bluuebunny/crossref_metadata_2025 huggingface dataset:
Daily physical activity, fasting glucose, uric acid, and body mass index are independent factors associated with serum fibroblast growth factor 21 levels
Authors: Cuevas-Ramos Daniel , Almeda-Valdes Paloma , Gómez-Pérez Francisco J , Meza-Arana Clara Elena , Cruz-Bautista Ivette , Arellano-Campos Olimpia , Navarrete-López Mariana , Aguilar-Salinas Carlos A
Published: June 2010

Objective

Fibroblast growth factor 21 (FGF21) levels have been linked with beneficial effects on glucose and lipid metabolism in animals. It is elevated in humans with the metabolic syndrome. This study investigates independent factors associated with serum FGF21 levels.

Design

Cross-sectional study done in healthy blue-collar workers.

Methods

A medical history was taken, and FGF21 (measured using an ELISA commercial kit), glucose, uric acid, plasma lipids, total/high-molecular weight (HMW) adiponectin, and retinal-binding protein 4 (RBP4) were measured in 210 individuals with (n=81) and without (n=129) metabolic syndrome.

Results

The median of serum FGF21 levels were higher in subjects with metabolic syndrome (339.5 vs 276.4 ng/l,P=0.01). Serum FGF21 levels correlated positively with body mass index (BMI;r=0.23,P=0.001) and age (r=0.17,P=0.01). After adjusting for age and BMI, a significant positive correlation persisted for fasting glucose, uric acid, and physical activity in both males (r=0.21,r=0.11, andr=0.19, allP<0.05) and females (r=0.20,r=0.19, andr=0.14, allP<0.05). In addition, FGF21 also correlates negatively with RBP4 (r=−0.27,P=0.02), total (r=−0.26,P=0.03), and HMW adiponectin (r=−0.30,P=0.01) in women. A multiple linear regression model analysis identified that BMI (standardized β (SB)=0.247;P=0.008), glucose (SB=0.226;P=0.003), uric acid (SB=0.191;P=0.04), and physical activity (SB=0.223;P=0.004) are independent factors influencing serum FGF21 levels (F=10.05,r2=0.19,P<0.001). In addition, fasting hyperglycemia ≥100 mg/dl, excess body weight with BMI ≥25 kg/m2, and uric acid ≥5.5 mg/dl predicted higher serum FGF21 levels.

Conclusion

Serum FGF21 levels are influenced by BMI, fasting glycemia, uric acid, and physical activity.
Erythropoietin and vascular endothelial growth factor as risk markers for severe hypoglycaemia in type 1 diabetes
Authors: Kristensen P L , Pedersen-Bjergaard U , Schalkwijk C , Olsen N V , Thorsteinsson B
Published: June 2010

Objective

Circulating erythropoietin (EPO) and vascular endothelial growth factor (VEGF) increase during hypoglycaemia and may represent protective hormonal counter-regulatory responses. We tested the hypothesis that low levels of EPO and VEGF are associated with a higher frequency of severe hypoglycaemia in a cohort of patients with type 1 diabetes.

Design

Prospective observational follow-up study.

Methods

Totally 219 patients with type 1 diabetes (41% females, age 46±13 years (mean±s.d.), duration of diabetes 21±12 years, and HbAlc 8.5±1.1%) were followed in a 1-year observational study. Plasma EPO and serum VEGF levels were measured at baseline with ELISA. Events of severe hypoglycaemia defined by third party assistance were recorded and validated in telephone interviews within 24 h.

Results

Totally 235 episodes of severe hypoglycaemia (1.1 episodes per patient-year) were reported by 82 patients (37%). At baseline, plasma EPO was 8.6 (3.1–34.3) U/l (median (range)), and serum VEGF was 52.2 (6.6–337) pg/ml. The levels of EPO and VEGF were not associated with frequency of severe and mild hypoglycaemia. The levels of EPO were not associated with age, sex, duration of diabetes, body mass index, HbAlc, C-peptide level or hypoglycaemia awareness status. The levels of VEGF were positively associated with age and female sex.

Conclusions

Although several studies suggest that VEGF and EPO may affect brain function during hypoglycaemia, this study does not support random VEGF or EPO levels to determine future risk of severe hypoglycaemia in people with type 1 diabetes.
Incidence of Delayed Intracranial Hemorrhage in Children After Uncomplicated Minor Head Injuries
Authors: Hamilton Mark , Mrazik Martin , Johnson David W.
Published: June 2010

OBJECTIVES:

This study sought to determine the incidence of delayed diagnosis of intracranial hemorrhage in the general population and the proportion of children who presented to emergency departments (EDs) with uncomplicated minor head injuries who received delayed diagnoses of intracranial hemorrhage.

METHODS:

This was an 8-year, retrospective, cohort study of children <14 years of age who presented to EDs in the Calgary Health Region between April 1992 and March 2000. Cases of uncomplicated minor head injuries and delayed diagnosis of intracranial hemorrhage (intracranial hemorrhage not apparent until ≥6 hours after injury) were identified.

RESULTS:

An estimated 17 962 children (95% confidence interval [CI]: 17 412–18 511 children) with uncomplicated minor head injuries were evaluated at Calgary Health Region EDs. Two and 8 children were identified as having delayed diagnoses of intracranial hemorrhage with and without delayed deterioration in level of consciousness (Glasgow Coma Scale scores of <15), respectively. The proportions of children with uncomplicated minor head injuries with delayed diagnoses of intracranial hemorrhage with and without deterioration in level of consciousness were ∼0.00% (0 of 17 962 children [upper limit of 95% CI: 0.02%]) and 0.03% (5 of 17 962 children [95% CI: 0.01%–0.07%]), respectively. On the basis of population data for the Calgary Health Region, the incidences of delayed diagnosis of intracranial hemorrhage with and without deterioration in level of consciousness were 0.14 and 0.57 cases per 100 000 children per year, respectively.

CONCLUSIONS:

The occurrence of delayed diagnosis of intracranial hemorrhage among children who present with uncomplicated minor head injuries is rare.
Infant Victimization in a Nationally Representative Sample
Authors: Turner Heather A. , Finkelhor David , Ormrod Richard , Hamby Sherry L.
Published: June 2010

OBJECTIVE:

The objectives of this research were to (1) obtain estimates of child maltreatment and other forms of personal, witnessing of, and indirect victimization among children aged 0 to 1 year in the United States and (2) examine associations between infant victimization exposure and the infant's level of emotional and behavioral symptoms.

METHODS:

The study is based on a cross-sectional national telephone survey that included caregivers of a sample of 503 children under 2 years of age.

RESULTS:

Nearly one-third of the sample of infants (31.6%) had experienced some form of personal, witnessing, or indirect form of victimization. The rate of infant maltreatment by caregivers (2.1%) was significantly lower than among older preschool-aged children. However, the rate of infant assault by siblings was considerable at 15.4%. The greatest risk of assault occurred in households with young siblings; nearly 35% of the infants with a sibling aged 2 to 3 years were assaulted in the year before the interview. Witnessing family violence was also relatively common among the infants (9.5%). Victimization was associated with emotional and behavioral problems; sibling assault and witnessing family violence had the highest correlations with infant symptom scores.

CONCLUSION:

The results of this study highlight the need for attention to infant victimization that considers a wider array of victimization sources and a broader scope of prevention efforts than has been typical in the child-maltreatment field.
Blood Sampling Through Peripheral Venous Catheters Is Reliable for Selected Basic Analytes in Children
Authors: Berger-Achituv Sivan , Budde-Schwartzman Britta , Ellis Martin H. , Shenkman Ze'ev , Erez Ilan
Published: June 2010

OBJECTIVE:

The goal was to determine the interchangeability of peripheral venous catheter (PVC) and venipuncture blood sampling (BS).

METHODS:

Paired blood samples from hospitalized children were obtained through venipuncture and from existing PVCs, following discard of 2 mL of blood. Comparisons of 9 complete blood count indices (white and red blood cell counts, hemoglobin and hematocrit levels, mean corpuscular volume, mean corpuscular hemoglobin level, red blood cell distribution width, platelet count, and mean platelet volume) and 5 basic chemical analysis indices (sodium, potassium, glucose, chloride, and urea levels) were performed, and hemolysis was documented.

RESULTS:

Irrespective of gauge, blood samples were obtained successfully from 40 (85.1%) of 47 PVCs, with no abnormal hemolysis. BS through venipuncture took longer than BS from PVCs (175.8 ± 229.6 vs 104.5 ± 53.4 seconds; P = .053) and was associated with significantly more distress/crying (73.1% vs 0%; P < .001). There were no significant differences between venipuncture and PVC samples (paired t test). Twenty-one (6%) of 348 pairs analyzed with the Clinical Laboratory Improvement Amendment standards fell outside the range of acceptable variance (8 of 21 aberrations were attributed to glucose measurements). Bland-Altman analysis indicated that, with the exclusion of glucose measurements, BS from PVCs is reliable, with 29 (6.5%) of 448 pairs exceeding the limits of agreement. Of those, 9 cases were clinically significant, but none would have altered clinical management.

CONCLUSIONS:

PVC sampling was shown to be a pain-reducing method that can be used for children for selected basic analytes. The findings for glucose were unreliable.
Development, Validation, and Utility of Internet-Based, Behavioral Health Screen for Adolescents
Authors: Diamond Guy , Levy Suzanne , Bevans Katherine B. , Fein Joel A. , Wintersteen Matthew B. , Tien Allen , Creed Torrey
Published: June 2010

OBJECTIVES:

The goals were to develop and to validate the Internet-based, Behavioral Health Screen (BHS) for adolescents and young adults in primary care.

METHODS:

Items assessing risk behaviors and psychiatric symptoms were built into a Internet-based platform with broad functionality. Practicality and acceptability were examined with 24 patients. For psychometric validation, 415 adolescents completed the BHS and well-established rating scales. Participants recruited from primary care waiting rooms were 12 to 21 years of age (mean: 15.8 years); 66.5% were female and 77.5% black.

RESULTS:

The BHS screens in 13 domains by using 54 required items and 39 follow-up items. The administration time was 8 to 15 minutes (mean: 12.4 minutes). The scales are unidimensional, are internally consistent (Cronbach's α = 0.75–0.87), and discriminate among adolescents with a range of diagnostic syndromes. Sensitivity and specificity were high, with overall accuracy ranging from 78% to 85%. Patients with scores above scale cutoff values for depression, suicide risk, anxiety, and posttraumatic stress disorder symptoms were ≥4 times more likely to endorse other risk behaviors or stressors.

CONCLUSIONS:

The BHS addresses practical and clinical barriers to behavioral health screening in primary care. It is a brief but comprehensive, self-report, biopsychosocial assessment. The psychiatric scales are valid and predictive of risk behaviors, which facilitates exclusion of false-positive results, as well as assessment and triage.
Least‐cost control of agricultural nutrient contributions to the Gulf of Mexico hypoxic zone
Authors: Rabotyagov Sergey , Campbell Todd , Jha Manoj , Gassman Philip W. , Arnold Jeffrey , Kurkalova Lyubov , Secchi Silvia , Feng Hongli , Kling Catherine L.
Published: June 2010

In 2008, the hypoxic zone in the Gulf of Mexico, measuring 20 720 km2, was one of the two largest reported since measurement of the zone began in 1985. The extent of the hypoxic zone is related to nitrogen and phosphorous loadings originating on agricultural fields in the upper Midwest. This study combines the tools of evolutionary computation with a water quality model and cost data to develop a trade‐off frontier for the Upper Mississippi River Basin specifying the least cost of achieving nutrient reductions and the location of the agricultural conservation practices needed. The frontier allows policymakers and stakeholders to explicitly see the trade‐offs between cost and nutrient reductions. For example, the cost of reducing annual nitrate‐N loadings by 30% is estimated to be US$1.4 billion/year, with a concomitant 36% reduction in P and the cost of reducing annual P loadings by 30% is estimated to be US$370 million/year, with a concomitant 9% reduction in nitrate‐N.
Widespread density‐dependent seedling mortality promotes species coexistence in a highly diverse Amazonian rain forest
Authors: Metz Margaret R. , Sousa Wayne P. , Valencia Renato
Published: June 2010

Negative density‐dependent mortality can promote species coexistence through a spacing mechanism that prevents species from becoming too locally abundant. Negative density‐dependent seedling mortality can be caused by interactions among seedlings or between seedlings and neighboring adults if the density of neighbors affects the strength of competition or facilitates the attack of natural enemies. We investigated the effects of seedling and adult neighborhoods on the survival of newly recruited seedlings for multiple cohorts of known age from 163 species in Yasuní National Park, Ecuador, an ever‐wet, hyper‐diverse lowland Amazonian rain forest. At local scales, we found a strong negative impact on first‐year survival of conspecific seedling densities and adult abundance in multiple neighborhood sizes and a beneficial effect of a local tree neighborhood that is distantly related to the focal seedling. Once seedlings have survived their first year, they also benefit from a more phylogenetically dispersed seedling neighborhood. Across species, we did not find evidence that rare species have an advantage relative to more common species, or a community compensatory trend. These results suggest that the local biotic neighborhood is a strong influence on early seedling survival for species that range widely in their abundance and life history. These patterns in seedling survival demonstrate the role of density‐dependent seedling dynamics in promoting and maintaining diversity in understory seedling assemblages. The assemblage‐wide impacts of species abundance distributions may multiply with repeated cycles of recruitment and density‐dependent seedling mortality and impact forest diversity or the abundance of individual species over longer time scales.
Managing resistance to Bt crops in a genetically variable insect herbivore, Ostrinia nubilalis
Authors: O'Rourke Megan E. , Sappington Thomas W. , Fleischer Shelby J.
Published: June 2010

To slow the resistance evolution of the European corn borer (ECB) to Cry proteins expressed in transgenic Bacillus thuringensis (Bt) corn, the United States Environmental Protection Agency (EPA) has adopted an insect resistance management (IRM) plan that relies on a “high dose/refuge” strategy. However, this IRM plan does not consider possible ecological differences between the two ECB pheromone races (E and Z). Using carbon isotope analysis, we found that unstructured (non‐corn) refuges contribute more to E race (18%) than to Z race (4%) populations of ECB in upstate New York (USA). Furthermore, feeding on non‐corn hosts is associated with decreased body mass and reduced fecundity. We also show that the geographic range of E‐race ECB is restricted within the range of the Z race and that E‐race ECB are increasingly dominant in regions with increasing non‐corn habitat. While the proportion of E‐race ECB developing in unstructured refuges is higher than previously assumed, low rates of unstructured refuge use by the Z race, evidence for reduced fecundity when reared on non‐corn hosts, and complete sympatry within the E race range all argue against a relaxation of current IRM refuge standards in corn based on alternative‐host use. We also discuss implications of this research for integrated pest management in vegetables and IRM in Bt cotton.
Interactive effects of historical logging and fire exclusion on ponderosa pine forest structure in the northern Rockies
Authors: Naficy Cameron , Sala Anna , Keeling Eric G. , Graham Jon , DeLuca Thomas H.
Published: June 2010

Increased forest density resulting from decades of fire exclusion is often perceived as the leading cause of historically aberrant, severe, contemporary wildfires and insect outbreaks documented in some fire‐prone forests of the western United States. Based on this notion, current U.S. forest policy directs managers to reduce stand density and restore historical conditions in fire‐excluded forests to help minimize high‐severity disturbances. Historical logging, however, has also caused widespread change in forest vegetation conditions, but its long‐term effects on vegetation structure and composition have never been adequately quantified. We document that fire‐excluded ponderosa pine forests of the northern Rocky Mountains logged prior to 1960 have much higher average stand density, greater homogeneity of stand structure, more standing dead trees and increased abundance of fire‐intolerant trees than paired fire‐excluded, unlogged counterparts. Notably, the magnitude of the interactive effect of fire exclusion and historical logging substantially exceeds the effects of fire exclusion alone. These differences suggest that historically logged sites are more prone to severe wildfires and insect outbreaks than unlogged, fire‐excluded forests and should be considered a high priority for fuels reduction treatments. Furthermore, we propose that ponderosa pine forests with these distinct management histories likely require distinct restoration approaches. We also highlight potential long‐term risks of mechanical stand manipulation in unlogged forests and emphasize the need for a long‐term view of fuels management.
Estimating interaction strengths in nature: experimental support for an observational approach
Authors: Novak Mark
Published: June 2010

The complexity of food webs poses a significant hurdle for our growing understanding of the structure and dynamics of ecological communities. Empirical methods that measure the per capita strengths of trophic species interactions offer a means to identify keystone species and bridge mathematical models and data to synthesize our knowledge of population dynamics and predator feeding behaviors. Many such methods have been proposed, but few have seen independent validation of their estimates or underlying assumptions. This is particularly so with respect to the nonlinear functional responses by which predators often respond to their prey. Here I describe an empirical test of a recently proposed observational method for estimating the nonlinear strength of predator–prey interactions in the field. By applying the method to two populations of a predatory intertidal whelk, Haustrum scobina, I estimated its per capita attack rates on all nine of its observed prey species. These spanned two orders of magnitude in per capita strength. Concurrent experimental manipulations of the two predator populations provided population time series for the response of a mussel prey species, Xenostrobus pulex. I obtained independent interaction strength estimates for this focal interaction by fitting a sequence of hypothesized predator–prey models to these time series. Overall, site‐specific models assuming linear functional responses performed better than all others. A direct comparison of the attack‐rate estimates from the observational method with those of the best‐performing nonlinear model nevertheless revealed high concordance between the two methods. The results of this study therefore support the use of the observational method in larger and more complex food webs and suggest that trophic interactions in the range of mean prey densities observed in nature are approximately linear.
Apparent competition with an invasive plant hastens the extinction of an endangered lupine
Authors: Dangremond Emily M. , Pardini Eleanor A. , Knight Tiffany M.
Published: June 2010

Invasive plants may compete with native plants by increasing the pressure of native consumers, a mechanism known as “apparent competition.” Apparent competition can be as strong as or stronger than direct competition, but the role of apparent competition has rarely been examined in biological invasions. We used four years of demographic data and seed‐removal experiments to determine if introduced grasses caused elevated levels of seed consumption on native plant species in a coastal dune system in California, USA. We show that the endangered, coastal dune plant Lupinus tidestromii experiences high levels of pre‐dispersal seed consumption by the native rodent Peromyscus maniculatus due to its proximity to the invasive grass, Ammophila arenaria. We use stage‐structured, stochastic population models to project that two of three study populations will decline toward extinction under ambient levels of consumption. For one of these declining populations, a relatively small decrease in consumption pressure should allow for persistence. We show that apparent competition with an invasive species significantly decreases the population growth rate and persistence of a native species. We expect that apparent competition is an important mechanism in other ecosystems because invasive plants often change habitat structure and plant–consumer interactions. Possible implications of the apparent‐competition mechanism include selective extinction of species preferred by seed consumers in the presence of an invasive species and biological homogenization of communities toward non‐preferred native plant species.
Weaver ants Oecophylla smaragdina encounter nasty neighbors rather than dear enemies
Authors: Newey Philip S. , Robson Simon K. A. , Crozier Ross H.
Published: June 2010

The evolution of territorial behavior requires that the benefits of territoriality outweigh the costs. The costs are primarily those of territorial defense against encroaching neighbors or against floaters seeking to establish their own territory. One way to reduce the cost of defense might be to restrict serious conflict to encounters with those posing the greatest threat. Studies of many animals have found that less aggression is shown toward neighbors than toward strangers, a phenomenon known as the “dear enemy” effect. However, the opposite can also be true, namely, that more aggression is shown toward neighbors than strangers: the “nasty neighbor” effect. This may be particularly true of group‐living species that defend a resource‐based territory. Here we show that (1) colonies of the weaver ant Oecophylla smaragdina were able to recognize a greater proportion of workers from neighboring colonies as non‐colony members; and (2) when recognized as non‐colony members, more aggression was exhibited toward neighbors than non‐neighbors. We present for the first time evidence that differential levels of aggression involve both a perceptual and behavioral component. On the other hand, we found no evidence that weaver ant workers were better able to recognize workers from previously unknown colonies or responded more aggressively to them, even after a 10‐day period of contact. This contrasts with other species in which rapid learning of the identity of new potential enemies has been demonstrated. We suggest that such a response is unnecessary for weaver ants, as encounters with intruders from non‐neighboring colonies are probably rare and of little consequence. This study adds to the growing body of evidence that the nasty neighbor effect may be much more common than the dear enemy effect among group‐living species.
Migration and growth potential of coho salmon smolts: implications for ecological impacts from growth‐enhanced fish
Authors: Sundström L. Fredrik , Lõhmus Mare , Devlin Robert H.
Published: June 2010

Wild‐genotype and growth hormone (GH) transgenic coho salmon (with dramatically enhanced growth potential) were used to examine the influence of genotype, age, body size, growth, and rearing conditions on the onset of seaward migration and to assess the potential consequences of the introduction of such transgenic fish on natural ecosystems and wild populations. When reared from the first feeding stage under naturalized stream conditions, there was no difference in survival or migratory timing between the two genotypes. However, larger fish migrated earlier in the season than smaller fish of both genotypes, and transgenic fish with higher specific spring growth rates migrated earlier in the season than slower‐growing transgenic fish. Stream‐reared fish of both genotypes also displayed increased migratory activity at dawn and dusk. Fish reared in the hatchery for 3 and 15 months before being released into the stream in August differed in onset of seaward migration due mainly to age (older fish migrated earlier in the season) and genotype (transgenic fish migrated before wild‐type in younger fish). Further, hatchery‐reared fish showed no diel pattern in activity during migration. In older fish, larger individuals migrated later in the season than small individuals, whereas there was no clear size effect in younger individuals. Thus, although small differences in spring migration timing were observed among groups, seaward migration in coho salmon was largely independent of major shifts in size and growth rate induced by GH transgenesis (i.e., transgenic fish migrated at approximately the normal time in the spring, rather than at the typical size). Further, early rearing conditions had a stronger effect on migratory behavior than did the growth‐promoting transgene. Taking into account effects of migratory timing, growth, survival, and differential food conversion efficiencies, these data suggest that transgenic fish escaped from hatcheries would have a greater impact on stream ecosystems during early life compared to escaped wild‐type fish. However, this difference may be reduced if rearing occurred in subsequent generations under wild conditions where growth rates of transgenic fish are reduced compared with hatchery conditions.
Biomanipulation: a tool in marine ecosystem management and restoration?
Authors: Lindegren Martin , Möllmann Christian , Hansson Lars-Anders
Published: June 2010

Widespread losses of production and conservation values make large‐scale ecosystem restoration increasingly urgent. Ecological restoration by means of biomanipulation, i.e., by fishing out planktivores to reduce the predation pressure on herbivorous zooplankton, has proved to be an effective tool in restoring degraded lakes and coastal ecosystems. Whether biomanipulation may prove a useful restoration method in open and structurally complex marine ecosystems is, however, still unknown. To promote a recovery of the collapsed stock of Eastern Baltic cod (Gadus morhua), large‐scale biomanipulation of sprat (Sprattus sprattus), the main planktivore in the Baltic Sea, has been suggested as a possible management approach. We study the effect of biomanipulation on sprat using a statistical food‐web model, which integrates internal interactions between the main fish species of the Central Baltic Sea, with external forcing through commercial fishing, zooplankton, and climate. By running multiple, stochastic simulations of reductions in sprat spawning stock biomass (SSB) only minor increases in cod SSB were detected, none of which brought the cod significantly above ecologically safe levels. On the contrary, reductions in cod fishing mortality and/or improved climatic conditions would promote a significant recovery of the stock. By this we demonstrate that an ecosystem‐scale biomanipulation, with the main focus of reinstating the dominance of cod in the Baltic Sea may likely be ecologically ineffective, operationally difficult, and costly. We argue that reducing exploitation pressure on Eastern Baltic cod to ecologically sound levels is a far more appealing management strategy in promoting a long‐term recovery and a sustainable fishery of the stock.
Cascading diversity effects transmitted exclusively by behavioral interactions
Authors: Steffan Shawn A. , Snyder William E.
Published: June 2010

Consumer diversity generally increases resource consumption. Consumers can also impact other species by altering their behavior, but it is unclear how such nonconsumptive effects scale with diversity. We independently manipulated predator species richness and the consumptive and nonconsumptive effects of predator communities to measure the role of each factor in protecting Brassica oleracea plants from caterpillar herbivory. Plant biomass was greatest when diverse predator assemblages induced antipredator behaviors in herbivores, an effect not further strengthened when predators could also kill caterpillars. Predators within diverse communities were more likely to forage on plants and to disrupt herbivore feeding, reflecting greater aversion to foraging among conspecific than heterospecific competitors. Predator diversity, therefore, initiated behavioral changes at the predator and then herbivore trophic levels, both to the benefit of plants. Our results indicate that strong, emergent species‐richness effects can be transmitted entirely through behavioral interactions, independent of resource consumption.
Effects of climate change and wildfire on stream temperatures and salmonid thermal habitat in a mountain river network
Authors: Isaak Daniel J. , Luce Charles H. , Rieman Bruce E. , Nagel David E. , Peterson Erin E. , Horan Dona L. , Parkes Sharon , Chandler Gwynne L.
Published: June 2010

Mountain streams provide important habitats for many species, but their faunas are especially vulnerable to climate change because of ectothermic physiologies and movements that are constrained to linear networks that are easily fragmented. Effectively conserving biodiversity in these systems requires accurate downscaling of climatic trends to local habitat conditions, but downscaling is difficult in complex terrains given diverse microclimates and mediation of stream heat budgets by local conditions. We compiled a stream temperature database (n= 780) for a 2500‐km river network in central Idaho to assess possible trends in summer temperatures and thermal habitat for two native salmonid species from 1993 to 2006. New spatial statistical models that account for network topology were parameterized with these data and explained 93% and 86% of the variation in mean stream temperatures and maximas, respectively. During our study period, basin average mean stream temperatures increased by 0.38°C (0.27°C/decade), and maximas increased by 0.48°C (0.34°C/decade), primarily due to long‐term (30–50 year) trends in air temperatures and stream flows. Radiation increases from wildfires accounted for 9% of basin‐scale temperature increases, despite burning 14% of the basin. Within wildfire perimeters, however, stream temperature increases were 2–3 times greater than basin averages, and radiation gains accounted for 50% of warming. Thermal habitat for rainbow trout (Oncorhynchus mykiss) was minimally affected by temperature increases, except for small shifts towards higher elevations. Bull trout (Salvelinus confluentus), in contrast, were estimated to have lost 11–20% (8–16%/decade) of the headwater stream lengths that were cold enough for spawning and early juvenile rearing, with the largest losses occurring in the coldest habitats. Our results suggest that a warming climate has begun to affect thermal conditions in streams and that impacts to biota will be specific to both species and context. Where species are at risk, conservation actions should be guided based on considerations of restoration opportunity and future climatic effects. To refine predictions based on thermal effects, more work is needed to understand mechanisms associated with biological responses, climate effects on other habitat features, and habitat configurations that confer population resilience.
Resprouting as a persistence strategy of tropical forest trees: relations with carbohydrate storage and shade tolerance
Authors: Poorter Lourens , Kitajima Kaoru , Mercado Pablo , Chubiña Jose , Melgar Israel , Prins Herbert H. T.
Published: June 2010

Resprouting is an important persistence strategy for woody species and represents a dominant pathway of regeneration in many plant communities, with potentially large consequences for vegetation dynamics, community composition, and species coexistence. Most of our knowledge of resprouting strategies comes from fire‐prone systems, but this cannot be readily applied to other systems where disturbances are less intense. In this study we evaluated sapling responses to stem snapping for 49 moist‐forest species and 36 dry‐forest species from two Bolivian tropical forests. To this end we compared in a field experiment the survival and height growth of clipped and control saplings for a two‐year period, and related this to the shade tolerance, carbohydrate reserves, and the morphological traits (wood density, leaf size) of the species.

Nearly all saplings resprouted readily after stem damage, although dry‐forest species realized, on average, a better survival and growth after stem damage compared to moist‐forest species. Shade‐tolerant species were better at resprouting than light‐demanding species in moist forest. This resprouting ability is an important prerequisite for successful regeneration in the shaded understory, where saplings frequently suffer damage from falling debris. Survival after stem damage was, surprisingly, only modestly related to stem reserves, and much more strongly related to wood density, possibly because a high wood density enables plants to resist fungi and pathogens and to reduce stem decay. Correlations between sapling performance and functional traits were similar for the two forest types, and for phylogenetically independent contrasts and for cross‐species analyses. The consistency of these results suggests that tropical forest species face similar trade‐offs in different sites and converge on similar sets of solutions. A high resprouting ability, as well as investments in stem defense and storage reserves, form part of a suite of co‐evolved traits that underlies the growth–survival trade‐off, and contributes to light gradient partitioning and species coexistence. These links with shade tolerance are important in the moist evergreen forest, which casts a deep, more persistent shade, but tend to diminish in dry deciduous forest where light is a less limiting resource.
Processing arctic eddy‐flux data using a simple carbon‐exchange model embedded in the ensemble Kalman filter
Authors: Rastetter Edward B. , Williams Mathew , Griffin Kevin L. , Kwiatkowski Bonnie L. , Tomasky Gabrielle , Potosnak Mark J. , Stoy Paul C. , Shaver Gaius R. , Stieglitz Marc , Hobbie John E. , Kling George W.
Published: June 2010

Continuous time‐series estimates of net ecosystem carbon exchange (NEE) are routinely made using eddy covariance techniques. Identifying and compensating for errors in the NEE time series can be automated using a signal processing filter like the ensemble Kalman filter (EnKF). The EnKF compares each measurement in the time series to a model prediction and updates the NEE estimate by weighting the measurement and model prediction relative to a specified measurement error estimate and an estimate of the model‐prediction error that is continuously updated based on model predictions of earlier measurements in the time series. Because of the covariance among model variables, the EnKF can also update estimates of variables for which there is no direct measurement. The resulting estimates evolve through time, enabling the EnKF to be used to estimate dynamic variables like changes in leaf phenology. The evolving estimates can also serve as a means to test the embedded model and reconcile persistent deviations between observations and model predictions.

We embedded a simple arctic NEE model into the EnKF and filtered data from an eddy covariance tower located in tussock tundra on the northern foothills of the Brooks Range in northern Alaska, USA. The model predicts NEE based only on leaf area, irradiance, and temperature and has been well corroborated for all the major vegetation types in the Low Arctic using chamber‐based data. This is the first application of the model to eddy covariance data.

We modified the EnKF by adding an adaptive noise estimator that provides a feedback between persistent model data deviations and the noise added to the ensemble of Monte Carlo simulations in the EnKF. We also ran the EnKF with both a specified leaf‐area trajectory and with the EnKF sequentially recalibrating leaf‐area estimates to compensate for persistent model‐data deviations. When used together, adaptive noise estimation and sequential recalibration substantially improved filter performance, but it did not improve performance when used individually.

The EnKF estimates of leaf area followed the expected springtime canopy phenology. However, there were also diel fluctuations in the leaf‐area estimates; these are a clear indication of a model deficiency possibly related to vapor pressure effects on canopy conductance.
Effects of fire on woody vegetation structure in African savanna
Authors: Smit Izak P. J. , Asner Gregory P. , Govender Navashni , Kennedy-Bowdoin Ty , Knapp David E. , Jacobson James
Published: June 2010

Despite the importance of fire in shaping savannas, it remains poorly understood how the frequency, seasonality, and intensity of fire interact to influence woody vegetation structure, which is a key determinant of savanna biodiversity. We provide a comprehensive analysis of vertical and horizontal woody vegetation structure across one of the oldest savanna fire experiments, using new airborne Light Detection and Ranging (LiDAR) technology. We developed and compared high‐resolution woody vegetation height surfaces for a series of large experimental burn plots in the Kruger National Park, South Africa. These 7‐ha plots (total area ∼1500 ha) have been subjected to fire in different seasons and at different frequencies, as well as no‐burn areas, for 54 years. Long‐term exposure to fire caused a reduction in woody vegetation up to the 5.0–7.5 m height class, although most reduction was observed up to 4 m. Average fire intensity was positively correlated with changes in woody vegetation structure. More frequent fires reduced woody vegetation cover more than less frequent fires, and dry‐season fires reduced woody vegetation more than wet‐season fires. Spring fires from the late dry season reduced woody vegetation cover the most, and summer fires from the wet season reduced it the least. Fire had a large effect on structure in the densely wooded granitic landscapes as compared to the more open basaltic landscapes, although proportionally, the woody vegetation was more reduced in the drier than in the wetter landscapes. We show that fire frequency and fire season influence patterns of vegetation three‐dimensional structure, which may have cascading consequences for biodiversity. Managers of savannas can therefore use fire frequency and season in concert to achieve specific vegetation structural objectives.
Bayesian change point analysis of abundance trends for pelagic fishes in the upper San Francisco Estuary
Authors: Thomson James R. , Kimmerer Wim J. , Brown Larry R. , Newman Ken B. , Nally Ralph Mac , Bennett William A. , Feyrer Frederick , Fleishman Erica
Published: June 2010

We examined trends in abundance of four pelagic fish species (delta smelt, longfin smelt, striped bass, and threadfin shad) in the upper San Francisco Estuary, California, USA, over 40 years using Bayesian change point models. Change point models identify times of abrupt or unusual changes in absolute abundance (step changes) or in rates of change in abundance (trend changes). We coupled Bayesian model selection with linear regression splines to identify biotic or abiotic covariates with the strongest associations with abundances of each species. We then refitted change point models conditional on the selected covariates to explore whether those covariates could explain statistical trends or change points in species abundances. We also fitted a multispecies change point model that identified change points common to all species. All models included hierarchical structures to model data uncertainties, including observation errors and missing covariate values. There were step declines in abundances of all four species in the early 2000s, with a likely common decline in 2002. Abiotic variables, including water clarity, position of the 2‰ isohaline (X2), and the volume of freshwater exported from the estuary, explained some variation in species' abundances over the time series, but no selected covariates could explain statistically the post‐2000 change points for any species.
Identifying signature of chemical applications on indigenous and invasive nontarget arthropod communities in vineyards
Authors: Nash Michael A. , Hoffmann Ary A. , Thomson Linda J.
Published: June 2010

Communities of arthropods providing ecosystem services (e.g., pest control, pollination, and soil nutrient cycling) to agricultural production systems are influenced by pesticide inputs, yet the impact of pesticide applications on nontarget organisms is normally evaluated through standardized sets of laboratory tests involving individual pesticides applied to a few representative species. By combining season‐long pesticide applications of various insecticides and fungicides into a metric based on the International Organization for Biological and Integrated Control (IOBC) toxicity ratings, we evaluate season‐long pesticide impacts on communities of indigenous and exotic arthropods across 61 vineyards assessed for an entire growing season. The composition of arthropod communities, identified mostly at the family level, but in some cases at the species level, was altered depending on season‐long pesticide use. Numbers of mostly indigenous parasitoids, predatory mites, and coccinellids in the canopy, as well as carabid/tenebrionid beetles and some spider families on the ground, were decreased at higher cumulative pesticide metric scores. In contrast, numbers of one invasive millipede species (Ommatoiulus moreletti Lucas, Julida: Julidae) increased under higher cumulative pesticide metric scores. These changing community patterns were detected despite the absence of broad‐spectrum insecticide applications in the vineyards. Pesticide effects were mostly due to indoxacarb and sulphur, applied as a fungicide. The reduction of beneficial arthropods and increase in an invasive herbivorous millipede under high cumulative pesticide metric scores highlights the need to manage nontarget season‐long pesticide impacts in vineyards. A cumulative pesticide metric, based on IOBC toxicity ratings, provides a way of assessing overall toxicity effects, giving managers a means to estimate and consider potential negative season‐long pesticide impacts on ecosystem services provided through arthropod communities.
The ghosts of predators past: population cycles and the role of maternal programming under fluctuating predation risk
Authors: Sheriff Michael J. , Krebs Charles J. , Boonstra Rudy
Published: June 2010

Maternal effects may be a major factor influencing the demography of populations. In mammals, the transmission of stress hormones between mother and offspring may play an important role in these effects. Laboratory studies have shown that stressors during pregnancy and lactation result in lifelong programming of the offspring phenotype. However, the relevance of these studies to free‐living mammals is unclear. The 10‐year snowshoe hare (Lepus americanus) cycle is intimately linked to fluctuating predation pressure and predation risk. The enigma of these cycles is the lack of population growth following the decline phase, when the predators have virtually all disappeared and the food supply is ample. We have shown that a predator‐induced increase in maternal stress hormone levels resulted in a decline in reproduction. Here we examine population and hormone changes over a four‐year period from the increase (2005) to the decline (2008). We report (1) that an index of maternal stress (fecal corticosteroid metabolite [FCM] concentrations) fluctuates in synchrony with predator density during the breeding season; (2) that maternal FCM levels are echoed in their offspring, and this occurs at a population‐wide level; and (3) that higher maternal FCM levels at birth are correlated with an increased responsiveness of the hypothalamic‐pituitary‐adrenal (HPA) axis in their progeny. Our results show an intergenerational inheritance of stress hormones in a free‐ranging population of mammals. We propose that the lack of recovery of reproductive rates during the early low phase of the hare cycle may be the result of the impacts of intergenerational, maternally inherited stress hormones caused by high predation risk during the decline phase.
Complementary resource use by tree species in a rain forest tree plantation
Authors: Richards Anna E. , Schmidt Susanne
Published: June 2010

Mixed‐species tree plantations, composed of high‐value native rain forest timbers, are potential forestry systems for the subtropics and tropics that can provide ecological and production benefits. Choices of rain forest tree species for mixtures are generally based on the concept that assemblages of fast‐growing and light‐demanding species are less productive than assemblages of species with different shade tolerances. We examined the hypothesis that mixtures of two fast‐growing species compete for resources, while mixtures of shade‐tolerant and shade‐intolerant species are complementary. Ecophysiological characteristics of young trees were determined and analyzed with a physiology‐based canopy model (MAESTRA) to test species interactions. Contrary to predictions, there was evidence for complementary interactions between two fast‐growing species with respect to nutrient uptake, nutrient use efficiency, and nutrient cycling. Fast‐growingElaeocarpus angustifoliushad maximum demand for soil nutrients in summer, the most efficient internal recycling of N, and low P use efficiency at the leaf and whole‐plant level and produced a large amount of nutrient‐rich litter. In contrast, fast‐growingGrevillea robustahad maximum demand for soil nutrients in spring and highest leaf nutrient use efficiency for N and P and produced low‐nutrient litter. Thus, mixtures of fast‐growingG. robustaandE. angustifoliusorG. robustaand slow‐growing, shade‐tolerantCastanospermum australemay have similar or even greater productivity than monocultures, as light requirement is just one of several factors affecting performance of mixed‐species plantations. We conclude that the knowledge gained here will be useful for designing large‐scale experimental mixtures and commercial forestry systems in subtropical Australia and elsewhere.
Differential tree and shrub production in response to fertilization and disturbance by coastal river otters in Alaska
Authors: Roe Aaron M. , Meyer Carolyn B. , Nibbelink Nathan P. , Ben-David Merav
Published: June 2010

We explored the interacting effects of marine‐derived nutrient fertilization and physical disturbance introduced by coastal river otters (Lontra canadensis) on the production and nutrient status of pristine shrub and tree communities in Prince William Sound, Alaska, USA. We compared production of trees and shrubs between latrines and non‐latrines, while accounting for otter site selection, by sampling areas on and off sites. Nitrogen stable isotope analysis (δ15N) indicated that dominant tree and shrub species assimilated the marine‐derived N excreted by otters. In association with this uptake, tree production increased, but shrub density and nonwoody aboveground shrub production decreased. The reduced shrub production was caused by destruction of ramets, especially blueberry (Vaccinium spp.), through physical disturbance by river otters. False azalea (Menziesia ferruginea) ramets were less sensitive to otter disturbance. Although surviving individual blueberry ramets showed a tendency for increased production per plant, false azalea allocated excess N to storage in leaves rather than growth. We found that plant responses to animal activity vary among species and levels of biological organization (leaf, plant, ecosystem). Such differences should be accounted for when assessing the influence of river otters on the carbon budget of Alaskan coastal forests at the landscape scale.