bluuebunny/crossref_metadata_2025 huggingface dataset:
A NEW TECHNIQUE FOR MAXIMUM‐LIKELIHOOD CANONICAL GAUSSIAN ORDINATION
Authors: Yee Thomas W.
Published: June 2007

Canonical correspondence analysis (CCA) is probably the most popular ordination method in community ecology. However, it is only a heuristic approximation to maximum‐likelihood estimated canonical Gaussian ordination (CGO), which is the “ideal” method. When proposed in the mid‐1980s, CCA held two advantages over CGO: it was computationally cheaper, and its algorithm was not complex. However, an exponential increase in computing speed over the last two decades has meant that computation cost is no longer such a compelling advantage. The computational complexity of CGO has always been its major difficulty, even though it is statistically more sound and simpler to understand than CCA. For these reasons, no general computational framework or software has appeared until now.

This article proposes a new class of statistical regression models called quadratic reduced‐rank vector generalized linear models (QRR‐VGLMs) for maximum‐likelihood estimated CGO. This is achieved by extending a recently developed class of statistical models called RR‐VGLMs. The extension is named QRR‐VGLMs because of the addition of a quadratic form to each linear predictor, with the consequence that bell‐shaped responses can be modeled as functions of latent environmental variables or gradients. QRR‐VGLMs have several major positive features; for example, their framework is unifying and broad, so that canonical Gaussian ordination can potentially be performed on a wide range of data types. The two most important special cases of CGO in ecology, multispecies presence/ absence and Poisson abundance data, are considered in this article. The methodology is illustrated with a real data set using a software implementation written by the author in the S statistical language. The code, called the VGAM package in R, is object‐oriented and free, and it allows QRR‐VGLMs to be fitted to moderate‐sized data sets conforming reasonably closely to the Gaussian model.
EFFECTS OF PAST LAND USE ON SPATIAL HETEROGENEITY OF SOIL NUTRIENTS IN SOUTHERN APPALACHIAN FORESTS
Authors: Fraterrigo Jennifer M. , Turner Monica G. , Pearson Scott M. , Dixon Philip
Published: June 2007

We examined patterns of nutrient heterogeneity in the mineral soil (0–15 cm depth) of 13 southern Appalachian forest stands in western North Carolina >60 yr after abandonment from pasture or timber harvest to investigate the long‐term effects of land use on the spatial distribution and supply of soil resources. We measured soil carbon (C), nitrogen (N), acid‐extractable phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations and pools, and potential net N mineralization and nitrification rates to evaluate differences in mean values, variance at multiple scales, and fine‐scale spatial structure.

While comparisons of averaged values rarely indicated that historical land use had an enduring effect on mineral soil or N cycling, differences in variance and spatial structure suggested that former activities continue to influence nutrient distributions by altering their spatial heterogeneity. Patterns differed by element, but generally variance of soil C, N, and Ca decreased and variance of soil P, K, and Mg increased with intensive past land use. Changes in variance were most conspicuous and consistent locally (<28 m), but C, Ca, P, and Mg also exhibited appreciable differences in variance at coarser scales (>150 m). High variability in soil compaction resulted in some changes in scale‐dependent patterns of nutrient pool variance compared with nutrient concentration variance. It also affected the variance of N cycling rates, such that mass‐based rates varied less and area‐based rates varied more in intensively used areas than in reference stands. Geostatistical analysis suggested that past land use homogenized the spatial structure of soil C, K, and P in former pastures. In contrast, logged stands had highly variable spatial patterning for Ca.

These results suggest that land use has persistent, multi‐decadal effects on the spatial heterogeneity of soil resources, which may not be detectable when values are averaged across sites. By interacting with patterns of variability in the plant and heterotrophic biota, differences in nutrient distribution and supply could alter the composition and diversity of forest ecosystems. Scale‐dependent changes in nutrient heterogeneity could also complicate efforts to determine biogeochemical budgets and cycling rates.
PATHWAYS IN OLD‐FIELD SUCCESSION TO WHITE PINE: SEED RAIN, SHADE, AND CLIMATE EFFECTS
Authors: Dovčak Martin , Frelich Lee E. , Reich Peter B.
Published: June 2007

Trees slowly colonize old fields on sandy outwash in the prairie–forest ecotone of the north‐central United States, and in the absence of fire, succession is expected to proceed toward oak woodland. We analyzed whether a case of unusually rapid and spatially extensive invasion by white pine (Pinus strobus) could be explained by the presence of specific temporal or spatial opportunity windows suitable for such invasion. We tested whether the invasion was temporally restricted to the period immediately after abandonment or to periods of favorable climate, and whether it was spatially restricted to areas of high seed rain or high forest‐edge shade. White pine invasion into the field occurred in two waves separated from each other by a 1987–1989 drought period. The first wave (1980– 1985) occurred during a period of average climate and led to the establishment of dense sapling patches in shade near forest edges. The second wave (1991–1994) occurred during a period of high precipitation and cooler than normal temperature, and resulted in colonization of the unshaded field center. In addition to the two temporal windows, white pine invasion occurred within two spatial windows: in areas highly sheltered by forest edge and in areas receiving high white pine seed rain. Overall these windows produced three different successional pathways: (1) a slow, creeping white pine invasion into highly shaded areas with low seed rain near forest edges; (2) a rapid, discrete‐step invasion in areas where seed rain was abundant enough to overcome mortality in lower shade and where early arrivals facilitate filling in by later arrivals; and (3) a deferred invasion in the field center where low seed rain and lack of shade allowed the persistence of a grassland stage until favorable climate resulted in a white pine recruitment pulse. Temporal variation in climate can accelerate or decelerate any of the three successional pathways.
INFLUENCE OF LANDSCAPE STRUCTURE AND CLIMATE VARIABILITY ON A LATE HOLOCENE PLANT MIGRATION
Authors: Lyford Mark E. , Jackson Stephen T. , Betancourt Julio L. , Gray Stephen T.
Published: June 2007

We analyzed and radiocarbon‐dated 205 fossil woodrat middens from 14 sites in central and northern Wyoming and adjacent Utah and Montana to document spatiotemporal patterns of Holocene invasion by Utah juniper (Juniperus osteosperma). Holocene migration into central and northern Wyoming and southern Montana from the south proceeded by a series of long‐distance dispersal events, which were paced by climate variability and structured by the geographic distribution and connectivity of suitable habitats on the landscape. The migration of Utah juniper into the region involved multiple long‐distance dispersal events, ranging from 30 to 135 km. One of the earliest established populations, on East Pryor Mountain in south central Montana, is currently the northernmost population of the species. Establishment by long‐distance dispersal of that population and another in the Bighorn Basin occurred during a period of relatively dry climate between 7500 and 5400 years ago. Further expansion of these initial colonizing populations and backfilling to occupy suitable sites to the south was delayed during a wet period from 5400 to 2800 years ago. Development of dry conditions 2800 years ago led to a rapid expansion in which Utah juniper colonized sites throughout its current range. Landscape structure and climate variability play important roles in governing the pattern and pace of natural invasions and deserve close attention in studying and modeling plant invasions, whether exotic or natural.

Corresponding Editor: D. R. Strong
DISTURBANCE AND STAND DYNAMICS IN PONDEROSA PINE FORESTS IN ROCKY MOUNTAIN NATIONAL PARK, USA
Authors: Ehle Donna S. , Baker William L.
Published: June 2007

Fire is thought to be the dominant disturbance agent in pure ponderosa pine (Pinus ponderosaLaws.) forests, but fire severity and disturbances other than fire, and the effects of these events over time, have rarely been analyzed. We first created systematic criteria to (1) identify the causes of tree regeneration and mortality events and (2) classify the severity of these events. These criteria were then applied to understand the effect of events on ponderosa pine forests in Rocky Mountain National Park (RMNP), Colorado.

For each of nine intensive study plots sampled in the pure ponderosa pine zone of RMNP, we mapped and dated live and dead trees and the spatial extent of fire and non‐fire events using dendrochronology. Events were identified using evidence of disturbance agents, such as blue‐stain fungus in the case of mountain pine beetles, fire scars, and climatic reconstructions. Disturbance severity was classified based on amounts and spatial distribution of regeneration, mortality, and survivors. We studied the temporal and spatial relationships between events and tree age structures to determine historical and contemporary stand dynamics.

We identified 103 events among the nine study plots; 97% of these events were fire. High‐severity events were 7% of events, 2% of events were mixed‐severity, and the other 70% were low‐severity. The severity of 20% of events could not be determined. All but one of the high‐severity events were fire. In seven plots, at least one crown fire occurred within the last 300 years. In RMNP, pre‐EuroAmerican settlement crown fires led to dense, even‐aged stands. Subsequent surface fires killed some trees and facilitated the regeneration of others, leading to less dense, uneven‐aged stands after ∼200–300 years. Climate may be the cause or co‐cause of one or two regeneration pulses within the last 300 years, but most regeneration and mortality is associated with fire. The historical occurrence of crown fires, as well as surface fires, in pure ponderosa pine forests in RMNP indicates that the fire regime is more variable than previously thought. Suppression of crown fires, though not completely possible, would move the fire regime outside its historical range of natural variability.

Corresponding Editor: D. R. Strong
QUANTIFYING SCALE IN ECOLOGY: LESSONS FROM AWAVE‐SWEPT SHORE
Authors: Denny Mark W. , Helmuth Brian , Leonard George H. , Harley Christopher D. G. , Hunt Luke J. H. , Nelson Elizabeth K.
Published: June 2007

Understanding the role of scale is critical to ecologists' ability to make appropriate measurements, to “scale up” from local, short‐term experiments to larger areas and longer times, to formulate models of community structure, and to address important conservation problems. Although these issues have received increased attention in recent years, empirical measurements of the scales of ecologically important variables are still rare. Here, we measure the spatial and temporal scales of variability of 15 ecologically relevant physical and biological processes in the wave‐swept intertidal zone at Mussel Point, near Hopkins Marine Station in California. We analyze temporal variability in wave height, ocean temperature, upwelling intensity, solar irradiance, and body temperature for periods ranging from ten minutes to fifty years. In addition, we measure spatial variation in shoreline topography, wave force, wave‐induced disturbance, body temperature, species diversity, recruitment, primary productivity, and the abundances of grazers, predators, and the competitive dominant occupier of space. Each of these spatial variables is measured along three horizontal transects in the upper intertidal zone: a short transect (44 m long with sampling locations spaced at ∼0.5‐m intervals), a medium transect (175 m long with sampling locations spaced at ∼1.7‐m intervals), and a long transect (334 m long with sampling locations spaced at ∼3.4‐m intervals). Six different methods are used to quantify the scale of each variable.

Distinct scales are evident in all but one of our temporal variables, demonstrating that our methods for quantifying scale can work effectively with relatively simple, periodic phenomena. However, our spatial results reveal basic problems that arise when attempting to measure the scale of variability for more complex phenomena. For a given variable and length of transect, different methods of calculating scale seldom agree, and in some cases estimates differ by more than an order of magnitude. For a given variable and method of calculating spatial scale, measurements are sensitive to the length of a transect; the longer the transect, the larger the estimate of scale. We propose that the “1/f noise” nature of the data can explain both the variability among methods for calculating scale and the length dependence of spatial scales of variation, and that the 1/f noise character of the data may be driven by the fractal geometry of shoreline topography. We conclude that it may not be possible to define a meaningful spatial scale of variation in this system. As an alternative to the boiled‐down concept of “scale,” we suggest that it is more appropriate to examine explicitly the pattern in which variability changes with the extent of measurement (e.g., the spectrum). Knowledge of this pattern can provide useful ecological scaling “rules” even when a well‐defined scale (or hierarchy of scales) cannot be discerned.
SYNTHESIS OF A SIX‐YEAR STUDY OF CALCAREOUS GRASSLAND RESPONSES TO IN SITU CO2ENRICHMENT
Authors: Niklaus P. A. , Körner Ch.
Published: June 2007

We exposed species‐rich temperate calcareous grassland to elevated CO2(600 μL/L) for six growing seasons and studied carbon (C) and nutrient (nitrogen [N] and phosphorus [P]) cycling, water relations, and plant community structure and diversity. CO2enrichment stimulated leaf‐ and ecosystem‐level daytime CO2uptake and increased plant community productivity; relative CO2effects on aboveground biomass were predicted withr<−0.98 (r2> 0.95) by precipitation prior to biomass harvests. The underlying mechanisms were water savings due to reduced leaf conductance under elevated CO2, allowing for more growth in this temporarily water‐limited ecosystem; this effect was more important in dry years. At the plant‐species level, no effects of [CO2] were found except for the subdominant sedgesCarex flaccaandC. caryophyllea, which responded positively to elevated CO2, mainly due to increased soil moisture. Bryophytes also responded to CO2enrichment for the same reason. At a more aggregate level, elevated CO2increased species evenness (but not richness). Community productivity was N‐limited; legumes derived >90% of their N from atmospheric N2, but did not respond to elevated CO2because they were limited by low P availability. This ultimately also prevented larger community‐level responses to elevated CO2because eventually extra legume N would have been transferred to nonlegumes, resulting in extra biomass. Higher biomass in elevated CO2was attained by increasing C:N and C:P ratios; total N and P in plant biomass remained unaffected by [CO2]. N retention, legume dinitrogen fixation (both assessed with15N), and microbial net N immobilization did not change. Based on our findings, our main conclusions are: (1) The effect of elevated CO2is mainly indirect via effects on the hydrological cycle in this water‐limited ecosystem; (2) the C cycle responds more than mineral nutrient cycles; (3) low available P ultimately limited community productivity and responses to CO2, and this limitation may not be atypical for many natural ecosystems in which N inventories often are controlled by biologically available P; and (4) that interactions with variable environmental conditions critically co‐determine CO2responses, which contrasts with greenhouse studies and emphasizes the importance of field studies in predicting long‐term effects of increasing [CO2] on natural ecosystems.
OAK FOREST CARBON AND WATER SIMULATIONS: MODEL INTERCOMPARISONS AND EVALUATIONS AGAINST INDEPENDENT DATA
Authors: Hanson P. J. , Amthor J. S. , Wullschleger S. D. , Wilson K. B. , Grant R. F. , Hartley A. , Hui D. , Hunt, Jr E. R. , Johnson D. W. , Kimball J. S. , King A. W. , Luo Y. , McNulty S. G. , Sun G. , Thornton P. E. , Wang S. , Williams M. , Baldocchi D. D. , Cushman R. M.
Published: June 2007

Models represent our primary method for integration of small‐scale, process‐level phenomena into a comprehensive description of forest‐stand or ecosystem function. They also represent a key method for testing hypotheses about the response of forest ecosystems to multiple changing environmental conditions. This paper describes the evaluation of 13 stand‐level models varying in their spatial, mechanistic, and temporal complexity for their ability to capture intra‐ and interannual components of the water and carbon cycle for an upland, oak‐dominated forest of eastern Tennessee. Comparisons between model simulations and observations were conducted for hourly, daily, and annual time steps. Data for the comparisons were obtained from a wide range of methods including: eddy covariance, sapflow, chamber‐based soil respiration, biometric estimates of stand‐level net primary production and growth, and soil water content by time or frequency domain reflectometry. Response surfaces of carbon and water flux as a function of environmental drivers, and a variety of goodness‐of‐fit statistics (bias, absolute bias, and model efficiency) were used to judge model performance.

A single model did not consistently perform the best at all time steps or for all variables considered. Intermodel comparisons showed good agreement for water cycle fluxes, but considerable disagreement among models for predicted carbon fluxes. The mean of all model outputs, however, was nearly always the best fit to the observations. Not surprisingly, models missing key forest components or processes, such as roots or modeled soil water content, were unable to provide accurate predictions of ecosystem responses to short‐term drought phenomenon. Nevertheless, an inability to correctly capture short‐term physiological processes under drought was not necessarily an indicator of poor annual water and carbon budget simulations. This is possible because droughts in the subject ecosystem were of short duration and therefore had a small cumulative impact. Models using hourly time steps and detailed mechanistic processes, and having a realistic spatial representation of the forest ecosystem provided the best predictions of observed data. Predictive ability of all models deteriorated under drought conditions, suggesting that further work is needed to evaluate and improve ecosystem model performance under unusual conditions, such as drought, that are a common focus of environmental change discussions.
PREDICTING THE TIME OF TREE DEATH USING DENDROCHRONOLOGICAL DATA
Authors: Bigler Christof , Bugmann Harald
Published: June 2007

Complex interactions of various environmental factors result in high variability of tree mortality in space and time. Tree mortality functions that are implemented in forest succession models have been suggested to play a key role in assessing forest response to climate change. However, these functions are based on theoretical considerations and are likely to be poor predictors of the timing of tree death, since they do not adequately reflect our understanding of tree mortality processes. In addition, these theoretical mortality functions and most empirical mortality functions have not been tested sufficiently with respect to the accuracy of predicting the time of tree death.

We introduce a new approach to modeling tree mortality based on different growth patterns of entire tree‐ring series. Dendrochronological data fromPicea abies(Norway spruce) in the Swiss Alps were used to calibrate mortality models using logistic regression. The autocorrelation of the data was taken into account by a jackknife variance estimator.

Model performance was assessed by two criteria for classification accuracy and three criteria for prediction error. The six models with the highest overall performance correctly classified 71–78% of all dead trees and 73–75% of all living trees, and they predicted 44– 56% of all dead trees to die within 0–15 years prior to the actual year of death. For these six models, a maximum of 1.7% of all dead trees and 5% of all living trees were predicted to die >60 years prior to the last measured year. Models including the relative growth rate and a short‐term growth trend as explanatory variables were most reliable with respect to inference and prediction.

The generality of the mortality models was successfully tested by applying them to two independentP. abiesdata sets from climatologically and geologically different areas. We conclude that the methods presented improve our understanding of how tree growth and mortality are related, which results in more accurate mortality models that can ultimately be used to increase the reliability of predictions from models of forest dynamics.
SPECIES‐SPECIFIC PATTERNS OF BAT ACTIVITY IN AN URBAN LANDSCAPE
Authors: Gehrt Stanley D. , Chelsvig James E.
Published: June 2007

Urbanization is currently considered to have a negative effect on biodiversity, including the abundance and diversity of bat (Chiroptera) communities. However, relatively little attention has been devoted to the urban ecology of bats despite their ubiquity and ecological importance. We conducted a study during 1997–1999 to acoustically monitor species‐specific distributions and activity patterns for bats in a highly urbanized landscape. Of 11 896 passes recorded during the study that satisfied our criterion for species classification, 8672 (73%) were identified to species. We identified calls from five species (Eptesicus fuscus, Lasionycteris noctivagans, Lasiurus borealis, Lasiurus cinereus, Pipistrellus subflavus) and the Myotis group. Few landscape variables were significantly related to E. fuscus activity; however, L. borealis and L. noctivagans activity had positive relationships with adjacent industrial/commercial land use and an urban index. We determined mean occurrence at monitoring sites for all identified species, and each species and the Myotis group exhibited positive relationships with the urban index. More species were detected in habitat fragments within urbanized landscapes, and each of these species was detected more frequently in urban areas than in more rural habitat fragments. Correspondence analysis suggested community structure was similar among classes of urbanization, with E. fuscus predominant, although fewer species occurred in rural areas. Urban areas may represent islands of habitat for some bats within larger landscapes dominated by intensive agriculture. Thus, the nature of the relationship between urbanization and bats is probably dependent on context at the macrogeographic scale and local habitat quality within the urban matrix.
DROUGHT AND PACIFIC DECADAL OSCILLATION LINKED TO FIRE OCCURRENCE IN THE INLAND PACIFIC NORTHWEST
Authors: Hessl Amy E. , McKenzie Don , Schellhaas Richard
Published: June 2007

Historical variability of fire regimes must be understood within the context of climatic and human drivers of disturbance occurring at multiple temporal scales. We describe the relationship between fire occurrence and interannual to decadal climatic variability (Palmer Drought Severity Index [PDSI], El Niño/Southern Oscillation [ENSO], and the Pacific Decadal Oscillation [PDO]) and explain how land use changes in the 20th century affected these relationships. We used 1701 fire‐scarred trees collected in five study sites in central and eastern Washington State (USA) to investigate current year, lagged, and low frequency relationships between composite fire histories and PDSI, PDO, and ENSO (using the Southern Oscillation Index [SOI] as a measure of ENSO variability) using superposed epoch analysis and cross‐spectral analysis. Fires tended to occur during dry summers and during the positive phase of the PDO. Cross‐spectral analysis indicates that percentage of trees scarred by fire and the PDO are spectrally coherent at 47 years, the approximate cycle of the PDO. Similarly, percentage scarred and ENSO are spectrally coherent at six years, the approximate cycle of ENSO. However, other results suggest that ENSO was only a weak driver of fire occurrence in the past three centuries. While drought and fire appear to be tightly linked between 1700 and 1900, the relationship between drought and fire occurrence was disrupted during the 20th century as a result of land use changes. We suggest that long‐term fire planning using the PDO may be possible in the Pacific Northwest, potentially allowing decadal‐scale management of fire regimes, prescribed fire, and vegetation dynamics.
TWO CENTURIES OF MULTIPLE HUMAN IMPACTS AND SUCCESSIVE CHANGES IN A NORTH ATLANTIC FOOD WEB
Authors: Lotze Heike K. , Milewski Inka
Published: June 2007

European colonization of North America severely altered terrestrial and aquatic ecosystems alike. Here, we integrate archaeological, historical, and recent data to derive the ecological history of the Quoddy Region, Bay of Fundy, Canada, an upwelling region rich in marine diversity and productivity. We document successive changes on all trophic levels from primary producers to top predators over the last centuries. Our objectives were to (1) construct a baseline of “what was natural in the coastal ocean,” and (2) analyze the sequence and potential interaction of multiple human impacts.

Archaeological records highlight the abundance and diversity of marine species used by indigenous people over the last 2000–3000 years. Europeans colonized the area in the late 1700s and rapidly transformed the environment by multiple “top‐down” (exploitation), “bottom‐up” (nutrient loading), and “side‐in” (habitat destruction, pollution) impacts. Most large vertebrates were severely overexploited by 1900, leading to the extinction of three mammal and six bird species. Diadromous fish dramatically declined after river damming in the early 1800s, and recovery was prevented by subsequent river pollution. Overfishing of groundfish stocks started in the late 1800s, gradually leading to a final collapse in the 1970s. In the 20th century, decline of traditional fisheries induced a shift to low trophic level harvesting and aquaculture, which increased exponentially over the past 20 years. Eutrophication caused shifts in seaweed and phytoplankton communities: Some long‐lived rockweeds were replaced by annual bloom‐forming algae, and diatoms were replaced by dinoflagellates.

Today, the once unique Quoddy Region shows the most common signs of degradation found in highly impacted coastal areas worldwide. Multiple human influences have altered abundance and composition of every trophic level in the food web and reduced upper trophic levels by at least one order of magnitude. We highlight cumulative and indirect effects that impair the ability to predict and manage highly impacted coastal ecosystems. On the other hand, simple protection and restoration measures in the 20th century led to the recovery of some species. It is these successes that provide guidance for a more sustainable interaction of humans with their marine environment.
RELATIVE FORAGING VALUE TO LESSER SCAUP DUCKS OF NATIVE AND EXOTIC CLAMS FROM SAN FRANCISCO BAY
Authors: Richman Samantha E. , Lovvorn James R.
Published: June 2007

Invasions of exotic invertebrates have greatly altered many aquatic communities, but impacts on the foraging energetics of predators seldom have been assessed. In San Francisco Bay, California (USA), a major community change occurred with introduction of the Asian clam (Potamocorbula amurensis) in 1986. This species now greatly outnumbers the previous clam prey of a variety of sharks, rays, sturgeon, flatfish, and crabs, as well as several diving duck species for which the bay is the most important wintering area on the U.S. Pacific Coast. P. amurensis also accumulates much higher levels of some contaminants than the formerly dominant prey. Because alteration of the food base or contaminated foods on wintering areas may be factors in the population decline of scaup ducks, effects of this exotic invasion are important to assess. For Lesser Scaup (Aythya affinis), we studied effects of differences in nutrient content, digestibility, crushing resistance of shells, areal density, size, and depth in the sediments on the relative foraging value of exotic P. amurensis vs. the formerly dominant native clam Macoma balthica. P. amurensis, including shells, had higher nitrogen and energy content per clam of the same length class, and higher digestibility of energy, than M. balthica. Gut retention time did not differ between clam species, so their relative profitability for scaup was determined mainly by the intake rate of digestible nutrients during short, costly dives. For scaup foraging in an aquarium 1.8 m deep, intake rates (number of prey per second) of food items buried in sand‐filled trays increased with increasing prey density up to at least 4000 prey/m2. For items buried 3 cm deep, intake rates did not differ for prey <6 mm long vs. prey 6–12 mm long; however, intake rates were much lower when prey were deeper in the sediments (6 cm vs. 3 cm). In the field, a much higher percentage of P. amurensis were in the length range most commonly eaten by Lesser Scaup (<12 mm), and unlike M. balthica, almost all P. amurensis were in the top 5 cm of sediments where scaup intake rates are highest. In tensometer measurements, shells of P. amurensis were much harder to crush than shells of M. balthica, which might partly offset the apparent energetic advantages of P. amurensis. In many respects, the exotic P. amurensis appears to be a more valuable food than the native M. balthica for Lesser Scaup. However, because P. amurensis accumulates much higher levels of some contaminants, this exotic invasion increases the risk of toxicity to scaup and a range of other benthic predators.
THE NORTHERN FLYING SQUIRREL AS AN INDICATOR SPECIES OF TEMPERATE RAIN FOREST: TEST OF AN HYPOTHESIS
Authors: Smith Winston P. , Gende Scott M. , Nichols Jeffrey V.
Published: June 2007

Management indicator species (MIS) often are selected because their life history and demographics are thought to reflect a suite of ecosystem conditions that are too difficult or costly to measure directly. The northern flying squirrel (Glaucomys sabrinus) has been proposed as an MIS of temperate rain forest of southeastern Alaska based on previous studies in the Pacific Northwest that demonstrated its habitat is multi‐factorial, i.e., an emergent property of old‐growth forest. We evaluated the suitability of flying squirrels as MIS in temperate rain forests of Alaska by modeling seasonal (spring, autumn) microhabitat use with stepwise logistic regression (SLR) using either individual habitat variables (n= 26) or multivariate habitat “factors,” which were linear combinations of individual habitat variables generated from factor analysis. We compared the efficacy of single variable vs. multivariate factor models in explaining variation in microhabitat use to test the hypothesis that the habitat of flying squirrels in southeastern Alaska was an emergent property of old‐growth rain forest. The underlying premise was that if factors were more thorough in explaining microhabitat use, the habitat of flying squirrels was multifactorial; that is, it consisted of multiple late‐seral forest attributes occurring coincidentally at usable spatial scales (e.g., home range). SLR models with multivariate factors performed poorer in predicting capture sites than models of individual habitat variables. Two variables, density of large (>74 cm dbh) trees and understory cover ofVaccinium, explained much of the variation in microhabitat use. We conclude that the habitat ofG. sabrinusin southeastern Alaska does not reflect emergent properties of old‐growth forest in southeastern Alaska and hypothesize that this pattern may be related to regional ecological differences that facilitate a more general lifestyle than populations in the Pacific Northwest. Furthermore, the effectiveness ofGlaucomys sabrinusas an MIS in north temperate rain forest is suspect, illustrating that regional differences in ecology of a species warrant caution when considering the suitability of MIS among geographic areas.
FOOD CHAIN AND THE REASONS FOR FISH FOOD TABOOS AMONG AMAZONIAN AND ATLANTIC FOREST FISHERS (BRAZIL)
Authors: Begossi Alpina , Hanazaki Natalia , Ramos Rossano M.
Published: June 2007

Food taboos or food prohibitions are still controversial in ecological anthropology and in human ecology. In the literature, the explanations for such taboos find their origin in the book of Leviticus in the Bible, or in the abundance of fat found in the tissue of different fish species, or on the consequences for conservation practices. In this comparative study, we show the various interpretations concerning the food taboos observed in tropical societies, including their association to the availability of resources, i.e., the protein coming from local fish resources. We show that, in the Amazon and on the Atlantic Forest coast, fish food taboos, or dietary prohibitions during illness, are associated with carnivorous fish, especially piscivorous fish, and the fish that are recommended for consumption during illness are usually herbivorous or invertebrate eaters. Explanation for this preference is based into the consideration that, at high trophic levels, animals may accumulate toxins by eating plants, invertebrates, or other fish. We therefore consider that fish food taboos may represent an adaptive strategy of local inhabitants of the Atlantic Forest coast and of Amazonian rivers.
HIERARCHICAL MODELS IMPROVE ABUNDANCE ESTIMATES: SPAWNING BIOMASS OF HOKI IN COOK STRAIT, NEW ZEALAND
Authors: Harley Shelton J. , Myers Ransom A. , Field Chris A.
Published: June 2007

It is often difficult to estimate abundance for a dynamic population, i.e., one that is moving through the survey area or in which birth or mortality rates are high. One approach is to estimate the proportion of animals present during each survey, using a model that estimates the dynamics of the survey proportion of the population. However, this can increase the uncertainty of the estimates if the dynamics parameters are not well estimated. Here we approached this problem by developing methods using hierarchical model structures, which allow us to share information on the dynamics parameters across years. We applied this modeling approach to the estimation of residence time and spawning biomass for New Zealand hoki (Macruronus novaezelandiae) in Cook Strait spawning grounds. By sharing parameters across years, we obtained better parameter estimates than by the traditional assumption that the dynamics in one year are independent of those of other years. By integrating the estimation of residence time into a dynamic model using simulated maximum likelihood methods, we also were able to calibrate acoustic estimates of spawning biomass for the fact that not all individuals are on the grounds at the time of the acoustic survey. We discuss alternative model formulations for the application of hierarchical methods to stage‐structured data and the analysis of data from acoustic surveys of spawning fish.
LITTER PRODUCTION AND LITTER NUTRIENT CONCENTRATIONS IN A FRAGMENTED AMAZONIAN LANDSCAPE
Authors: Vasconcelos Heraldo L. , Luizão Flávio J.
Published: June 2007

We analyzed the effects of distance to forest edge and soil texture on fine‐litter production and on nutrient concentrations in the leaf fall in an experimentally fragmented landscape in Brazilian Amazonia. Production of fine litter (leaves, twigs <2 cm in diameter, flowers, and fruits) was measured over a 3‐yr period. Litter traps were installed in plots located near (<100 m) and far (>250 m) from forest edges, and in clayey or sandy soils. In total, 28 plots were established, with 10 litter traps per plot. Results reveal a significant effect of distance to forest edge on litter production, but no significant effect of soil type or interaction between soil type and edge distance. On average, annual litter production on edge plots exceeded that on the interior plots by 0.68 Mg/ha (9.50 ± 0.23 vs. 8.82 ± 0.14 Mg·ha−1·yr−1, mean ± 1 se, based on a 3‐yr period). With regard to nutrient concentrations in the leaf fall, we detected a significant effect of soil type on three of eight nutrients analyzed. Concentrations of N, Mg, and Mn were greater in leaves on clayey than on sandy soils. Distance to forest edge only significantly affected the concentration of Ca, which was greater near than far from edges, perhaps due to strong Ca mobilization by the roots of pioneer trees.

Several factors may account for the observed increase in litterfall near forest edges, including the greater prevalence of winds, increased plant desiccation stress, and higher rates of tree recruitment, especially of pioneer trees, near edges. Elevated rates of litterfall are likely to have cascading effects on the ecology of fragmented forests, affecting the invertebrate fauna, increasing seed and seedling mortality, and causing forest fragments to be more vulnerable to destructive surface fires.
LOCAL DISPERSAL SOURCES STRONGLY AFFECT COLONIZATION PATTERNS OF WOOD‐DECAYING FUNGI ON SPRUCE LOGS
Authors: Edman Mattias , Kruys Nicholas , Jonsson Bengt Gunnar
Published: June 2007

Coarse woody debris (CWD) is an important habitat for many species in forest ecosystems. However, forestry has decreased the abundance of CWD so that many wood‐dependent species have become threatened. To alleviate this problem, guidelines for a more biodiversity‐oriented forestry focus on increasing CWD in managed forests. Unfortunately, how this increase is to be allocated on a landscape scale is not well understood. The present study reports an experiment in which freshly cut logs of varying sizes were placed in stands with contrasting abundance of natural CWD and subsequently varying pools of wood‐inhabiting species. The first six years of colonization by wood fungi show that local abundance and composition of the fungal flora strongly influenced colonization. Higher species richness was observed in CWD‐rich sites, and several species were more frequent on the experimental logs at CWD‐rich sites. The strong within‐site effect is interpreted as resulting from high spore deposition from the local species pool. This is supported by spore deposition estimates of Fomitopsis rosea, a red‐listed species that only occurred on experimental logs at the CWD‐rich sites. F. rosea had a 9–180 times higher spore deposition at the CWD‐rich sites compared to the CWD‐poor sites. The species richness and composition on small logs differed from that of large logs with higher richness on the latter. The results strongly suggest that restoration efforts would be more efficient if directed toward sites close to CWD‐rich sites and that preferably large logs should be created.
EFFECTS OF AN INTRODUCED PATHOGEN AND FIRE EXCLUSION ON THE DEMOGRAPHY OF SUGAR PINE
Authors: van Mantgem Phillip J. , Stephenson Nathan L. , Keifer MaryBeth , Keeley Jon
Published: June 2007

An introduced pathogen, white pine blister rust (Cronartium ribicola), has caused declines in five‐needled pines throughout North America. Simultaneously, fire exclusion has resulted in dense stands in many forest types, which may create additional stress for these generally shade‐intolerant pines. Fire exclusion also allows fuels to accumulate, and it is unclear how affected populations will respond to the reintroduction of fire. Although white pine blister rust and fire exclusion are widely recognized threats, long‐term demographic data that document the effects of these stressors are rare. We present population trends from 2168 individuals over 5–15 years for an affected species, sugar pine (Pinus lambertiana), at several burned and unburned sites in the Sierra Nevada of California. Size‐based matrix models indicate that most unburned populations have negative growth rates (λ range: 0.82–1.04). The growth rate of most populations was, however, indistinguishable from replacement levels (λ = 1.0), implying that, if populations are indeed declining, the progression of any such decline is slow, and longer observations are needed to clearly determine population trends. We found significant differences among population growth rates, primarily due to variation in recruitment rates. Deaths associated with blister rust and stress (i.e., resource competition) were common, suggesting significant roles for both blister rust and fire exclusion in determining population trajectories. Data from 15 prescribed fires showed that the immediate effect of burning was the death of many small trees, with the frequency of mortality returning to pre‐fire levels within five years. In spite of a poor prognosis for sugar pine, our results suggest that we have time to apply and refine management strategies to protect this species.
LANDSCAPE VS. LOCAL HABITAT SCALE INFLUENCES TO INSECT COMMUNITIES FROM TALLGRASS PRAIRIE REMNANTS
Authors: Stoner Kristal J. L. , Joern Anthony
Published: June 2007

Habitat loss and fragmentation currently threaten ecosystems worldwide, yet remain difficult to quantify because within‐fragment habitat and landscape‐scale influences often interact in unique ways. Although individual species respond to fragmentation differently, large‐scale conservation planning must unavoidably target multiple species. Although information on a population's response to fragmentation is critical, and measurements of species richness provide useful insights, exclusive reliance on these responses may mask important information about the taxonomic composition of assemblages in response to fragmentation. The North American tallgrass prairie ecosystem is one of the most threatened and fragmented ecosystems in the world, and insects are significant contributors to its biodiversity. In remaining grassland fragments, we evaluated within‐fragment influences in conjunction with landscape‐scale responses of representative insect communities from four feeding guilds: generalists, specialists, multiple life stage habitat use, and predators. Fragment‐specific attributes capable of influencing insect diversity include plant species composition, plant biomass, abundance of blooming flowers, and vertical habitat heterogeneity created by the vegetation. Landscape‐scale factors expected to influence patterns of insect species diversity include fragment size and shape as well as the spatial configuration of fragments. Ordination techniques were used to summarize composition of each feeding guild assemblage of each fragment, and structural equation modeling was used to examine the direct and indirect effects of fragmentation with influences from local habitats. Generalists (Orthoptera), mixed‐modality feeding that changes with life stage (Lepidoptera), and specialist herbivores (Curculionidae) all responded directly to within‐site characterizations of the plant community. Site management from large ungulate grazing or mowing for hay production consistently had an indirect effect on the insect community through influences on plant community composition. The predator assemblage (Coccinellidae) was influenced directly by fragment shape. To maintain insect biodiversity in tallgrass prairie fragments, these results indicate that conservation practices should focus on communities in order to maintain insect biodiversity in tallgrass prairie fragments. Landscape‐scale factors must also be considered when making conservation decisions, primarily because predators (top trophic level organisms) are more likely to respond to regional changes.
NITROGEN DEPOSITION MODIFIES SOIL CARBON STORAGE THROUGH CHANGES IN MICROBIAL ENZYMATIC ACTIVITY
Authors: Waldrop Mark P. , Zak Donald R. , Sinsabaugh Robert L. , Gallo Marcy , Lauber Chris
Published: June 2007

Atmospheric nitrogen (N) deposition derived from fossil‐fuel combustion, land clearing, and biomass burning is occurring over large geographical regions on nearly every continent. Greater ecosystem N availability can result in greater aboveground carbon (C) sequestration, but little is understood as to how soil C storage could be altered by N deposition. High concentrations of inorganic N accelerate the degradation of easily decomposable litter and slow the decomposition of recalcitrant litter containing large amounts of lignin. This pattern has been attributed to stimulation or repression of different sets of microbial extracellular enzymes. We hypothesized that soil C cycling in forest ecosystems with markedly different litter chemistry and decomposition rates would respond to anthropogenic N deposition in a manner consistent with the biochemical composition of the dominant vegetation. Specifically, oak‐dominated ecosystems with low litter quality should gain soil C, and sugar maple ecosystems with high litter quality should lose soil C in response to high levels of N deposition (80 kg N·ha−1·yr−1). Consistent with this hypothesis, we observed over a three‐year period a significant loss of soil C (20%) from a sugar maple‐dominated ecosystem and a significant gain (10%) in soil C in an oak‐dominated ecosystem, a result that appears to be mediated by the regulation of the microbial extracellular enzyme phenol oxidase. Elevated N deposition resulted in changes in soil carbon that were ecosystem specific and resulted from the divergent regulatory control of microbial extracellular enzymes by soil N availability.
EVALUATION OF CLOSED CAPTURE–RECAPTURE METHODS TO ESTIMATE ABUNDANCE OF HAWAIIAN MONK SEALS
Authors: Baker Jason D.
Published: June 2007

Numerous capture–recapture methods have been developed to estimate abundance, yet the performance of these models is only rarely judged by comparison with true abundance. This study presents a rare opportunity to assess capture–recapture estimates in a free‐ranging population with known minimum abundance. Hawaiian monk seal abundance historically has been characterized using a trend index or has been estimated using simple enumeration. Here, I evaluate the applicability of various closed‐population capture–recapture models to estimating Hawaiian monk seal abundance and its associated error. I analyzed 12 data sets (two years from each of six subpopulations) representing a wide variety of sampling and logistical scenarios, using models that explored the effects of animal size class (juvenile, subadult, or adult), tag status, and sighting location on initial capture and recapture probabilities. I also explored various models to account for capture heterogeneity among individuals. Size and sex effects always significantly improved model fits, and tag status and location effects were also frequently influential. In most cases, abundance estimated from capture–recapture models was substantially lower than known minimum abundance, suggesting the influence of individual capture heterogeneity. Attributes of individuals known to be alive, but not captured during systematic surveys, did not reveal patterns that explained sources of capture heterogeneity. In some cases, mixture models produced estimates that were less biased but were associated with very large confidence intervals. Among the model types examined, those available in Program CAPTURE performed best; although they are still prone to negative bias, these models nevertheless may prove useful in characterizing population trends in Hawaiian monk seals. This study demonstrates that selection of appropriate closed capture–recapture models can be substantially improved by independent validation.