bluuebunny/crossref_metadata_2025 huggingface dataset:
Height of White‐Flowered Trillium (Trillium Grandiflorum) as an Index of Deer Browsing Intensity
Authors: Anderson Roger C.
Published: April 2006

The height of white—flowered trillium (Trillium grandiflorum) is a useful indicator of deer browsing intensity. In their foraging activities deer select larger plants over smaller plants. Because flowering plants are larger than nonflowering plants, the number of plants in flower decreases with increasing browsing intensity. As browsing intensity increases, the height of the Trillium becomes shorter in successive growing seasons, presumably due to the loss of photosynthetic capacity and reduction in belowground resources. Trillium stem height was positively correlated with reproductive output by perennial herbaceous plants and negatively correlated with the percent of the herbaceous understory that is browsed. This indicates change in stem height is as indication of the general status of the herbaceous flora as influenced by deer browsing. Based on deer population densities associated with study sites supporting Trillium populations with stable stem heights and flowering plants, maintenance of deer densities of 4—6 individuals/km2 is recommended for deciduous forests in northeastern Illinois. In eastern United States, research workers who assume they are studying relatively undisturbed sites should be aware that intense deer browsing may have imposed an alteration on their study sites.
Microhabitat Variables Influencing Nest‐Site Selection by Tundra Birds
Authors: Rodrigues Robert
Published: April 2006

Studies were performed to determine what types of microhabitat characteristics attract the most common bird species to nest at particular sites on tundra habitats in the Prudhoe Bay oil field. Microhabitat variables of 2 x 2 m plots centered on bird nests were measured and compared with those of plots centered on random points. Results indicated differences in amount of microrelief, graminoid and shrub/forb cover, roughness of topography, and presence of water among species. These differences have implications for management of abandoned gravel sites as oil production declines in the Prudhoe Bay oil field. The amount and variability of microrelief plays an important role in influencing nest—site selection. Birds do not require total coverage by graminoid and shrub/forb plant species at nest sites. Water plays an important role by influencing plant growth at disturbed gravel sites.
Sea‐Level Rise and the Reduction in Pine Forests in the Florida Keys
Authors: Ross Michael S. , O'Brien Joseph J. , da Silveira Lobo Sternberg Leonel
Published: April 2006

Forests dominated by Pinus elliottii var densa have undergone a reduction in area in the Florida Keys (USA). A previous investigation interpreted the presence of halophytic species in a former pine forest in Key Largo as evidence of sea—level rise. We therefore examined aerial photos and field evidence to learn how the 15—cm rise in local sea level over the last 70 yr had affected the distribution of pines on a second island, where intact pine forests still remained in 1991. The distribution of in situ dead pine stems showed that the area occupied by pines on Sugarloaf Key was 88 ha at some time prior to the earliest available aerial photographs, in 1935. The area of pine forest was reduced to 46 ha by 1935, and continued to decrease through 1991, when it covered 30 ha. The pattern of pine mortality was related to topographic position, with the areas where pines died earliest occupying the lowest elevations. Our analysis of current vegetation patterns showed that the areas of earliest pine mortality are now populated by a higher proportion of halophytic plant assemblages than areas of more recent pine mortality. We also compared the physiological responses of pines in two portions of the island: one where pine forest reduction had been most pronounced, and a second where the extent of the forest had changed little over the past 50 yr. Both groundwater and soil water salinity were higher in the area of rapid pine forest reduction, and the pines sampled there exhibited higher physiological stress, as indicated by pre—dawn water potential and stemwood carbon isotope ratios. These results suggest that the salinization of ground— and soil water that occurs as sea level rises is a major factor in the reduction of pine forests of Sugarloaf Key. If sea level continues to increase, the Florida Keys will experience a decline in both landscape and species diversity, as species—rich upland communities are replaced by simpler mangrove communities. This pattern may also occur in other low—lying island ecosystems with limited freshwater resources.
Recent Accretion in Two Managed Marsh Impoundments in Coastal Louisiana
Authors: Cahoon Donald R.
Published: April 2006

Recent accretion was measured by the feldspar marker horizon method in two gravity—drained, managed, marsh impoundments and unmanaged reference marshes located on the rapidly subsiding coast of Louisiana. Water level management was designed to limit hydrologic exchange to the managed marsh by regulating the direction and rate of water flows. During a drawdown—flooding water management cycle, the unmanaged reference marshes had significantly higher vertical accretion rates, higher soil bulk density and soil mineral matter content, lower soil organic matter content, and higher rates of organic matter accumulation than the managed marsh. The rate of mineral matter accumulation was higher in both reference marshes, but was significantly higher in only one. Spatial variability in accumulation rates was low when analyzed in one managed marsh site, suggesting a primarily autochthonous source of matter. In contrast, the associated reference marsh apparently received allochthonous material that settled out in a distinct spatial pattern as water velocity decreased. The impoundment marshes experienced an accretion deficit of one full order of magnitude (0.1 vs. 1,0 cm/yr) based on comparison of accretion and sea level rise data, while the unmanaged reference marshes experienced a five—fold smaller deficit or no deficit. These data suggest that the gravity—drained impoundments likely have a shorter life expectancy than the reference marshes in the rapidly subsiding Louisiana coast.
Non‐Timber Forest Products Integrated with Natural Forest Management, Rio San Juan, Nicaragua
Authors: Salick Jan , Mejia Alejandro , Anderson Todd
Published: April 2006

In the Atlantic lowland tropical rainforests of the Rio San Juan region, Nicaragua, we are conducting applied vegetation community analyses within an attempt to integrate non—timber forest products with natural forest management. Two long—term sampling plots were evaluated: one primary tropical rainforest plot before and 1 yr after selective logging, and another plot 9 yr after selective logging with and without Hutchinson Liberation Silviculture treatment (in which selected young trees are released from competition for light). The purpose of the study was to evaluate changes in community ecology variables with logging, damage, regeneration, and silviculture, both for useful plant species and for the plant community as a whole, and to evaluate the potential for incorporating non—timber forest product management with silvicultural management. One year after logging there was an increase in species (from 19± 5 to 33± 10 species/10m2) and density (from 42 ± 19 to 120 ± 60 plants/10m2) due to establishment or increase of secondary species (vines, grasses, balsa, cecropia) and to seedling regeneration after logging. The more severe the logging damage the more severe were the effects on some variables, particularly increased densities of vines and secondary species. Forest plots 9 yr post—harvest appeared to be returning to pre—harvest levels of species (28 ± 6 species/10m2) and density (76 ± 21 plants/10m2). Hutchinson Liberation Silviculture, while promoting growth of desired timber, did not significantly affect either non—timber forest products or the basic physiognomy of the forest. These results are contrasted with other silvicultural systems, particularly the Hartshorn Strip Clearcut, in which regeneration was dominated by resprouts and the proportion of vines was even higher. Hutchinson Liberation Silviculture provides the potential for simultaneous management of non—timber forest products, and moreover, non—timber forest product management holds the potential for significantly reinforcing silvicultural management.
Approaches to Developing Sustainable Extraction Systems for Tropical Forest Products
Authors: Boot Rene G. A. , Gullison R. E.
Published: April 2006

There are few if any examples of the demonstrably sustainable extraction of either timber or non—timber forest products. Even well—known products such as brazil nuts and mahogany lack a sufficient knowledge base to design a sustainable extraction system. Potential extraction systems for timber and non—timber forest products from tropical forests should be evaluated both in terms of their sustainability and their impact at the ecosystem level. The impact of forest product harvest on the demographics of the target species can be explored with the use of mathematical models, although we still lack an adequate understanding of some of the basic processes that are structuring tropical tree communities. Matrix models are relatively quick to construct, and they may be appropriate for modeling the dynamics of populations that are harvested without introducing large changes to the ecosystem, while individual—based mechanistic models are more appropriate for modeling the effects of harvest that cause large changes in population and ecosystem structure. Once the maximum sustainable level of harvest has been identified with the use of models, an economic analysis of the range of harvest intensities between zero and maximum sustainable yield should be conducted, with the goal of identifying the range of possible harvest intensities that are both sustainable and economically viable. This range of harvest intensities should then be analyzed in terms of its impact on the ecosystem, so that the harvest intensity that is chosen will not result in impacts to the forest that are unacceptably high.
Basic and Applied Research for Sound Rain Forest Management in Guyana
Authors: Steege H. ter , Boot R. , Brouwer L. , Hammond D. , van der Hout P. , Jetten V. G. , Khan Z. , Polak A. M. , Raaimakers D. , Zagt R.
Published: April 2006

Five years of research have increased our understanding of the effects of disturbances on some forest processes and given directions for forest management in Guyana. At present most logging concentrates on Chlorocardium rodiei (greenheart) and current practices are damaging, but they may have little effect on the overall water balance and nutrient cycle if some simple rules are adhered to. The basic research results do not lead to a fully documented sustainable forest management system, as translation to practical management is not always simple. In general it would appear that applied research may give fast results in an often quick and dirty approach. Basic research, if directed at the right forest processes, may provide answers when the quick and dirty approach does not fulfil its objectives. As such they are complementary. In tropical forest management we cannot wait until basic research provides all answers leading to proper forest management, and a combination of the two would probably provide most answers in the long term.
Possible Ecological Mechanisms for Loss of Vernal‐Herb Diversity in Logged Eastern Deciduous Forests
Authors: Meier Albert J. , Bratton Susan Power , Duffy David Cameron
Published: April 2006

The ecological literature on eastern forest‐floor herbs and data collected in the southern Appalachians in Tennessee and North Carolina suggest five possible ecological mechanisms for reducing or limiting alpha diversity of vernal herbs in logged stands, three of which may also account for the slow recovery of some herbaceous species: (1) logging reduces populations of rarer herbs; (2) populations of forest‐floor species are further reduced during the successional stages following logging, either by inability to adapt to changed microclimate or by competition with r‐selected species that are better dispersers and better able to tolerate desiccation and increased radiation; (3) forest‐floor herbs have slow growth and reproduction rates, thus population densities increase slowly; (4) many forest‐floor herbs are clonal, ant‐dispersed, or gravity‐dispersed, thus they are slow to reoccupy suitable habitat once extirpated or greatly reduced in population numbers; and (5) logging results in less‐than‐optimal conditions for forest‐floor herb reproduction by modifying microhabitats on the forest floor and by temporarily eliminating gap‐phase succession. The data indicate some species of vernal herbs are far more tolerant of disturbance than others, and that sensitive species can be identified and utilized as indicators of community integrity and diversity.
Patterns and Mechanisms of Plant Diversity in Forested Ecosystems: Implications for Forest Management
Authors: Roberts Mark R. , Gilliam Frank S.
Published: April 2006

The objectives of this paper are to (1) review existing diversity models, (2) identify principles that explain patterns of plant species diversity, (3) discuss implications for forest management, and (4) identify research needs. Many current theories cast disturbance as the key player in maintaining species diversity by preventing competitive dominance of one or a few species. Equilibrium and nonequilibrium theories alike agree that maximum diversity should occur at intermediate size, frequency, and intensity of disturbance. These models do not adequately predict patterns at all spatial scales or across community types. A mechanistic theory is needed to explain diversity patterns at the patch, stand, and landscape scales, as well as across site quality and successional gradients. Such a theory should be based upon the interaction between species' life‐history characteristics and the nature of disturbance. New research is needed in the following areas: identifying disturbance‐life‐history interactions, particularly with respect to the short‐term and long‐term effects of disturbance; quantifying patch diversity and determining its relationship with species diversity; determining relationships between species diversity and structural and functional diversity; and identifying appropriate standards of comparison for managed stands. Comparative studies in different ecosystem types, such as boreal and tropical forests, should be encouraged to help clarify the relative importance of processes that influence diversity.
Transition and Gap Models of Forest Dynamics
Authors: Acevedo M. F. , Urban D. L. , Ablan M.
Published: April 2006

We describe and apply a correspondence between two major modeling approaches to forest dynamics: transition markovian models and gap models or JABOWA‐FORET type simulators. A transition model can be derived from a gap model by defining states on the basis of species, functional roles, vertical structure, or other convenient cover types. A gap‐size plot can be assigned to one state according to dominance of one of these cover types. A semi‐Markov framework is used for the transition model by considering not only the transition probabilities among the states, but also the holding times in each transition. The holding times are considered to be a combination of distributed and fixed time delays. Spatial extensions are possible by considering collections of gap‐size plots and the proportions of these plots occupied by each state. The advantages of this approach include: reducing simulation time, analytical guidance to the simulations, direct analytical exploration of hypothesis and the possibility of fast computation from closed‐form solutions and formulae. These advantages can be useful in the simulation of landscape dynamics and of species‐rich forests, as well as in designing management strategies. A preliminary application to the H. J. Andrews forest in the Oregon Cascades is presented for demonstration.
Weevils and Watermilfoil: Did a North American Herbivore Cause the Decline of an Exotic Plant?
Authors: Creed Robert P. , Sheldon Sallie P.
Published: April 2006

The Eurasian watermilfoil (Myriophyllum spicatum) population in Brownington Pond, Vermont, declined between 1986 and 1989. Watermilfoil covered ≈10‐11 ha of the littoral zone in 1986. Less than 0.5 ha remained in 1989. An herbivorous weevil (Euhrychiopsis lecontei), which is native to North America, was found associated with this watermilfoil population and we hypothesized that this weevil played a role in the decline. We monitored watermilfoil and E. lecontei populations in Brownington Pond from 1990 through 1992 by (1) mapping the location and extent of beds in the pond, and (2) determining watermilfoil biomass along permanent transects. The abundance of weevil eggs, larvae, pupae, and adults were monitored by sampling individual watermilfoil stems. Watermilfoil cover increased to ≈ 2.5 ha by 1991 and then declined again to ≈1 ha by 1992. The reduction in watermilfoil biomass from 1991 to 1992 ranged from 4‐ to 30‐fold depending on location. Mean weevil abundance increased from 1990 (<1/stem) through early 1992 (3‐4/stem) and then began to decline. The number of weevil eggs/stem also peaked in early 1992 and then declined. These survey results are consistent with the hypothesis that the weevil played an important role in producing both observed declines. The effect of weevils on watermilfoil was evaluated in two experiments. In an aquarium experiment, we found that the viability of stem fragments damaged by weevils was reduced compared to stem fragments without weevil damage. Watermilfoil commonly spreads by producing fragments so the spread of watermilfoil beds by fragmentation may be reduced when weevil abundances are high. In a pond enclosure experiment, weevils suppressed the production of new watermilfoil biomass. The biomass of lateral stems and roots of watermilfoil plants damaged by weevils was significantly less than those of control plants. There was no significant difference in the biomass of the stems originally planted in the enclosures. Weevil damage did have a negative effect on the buoyancy of these original stems, however. These experimental results also support the hypothesis that this native weevil played an important role in the two watermilfoil declines observed at Brownington Pond.
Controlling Lyme Disease by Modifying the Density and Species Composition of Tick Hosts
Authors: Van Buskirk Josh , Ostfeld Richard S.
Published: April 2006

We used computer simulation of Lyme disease to test the hypothesis that infection rates of ticks and risk to humans could be reduced by controlling populations of the vertebrate hosts of vector ticks. The model was patterned after the life cycle of the deer tick (Ixodes scapularis). Annual survival and fecundity were dependent on the availability of hosts. The likelihood of ticks becoming infected depended on the reservoir competence of hosts and the previous exposure of hosts to infected ticks. Our results demonstrated that the density of ticks was more sensitive to the availability of hosts for juveniles than hosts for adults, suggesting that control of Lyme disease by reducing host densities would prove difficult, since the numerous alternative hosts for juvenile ticks are not amenable to control. The infection rate of ticks depended critically on the reservoir competence of host species parasitized by juveniles. We conclude that measures that alter the species composition of small mammals and birds, and hence modify the average reservoir competence of hosts for juveniles, could be used to manipulate the risk of Lyme disease without actually changing the density of ticks.
A 20‐Yr Study Documenting the Relationship Between Turtle Decline and Human Recreation
Authors: Garber Steven D. , Burger Joanna
Published: April 2006

This study documents the detrimental effects of human recreation on the North American wood turtle (Clemmys insculpta) in Connecticut. We chronicled the dynamics of two allopatric wood turtle populations in a protected southern New England wildlife reserve for 20 yr (1974‐1993). Both wood turtle populations were reproductively isolated from one another, physically separated ≈100 yr ago when a 1.5 km long human‐made pond was constructed. We conducted a mark‐and‐recapture study on a 1000‐ha section of a protected watershed in south‐central Connecticut (New Haven County). During this study we monitored 133 different wood turtles, observing them a total of 1176 times. Human and wood turtle demographics were recorded throughout this period. The data support the following conclusions: (1) following a period of apparent stability, two populations of wood turtles declined; (2) the declines were more or less synchronous in both populations; (3) the beginning of each decline corresponded to the opening of the habitat for recreation; (4) an increase in mean turtle age suggests a failure of recruitment; however, (5) a simultaneous reduction in numbers of adult females suggests that the failure of recruitment alone is not sufficient to explain the declines. Throughout our study the size of the forest remained the same, road building was restricted, and the quality of the air and water were constant. The wood turtle populations remained stable when people were denied access to the property. When this area was opened to human recreation (hiking, fishing) the two discrete wood turtle populations declined steadily; the total number of turtles in both populations declined by 100% in 10 yr. As wilderness areas become mixed‐use recreation areas, wood turtle populations may suffer. We conclude that without proper management, the increasing recreational use of parks, reservoirs, and wildlife reserves will adversely affect the long‐term survival of the North American wood turtle.
Feeding Responses to Predator‐Based Repellents in the Mountain Beaver (Aplodontia Rufa)
Authors: Epple Gisela , Mason J. Russell , Aronov Evgueny , Nolte Dale L. , Hartz Richard A. , Kaloostian Ron , Campbell Dan , Smith Amos B.
Published: April 2006

Predator odors have potential as feeding repellents for mammalian herbivores, including Aplodontia rufa, the mountain beaver. However, the repellency of major chemical constituents of natural predator scents for this species has not been evaluated. In this study, the effects of several synthetic sulfur compounds from predator scents on feeding by mountain beavers were assessed and compared to the effects of coyote (Canis latrans) urine. Retrieval of food by mountain beavers from bowls scented with either coyote urine, diluted with water to different concentrations, synthetic components of predator scents, or control odorants was studied. The following synthetic compounds were tested: δ3‐Isopentenyl methyl sulfide (IMS), a compound present in urine from several canid species; 2,2 dimethylthietane (DMT), a major constituent in anal gland secretion from the mink (Mustela vison); a 1:1 mixture of 2‐propylthietane (PT) and 3‐propyl‐1,2‐dithiolane (PDT), compounds occurring in anal gland secretions from the stoat (Mustela erminea) and the ferret (Mustela putorius). Habituation to PT plus PDT was studied by measuring consumption of dry pellets during continuous exposure to these compounds for 5 d. In two‐choice feeding trials mountain beavers retrieved significantly more food from bowls scented with water than from bowls scented with coyote urine. Dilution of urine had no statistically significant effect on food retrieval, but repellency tended to decrease with decreasing concentration. Mountain beavers retrieved less food scented with a 1:1 mixture of PT and PDT, compared to controls. However, they rapidly habituated to this mixture. None of the other compounds caused an avoidance response. These results show that complex natural predator scents are more effective feeding repellents than some of their major volatile components alone.
Land Use and Avian Species Diversity Along an Urban Gradient
Authors: Blair Robert B.
Published: April 2006

I examined the distribution and abundance of bird species across an urban gradient, and concomitant changes in community structure, by censuring summer resident bird populations at six sites in Santa Clara County, California (all former oak woodlands). These sites represented a gradient of urban land use that ranged from relatively undisturbed to highly developed, and included a biological preserve, recreational area, golf course, residential neighborhood, office park, and business district. The composition of the bird community shifted from predominantly native species in the undisturbed area to invasive and exotic species in the business district. Species richness, Shannon diversity, and bird biomass peaked at moderately disturbed sites. One or more species reached maximal densities in each of the sites, and some species were restricted to a given site. The predevelopment bird species (assumed to be those found at the most undisturbed site) dropped out gradually as the sites became more urban. These patterns were significantly related to shifts in habitat structure that occurred along the gradient, as determined by canonical correspondence analysis (CCA) using the environmental variables of percent land covered by pavement, buildings, lawn, grasslands, and trees or shrubs. I compared each formal site to four additional sites with similar levels of development within a two‐country area to verify that the bird communities at the formal study sites were representative of their land use category.
Elk Population Processes in Yellowstone National Park Under the Policy of Natural Regulation
Authors: Coughenour Michael B. , Singer Francis J.
Published: April 2006

The interrelations of weather, plant production and abundance, and elk population dynamics on Yellowstone's northern winter range were examined for a 23‐yr period when there was minimal human offtake from the herd. Significant correlations between precipitation and plant production, between elk population responses and precipitation, and between elk population responses and elk population density strongly suggested that forage limited elk population growth. Although population responses to density have been documented previously in Yellowstone, responses to precipitation have not. Correlations between elk population responses and annual precipitation were presumably consequences of plant growth responses to precipitation and subsequent effects on elk nutritional status. Population regulation was most consistently achieved through the response of juveniles rather than adults. Winter mortality of juveniles was primarily correlated with elk numbers, whereas recruitment was primarily correlated with precipitation. Adult mortality rates were not significantly correlated with elk numbers, but were correlated with precipitation. Per capita rate of increase was negatively correlated with elk number, but 55% of the variance was density‐independent. There was evidence that winter weather affected the elk, but season‐long weather indices had poor predictive power. A stage‐structured population model using regression equations of mortality and recruitment rate responses to precipitation and elk numbers, predicted that the population could vary within a range of ≈ 16 400 ± 2500 sighted elk (mean ± 1 SD).
Spatial and Temporal Patterns in Terrestrial Carbon Storage Due to Deposition of Fossil Fuel Nitrogen
Authors: Townsend A. R. , Braswell B. H. , Holland E. A. , Penner J. E.
Published: April 2006

Fertilization of the biosphere by nitrogen deposition represents an important connection between atmospheric chemistry and the global carbon cycle. We describe a modeled estimate of terrestrial carbon storage arising from deposition of nitrogen derived from fossil fuels that accounts for spatial distributions in deposition and vegetation types, turnover of plant and soil carbon pools, and the cumulative effects of deposition. Vegetation type has a pronounced effect on C uptake; the combination of high C : N ratios and long lifetimes in wood may create a significant sink in forests, but much of the nitrogen falls on cultivated areas and grasslands, where there is limited capacity for long‐term carbon storage. We estimate 1990 net carbon uptake due to deposition of fossil‐fuel N to be between 0.3 and 1.3 Pg C/yr [1 Pg = 1015 g], depending on the fraction of C allocated to wood, with a best estimate of 0.44‐0.74 Pg/yr. Cumulative C storage since 1845 is estimated to be about 25% of the proposed terrestrial sink for anthropogenic CO2. Continued exposure to high N deposition, however, will decrease the extent of N limitation in terrestrial ecosystems, thereby limiting the persistence of any N‐derived carbon sink.
Local Dispersal by the Cinnabar Moth Tyria Jacobaeae
Authors: Rudd Nathan T. , McEvoy Peter B.
Published: April 2006

We used mark‐recapture data to measure and model movement by the adult stage of the cinnabar moth Tyria jacobaeae (Lepidoptera, Arctiidae). Our objectives were: (1) to standardize the description of cinnabar moth movement and thereby provide a more reliable basis for comparison and extrapolation, and (2) to screen the potential influence of gender, physical condition, time, spatial location, and spatial heterogeneity in the environment on movement parameters. Recapture rates depended on wing wear (low 16%, high 11%) but were independent of behavior immediately after release (mobile 15%, immobile 14%), gender (male 13%, female 16%), or location in the study area (central 15%, peripheral 15%). Thus, mortality and/or emigration was greater for individuals with high wing wear compared to those with low wing wear. Moths were aggregated at the southwest margin of the study area both at initial capture and recapture. The direction of movement was biased in north and south directions, perhaps because forests on the east and west boundaries created a corridor channeling movement. The movement observed within a single generation did not conform to simple diffusion, which predicts that the mean square displacement (MSD) increases linearly with time. Instead, observed movement rates varied over time, and the relationship between MSD and time varied by gender, smoothly decelerating in males and erratically increasing in females. Observed movement (represented by the frequency distribution of displacements x for each time t with time measured at a daily resolution) was adequately approximated by a Weibull distribution, for which estimates of the shape and scale parameters were calculated. Male distributions were more frequently mounded, associated with higher values of the shape parameter α, and the scale of male distributions shifted sooner to longer distances, associated with higher values of the scale parameter β. The Weibull parameters varied by sex and time, suggesting that males were initially more mobile than females, but the magnitude of the difference varied over time. The speed and direction of individual movement were independent of the moth's spatial location within the field. We conclude that (1) movement speed depended on gender and time, while movement direction was related to spatial heterogeneity in the environment, and (2) much of the disagreement about movement rates among studies of the cinnabar moth can be related to researchers taking measurements and drawing inferences on different scales of observation, and therefore arriving at conflicting results.
Socioeconomic Equity, Sustainability, and Earth's Carrying Capacity
Authors: Daily Gretchen C. , Ehrlich Paul R.
Published: April 2006

We examine the relationship between socioeconomic equity in opportunity and sustainability, as reflected in patterns of food production and fertility. Our analysis spans various levels of social organization, from within the household (gender‐ and age‐related equity) to relations among households (of different material wealth), among regions (particularly rural vs. urban), and among nations (rich and poor). Our preliminary results in this complex area suggest that increasing equality of opportunity at each of these levels can help to increase food production and to lower fertility rates, through varied mechanisms. Working toward such equity constitutes a no regrets strategy for transitioning to a sustainable society and increasing Earth's carrying capacity for human beings, as measures to reduce the growing disparity between rich and poor have merit on ethical grounds alone. An important caveat, however, is that equity in consumer lifestyles within and between nations cannot be achieved globally by leveling up to consumption from the bottom. Runaway consumption in rich countries must be curbed as part of an effort to reduce the scale of human enterprise to below carrying capacity while still permitting needed development among the poor.
An Introduction to Bayesian Inference for Ecological Research and Environmental Decision‐Making
Authors: Ellison Aaron M.
Published: April 2006

In our statistical practice, we ecologists work comfortably within the hypothetico‐deductive epistemology of Popper and the frequentist statistical methodology of Fisher. Consequently, our null hypotheses do not often take into account pre‐existing data and do not require parameterization, our experiments demand large sample sizes, and we rarely use results from one experiment to predict the outcomes of future experiments. Comparative statistical statements such as we reject the null hypothesis at the 0.05 level, which reflect the likelihood of our data given our hypothesis, are of little use in communicating our results to nonspecialists or in describing the degree of certitude we have in our conclusions. In contrast, Bayesian statistical inference requires the explicit assignment of prior probabilities, based on existing information, to the outcomes of experiments. Such an assignment forces the parameterization of null and alternative hypotheses. The results of these experiments, regardless of sample size, then can be used to compute posterior probabilities of our hypotheses given the available data. Inferential conclusions in a Bayesian mode also are more meaningful in environmental policy discussions: e.g., our experiments indicate that there is a 95% probability that acid deposition will affect northeastern conifer forests. Based on comparisons with current statistical practice in ecology, I argue that a Bayesian ecology would (a) make better use of pre‐existing data; (b) allow stronger conclusions to be drawn from large‐scale experiments with few replicates; and (c) be more relevant to environmental decision‐making.
Uncertainty and the Assessment of Extinction Probabilities
Authors: Ludwig Donald
Published: April 2006

A proper assessment of the probability of early collapse or extinction of a population requires consideration of our uncertainty about crucial parameters and processes. Simple simulation approaches to assessment consider only a single set of parameter values, but what is required is consideration of all more or less plausible combinations of parameters. Bayesian decision theory is an appropriate tool for such assessment. I contrast standard (frequentist) and Bayesian approaches to a simple regression problem. I use these results to calculate the probability of early population collapse for three data sets relating to the Palila, Laysan Finch, and Snow Goose. The Bayesian results imply much higher risk of early collapse than maximum likelihood methods. This difference is due to large probabilities of early collapse for certain parameter values that are plausible in light of the data. Because of simplifying assumptions, these results are not directly applicable to assessment. Nevertheless they imply that maximum likelihood and similar methods based upon point parameter estimates will grossly underestimate the risk of early collapse.
Foraging of Gray Squirrels on an Urban‐Rural Gradient: Use of the Gud to Assess Anthropogenic Impact
Authors: Bowers Michael A. , Breland Bianca
Published: April 2006

Responses of organisms to urbanization may involve adjustments in behavior. To qualify such behavioral plasticity we measured the degree to which gray squirrels (Sciurus carolinensis) exploited sunflower seeds in pans distributed over an urban‐rural gradient of 78 sites in Virginia. Our objective was to use squirrel GUDs as a functional, relativistic measure of the effects of urbanization. Results showed that a higher proportion of pans were foraged from and that the GUDs were lower (more seeds were removed) in relatively high‐density urban and suburban areas than in more rural agricultural areas, or in relatively human‐free forest controls. For sites near or within human settlements, GUDs were lower nearer to human‐occupied structures than at a greater distance from them, where more squirrels were observed, and where the density of trees was higher; GUDs were higher where there was substantial ground cover and where domestic pets (i.e., cats/dogs) were present nearby. Squirrels living in close proximity to humans appear to be either more limited by food or less sensitive to predatory risk than those living in more natural areas. We argue that the GUD represents a valuable metric with utility for measuring the separate and combined impact of anthropogenic actions at the individual and population levels.
Trends in Vital Rates of the European Eel: Evidence for Density Dependence?
Authors: De Leo G. A. , Gatto M.
Published: April 2006

We used a population model to investigate possible density‐dependent processes in the European eel (Anguilla anguilla L.). We derived this model to include fundamental features of this catadromous fish that have been historically neglected, such as high plasticity in individual growth, length‐dependent sexual maturation, sexual dimorphism, and skewed sex distributions. Populations were sampled three times in the Valli di Comacchio lagoons during 1974 through 1989, a period during which both commercial yield and density declined. A bootstrap procedure permitted us to estimate demographic parameters and evaluate their uncertainty. With the model we could estimate eel recruitment to lagoons and the density of prereproductive eels per length and age class, especially useful information because these data cannot be collected directly. With the exception of age 1, survival increased as density declined. In addition, as density declined, the proportion of females and female body size, as well as age and length of both sexes at sexual maturity, increased. Density‐dependent processes, such as competition for limited food and space, and trade‐offs between reproductive success and survival provide a parsimonious explanation (though not one we could test) for these shifts in population parameters.
pH‐Mediated Predator‐Prey Interactions Between Ambystoma Tigrinum and Pseudacris Triseriata
Authors: Kiesecker Joseph
Published: April 2006

Recent reports of declining amphibian populations have led researchers to investigate how various factors, including pH, can influence amphibian survival and ecology. It is now known that larval amphibians exposed to acid water may experience increased mortality or reduced rates of growth. At the interspecific level, species that respond differently to variation in abiotic factors such as pH may experience a shift in their interactions. I used naturally occurring pH levels (4.5, 5.5, 6.0, and 7.0) in laboratory experiments to examine the effects of pH on the growth and predator‐prey interaction of Ambystoma tigrinum and Pseudacris triseriata. Larvae of A. tigrinum exhibited reduced growth and increased developmental time at lower pH levels. However, pH had no significant effect on growth or developmental time in larvae of P. triseriata. In combination, these factors led to decreased predatory success of A. tigrinum larvae on P. triseriata larvae at lower pH levels. These results suggest that surface water acidification and perhaps other abiotic factors may have consequences at the community level that extend beyond direct lethal effects on amphibian populations in temporary ponds.
Rational Choice and the Dynamics of Collective Political Action: Evaluating Alternative Models with Panel Data
Authors: Finkel Steven E. , Muller Edward N.
Published: April 2006

Causal inference in research testing rational choice models of unconventional political behavior has been hampered by the inability to use perceptions of the costs and benefits of participation at a given time to predict behavior that necessarily occurred in the past and by ambiguities associated with analyzing behavioralintentionsinstead of actual participation. Using panel data collected on a national sample in West Germany between 1987 and 1989, we show that variables from a “collective interest” model measured in 1987—individuals' dissatisfaction with the provision of collective goods, beliefs that group actions can be successful, and beliefs in the importance of their own participation—predict subsequent participation in collective protest activities. Variables corresponding to the private “selective incentives” associated with protest are found to be less relevant. Furthermore, we find that engaging in protest changes many of the perceptions that influence future participation. We discuss the implications for theories of political mobilization.
Liberal Theory and the Idea of Communist Justice
Authors: Diquattro Arthur
Published: April 2006

My aim is to bring Marx's general theory of exploitation into line with contemporary theories of distributive justice advanced by liberal egalitarians, theories that stress the ideal of equal concern and respect for personsquapersons and require implementation of the ideal consistent with what historical circumstances permit. I begin by dismissing the labor theory of value as relevant to Marx's general theory, emphasizing instead a “property rights matching power” account. I conclude with some speculative comments about Kantian influences in Marx's sense of justice. Throughout, I assume that Marx believes that exploitation is unjust, and I pursue and sharpen this view in my analysis of Marx's criticism of the distributive principle of socialism.
Partisan Cues and the Media: Information Flows in the 1992 Presidential Election
Authors: Dalton Russell J. , Beck Paul A. , Huckfeldt Robert
Published: April 2006

Electoral research acknowledges the growing significance of the mass media in contemporary campaigns, but scholars are divided on the nature of this influence. Using a unique database that includes both media content and public opinion, we examine the flow of partisan information from newspapers to the voters and assess the press's role in electoral politics and citizen learning. We find that the American press does not present clear and singular messages about presidential elections but, rather, multiple messages about the candidates and the campaign. In addition, perception of the information is shaped as much by an individual's political views as by the objective content. Despite the mixed messages, we find that a newspaper's editorial content is significantly related to candidate preferences in 1992. These results challenge the minimal effects interpretation of the media, because local newspapers can play a significant role in providing cues that influence voters' electoral calculus.
The Dynamics of Foreign Policy Agenda Setting
Authors: Wood B. Dan , Peake Jeffrey S.
Published: April 2006

Theoretical and empirical work on public policy agenda setting has ignored foreign policy. We develop a theory of foreign policy agenda setting and test the implications using time-series vector autoregression and Box-Tiao (1975) impact assessment methods. We theorize an economy of attention to foreign policy issues driven by issue inertia, events external to U.S. domestic institutions, as well as systemic attention to particular issues. We also theorize that the economy of attention is affected by a law of scarcity and the rise and fall of events in competing issue areas. Using measures of presidential and media attention to the Soviet Union, Arab-Israeli conflict, and Bosnian conflict, we show that presidential and media attentions respond to issue inertia and exogenous events in both primary and competing issue areas. Media attention also affects presidential attention, but the president does not affect issue attention by the media.
Small forcing makes any cardinal superdestructible
Authors: Hamkins Joel David
Published: April 2006

Small forcing always ruins the indestructibility of an indestructible supercompact cardinal. In fact, after small forcing, any cardinal κ becomes superdestructible—any further <κ-closed forcing which adds a subset to κ will destroy the measurability, even the weak compactness, of κ. Nevertheless, after small forcing indestructible cardinals remain resurrectible, but never strongly resurrectible.
On effective topological spaces
Authors: Spreen Dieter
Published: April 2006

Starting with D. Scott's work on the mathematical foundations of programming language semantics, interest in topology has grown up in theoretical computer science, under the slogan ‘open sets are semidecidable properties’. But whereas on effectively given Scott domains all such properties are also open, this is no longer true in general. In this paper a characterization of effectively given topological spaces is presented that says which semidecidable sets are open.

This result has important consequences. Not only follows the classical Rice-Shapiro Theorem and its generalization to effectively given Scott domains, but also a recursion theoretic characterization of the canonical topology of effectively given metric spaces. Moreover, it implies some well known theorems on the effective continuity of effective operators such as P. Young and the author's general result which in its turn entails the theorems by Myhill-Shepherdson, Kreisel-Lacombe-Shoenfield and Ceĭtin-Moschovakis, and a result by Eršov and Berger which says that the hereditarily effective operations coincide with the hereditarily effective total continuous functionals on the natural numbers.
Cooperative or Controlling? The Effects of CEO-Board Relations and the Content of Interlocks on the Formation of Joint Ventures
Authors: Gulati Ranjay , Westphal James D.
Published: April 2006

This study examines the influence of the social network of board interlocks on strategic alliance formation. Our theoretical framework suggests how board interlock ties to other firms can increase or decrease the likelihood of alliance formation, depending on the content of relationships between CEOs (chief executive officers) and outside directors. Results suggest that CEO-board relationships characterized by independent board control reduce the likelihood of alliance formation by prompting distrust between corporate leaders, while CEO-board cooperation in strategic decision making appears to promote alliance formation by enhancing trust. The findings also show how the effects of direct interlock ties are amplified further by third-party network ties.
Status, Quality, and Social Order in the California Wine Industry
Authors: Benjamin Beth A. , Podolny Joel M.
Published: April 2006

This paper examines how a producer's status in the market influences its choices about product quality, and the outcomes that result. We compare economic models of reputation that emphasize the role of past quality as a source of information about current quality with sociological models of status that emphasize the role of affiliations. We test hypotheses about the complementary effects of status and reputation in an analysis of more than 10,000 affiliation decisions made by 595 wineries over a 10-year period. Results show that actors occupying high-status positions obtain greater benefit from subsequent high-status affiliations than do actors occupying low-status positions. As such, these actors are more willing and able to pay for subsequent high-status affiliations and to use them to advance their position in the larger status ordering.