bluuebunny/crossref_metadata_2025 huggingface dataset:
The Seasonal Decline in Tree Swallow Clutch Size: Physiological Constraint or Strategic Adjustment?
Authors: Winkler David W. , Allen Paul E.
Published: May 2006

The seasonal decline in clutch size has been explained as being due to either: (1) a constraining effect of female condition on both laying date and clutch size; or (2) a seasonal decline in the prospects of chick recruitment, leading to a strategic decrease in clutch size with laying date. In an effort to shed light on this area of disagreement, we analyzed the physiological condition (as measured by body mass, breast muscle thickness, and fat stores) and body size (as measured by wing and head lengths) of 184 female Tree Swallows (Tachycineta bicolor) nesting near Ithaca, New York in 1993, 1994, and 1995, and related their condition to their laying date and clutch size. Through multiple regressions, we found that female age and wing length were the only significant predictors of laying date and that female age and laying date were the only significant predictors of clutch size. Thus, when the effects of laying date were held constant, there was no detectable effect of condition on clutch size in this species. This result is inconsistent with the constraining—condition hypothesis, and it suggests that the seasonal decline of clutch size in Tree Swallows is most appropriately seen as a strategic adjustment by the female to varying prospects for her offspring. The lack of evolution in laying date in at least the Tree Swallow remains a paradox.
The Effect of Age on Timing of Breeding and Reproductive Success in the Thick‐Billed Murre
Authors: de Forest Leah N. , Gaston Anthony J.
Published: May 2006

A seasonal decline in reproductive success is common to many birds breeding in seasonal environments. We examined the reproductive success of Thick—billed Murres breeding at Coats Island, Northwest Territories, Canada to assess the extent to which a seasonal decline in success could be accounted for by correlations between the age of the birds and their date of laying. In 1990 and 1991 reproductive success declined with date of laying: this decline was due mainly to a decline in the proportion of eggs that hatched. No corresponding decline was found in the proportion of hatchlings that reached fledging age. Pairs containing at least one young (4— or 5—yr—old) bird laid later and hatched a lower proportion of eggs than those containing at least one older (> 7—yr—old) bird. The two groups did not differ in the proportion of hatchlings reared. When looked at separately, the proportions of young and older birds that succeeded in hatching their egg were not affected by date of laying. When the two age groups were combined, the trends with date were similar to those found for a large sample, mostly birds of unknown age. To correct for differences in timing of laying, a sample of early breeders was induced to lay replacement eggs 14 d later. These experimental pairs were as successful as early control breeders. A greater proportion of the experimentally delayed pairs hatched chicks than birds laying for the first time at a similar date. The experimental pairs were also more successful than young birds that bred earlier. The growth of experimental and control chicks did not differ. However, the 14—d—old chicks of young pairs were lighter than those of experienced breeders, suggesting poorer provisioning by the young breeders. We concluded that there was no evidence for a deterioration in feeding conditions with date and that the relationship between age and/or experience and date of laying was the most important factor in causing the decline in reproductive success with date of laying was the most important factor in causing the decline in reproductive success with date. Our conclusions may apply to other studies of reproductive success in marine birds.
Susceptibility to Herbivores Depends on Recent History of both the Plant and Animal
Authors: Cronin Greg , Hay Mark E.
Published: May 2006

Physical stress to seaweeds and hunger stress of herbivores can influence the outcome of chemically mediated seaweed—herbivore interactions. The unpalatable brown seaweed Dictyota ciliolata produces the diterpenoid secondary metabolites pachydictyol A, dictyol B acetate, and dictyodial. At natural concentrations, pachydictyol A deterred the sea urchin Arbacia punctulata but did not inhibit feeding by the pinfish Lagodon rhomboides or the amphipod Ampithoe longimana until concentrations were 2.5—5 times natural levels. Dictyol B acetate deterred the urchin, amphipod, and pinfish at, or far below, natural concentrations. Dictyodial was too unstable to assay directly, but indirect experiments suggested that natural concentrations deterred the urchin, but not the pinfish or amphipod. Mild desiccation of D. ciliolata reduced concentrations of the different secondary metabolites by 7—38% and plants became 2.6—3.4 times more susceptible to urchin and amphipod grazing. The combined concentrations of pachydictyol A and dictyol B acetate found in undesiccated Dictyota ciliolata deterred feeding by urchins, but this deterrent effect was lost at concentrations found in the desiccated plants. Desiccated and undesiccated plants did not differ in nutritive value (as measured by protein and total N content) or toughness. Thus, desiccated plants became more palatable because chemical defenses were lost, not because nutritive value was increased. The stress of near—surface ultraviolet radiation also caused significant physiological changes in Dictyota ciliolata. UV—exposed blades bleached, senesced, and grew 84% less than blades protected from UV radiation. Tissue loss and minimal growth of UV—stressed plants constrained our sample sizes, but the limited assays that could be run suggested that UV stress may lower chemical defenses and increase plant susceptibility to herbivores. Because many previous investigations of herbivore feeding patterns used animals that had been starved for days before an assay, we tested the effects of this commonly used procedure on feeding discrimination. Recently fed urchins always avoided food containing natural concentrations of pachydictyol A during separate feeding trials performed on each of four consecutive days. In contrast, urchins deprived of food for 3 d before this assay did not avoid the treated food on days 1 and 2 of feeding trials, but did avoid it on days 3 and 4 after their hunger was reduced by feeding during days 1 and 2. If we had used only starved urchins (a common procedure in previous investigations), we could have concluded, with apparent justification, that urchins were unaffected by pachydictyol A (if the assays were run for only 1—2 d) or that they needed 2 d of exposure to the compound in order to learn to avoid it. Both of these conclusions would have been incorrect.
Competition between Viruses in a Complex Plant‐‐Pathogen System
Authors: Power Alison G.
Published: May 2006

Interactions among viruses, vectors, and host plants may influence the spread and success of plant viruses. Major factors include direct competition within host plants, direct competition within vectors, differences in transmission rates, and virus influences on vector behavior and population dynamics. The aphid—transmitted barley yellow dwarf viruses (BYDVs), which infect a broad range of grasses worldwide, represent a model system for addressing questions about the outcome of direct and indirect competition between viruses. Historical shifts in the relative prevalence of BYDV strains document the apparent displacement of one virus strain (PAV) by another (MAV) over 20 yr. In the barley yellow dwarf system, transmission rate appears to play an important role in determining the outcome of competition between viruses. Moreover, the interaction between transmission rate and vector behavior may be particularly important. PAV is the stronger competitor within hosts, where double infections occur more often than in insect vectors. PAV also has significant advantages due to higher overall transmission rates than MAV. In addition, vector aphids show a strong nonpreference for PAV that may lead to greater rates of virus spread.
Host Preferences of Rhus Radicans (Anacardiaceae) in a Southern Deciduous Hardwood Forest
Authors: Talley Sharon M. , Lawton Robert O. , Setzer William N.
Published: May 2006

Rhus radicans, a root—climbing liana, is not distributed randomly among potential host tree species in old—growth mixed mesophytic forest on the southern Cumberland Plateau of north Alabama, USA. Vines are more abundant than expected on Carya ovata and Quercus rubra, but less abundant than expected on Juglans nigra, Acer saccharum, and Sassafras albidum. Seed germination and early seedling growth in the presence of bark extracts suggest allelochemical interactions may influence the observed host preferences.
The Effects of Disturbance Architecture on Landscape‐Level Population Dynamics
Authors: Moloney Kirk A. , Levin Simon A.
Published: May 2006

Phenomena such as disturbance play a major role in structuring ecological systems by producing a spatiotemporal mosaic of patches at different successional states. The distribution of species within the resulting mosaic depends upon an interaction between species' life history traits and the spatial and temporal structure of the ecological processes controlling species' distributions. We have used a spatially explicit simulation model (Jasper) of a serpentine grassland to examine the importance of some of these relationships, focusing primarily on the role of disturbance. The model Jasper is hierarchical in design and was developed to simulate the population dynamics of three interacting plant species: Bromus mollis, Calycadenia multiglandulosa, and Plantago erecta. Population dynamics were modeled as occurring within local sites, which were then arranged in a square array to form a landscape. Connections among sites within a landscape were made primarily through seed dispersal. Several components of disturbance architecture were varied systematically among model runs to determine their impact on population dynamics at the scale of the landscape. We considered three levels of organization in modeling disturbance: (1) overall rate of disturbance, (2) size of individual disturbances, and (3) temporal and spatial autocorrelation among individual disturbances. The results demonstrate that the impact of disturbance depends upon a complex interaction between the life history characteristics of the species making up the community and the spatial and temporal structure of the disturbance regime. For example, we found that the biggest impact on species abundance occurred in response to a shift in the temporal autocorrelation structure of the disturbance regime. Also, species diversity was found to increase at intermediate levels of disturbance (as has been shown in several other studies). However, what can be considered an intermediate level of disturbance depends as much upon the temporal autocorrelation structure of the disturbance regime as it does upon the absolute rate of disturbance. These results suggest that predicting the impact of disturbance on ecological communities will require an explicit understanding of at least some aspects of the spatial and temporal architecture of the disturbance regime.
Exploitation Competition in Mobile Grazers: Trade‐offs in Use of a Limited Resource
Authors: Schmitt Russell J.
Published: May 2006

Mechanisms underlying competitive effects between two species of marine snails (Tegula aureotincta and Tegula eiseni) were examined; results indicated that the interaction involved exploitation of microalgae and not interference. A behavioral experiment demonstrated that an individual of either species was less likely to feed on a recently grazed patch when the prior forager was T. aureotincta. Both snails responded only to the amount of food available on a patch, and, except at very low food levels, the likelihood that a snail would remain to feed was identical for the two species across microalgal densities. Where food was scarce, T. eiseni was more likely than T. aureotincta to feed in that patch. Density—dependent effects on microalgal standing stock differed between the snails; at low grazer densities, T. aureotincta depressed food levels to a comparatively greater degree, whereas at high grazer densities, T. eiseni had a relatively greater effect. The relative growth performance of the snails differed as a function of available food: T. aureotincta had superior body growth at high resource densities, while T. eiseni grew comparatively better at low microalgal densities. Differences in effects on and growth responses to microalgae arose from dissimilar foraging characteristics of the snails. Compared with T. eiseni, T. aureotincta moved more rapidly while feeding, harvested twice as great an area per unit time, but was unable to crop microalgae as close to rock surfaces. While T. eiseni grazed a smaller area per unit time, it removed relatively more microalgae per area grazed. These differing suites of foraging attributes may represent a trade—off to harvest food at different densities: cropping closer to the substratum (area intensive grazing) yields more food when microalgae are scarce, but precludes grazing a larger area per unit time (area extensive grazing) through fast movement, which provides a greater food intake when microalgae are abundant. If an area extensive (moves faster)—intensive (digs deeper) trade—off is a common feature of benthic grazer systems, knowledge of this aspect could provide great predictive insight into the patterns and causes of density dependence arising from exploitation.
Disappearance of Female Pied Flycatchers in Relation to Breeding Stage and Experimentally Induced Molt
Authors: Slagsvold Tore , Dale Svein
Published: May 2006

According to life history theory, adult mortality during the breeding season may have an important influence on the evolution of several aspects of breeding ecology in birds, yet few studies have tried to quantify such mortality. We studied disappearance of Pied Flycatchers (Ficedula hypoleuca) during four breeding seasons in a woodland area in Norway provided with nest boxes. The main cause of disappearance was probably predation by the European Sparrowhawk (Accipiter nisus). Disappearance was nonsignificantly higher in females (10% per season, n = 305) than in males (7% per season, n = 269). Female disappearance peaked during egg—laying (0.53% per day), but was also high during the nest—building (0.42% per day) and nestling (0.36% per day) stages. It was low during incubation (0.05% per day), probably because less time was spent outside the nest. Low risk of predation during incubation may help to explain why female body mass remains high during this stage of breeding but drops soon after hatching. Females with selected flight feathers experimentally removed to simulate molt suffered a much higher disappearance per season (24%, n = 109) than did control females (10%, n = 305). This may help to explain why breeding and molt usually are temporally segregated activities in birds. Variation in female body mass and size (wing length, tarsus length), age, previous breeding experience, mating date, laying date, clutch size, and mating status could not account for the variation found in female disappearance. Disappearance was lower in males than in females during the nest—building period, despite the more conspicuous plumage color of males. This may be explained by the fact that only the female builds the nest. We suggest that risk of predation is an important constraint on sexual selection of male plumage color in species in which males take part in nest building.
Interspecific Pollen Loss by Hummingbirds Visiting Flower Mixtures: Effects of Floral Architecture
Authors: Murcia Carolina , Feinsinger Peter
Published: May 2006

Tropical hummingbirds often forage in mixtures of several plant species. As a result, pollen is often transferred among heterospecific flowers. The "Sexual Architecture Hypothesis," a paradigm of pollination ecology and angiosperm evolution, suggests that the severity of such interspecific pollen transfer should reflect the similarity in the architecture of sexual structures (specifically, placement of stigma and anthers) among the flowers involved. We evaluated the hypothesis with six species of Costa Rican cloud—forest plants varying greatly in sexual architecture but all pollinated by the same hummingbird, Lampornis calolaema. Captive Lampornis visited five long—styled, "pollen—donor" flowers of distylous, self—incompatible Palicourea lasiorrachis (Rubiaceae), then 20 short—styled recipient flowers of Palicourea, with or without five flowers of a second species intervening. We assessed intraspecific pollen transfer from Palicourea donors by counting pollen tubes in styles of the recipients. We examined interspecific pollen transfer between Palicourea and each of the five other species by counting heterospecific grains deposited on stigmas of Palicourea recipients, and Palicourea grains deposited on stigmas and anthers of the heterospecific flowers. In a separate experiment, we examined how mixed—species flower visits modified the pollen loads actually carried by birds. Results did not uphold the Sexual Architecture Hypothesis. A single visit to any heterospecific flower greatly affected the hummingbird's prior load of Palicourea pollen, regardless of where the second species placed its own pollen on the bird. Interspecific pollen transfer occurred consistently, but (1) heterospecific grains usurped little space on stigmas of Palicourea recipients and had no discernible effect on pollen—tube growth, whereas (2) few Palicourea grains landed specifically on anthers and stigmas of heterospecific flowers. Instead, numerous Palicourea grains apparently were scraped off on other floral structures such as the corolla. Consequently, every species of intervening flowers, regardless of its sexual architecture per se, strongly reduced pollen transfer from donor to recipient Palicourea flowers, on average by 76%. In fact, the most drastic reductions resulted from the two species whose sexual architectures least resembled that of Palicourea. Results imply that "pollen scraping" by floral structures other than anthers and stigmas may be important and widespread among some animal—pollinated flowers. Thus, except in cases where no other floral structures contact pollinators, the positions of anthers and stigmas alone may have little bearing on the severity of interspecific pollen transfer and competitive interactions among plants sharing pollinators.
Positive Indirect Effects Between Prey Species that Share Predators
Authors: Abrams Peter A. , Matsuda Hiroyuki
Published: May 2006

Mathematical models are used to explore the interaction between two prey species that share a common predator. The models assume that the predator experiences density dependence via some mechanism other than prey depletion. The models also assume that the predator's functional response to each prey decreases as the density of the other prey species increases. This can occur either because of predator satiation or predator switching. The results suggest that positive indirect effects of one prey on the equilibrium density of others should occur frequently, especially when there is predator switching. Decreasing the mortality rate of one prey or adding a prey species may make it easier for additional prey species to invade the system and coexist. This occurs because the resulting decrease in the predator's functional response is greater than its positive numerical response. In many cases, different magnitudes of perturbation to one prey species will have opposite effects on the population density of the other prey species.
A Statistical Test for a Difference between the Spatial Distributions of Two Populations
Authors: Syrjala Stephen E.
Published: May 2006

A statistical hypothesis test for a difference between the spatial distributions of two populations is presented. The test is based upon a generalization of the two—sample Cramer—von Mises test for a difference between two univariate probability distributions. It is designed to be sensitive to differences in the way the populations are distributed across the study area but insensitive to a difference in abundance between the two populations. The procedure is nonparametric and uses the methodology of a randomization test to determine the level of significance of the test statistic.
Seasonal Migration of Predators and Prey‐‐A Study of Pythons and Rats in Tropical Australia
Authors: Madsen Thomas , Shine Richard
Published: May 2006

Although seasonal migrations of large predatory mammals that follow migrating prey are well documented, no equivalent phenomenon has been described previously in terrestrial reptiles. We surveyed and radio—tracked water pythons (Liasis fuscus) in Fogg Dam and its adjacent floodplain in the wet—dry tropics of northern Australia to document patterns of movement, with particular emphasis on the ways in which the snakes exploit their major prey species, the dusky rat (Rattus colletti). The distribution and abundance of these rodents vary seasonally. During the dry season the rats live in soil crevices in the floodplain, but wet—season flooding forces them to higher ground, primarily to natural levee banks. Python and rat abundances on the floodplain adjacent to Fogg Dam were significantly correlated through time: both reached a maximum during the dry season, and fell dramatically during the wet season. Activity of pythons was centered around Fogg Dam during the dry season, but all of the radio—tracked snakes moved away from this area during the wet season. Most pythons migrated to the vicinity of levee banks on the floodplain up to 12 km away from their dry—season range. By migrating seasonally, water pythons can efficiently utilize a migratory prey species that would otherwise be unavailable for much of the year.
Trade‐Offs of Ecological Specialization: An Intraspecific Comparison of Pumpkinseed Sunfish Phenotypes
Authors: Robinson Beren W. , Wilson David Sloan , Shea Gabriel O.
Published: May 2006

Most empirical studies of specialists and generalists have focused on comparisons among different species. Interspecific comparisons have recently been criticized because phenotypic trade—offs can evolve after ecological specialization. As a result, it has been suggested that intraspecific variation is the appropriate level to demonstrate functional trade—offs. We demonstrate functional trade—offs for two components of fitness in pumpkinseed sunfish (Lepomis gibbosus) from a single trophically polymorphic population: condition factor and growth rate. Condition factor was estimated using somatic lipid content, while growth rate was determined from scale measurements. Fish with extreme benthic and limnetic morphologies are on average superior to fish with intermediate morphologies, especially in the pelagic habitat. Our study is a particularly stringent test of functional trade—offs at the intraspecific level because the morphological variation is very subtle in this population.
Differential Reproductive Responses to Fluctuating Resources in Two Seaweeds with Different Reproductive Strategies
Authors: Reed Daniel C. , Ebeling Alfred W. , Anderson Todd W. , Anghera Michele
Published: May 2006

Reproduction is closely tied to environmental conditions and the availability of resources, and thus typically varies with season. Consequently, perennial organisms that reproduce continuously are generally restricted to tropical regions with relatively aseasonal climates. The temperate marine alga Macrocystis pyrifera is a rare exception in this regard, as most individuals reproduce throughout the year in a seasonally variable habitat. Here we measure reproductive responses of the giant kelp Macrocystis during a period in which resources and environmental conditions fluctuated greatly and contrast these responses with those of the palm kelp, Pterygophora californica, a sympatric species that exhibits strictly seasonal reproduction. The quantity and quality of spore production tracked resource availability within and among years for Macrocystis, but not for Pterygophora. Reproductive allocation and spore standing stock in Macrocystis were negatively correlated with seawater temperature and positively correlated with the nitrogen content of adult plants. Macrocystis generally displayed two seasonally distinct peaks in spore production per year (winter and spring). The only disruption of this pattern coincided with a warmwater El Nino event. Although seawater temperature and the nitrogen content of adults were inversely related in Pterygophora, neither variable was significantly correlated with the quantity or quality of spore production in this species. Unlike Macrocystis, Pterygophora exhibited a well—defined reproductive season in which plants displayed a single broad peak in spore production that varied little in timing and magnitude among years, even during El Nino conditions. Spore C/N ratios remained relatively constant over time in both species, despite large seasonal fluctuations in C/N ratios of vegetative tissue of adults plants. Nonetheless, spore C/N ratios were positively correlated with seawater temperature in Macrocystis, but not in Pterygophora. Spore viability (swimming and germination) varied considerably, and often unpredictably, over time for both species. Our results support the general idea that environmental conditions and resources exert a much greater influence on the quantity and quality of reproduction in species that reproduce continuously than on the majority of species that are strictly seasonal in onset of reproduction. The differential responses of Macrocystis and Pterygophora may reflect their different morphologies and life—spans. Macrocystis is relatively short lived and may hedge its bets by reproducing continuously rather than risk delaying reproduction. Conversely, since Pterygophora lives much longer, plants can afford to release spores only during times when the chances for reproductive success are predictably greatest because these plants are likely to reproduce again in subsequent years.
A Hypothesis Regarding the Abruptness of Density Dependence and the Growth Rate of Populations
Authors: Getz Wayne M.
Published: May 2006

Most population models incorporate density dependence in a manner that implies the effects of density set in at increasingly higher rates as population densities decrease to zero. For many populations, it may be more plausible to assume that the effects of density set in at a maximum rate around some characteristic density K > 0: that is, the per capita rate of increase of the population has an inverted sigmoidal form as a function of population density. In the model discussed here, the rate at which density dependence sets in around K is governed by a parameter γ, which I refer to as the "abruptness" parameter: the larger the parameter γ, the weaker the effects of density dependence are for population densities below K, the more rapidly density dependence sets in around K, and the more severe the effects of density dependence are beyond K. Results obtained from an Evolutionary Stable Strategy (ESS) analysis of the abruptness parameter γ suggest the hypothesis that populations with a density‐independent growth rate of <100% from one generation to the next (i.e., a reproductive value of <2) will exhibit a relatively high level of abruptness in their response to density, while the reverse will be true for populations with a density‐independent growth rate of >100%. Further, if true, this hypothesis suggests that females with high reproductive rates who deposit young on resources and provide no further maternal care should clump their young to reduce the level of abruptness in density dependence. Also, this hypothesis, together with the fact that high levels of abruptness promote oscillations in populations, implies that we are more likely to observe cyclic and chaotic behavior in relatively slower growing populations than previously thought.
Modeling Invasive Plant Spread: The Role of Plant‐Environment Interactions and Model Structure
Authors: Higgins Steven I. , Richardson David M. , Cowling Richard M.
Published: May 2006

Alien plants invade many ecosystems worldwide and often have substantial negative effects on ecosystem structure and functioning. Our ability to quantitatively predict these impacts is, in part, limited by the absence of suitable plant—spread models and by inadequate parameter estimates for such models. This paper explores the effects of model, plant, and environmental attributes on predicted rates and patterns of spread of alien pine trees (Pinus spp.) in South African fynbos (a mediterranean—type shrubland). A factorial experimental design was used to: (1) compare the predictions of a simple reaction—diffusion model and a spatially explicit, individual—based simulation model; (2) investigate the sensitivity of predicted rates and patterns of spread to parameter values; and (3) quantify the effects of the simulation model's spatial grain on its predictions. The results show that the spatial simulation model places greater emphasis on interactions among ecological processes than does the reaction—diffusion model. This ensures that the predictions of the two models differ substantially for some factor combinations. The most important factor in the model is dispersal ability. Fire frequency, fecundity, and age of reproductive maturity are less important, while adult mortality has little effect on the model's predictions. The simulation model's predictions are sensitive to the model's spatial grain. This suggests that simulation models that use matrices as a spatial framework should ensure that the spatial grain of the model is compatible with the spatial processes being modeled. We conclude that parameter estimation and model development must be integrated procedures. This will ensure that the model's structure is compatible with the biological processes being modeled. Failure to do so may result in spurious predictions.
Determinants of Dispersal in Breeding Merlins (Falco Columbarius)
Authors: Wiklund Christer G.
Published: May 2006

Determinants of adult dispersal were studied in a population of color—banded Merlins (Falco columbarius). In the analysis, I examined the effects of local population density, breeding performance, survival, and characteristics of the mate on movements between breeding seasons. The distance moved between successive breeding seasons varied greatly, both between and within individuals. Fidelity to the breeding areas was higher in males than females, and females dispersed nearly three times as far as males did. Males breeding at high density dispersed shorter distances than other males. Dispersal distances of females were related to aspects of the mate. Females that mated with older males, and with males that survived to the next season, made shorter movements than other females. In both sexes, low reproductive success was associated with long dispersal distances in the next year. Moreover, nest predation in one season resulted in lower return rate by females, but not males. Hence, breeding Merlins responded to their social as well as natural environment by dispersing from areas associated with low survival and poor reproductive performance.
Estimating Annual Survival and Movement Rates of Adults within a Metapopulation of Roseate Terns
Authors: Spendelow Jeffrey A. , Nichols James D. , Nisbet Ian C. T. , Hays Helen , Cormons Grace D. , Burger Joanna , Safina Carl , Hines James E. , Gochfeld Michael
Published: May 2006

Several multistratum capture—recapture models were used to test various hypotheses about possible geographic and temporal variation in survival, movement, and recapture/resighting probabilities of 2399 adult Roseate Terns (Sterna dougallii) color—banded from 1988 to 1992 at the sites of the four largest breeding colonies of this species in the northeastern USA. Linear—logistic ultrastructural models also were developed to investigate possible correlates of geographic variation in movement probabilities. Based on goodness—of—fit tests and comparisons of Akaike's Information Criterion (AIC) values, the fully parameterized model (Model A) with time— and location—specific survival, movement, and capture probabilities, was selected as the most appropriate model for this metapopulation structure. With almost all movement accounted for, on average >90% of the surviving adults from each colony site returned to the same site the following year. Variations in movement probabilities were more closely associated with the identity of the destination colony site than with either the identity of the colony site of origin or the distance between colony sites. The average annual survival estimates (0.74—0.84) of terns from all four sites indicate a high rate of annual mortality relative to that of other species of marine birds.
An Extreme‐Value Function Model of the Species Incidence and Species‐‐Area Relations
Authors: Williams Matthew R.
Published: May 2006

The power function model S = CAz of the species—area relation has a number of shortcomings: it is unbounded, is unable to deal with islands with zero species, and is inappropriate to the known sampling distribution of S. Using only the null assumption that species are randomly allocated to areas, I propose an extreme—value function (EVF) model of the species—area relation derived from Coleman's theory of random placement. This model accords with empirical and theoretical results that have called into question the accuracy of the power function model at large areas, and resolves two dilemmas in the power function model: the lack of any bound to species number, and heteroscedasticity in the sampling distribution of species number. The model is also able to deal with islands with zero species, without modification. The EVF is comparable to the power function model over most practical ranges of island sizes, but has properties that make it superior to the power function model. The EVF model also provides a logical synthesis of single—species incidence and multiple—species models, and as a model of single—species incidence has parameters with biological meaning.
Plant Traits and Resource Reduction For Five Grasses Growing on a Nitrogen Gradient
Authors: Tilman David , Wedin David
Published: May 2006

Five grass species (Agrostis scabra, Agropyron repens, Poa pratensis, Schizachyrium scoparium and Andropogon gerardi) were grown in monoculture for 3 yr on an experimental nitrogen gradient. The species differed significantly in the levels to which they reduced soil solution (0.01 mol/L KCI extractable) nitrate and ammonium concentrations and light penetration to the soil surface. Soil nitrate concentration was an inverse function of root mass, which explained 73% of the observed variance in nitrate. Other species differences explained an additional 9.2%, and total soil N an additional 5% of this variance. Extractable soil ammonium also depended on these variables, but total soil N explained the most variance. Light penetration to the soil surface in these monocultures was a negative exponential function of aboveground biomass (R2 — 0.79). Schizachyrium and Andropogon, the species that reduce soil solution N to the lowest levels on infertile soils, had lower vegetative growth rates, higher root allocation, lower reproductive allocation, and lower tissue N than the other species. Many of these traits are associated with plants on infertile habitats, suggesting a direct link between ecophysiology, resource reduction, and distributional patterns. Because all species survived on even our most nitrogen—poor soil (subsurface sand), differential nutrient reduction, not tolerance, may be the main mechanism favoring these traits in infertile habitats. On infertile soils, the three earlier successional species (Agrostis, Agropyron, and Poa) allocated more to reproduction (rhizome or seed) than the later successional species, but did not reduce soil solution nitrate and ammonium to as low levels. This suggests that our early successional species may be superior colonists but inferior nitrogen competitors compared to the prairie bunchgrasses. Our results can be used to make explicit predictions as to the outcome of nitrogen competition among all possible combinations of these five species.
How long does it take for epilepsy to become intractable? A prospective investigation
Authors: Berg Anne T. , Vickrey Barbara G. , Testa Francine M. , Levy Susan R. , Shinnar Shlomo , DiMario Frances , Smith Susan
Published: May 2006

Objective

To determine prospectively when in the course of epilepsy intractability becomes apparent.

Methods

Data are from a prospective cohort of 613 children followed for a median of 9.7 years. Epilepsy syndromes were grouped: focal, idiopathic, catastrophic, and other. Intractability was defined in two ways: (1) 2 drugs failed, 1 seizure/month, on average, for 18 months (stringent), and (2) failure of 2 drugs. Delayed intractability was defined as 3 or more years after epilepsy diagnosis.

Results

Eighty‐three children (13.8%) met the stringent and 142 (23.2%) met the two‐drug definition. Intractability depended on syndrome (p < 0.0001): 26 (31.3%) children meeting stringent and 39 (27.5%) meeting the 2‐drug definition had delayed intractability. Intractability was delayed more often in focal than catastrophic epilepsy (stringent: 46.2 vs 14.3%, p = 0.003; two‐drug: 40.3 vs 2.2%, p ≤ 0.0001). Early remission periods preceded delayed intractability in 65.4 to 74.3% of cases. After becoming intractable, 20.5% subsequently entered remission and 13.3% were seizure free at last contact.

Interpretation

Intractable epilepsy may be delayed, especially in focal epilepsy. It often is preceded by a quiescent period, followed by further remissions. These findings help explain why surgically treatable epilepsies may take 20 years or longer before referral to surgery. Ann Neurol 2006
Reading and writing book reviews across the disciplines
Authors: Hartley James
Published: May 2006

Reading and writing book reviews for learned journals plays an important part in academic life but little is known about how academics carry out these tasks. The aim of this research was to explore these activities with academics from the arts and humanities, the social sciences, and the natural sciences. An electronic questionnaire was used to ascertain (a) how often the respondents read and wrote book reviews, (b) how useful they found them, and (c) what features they thought important in book reviews. Fifty‐two academics in the arts, 53 in the social sciences, and 51 in the sciences replied. There were few disciplinary differences. Most respondents reported reading between one and five book reviews a month and writing between one and two a year. There was high overall agreement between what the respondents thought were important features of book reviews, but there were also wide individual differences between them. This agreement across the disciplines supports the notion that book reviews can be seen as an academic genre with measurable features. This has implications for how they are written, and how authors might be taught to write them better. A potential checklist for authors is suggested.
A pilot study with a new, rapid‐exchange, thrombus‐aspirating device in patients with thrombus‐containing lesions: The Diver C.E. study
Authors: Burzotta Francesco , Trani Carlo , Romagnoli Enrico , Belloni Flavia , Biondi‐Zoccai Giuseppe G.L. , Mazzari Mario Attilio , De Vita Maria , Giannico Floriana , Garramone Barbara , Niccoli Giampaolo , Rebuzzi Antonio Giuseppe , Mongiardo Rocco , Schiavoni Giovanni , Crea Filippo
Published: May 2006

Background: In patients with acute coronary syndromes (ACS), distal embolization of thrombotic material is more likely to play a key role in the pathogenesis of myocardial no‐reflow during percutaneous coronary intervention (PCI). Thus, interventional techniques able to reduce thrombus burden at the culprit vessel might improve final myocardial reperfusion. Objective: To evaluate a new rapid‐exchange thrombus‐aspirating catheter, the Diver C.E., in patients with thrombotic coronary lesions undergoing PCI. Methods: Fifty patients with acute myocardial infarction (n = 44) or with non‐ST‐elevation ACS and angiographic evidence of coronary thrombus (n = 6) undergoing urgent PCI were prospectively enrolled. The Diver C.E. was used to aspirate coronary thrombus from the culprit lesion after placement of the guidewire. Adjunctive balloon inflations and stent implantation were used to achieve good angiographic result. Angiographic coronary flow (by means of TIMI score and corrected TIMI frame count, cTFC), thrombus score (TS), and myocardial perfusion (by means of postintervention myocardial blush grade, MBG) were assessed in all patients. Results: The device could be successfully employed in 96% of the cases (48/50) and yielded significant (P < 0.0001) acute reduction in thrombus burden (TS: predevice 3.5 ± 0.8, postdevice 2.5 ± 0.9) and improvement in coronary flow (TIMI grade: predevice 1.0 ± 0.9, postdevice 2.0 ± 0.9; CTFC predevice 71 ± 31, postdevice 39 ± 26). Final TIMI grade 0–1 was observed in one patient only (2%). A significant (P = 0.02) correlation was found between preintervention TS and efficacy of thrombus aspiration. A more pronounced acute reduction of thrombus burden after thrombus aspiration (TS reduction ≥2) was associated with a better postintervention angiographic myocardial perfusion (MBG 2.3 ± 0.9 vs 1.7 ± 0.8; P = 0.05). Conclusions: This new, easy‐to‐use, device is able to reduce thrombus burden and to improve coronary flow in patients with thrombus‐containing lesions. The improvement in myocardial perfusion associated to greater thrombus removal highlights the importance of thrombus aspiration in the management of thrombus‐burdened coronary lesions. © 2006 Wiley‐Liss, Inc.
Estimating the power of variance component linkage analysis in large pedigrees
Authors: Chen Wei‐Min , Abecasis Gonçalo R.
Published: May 2006

Variance component linkage analysis is commonly used to map quantitative trait loci (QTLs) in general pedigrees. Large pedigrees are especially attractive for these studies because they provide greater power per genotyped individual than small pedigrees. We propose accurate and computationally efficient methods to calculate the analytical power of variance component linkage analysis that can accommodate large pedigrees. Our analytical power computation involves the approximation of the noncentrality parameter for the likelihood‐ratio test by its Taylor expansions. We develop efficient algorithms to compute the second and third moments of the identical by descent (IBD) sharing distribution and enable rapid computation of the Taylor expansions. Our algorithms take advantage of natural symmetries in pedigrees and can accurately analyze many large pedigrees in a few seconds. We verify the accuracy of our power calculation via simulation in pedigrees with 2–5 generations and 2–8 siblings per sibship. We apply this proposed analytical power calculation to 98 quantitative traits in a cohort study of 6,148 Sardinians in which the largest pedigree includes 625 phenotyped individuals. Simulations based on eight representative traits show that the difference between our analytical estimation of the expected LOD score and the average of simulated LOD scores is less than 0.05 (1.5%). Although our analytical calculations are for a fully informative marker locus, in the settings we examined power was similar to what could be attained with a single nucleotide polymorphism (SNP) mapping panel (with >1 SNP/cM). Our algorithms for power analysis together with polygenic analysis are implemented in a freely available computer program, POLY. Genet. Epidemiol. 2006. © 2006 Wiley‐Liss, Inc.
Innovative wavelengths in endodontic treatment
Authors: Schoop Ulrich , Kluger Wolf , Dervisbegovic Selma , Goharkhay Kawe , Wernisch Johann , Georgopoulos Apostolos , Sperr Wolfgang , Moritz Andreas
Published: May 2006

Background and Objectives

The sanitation of the root canal system and the adjacent dentin has always been a key requirement for successful endodontics. In recent years, various laser systems have provided a major contribution to this aim, namely the Nd:YAG‐, the 810 nm Diode‐, the Er:YAG‐, and the Er,Cr:YSGG laser. Numerous studies could prove their efficiency within the endodontic procedure. Recently, two new wavelengths have been introduced to the field of oral laser applications: The KTP laser emitting at 532 nm and the 980 nm diode laser. The present in vitro investigation was performed to evaluate the effects of these laser systems focusing on their antibacterial effect in deep layers of dentin and their impact on the root canal dentin.

Study Design/Materials and Methods

Two‐hundred slices of root dentin with a thickness of 1 mm were obtained by longitudinal cuts of freshly extracted human premolars. The samples were steam sterilized and subsequently inoculated with a suspension of either Escherichia coli or Enterococcus faecalis. After the incubation, the samples were randomly assigned to the two different laser systems tested. Each laser group consisted of two different operational settings and a control. The dentinal samples underwent “indirect” laser irradiation through the dentin from the bacteria‐free side and were then subjected to a classical quantitative microbiologic evaluation. To assess the temperature increase during the irradiation procedure, additional measurements were carried out using a thermocouple. To assess the impacts on the root canal walls, 20 additional samples underwent laser irradiation at two different settings and were subjected to scanning electron microscopy.

Results

Microbiology indicated that both laser systems were capable of significant reductions in both test strains. At an effective output power of 1 W, E. coli was reduced by at least 3 log steps in most of the samples by the tested wavelengths, with the best results for the KTP laser showing complete eradication of E. coli in 75% of the samples. E. faecalis, a stubborn invader of the root canal, showed minor changes in bacterial count at 1 W. Using the higher setting of 1.5 W, significant reductions of E. coli were again observed with both laser systems, where the lasers were capable of complete eradication of E. faecalis to a significant extent. There was no significant relation between the temperature increase and the bactericidal effect.

Conclusions

The present study demonstrates that both wavelengths investigated could be suitable for the disinfection of even the deeper layers of dentin and equal the results achieved by established wavelengths in state‐of‐the‐art endodontics. Lasers Surg. Med. 38:624–630, 2006. © 2006 Wiley‐Liss, Inc.
Multiscale white matter fiber tract coregistration: A new feature‐based approach to align diffusion tensor data
Authors: Leemans A. , Sijbers J. , De Backer S. , Vandervliet E. , Parizel P.
Published: May 2006

In this paper an automatic multiscale feature‐based rigid‐body coregistration technique for diffusion tensor imaging (DTI) based on the local curvature κ and torsion τ of the white matter (WM) fiber pathways is presented. As a similarity measure, the mean squared difference (MSD) of corresponding fiber pathways in (κ, τ)‐space is chosen. After the MSD is minimized along the arc length of the curve, principal component analysis is applied to calculate the transformation parameters. In addition, a scale‐space representation of the space curves is incorporated, resulting in a multiscale robust coregistration technique. This fully automatic technique inherently allows one to apply region of interest (ROI) coregistration, and is adequate for performing both global and local transformations. Simulations were performed on synthetic DT data to evaluate the coregistration accuracy and precision. An in vivo coregistration example is presented and compared with a voxel‐based coregistration approach, demonstrating the feasibility and advantages of the proposed technique to align DT data of the human brain. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.