bluuebunny/crossref_metadata_2025 huggingface dataset:
Aurora kinases orchestrate mitosis; who are the players?
Authors: Molla Annie
Published: June 2010

The Aurora are a conserved family of serine/threonine kinases with essential functions in cell division. In mitosis, Aurora kinases are required for chromosome segregation, condensation and orientation in the metaphase plate, spindle assembly, and the completion of cytokinesis. This review presents the Aurora kinases, their partners and how their interactions impact on the different mitotic functions.
Desintegration und Interpretation: Weil-V2-Sätze an der Schnittstelle zwischen Syntax, Semantik und Pragmatik
Authors: Antomo Mailin , Steinbach Markus
Published: June 2010

In spoken varieties of German, causal adverbial clauses introduced by weil are frequently used with V2 order. Interestingly, weil-V2 clauses are not simply a colloquial variant of standard verb-final clauses, but have also many specific syntactic, semantic, and pragmatic properties. On the one hand, weil-V2 clauses differ systematically from their verb-final counterparts. While V2 clauses yield causal interpretations not available for the corresponding verb-final clauses, verb-final clauses show a higher degree of syntactic integration and syntactic flexibility than V2 clauses. On the other hand, weil-V2 clauses share crucial formal and functional properties with other kinds of embedded V2 clauses such as V2-complement clauses and V2-relative clauses. Weil-V2 clauses can therefore be subsumed under the notion of ‘embedded root phenomena’. In this paper, we develop an analysis that derives all syntactic, semantic, and pragmatic properties of weil-V2 clauses at the interfaces between syntax, semantics, and pragmatics from their paratactic syntactic structure and the assertional force potential triggered by V-to-C movement. The results of a questionnaire study provide independent empirical evidence for our analysis.
Immobilization of Cellulase and Hemicellulases on Porous Glass Beads
Authors: Mandali Pavani , Dalaly Basil K.
Published: June 2010

Experiments on immobilization of cellulase complex (cellulase, Novozymes) and enzyme complex (cellulases and hemicellulases, Novozymes) were performed on porous Siran™ beads using covalent and non-covalent bonding methods. Free enzyme complex was used for hydrolyzing various pretreated biomass such as corn stover, distillers dried grain with solubles, switch grass and blue stem grass. Maximum activity of enzyme complex was found with corn stover and was used as a substrate for measuring cellulase and hemicellulases activities. Protein loading for immobilized cellulase complex and enzyme complex on Siran™ carriers was found in the range of 10.776–18.000 % and 19.932–23.082 %, respectively. Activity loading for immobilized cellulase complex with avicel was in the range of 16.610–22.026 %. For enzyme complex, activity loading was found in the range of 43.558–61.222 %, 8.274–19.124 %, and 7.180–14.114 % with avicel, xylan, and corn stover as substrates, respectively. Recycling experiments for immobilized cellulase complex and enzyme complex were carried out using various substrates, and the residual enzyme activity was measured after the third cycle. Carbodiimide bonded cellulase complex retained more residual enzyme activity with avicel (49.460 %), which indicates a good cross linker for cellulase immobilization. The enzyme complex bonded to carbodiimide, and glutaraldehyde retained residual activity of 44.160 % with xylan and 73.230 % with corn stover, respectively. Recycling studies showed greater retention in residual enzyme activity with covalent bonded enzymes than non-covalent bonded enzymes. Glutaraldehyde and carbodiimide were found to be effective cross linkers for immobilizing both cellulase and hemicellulases in covalent bonding method.
Common Sense and Masonry Repair
Authors: Pashina Keith A. , Talafous Steven M.
Published: June 2010

The maintenance and restoration of masonry structures are often repetitive processes. Many of the problems encountered are very common. Many problems requiring maintenance and repair could have been mitigated or prevented with a little foresight and coordination during the design and construction period. Why is so much effort expended on “repairing the repairs”? This paper discusses how common mistakes occur and why. Many of the perceived restraints on the design and construction phases such as time, budget, level of craftsmanship, and material costs do and should affect the project. However, these constraints must be balanced against the functionality of the masonry, such as durability, structural stability, weather barrier, and aesthetics. Through real-life examples, this paper describes a simple repair of rehabilitation process that will lead to a successful project outcome: Long lasting, low maintenance masonry structures. It takes into account the owner’s needs, priorities, and budgetary, physical, and time constraints before any design development or repair begins. For comparison, unsuccessful project outcomes from actual projects will also be explored.
Severe Ulcerative Colitis After Rituximab Therapy
Authors: Ardelean Daniela S. , Gonska Tanja , Wires Shannon , Cutz Ernest , Griffiths Anne , Harvey Elizabeth , Tse Shirley M. L. , Benseler Susanne M.
Published: June 2010

B-cell–depletion therapy with rituximab is efficacious against steroid-dependent nephrotic syndrome (NS) in children and adults. Safety data are limited. Results of small studies have suggested that rituximab is usually well tolerated but that adverse events (such as severe mucocutaneous reactions, fatal infusion reactions, progressive multifocal leukoencephalopathy, and bowel perforation) can occur. We report here the first case (to our knowledge) of a pediatric patient with refractory minimal-change NS who developed severe immune-mediated ulcerative gastrointestinal disease 42 days after rituximab therapy. The disease was characterized by deep ulcers throughout the intestines and predominantly affected the colon. The child presented with severe abdominal pain, bloody diarrhea, weight loss, and fever. Her inflammatory markers were significantly elevated. Extensive evaluation revealed no evidence of infections and no characteristics of defined inflammatory bowel disease or Behçet disease. Colonoscopy revealed severe intestinal inflammation with deep ulcers. Histology of the colonic biopsy specimens revealed extensive infiltrates predominantly composed of CD8+ T lymphocytes and evidence of high forkhead box P3 (FOXP3) expression. During this significant gastrointestinal disease, the NS remained quiescent. Corticosteroid therapy successfully controlled the severe immune-mediated intestinal inflammation after rituximab therapy. NS relapsed subsequently when CD19+ and CD20+ B-cell populations recovered.
Fire ant alate wing motion data and numerical reconstruction
Authors: Gui L. , Fink T. , Cao Z , Sun D. , Seiner J.M , Streett D.A.
Published: June 2010

The wing motions of a male and a female fire ant alate, which beat their wings at 108 and 96 Hz, respectively, were captured with a stereo imaging system at a high frame rate of 8,000 frames per second. By processing the high-speed image frames, the three-dimensional wingtip positions and the wing surface orientation angles were determined with a high phase resolution, i.e. 74 and 83 phases per period for the male and the female, respectively. A numerical reconstruction of the stereo wingbeat images demonstrated that the data collected described almost all the details of the wing surface motion, so that further computational fluid dynamic simulations are possible for fire ant alate flight.
Herbivores on a dominant understory shrub increase local plant diversity in rain forest communities
Authors: Dyer Lee A. , Letourneau Deborah K. , Chavarria Gerardo Vega , Amoretti Diego Salazar
Published: June 2010

Indirect effects of trophic interactions on biodiversity can be large and common, even in complex communities. Previous experiments with dominant understory Piper shrubs in a Costa Rican rain forest revealed that increases in herbivore densities on these shrubs caused widespread seedling mortality as a result of herbivores moving from Piper to seedlings of many different plant genera. We tested components of the Janzen‐Connell hypothesis by conducting focused studies on the effects of specialist and generalist Piper herbivores on local seedling diversity. Whereas specialist herbivores are predicted to increase mortality to neighboring seedlings that are closely related to the source plant, true generalists moving from source plants may cause density‐dependent mortality of many species, and possibly increase richness if new species replace abundant species that have been thinned by herbivores. Therefore, we hypothesized that seedling richness would be greater in understory control plots created in patches of Piper that had normal densities of generalist herbivores compared to plots from which we removed generalist herbivores manually from all Piper shrubs. After 15 months, generalist‐herbivore‐removal plots had >40% fewer seedlings, >40% fewer species, and 40% greater seedling evenness, on average, than control plots with generalist herbivores intact. Using a complementary approach in unmanipulated plots in four forests, we used path analysis to test for a positive association between seedling diversity and herbivore damage on Piper species. In unmanipulated plots, for both generalist and specialist herbivores, our data were significant fits to the causal model that Piper herbivores decrease evenness and increase plant species richness, corroborating the experimental results. Because herbivores changed how individuals were apportioned among the species and families present (lower evenness), one interpretation of these associations between herbivores on Piper shrubs and local seedling richness is that high seedling mortality in dominant families allowed the colonization or survival of less common species. If interspecific or apparent competition allowed for a relative increase in species richness, then the Janzen‐Connell hypothesis may extend its predictions to generalist seedling predators. We speculate that apparent competition may explain some of the deviations from neutral model predictions, especially at small scales.
Resource distribution influences positive edge effects in a seagrass fish
Authors: Macreadie Peter I. , Hindell Jeremy S. , Keough Michael J. , Jenkins Gregory P. , Connolly Rod M.
Published: June 2010

According to conceptual models, the distribution of resources plays a critical role in determining how organisms distribute themselves near habitat edges. These models are frequently used to achieve a mechanistic understanding of edge effects, but because they are based predominantly on correlative studies, there is need for a demonstration of causality, which is best done through experimentation. Using artificial seagrass habitat as an experimental system, we determined a likely mechanism underpinning edge effects in a seagrass fish. To test for edge effects, we measured fish abundance at edges (0–0.5 m) and interiors (0.5–1 m) of two patch configurations: continuous (single, continuous 9‐m2 patches) and patchy (four discrete 1‐m2 patches within a 9‐m2 area). In continuous configurations, pipefish (Stigmatopora argus) were three times more abundant at edges than interiors (positive edge effect), but in patchy configurations there was no difference. The lack of edge effect in patchy configurations might be because patchy seagrass consisted entirely of edge habitat. We then used two approaches to test whether observed edge effects in continuous configurations were caused by increased availability of food at edges. First, we estimated the abundance of the major prey of pipefish, small crustaceans, across continuous seagrass configurations. Crustacean abundances were highest at seagrass edges, where they were 16% greater than in patch interiors. Second, we supplemented interiors of continuous treatment patches with live crustaceans, while control patches were supplemented with seawater. After five hours of supplementation, numbers of pipefish were similar between edges and interiors of treatment patches, while the strong edge effects were maintained in controls. This indicated that fish were moving from patch edges to interiors in response to food supplementation. These approaches strongly suggest that a numerically dominant fish species is more abundant at seagrass edges due to greater food availability, and provide experimental support for the resource distribution model as an explanation for edge effects.
Predicting feeding success in a migratory predator: integrating telemetry, environment, and modeling techniques
Authors: Bestley Sophie , Patterson Toby A. , Hindell Mark A. , Gunn John S.
Published: June 2010

Foraging theory predicts that mobile predators should target high profitability areas with plentiful resources and minimize time spent moving between these areas. This has led to a focus in recent literature on the identification of “hotspots” important for migratory marine predators, i.e., regions where predators spend disproportionate amounts of time ostensibly due to high prey abundance; and determination of the environmental features characteristic of such areas. We investigated factors predicting foraging success in southern bluefin tuna (SBT;Thunnus maccoyii), by integrating telemetry‐based feeding and movement data (n= 19 fish, length to caudal fork [LCF] = 99 ± 3 cm) with environmental data over the scale of their annual oceanic migrations during 1998–2000. We used widely available statistical modeling techniques, generalized linear models, and generalized linear mixed models, formulated to represent feeding as a Markov process. The results showed increased feeding and predictability of feeding occurs in the coastal waters of southern Australia, providing some evidence that this area represents a fixed foraging “hotspot” for juvenile tuna during the austral summer. However, in oceanic waters southern bluefin tuna did not fit the common model of migration, but rather showed a pattern of relatively high foraging success throughout their migratory range, especially during periods of continuous travel. Interestingly, foraging “coldspots” (prolonged low‐feeding periods) as well as “hotspots” were apparent across individual tracks, predicted most strongly by warm ocean temperatures. These results provide a new perspective on the ecology of large‐scale feeding migrations within the context of the heterogeneous ocean environment, where the continuous and opportunistic feeding of generalist predators may be more common, particularly in predatory large pelagic fishes, than is currently documented.
Overrun by the neighbors: Landscape context affects strength and sign of local adaptation
Authors: Tack Ayco J. M. , Roslin Tomas
Published: June 2010

The adaptive deme formation hypothesis states that plant‐feeding insects may adapt to individual host plants. To date, no empirical study has examined the strength of such adaptations from a spatially explicit perspective. In this study, we quantify local adaptation of six specialist insect species at multiple sites, predicting that spatial variation in local immigration rates will result in variation in the strength of local adaptation. We use a previously parameterized metapopulation model to estimate the proportion of immigrants in focal populations, clonal trees to measure local adaptation in a reciprocal common garden experiment, and a linear model to test for a link between the strength of immigration and local adaptation across species. As predicted, local adaptation generally varies inversely with the fraction of immigrants in a population. When immigration is high, local populations remain in a maladapted state. Importantly, our results imply that patterns of adaptation may vary predictably at a relatively small spatial scale (among individual host trees within a landscape) and that, hence, measures of local adaptation will make most sense in a spatial context.
Specificity between Neotropical tree seedlings and their fungal mutualists leads to plant–soil feedback
Authors: Mangan Scott A. , Herre Edward A. , Bever James D.
Published: June 2010

A growing body of evidence obtained largely from temperate grassland studies suggests that feedbacks occurring between plants and their associated soil biota are important to plant community assemblage. However, few studies have examined the importance of soil organisms in driving plant–soil feedbacks in forested systems. In a tropical forest in central Panama, we examined whether interactions between tree seedlings and their associated arbuscular mycorrhizal fungi (AMF) lead to plant–soil feedback. Specifically, do tropical seedlings modify their own AMF communities in a manner that either favors or inhibits the next cohort of conspecific seedlings (i.e., positive or negative feedback, respectively)? Seedlings of two shade‐tolerant tree species (Eugenia nesiotica, Virola surinamensis) and two pioneer tree species (Luehea seemannii, Apeiba aspera) were grown in pots containing identical AMF communities composed of equal amounts of inoculum of six co‐occurring AMF species. The different AMF–host combinations were all exposed to two light levels. Under low light (2% PAR), only two of the six AMF species sporulated, and we found that host identity did not influence composition of AMF spore communities. However, relative abundances of three of the four AMF species that produced spores were influenced by host identity when grown under high light (20% PAR). Furthermore, spores of one of the AMF species, Glomus geosporum, were common in soils of Luehea and Eugenia but absent in soils of Apeiba and Virola. We then conducted a reciprocal experiment to test whether AMF communities previously modified by Luehea and Apeiba differentially affected the growth of conspecific and heterospecific seedlings. Luehea seedling growth did not differ between soils containing AMF communities modified by Luehea and Apeiba. However, Apeiba seedlings were significantly larger when grown with Apeiba‐modified AMF communities, as compared to Apeiba seedlings grown with Luehea‐modifed AMF communities. Our experiments suggest that interactions between tropical trees and their associated AMF are species‐specific and that these interactions may shape both tree and AMF communities through plant–soil feedback.
Risk‐based determination of critical nitrogen deposition loads for fire spread in southern California deserts
Authors: Rao Leela E. , Allen Edith B. , Meixner Thomas
Published: June 2010

Fire risk in deserts is increased by high production of annual forbs and invasive grasses that create a continuous fine fuel bed in the interspaces between shrubs. Interspace production is influenced by water, nitrogen (N) availability, and soil texture, and in some areas N availability is increasing due to anthropogenic N deposition. The DayCent model was used to investigate how production of herbaceous annuals changes along gradients of precipitation, N availability, and soil texture, and to develop risk‐based critical N loads. DayCent was parameterized for two vegetation types within Joshua Tree National Park, California, USA: creosote bush (CB) and piñon–juniper (PJ). The model was successfully calibrated in both vegetation types, but validation showed that the model is sensitive to soil clay content. Despite this fact, DayCent (the daily version of the biogeochemical model CENTURY) performed well in predicting the relative response of production to N fertilization and was used to determine estimates of fire risk for these ecosystems. Fire risk, the probability that annual biomass exceeds the fire threshold of 1000 kg/ha, was determined for each vegetation type and began to increase when N deposition increased 0.05 g/m2 above background levels (0.1 g/m2). Critical loads were calculated as the amount of N deposition at the point when fire risk began to increase exponentially. Mean critical loads for all soil types and precipitation <21 cm/yr, representing the majority of our study region, were 0.32 ± 0.07 and 0.39 ± 0.09 g N/m2 for CB and PJ, respectively. Critical loads decreased with increasing soil clay content and increasing precipitation, such that the wettest areas with clay contents of 6–14% may have critical loads as low as 0.15 g N/m2. Mean fire risks approached their maximum at 0.93 ± 0.21 and 0.87 ± 0.17 g N/m2 in CB and PJ, indicating that precipitation is the driver of fire above these N deposition levels, which are currently observed in some areas of the Sonoran and Mojave Deserts. Overall, this analysis demonstrates the importance of considering both N deposition and precipitation when evaluating fire risk across arid landscapes.
Physical and biological disturbances interact differently with productivity: effects on floral and faunal richness
Authors: Svensson J. Robin , Lindegarth Mats , Pavia Henrik
Published: June 2010

Physical and biological disturbances are ecological processes affecting patterns in biodiversity at a range of scales in a variety of terrestrial and aquatic systems. Theoretical and empirical evidence suggest that effects of disturbance on diversity differ qualitatively and quantitatively, depending on levels of productivity (e.g., the dynamic equilibrium model). In this study we contrasted the interactive effects between physical disturbance and productivity to those between biological disturbance and productivity. Furthermore, to evaluate how these effects varied among different components of marine hard‐substratum assemblages, analyses were done separately on algal and invertebrate richness, as well as richness of the whole assemblage. Physical disturbance (wave action) was simulated at five distinct frequencies, while biological disturbance (grazing periwinkles) was manipulated as present or absent, and productivity was manipulated as high or ambient. Uni‐ and multivariate analyses both showed significant effects of physical disturbance and interactive effects between biological disturbance and productivity on the composition of assemblages and total species richness. Algal richness was significantly affected by productivity and biological disturbance, whereas invertebrate richness was affected by physical disturbance only. Thus, we show, for the first time, that biological disturbance and physical disturbance interact differently with productivity, because these two types of disturbances affect different components of assemblages. These patterns might be explained by differences in the distribution (i.e., press vs. pulse) and degree of selectivity between disturbances. Because different types of disturbance can affect different components of assemblages, general ecological models will benefit from using natural diverse communities, and studies concerned with particular subsets of assemblages may be misleading. In conclusion, this study shows that the outcome of experiments on effects of disturbance and productivity on diversity is greatly influenced by the composition of the assemblage under study, as well as on the type of disturbance that is used as an experimental treatment.
Phylogeny and metabolic scaling in mammals
Authors: Capellini Isabella , Venditti Chris , Barton Robert A.
Published: June 2010

The scaling of metabolic rates to body size is widely considered to be of great biological and ecological importance, and much attention has been devoted to determining its theoretical and empirical value. Most debate centers on whether the underlying power law describing metabolic rates is 2/3 (as predicted by scaling of surface area/volume relationships) or 3/4 (“Kleiber's law”). Although recent evidence suggests that empirically derived exponents vary among clades with radically different metabolic strategies, such as ectotherms and endotherms, models, such as the metabolic theory of ecology, depend on the assumption that there is at least a predominant, if not universal, metabolic scaling exponent. Most analyses claimed to support the predictions of general models, however, failed to control for phylogeny. We used phylogenetic generalized least‐squares models to estimate allometric slopes for both basal metabolic rate (BMR) and field metabolic rate (FMR) in mammals. Metabolic rate scaling conformed to no single theoretical prediction, but varied significantly among phylogenetic lineages. In some lineages we found a 3/4 exponent, in others a 2/3 exponent, and in yet others exponents differed significantly from both theoretical values. Analysis of the phylogenetic signal in the data indicated that the assumptions of neither species‐level analysis nor independent contrasts were met. Analyses that assumed no phylogenetic signal in the data (species‐level analysis) or a strong phylogenetic signal (independent contrasts), therefore, returned estimates of allometric slopes that were erroneous in 30% and 50% of cases, respectively. Hence, quantitative estimation of the phylogenetic signal is essential for determining scaling exponents. The lack of evidence for a predominant scaling exponent in these analyses suggests that general models of metabolic scaling, and macro‐ecological theories that depend on them, have little explanatory power.
Applications of particle image velocimetry for seed release studies
Authors: Marchetto Katherine M. , Williams Matthew B. , Jongejans Eelke , Auhl Richard , Shea Katriona
Published: June 2010

Nonrandom seed release is an important determinant of how far seeds disperse, but the mechanisms that promote wind‐related seed release under varying atmospheric conditions are poorly understood. We explored the use of particle image velocimetry (PIV) to gain a better mechanistic understanding of seed release by visualizing the flow velocities and vorticity in a two‐dimensional slice of air around inflorescences. Pilot data taken in a wind tunnel show gradients in air velocity at the top ofCarduus nutanscapitula that may contribute to lift generation. Additionally, von Kármán vortex streets (vortices of opposite spin that are shed from the wake of an object) were observed shedding from capitula, which cause lateral forces on capitula and increase turbulence downwind at other locations. Avenues for further research include using PIV to examine the mechanisms of seed release and dispersal in wind tunnels and in the field. We found PIV to be a promising method to further explore the mechanisms behind seed release in wind dispersed plants, and a technique rich with opportunities for collaborations between plant dispersal ecologists and fluid dynamics specialists.
Multiple stressors and the cause of amphibian abnormalities
Authors: Reeves Mari K. , Jensen Peter , Dolph Christine L. , Holyoak Marcel , Trust Kimberly A.
Published: June 2010

The repeated occurrence of abnormal amphibians in nature points to ecological imbalance, yet identifying causes of these abnormalities has proved complex. Multiple studies have linked amphibian abnormalities to chemically contaminated areas, but inference about causal mechanisms is lacking. Here we use a high incidence of abnormalities in Alaskan wood frogs to strengthen inference about the mechanism for these abnormalities. We suggest that limb abnormalities are caused by a combination of multiple stressors. Specifically, toxicants lead to increased predation, resulting in more injuries to developing limbs and subsequent developmental malformations. We evaluated a variety of putative causes of frog abnormalities at 21 wetlands on the Kenai National Wildlife Refuge, south‐central Alaska, USA, between 2004 and 2006. Variables investigated were organic and inorganic contaminants, parasite infection, abundance of predatory invertebrates, UVB, and temperature. Logistic regression and model comparison using the Akaike information criterion (AIC) identified dragonflies and both organic and inorganic contaminants as predictors of the frequency of skeletal abnormalities. We suggest that both predators and contaminants alter ecosystem dynamics to increase the frequency of amphibian abnormalities in contaminated habitat. Future experiments should test the causal mechanisms by which toxicants and predators may interact to cause amphibian limb abnormalities.
Spatial location dominates over host plant genotype in structuring an herbivore community
Authors: Tack Ayco J. M. , Ovaskainen Otso , Pulkkinen Pertti , Roslin Tomas
Published: June 2010

Recent work has shown a potential role for both host plant genotype and spatial context in structuring insect communities. In this study, we use three separate data sets on herbivorous insects on oak (Quercus robur) to estimate the relative effects of host plant genotype (G), location (E), and theG×Einteraction on herbivore community structure: a common garden experiment replicated at the landscape scale (~5 km2); two common gardens separated at the regional scale (~10 000 km2); and survey data on wild trees in various spatial settings. Our experiments and survey reveal that, at the landscape scale, the insect community is strongly affected by the spatial setting, with 32% of the variation in species richness explained by spatial connectivity. In contrast,GandG×Eplay minor roles in structuring the insect community. Results remained similar when extending the spatial scale of the study from the more local (landscape) level to the regional level. We conclude that in our study system, spatial processes play a major role in structuring these insect communities at both the landscape and regional scales, whereas host plant genotype seems of secondary importance.
Environmentally sensitive life‐cycle traits have low elasticity: implications for theory and practice
Authors: Forbes Valery E. , Olsen Mette , Palmqvist Annemette , Calow Peter
Published: June 2010

The relationships between population growth rate and the life‐cycle traits contributing to it are nonlinear and variable. This has made it difficult for ecologists to consistently predict changes in population dynamics from observations on changes in life‐cycle traits. We show that traits having a high sensitivity to chemical toxicants tend to have a low elasticity, meaning that changes in them have a relatively low impact on population growth rate, compared to other life‐cycle traits. This makes evolutionary sense in that there should be selection against variability in population growth rate. In particular, we found that fecundity was generally more sensitive to chemical stress than was juvenile or adult survival or time to first reproduction, whereas fecundity typically had a lower elasticity than the other life‐cycle traits. Similar relationships have been recorded in field populations for a wide range of taxa, but the conclusions were necessarily more tentative because stochastic effects and confounding variables could not be excluded. Better knowledge of these relationships can be used to optimize population management and protection strategies and to increase understanding of the drivers of population dynamics.
Tropical land‐cover change alters biogeochemical inputs to ecosystems in a Mexican montane landscape
Authors: Ponette-González A. G. , Weathers K. C. , Curran L. M.
Published: June 2010

In tropical regions, the effects of land‐cover change on nutrient and pollutant inputs to ecosystems remain poorly documented and may be pronounced, especially in montane areas exposed to elevated atmospheric deposition. We examined atmospheric deposition and canopy interactions of sulfate‐sulfur (SO42−‐S), chloride (Cl−), and nitrate‐nitrogen (NO3−‐N) in three extensive tropical montane land‐cover types: clearings, forest, and coffee agroforest. Bulk and fog deposition to clearings was measured as well as throughfall (water that falls through plant canopies) ion fluxes in seven forest and five coffee sites. Sampling was conducted from 2005 to 2008 across two regions in the Sierra Madre Oriental, Veracruz, Mexico.

Annual throughfall fluxes to forest and coffee sites ranged over 6–27 kg SO42−‐S/ha, 12–69 kg Cl−/ha, and 2–6 kg NO3−‐N/ha. Sulfate‐S in forest and coffee throughfall was higher or similar to bulk S deposition measured in clearings. Throughfall Cl− inputs, however, were consistently higher than Cl− amounts deposited to cleared areas, with net Cl− fluxes enhanced in evergreen coffee relative to semi‐deciduous forest plots. Compared to bulk nitrate‐N deposition, forest and coffee canopies retained 1–4 kg NO3−‐N/ha annually, reducing NO3−‐N inputs to soils. Overall, throughfall fluxes were similar to values reported for Neotropical sites influenced by anthropogenic emissions, while bulk S and N deposition were nine‐ and eightfold greater, respectively, than background wet deposition rates for remote tropical areas.

Our results demonstrate that land‐cover type significantly alters the magnitude and spatial distribution of atmospheric inputs to tropical ecosystems, primarily through canopy‐induced changes in fog and dry deposition. However, we found that land cover interacts with topography and climate in significant ways to produce spatially heterogeneous patterns of anion fluxes, and that these factors can converge to create deposition hotspots. For land managers, this finding suggests that there is potential to identify species and ecosystems at risk of excess and increasing deposition in montane watersheds undergoing rapid transformation. Our data further indicate that montane ecosystems are vulnerable to air pollution impacts in this and similar tropical regions downwind of urban, industrial, and agricultural emission sources.
Restoration through eradication? Removal of an invasive bioengineer restores some habitat function for a native predator
Authors: Holsman Kirstin K. , McDonald P. Sean , Barreyro Pablo A. , Armstrong David A.
Published: June 2010

Invasive aquatic macrophytes increase structural complexity in recipient systems and alter trophic and physical resources; thus, eradication programs that remove plant structure have potential to restore some impaired ecological functions. In this study we evaluate how an invasive ecosystem engineer, Atlantic smooth cordgrass (Spartina alterniflora), interferes with the movement and foraging activity of a mobile predator, Dungeness crab (Cancer magister), and whether removal of aboveground cordgrass structure rapidly reestablishes access to foraging habitats. By 2004, smooth cordgrass had invaded >25% of crab foraging habitat in Willapa Bay, Washington (USA), and transformed it into a highly structured landscape. However, by 2007 successful eradication efforts had eliminated most meadows of the cordgrass. In order to investigate the effect of smooth cordgrass on the habitat function of littoral areas for foraging crabs, we integrated field, laboratory, and statistical modeling approaches. We conducted trapping surveys at multiple sites and used a hierarchical model framework to examine patterns in catches prior to and following cordgrass removal (i.e., before–after control–impact design, BACI). Prior to eradication, catches of Dungeness crabs in unstructured habitats were 4–19 times higher than catches in adjacent patches of live cordgrass. In contrast, the results of post‐eradication trapping in 2007 indicated similar catch rates of crabs in unstructured habitats and areas formerly invaded by the cordgrass. Subsequent laboratory experiments and video observations demonstrated that the rigid physical structure of smooth cordgrass shoots reduces the ability of Dungeness crabs to access prey resources and increases the risk of stranding. Taken together, these findings suggest that eliminating the structural complexity of invasive macrophytes may rapidly restore some ecological function (i.e., foraging area) for migratory predators like Dungeness crab. However, restoration of affected areas to a preinvasion state will also depend on long‐term patterns of succession in invaded areas and the degree of persistence of physical changes that continue to alter biotic characteristics of the habitat. Our work highlights: (1) the efficacy of employing multiple methods of inquiry to evaluate causal relationships through mechanisms of interaction, and (2) the importance of targeting particular ecological functions when identifying both short‐ and long‐term goals of restoration efforts.
Origin of compartmentalization in food webs
Authors: Guimerà R. , Stouffer D. B. , Sales-Pardo M. , Leicht E. A. , Newman M. E. J. , Amaral L. A. N.
Published: June 2010

The response of an ecosystem to perturbations is mediated by both antagonistic and facilitative interactions between species. It is thought that a community's resilience depends crucially on the food web—the network of trophic interactions—and on the food web's degree of compartmentalization. Despite its ecological importance, compartmentalization and the mechanisms that give rise to it remain poorly understood. Here we investigate several definitions of compartments, propose ways to understand the ecological meaning of these definitions, and quantify the degree of compartmentalization of empirical food webs. We find that the compartmentalization observed in empirical food webs can be accounted for solely by the niche organization of species and their diets. By uncovering connections between compartmentalization and species' diet contiguity, our findings help us understand which perturbations can result in fragmentation of the food web and which can lead to catastrophic effects. Additionally, we show that the composition of compartments can be used to address the long‐standing question of what determines the ecological niche of a species.
Maternal influences on population dynamics: evidence from an exploited freshwater fish
Authors: Venturelli Paul A. , Murphy Cheryl A. , Shuter Brian J. , Johnston Thomas A. , van Coeverden de Groot Peter J. , Boag Peter T. , Casselman John M. , Montgomerie Robert , Wiegand Murray D. , Leggett William C.
Published: June 2010

We used a field experiment, population modeling, and an analysis of 30 years of data from walleye (Sander vitreus; a freshwater fish) in Lake Erie to show that maternal influences on offspring survival can affect population dynamics. We first demonstrate experimentally that the survival of juvenile walleye increases with egg size (and, to a lesser degree, female energy reserves). Because egg size in this species tends to increase with maternal age, we then model these maternal influences on offspring survival as a function of maternal age to show that adult age structure can affect the maximum rate at which a population can produce new adults. Consistent with this hypothesis, we present empirical evidence that the maximum reproductive rate of an exploited population of walleye was approximately twice as high when older females were abundant as compared to when they were relatively scarce. Taken together, these results indicate that age‐ or size‐based maternal influences on offspring survival can be an important mechanism driving population dynamics and that exploited populations could benefit from management strategies that protect, rather than target, reproductively valuable individuals.
A genetic basis to community repeatability and stability
Authors: Keith Arthur R. , Bailey Joseph K. , Whitham Thomas G.
Published: June 2010

Recent studies have shown that genetically based traits of plants can structure associated arthropod and microbial communities, but whether the effects are consistent and repeatable across years is unknown. If communities are both heritable (i.e., related individuals tend to support similar communities) and repeatable (i.e., the same patterns observed over multiple years), then plant genetics may also affect community properties previously thought to be emergent, such as “stability.” Using replicated clones of narrowleaf cottonwood (Populus angustifolia) and examining an arthropod community of 103 species, we found that (1) individual tree genotypes supported significantly different arthropod communities, which exhibited broad‐sense heritability; (2) these findings were highly repeatable over three consecutive years (repeatability = 0.91) indicating that community responses to individual tree genotypes are consistent from year to year; (3) differences among tree genotypes in community stability (i.e., changes in community composition over multiple years) exhibited broad‐sense heritability ( = 0.32). In combination, these findings suggest that an emergent property such as stability can be genetically based and thus subject to natural selection.
Mycorrhizal benefit differs among the sexes in a gynodioecious species
Authors: Varga Sandra , Kytöviita Minna-Maarit
Published: June 2010

Both plant sex and arbuscular mycorrhizal (AM) symbiosis influence resource acquisition and allocation in plants, but the interaction between these two components is not well established. As the different plant sexes differ in their resource needs and allocation patterns, it is logical to presume that they might differ in their relationship with AM as well. We investigate whether the association with AM symbiosis is different according to the host plant sex in the gynodioecious Geranium sylvaticum, of which, besides female and hermaphrodite plants, intermediate plants are also recognized. Specifically, we examine the effects of two different AM fungi in plant mass allocation and phosphorus acquisition using a factorial greenhouse/common garden experiment. Cloned G. sylvaticum material was grown in symbiosis with AM fungi or in non‐mycorrhizal condition. We evaluated both the symbiotic plant benefit in terms of plant mass and plant P content and the fungal benefit in terms of AM colonization intensity in the plant roots and spore production. Our results suggest that G. sylvaticum plants benefit from the symbiosis with both AM fungal species tested but that the benefits gained from the symbiosis depend on the sex of the plant and on the trait investigated. Hermaphrodites suffered most from the lack of AM symbiosis as the proportion of flowering plants was dramatically reduced by the absence of AM fungi. However, females and intermediates benefited from the symbiosis relatively more than hermaphrodites in terms of higher P acquisition. The two AM fungal species differed in the amount of resources accumulated, and the fungal benefit was also dependent on the sex of the host plant. This study provides the first evidence of sex‐specific benefits from mycorrhizal symbiosis in a gynodioecious plant species.
Evaluation of restoration effectiveness: community response to the removal of alien plants
Authors: Heleno Ruben , Lacerda InÊs , Ramos Jaime A. , Memmott Jane
Published: June 2010

Plant invasions are a key cause of biodiversity loss and motivate many restoration programs worldwide. We assessed restoration success of an invaded forest in the Azores using two complementary experimental designs: a before–after control–impact (BACI) design compared a restored and a control (unmanipulated) site over three years, while a control–impact (CI) design evaluated the short‐term effects of restoration on restored–control replicated pairs. In both designs, a food web approach was used to evaluate both structural and functional aspects of the restoration. Two years after removing alien plants from the BACI design, there were increases in the abundance of native seeds (110%), herbivorous insects (85%), insect parasitoids (5%), and birds (7%) in the experimental plot compared to the unmanipulated plot. In the CI design, five experimental plots were weeded and paired with five adjacent unmanipulated plots. Immediately following the removal of alien plants within the experimental plots, there was a significant decrease in native plant species, likely attributed to the effect of disturbance. Nevertheless, the production of native seeds increased by 35% in year 1, and seed production of the focal endemic plant, Ilex perado (holly), increased 159% in year 2. Weeding increased the survivorship and growth of seedlings transplanted into the plots, particularly those of alien species. Both experiments provide evidence of the positive effects of weeding cascading through the food web from native plants to herbivorous insects, insect parasitoids, and birds. Two aspects that could prove critical to the outcome of restoration programs deserve further attention: most bird‐dispersed seeds were alien, and weeding favored alien over native seedling growth.
Evidence for ecological matching of whole AM fungal communities to the local plant–soil environment
Authors: Ji Baoming , Bentivenga Stephen P. , Casper Brenda B.
Published: June 2010

The range of ecological roles exhibited by arbuscular mycorrhizal (AM) fungi depends on functional differences among naturally occurring local assemblages of AM species. While functional differences have been demonstrated among AM fungal species and among geographic isolates of the same species, almost nothing is known about functional differences among whole communities of naturally occurring AM fungi. In the greenhouse, we reciprocally transplanted whole AM fungal communities between plant–soil systems representing a serpentine grassland and a tallgrass prairie, using as hosts two grasses common to both systems. For Sorghastrum nutans, native fungi consistently enhanced plant growth more than fungi switched from the alternate system. For Schizachyrium scoparium, foreign and native fungi promoted plant growth similarly in both the serpentine and prairie systems. Thus, the use of foreign inoculum in restoration could change the relative performance, and potentially the competitive abilities, of co‐occurring plant species. Moving AM fungal inocula into foreign environments also caused changes in the taxonomic composition of the resultant spore communities, demonstrating their response to environmental influences. These results provide strong evidence for functional differences among naturally occurring AM communities and suggest that a particular AM fungal community may be better matched ecologically to its local habitat than communities taken from other locations.
Variation in δ13C and δ15N diet–vibrissae trophic discrimination factors in a wild population of California sea otters
Authors: Newsome Seth D. , Bentall Gena B. , Tinker M. Tim , Oftedal Olav T. , Ralls Katherine , Estes James A. , Fogel Marilyn L.
Published: June 2010

The ability to quantify dietary inputs using stable isotope data depends on accurate estimates of isotopic differences between a consumer (c) and its diet (d), commonly referred to as trophic discrimination factors (TDFs) and denoted by Δc‐d. At present, TDFs are available for only a few mammals and are usually derived in captive settings. The magnitude of TDFs and the degree to which they vary in wild populations is unknown. We determined δ13C and δ15N TDFs for vibrissae (i.e., whiskers), a tissue that is rapidly becoming an informative isotopic substrate for ecologists, of a wild population of sea otters for which individual diet has been quantified through extensive observational study. This is one of the very few studies that report TDFs for free‐living wild animals feeding on natural diets. Trophic discrimination factors of 2.2‰ ± 0.7‰ for δ13C and 3.5‰ ± 0.6‰ for δ15N (mean ± SD) were similar to those reported for captive carnivores, and variation in individual δ13C TDFs was negatively but significantly related to sea urchin consumption. This pattern may relate to the lipid‐rich diet consumed by most sea otters in this population and suggests that it may not be appropriate to lipid‐extract prey samples when using the isotopic composition of keratinaceous tissues to examine diet in consumers that frequently consume lipid‐rich foods, such as many marine mammals and seabirds. We suggest that inherent variation in TDFs should be included in isotopically based estimates of trophic level, food chain length, and mixing models used to quantify dietary inputs in wild populations; this practice will further define the capabilities and limitations of isotopic approaches in ecological studies.