bluuebunny/crossref_metadata_2025 huggingface dataset:
Mowing and Fertilization Effect on Productivity and Spectral Reflectance in Bromus Inermis Plots
Authors: Dyer M. I. , Turner C. L. , Seastedt T. R.
Published: April 2006

Experiments were conducted to examine the potential role of grazing on ecosystem—level parameters as part of the NASA—sponsored First Isabela (International Satellite Land Surface Climatology Programmed) Field Experiment (FIFE) conducted at Konza Prairie Research Natural Area in 1987. Here we report results of one experiment conducted in a field consisting primarily of Bromus inermis, a cool season C3 grass. The experiment involved four simulated grazing components (unmowed control, 20—, 10—, and 5—cm mowing heights) and fertilization (untreated control and ammonium nitrate application). The plots were mowed to ground level and raked in April, following which they were mowed seven times during the growing season from May to October. Biomass production, N production, and spectral reflectance data were collected with a hand—held radiometer throughout the growing season, with standing crop estimates taken at two periods (7 August [day 219] and 27 October [day 300]) to correlate with the remote sensing information base. Standing crop values of mowed plots were as much as 67—70% lower than controls, but they produced significantly larger amounts of both biomass and total N. Maximum seasonlong production values in the mowed plots were °43% above controls, with major differences developing as a result of fertilization. Fertilized plots produced 67% more foliage than unfertilized plots. Our data show over—compensatory growth as a result of the simulated grazing treatments. Indexes (NDVI [normalized difference vegetation index] and greenness) derived from the reflectance data were poorly correlated with biomass. The correlation of NDVI with N content of the canopy foliage was somewhat stronger, particularly if stratified by mowing class. NDVI was a better predictor of vegetation status than the greenness indexes, but in plots stimulating heavily grazed areas where leafy vegetation was sparse and soil became more visible from above the canopy its utility decreased significantly.
Effects of Habitat Enrichment on Patterns of Diet Selection
Authors: Murden Steven B. , Risenhoover Ken L.
Published: April 2006

Foraging theory predicts that animals should feed more selectively in response to an increased abundance of high—quality foods. We tested these predictions by examining changes in patterns of diet selection by white—tailed deer (Odocoileus virginianus) and Angora goats (Capri hircus) in response to habitat enrichment. When a high—quality supplement was provided ad libitum, both species responded by increasing foraging effort and by feeding more selectively on natural forages. Supplemented animals consumed a greater proportion of plants containing high concentrations of crude protein (CP) and digestible energy (DE), which resulted in an increase in average diet quality. Responses of individual deer and goats varied and appeared to be related to differences in habitat heterogeneity between trial enclosures. Our results suggest that supplementation may be disruptive to normal behavioral processes affecting the distribution of free—ranging herbivores on the landscape. These processes may be important in reducing the probability of excessive utilization of palatable forage species, and to the competitive relationships between range plants.
Predicting the Impact of Turtle Excluder Devices on Loggerhead Sea Turtle Populations
Authors: Crowder Larry B. , Crouse Deborah T. , Heppell Selina S. , Martin Thomas H.
Published: April 2006

In this paper, we modified and updated a stage—based population model for loggerhead sea turtles (Caretta caretta) and used the model to project potential population—level effects of the use of turtle excluder devices (TEDs) in trawl fisheries of the southeastern US. We reduced the seven—stage model of Crouse et al. (1987) to a five—stage model and performed sensitivity analyses on the matrix. The most sensitive matrix parameters were those dealing with survival while remaining in a stage, rather than growth from one stage to the next or reproductive output. Population growth rate was most sensitive to survival in the large juvenile stage, followed by small juvenile survival. Large juveniles are the most common size class among stranded dead turtles found on beaches; 70—80% of strandings are thought to be related to trawl fisheries. Simulations of our loggerhead model based on estimated effects of TED regulations on stage—specific survivorship suggested that southeastern US loggerhead populations should increase, but rather slowly. If TEDs were required during the shrimping season in offshore areas only (as they were from 1990 to 1992), 70 yr or more would be required for the simulated population to increase by an order of magnitude. Recent estimates of TED effects from South Carolina strandings data suggest a similar recovery rate. Good compliance with regulations requiring TEDs year—round in all waters could allow the population to increase nearly twice as fast as that expected under the "seasonal offshore" regulations. We also used a Leslie matrix version of the model to illustrate the expected transient response in the numbers of females expected on nesting beaches (due to shifting age—size structures with TED use). Rather than a monotonic increase, we expect an initial increase in the number of nesting females, followed by a leveling off or slight decline (perhaps 10—15 yr from now), followed by another increase. The magnitude of the projected population increase will depend upon the actual increases in stage—specific survivorship due to TED regulations. New, or compensatory, sources of mortality could slow or reverse this projected recovery.
Relating Riparian Vegetation to Present and Future Streamflows
Authors: Auble Gregor T. , Friedman Jonathan M. , Scott Michael L.
Published: April 2006

The intense demand for river water in arid regions is resulting in widespread changes in riparian vegetation. We present a direct gradient method to predict the vegetation change resulting from a proposed upstream dam or diversion. Our method begins with the definition of vegetative cover types, based on a census of the existing vegetation in a set of 1 ° 2 m plots. A hydraulic model determines the discharge necessary to inundate each plot. We use the hydrologic record, as defined by a flow duration curve, to determine the inundation duration for each plot. This allows us to position cover types along a gradient of inundation duration. A change in river management results in a new flow duration curve, which is used to redistribute the cover types among the plots. Changes in vegetation are expressed in terms of the area occupied by each cover type. We applied this approach to riparian vegetation of the Black Canyon of the Gunnison National Monument along the Gunnison River in Colorado. We used TWINSPAN to cluster plots according to species occurrence. This analysis defined three vegetative cover types that were distinct in terms of inundation duration. Quantitative changes in the extent of cover types were estimated for three hypothetical flow regimes: two diversion alternatives with different minimum flows and a moving average modification of historical flows. Our results suggest that (1) it is possible to cause substantial changes in riparian vegetation without changing mean annual flow, and (2) riparian vegetation is especially sensitive to changes in minimum and maximum flows. Principal advantages of this method are simplicity and reliance on relatively standard elements of plant community ecology and hydrologic engineering. Limitations include use of a single environmental gradient, restrictive assumptions about changes in channel geometry, representation of vegetation as quasi—equilibrium cover types, and the need for model validation.
Ambient Ultraviolet Radiation Causes Mortality in Salamander Eggs
Authors: Blaustein Andrew R. , Edmond Brian , Kiesecker Joseph M. , Beatty Joseph J. , Hokit D. Grant
Published: April 2006

Previous research has shown that amphibian species have differential sensitivity to ultraviolet‐B (UV‐B) radiation. In some anuran species, ambient levels of UV‐B cause mortality in embryonic stages and hatching success is significantly reduced. Projected increases in UV‐B may affect an increasing number of species. The adverse effects of UV‐B may eventually be manifested at the population level and may ultimately contribute to population declines. Using field experiments, we investigated the effects of ambient UV‐B on salamander (Ambystoma gracile) embryos developing at natural oviposition sites. We show that the hatching success of eggs of A. gracile shielded from UV‐B is significantly higher than those not shielded from UV‐B.
Changes in Lead Biogeochemistry in Response to Decreasing Atmospheric Inputs
Authors: Johnson Chris E. , Siccama Thomas G. , Driscoll Charles T. , Likens Gene E. , Moeller Robert E.
Published: April 2006

In the 1970s, the U.S. Congress passed legislation restricting the sale of gasoline with alkyl‐lead additives. In the intervening years, the amount of lead (Pb) consumed in gasoline has declined sharply, resulting in lower rates of atmospheric Pb deposition. At the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, the input of Pb in precipitation has declined by 97% between 1976 and 1989. The purpose of this paper is to evaluate the long‐term response of forest and associated aquatic ecosystems to these declining inputs of Pb. Lead continues to accumulate in the forest ecosystem of the HBEF, in spite of lower inputs, due to extremely low losses in drainage water. However, between 1977 and 1987 the Pb content in the forest floor declined by 29%. Lead now appears to be accumulating in the mineral soil. The stratigraphy of Pb in sediment from a nearby lake shows continued Pb deposition, though at a declining rate. Much of our understanding of the long‐term patterns of lead accumulation in ecosystems has been shaped by paleoecological studies, in which inputs of lead are assumed to be irreversibly retained. Using a regression model and historical information concerning Pb consumption in gasoline, we estimated Pb inputs to the HBEF ecosystem during the period 1926‐1989. Based on this analysis and our field observations, it is clear that Pb mobility at the HBEF is greater than previously reported: °30% of the total atmospheric Pb input between 1926 and 1987 was not retained in organic soils or pond sediments. The potential for Pb pollution in drainage water may therefore be greater than suspected in regions with continued high rates of atmospheric Pb deposition.
Mechanisms of Alteration in Bean Rust Development Due to Intercropping, in Computer‐Simulated Epidemics
Authors: Boudreau M. A. , Mundt C. C.
Published: April 2006

Computer simulations were performed to study the dynamics of disease in species mixtures. Input variables for the simulator EPIMUL were manipulated to reflect factors evaluated in 1989—1990 field experiments using a bean—maize intercrop and the bean rust pathogen. The variables were maize interference effects on spore dispersal, maize—bean competition as it affected spore dispersal, and effects of maize on infection efficiency of the rust pathogen after dispersal. When simulations were run at a low rate of disease progress (conditions less than optimal for disease development), intercrops reduced disease to 32% of the monocrop level using 1989 data, but had no effect using 1990 data. Reductions of infection efficiency were largely responsible for lowered disease in 1989—based simulations. Interference and competition effects on dispersal when acting together reduced disease to 81% of the monocrop level using 1989 data, but only affected epidemics in 1990—based simulations when acting independently. Disease alteration due to dispersal effects was caused by changes in spore escape from plots and not changes in the spore dispersal gradient slope. All treatment effects diminished as the rate of disease progress increased. We have thus identified potential sources of the variability seen in field studies: effects of intercropping may depend highly on the rate of disease progress; infection efficiency effects, probably microclimatic, can have a strong impact on disease; and dispersal effects, which may be qualitatively consistent among years, can produce very different epidemics in different years.
Community‐Wide Consequences of Trout Introduction in New Zealand Streams
Authors: Flecker Alexander S. , Townsend Colin R.
Published: April 2006

Trout provide one of the prime illustrations of the willful introduction of living organisms for recreational purposes. In New Zealand, brown trout were first liberated in the 1860s; today trout are so ubiquitous in the country that they have become enshrined in New Zealand culture. There is abundant evidence that in many streams, trout have largely replaced the indigenous galaxiid fishes. It remains unclear, however, whether their effects in stream communities have propagated through multiple trophic levels. Here we performed a pair of field experiments to compare the relative impacts of introduced and native fishes on the structure of a New Zealand stream community. We found large differences in the insect assemblages colonizing experimental channels, depending on the fish species present. In general, insect densities and biomass were lowest in channels containing trout compared to either galaxias or no fish treatments. Effects of trout on insect diversity were, however, relatively minor. The influence of fishes on insect abundance cascaded to the bottom trophic level, as algal standing crop was greatest in the presence of trout. These results suggest that the consequences of trout may extend beyond the replacement of native fish species. Although our approach allows us to ask whether the potential exists for community—wide impacts of invasive fishes, it remains unclear whether multiple trophic—level effects will be readily detectable in many ecological settings. The high degree of spatial and temporal heterogeneity common to running water systems, and the confounding effects of land—use transformations, may impede our ability to discern community—level changes following this and other species introductions.
Inertia in Plant Community Structure: State Changes After Cessation of Nutrient‐Enrichment Stress
Authors: Milchunas D. G. , Lauenroth W. K.
Published: April 2006

Water, nitrogen, and water‐plus‐nitrogen at levels beyond the range normally experienced by shortgrass steppe communities were applied from 1971 through 1975, plant populations were sampled through 1977, and the results of the experiment were published. Upon revisiting the plots in 1982, we found it apparent that large changes had occurred since 1977. Sampling was re‐established in 1982 to follow trajectories of recovery. Our purposes in this paper are to examine how conclusions from this study changed through time, and discuss implications of these changes for monitoring potentially stressed ecosystems. Although productivities increased, dissimilarities in plant species composition at the end of the 5 yr of nutrient treatments were not significantly different from controls. Two years after cessation of the treatments exotic "weed" species were increasing in water‐plus‐nitrogen treated communities, and community dissimilarities were diverging in water and water‐plus‐nitrogen treated communities. Seven years after cessation of treatments all communities were significantly different from controls. Exotics were more than ten times more abundant in water‐plus‐nitrogen and nitrogen treated communities than they had been 2 yr post‐treatment. A consistent trend in recovery of all treated communities was evident over the next 5 yr. However, the trend towards recovery reversed over the next four consecutive years in the previously water‐plus‐nitrogen and water treated communities. The four‐to‐five year cycles in species composition and abundance of exotics towards, and then away from, conditions in undisturbed control communities were not related to weather, but large accumulations of litter suggested biotic regulation. Inertia of existing plant populations, or the tendency to continue to occupy a site when conditions become unfavorable, can mask both future deterioration in ecosystem condition and unstable behavior resulting from environmental stressors. Time lags in initial response means that an ecosystem can pass a threshold leading to transitions to alternate states before it is evident in structural characteristics such as species composition. Global climate change and sulfur and nitrogen oxide pollutants also have the potential to act as enrichment‐stressors with initial time lags and/or positive effects and cumulative, subsequent negative effects, rather than as disturbance forces with immediate negative impacts. Sociopolitical systems, however, often require change in biological variables or negative impacts before acting to ameliorate environmental problems. The manner in which conclusions changed at various periods in time, and the potential for time lags in responses of species populations, raises questions about which variables are most useful for detection of stress and how long studies must last to be useful.
Juvenile Tree Survivorship as a Component of Shade Tolerance
Authors: Kobe Richard K. , Pacala Stephen W. , Silander John A. , Canham Charles D.
Published: April 2006

With a view toward understanding species‐specific differences in juvenile tree mortality and the community‐level implications of these differences, we characterized juvenile survivorship of 10 dominant tree species of oak transition‐northern hardwood forests using species‐specific mathematical models. The mortality models predict a sapling's probability of dying as a function of its recent growth history. These models and species‐specific growth functions (published elsewhere), characterize a species' shade tolerance. Combined growth and mortality models express a sapling's probability of mortality as a function of light availability. We describe the statistical bases and the field methods used to calibrate the mortality models. We examined inter‐ and intraspecific variation in juvenile mortality across three sites: Great Mountain Forest (low pH, nutrient poor soils) in northwestern Connecticut, a calcareous bedrock region (neutral pH, nutrient rich soils) also in northwestern Connecticut, and a site in central‐western Michigan (low pH, nutrient poor soils). Interspecific differences in juvenile mortality have profound effects on community dynamics and composition; the importance of these effects is demonstrated through a spatially explicit simulator of forest dynamics (SORTIE). The 10 species we examined occupy a continuum of survivorship levels at 1% of full sun. There was surprisingly little intraspecific variation in mortality functions for sugar maple, American beech, eastern hemlock, and white ash between the Great Mountain and Michigan sites. However, there was a striking increase in survivorship for sugar maple in the calcareous site. Differences in survivorship among the sites are correlated with soil pH and presumably nutrient availability. Growth rates in high‐light and low‐light survivorship are inversely correlated across species; as level of shade tolerance increases, a species grows more slowly in high light and exhibits increased survivorship under low light. Our results indicate that interspecific differences in sapling mortality are critical components of forest community dynamics.
Evidence That PCBs Are Approaching Stable Concentrations In Lake Michigan Fishes
Authors: Stow Craig A. , Carpenter Stephen R. , Eby Lisa A. , Amrhein James F. , Hesselberg Robert J.
Published: April 2006

We examined PCB concentration data for seven species of Lake Michigan fishes to determine what trends were apparent °20 yr after PCB restrictions became effective. Total PCB concentrations in all seven species, lake trout (Salvelinus namaycush), rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta), chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), alewife (Alosa pseudoharengus), and bloater chub (Coregonus hoyi) declined and appeared to stabilize in the mid‐to‐late 1980s. Concentrations in two species, chinook and coho salmon, appear to have increased slightly since the late 1980s. All species are currently well below the high PCB levels that existed when PCB use was curtailed in the 1970s. We believe stabilizing concentrations are the result of large pools of PCBs that are being recycled in the environment. Atmospheric and sediment PCB inputs to the lake probably constitute current PCB sources. Increasing concentrations in chinook and coho salmon are likely the result of changing growth dynamics caused by alterations in the mid‐trophic levels of the food web. Median stable PCB concentrations estimated in this analysis are below the current FDA action level of 2 mg/kg, but not appreciably below this threshold. Improvements beyond these levels may result if management practices that maximize fish growth rates are implemented. Detection of future improvements in PCB levels may require samples in the range of 1000‐2000 fish because of the high variability in PCB concentrations among individuals.
Shrub Invasion of a Tropical Wetland: Implications for Weed Management
Authors: Cook G. D. , Setterfield S. A. , Maddison J. P.
Published: April 2006

Records of the distribution and control of the shrubby weed Mimosa pigra in wetlands within, and adjacent to, Kakadu National Park (KNP), northern Australia, were examined to determine the effects of habitat variation and distance from large stands on the density and persistence of the satellite outbreaks. The cumulative density of outbreaks decreased with distance from the large stands to the east and west of KNP. There was, however, no trend in the number of new outbreaks discovered each year from 1984 until 1993, despite the doubling in area of the larger stand of M. pigra to the east of KNP every 1.4 yr from the early 1980s until 1991. The highest densities of outbreaks of M. pigra in KNP were found in the wetland margins that had been disturbed by feral animals, and in wetland habitats with a relatively long period of inundation, but where trees were absent. The dispersal gradient provided a useful model for predicting the occurrence of outbreaks on wetlands to the east of KNP that had not previously been surveyed systematically. More than 20% of outbreaks required sustained control for 7 yr or more because of the establishment of plants from the persistent seedbank. The control of satellite outbreaks of M. pigra has successfully prevented large stands developing in KNP. Detailed record‐keeping by the control program has facilitated essential follow‐up control and enabled the analysis of the spread of M. pigra, which should contribute to its efficient control elsewhere.
Mapping of Species Richness for Conservation of Biological Diversity: Conceptual and Methodological Issues
Authors: Conroy Michael J. , Noon Barry R.
Published: April 2006

Biodiversity mapping (e.g., the Gap Analysis Program [GAP]), in which vegetative features and categories of land use are mapped at coarse spatial scales, has been proposed as a reliable tool for land use decisions (e.g., reserve identification, selection, and design). This implicitly assumes that species richness data collected at coarse spatio‐temporal scales provide a first‐order approximation to community and ecosystem representation and persistence. This assumption may be false because (1) species abundance distributions and species richness are poor surrogates for community/ecosystem processes, and are scale dependent; (2) species abundance and richness data are unreliable because of unequal and unknown sampling probabilities and species‐habitat models of doubtful reliability; (3) mapped species richness data may be inherently resistant to scaling up or scaling down: and (4) decision‐making based on mapped species richness patterns may be sensitive to errors from unreliable data and models, resulting in suboptimal conservation decisions. We suggest an approach in which mapped data are linked to management via demographic models, multiscale sampling, and decision theory. We use a numerical representation of a system in which vegetation data are assumed to be known and mapped without error, a simple model relating habitat to predicted species persistence, and statistical decision theory to illustrate use of mapped data in conservation decision‐making and the impacts of uncertainty in data or models on the decision outcome.
Marine Reserves: Rates and Patterns of Recovery and Decline of Large Predatory Fish
Authors: Russ Garry R. , Alcala Angel C.
Published: April 2006

A major objective of the use of marine reserves in management of coral reef fisheries is protection of a critical spawning stock biomass to ensure recruitment supply to fished areas via larval dispersal. However, very little empirical evidence exists on the rates and patterns of increase of density and biomass of target species following the closure of a coral reef or part of a reef, nor on how quickly any gains potentially useful to fisheries can be lost if reserves are subsequently opened to fishing. This paper presents empirical evidence derived from the visual monitoring of density and biomass of large predatory coral reef fish (Serranidae (Epinephelinae), Lutjanidae, Lethrinidae and Carangidae as a group) in two small marine reserves and at two control sites in the Philippines from 1983 to 1993. At one reserve (Sumilon) a complex history of management allowed seven measurements of density and biomass at durations of reserve protection ranging from ‐2 (i.e., fished for 2 yr) to 9 yr. At the second reserve (Apo), seven measurements were taken at durations of reserve protection ranging from 1 to 11 yr. Density of large predators provided an excellent indicator of the effects of marine reserve protection and fishing. Density decreased significantly twice when the Sumilon reserve was opened to fishing (1985, 1993), and increased significantly three times following durations of marine reserve protection of 5 yr (Sumilon reserve and nonreserve sites, 1987‐1991) and >6 yr (Apo reserve beyond 1988). Density of large predators at the Apo nonreserve site (open to fishing) did not change significantly, remaining low throughout the study. Significant positive linear correlations of mean density of large predators with years of reserve protection were observed at both reserves. The rates of increase were 1.15 and 0.72 fish·1000 m‐2·yr‐1 at Sumilon and Apo reserves, respectively, with mean density ranges of ≈ 4‐17 fish/1000 m2 (‐2 to 9 yr of protection) at Sumilon and 0.5‐9.5 fish/1000 m2 (1‐11 yr of protection) at Apo. The pattern of increase of mean biomass with years of reserve protection was more curvilinear than that of mean density, particularly at Sumilon, where a slow increase was observed in the first 3‐5 yr (reflecting delayed recruitment and a natural delay to the period of maximum individual mass growth), followed by an increasing rate over the next 4 yr. Mean biomass ranges were ≈ 1.5‐18 kg/1000 m2 (‐2 to 9 yr of protection) at Sumilon and 1‐10.5 kg/1000 m2 (1‐11 yr of protection) at Apo. At Sumilon reserve, 2 and 1.5 yr of unregulated fishing, respectively, eliminated density and biomass gains accumulated over 5 and 9 yr of marine reserve protection.
Influence of Vegetational Structure on Capture of Salt and Nutrient Aerosols in a Maine Peatland
Authors: Schauffler Molly , Jacobson George L. , Pugh Alexander L. , Norton Stephen A.
Published: April 2006

Concentrations and fluxes of Cl‐ and Na+ in bulk precipitation and throughfall in an inland, acidic peatland (Alton Bog, Maine, USA) reveal the influence of canopy structure on the deposition rate of road‐salt and nutrient‐bearing aerosols. Alton Bog borders a four‐lane highway that is salted in winter. In open areas of the peatland steep gradients occurred in both Cl‐ and Na+ influxes in bulk precipitation and in surface‐water concentrations within ≈ 200 m of the highway. In winter, wooded sites had consistently higher atmospheric influxes of Cl‐ (up to 4X) than did treeless sites at the same distance from the highway. These results were consistent with expectations based on studies of dry deposition in nonpeatland areas. The increased influx of Cl‐ at wooded sites implies a significantly higher total influx of nutrients in peatlands where trees occur (especially unevenly spaced trees of mixed heights) than in peatlands with no trees. The effect is likely to be especially important in peatlands that receive all or most incoming nutrients from the atmosphere
Population Delineation of Polar Bears Using Satellite Collar Data
Authors: Bethke Ray , Taylor Mitchell , Amstrup Steve , Messier Francois
Published: April 2006

To produce reliable estimates of the size or vital rates of a given population, it is important that the boundaries of the population under study are clearly defined. This is particularly critical for large, migratory animals where levels of sustainable harvest are based on these estimates, and where small errors may have serious long‐term consequences for the population. Once populations are delineated, rates of exchange between adjacent populations can be determined and accounted/corrected for when calculating abundance (e.g., based on mark‐recapture data). Using satellite radio‐collar locations for polar bears in the western Canadian Arctic, we illustrate one approach to delineating wildlife populations that integrates cluster analysis methods for determining group membership with home range plotting procedures to define spatial utilization. This approach is flexible with respect to the specific procedures used and provides an objective and quantitative basis for defining population boundaries.
Parametric Empirical Bayes Methods for Ecological Applications
Authors: Ver Hoef Jay M.
Published: April 2006

This paper reviews parametric empirical Bayes (PEB) methods and their application to ecological data. One of the main objections to Bayesian statistics is the subjectivity caused by specifying parameters. Attempting to remove that subjectivity, the PEB philosophy uses the Bayesian mathematical framework, but then estimates, rather than specifies, all unknown parameters. Three examples are given to illustrate PEB methods. The first is a PEB analysis for monitoring the yearly population of harbor seals, the second uses simulated data and shows how a PEB analysis combines single capture‐recapture estimates, and the third is a PEB method for spatial patch analysis of data from a transect through grassland vegetation. From the examples, the general methodology and philosophy of a PEB analysis are explained.
A Bayesian Approach to Classification Criteria for Spectacled Eiders
Authors: Taylor B. L. , Wade P. R. , Stehn R. A. , Cochrane J. F.
Published: April 2006

To facilitate decisions to classify species according to risk of extinction, we used Bayesian methods to analyze trend data for the Spectacled Eider, an arctic sea duck. Trend data from three independent surveys of the Yukon‐Kuskokwim Delta were analyzed individually and in combination to yield posterior distributions for population growth rates. We used classification criteria developed by the recovery team for Spectacled Eiders that seek to equalize errors of under‐ or overprotecting the species. We conducted both a Bayesian decision analysis and a frequentist (classical statistical inference) decision analysis. Bayesian decision analyses are computationally easier, yield basically the same results, and yield results that are easier to explain to nonscientists. With the exception of the aerial survey analysis of the 10 most recent years, both Bayesian and frequentist methods indicated that an endangered classification is warranted. The discrepancy between surveys warrants further research. Although the trend data are abundance indices, we used a preliminary estimate of absolute abundance to demonstrate how to calculate extinction distributions using the joint probability distributions for population growth rate and variance in growth rate generated by the Bayesian analysis. Recent apparent increases in abundance highlight the need for models that apply to declining and then recovering species.
Discussion: Should Ecologists Become Bayesians?
Authors: Dennis Brian
Published: April 2006

Bayesian statistics involve substantial changes in the methods and philosophy of science. Before adopting Bayesian approaches, ecologists should consider carefully whether or not scientific understanding will be enhanced. Frequentist statistical methods, while imperfect, have made an unquestioned contribution to scientific progress and are a workhorse of day‐to‐day research. Bayesian statistics, by contrast, have a largely untested track record. The papers in this special section on Bayesian statistics exemplify the difficulties inherent in making convincing scientific arguments with Bayesian reasoning.
Optimal Translocation Strategies for Enhancing Stochastic Metapopulation Viability
Authors: Lubow Bruce C.
Published: April 2006

Numerous methods have been proposed for enhancing species viability. Much attention has been given to the minimum required number of individuals, size and number of nature reserves, and value of habitat corridors. Surprisingly, however, the potential value of active management of a population through a program of translocations has only rarely been suggested, and explicit formulations of a theoretical basis for such a program are nonexistent. By drawing on the mathematical optimization technique known as dynamic programming, I develop an optimal dynamic strategy for translocation in a model population. I demonstrate this approach using a simple model for a hypothetical remnant population with two available habitat reserves incorporating demographic, environmental, and catastrophic forms of stochasticity. I then generalize the results by examining the effect on the cost and effectiveness of optimal translocation management of reserve size, population growth rate, environmental stochasticity, catastrophe size and frequency, translocation mortality rate, spatial correlation of population dynamics, and reserve size asymmetry. Simulated application of the optimal strategies, under a wide range of conditions, demonstrates that managed translocations averaging between 1 and 6 individuals/yr might dramatically enhance the probability of species persistence and reduce the required size of nature reserves, potentially by >1 order of magnitude. Given prohibitive financial and political costs of land acquisition for nature reserves, this technique could provide an important alternative for saving many endangered species.
Constructing a Supranational Constitution: Dispute Resolution and Governance in the European Community
Authors: Sweet Alec Stone , Brunell Thomas L.
Published: April 2006

We present a theory of European legal integration that relies on three causal factors: transnational exchange, triadic dispute resolution, and the production of legal norms. After stating the theory in abstract terms, we explain the construction of the legal system and test the relationship among our three variables over the life of the European Community. We then examine the effect of the EC legal system on policy outcomes at both the national and supranational levels in two policy domains: the free movement of goods and gender equality. Our theory outperforms its leading rival, intergovernmentalism. The evidence shows that European integration has generally been driven by transnational activity and the efforts of EC institutions to reduce transaction costs, behavior which governments react to but do not control.
Institutional and Rational Determinants of Organizational Practices: Human Resource Management in European Firms
Authors: Gooderham Paul N. , Nordhaug Odd , Ringdal Kristen
Published: April 2006

This paper tests predictions from institutional and rational perspectives about the adoption of organizational practices through a comparative study of human resource management in firms located in six European countries. Distinguishing between calculative practices—aimed at efficient use of human resources—and collaborative practices—aimed at promoting the goals of both employees and employer—the paper predicts differences in adoption across countries. Results show that institutional determinants, as indicated by the national embeddedness of firms, have a strong effect on the application of both calculative and collaborative human resource management practices. Firm size, a rational determinant, has a considerable impact on calculative practices, whereas the effect of industrial embeddedness is quite modest for both practices.
Agency and Social Networks: Strategies of Action in a Social Structure of Position, Opposition, and Opportunity
Authors: Stevenson William B. , Greenberg Danna
Published: April 2006

This study uses social movement concepts to explain the success and failure of actors in a network of relationships trying to influence policies on environmental issues in a small city. Results show that strategies to take action and mobilize others in a network of interorganizational relationships can vary depending on the social context, which consists of the political opportunity structure defined by government regulators, whether the actor faces opposition, and the actor's position in the network. Decisions to engage in strategies to try to influence government regulators directly, to use a broker to reach agreements with the opposition, or to form a coalition with actors in other organizations to influence government decision makers are affected by this social context. Results also show that even peripheral actors, usually assumed to be powerless in network studies, can influence policy if they use a direct-contact strategy and the political opportunity structure is favorable.
Organizational Improvisation and Learning: A Field Study
Authors: Miner Anne S. , Bassof Paula , Moorman Christine
Published: April 2006

An inductive study of improvisation in new product development activities in two firms uncovered a variety of improvisational forms and the factors that shaped them. Embedded in the observations were two important linkages between organizational improvisation and learning. First, site observations led us to refine prior definitions of improvisation and view it as a distinct type of real-time, short-term learning. Second, observation revealed links between improvisation and long-term organizational learning. Improvisation interfered with some learning processes; it also sometimes played a role in long-term trial-and-error learning, and the firms displayed improvisational competencies. Our findings extend prior research on organizational improvisation and learning and provide a lens for research on entrepreneurship, technological innovation, and the fusion of unplanned change and order.
Institutions, Exchange Relations, and the Emergence of New Fields: Regulatory Policies and Independent Power Production in America, 1978–1992
Authors: Russo Michael V.
Published: April 2006

This paper analyzes how a new field, independent (or non-utility) power production, was created by a federal mandate that electric utilities purchase power from private generating sources and how the field was populated. Results show that key rules that state regulatory bodies adopted or rejected regulating exchange between independent power producers and utilities were influential predictors of organizational foundings. Results also show that collective action by independent power producers boosted foundings. Finally, if the preexisting relationship between utilities and regulators was one of accommodation, foundings were suppressed. The paper examines these results in view of economic and sociological perspectives on public policies, spotlighting the vital role of institutions in early population dynamics.
An Archaeological Reconnaissance of the Middle and Lower Yukon Valley, Alaska
Authors: Laguna Frederica de
Published: April 2006

During the summer of 1935, the University of Pennsylvania Museum sponsored an archaeological and geological survey of the middle and lower Yukon valley, Alaska. The work was financed through the generosity of the National Research Council and the American Philosophical Society. The party consisted of: Dr. A. J. Eardley, Department of Geology, University of Michigan; Mr. Kenneth Gorton, a student of geology at the same institution; Mr. Norman Reynolds, a student of anthropology at the University of Washington; and the writer.

The principal object of the expedition was to investigate the possibilities of finding ancient human remains in the Yukon valley. The discoveries of ancient artifacts (belonging to the so-called Folsom culture) in association with bones of extinct animals, show that human beings lived on the southern High Plains east of the Rockies at the end of the Pleistocene or during the early post-Pleistocene.
The Archaeological Survey of the Natchez Trace
Authors: Jennings Jesse D.
Published: April 2006

The Natchez Trace Parkway is an area, still in a construction stage, controlled by the National Park Service. The Park Service's three general policies of presentation, protection, and interpretation are familiar to most Americans through either reading or travel, or both. Recently an innovation in Park Service areas—on a grand scale—has been introduced by congressional action, so that the Service has begun the development of a series of parkways. These parkways—sired by the East's super-highways with restricted traffic—are in effect elongated parks consisting of a high-standard roadway insulated from unsightly commercial encroachment and despoliation by the usual Park Service regulations regarding protection of natural beauty. Of the three parkways, the George Washington in Virginia is both scenic and utilitarian, the Blue Ridge is essentially a scenic recreational effort, while the Natchez Trace Parkway is commemorative of an ancient road of considerable importance in the early history of the nation.
Unique Artifact from Manitoba
Authors: Vickers Chris
Published: April 2006

During the month of May, 1948, Dr. Douglas Leechman of the National Museum, Ottawa, spent some time on the northern Plains. Included in his Manitoba itinerary was a rapid survey of the more important sites in the southcentral portion of the province. While on the Lowton site (S. W. Sec. 26, T. 5, R. 16, W. 1st.), one of the party, Dr. R. D. Bird of Brandon, Manitoba, recovered from the surface the curved knife with the deliberately fashioned scraper end illustrated in Figure 21.
Eskimo Stone House Ruins on the East Side of Hudson Bay: A Correction
Authors: Manning T. H.
Published: April 2006

In 1944 when I was at Port Harrison, I enquired if there were any Eskimo stone house ruins in the region, but the Eskimos knew of none except ”strong“ tent rings. Because of this, and from the reactions of our Eskimo crew to the houses and strong tent rings on the King. George and Marcopeet islands, I concluded1 that if there were any Thule type houses on the mainland they were too old to be easily recognized.

In 1946, I was again working for the Geodetic Service in that area. Through enquiries at Port Harrison, I heard of two groups of ruins, and at three out of our five stops on the Hudson Bay coast, I accidentally stumbled on other groups. Thus, not only are there house ruins on this coast, but they appear to be quite numerous.
A Tentative Classification of the Prehistoric Cultures of Minnesota
Authors: Wilford Lloyd A.
Published: April 2006

The archaeology of Minnesota is of interest for three principal reasons. Its geographical situation near the center of the continent, where it is the only state having drainage to the Arctic Ocean, the Gulf of St. Lawrence and the Gulf of Mexico, gives it importance in the consideration of migrations of early man and of the late prehistoric westward movements of various Indian groups. Until recently, the archaeology of this large area was less well known than that of other areas in the region, so an increased knowledge of it will be of value in contributing to a better understanding of the known archaeological manifestations of the central and northeastern parts of the United States. Finally, over most of the state the last prehistoric remains are of the Woodland pattern, giving an especially good opportunity for a study of that pattern in a relatively unaffected form.
Gold Ornaments of Chavín Style from Chongoyape, Peru
Authors: Lothrop S. K.
Published: April 2006

Chavín de Huántar is a small village located in the Department of Ancash in the high mountains of central Peru. Near the modern town is a vast, partly subterranean temple, dating from prehistoric times, within and near which have been found numerous stone carvings of distinctive styles. The name Chavín has thus been applied to a very ancient culture which apparently once dominated the northern interior of Peru and, in places, emerged in the coastal valleys.

The existence, if not the status, of Chavín culture was brought to the attention of the outside world many years ago by Antonio Raimondi, whose name clings to the celebrated stone carvings seen in Fig. 27, b. Charles Wiener has left a description of the great temple at Chavín and the huge dagger-like stone carving that was its chief idol. Plans and photographs have been recently published by Cornelius Roosevelt. In 1919, Dr. Julio C.
Note on an Apocynum Fabric
Authors: O'Neale Lila M.
Published: April 2006

A textile specimen in the University of California Museum of Anthropology, perhaps to be identified as a sling pocket, adds a new item to the growing list of fabrications made of twisted dogbane fiber (Apocynum cannabinum).It is, moreover, constructed by a technique not to my knowledge previously reported. I am indebted to Professor Robert F. Heizer for calling my attention to this unique object and for the following paragraphs placing it in its relation to Nevada archeology.

“The piece comes from a dry cave site (Humboldt Cave) in west central Nevada about 10 miles southwest of Lovelock Cave. The cave was excavated in 1936 by the University of California Department of Anthropology, and the final report on the excavation is now nearly completed.
A Prehistoric Method of Collecting Water
Authors: Schroeder Albert H.
Published: April 2006

While in the field, running a stabilization survey at Wupatki National Monument, the writer and Phillip Van Cleave, an assistant, encountered a site which illustrates another method utilized by the prehistoric Indians in dealing with the problem of water supply in this arid region.
Bone Implements from Shell Heaps around Frenchman's Bay, Maine
Authors: Hadlock Wendell S.
Published: April 2006

There are several hundred known shell heaps, along the coast of Maine, some of which have been hardly dug into while others have been completely excavated. Except for their size, they appear much alike both on the surface and in their internal structure.

It is not possible to say with certainty that one tribe or group of Indians inhabited each shell heap from the time of its beginning until the heap reached its present size. It is probable that many of the shell heaps were not, in many instances, occupied year after year, while others show a continual growth without any marked indication of periods when the areas were not in use.
Great Basin Prehistory: A Review
Authors: Jennings Jesse D. , Norbeck Edward
Published: April 2006

Since the Publication of Steward's interpretations of Great Basin prehistory, which were based upon field research ending about 1935, no attempt has been made in published form to collate and analyze currently available data on the full range of the prehistory of the area. Steward's conclusions are thoughtful and represent conservative, sound reasoning upon the basis of the data available and the theories current at the time. As might reasonably be expected, however, subsequent findings have cast doubt upon some of his interpretations and have made others unacceptable. This paper is a brief attempt, deliberately kept at a general level, to review both old and new data, with special reference to the cultural relationships between the Great Basin and San Juan Anasazi, and to call attention to current developments and problems.