bluuebunny/crossref_metadata_2025 huggingface dataset:
Diel and Interannual Variation of Size Distribution of Oceanic Zooplanktonic Biomass
Authors: Rodriguez Jaime , Mullin Michael M.
Published: May 2006

A negative temperature anomaly with an increase in primary production affected the size distribution of zooplanktonic biomass in the central gyre of the North Pacific Ocean, a very large, old, oligotrophic, and highly diverse ecosystem with little seasonal change. Previous reports showed no effect of this anomaly on the species structure of the macrozooplanktonic community. Composite zooplankton samples from the euphotic zone for five cruises corresponding to the normal or steady state (two summers, two winters, and one spring) and one corresponding to the perturbation or anomaly (summer 1969) were size fractionated by filtration through a column with 4, 2, 1, 0.5, 0.3, and 0.183 mm mesh, after manual removal of organisms larger than °8 mm. Total biomass was higher during summer than during winter. Also, the size distributions of biomass were more similar between summers or winters of different years than between different seasons. Vertical migration of zooplankton causes the important scale of variability; the size—differential migration (larger size classes migrate more than smaller ones) has a seasonal pattern: during winter, biomass of all sizes classes increases nocturnally in the euphotic zone; during summer, the nocturnal increase of biomass is due almost exclusively to the largest size classes. The effect of the summer climatic anomaly were: (1) increase of total biomasss; (2) elimination of diel variability in size distribution typical of summer steady state through enhanced migration of small animals, the resulting distribution being similar to the winter steady state with migration of all size categories; (3) increase in the dominance of the 0.5—1.0 mm class. There is some evidence of a modification of age structure rather than an increase of population of small—sized species. We interpret the changes as the summation of the wave of perturbation moving up the biomass spectrum as a result of its input at the smallest size classes of the spectrum, the primary producers, plus an effect on migratory behavior of zooplankton.
Ecological Use of Failure Time Analysis
Authors: Muenchow Gayle
Published: May 2006

Failure time analysis (FTA), or survival analysis, addresses data of the form “time” until an event occurs. The survival times of medical patients or industrial products have been the usual subjects of FTA, but data from a wide variety of ecological studies may be cast in these terms, including survival times of organisms or parts of organisms and times until certain behaviors are exhibited. FTA can accommodate censored data: cases in which the actual time of occurrence is not know but a minimum time during which the event did not occur is known. As an examples, I used FTA probability distribution and the Cox Model, a nonparametric multiple regression analog, to analyze data in which the event of interest was the arrival of any flying insect onto a male versus a female flower of Clematis ligusticifolia. It was determined that males were visited significantly faster than females.
Estimated Net Aerial Primary Productivity for Selected Estuarine Angiosperms in Maine, Delaware, and Georgia
Authors: Linthurst Rick A. , Reimold Robert J.
Published: May 2006

Annual net aerial primary production (NAPP) was estimated for Distichlis spicata (L.) Greene, Juncus gerardii Loisel., Phragmites communis Trin., Spartina alterniflora Loisel., Spartina cynosuroides (L.) Roth, Spartina patens (Aiton) Muhl. and Sporobolus virginicus (L.) Kunth utilizing the Wiegert and Evans paired plot harvest method in selected east coast salt marshes. Estimates of NAPP ranged from 616 g°m—2°m—2°yr6—1 for highmarsh J. gerardii in Maine to 6.040 g°m—2yr—1 for S. cynosuroides in Georgia. Estimated "turnover" based on maximum living standing crop ranged from 9.6 times/yr (Georgia, D. spicata) to 1.8 times/yr (Delaware, D. spicata). As a result of periodic to erratic tidal inundation and associated removal and/or deposit of detritus, the Wiegert and Evans method could not be adequately evaluated for its accuracy in computing NAPP. The variability of the computed instantaneous rate of detritus flux which ranged from —39 mg°g—1°day—1 (Georgia, Spartina cynosuroides) to 84 mg°g—1°day—1 (Maine, S. patens) was considered to be the weak component. The complexity of the system parameters and the resultant variability of the method indicated that the method may present difficulties when used in salt marsh ecosystems.
Reproductive Seasonality in the Fishes of a Tropical Stream
Authors: Kramer Donald L.
Published: May 2006

The reproductive seasons of 6 species of characoid fishes inhabiting a tropical forest stream in Panama were determined from observations on gonadal condition and size frequency distribution of the populations over an 18—mo period. In this area the relatively mild dry season lasts °4 mo, stream discharge increases moderately during the rainy season, floods are intense but brief and temperature is very stable. Bryconamericus emperador and Piabucina panamensis spawned in temporary tributaries in June with the first floods of the rainy season. Brycon petrosus and Hyphessobrycon panamensis spawned in the dry season. The majority and adult Gephyrocharax atricaudata were mature in most months, but fry appeared in several peaks scattered through both dry and rainy seasons. Roeboides guatemalensis seemed to breed throughout the year but with a dry season peak. Previous studies of tropical freshwater fishes have emphasized the widespread tendency toward a flood spawning pattern but have investigated primarily highly seasonal savanna environments. I suggest that the diversity in the present study is related to the relatively stable habitat. Five hypotheses to explain the diversity in the timing of reproduction are proposed and briefly discussed: reproductive seasonality (1) is controlled by adult or juvenile food availability, (2) is controlled by interspecific competition for food among juveniles, (3) is controlled by competition for spawning sites, (4) is a mechanism for reproductive isolation, or (5) is unrelated to local conditions but is a reflection of earlier evolution of specializations for spawning under particular conditions.
Radiation Dosimetry of Small Mammals Inhabiting a Liquid Radioactive Waste Disposal Area
Authors: Halford Douglas K. , Markham O. Doyle
Published: May 2006

Radiation doses received by small mammals inhabiting a dry radioactive leaching pond on the Idaho National Engineering Laboratory Site in southeastern Idaho were determined by surgically implanting lithium fluoride thermoluminescent dosimeter (TLD) chips. One hundred eight—two TLD packets were implanted in 3 species; white—footed deer mouse (Peromyscus maniculatus), least chipmunk (Eutamias minimus), and Ord's kangaroo rat (Dipodomys ordii), with 65% recovery. All species from the radioactive leaching pond received significantly greater (P <.001) doses than control species. The deer mice received a mean dose equivalent rate of 160 mrem/day which was significantly greater (P <.001) than the mean dose equivalent rates received by least chipmunks (17 mrem/day) and Ord's kangaroo rats (6 mrem/day). The mean dose received by deer mice was 8% of the maximum air exposure recorded near the ground surface of the leaching pond. The maximum dose rate received by an individual deer mouse was nearly 50% of the maximum exposure rates in the study plot. Interspecific dose differences appeared to be related to habitat preference. Deer mice were most frequently captured on the gravelly and sparsely vegetated dry pond bed which had site exposure rates of 200 to 2000 mRoentgen/day. Conversely, chipmunks and kangaroo rats were usually captured on the pond banks which were adjacent to areas with sandy soil and denser vegetation. Site exposure rates on the pond banks ranged from 10 to 30 mRoentgen/day. Doses received by individuals of each species had high variation which appeared to be caused by the variable air exposure rates and the mobility of the small mammals. Intraspecific differences in activity, behavior and home range may have also influenced the dose variability in individual rodents. The advantage of implanted TLD over externally attached TLD and possible radiation effects on small mammal populations are discussed.
Kudzu Leaf Energy Budget and Calculated Transpiration: The Influence of Leaflet Orientation
Authors: Forseth Irwin N. , Teramura Alan H.
Published: May 2006

Leaflet orientation in exposed and shaded leaves of Pueraria lobata, kudzu, was measured during four phenological periods in central Maryland. Exposed leaflets had random azimuths but showed a strong diurnal orientation away from direct solar radiation. Shaded leaflets oriented towards diffuse light sources and did not change angle or azimuth diurnally. Energy budget simulations and field manipulations revealed that the orientation response reduced incident midday irradiance by one—half, leaf temperature by 5°—6°C, and calculated transpirational water loss by 18—26% under midsummer conditions, compared to horizontal leaves. We hypothesize that these movements may also play a role in improving water use efficiency and in avoiding thermal and photoinhibitory damage to the photosynthetic apparatus. Preliminary evidence suggests that kudzu may represent a widespread group of perennial, canopy—developing species in subtropical and temperate biomes that share this particular suite of leaf movement responses.
Large‐Scale Perturbations: Opportunities for Innovation
Authors: Carpenter Stephen R.
Published: May 2006

Several approaches are discussed for statistical analysis of large—scale (and possibly unreplicated) ecological experiments. These include intervention analyses and comparisons of alternative models using Bayes' formula. Such techniques are unfamiliar to many ecologists and are not typically included in graduate curricula in ecology. I argue for increased training in these areas and for collaborations between statisticians and ecologists to develop innovative approaches to the analysis of large—scale perturbations.
Food Resources, Survivorship, and Reproduction of the Omnivorous Calanoid Copepod Epischura Lacustris
Authors: Schulze Peter C. , Folt Carol L.
Published: May 2006

Previous studies have shown that many if not most copepods are omnivores and that all zooplankton experience substantial fluctuation in the abundance of food resources. We attempt to integrate these two observations by determining the implications of fluctuations in both the abundance and type of available food resources for the survival and reproduction of the omnivorous calanoid copepod Epischura lacustris. Egg production and survivorship were measured in laboratory experiments as food type (zooplankton and phytoplankton) and concentration were experimentally manipulated. In addition, the reproductive activity of a field population was monitored as the abundance and composition of the food resources varied through the year. There are three main results. (1) The alga Cryptomonas erosa and the rotifer Euchlanis dilatata both, when offered alone, serve as adequate foods to support survival and reproduction of Epischura. (2) However, survival and reproduction of individuals feeding on Cryptomonas vary temporally, even when resource availability is held constant. Extended survival and high egg production rates in the spring are followed by poor survival and minimal egg production rates later in the year. In contrast, survival and reproduction of individuals given the rotifer do not vary significantly across the seasons. (3) Field measurements suggest that Epischura lacustris reproduction in situ may depend upon relatively large or evasive animal prey, such as the cladoceran Holopedium gibberum and the rotifer Polyarthra remata.
Ecology of Ectomycorrhizal‐Basidiomycete Communities on a Local Vegetation Gradient
Authors: Natel Patrick , Neumann Peter
Published: May 2006

To understand the factors that structure ectomycorrhizal—basidiomycete communities at a local scale, we measured the strength of the relations among the fungal communities, the tree communities, and the environment of a series of forest ecosystems in southern Quebec. We collected fruit bodies belonging to ectomycorrhizal—basidiomycete families and genera, sampled the woody vegetation, and described soils and landforms at 11 permanent sampling stations. We first calculated similarity matrices among stations, one for each descriptor (fungal species abundance, woody species abundance, and abiotic variables). We then explored the dependence among these matrices using Mantel and partial Mantel tests, path analysis, and comparisons of ordinations and classifications. Similarity among ectomycorrhizal fungus communities was strongly and significantly correlated with tree community similarity, even when controlling for the effect of environmental similarity. When the tests were made with a similarity matrix based on those tree species that are known to be hosts of ectomycorrhizal fungi, abiotic similarity explained a significant portion of the residual variation in the similarity among fungus communities. To explore this complex relationship further, we analyzed species associations. The preference of fungus associations for different sets of abiotic conditions showed that some factors affecting fungal species distribution were different from those affecting the distribution of their tree hosts. Direct and indirect gradient analyses showed that humus characteristics seemed to be important niche dimensions of ectomycorrhizal fungi. The continuum concept was useful to interpret the complex relations among symbiotic species. Trees were the main component of the realized niche of ectomycorrhizal Basidiomycetes, but the fungal symbionts of a particular tree species followed that tree species for only a part of the abiotic gradients over which the host tree was found. This type of distribution predicts that beta diversity of fungi would be generally higher than beta diversity of ectomycorrhizae—forming trees. It also means that the ratio of fungus species richness to woody species richness would be high for most community gradients. Our results and those of previous mycosynecological studies agree with these predictions. The results have implications for the conservation of biodiversity: site selection for conservation based on vegetation classification or mapping, or on distribution of tree species, may miss important fungal species.
The Ecology and Bioenergetics of the Acridid Grasshopper, Bootettix Punctatus on Creosotebush, Larrea Tridentata, in the Northern Mojave Desert
Authors: Mispagel Michael E.
Published: May 2006

An 5—yr investigations was conducted of the population structure and bioenergetics of the host specific acridid, Bootettix punctatus, on creosotebush, Larrea tridentata, in the northern Mojave Desert of southern Nevada. Maximum densities ranged from 330—1360 insects/ha in mid—summer on a shrub density of 1000 plants/ha. Energy used for respiratory maintenance accounted for 55—68% of the energy assimilated by the populations. Assimilation was 20—23% of the 207—1681 J/m2 energy ingested per season. The estimated proportion of the host plants annual leaf biomass consumed during the first 3 yr of this study ranged from 0.8—1.9%. Nutrient availability in Larrea as a function of available soil moisture is suggested as a possible factor influencing the survivorship of early instar nymphs and of the population as a whole. Normal effects on the host plant due to phytophagy are probably negligible but, under certain climatic conditions, phytophagy by Bootettix in the late summer may stimulate primary production or improve the drought resistance of the shrub by defoliation.
Wind Dispersal of Artifical Fruits Varying in Mass, Area, and Morphology
Authors: Augspurger Carol K. , Franson Susan E.
Published: May 2006

We used a field experiment to quantify the independent effects of variation in several fruit characteristics and in wind speed on dispersal of the windblown samaras of the tropical tree, Tachigalia versicolor. On Barro Colorado Island, Panama, we simultaneously released 15 different types of artificial models of these fruits, varying in seed mass, fruit area, and basic morphology, from the top of a 40—m tower, dropping them under five different wind conditions. In general, the horizontal distance a model fruit moves from the base of the tower is proportional to the average wind speed to which it was subject during the whole of its descent, divided by the square root of its wing—loading (wing—loading is the force of gravity on the fruit divided by its projected surface area). This relation was observed for fruits with masses from 1.0 to 1.9 g, with areas from 9 to 76 cm2, and with (wing—loading)1/2 from 15.3 to 30.6 mPa. Two separate changes in the design of the fruit, but with no change in the wing—loading value from that of T. versicolor, caused the models to have either a more rapid rate of descent despite the appropriate aerodynamic motion, or an improper aerodynamic motion resulting in a pronounced increase in rate of descent. Model fruits that had the lowest wing—loading (achieved by decreasing seed mass or increasing fruit area) or that were blown by the strongest mean winds were dispersed the greatest mean distances and were scattered most evenly and over the widest area. A change in wing—loading or wind speed changed dispersal distance the least and the evenness of the distribution the most. Variation in wind speed has the potential to override the effect of variation in mass or area on dispersal, unless the differences in mass or area among models are quite large.
Herbivory in Complex and Simple Tropical Successional Ecosystems
Authors: Brown Becky J. , Ewel John J.
Published: May 2006

To investigate the relationship between herbivory and floristic complexity, we measured losses to herbivores in four 0.1— to 4—yr—old tropical ecosystems: (1) unmanipulated successional vegetation, (2) successional vegetation with higher plant diversity than the unmanipulated succesion, (3) an ecosystem of investigator—controlled species composition, designed to imitate the physiognomy and species richness of the successional vegetation, and (4) monocultures of maize, cassava, and Cordia alliodora. We measured herbivory rates (loss of leaf area per day) on dominant plant species in each system and aggregated over species to estimate rates for plant communities. Although herbivory rates varied widely among species, losses to herbivores in terms of mass of leaf tissue lost per unit of ground area were approximately equal in the four systems, 71.5 to 78.5 g°m—2. yr—1. Ecosystems with greater plant species richness lost a lower proportion of available leaf area and exhibited lower temporal variability in herbivory. Species—rich ecosystems had relatively constant, predictable rates of herbivory due to counterbalancing of low rates on some species with high rates on others. The rate of herbivory on any species was strongly influenced by the nature of the surrounding vegetation. Although surrounding vegetation often conferred protection upon potential pest targets, in some cases a plant species experienced increased susceptibility to herbivores through association with other species.
Population Dynamics and Standing Biomass of the Freshwater Sponge Spongilla Lacustris
Authors: Frost Thomas M. , De Nagy George S. , Gilbert John J.
Published: May 2006

In a sphagnum bog—pond in central New Hampshire, USA, the common freshwater sponge Spongilla lacustris exhibits a high growth rate and reaches a large standing biomass (ash—free dry biomass is 1.7 g/m2) by the end of its growing season in October. The sponge overwinters as gemmules, and the conversions between these dormant forms and active sponge tissue in the spring and fall are very conservative in terms of biomass. With the high growth rate and efficiency of these transfers, 10 mg of gemmulated sponge (AFDM) in the spring could eventually produce 18 g upon resting stage formation in the fall. S. lacustris does not require a hard substratum. The greatest part of this population grows as upright branches from the pond bottom or attached to aquatic macrophytes. In winter, the gemmulated sponges, including those attached to macrophytes, collapse into the bottom sediments. There is a high mortality during this period, resulting from the accumulation of sediments over the gemmulated sponges, which prevents their successful hatching. It appears that sponges derived from sexually produced larvae would be particularly unlikely to survive the winter. A sexual growth processes are thus of primary quantitative importance in this system and must be considered in evaluating reproductive effort.
Effects of Forest Cutting on Two Carabus Species: Evidence for Competition for Food
Authors: Lenski Richard E.
Published: May 2006

I investigated the effects of forest clear—cutting on two predatory beetles. Carabus limbatus was numerically dominant in the forest, but its density was significantly reduced on the clear—cut. C. sylvosus density was little affected by forest cutting. An enclosure experiment was conducted in order to distinguish between the effects of habitat and density on the foraging success of C. limbatus. Individual beetle mass served as an operational measure of foraging success. On the clear—cut, the foraging success of C. limbatus was subject to opposing pressures. Lower density of conspecifics tended to improve foraging success, while other attributes of the clear—cut tended to reduce foraging success. C. sylvosus is similar to C. limbatus in habitat, diet, and temporal activity pattern. C. sylvosus foraged significantly more successfully on the clear—cut, where C. limbatus was less abundant, than in the forest. I hypothesized that Carabus species compete for limiting food in the undisturbed forest, and that clear—cutting ameliorates competition by reducing the numerically dominant C. limbatus.
Habitat Selection and the Community Matrix of a Desert Small‐Mammal Fauna
Authors: Hallett James G.
Published: May 2006

This study considers several questions about interspecific competition and habitat use by desert small mammals. From 1971 through 1973, rodent population data were collected by live—trapping on a creosote bush bajada located near Las Cruces, New Mexico, USA. At each trap station, measurements of the vegetation were taken to provide a description of the microhabitat surrounding each station. Multiple regression analysis was used to estimate the effects of competition and habitat selection in determining the local distributions and abundances of the rodent species in each year. The 10 species form four guilds: (1) Onychomys arenicola, (2) Neotoma albigula and N. micropus, (3) Dipodomys merriami and D. ordii, and (4) Perognathus intermedius, Pg. penicillatus, Peromyscus eremicus, P. maniculatus, and P. leucopus. None of the competition estimates for between—guild interactions was significantly negative, indicating that a species in one guild did not have any inhibitory effects on species in other guilds. Coexistence of the four guilds was attributable in some cases to differences in food and habitat preferences, and in others to differences in foraging methods related to body size. Competition was not observed within the Dipodomys guild because of the different microhabitat specializations of the two species. The three Peromyscus spp. appear to avoid competition with each other by complementary habitat use; competition was observed within the Perognathus—Peromyscus guild, but only among Perognathus intermedius, Pg. penicillatus, and Peromyscus eremicus. The magnitudes of the observed competitive interactions varied significantly from year to year with changes in both rodent densities and resource availabilities. The competitive relationships within the guild were consistent, however, and the three species were ranked in increasing competitive ability; Perognathus penicillatus < Perognathus intermedius < Peromyscus eremicus. Some evidence suggests that competitive ability increases with increasing habitat specialization.
Mat‐Water Phosphorus Exchange in an Acid Bog Lake
Authors: Hooper Frank F. , Morris Laura S.
Published: May 2006

The exchange of phosphorus between a bog lake and its surrounding Sphagnum mat and the fate of mat phosphorus entering the limnetic zone of a lake were studied by means of a series of mat—labeling using 32P, and by an analysis of water budgets of the lake and mat. A 32P solution applied directly to the Sphagnum, so as to simulate phosphorus input from rainfall, produced a labeled soluble but biologically refractory phosphorus fraction which persisted in the lake at the initial concentration level for >16 d. Labeling the interstitial water of the mat directly with 32P produced a labeled particulate fraction which was biologically active and was quickly concentrated in the limnetic food web. Heavy rainfall flushed both labeled components into the lake. The pathway phosphorus takes to enter the lake from the mat was determined by temperature gradients in the mat and the degree of decomposition of the mat material. In early spring, with low water temperatures, phosphorus moves along isotherms from the mat directly to the hypolimnion and bypasses the thermocline. In late spring movement is to the epilimnion and thermocline. The maximum phosphorus concentrations in the mat were above a compacted zone at the 2—m depth. This maximum coincided with an open—water phosphorus maximum at 2 m, which indicated that there were frequent inputs of mat phosphorus to this stratum. The direction of net phosphorus movement was largely controlled by the water balance of the system. During periods of high precipitation, low temperatures, and low evapotranspiration, as was found in early spring, net phosphorus movement was toward the lake. During midsummer high evapotranspiration of the mat vegetation increased the storage capacity of the mat. This reduced phosphorus flow toward the lake so that net flow was often toward the mat.
Overlap Summary Indices and the Detection of Community Structure
Authors: Thomson James D. , Rusterholz Kurt A.
Published: May 2006

Overlaps in resource use have been used to summarize community structure. It is ofen desirable to compare the amount of intensity of overlaps (or other pairwise measures such as competition coefficients) in different communities, especially in the context of comparing actual communities to "neutral model" simulations. We show that the most commonly used index for such comparisons, the mean pairwise overlap, is often unsuitable, and suggest alternate approaches.
Phenology and Ecophysiology of the Tropical Tree, Tabebuia Neochrysantha (Bignoniaceae)
Authors: Reich Peter B. , Borchert Rolf
Published: May 2006

Phenology and seasonal variations in water stress, as reflected in variations in stem circumference, were monitored throughout 1978 in numerous Tabebuia neochrysantha growing at several dry and wet sites in a lowland deciduous forest in Guanacaste, Costa Rica. The rate of leaf fall during the early dry season was strongly correlated with the decline in soil moisture and increasing water stress of the trees. Without exception, recovery from water stress was required for flowering and shoot emergence. At dry sites rehydration ocurred only after isolated rain showers or irrigation; at wet sites it took place during continued drought, probably as a consequence of the decrease in transpiration during leaf fall. Flowering has been observed to occur at any time between the beginning (December) and end (May) of the dry season. Differences in the timing and intensity of flowering as well as in the timing of leaf fall and shoot emergence can be accounted for by site—dependent differences in the rates of desiccation and rehydration of trees in conjunction with year—to—year variation in the timing and intensity of rainfall. No evidence for the control of seasonal development by other environmental factors, such as variations in temperature of photoperiod, was obtained.
Phenological Relationships of Wasps, Bumblebees, Their Mimics, and Insectivorous Birds In an Illinois Sand Area
Authors: Waldbauer G. P. , Sternburg J. G. , Maier C. T.
Published: May 2006

Surveys in a xerophytic forests association in an Illinois sand area showed that specialized Batesian mimics of stinging bumblebees or wasps are numerous in spring and early summer, generally absent in midsummer, and present but infrequent in late summer. This extends the known occurrence of this sort of seasonal distribution among mimics to a group of mimetic species which are rare or do not occur in the mesophytic forest associations in Illinois which were surveyed by two previous investigators. Our findings support the hypothesis of these previous investigators that some temperate zone Batesian mimics may be selected to avoid the midsummer season when newly fledged, insectivorous birds are abundant and have not yet learned to shun the models which the mimics resemble.
On Fitting the Truncated Lognormal Distribution to Species‐Abundance Data Using Maximum Likelihood Estimation
Authors: Slocomb John , Stauffer Barbara , Dickson Kenneth L.
Published: May 2006

The truncated lognormal distribution can be used to graduate certain species—abundance data, provided that estimates of the location and scale parameters are obtained. A computer program has been written which groups the data on a log2 scale and numerically solves the maximum likelihood equations for this type of distribution. Results show that the estimates obtained by this method compared well with those of Hald and Cohen. Examples are presented using the diatom data of Hohn and Hellerman, and it is shown that a better fit is obtained by using the entire data set instead of selectively disregarding the most abundant tail intervals. Other published techniques for this type of analysis are also discussed.
Competition Between Exotic Species: Scale Insects on Hemlock
Authors: McClure Mark S.
Published: May 2006

Two exotic armored scales, Fiorinia externa Ferris and Tsugaspidiotus tsugae (Marlatt), native to Japan occur sympatrically in the northeastern United States where they often attain high population densities on eastern hemlock, Tsuga canadensis Carriere. Both scales preferentially colonize the young needles of the lower hemlock crown, which intensities competition between them when food and space become limiting at high scale densities. Studies conducted for 2 yr in the greenhouse and in a hemlock forest located in Darien, Connecticut, demonstrated that summer generations of F. externa and T. tsugae compete intraspecifically and interspecifically at densities occurring in the field. F. externa had a greater advderse affect (reduced survival and fecundity) on itself and on T. tsugae than did T. tsugae have either on itself or on F. externa. The superior competitive ability of F. externa over T. tsugae was likely due to its earlier colonization time. Hatching in early June some 2—4 wk prior to its competitor, F. externa is afforded a distinct spatial and nutritional advantage (1) by colonizing young, nitrogen—rich needles at a time during the year when concentrations of foliar nitrogen and water are high, (2) by reducing the amount of foliar nitrogen available to T. tsugae nymphs, and (3) by forcing T. tsugae crawlers to colonize older, nitrogen—poor foilage where they subsequently suffer significantly greater mortality. Aspidiotihagus citrinus Crawford (Hymenoptera: Aphelinidae), a primary internal parasitoid of F. externa and T. tsugae, exhibited a density dependent response to both scales in single—species infestations in the Darien forest. In mixed infestations, however, the parasitoid did not selectively attack the more abundant species but parasitized each scale in proportion to its frequency. Because it did not discriminate between hosts, A. citrinus did not alter the outcome of the competition between summer generations of the two scales. The geographical distributions of the two scales in Faifield County, Connecticut, and their population trends for 3 yr at 20 sites where they occur sympatrically indicate that competition has excluded T. tsugae. At 18 to 20 sites coinhabited at different densities during 1976, T. tsugae was excluded or nearly excluded within 3 yr. Only at two sites, where T. tsugae was abundant and F. externa was sparse, was T. tsugae able to maintain its initial relative density.
Relationships Between Sunfleck Dynamics and Red Fir Seedling Distribution
Authors: Ustin S. L. , Woodward R. A. , Barbour M. G. , Hatfield J. L.
Published: May 2006

Red fir (Abies magnifica) Seedings show a patcy distribution in much of the species' range. Patterns of irradiance in the understory of a red fir forest in the central Sierra Nevada Mountains of California were measured in an effort to determine whether a correlation existed between the irradiance patterns on the forest floor and the distribution of seedlings. Replicate pairs of plots ona south exposure with significant differences in seedling density were compared with each other and with plots on a contiguous north exposure. No significant differences between plots or south exposures were found for either physical characteristics, soil chemistry, water, or liter layer traits. On the south aspect, plots with few seedlings had mean daily irradiances 2.1 times higher than plots with many seedlings, primarily due to 3.5 times more frequent occurrence of sunflecks at irradiance levels above 1025 μE°m—2°s—1. Analysis of solor tracks on fish—eye—lens photographs of overstory canopies and measurement of sunflecks on the forest floor indicated that plots with few seedlings had larger sunflecks, particularly during midday hours. In contrast, seedling distribution on the north exposure was not correlated with patterns of irradiance or temperature, apparently because of less intense direct—beam irradiance on these slopes. Apparently the high irradiance on open south slopes is inhibitory to red fir seedlings compared with the low—intensity irrandance on more shaded south slope sites and on all north slope sites. Phonon flux densities >500 μE°m—2°s—1 are beyond the light saturation point for net photosynthesis, as determined in the laboratory from field—collected seedlings. Absorption of light >500 μE°m—2°s—1 by seedlings will substantially increase the energy load without corresponding increases in carbon gain. We suggest seedlings are absent from high—light plots because of temperature and water stresses induced by higher irradiances early in the growing season.
The Optimization of Growth Rate in Altricial Birds
Authors: Ricklefs Robert E.
Published: May 2006

I have developed models relating the rate of growth of altricial birds to annual production of fledglings, a measure of evolutionary fitness. In the models, growth rate influences production through its effect on the power requirements of the nestling and the length of the nesting cycle; the latter in turn affects probability of survival to fledging and number of broods reared per year. The models were evaluated to determine whether empirically reasonable estimates of power requirements and nesting mortality resulted in predicted optimum growth rates within the range of observed values. By and large the models were successful. They do not adequately explain the reduced growth rates of tropical altricial species compared to their temperate—zone counterparts. Moreover, they do not address the phenomenon of slow growth in self—feeding, precocial species. But the confirmation of the model for many altricial birds suggests that it may be possible to understand interspecific variation in growth rates as the result of adaptations to levels of predation and the requirement for, availability of, energy to the nestling.
Priority Effects in Experimental Pond Communities: Competition between Bufo and Rana
Authors: Alford Ross A. , Wilbur Henry M.
Published: May 2006

The effect of order to hatching on the outcome of larval competition between two species of frogs breeding in 27 artificial ponds was studied. There were nine different treatments, each replicated three times: all combinations of various introductions of Bufo americanus hatchlings (none added, 500 added on day 0, or 500 added on day 6) and various introductions of Rana sphenocephala hatchlings (none added, 100 added on day 0, or 100 added on day 6). Response variables were the body size at metamorphosis, the length of the larval period of each individual, and the number of survivors of each species in each experimental pond. Bufo individuals and populations did best when alone. Also, they did better when introduced on day 6 rather than day 0. This may have been because the standing crop of food was greater in the communities that were 6 d older. When present with Rana, Bufo did better if added before Rana and worse if added after Rana, as compared to when both species were added at the same time. These results are consistent with a mechanism of size—specific competition. Rana also did best when alone and when introduced late rather than early. Rana did better when added after Bufo and worse when added before Bufo as compared to when both species were introduced at the same time. These results are not consistent with simple size—specific competition. When the species were together, both species did best when Bufo was added early and Rana was added late. These results suggest that optimal oviposition behavior is problematical for female frogs: the time that will be best depends on whether or not another species will be present at the time of hatching.
Phenotypic Variation in Metamorphosis and Paedomorphosis in the Salamander Ambystoma talpoideum
Authors: Semlitsch Raymond D. , Gibbons J. Whitfield
Published: May 2006

Phenotypic variation in metamorphosis and paedomorphosis in the salamander Ambystoma talpoideum was examined to determine its environmental or genetic basis. Eight artificial ponds were maintained, four at each of two environmental treatments: constant water level, to simulate fish free permanent breeding ponds, and gradual drying out, to simulate temporary breeding ponds. Two populations of salamanders were used, derived from two breeding ponds having different frequencies of paedomorphosis. The water level in the drying treatment was lowered during the last 10 wk of the experimental period with no apparent differences in water chemistry parameters between treatments and only a slight change in water temperatures during the last 2 wk. The quality of the growth environment for larvae, as measured by body size and survivorship, was the same in the four experimental treatments. The frequency of metamorphosis was significantly higher in the drying treatment that under constant water level, and also differed between populations. The frequency of paedomorphosis was significantly different between populations but not between water level treatments. The effects of water level were potentially confounded by those of water temperature, density of larvae, and amount of food. Population differences in the frequency of metamorphosis and paedomorphosis could potentially represent genetic differences resulting from the different selective regimes that individuals encounter in breeding ponds varying in drying frequency. However, phenotypic plasticity and nongenetic maternal effects cannot be dismissed without further experimentation.
Statistical Inference on Measures of Niche Overlap
Authors: Mueller Laurence D. , Altenberg Lee
Published: May 2006

Estimates of measures of niche overlap are often reported without any indication of sampling variance or an accompanying confidence interval. We have investigated the delta, jackknife, and bootstrap methods for making statistical inferences on four measures of niche overlap: the coefficient of community, Morisita's index, Horn's index, and the Euclidian distance. Our qualitative conclusions are: (1) The bias of these estimators was usually @<10% of the mean unless the sample size was small and the number of resource categories large. The jackknife and bootstrap can significantly reduce this bias. (2) The variance of the bootstrap and jackknife estimators was usually greater than that of the “standard” estimator. (3) Under a variety of circumstances, the population sampled may actually represent several unrecognized subpopulations. In such cases confidence intervals generated by the jackknife and delta techniques can be quite inaccurate, while the nonparametric confidence intervals derived from the bootstrap are highly accurate.
Environmentally Influenced Changes in Sex Expression in an Andromonoecious Plant
Authors: Solomon Bruce Peary
Published: May 2006

Sexual expression and maternal investment were investigated in the herbaceous perennial Solanum carolinense (Solanaceae). Field censuses, pollen germination studies, and the results of hand—pollination experiments in a greenhouse revealed that there are three flower types. Morphological males (M) are found near the tip of the inflorescence and have short styles; these flowers did not set fruit when pollinated. All other flowers have long styles and are morphological hermaphrodites (H); among these, those near the base of an inflorescence set fruit when pollinated (fruiting hermaphrodites, FH) while those in intermediate positions did not (functional males, FM). No morphological differences were apparent between FH and FM flowers. Male function of M and H flowers was indistinguishable in terms of pollen germination and quantity and quality of seed produced. The proportions of FM flowers decreased with later inflorescences, but the proportion of FM flowers increased correspondingly. Thus, the morphological sex ratio, M/(M + H), decreased with plant size, while the functional sex ratio, (M + FM)/(M + FM + FH) did not vary. These data do not support evolutionary theories that predict increased allocation to female versus male function with increasing plant size. In addition, experimental manipulations were performed on greenhouse plants. Morphological sex ratio changed in response to various plant hormones, which suggests hormone involvement. Sex ratio increased in response to increased shade and water stress, which supports those evolutionary theories that predict a shift to maleness in response to stress. However, increasing levels of fertilizer also increased the morphological sex ratio Pollination did not influence the morphological sex of subsequent flowers; rather, regulation of fruit—set after pollination occurred via changes in the proportion of H flowers that did (FH) or did not (FM) set fruit. The results are discussed in terms of three stages at which maternal investment can be regulated: flower initiation, flower maturation, and fruit maturation.
Decomposition of Chaparral Shrub Foliage
Authors: Schlesinger William H.
Published: May 2006

Decomposition of leaf litter from two chaparral shrubs, Ceanothus megacarpus (an evergreen sclerophyll) and Salvia mellifera (a drought—deciduous species), with studied using litter bag methods for a 3—yr period at two elevations in the coastal mountains of southern California. The decomposition rates were similar between species. Mean residence time for the organic matter in the litter layer was 5.3—7.7 yr. N and P were immobilized in the litter of Ceanothus, which showed no net release of these nutrients during the 3—yr period. Only N was immobilized in Salvia litter, which had high initial concentrations of P. During decomposition the amount of resistant “lignin” substances increased, but there was no indication that these substances contained the immobilized N and P. The growth of Ceanothus chaparral may be limited by P. especially in old stands. The mean residence time for the litter layer suggests that decomposition is important to the supply of available nutrients in mature chaparral.
Desiccation of Rotifers (Macrotrachela Quadricornifera): Survival and Reproduction
Authors: Ricci Claudia , Vaghi Luisella , Manzini Maria Lucia
Published: May 2006

Eggs and adults of the bdelloid rotifer Macrotrachela quadricornifera aged 3, 5, 8, and 14 d were dried for 4 d, and 5— and 8—d—old animals for 30 d, to determine ability to recover. The highest percentage recovery was obtained with 8—d rotifers stressed for 4 d., while no animals aged 5 d recovered from 30 d of drying. Age—specific survival and fecundity of animals that recovered from drying generally were similar to controls. Only 5—d—old stressed rotifers had significantly decreased fecundity, while 14—d—old stressed animals had shorter life—spans. Age—specific fecundity and survivorship of stressed were also similar to controls. Age effect ability to recover but not the remaining life of the recovered animals. The life cycle seems to follow a fixed program regardless of the time spent in the anhydrobiotic state.
Influence of Refuging Consumers (Pikas: Ochotona Princeps) on Subalpine Meadow Vegetation
Authors: Huntly Nancy J.
Published: May 2006

Talus slopes in western North America frequently are bordered by vegetation that differs in biomass, cover, height, and species composition from vegetation located farther from talus. These areas are grazed by pikas (Ochotona princeps), which nest in that talus. Foraging theory predicts that pikas will produce a gradient of grazing pressure, which could produce the observed vegetational zonation. In a subalpine meadow in west—central Colorado, pikas produced the predicted gradient of grazing pressure, along which plant groups varied clinally in abundance. The effects of pikas on talus—border vegetation were tested by excluding pikas from small plots at several distances from talus. Vegetational cover and species richness increased in exclosures relative to control plots. These changes in vegetation following exclusion of pikas were greatest near talus and decreased with distance, paralleling the gradient of foraging by pikas. The effect of pika exclusion on cushion plants changed quantitatively and qualitatively with distance from talus and with time since grazing was stopped. These patterns were predicted from a model of the interaction of competition and predation along a gradient of grazing pressure. Mechanisms similar to those proposed for pikas are also expected for other small herbivores that forage from fixed nest sites.
Food Caching By Willow and Crested Tits: A Test of Scatterhoarding Models
Authors: Jokinen Simo , Suhonen Jukka
Published: May 2006

In coniferous forests of Central Finland, Willow (Parus montanus) and Crested Tits (P. cristatus) store seeds in a scattered distribution within their territory during the autumn. Individuals cache and recover food items while moving together as members of mixed—species flocks. The purpose of this study was to test certain predictions of scatter—hoarding models (Stapanian and Smith 1978, Clarkson etal. 1986), which predict how the animal should hoard food items from a superabundant source to maximize the number of caches recovered. Our field experiments gave support to most of the predictions of the models. Individual tits stored seeds closer to the food source when food had been available for first time (new feeder with seeds not previously available) than to feeders with seed available for 1 mo. Individual birds of both species carried large food items (hulled sunflower seeds) father than small items (spruce seeds) before caching them. Crested Tits distributed their catches uniformly around the feeder while most of the Willow Tits favored certain sectors around the feeder. Subdominant individuals carried seeds the same distances as did dominant birds when the food source was ephemeral, but farther from a continuously available food source.