bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional and Numerical Responses: A Framework for Fish‐Angler Interactions?
Authors: Johnson Brett M. , Carpenter Stephen R.
Published: April 2006

A conceptual framework for sport fisheries in which fish—angler interactions are viewed as a dynamic predator—prey relationship was evaluated with data from the walleye fishery in Lake Mendota, Wisconsin. A detailed 7—yr creel survey data set for this fishery revealed a link between fish and angler dynamics. Angler catch rates were positively and linearly related to fish abundance over the range of data in the study. Angling effort was positively related to catch rate. Fish—angler relationships were obscured by three difficulties commonly associated with fishery data sets: seasonal responses, measurement errors in predictor variables, and time series bias. Statistical techniques removed each of these biases, but the data were still insufficient to conclusively identify an appropriate model for the interaction. Nevertheless, it is clear that assumptions of static angler response to sport fish manipulations are unwarranted and capable of seriously confounding management efforts. Interactions among anglers and the influence of alternative fisheries outside the observed system appeared to be important. A combination of longer duration studies on a broader geographic scale and manipulative management experiments is probably necessary to advance our understanding of fish—angler interactions.
Fire, Global Warming, and the Carbon Balance of Boreal Forests
Authors: Kasischke Eric S. , Christensen N. L. , Stocks Brian J.
Published: April 2006

Fire strongly influences carbon cycling and storage in boreal forests. In the near‐term, if global warming occurs, the frequency and intensity of fires in boreal forests are likely to increase significantly. A sensitivity analysis on the relationship between fire and carbon storage in the living‐biomass and ground‐layer compartments of boreal forests was performed to determine how the carbon stocks would be expected to change as a result of global warming. A model was developed to study this sensitivity. The model shows if the annual area burned in boreal forests increases by 50%, as predicted by some studies, then the amount of carbon stored in the ground layer would decrease between 3.5 and 5.6 kg/m2, and the amount of carbon stored in the living biomass would increase by 1.2 kg/m2. There would be a net loss of carbon in boreal forests between 2.3 and 4.4 kg/m2, or 27.1‐51.9 Pg on a global scale. Because the carbon in the ground layer is lost more quickly than carbon is accumulated in living biomass, this could lead to a short‐term release of carbon over the next 50‐100 yr at a rate of 0.33‐0.8 Pg/yr, dependent on the distribution of carbon between organic and mineral soil in the ground layer (which is presently not well‐understood) and the increase in fire frequency caused by global warming.
Linking Contemporary Vegetation Models with Spatially Explicit Animal Population Models
Authors: Holt Robert D. , Pacala Stephen W. , Smith Thomas W. , Liu Jianguo
Published: April 2006

Spatially explicit models for animal populations (SEPMs) necessarily embody assumptions about plant community structure and dynamics. This paper explores the advantages and limitations of directly linking animal SEPMs with models for vegetation dynamics. Such linkages may often be unnecessary. For instance, in research focussed on questions with short time horizons, the spatial patterning of vegetation can be reasonably approximated as a fixed landscape templet for animal population dynamics. But if one needs to consider longer time scales (e.g., decades to centuries), landscapes will be dynamic. Models of vegetation dynamics provide useful tools for predicting landscape dynamics. We outline the sorts of output from vegetation models that might be useful in animal SEPMs. We discuss as a concrete example recent forest simulators, which predict with reasonable accuracy some variables (e.g., tree species composition), but which, to date, are quite poor for others (e.g., seed production). Moreover, because vegetation models target a restricted range of temporal and spatial scales, they may be more useful for certain consumer groups than for others. Despite these cautionary observations, we believe that the time is ripe for fruitful linkages between models of vegetation dynamics and animal SEPMs.
Relationships Between NDVI, Canopy Structure, and Photosynthesis in Three Californian Vegetation Types
Authors: Gamon John A. , Field Christopher B. , Goulden Michael L. , Griffin Kevin L. , Hartley Anne E. , Joel Geeske , Penuelas Josep , Valentini Riccardo
Published: April 2006

In a range of plant species from three Californian vegetation types, we examined the widely used "normalized difference vegetation index" (NDVI) and "simple ratio" (SR) as indicators of canopy structure, light absorption, and photosynthetic activity. These indices, which are derived from canopy reflectance in the red and near‐infrared wavebands, highlighted phenological differences between evergreen and deciduous canopies. They were poor indicators of total canopy biomass due to the varying abundance of non‐green standing biomass in these vegetation types. However, in sparse canopies (leaf area index [LAI]°0‐2), NDVI was a sensitive indicator of canopy structure and chemical content (green biomass, green leaf area index, chlorophyll content, and foliar nitrogen content). At higher canopy green LAI values (>2; typical of dense shrubs and trees), NDVI was relatively insensitive to changes in canopy structure. Compared to SR, NDVI was better correlated with indicators of canopy structure and chemical content, but was equivalent to the logarithm of SR. In agreement with theoretical expectations, both NDVI and SR exhibited near‐linear correlations with fractional PAR intercepted by green leaves over a wide range of canopy densities. Maximum daily photosynthetic rates were positively correlated with NDVI and SR in annual grassland and semideciduous shrubs where canopy development and photosynthetic activity were in synchrony. The indices were also correlated with peak springtime canopy photosynthetic rates in evergreens. However, over most of the year, these indices were poor predictors of photosynthetic performance in evergreen species due to seasonal reductions in photosynthetic radiation‐use efficiency that occurred without substantial declines in canopy greenness. Our results support the use of these vegetation indices as remote indicators of PAR absorption, and thus potential photosynthetic activity, even in heterogeneous landscapes. To provide accurate estimates of vegetation‐atmosphere gas fluxes, remote NDVI and SR measurements need to be coupled with careful estimates of canopy photosynthetic radiation‐use efficiency.
Response of Wetlands to Rising Sea Level in the Lower Coastal Plain of North Carolina
Authors: Moorhead Kevin K. , Brinson Mark M.
Published: April 2006

Most of the coastal wetlands of the South Atlantic region of the United States are expected to diminish in size in response to the opposing forces of increasing human population growth and accelerating rates of rising sea level. We evaluated several models that project the response of coastal wetlands to rising sea level and concluded that current models appear unsuited for wetlands of the Albermarle‐Pamlico peninsula of North Carolina. We came to this conclusion after we examined the distribution of wetlands, elevation contours, estimates of surface slope, soil types, and peat deposits on the peninsula. Most of the data were obtained from U.S. Geological Survey topographic quadrangle maps, U.S. Fish and Wildlife Service National Wetlands Inventory maps, U.S. Soil Conservation Service soil surveys, and inventories of peat deposits. Some unusual features of this peninsula are low elevation (56% of total area <1.5 m), extensive coverage by wetlands (53%) and hydric soils (90%), negligible slopes of the land surface, virtual absence of tides, and lack of abundant sources of sediment. In the process of reconstructing how past rises in sea level most likely led to present conditions, it became apparent that vertical accretion of peat in situ is largely responsible for landscape features in areas where elevations are lowest. Were it not for these deposits, the land surface area of the peninsula would be decreasing relative to sea level. This situation contrasts sharply with areas in the eastern United States fringed by tidal marshes, which are undergoing overland migration at a rate dictated by landward slope and the rate of rising sea level. If the rate of sea level rise accelerates, it is doubtful if vertical accretion rates of peat can prevent submergence of extensive areas of wetlands in the Albermarle‐Pamlico peninsula. Land use and drainage in the lowest elevations of the peninsula are currently being affected by sea level. Future land management of the peninsula will be constrained by potential landscape changes as a result of rising sea level.
On Beyond BACI: Sampling Designs that Might Reliably Detect Environmental Disturbances
Authors: Underwood A. J.
Published: April 2006

Much sampling to detect and quantify human environmental disturbances is flawed by a lack of appropriate replication. BACI (Before—After—Control—Impact) designs have only a single control location, and any conclusions from them are illogical. Asymmetrical designs using one putatively impacted and several control locations can reliably detect a variety of environmental impacts, including those that do not affect long—run mean abundances, but do alter temporal variance. When abundances of populations in different locations show temporal interaction, the asymmetrical designs allow tests for impact that are not possible in BACI designs. Asymmetrical designs are also extendable to sample at hierarchical spatial and temporal scales. The power of tests using asymmetrical designs is great for non—interactive sets of abundances, but greatest for pulse (short—term) responses to disturbances, large alterations of temporal variance, or combinations of temporal variance, or combinations of sustained, press responses in mean abundance coupled with altered temporal heterogeneity. Power in temporally interactive sets of data is generally poor. Alternatives to pre—disturbance sampling, including generalized assessment of spatial and temporal variances and experimental impacts, may provide better guidance for detection of human disturbances.
Impacts on Soft‐Sediment Macrofauna: The Effects of Spatial Variation on Temporal Trends
Authors: Thrush Simon F. , Pridmore Rick D. , Hewitt Judi E.
Published: April 2006

Long—term studies provide useful insight into the functioning of populations and communities. Gaining a long—term perspective may be important in providing back—ground information upon which BACI (Before–After—Control–Impact)—type impact studies can be designed or in identifying many types of impact, particularly those of a large—scale and diffuse nature. Although marine soft—bottom communities commonly exhibit patchy distributions, in many long—term studies few replicates, from each site, are collected on each occasion. To illustrate potential problems encountered when spatial variation confounds temporal patterns, we use data collected from a monitoring program of the intertidal sandflat communities of Manukau Harbour, New Zealand. Randomization techniques were used to generate possible temporal sequences, based on a sample size similar to that used in many long—term studies. In the generated sequences the timing and size of annual density changes were often different from the observed sequence, and indicators of trends in density were often missed. In order to provide accurate descriptions of temporal variability in the soft—bottom communities of estuaries and coastal embayments, low bias and highly precise density estimates from each sampling occasion are required.
Remote Sensing of Tropical Wetlands for Malaria Control in Chiapas, Mexico
Authors: Pope Kevin O. , Rejmankova Eliska , Savage Harry M. , Arredondo-Jimenez Juan I. , Rodriguez Mario H. , Roberts Donald R.
Published: April 2006

Malaria, transmitted by anopheline mosquitoes, remains a serious health problem in the tropics. Most malaria eradication efforts focus on control of anopheline vectors. These efforts include the NASA Di—Mod project, whose current goal is to integrate remote sensing, geographic information systems (GIS), and field research to predict anopheline mosquito population dynamics in the Pacific coastal plain of Chiapas, Mexico. Field studies demonstrate that high larval production of Anopheles albimanus, the principal malaria vector in the plain, can be linked to a small number of larval habitat—types, determined by larval sampling and cluster analysis of wetlands in the coastal plain. Analysis of wet and dry season Landsat Thematic Mapper (TM) satellite imagery identified 16 land cover units within an 185—km2 study area in the coastal zone. A hierarchical approach was used to link the larval habitat—types with the larger land cover units and make predictions of potential and actual low, medium, and high anopheline production. The TM—based map and GIS techniques were then used to predict differences in anopheline production at two villages, La Victoria and Efrain Gutierrez. La Victoria was predicted to have much higher Anopheles albimanus production, based upon a 2—10 times greater extent of medium— and high—producing land cover units in its vicinity. This difference between villages was independently supported by sampling (with light traps) of adults, which were 5—10 times more abundant in La Victoria.
Importance of GIS to Community‐Based Management of Wildlife: Lessons from Zambia
Authors: Lewis Dale M.
Published: April 2006

Wildlife resources under the protective custodianship of skilled managers can thrive and sustain important revenues. Such custodianship is generally lacking among communal rural societies in Africa because of land use policies that overlook the capacity and the practical importance of actively engaging these societies in wildlife management. In Zambia participation by local village communities in this management is recognized as a prerequisite for wildlife development and conservation. This participation is permitted through the administrative management design (called ADMADE) for game management areas. To help improve the capacity of rural communities to become more knowledgeable and effective in managing their wildlife resources, a geographical information system (GIS), based on ARC/INFO software, was applied and tested as an appropriate technology. It was hypothesized that maps composed of easily recognizable information about land use issues affecting the welfare of local residents and their natural resources would facilitate communal societies to make technically improved land use decisions with broad‐based support within the community. Results offered a growing set of achievements in land use planning by local community leaders in support of this hypothesis. Custom designed maps produced by this technology were used by these leaders to explain and build consensus at the community level on ways to resolve resource use conflicts. Results also demonstrated the pragmatic and cost‐effective value of training local residents to participate in the collection of GIS data as a way of making maps more locally acceptable and better focused on relevant issues and needs.
Managing Amazonian Wildlife: Biological Correlates of Game Choice by Detribalized Hunters
Authors: Bodmer Richard E.
Published: April 2006

Wildlife management in tropical areas inhabited by rural people requires an understanding of the interactions between game choice of hunters and the biology of game species. This paper presents an analysis that combines information on game use and game biology in an attempt to understand better the game hunting system and its effect on mammalian populations. Game choice by non—tribal inhabitants was studied in the north—eastern Peruvian Amazon within the Reserva Communal Tamshiyacu—Tahuayo (RCTT). The correlation between game preferences and actual harvests was calculated using Ivlev's index of selectivity. Hunters preferred large—bodied mammals and mammals with high economic value. Actual harvests did not reflect preferences of hunters, but were correlated with reproductive productivity of game species, measured as the species rmax. Impact of hunting on the biomass of game was not correlated with preferences of hunters or actual harvests. Both game choice by hunters and susceptibility of species to hunting depended mainly on the reproductive productivities of game species. Thus, game management in the RCTT must consider the dominating effects of reproductive biology and consider variance in rmax when determining harvests.
Disturbance and Diversity in Tropical Rain Forests: The Density Effect
Authors: Denslow Julie Sloan
Published: April 2006

A null model for the effects of treefall gaps on tree species diversity of tropical rain forests is based on the well‐known relationship between abundance and diversity: habitats supporting larger numbers of individuals can support more populations and more species than habitats supporting small numbers of individuals. Because seedling establishment and sapling density increase following canopy opening, gaps are often also sites of high species diversity. Both tree density and diversity are likely to be greater in areas of high stand‐turnover rates. Thinning and non‐catastrophic mortality reduce both density and diversity in areas of low gap frequency. Nevertheless, natural and anthropogenic disturbances, such as logging, have been hypothesized to both enhance and limit species diversity through changes in habitat heterogeneity, shifts in competitive balances among species, and creation of otherwise‐rare habitats. Species‐accumulation curves can be used to evaluate these alternatives by comparing observed species‐abundance patterns with expected changes in diversity due to density effects alone. Topographic variation in density and diversity of shrubs and small saplings at the La Selva (Costa Rica) Biological Station preserve was analyzed as an example. The total number of species for each of 18 sites was estimated by fitting a two‐parameter hyperbola (similar to the Michaelis‐Menten equation) to sample data using a maximum‐likelihood method. Although both density and diversity were higher on slopes than on ridges, total species richness was nevertheless higher on slopes than is predictable from density effects alone. High stand‐turnover rates on slopes may enhance tree species diversity through increases in tree density and in habitat heterogeneity.
Impacts of Pastoralists on Woodlands in South Turkana, Kenya: Livestock‐ Mediated Tree Recruitment
Authors: Reid Robin S. , Ellis James E.
Published: April 2006

Since the turn of the century, African pastoralists have been held responsible for overuse of woody plants and for the degradation and desertification of many arid and semiarid lands. We analyzed the impacts of pastoral nomads and their livestock on the recruitment (establishment to first reproduction) of Acacia tortilis, a dominant tree in the dry woodlands of South Turkana, Kenya, where Acacia seedpods make up an important part of livestock diets. Seed density averaged over 85 times higher in bush‐fenced livestock corrals than in the surrounding environment. The survival and growth of 14 cohorts of trees ranging in age from 1 to 39 yr were investigated comparing tree stands originating inside livestock corrals with those originating outside. Corral soils contained nine times more C, three times more N, and six times more P than adjacent noncorral soils immediately following corral abandonment. Corral soils also retained more moisture than noncorral soils after rainfall. These soil conditions accelerated seedling emergence in corrals, and enhanced survival and growth of 1st‐yr seedlings. Survival of older trees in corral stands was not significantly different from those established outside corrals during this study. However, comparison of tree densities over time suggests that corral stands thin more rapidly than noncorral stands, probably because of crowding. The early survival and growth advantages of the corral environment appear to stabilize the reproductive patterns of A. tortilis in this arid ecosystem, where successful recruitment in noncorral sites may be restricted to the few years with high rainfall. Contrary to the conventional wisdom, pastoralists may be improving rangelands in South Turkana by enhancing recruitment reliability in this important tree species.
Flow Regulation, Geomorphology, and Colorado River Marsh Development in the Grand Canyon, Arizona
Authors: Stevens Lawrence E. , Schmidt John C. , Ayers Tina J. , Brown Bryan T.
Published: April 2006

New, productive fluvial marshes may develop along regulated canyon rivers through reduction in flood frequency, thereby increasing diversity, production, and wildlife habitat availability. Few fluvial marshes occurred along the eddy‐dominated Colorado River in the Grand Canyon prior to construction of Glen Canyon Dam in 1963. Reduction of flooding after 1963 permitted widespread marsh development. Fluvial marshes exhibited low stability but high resilience, quickly redeveloping after scouring by high flows between 1983 and 1986. In 1991, 253 fluvial wet marshes (cattail/reed and horseweed/Bermudagrass) and 850 dry marshes (horsetail/willow) occupied 25.0 ha (1%) of the 363 km mainstream riparian corridor between Lees Ferry and Diamond Creek, Arizona. Fluvial marsh development and composition varied in relation to local and reach‐based geomorphology, and microsite gradients in inundation frequency and soil texture. Colorado River marsh density (number/km2) increased with distance downstream, and marshes were larger and more abundant in wide reaches. Wet marsh cattail/reed stands developed on silty loam soils in low velocity depositional environments that were inundated 54% of the days from 1986 to 1991, whereas dry horsetail/willow marshes occupied less frequently inundated sites with sandy soils. Mean marsh standing mass (641 g C/m2) was comparable with values from regulated alluvial river marshes, but litter retention appeared limited by flow variability in both regulated and unregulated fluvial marshes. We discuss implications of flow management on the four marsh assemblages, and the need for consensus on priorities for management of regulated fluvial wetlands.
Analyzing the Effects of Accidental Environmental Impacts: Approaches and Assumptions
Authors: Wiens John A. , Parker Keith R.
Published: April 2006

Because studies of environmental accidents must be initiated after the fact and because the accidents cannot (or should not) be replicated, sampling cannot be entirely randomized, and investigations involve some degree of confounding and pseudoreplication. The study designs that can be used carry methodological limitations and ecological assumptions, which must be considered in evaluating results. The methodological issues relate to consistency in sampling methods and to the adequacy of sampling of levels of environmental disturbance or contamination, while the ecological assumptions derive from spatial and temporal variation in biological resources and the factors that affect them. We assess how these methodological issues and ecological assumptions affect study designs based on before–after comparisons and on single‐time or multiple‐time sampling after an accident. Designs that rest on the assumption of a steady‐state equilibrium in resource‐environment relationships (baseline and time‐series designs) must be interpreted with particular care, and baseline designs are sensitive to the effects of pseudoreplication and inconsistencies in methods. Other designs (pre/post paired samples, impact level‐by‐time, impact trend‐by‐time) assume only that environmental variations are equivalent among areas and/or contamination levels (a dynamic equilibrium) and are less affected by pseudoreplication. Single‐time designs (comparisons between impact and reference sites, between matched paired sites, or over a contamination gradient) have fewer methodological limitations, but assume that other natural factors that may influence the response of a resource are equal among all samples. If measurements of other factors are included in the design, covariance analysis may help to reduce this problem. In evaluating the effects of unplanned environmental impacts, post facto study designs that document both initial effects and subsequent recovery (impact level‐by‐time, impact trend‐by‐time) or that treat effects as continuous rather than categorical variables (gradient or trend designs) may be more useful than before–after comparisons.
Lightning Estimates of Precipitation Location and Quantity on the Sevilleta Lter, New Mexico
Authors: Gosz James R. , Moore Douglas I. , Shore Gregory A. , Grover Herbert D. , Rison William , Rison Carol
Published: April 2006

Typically, 50‐70% of the total annual precipitation in New Mexico can be produced by convective thunderstorms during the period June through September. These thunderstorms are accompanied by intense lightning and characteristically produce heavy, localized rainfall resulting in high spatial variation in precipitation inputs. During other months precipitation over the entire Sevilleta (105 ha) often occurs from broad‐scale storm systems and is much less spatially variable on a per‐storm basis. Summer precipitation is a primary factor driving plant productivity as well as influencing nutrient cycling, herbivore activity, and detritivore activity. Knowledge of the timing, location, and amounts of precipitation is important in planning or monitoring research activities and spatial modeling of the dynamics in this semiarid region. Technology exists for locating cloud‐to‐ground lightning strikes that has the potential to locate these intense precipitation events, quantify the volume of water associated with them, and document the spatial and temporal variability of this phenomenon over large areas. Near real‐time analysis capability can identify areas receiving precipitation that will experience rapid vegetation growth in this semiarid region. This study developed algorithms relating lightning and precipitation quantity and used lightning location to determine rainfall depth and distribution for areas in New Mexico. There was a significant correlation between rain‐gauge measured precipitation and lightning within a 3‐km radius of the gauge location, with best predictions occurring from regressions that included lightning strikes and relative humidity. Average precipitation volume per cloud‐to‐ground lightning strike averaged 36 190 m3 for the 3 km radius circle, resulting in an average rainfall depth of 1.3 mm per lightning strike. Lightning location technology, combined with a Geographic Information System (GIS), defined the spatial and temporal resolution of these intense, summer precipitation patterns and provided a more detailed estimate of total precipitation and precipitation distribution than was provided by the sparse network of precipitation gauges. Combining this information with satellite sensing of vegetation growth (e.g., greenness index) can identify causal mechanisms for temporal and spatial patterns in short‐term vegetation processes (e.g., primary production) and long‐term vegetation dynamics for this area.
Episodic Acidification of Small Streams in the Northeastern United States: Effects on Fish Populations
Authors: Baker J. P. , Van Sickle J. , Gagen C. J. , DeWalle D. R. , Sharpe W. E. , Carline R. F. , Baldigo B. P. , Murdoch P. S. , Bath D. W. , Krester W. A. , Simonin H. A. , Wigington P. J.
Published: April 2006

As part of the Episodic Response Project (ERP), we studied the effects of episodic acidification on fish in 13 small streams in the northeastern United States: four streams in the Adirondack region of New York, four streams in the Catskills, New York, and five streams in the northern Appalachian Plateau, Pennsylvania. In situ bioassays with brook trout (Salvelinus fontinalis) and a forage fish species (blacknose dace (Rhinichthys atratulus), mottled sculpin (Cottus bairdi), or slimy sculpin (Cottus cognatus), depending on the region) measured direct toxicity. Movements of individual brook trout, in relation to stream chemistry, were monitored using radiotelemetry. Electrofishing surveys assessed fish community status and the density and biomass of brook trout in each stream. During low flow, all streams except one had chemical conditions considered suitable for the survival and reproduction of most fish species (median pH 6.0‐7.2 during low flow; inorganic Al < 60 μg/L). ERP streams with suitable conditions during low flow, but moderate‐to‐severe episodic acidification during high flow, had higher fish mortality in bioassays, net down‐stream movement of brook trout during events, and lower brook trout density and biomass compared to nonacidic streams, and lacked acid‐sensitive fish species (blacknose dace and sculpin). Movement of trout into refugia (areas with higher pH and lower Al) during episodes partially mitigated the adverse effects of episodes. Recolonization from alkaline tributaries or microhabitats can maintain low densities of fish in streams that experience severe acidic episodes, but it is not sufficient to sustain fish densities and community composition at levels expected in the absence of these episodes. Fish responses to acid‐base chemistry were fairly consistent across regions. In general, trout abundance was reduced and acid‐sensitive fish species were absent from ERP streams with median pH < 5.0‐5.2 during high flow and inorganic Al > 100‐200 μg/L. We conclude that episodic acidification can have long‐term effects on fish communities in small streams.
Applications of the Menge‐Sutherland Model to Acid‐Stressed Lake Communities
Authors: Locke Andrea
Published: April 2006

The predictions of the Menge‐Sutherland model with respect to the effects of environmental stress on species richness, food web complexity, food chain length, and the relative importance of predation, competition, and disturbance in structuring communities were examined using midsummer zooplankton communities of 46 lakes near Sudbury, Ontario with pHs of 3.8‐7.2. The lakes were sampled in the 1970s and in 1990 yielding a total of 92 food webs. Species richness increased linearly with pH rather than peaking at intermediate levels of stress as predicted by the model. Food web complexity and food chain length increased with pH, as predicted. The importance of competition in food web structure was variable at low pH and consistently high at moderate pH, a result that does not support model predictions that disturbance, competition, and predation should sequentially predominate with increasing pH. High variability in the relative importance of competition in acidic lakes was explained by fish presence or absence; in lakes without fish, a larger proportion of links in the zooplankton food web was due to predation by invertebrates. Persistence of predators (fish) in some acidic lakes reduces the applicability of the Menge‐Sutherland model.
A Method for Monitoring Long‐Term Population Trends: An Example Using Rare Arctic‐Alpine Plants
Authors: Lesica Peter , Steele Brian M.
Published: April 2006

Populations of arctic‐alpine plants at the southern periphery of their range should respond rapidly to projected global warming. We established a study to monitor the density and reproductive effort of six such species in tundra of Glacier National Park, Montana to help project the fate of these species in the center of their range. For many species, detecting long‐term population trends is confounded by short‐term variation. Our study design employs temporal resampling of permanent plots on multiple sites and a repeated‐measures model that accommodates the effects of high frequency variation and allows assessment of the significance of long‐term trends. Statistical analysis compares site‐specific estimates of annual mean density between two time periods and uses between‐plot, within‐site, within‐year variation to estimate error. Power calculations using data from the 3‐yr baseline period indicate that measurements of fecundity will be less sensitive for detecting long‐term trends than measurements of plant density. Furthermore, our results suggest that perennial species of closed‐turf communities may be better bioassays of long‐term change than annuals or species of open, ephemeral microsites.
Coastal Mitigation in Southern California: The Need for a Regional Restoration Strategy
Authors: Zedler Joy B.
Published: April 2006

Along the southern California coast there are few opportunities to create new wetlands; hence, mitigators often propose to remodel existing wetlands to achieve greater value rather than offering to create new habitat. Restoration and/or mitigation plans have been proposed for about half the region's 29 coastal wetland systems, with debate over which objectives can be met and little ability to predict the cumulative result. I briefly summarize what is known of the historic functioning of southern California wetlands, and describe four specific mitigation case studies to document problems and concerns. There is an urgent need for wetland modifications to be guided by a regional wetland restoration plan, and I therefore propose a strategy to this end. Knowledge of the dilemma in southern California may help other regions avoid similar problems by developing landscape‐level approaches to habitat protection and restructuring before too much of the resource is lost.
Fixing Compensatory Mitigation: What Will it Take?
Authors: Race Margaret S. , Fonseca Mark S.
Published: April 2006

This study was undertaken to review the current status of permit‐linked mitigation policies and practices in order to determine implications of the continued use of mitigation as a wetlands management tool within the United States. Based on reviews of both published literature and agency reports, our survey of past mitigation projects nationwide indicates that the success rate of permit‐linked mitigation projects remains low overall. In addition, there is continuing difficulty in translating mitigation concepts into legal principles, regulatory standards, and permit conditions that are scientifically defensible and sound. Based on the record of past poor performance, we assert that continued piecemeal revision efforts focused on technical or scientific details are not likely to make compensatory mitigation more effective. There is need to acknowledge the extent to which non‐scientific, real‐world complications plague current policies and practices. To prevent continued loss of wetlands under compensatory mitigation, decisive action must be taken by placing emphasis on improving compliance, generating desired acreages, and maintaining a true baseline. Without selective changes in the status quo, current policies and poor implementation are likely to lead to further wetland losses.
Biotic Indices and Stream Ecosystem Processes: Results from an Experimental Study
Authors: Wallace J. Bruce , Grubaugh Jack W. , Whiles Matt R.
Published: April 2006

We investigated the ability of the North Carolina Biotic Index (NCBI) and the Ephemeroptera + Plecoptera + Trichoptera (EPT) index to track an experimental manipulation of the invertebrate community and resultant alteration of several ecosystem‐level processes in a headwater stream at the Coweeta Hydrologic Laboratory in western North Carolina. Indices were calculated from quantitative monthly or bimonthly benthic samples of moss‐covered rockface and mixed substrate habitats, as well as habitat‐weighted values based on the proportion of each habitat in the two streams. One stream (C 55) served as a reference stream over the 6‐yr period of late 1984 through 1990, whereas the other (C 54) received seasonal treatments with an insecticide for 3 yr (1986‐1988). Throughout pretreatment, treatment, and recovery, both the NCBI and EPT indices tracked the disturbance regime of the treatment stream. Indices for the reference stream varied little during the 6‐yr period. Both the NCBI and EPT suggested strong changes in the treatment stream during treatment relative to both pretreatment and the reference stream. Following cessation of insecticide treatments, both indices reflected improved biotic conditions during first and second years of recovery in C 54. Compared with fauna of mixed substrates, rockface fauna had lower (better) NCBI values during pretreatment, and exhibited a greater proportional increase in tolerant taxa during treatment than mixed substrates, emphasizing the importance of including rockface communities in environmental monitoring programs. Changes in both the EPT and NCBI indices closely corresponded to changes in ecosystem‐level processes observed in C 54 from pretreatment to treatment, and recovery periods. These processes include: leaf litter processing rates, organic matter storage, fine particulate organic matter generation and export, and secondary production. With the exception of organic matter storage, all of these processes declined during treatment of C 54, and subsequently increased during recovery. Our results demonstrate the potential of such indices to detect and monitor stream ecosystem changes during and following disturbance. The EPT index was by far the easiest to use from both the standpoint of time required for sample processing and ease of application. Compared with the labor‐intensive sample processing, specimen identification and measurement, and data entry required for secondary production calculations, the EPT index was relatively simple and displayed a remarkable ability to track secondary production of invertebrates in the treatment stream. Our data strongly support the inclusion of the EPT and NCBI indices in these southern Appalachian headwater streams as indicators of both degradation and recovery of stream ecosystem processes from chemical‐induced disturbance.
Bayesian Environmental Policy Decisions: Two Case Studies
Authors: Wolfson Lara J. , Kadane Joseph B. , Small Mitchell J.
Published: April 2006

Statistical decision theory can be a valuable tool for policy‐making decisions. In particular, environmental problems often benefit from the application of Bayesian and decision‐theoretic techniques that address the uncertain nature of problems in the environmental and ecological sciences. This paper discusses aspects of implementing statistical decision‐making tools in situations where uncertainty is present, looking at issues such as elicitation of prior distributions, covariate allocation, formulation of loss functions, and minimization of expected losses subject to cooperation constraints. These ideas are illustrated through two case studies in environmental remediation.
Contrast of Constant and Bioenergetics‐Based Assimilation Efficiencies in Describing Ecosystems
Authors: Jackson Leland J.
Published: April 2006

Ecosystem models often follow the mass flow of matter (e.g., carbon, nutrients, trace metals, and contaminants) through food webs. Many ecosystem models (≈ 75% in a survey of recent literature) assume that carbon allocated to growth is a constant fraction of consumption. I use a simple predator‐prey model to demonstrate that the method of allocating consumed carbon to predator biomass (as a constant fraction or as a variable based on bioenergetics) can greatly affect the predicted dynamics of carbon and other matter. I then evaluate the potential disparity in the two carbon allocation methods by comparing predictions of constant and bioenergetics‐based assimilation versions of a Lake Ontario pelagic food web model under hypothetical management scenarios. Given current lake productivity and salmonid stocking, the version with constant assimilation efficiency predicted 22% more alewife (Alosa pseudoharengus) biomass than the bioenergetics‐based version at year 2005. When these models were calibrated to produce similar whole‐lake adult sport fish biomass, the constant assimilation model predicted 27% less alewife biomass at year 2005 than the bioenergetics‐based version. The two approaches predicted opposite directions of change in polychlorinated biphenyl (PCB) concentrations of stocked sport fish as their growth rates declined. Differences in the predicted PCB concentrations were as much as 450% when lake trout (Salvelinus namaycush) growth rates declined 60%. Assuming constant carbon assimilation may be acceptable for models of biomass when interest is only in one trophic level or where growth rates are static. However, constant assimilation efficiencies are inappropriate for models of trophic interactions (e.g., predictions of predation rates and prey sustainability), nutrient recycling, contaminants, trace metals, or changes in productivity.
Ecology Should Apply to Ecosystem Management: A Comment
Authors: Carpenter Richard A.
Published: April 2006

The recent Forum in this journal, Perspectives on Ecosystem Management, prompts a comment that may seem obvious: ecology, and associated environmental disciplines are, and will become more so, the undergirding sciences for ecosystem management–just as the health sciences are for medicine. But, the readiness of ecology for such applications is a matter of debate among leaders in the field, while it is being taken for granted, in terms of limited research support, by landscape managers. The ongoing manipulations (e.g., production, conservation, restoration) on federal lands can be a vehicle for needed research at management scales of space and time–if ecological scientists bring a consensus to, and initiate, collaborative planning with federal officials for a strategy to implement ecosystem management.
Political Liberalism, Deliberative Democracy, and the Public Sphere
Authors: Charney Evan
Published: April 2006

Theorists of democracy emphasize the importance of a public sphere, distinct from the apparatus of the state, where citizens can freely associate, deliberate, and engage in collective will formation. Discourse ethicists and deliberative democrats locate the public sphere within civil society and the manifold associations that comprise it. For Seyla Benhabib, the public sphere is constituted by the anonymous “public conversation” of civil society. By contrast, John Rawls has a much more limited conception of the public sphere. For Rawls, public reason, which establishes norms for democratic discourse, applies to a limited domain. I defend Rawls's view against the charge that it depends upon an untenable distinction between the public and nonpublic spheres. I argue that Rawls's more limited “liberal” conception better guarantees the heterogeneity of associational life in civil society. I then argue that Rawls violates his own principles by partially collapsing the public-nonpublic distinction with potentially illiberal consequences.
Generic saturation
Authors: Friedman Sy D.
Published: April 2006

Assuming that ORD is ω + ω-Erdös we show that if a class forcing amenable to L (an L-forcing) has a generic then it has one definable in a set-generic extension of L[O#]. In fact we may choose such a generic to be periodic in the sense that it preserve the indiscernibility of a final segment of a periodic subclass of the Silver indiscernibles, and therefore to be almost codable in the sense that it is definable from a real which is generic for an L-forcing (and which belongs to a set-generic extension of L[0#]). This result is best possible in the sense that for any countable ordinal α there is an L-forcing which has generics but none periodic of period ≤ α. However, we do not know if an assumption beyond ZFC+“O# exists” is actually necessary for these results.

Let P denote a class forcing definable over an amenable ground model 〈L, A〉 and assume that O# exists.

Definition. P is relevant if P has a generic definable in L[0#]. P is almost relevant if P has a generic definable in a set-generic extension of L[0#].

Remark. The reverse Easton product of Cohen forcings 2<κ, κ regular is relevant. So are the Easton product and the full product, provided κ is restricted to the successor cardinals. See Chapter 3, Section Two of Friedman [3]. Of course any set-forcing (in L) is almost relevant.

Definition. κ is α-Erdös if whenever C is CUB in κ and f: [C]<ω → κ is regressive (i.e., f(a) < min(a)) then f has a homogeneous set of ordertype α.
Wages and Unequal Access to Organizational Power: An Empirical Test of Gender Discrimination
Authors: Hultin Mia , Szulkin Ryszard
Published: April 2006

This study of Swedish workers investigates gender wage inequality, specifically, whether earnings are affected by the gender composition of establishments' managerial and supervisory staff. Theoretical arguments focus on managers' propensity to create and maintain or to undermine institutionalized gender bias and employees' capacity to mobilize resources and establish claims in the wage distribution process, mainly through social networks. Results show that gender-differentiated access to organizational power structures is essential in explaining women's relatively low wages. Women who work in establishments in which relatively many of the managers are men have lower wages than women with similar qualifications and job demands in establishments with more women in the power structure.
The Effect of Core Change on Performance: Inertia and Regression toward the Mean
Authors: Greve Henrich R.
Published: April 2006

This paper examines the consequences of changes in the organization's market position on its market share, testing arguments of inertia and regression toward the mean and taking into account recent methodological critiques of studies on the consequences of organizational change. A study of format change in the U.S. radio industry, 1984—1992, shows that changes cause performance to decline, as inertia theory predicts, but this is moderated by organizational size and performance before the change, so change can be beneficial for low-performing organizations but may be harmful for large and successful organizations.
The Role of Institutional and Market Forces in Divergent Organizational Change
Authors: D'Aunno Thomas , Succi Melissa , Alexander Jeffrey A.
Published: April 2006

This paper focuses on a radical change, in which organizations abandon an institutionalized template for arranging their core activities, that is likely to occur in organizational fields that have strong, local market forces and strong but heterogeneous institutional forces. We examine the role of market forces and heterogeneous institutional elements in promoting divergent change in core activities among all U.S. rural hospitals from 1984 to 1991. Results support the view that divergent change depends on both market forces (proximity to competitors, disadvantages in service mix) and institutional forces (state regulation, ownership and governance norms, and mimicry of models of divergent change).
Making the Next Move: How Experiential and Vicarious Learning Shape the Locations of Chains' Acquisitions
Authors: Baum Joel A. C. , Li Stan Xiao , Usher John M.
Published: April 2006

We examine acquisitions by multiunit chain organizations to determine why they acquire a particular target rather than others that are available to them and thus better understand chain growth. We advance experiential and vicarious learning processes as an explanation for chains' next spatial move. Our analysis of Ontario nursing home chains' acquisition location choices from 1971 to 1996 provides broad support for a learning perspective, demonstrating how experiential and vicarious processes shape and constrain the locations of chains' acquisitions. Experiential processes lead chains to replicate themselves by acquiring components geographically and organizationally similar to their own most recent and most similar prior acquisitions and their own current components. Vicarious processes lead chains to imitate location choices of other visible and comparable chains' most recent acquisitions, prior acquisitions nearest to potential targets, and their current components. Our study thus establishes organizational learning as a conceptual foundation for predicting the location of a chain's next acquisition and, more generally, the spatial expansion of chains over time.