bluuebunny/crossref_metadata_2025 huggingface dataset:
Water Losses of the Sand Goanna (Varanus Gouldii) In Its Natural Environments
Authors: Green Brian
Published: May 2006

Rates of water loss were measured in Varanus gouldii inhabiting two areas of different aridity. In the subhumid area a distinct seasonal cycle in water loss was evident, the rates being highest in summer and lowest in winter. Water losses in the semiarid area in summer were highly variable and were closely correlated with the variable activity of the goannas. Animals in the semiarid environment are able to reduce water output by remaining in burrows for extended periods. The water turnover rates of V. gouldii are much lower than those reported so far for other vertebrates. This study demonstrates the effectiveness of physiological and behavioral mechanisms of water conservation in terrestrial reptiles.
Delay‐Line Models of Population Growth
Authors: Lewis E. R.
Published: May 2006

Replacing the usual principle of conservation of numbers with the equivalent principle of continuity of flow (or rates) leads to a very heuristic approach to modeling time lags in populations. The approach allows the direct use of unequal time lags (or age classes of unequal lengths) without the implicit assumption of a stable age distribution. Furthermore, for simple, linear natality processes, it allows direct estimation of the biotic potential and of the frequencies of inherent oscillations.
Adaptation in Clarkia, Section Myxocarpa
Authors: Small Ernest
Published: May 2006

The adaptive relationships of the eight diploid taxa of Clarkia, section Myxocarpa, are documented. The phylogeny of these taxa is well understood, allowing precise comparisons of the state of adaptiveness between related taxa in relationship to differences in their habitats. The habitats of these taxa comprise distinctive combinations of precipitation, temperature, and soil characteristics. Differences between the taxa were found with respect to rates of maturation, photosynthesis, transpiration, and leaf characteristics, all of these apparently adaptive in relation to drought. The two populations from the most unfertile soils produced the smallest seeds in a standard garden, and it is suggested that small seeds may be advantageous in annual plants in an unfertile substrate when droughts depauperize and decimate the population.
Comparison of Ordination Techniques
Authors: Gauch H. G. , Whittaker R. H.
Published: May 2006

Eight ordination techniques are described and their performances measured by two statistics under a variety of conditions using simulated coenocline data. The Bray—Curtis ordination using S°rensen's coefficient of community, is found to be best in general, and Principal components analysis the worst. The resemblance functions are found to work from best to worst in the order: coefficient of community, percentage similarity, and Euclidean distance. Beta diversity has a very strong impact upon ordination efficacy, and sampling errors exert some effect; relativizing data or varying alpha diversity has relatively little effect. Causes of these results are implications for improving ordination techniques are discussed.
Distance Measurements in Vegetation Study
Authors: Ashby William C.
Published: May 2006

Plotless vegetation sampling including the quarter method results in a systematic bias if measurements "to the tree" are used in place of the center of the tree trunk. Widely used references show "to the tree" measurements which lead to overestimates of density, productivity, and other parameters.
Reproduction, Growth, and Development in Myotis Thysanodes and M. Lucifugus (Chiroptera: Vespertilionidae)
Authors: O'Farrrell Michael J. , Studier Eugene H.
Published: May 2006

Studies of reproduction and pre— and postnatal growth and development in Myotis thysanodes and M. lucifugus showed that female M. lucifugus copulated in the fall prior to their exodus from the summer roost while M. thysanodes copulated sometime after leaving the summer roost but before their spring return. Ovulation, fertilization, and implantation occurred during the first 2 weeks of May for both species. Gestation has been calculated as 50—60 days for both species. Parturition in M. thysanodes is synchronous with nearly all births within a 2—week period at the end of June and beginning of July. Myotis lucifugus, however, gave birth over a period from June through August. Logarithmic regression lines were calculated for daily prenatal weight increase for both species. Myotis lucifugus grow more rapidly and weigh significantly less than M. thysonades. Regression equations for daily postnatal weight, forearm length, wing span, and fifth—finger length increase in M. thysanodes were calculated and found to be good criteria for estimating age to about 21 days, after which this species has attained adult size. Estimated neonate mortality was low, about 1% for M. thysanodes and 2% for M. lucifugus. Myotis thysanodes was capable of limited flight by 16.5 days of age and of adultlike flight by 20.5 days of age. Myotis lucifugus parallels this attainment of flight quite closely. Wing loading for both species increases slightly from birth to 6 days, followed by a decline to half the birth value at day 20. Aspect ratio for both species increases at steady rate from birth to about 16 days, when it decreases slightly to the adult value. There was no relation of fat index to age in either species, but significant decreases in water index were found with increasing age. Both species demonstrated significant decreases in percentage water and increases in percentage organic and mineral content with increasing age of juveniles. Myotis lucifugus exhibited a significant decrease in spleen weight with age, whereas M. thhysanodes showed no such trend. Neither species showed trends in adrenal weights through the growth period. Several guardian M. thysanodes females stayed with the young during the night. They nursed, retrieved, and in general protected the young throughout the night. Myotis lucifugus did not exhibit this behavior, but large groups of adults would return periodically throughout the night to nurse the young. While M. lucifugus juveniles exhibited practice flight behavior at night, M. thysanodes juveniles were never observed performing this learning process.
Habitat Preferences and Competition of Wintering Juncos and Golden‐Crowned Sparrows
Authors: Davis John
Published: May 2006

Trapping and banding of wintering juncos and golden—crowned sparrows was carried out from 1964 to 1968 along the opposite edges of an old field. The juncos ranged freely along the field borders but the golden—crowns were largely restricted to dense willow thickets in one part of the field. An attempt to assess possible competition between the two species by removing juncos in 1966—67 was unsuccessful because of infiltration of new birds from outside the study area. Removal of golden—crowns in 1967—68 reduced their population markedly and resulted in significant increase in use of the willow thickets by juncos. Although juncos are primarily seed eaters in winter, and seeds are a steadily dwindling resource at that season, competition for food between the two species was alleviated because the sparrows subsisted in large part on sprouting annuals, a resource renewed continuously after sprouting started following the fall rains. Further, the green food eaten by the sparrows undoubtedly satisfied their water requirements to a great extent and reduced competition for water sources. The competition demonstrated by removal experiments resulted not from direct competition for the same set of resources but from the proximity of a water trough, an important junco resource, to the heavy cover preferred by the sparrows. Although outnumbered about 5:2, the larger sparrows were able to exclude the juncos from this cover to an appreciable extent.
Optimal Exploitation Strategies for an Animal Population in a Markovian Environment: A Theory and an Example
Authors: Anderson David R.
Published: May 2006

Optimal exploitation strategies were studied for an animal population in a Markovian (stochastic, serially correlated) environment. This is a general case and encompasses a number of important special cases as simplifications. Extensive empirical data on the Mallard (Anas platyrhynchos) were used as an example of general theory. The number of small ponds on the central breeding grounds was used as an index to the state of the environment. A general mathematical model was formulated to provide a synthesis of the existing literature, estimates of parameters developed from an analysis of data, and hypotheses regarding the specific effect of exploitation on total survival. The literature and analysis of data were inconclusive concerning the effect of exploitation on survival. Therefore, two hypotheses were explored: (1) exploitation mortality represents a largely additive form of mortality, and (2) exploitation mortality is compensatory with other forms of mortality, at least to some threshold level. Models incorporating these two hypotheses were formulated as stochastic dynamic programming models and optimal exploitation strategies were derived numerically on a digital computer. Optimal exploitation strategies were found to exist under the rather general conditions. Direct feedback control was an integral component in the optimal decision—making process. Optimal exploitation was found to be substantially different depending upon the hypothesis regarding the effect of exploitation on the population. If we assume that exploitation is largely an additive force of mortality in Mallards, then optimal exploitation decisions are a convex function of the size of the breeding population and a linear or slight concave function of the environmental conditions. Under the hypothesis of compensatory mortality forces, optimal exploitation decisions are approximately linearly related to the size of the Mallard breeding population. Dynamic programming is suggested as a very general formulation for realistic solutions to the general optimal exploitation problem. The concepts of state vectors and stage transformations are completely general. Populations can be modeled stochastically and the objective function can include extra—biological factors. The optimal level of exploitation in year t must be based on the observed size of the population and the state of the environment in year t unless the dynamics of the population, the state of the environment, and the result of the exploitation decisions are completely deterministic. Exploitation based on an average harvest, or harvest rate, or designed to maintain a constant breeding population size is inefficient.
Anomalous Diurnal Patterns of Stem Xylem Water Potentials in Larrea tridentata
Authors: Syvertsen James P. , Cunningham G. L. , Feather T. V.
Published: May 2006

Diurnal stem xylem H2O potentials of Larrea tridentata (DC.) Cov. were measured with a pressure chamber during the summers of 1973, 1974. Plants growing in dry soils had minimum stem xylem H2O potentials at night and maximum values during the daylight hours. Vertical H2O vapor movements in the soil profile in response to temperature gradients may be implicated although further data are needed to establish their role conclusively. Water vapor apparently moves up out of the rooting One at night and back down into the rooting zone during the day. The occurrence of this phenomenon probably enhances the ability of Larrea shrubs to maintain photosynthetic activity when soil H2O potentials are low and makes questionable the use of predawn stem xylem H2O potential measurements to assess seasonal trends in plant H2O status.
Three Central American Bat Communitis: Structure, Reproductive Cycles, and Movement Patterns
Authors: Fleming Theodore H. , Hooper Emmet T. , Wilson Don E.
Published: May 2006

Three bat communities were studied for 1 year at each of two localities in the Panama Canal Zone and one locality in western Costa Rica. Removal sampling and banding techniques using Japanese mist nets were employed to document community structure, food habits, reproductive cycles, and movement patterns of these bats. Results indicated that 27—31 species occur at or near ground level at each locality. Species diversity, as measured by H', was highest in the Costan Rican community; each community contained 3—4 common species and many uncommon species. Based on body size and general food habits, niche overlap appears to be greatest among small to intermediate—sized insectivores and frugivores, many of which, however, are apparently uncommon. Four basic reproductive patterns are found among the species. Most frugivores are seasonally polyestrous whereas some insectivores are monestrous and at least one is polyestrous. It is postulated that in both insectivores and frugivores birth peaks coincide with maximum food levels. Recapture patterns of several species suggest that home range size may be positively correlated with body size; omnivorous species may have larger home ranges than similarly size species with more restricted diets.
Seasonal Ionic Fluctuations in a Typha Glauca Community
Authors: Bayly Isabel L. , O'Neill Tom A.
Published: May 2006

Calcium, magnesium, potassium, sodium, iron, and phosphorus concentrations were measured in rhizomes, leaves, and floral stalks of a Typha glauca community during the growth season of 1968. Leaf—length and plant—organ moisture contents were also determined and used as indicators of physiological aging. Seasonal fluctuation was found in all ions examined in the soil and plant parts analyzed. The ions studied were grouped into three categories with reference to apparent seasonal fluctuations of ionic concentrations. Concentration changes of calcium and possibly magnesium in plant tissue were inversely related to apparent changes in substrate concentration. Changes in concentration of potassium and phosphorus in floral stalks and leaves were inversely related to apparent changes in ion concentration in the rhizome, although not related to changes in the substrates. Changes in concentration of sodium and iron in all plant parts sampled were directly related, but no relationship was detected between the apparent changes in concentration in plant tissue and those in the substrates.
Simulation of Phosphorus Cycling in Semiarid Grasslands
Authors: Cole C. Vernon , Innis George S. , Stewart J. W. B.
Published: May 2006

A simulation model of the phosphorus cycle in semiarid grasslands was developed and tested. When used with data sets for biotic and abiotic driving variables of the Pawnee (Colorado) and Matador (Saskatchewan) Sites, this model predicted plant and decomposer uptakes and turnover rates of the principal phosphorus compartments. Daily P requirements for plant and decomposer uptake are taken from pools of labile inorganic P in each soil layer. These pools are replenished mainly by mineralization of labile organic P as well as leaching of water—soluble forms from standing dead biomass and litter. Phosphorus solubility (recalculated daily from relationships to the labile inorganic pools), soil H2O content, and rates of diffusion of P through soil are the major controls on rates of uptake by the active fraction of the live root biomass. Model operation was found to be more sensitive to soil parameters than to plant parameters. Simulation results indicated rates of decomposer uptake 4—4x greater than plant uptake in semiarid grasslands. Simulated P concentrations in live plant tops were highly responsive to the pattern of seasonal rainfall which agreed well with published data. The most critical informational needs revealed by model development and operation were in the areas of activity and morphology of roots and the rates of mineralization of organic P as affected by soil depth.
Bias in Estimating the Diversity of Large, Uncensused Communities
Authors: Routledge R. D.
Published: May 2006

If a community is too large to be censused, quantities such as the diversity must be estimated from a sample. Methods using data from a sample random sample of individuals to estimate either the Shannon—Wiener or the Simpson Index of diversity are of limited use. Seldom is it practical to obtain such a sample. It is usually easier to use sampling unit such as the plants in a quadrat or the animals trapped in a net. Methods which use the data from such a scheme to estimate the two commonly used indices are discussed here. (Computational procedures are outlined in a separate display.) The small sample bias, at least in the particular case examined in detail, is much smaller for an estimator of the Simpson Index than for any proposed estimator of the Shannon—Wiener Index. This property appears to provide the former index with a distinct advantage for measuring diversity and its ecological components.
Aerial Production, Mortality, and Mineral Accumulation‐Export Dynamics in Spartina Alterniflora and Juncus Roemerianus Plant Stands in a Georgia Salt Marsh
Authors: Gallagher John L. , Reimold Robert J. , Linthurst Rick A. , Pfeiffer William J.
Published: May 2006

Biomass and disappearance of dead material were measured in stands of tall creekbank Spartina alterniflora, short high marsh S. alterniflora, and Juncus roemerianus in Georgia, USA at 4—wk intervals for 1 yr and at 8—wk intervals for a 2nd yr. Growth and mortality were calculated from these data. Net primary production estimates, using changes in biomass only, ranged from 10 to 75% lower than estimates which included the disappearance of dead material. Agreement between the methods was closest when the interval between harvest was shortest and the rate of dead material disappearance the slowest. Estimates of mean annual net primary production, computed from changes in biomass and disappearance of dead plant material, were: creekbank S. alterniflora 3700g/m2, high marsh S. alterniflora 1300 g/m2, and J. roemerianus 2200g/m2. The seasonal amplitude in the amount of N, P, K, Ca, and Mg in the living tissue was greatest in the creekbank S. alterniflora. The maximum accumulation of most elements was in late summer. In the tissue of S. alterniflora, N and P were highest in concentration in late winter and early spring. In summer, growth occurred faster than nutrient accumulation therefore, tissue concentrations decreased. Seasonal p patterns of element disappearance from the "dead plant community" showed that maximum export depended on community type and the element under consideration.
The Distribution of Duckweed Lemna Perpusilla in a Small Southern California Lake: An Experimental Approach
Authors: McLay C. L.
Published: May 2006

The duckweed Lemna perpusilla in a small, alkaline lake was studied during 1970 and a map of its distribution was prepared. Duckweed, the only floating, unrooted higher aquatic plant present, was distributed around most of the edge of the lake but its density was extremely patchy. Experiments were made involving manipulation of the duckweed density, modification of its distribution, and measurement of the factors which experiments suggested were significant influences on its pattern of abundance. Attention was particularly focused on the importance of other plants in molding the duckweed pattern. Duckweed was absent from the central area of the lake primarily because there was nothing to prevent the plants from being transported by waves generated by the prevailing winds from the southwest. Growth on water taken from the center of the lake was poor compared to growth on water from near the shore. Duckweed can exist in the Potamogeton zone at a much higher density, and the low density does not result from grazing by animals. Growth of plants exchanged between the zone and a zone nearer the shore was depressed in the Potamogeton zone and stimulated in the other. Several experiments suggested that the lowered growth rate was attributable to the higher pH of the water, probably produced by the photosynthesis of other aquatic plants. Where it was dense enough, duckweed was able to overcome this effect by shading the plants beneath. It can be reasoned, from the structure of plants that retain their progeny inserted in the reproductive pockets, that the average ability per frond to produce further progeny is thereby impaired. Also, plants broken up into single fronds produced progeny at a faster rate than unbroken plants. Dense patches of duckweed occurred among the Scirpus plants and along the edge of the shore. Duckweed growth was more rapid on mud than on water but plants transplanted to selected places around the lakeshore did not reveal any differences in the ability of the mud to support their growth. Dense populationswere associated with breaks in the dense cover of Scirpus stems, which reduced the light intensity beneath them by 80%—90%. Comparison of growth of plants on mud in situ, in shaded and unshaded areas, indicated that these openings in the cover are responsible for allowing dense populations to develop. Development of dense patches along the unshaded shore of the lake was limited by their inability to grow fast enough to keep pace with the receding water and hence appeared only where the slope was steep. Most dense patches were eventually stranded on the mud and died, drastically reducing the density because very few new plants (growing from turions or seeds) could be recovered when water was added to dried mud. Therefore the patches must be built up again the following summer. Traditional methods of distribution study would not detect the two distinct causes of patchiness of duckweed in this lake.
Vertical Stratification in Orb‐Web Spiders (Araneidae, Araneae) and a Consideration of Other Methods of Coexistence
Authors: Enders Frank
Published: May 2006

Measurements of the web height and counts of the number of webs on randomly selected plots in lespedeza fields reveal that immature Argiope aurantia and Argiope trifasciata, very large araneid spiders, place their webs at different heights. In late summer this vertical stratification disappears, while the numbers of the two species on plots become positively correlated. Coexistence of the two spider species may depend in part upon the usual occurrence of high mortality during the immature stages. Invasion of webs by araneids is reported as possible competitive interference. The two larges species of European araneids also show vertical stratification only as immatures. However, the niches of most Polish Araneus species in fields seem differentiated by parameters related to prey size: season of breeding and size differences between species.
Growth and Dormancy in Talinum Rhizomes
Authors: Ware Stewart
Published: May 2006

Plants of Talinum calcaricum and T. mengesii (Portulacaceae) flower throughout the hottest, driest part of the summer on the rock outcrops where they are found, and die back to their rhizomes each fall. Once dormant, the rhizomes will not resume growth until subjected to a period of cold. Six to eight weeks 4° C were sufficient to end dormancy, and simple after—ripening would not substitute for cold. Sufficient cold is received in nature to end dormancy by mid—winter, and quiescene is thereafter environmentally impressed. The length of the growth period is apparently endogenously controlled, for dormancy ensues even when there has been no change in the environment during the entire life of the plant, and the length of the growth period is consistent under a variety of environmental conditions. The onset of dormancy in T. calcaricum occurs 23—34 weeks after rhizomes break dormancy or the seeds germinate. Both the length of the growth cycle and the requirement for cold treatment are in harmony with the natural environment of the two species.
Ordination of Vegetation Samples by Gaussian Species Distributions
Authors: Gauch Hugh G. , Chase Gene B. , Whittaker Robert H.
Published: May 2006

Direct gradient analysis has shown that along many environmental gradients species distributions show bell—shaped forms, overlap broadly, and have their centers and limits scattered. This finding is the basis of a technique called “Gaussian ordination” presented here, which arranges samples by maximizing the fit of Gaussian curves to the individual species' distributions. Ordination proceeds by (1) a first—guess arrangement of samples, (2) sorting of species for relative usefulness in ordination, and (3) fitting of least—squares Gaussian curves to the individual species, followed by (4) iterative fitting that changes the ordination values to produce an optimal Gaussian fit for all species together. Gaussian ordination is appropriate for sample sets with a major axis of environmental and community variation. The technique has produced successful ordinations of simulated and field data. Because Gaussian ordination is based on an explicit model of vegetation structure and computes the species and sample parameters for this model, the technique represents a convergence of research in direct and indirect ordination.
Macroinvertebrate Composition and Production in Some Sierra Nevada Minerotrophic Peatlands
Authors: Erman Don C. , Erman Nancy A.
Published: May 2006

Macroinvertebrates were identified from seven (0.2—2.7) minerotrophic peatlands (fens) in the Sagehen Creek basin, northern California, at 1,943—m elevation. Mean peat depth was 17.3—87.4 cm. Aquatic oligochaetes, certain species typical of oligotrophic lake benthos, dominated the fauna. Kincaidiana freidris (Lumbriculidae) and Mesenchytraeus sp. (Enchytraidae) were the most abundant species. Annual production of major groups was estimated by the Hynes and Coleman method. Oligochaete production ranged from 7.4 to 58 g°m—2 yr—1 and was positively correlated (r = 0.951) with mean peat depth of the seven fens. Production of ceratopogonids, chironomids, and nematodes was much less than that of oligochaetes (0.05—1.0 g°m—2 yr—1). Annual turnover ratios averaged 6.7 oligochaets, 6.1 for ceratopognids, and 7.0 for chironomids.
Late‐Quarternary Paleoecology of the Cuatro Cienegas Basin, Coahuila, Mexico
Authors: Meyer Edward R.
Published: May 2006

Two sediment cores drawn from springs in the Cuatro Cienegas Basin, a small desert valley in central Coahuila, yielded fossil pollen chronologies transgressing more than 30,000 radiocarbon years. Comparisons of modern pollen spectra from the basin floor with the fossil records indicate that vegetation ecologically equivalent, if not identical, to that now present has occupied the floor of the basin since mid—Wisconsin time. A highly—endemic fauna and a lack of geological evidence for large Pleistocene lakes in the area afford strong support for this interpretation, and suggest that aquatic and terrestrial habitats of the valley lowlands remained stable environments throughout the Quaternary, regardless of fluctuations in regional climate. Fossil arboreal and Compositae pollen sequences provide a means for making stratigraphic correlations between the cores, and are the first late—Quarternary palynoclimatic chronologies available from northeastern Mexico. Trends in those components of the fossil records indicate that regional climate was cooler and perhaps more moist during the last Pluvial than at present. It became progressively warmer and drier during late—Pluvial time, and approximated modern climate during the Holocene. Holocene Altithermal or Hypsithermal intervals were undetected, but may be obscured by gaps in the fossil records.
Population Structure and Dispersal in Richardson's Ground Squirrels
Authors: Michener Gail R. , Michener Daniel R.
Published: May 2006

Populations structure and dispersal were studied over a 4—yr period in a population of Richardson's group squirrels (Spermophilus richardsonii) on a 135—ha tract of natural prairie in southern Saskatchewan, Canada. Overall, fewer than 30% of juveniles and 50% of adults were recaptured in a subsequent year. More ♂ ♂ than ♀ ♀ disappeared from the population. The 1:1 juvenile sex ration was readjusted to °0.3 ♂ ♂ / ♀ in the adult population. Females generally remained within 100 m of their initial capture point, and fidelity to the original area lasted at least 3 yr. There was no substantive evidence to account for the loss of ♀ ♀ between successive years on the basis of dispersal. Males generally moved further than ♀ ♀. About 90% of the observed between—year movements made by ♂ ♂ could be explained on the basis of movements during the breeding season. Within their first year of life, ♂ ♂ moved further in the spring when mature than in the previous year as juveniles. Some dispersal by juvenile ♂ ♂ occurred, predominantly in July. In each year the population fit the Hardy—Weinberg equilibrium with respect to the transferrin locus, and there was no evidence of differential loss of genotypes between generations, between years between sexes, or between marked and unmarked adults. The potential effect of spring dispersal by yearling as opposed to fall dispersal by juveniles on population dynamics is considered. The roles of dispersal, predation, and overwinter mortality in accounting for losses of squirrels for losses of squirrels are examined.
Resource Utilization and Coexistence of Seed‐Eating Desert Rodents in Sand Dune Habitats
Authors: Brown James H. , Lieberman Gerald A.
Published: May 2006

As many as five species of seed—eating rodents coexist in sand dune habitats in the North American deserts. Among species occuring together the ratio of body weights of adjacent species pairs is usually greater than 1.5. The seed resources of the habitats appear to be apportioned among species chiefly in two ways: (1) rodents differentially harvest seeds of different sizes, and seed size selection is positively correlated with body size: (2) species forage in different areas relative to the cover of perennial shrubs. The species also differ in their annual activity (some are active all year, others may go torpid for short periods or hibernate for several months), but is difficult to evaluate how these differences affect the utilization of seeds. Our estimates of total overlap in resource utilization between species indicate that competition for seeds have an important influence on community structure in desert rodents. In productive habitats species that are quite similar (overlap values greater than 80%) in resource utilization are able to coexist and species diversity is high, but in less productive habitats ecologically similar species are excluded, resulting in decreased species diversity.
The Present Composition of a Former Oak‐Chestnut Forest in the Allegheny Mountains of Western Pennsylvania
Authors: Mackey Halkard E. , Sivec Neal
Published: May 2006

A blighted and lumbered oak—chestnut forest in the Allegheny Mountains of western Pennsylvania was studied 50 years after elimination of the American chestnut (Castanea dentata). This slope revealed a regeneration pattern not typical of previously studied chestnut sites. The removal of chestnut by lumbering has generated an area that resembles a mid—successional stand mixed with species associated with the former chestnut. Once dominated by chestnut, a mixture of oaks, and numerous co—dominant species, the study area is presently occupied by black cherry (Prunus serotina), red maple (Acer rubrum), sugar maple (Acer saccharum), black oak (Quercus velutina), black birch (Betula lenta), and sour gum (Nyssa sylvatica). Anticipated loss of blackcherry, a few remaining larger trees, and some red maple indicates that this forest will continue to change gradually throughout the next few decades.
Some Current‐Directed Movements of Macrobrachium Acanthurus (Wiegmann 1836) (Decapoda, Palaemonidae) Under Laboratory Conditions
Authors: Hughes David A. , Richard Joseph D.
Published: May 2006

The larvae of some species of freshwater shrimp of the genus Macrobrachium will develop only in brackish water. The increased incidence of these shrimp within estuaries and in the lower reaches of rivers at certain times of the year suggests that regular down—stream migrations are carried out to facilitate the transport of larvae to a brackish estuarine environment. Current chamber experiments conducted in the laboratory indicated that gravid individuals tend to swim consistently downstream whereas other adult females tend to swim consistently upstream. Other current chamber experiments showed that larval stages, held in brackish water, will drop to a position low in the water column when salinity is reduced (simulating an ebb tide) and revert to swimming higher in the water column when the salinity is increased (simulating a flood tide). These responses are interpreted as a mechanism whereby larvae are prevented from being carried out to sea, thus facilitating their eventual migration upstream to a freshwater environment.
A Recensus of Vervet Monkeys in the Masai‐Amboseli Game Reserve, Kenya
Authors: Struhsaker Thomas T.
Published: May 2006

Between 1964 and 1971 the population of vervet monkeys in the Amboseli Reserve, Kenya, has declined 33.3%. There were significantly fewer young juveniles (0.5—1.5 years) in 1971 than in 1963—1964. The same birth season was adhered to in 1971 as in 1963—1964.
Effect of Varying Oxygen Concentrations on the Filtering Rate of Daphnia Pulex
Authors: Kring R. Lynn , O'Brien W. John
Published: May 2006

Knowledge of factors affecting feeding efficiency is of vital importance to understanding any organism's relationship to its environment. The present study reports on the effect of one factor–variation in O_2 concentration–on the filtering rate of a common freshwater zooplankton species, Daphnia pulex. Measurements of D. pulex filtering rate were made under exposure to a wide range of O_2 concentrations and over periods of time ranging from < 1 h to 15 days. Oxygen was found to have a significant effect on the filtering rate in that below concentrations of 3 mg O_2/l the rate decreased sharply; however, following prolonged exposure (> 8—12 h) to low O_2 conditions the filtering rate gradually increased and eventually D. pulex were able to filter much more rapidly than under normal O_2 concentrations. These increases in filtering rates under conditions of low O_2 are directly correlated with the animals' increased production of hemoglobin when little O_2 is present.
Colonization Success of a "Biennial" Plant Species: Experimental Field Studies of Species Cohabitation and Replacement
Authors: Werner Patricia A.
Published: May 2006

In order to gain understanding of the relationships of life history characteristics to colonization success, species cohabitation, and species replacement, a known number of seeds (fruits, achenes) of teasel, a biennial' plant species, Dipsacus sylvestris Huds. were experimentally introduced into 52 permanent plots within each of 8 contiguous abandoned fields of various vegetation types in Michigan, USA. The nearest naturally occurring teasel population was 11.2 km from the study site; no teasel seeds or plants were present in the fields except where controlled introductions were made for this study. Permanently marked teasel and control plots were monitored over a 5—yr period for colonization success of teasel, species compositions, and species net annual primary production. Results fall into three categories, the first of which has implications for studies of plants strategies and the last 2 have implications for studies of community structure and succession. 1) Life history characteristics of teasel and initial colonization success: A cohort of teasel seeds spreads its germination over more than one growing season; the length of time in the rosette stage may extend to 4 yr or more. Teasel did not successfully colonize the field that had thick quackgrass litter due to low germination of seed and high mortality of seedlings. In other fields, teasesl rosettes grew ate various mean rates, depending upon the presence of grass, other herbaceous dicots, and shading shrubs. Critical size for flowering was reached in either 2, 3, or 4 yr in six of the eight fields and these populations produced °7x more seeds than was originally introduced. 2) A mechanism for recolonizaton on a site: A teasel rosette creates an opening in vegetation that is colonized by teasel seedlings, or if teasel seeds are unavailable, by short—lived winter annuals, specially Barbarea vulgaris L. The number of species in a field (excluding teasel) increased with teasel colonization, probably due to the creation of these openings by teasel rosettes. 3) Cohabitation with teasel: Grass growing with teasel was not reduced in productivity (compared to that in Control plots), despite the significant production by teasel. However, the herbaceous dicotyledonous plants were slowly reduced over 4 yr as teasel increased in biomass. Roots of flowering teasel plants do not occupy the same soil layer as roots of the shallow grasses in this study, but probably do compete with those of the morphologically similar herbaceous dicots. Studies of communinty succession have often recorded changes in the number of species and in site productivity; such changes can here be directly attributed to colonization of the sites by a new species.
Competition and Habitat Shift in Two Sunfishes (Centrarchidae)
Authors: Werner Earl E. , Hall Donald J.
Published: May 2006

The bluegill sunfish (Lepomis marcrochirus) in small ponds feeds on relatively large prey associated with the vegetation. However, in the presence of the green sunfish (L. cyanellus) it shifts to feeding on smaller, less preferred prey in the open water column. The mechanisms responsible for this habitat shift were examined by experimentally confining both species, alone and together, in homogeneous patches of the preferred habitat (vegetation). When confirmed together in the vegetation the green sunfish exhibited higher survivorship, growth rates, and amount of food in the stomachs that the bluegill. The bluegill fed on smaller items and consumed benthic prey than did the green sunfish. The presence of the congener did not alter the food habits of either species or the growth rates of the green sunfish in relation to species stocked alone. Presence of the congener did affect the growth rates of the bluegill. Overlap in the diet was 70% when these species were confined to the vegetation as compared to 44% in an earlier study where habitat separation was permitted. The green sunfish is more of a sit—and—wait predator and is able to utilize a wider food size spectrum than the bluegill. This results in a strong asymmetry in the competition function favoring the green sunfish in the vegetation. However, in the open water column the distribution of food sizes is truncated and this provides a competitive refuge for the bluegill which handles small foods more efficiently. The bluegill appears to be more flexible in its habitat use while the green sunfish is more aggressive and limited in the habitats utilized. Comparisons with studies of habitat shifts in salmonids suggest that the competitive mechanisms outlined are of general relevance in fish communities. Considerations of the relation between habitat structure, the correlated distribution of food sizes, and species morphology provides a framework for specifying the occurence of habitat shifts and which species of the interactive set will shift.
Factors Influencing the Distributions of Two Species of Perognathus
Authors: Hoover Kenneth D. , Whitford Walter G. , Flavill Paul
Published: May 2006

Perognathus penicillatus and Perognathus intermedius were studied in two areas in Dona Ana County, New Mexico, from 1970—1972. Perognathus penicillatus was associated with sandy soils and P. intermedius with soils composed of predominantly larger particles. Soils from areas where P. intermedius was found had a lower heat buffereing capacity than soils from areas occupied by P. penicillatus. Artificial burrows when occupied by either species had a higher concentration of CO2 in P. intermedius type soils. Perognathus penicillatus occupied burrows in cooler places, survived a narrower temperature range, and exhibited higher rates of evaporative H2O loss with increased ambient temperature and CO2 concentration than did P. intermedius. Perognathus penicillatus was the more aggressive species, and dominated P. intermedius in laboratory encounters. Perognathus penicillatus can probably exclude P. intermedius from habitat that provides a burrow microclimate that the former can tolerate. Perognathus intermedius is physiologically able to survive in the more extreme habitat not suitable for P. penicillatus. The distribution of soil types and other microgeographical features that affect the burrow microenvironment, together with rainfall and temperature patterns, determine the areas where the two species will persist. The climatic variability of this desert site can result in changes in overall suitability of an area and hence in distribution and range of each species.
Convergence in Vegetation Structure along Analogous Climatic Gradients in California and Chile
Authors: Parsons David U. , Moldenke Andrew R.
Published: May 2006

A series of plant communities along analogous climatic gradients in southern California and central Chile has been analyzed to determine the extent of convergence in a variety of ecologically significant characters. Results show that, despite distinct genetic histories, the structure of the vegetations of these areas has converged under similar climatic constraints. Such characters as species richness, growth form, leaf duration, leaf size, and spines are quantitatively more similar between floristically distinct yet climatically analogous sites on the two continents than between floristically similar but climatically distinct sites a short distance apart on the same continent. Such findings, which hold true for both the native woody vegetation and the partially exotic herbaceous understory, provide quantitative support for the general hypothesis that plant form and community structure are higherly determined, regardless of genetic constrains, by environmental parameters.
Refuges, Disturbance, and Community Structure: A Marine Soft‐Bottom Example
Authors: Woodin Sarah Ann
Published: May 2006

Disturbance is a significant mortality source in many assemblages. The susceptibility of organisms to this mortality source is, in part, a function of the availability of substrate heterogeneities that act as refuges from the disturbance process. There are at least 5 major categories of temporal and spatial refuges from disturbance: (1) temporal periods outside the activity range of the disturbance process; (2) temporal periods within the activity range of the disturbance process; (3) spatial zones beyond the activity range of the disturbance process; (4) physical heterogeneities within the activity range of the disturbance process; and (5) biologically generated refuges within the activity range of the disturbance process. The last category is particularly interesting because it involves an organism's utilization of a refuge which is the product of another organism or organisms. Data from a marine system are used to demonstrate the effectiveness of several types of refuges, particularly biologically generated refuges. The refuge—forming species is Diopatra cuprea, an onuphid polychaete which inhabits shallow water, medium—grained sand flats from Cape Cod to Florida. The abundance and species richness of other members of the infauna are shown to be positively associated with the presence of the tubes of Diopatra. This effect is confined to the area immediately surrounding the tubes of Diopatra. I demonstrated experimentally that a tube—like structure, such as a plastic straw, has the same effect on the infauna as does the tube of Diopatra. Thus, as predicted, the physical and biological refuges affect infaunal abundances similarly. They should not show similar patterns of distribution in space and time however and this is discussed.
Polymorphism in the Rotifer Asplanchna Sieboldi: Biomass, Growth, and Reproductive Rate of the Saccate and Campanulate Morphotypes
Authors: Gilbert John J.
Published: May 2006

Saccate and campanulate ♀ ♀ of the 12C1 clone of Asplanchna sieboldi were cultured at 25 degrees C, the former on Paramecium aurelia and the latter on Asplanchna brightwelli or A. sieboldi together with 10(—7) M d—alpha—tocopherol. The dry weights of newborn and gravid, adult saccates were 0.49 and 2.14 mg/♀; corresponding weights for A. brightwelli—fed campanulates were 2.14 and 6.37 ♀♂. Thus, the campanulates were 4.37 and 2.98 ° heavier than saccates as neonates and gravid adults, respectively. The disproportionately great birth size and slight postnatal growth of campanulates may be adaptative in decreasing mortality from canibalistic adults and in maximizing the ability of young individuals to capture and eat large prey available to adults. Gravid, adult campanulates fed on conspecific saccates were heavier than those fed on the smaller A brightwelli–7.03 and 6.37 mg/♀, respectively. The ability of ♀ ♀ of this and the other morphotypes to alter their size in direct response to the size of their prey may be adaptive in maximizing the efficiency of prey capture and ingestion. In four experiments conducted at 22 degrees , 25 degrees , and 28 degrees , the intrinsic rates of natural increase of A. brightwelli—fed campanulates were significantly greater (p = 0.0260 and 1.10—1.29 ° higher than those of P. aurelia—fed saccates; at these temperatures, the r—values for the campanulates were 0.717, 0.854, and 1.058 or 1.216 per day, respectively. The campanulates lived slightly longer and produced more offspring than the saccates; their net reproduction rates varied from 9.08 to 12.18 and were significantly greater (p = 0.023) as well as 1.19 to 2.01 ° higher than those of saccates. The mean generation times of the saccate and campanulate ♀ ♀ were similar. The productivity of the campanulate ♀ ♀ at 25 degrees C was estimated to be about 4 x that of saccate ♀ ♀. Campanulates fed from birth on the rotifer Brachionus calyciflorus had life—table—parameter responses similar to those fed on A. brightwelli. Saccate ♀ ♀ of the 10C6 clone fed on B. calyciflorus produced about 2 x as many offspring and lived about 2 x as long as those fed on P. aurelia; the respective r—values were 1.298 and 1.664. The superiority of the rotifer—diet suggests that, in the experiments with the 12C1 clone, the reproductive potential of campanulates was greater than that of saccates primarily because of the diets used to maintain the two morphotypes. The well—known, inverse relationship between the size and the reproductive potential of an organism does not hold for the genetically identical @V @V of the saccate and campanulate morphotypes. Transformation of saccate ♀ ♀ to campanulate ♀ ♀ is not at a reproductive cost to the population. Both morphotyes appear to be designed for comparably rapid, parthenogenetic reproduction, and in concert they may maximize the ability of a population to utilize a wide variety of prey in a very large size range.
Herbicide Effects on Leaf Litter Decomposition Processes in An Oak‐Hickory Forest
Authors: Gottschalk Marlin R. , Shure Donald J.
Published: May 2006

Herbicide treatments (2, 4, 5—Trichlorophenoxyacetic acid) of 0.225 g/m2 and 2.250 g/m2 were applied in a Latin square design to the forest floor of an oak—hickory forest in Georgia. White oak (Quercus alba) leaf litter decomposition and litter and soil microarthropod populations were studied in control and treated areas. Weight loss of natural white oak leaf litter averaged 35% for the 1st yr and reached 67% after 2 yr. Litter decomposition rates were similar in control and treated areas. However, white oak leaves defoliated through stem injections lost 59% of their biomass in 1 yr. Decomposition was increased because of initially higher N levels and a lower C:N ratio in defoliated leaf tissue. Herbicide spray treatment increased microarthropod densities for up to 8 mo after application. The herbicide spray apparently influenced springtail and mite reproductive activity in treated areas. The increases in soil and litter microarthropod densities were not sufficient to affect leaf litter weight losses. Repeated defoliation of plant communities and the resulting increased decomposition rates could cause imbalances in litter dynamics and cycling processes. Changes in the timing of annual litterfall and the rates of nutrient release may thus lead to soil desiccation and the depletion of available nutrient pools.