. The prey energy available per square meter of forest floor during the summer is estimated to be about eight times that available during the winter. A population of 20 adult Blarina should experience little difficulty in obtaining sufficient food both during summer and winter.
Effects of Herbicidies on Species Diversity of Two Plant Communities
Authors: Tomkins D. J. , Grant W. F.
Published: May 2006

Six community statistics were computed to describe the structure of two plant communities and the effects of herbicide perturbation on community structure and composition. It was found that the number of individuals and the total plant height were correlated, and the three diversity components (species number, community dominance, and information content) were highly correlated. Auxin herbicides caused an increased in the number of grass with marked and persistent simplification of both community types. the nonselective herbicide, Diuron®, also induced a very simplified community, but with no change in the graminoid: forb ratio. Simazine® treatment also had long—lasting effects on species diversity, but resulted in a more complex vegetation than found in control plots with a much lower cover of broadleaf weeds. Paraquat® initially eliminated both monocotyledons and dicotyledons, but vegetation recovered rapidly. However there was a long term effect on the composition of the recovered vegetation. The resistance to modification by herbicides was greater in the old field community that in the recently disturbed one.
Tritium‐Determined Water Flux in The Free‐Roaming Desert Tenebrionid Beetle, Eleodes Armata
Authors: Bohm Bruce C. , Hadley Neil F.
Published: May 2006

Tritated H2O was used to measure H2O exchange in field and laboratory populations of the desert tenebrionid beetle, Eleodes armata. Free—roaming individuals were monitored in natural desert enclosures. Mean total body H2O determined istopically (TBWi) was 74.5% compared to 65.9% measured gravimetrically. Water loss rates determined istopically (WLRi) for beetles decreased as the summer progressed (early summer, .079 ml ° g—1 ° day1; late summer, .062 ml ° g—1 ° day—1). The biological half—life of tritium (T½b) for these respective groups was 6.4 and 8.2 days. Significantly lower WLRi (.032 ml ° g—1 ° day—1) were obtained for noncaptive winter beetles. WLRi and T½b values for beetle confined to artificial burrows (no food or water) were not significantly different from values for free—roaming beetles during either season. WLRi for fed and hydrated beetles maintained in the laboratory under simulated summer conditions were four times higher than WLRi for food and water—deprived beetles. Tests conducted on similar groups under simulated winter conditions produced no significant differences in WLRi or T@2b. These data are discussed in reference to biotic and physical factors affecting H2O flux, limitations of the isotope technique and the research design employed, and compared to published data on other desert species.
Aspects of the Biology of Trientalis Borealis Raf
Authors: Anderson Roger C. , Loucks Orie L.
Published: May 2006

Three species and one subspecies of Trientalis are recognized in North America, but only Trientalis borealis Raf., the northern starflower, occurs in eastern North America. The life cycle consists of three distinct phases each year: shoot development, rhizome growth, and tuber formation. Asexual reproduction by tubers is more important than reproduction by seed. Of the annual dry matter produced, 64.8% is apportioned to asexual reproduction and less than 2% to sexual tissue. Rhizome growth and tuber formation are regulated by photo—period; short days favor tuberization and long days favor rhizome growth. Tuber formation under field conditions began in July, when the photoperiod was about 15 hr. Cool nights and warm days were more favorable for the accumulation of dry matter than warm nights and days. The number of degree—hours accumulated during shoot development of northern and southern populations was similar at sites 200 miles apart on a north—south gradient, but shoot development occurred during a shorter period of time at the northern site. Seedlings of T. borealis have not been found in the field, but relatively high germination rates were achieved under laboratory conditions, Cold treatment increased the percentage germination of trientalis borealis seeds. Ninety days of stratification delayed the period of peak germination and increased the length of time before germination began after the seeds were exposed to room temperatures. The duration of germination and peak period of germination after stratification were about the same for controls and seeds exposed to 30— or 60—day periods of stratification.
Changes in Arctic Eriophorum Tussock Communities Following Fire
Authors: Wein Ross W. , Bliss L. C.
Published: May 2006

The arctic cottongrass (Eriophorum vaginatum ssp. spissum) tussock community is susceptible to fire even though it has a relatively small aboveground standing crop and the peaty substrate is wet even in years of low precipitation. While burns can be severe enough to kill all aboveground plant parts, differential protection is provided new shoots by tussocks bases, moss mats, and peat. Plant succession following fire was unique in that no new species invaded the area. Growth came principally from root stocks protected by the organic surface. Cottongrass and Carex spp. were the first to show regrowth following a June fire at one site. The role of cottongrass seedlings in colonizing these tussock communities was minor, because few seedlings older than 1 year were found on any of the sites. Epilobium angustifolium ssp.angustifolium and some Calamagrostis canadensis ssp. canadensis originated from seed although most plants of the latter species had long vigorous rootstocks. These plants occurred as minor components in the undisturbed community and increased when fire destroyed the competing species. The charred organic surface, being very dark, absorbed more short wave energy and the active layer depth increased by 35 to 50% in June and as much as 25% by late autumn. The same thermal regime was found in burns several years old. This warmer soil mass, over a longer period of time, was conducive to better growing conditions. Annual plant production had almost recovered after two growing seasons, and nutrient content of the plants was higher in the burned area. This may be due to the greater soil mass available for root exploration, to nutrient release by fire, and to greater microbial activity in the warmer soils. If other tundra communities respond to fire in a similar manner as cottongrass tussock communities, fires may act as a rejuvenating factor, as they do in other biomes
The Influence of Feral Goats on Koa Tree Reproduction in Hawaii Volcanoes National Park
Authors: Spatz Gunter , Mueller-Dombois Dieter
Published: May 2006

Goats were introduced to the Hawaiian Islands nearly 200 years ago. They have become wild and today roam in many Hawaiian ecosystems with dry—season climates from the lowlands to the mountains. A quantitative analysis was made to evaluate the influence of feral goats on tree reproduction of Acacia Koa var, hawaiiensis Rock in the mountain park—land ecosystem on the east flank of Mauna Loa. In this ecosystem, the endemic koa is the only important tree species. Here it reproduces vegetatively from root suckers. Suckering has resulted in the formation of small, dense tree colonies. Ten transects were established through a goat exclosure constucted 3 years earlier (in 1968). In addition, six transects were run across several typical nonfenced koa colonies. All suckers were counted, measured for height, and mapped. It was shown that koa reproduction below 10 cm height is abundant outside the exclosure and at the unfenced colonies, but almost totally missing are suckers between 0.5 m and 2 m height. However, hundreds of this height grow inside the goat exclosure. Most of the few trees of this height found outside the fenced area were dying or dead, showing that the current goat pressure is so high that the replacement cycle of koa is nearly disrupted. The vigorous growth of suckers inside the exclosure was a direct response to their release from goat browsing. In contrast, the high stocking density of suckers was a response to goat browsing prior to fence construction, since it was found that goat feeding of small herbaceous suckers increased suckering density at the fringes of the existing koa colonies. Trampling on shallow roots may contribute to an increase in suckering density. When released from goat pressure these suckers grow into stands probably much denser than those that existed before goats were introduced to the islands. From the viewpoint of community evolution on islands, this distortion of stocking density is unnatural.
Preliminary Measurements of Midsummer Metabolism in Beds of Eelgrass, Zostera Marina
Authors: Nixon Scott W. , Oviatt Candace A.
Published: May 2006

Measurement of community metabolism in a coastal pond eelgrass bed gave values of 2.9 g O2 m—2 day —1 for apparent production and 3.6 g O2 m—2 day—1 for night respiration. The excess of consumption over production during a full day in early August is indicative of the declining state of the plants by midsummer. Measurements of upstream—downstream dissolved oxygen in a tidal river eelgrass bed showed unusual transients and occasional high values for production and respiration. These observations may have been related to turbulent tidal transport, to exchanges of oxygen between the water and lacunar spaces within the Zostera, and to higher metabolic rates in faster currents.
Influences of Ambient Temperature on Ground Squirrel Activity
Authors: Kavanau J. Lee , Rischer Carl E.
Published: May 2006

Detailed observations of the locomotor activities of antelope ground squirrels reveal what may be an important avenue for thermoregulation. Four squirrels in an indoor enclosure were exposed to temperature cycles of various amplitudes with upper limits from 28° to 37°C. By monitoring properties of the volitional running performance in an activity wheel, sensitive behavioral responses to the temperature changes were detected. The time spent running, the average duration of running bouts, and the speed of running were affected–the first two properties to a much greater extent than the third. In one test the time decreased over 11% per degree rise; in another the length of the running bouts decreased over 8% per degree rise. These behavioral responses are interpreted along thermoregulatory lines. The responses were undetected in previous studies, for the animals either were unable to run or were forced to run continuously at fixed speeds. Since one can determine both behavioral and physiological responses of animals running voliationally, and many mammals will run wheels, this technique has promise for comparative studies for thermoregulation.
A Computer Technique for Illustrating Three Variables in a Pictogram
Authors: Siccama Thomas G.
Published: May 2006

A technique is described for displaying three—dimensional data by using the overprinting capability of digital computer printing units. The procedure is illustratd by mapping the distribution of species—abundance characteristics and physical features on several study areas based on data from systematically placed field sampling points.
Seasonal Food Habits of Anolis Limifrons
Authors: Sexton Owen J. , Bauman Joan , Ortleb Edward
Published: May 2006

The seasonal food habits of Anolis limifrons, an iguanid lizard, were studied by examining the stomachs of 512 individuals collected on Barro Colorado Island, Panama Canal Zone, during three periods. Frequency and length of prey and length of predators were determined. Frequency distributions of different size classes of potential prey were obtained from leaf litter and low vegetation samples. The lizards selected larger size classes of potential prey. All size classes of predators captured the smaller size classes of prey, but the larger prey were taken by larger predators. More female than male lizards had food in their stomachs. There was no wet season—dry season difference in frequency of food found in the stomachs.
Diel Metabolism and Nutrient Dynamics in a Salt Marsh Embayment
Authors: Nixon Scott W. , Oviatt Candace A. , Garber Jonathan , Lee Virginia
Published: May 2006

Simultaneous measurements of the diel patterns of dissolved O_2, pH—CO_2, dissolved organic nitrogen, ammonia, nitrite, nitrate, dissolved organic phosphorus, phosphate, and silicate were made on four occasions in a shallow salt marsh embayment (Bissel Cove, Narragansett Bay, Rhode Island, USA) that was closed to tidal water exchanges for 24—h periods. In spite of high rates of community photosynthesis and respiration, there appeared to be little diel change in dissolved nutrient concentrations, especially with respect to inorganic nitrogen. During summer and early fall, inorganic nutrients appeared to cycle within the sediment—detritus system of the embayment bottom, rather than being released to the overlying water. This suggests that there would be little export of inorganic nutrients from the marsh during tidal exchanges with the estuary. The behavior of this marsh embayment contrasts with reports from other marsh areas where large net imports or exports of nutrients have been observed. The concentrations of dissolved organic phosphorus and nitrogen were higher than inorganic forms, and showed substantial variation over each diel sampling period. The relationship between photosynthetic or respiratory gas exchange and nutrient cycling in water influenced by benthic community metabolism is subtle and complex, and cannot be adequately approximated by simple models such as the Redfield ratio.
Linear Population Models with Stochastic Time Delays
Authors: Lewis E. R.
Published: May 2006

Previously it was shown that reproductive—cycle parameters such as time to maturity, ovulation interval, gestation period, duration of regression, duration of nonreproductive lactation period, and the like, can be incorporated into population models rather easily through the use of a simple network approach. In this paper, the network approach is extended to include the same types of reproductive parameters when their values are not necessarily fixed, but may vary randomly from one member of a population to the next and/or for a given member from one time to the next. It is shown that linear transforms of the parameter distribution functions can be incorporated directly into the network models and that analysis of the resulting dynamics follows in a straightforward manner, the characteristic dynamical equation being obtainable by inspection with Mason's algorithm and the roots of the equation being obtainable by direct analysis in simple cases or by well—established numerical methods in complicated cases. The roots themselves can be interpreted directly in terms of dominant patterns of population growth and deduced propensity of the population to sustain oscillations triggered by external stimuli. In the case of a simple natality cycle with gamma, negative binomial, and binomial distributions of maturation times, it is shown that the dominant growth pattern approximates rather closely that expected for a nonrandom maturation time equal to the mean of the distribution, and that the propensity to sustain population oscillations decreases markedly both with increasing standard deviation and with increasing (positive) skewness in the distribution.
Distribution of Summer Birds Along a Forest Moisture Gradient in an Ozark Watershed
Authors: Smith Kimberly G.
Published: May 2006

Vegetational and physical habitat factors were measured in 110.0.05—ha circular plots around singing ♂ ♂ of eight bird species in a small watershed in northwestern Arkansan during June and July 1973. Sixty birdless plots were similarly sampled in the driest and most moist areas of the watershed to determine a forest moisture gradient. Principal component analysis of the combined avian community habitat data determined that the forest moisture gradient is important in the distribution of the birds, although multiple analysis of variance showed that no one factor can account for the significant distribution. Principal component analysis of the individual species determined the unique characteristics of the realized niches of each species. An ordination of the species using linear discriminant function analysis of the 60 forest samples was similar to the ordination based on the bird distribution, but suggests that other factors are determining the precise distribution of the birds. No species shows a great affinity for the drier forest, although Tufted Titmice seem able to utilize the moist and dry forests equally. The Hooded Warbler, Ovenbird, and Acadian Flycatcher have shorter niche widths than early arriving migrants and permanent residents and can be considered obligatory moist forest species. The results show that the moist forests is of great importance to the avian community and reasons for the lack of birds in the dry forest are discussed.
A Comparison of Ecological and Morphological Overlap in a Peromyscus Community
Authors: Smartt Richard A.
Published: May 2006

The hypothesis that morphological structure of a community should reflect ecological structure (trophic relationships) was tested in this paper. An assemblage of closely related sympatric species of Peromyscus was studied to see how closely morphological structuring can describe actual food—use relationships in a community. Animals were collected during 4 different seasons and stomach contents were analyzed to reveal the diet of each species. A morphological analysis of the assemblage of Peromyscus was accomplished through the analysis of 4 external and 69 skeletal characters. Morphological and trophic relationships were computed using principal components and distance analysis. A positive relationship between morphological and ecological packing is shown by a correlation coefficient computed between food—use distances and morphological distances. Microhabitat use and foraging behavior are discussed in an attempt to expose actual mechanisms of competitive interactions.