bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differences between symmetric and asymmetric facilitation matter: exploring the interplay between modes of positive and negative plant interactions
Authors: Lin Yue , Berger Uta , Grimm Volker , Ji Qian‐Ru 
Published: May 2013

Summary
Facilitation (positive interaction) has received increasing attention in plant ecology over the last decade. Just as for competition, distinguishing different modes of facilitation (mutualistic, commensal or even antagonistic) may be crucial.
We therefore introduce the new concept of symmetric versus asymmetric facilitation and present a generic individual‐based zone‐of‐influence model. The model simultaneously implements different modes of both facilitation and competition among individual plants via their overlapping zone of influence. Because we consider facilitation modes as a continuum related to environmental context, we integrated this concept with the stress‐gradient hypothesis (SGH) by exploring differences in spatial pattern formation in self‐thinning plants along a stress gradient in our model.
The interplay among modes of interaction creates distinctly varied spatial patterns along stress gradients. When competition was symmetric, symmetric facilitation (mutualism) consistently led to plant aggregation along stress gradients. However, asymmetric facilitation (commensalism) produces plant aggregation only under more benign conditions but tends to intensify local competition and spatial segregation when conditions are harsh. When competition was completely asymmetric, different modes of facilitation contributed little to spatial aggregation.
Symmetric facilitation significantly increased survival at the severe end of the stress gradient, which supports the claim of the SGH that facilitation should have generally positive net effects on plants under high stress levels. Asymmetric facilitation, however, was found to increase survival only under intermediate stress conditions, which contradicts the current predictions of the SGH.
Synthesis. Our modelling study demonstrates that the interplay between modes of facilitation and competition affects different aspects of plant populations and communities, implying context‐dependent outcomes and consequences. The explicit consideration of the modes and mechanisms of interactions (both facilitation and competition) and the nature of stress factors will help to extend the framework of the SGH and foster research on facilitation in plant ecology.
Direct and productivity‐mediated indirect effects of fertilization, mowing and grazing on grassland species richness
Authors: Socher Stephanie A. , Prati Daniel , Boch Steffen , Müller Jörg , Klaus Valentin H. , Hölzel Norbert , Fischer Markus 
Published: May 2013

Summary

Recent declines in biodiversity have given new urgency to questions about the relationship between land‐use change, biodiversity and ecosystem processes. Despite the existence of a large body of research on the effects of land use on species richness, it is unclear whether the effects of land use on species richness are principally direct or indirect, mediated by concomitant changes in ecosystem processes. Therefore, we compared the direct effects of land use (fertilization, mowing and grazing) on species richness with indirect ones (mediated via grassland productivity) for grasslands in central Europe.

We measured the richness and above‐ground biomass in 150 grassland plots in 3 regions of Germany (the so‐called Biodiversity Exploratories). We used univariate and structural equation models to examine direct and indirect land‐use effects.

The direct effects of mowing (−0.37, effect size) and grazing (0.04) intensity on species richness were stronger compared with the indirect effects of mowing (−0.04) and grazing (−0.01). However, the strong negative effect of fertilization (−0.23) on species richness was mainly indirect, mediated by increased productivity compared with the weak direct negative effect (−0.07).

Differences between regions in land‐use effects showed five times weaker negative effects of mowing (−0.13) in the region with organic soils (Schorfheide‐Chorin), strong overall negative effects of grazing (−0.29) for the region with organic soils opposed to a similar strong positive effect (0.30) in the Hainich‐Dün region, whereas the Schwäbische Alb region displayed a five times weaker positive effect (0.06) only. Further, fertilization effects on species richness were positive (0.03) for the region with organic soils compared to up to 25 times stronger negative effects in the other two regions.

Synthesis. Our results clearly show the importance of studying both direct and indirect effects of land‐use intensity. They demonstrate the indirect nature, via productivity, of the negative effect of fertilization intensity on plant species richness in the real‐world context of management‐induced gradients of intensity of fertilization, mowing and grazing. Finally, they highlight that careful consideration of regional environments is necessary before attempting to generalize land‐use effects on species diversity.
Pollination linkage between canopy flowering, bumble bee abundance and seed production of understorey plants in a cool temperate forest
Authors: Inari Naoki , Hiura Tsutom , Toda Masanori J. , Kudo Gaku 
Published: May 2013

Summary

In forest ecosystems, canopy trees provide a large amount of floral resources for pollinators but flower production fluctuates highly from year to year. Temporal variation in floral resources may influence the population dynamics of pollinators.
We investigated the relationship between the population dynamics of bumble bees (Bombus spp.) and canopy floral resources over 5 years in a cool temperate forest. We predicted that the yearly fluctuation of canopy resources affects colony development and queen production, resulting in the variation of the pollination success of understorey plants the following spring.
Flower production of canopy trees showed clear biyearly fluctuations, synchronously among most species. Worker production of Bombus ardens and Bombus hypocrita were positively related to floral resources during colony establishment by overwintered queens, while that of Bombus diversus was positively related to floral resources during the worker‐active period.
An abundance of overwintered queens was positively related to both worker abundance and floral resources in the previous summer in B. ardens and to only previous‐year worker abundance in B. hypocrita but was dependent on neither factor in B. diversus. These differences in causal effects on queen production among species might be a reflection of interspecific differences in the degree of dependence on canopy resources for queen production due to species‐specific phenologies and/or foraging preferences of other species of flowers.
The extent of pollen limitation in the spring‐ephemeral Corydalis ambigua, which is exclusively pollinated by overwintered queens, was negatively correlated with the abundance of B. hypocrita queens. Thus, population dynamics of bumble bees has a crucial effect on seed production of understorey plants.
Synthesis. The dynamics of flower production in overstory trees can indirectly affect the pollination efficiency of understorey plants in the next season via the population dynamics of pollinators. Our results suggest that a cascade effect occurs through pollination networks in a cool temperate forest ecosystem.
Biotic resistance: exclusion of native rodent consumers releases populations of a weak invader
Authors: Pearson Dean E. , Potter Teal , Maron John L. 
Published: May 2013

Summary

Biotic resistance is a commonly invoked hypothesis to explain why most exotic plant species naturalize at low abundance. Although numerous studies have documented negative impacts of native consumers on exotic plant performance, longer‐term multi‐generation studies are needed to understand how native consumer damage to exotics translates to their population‐level suppression over large landscapes.
We used rodent exclosures and embedded seed‐addition experiments to evaluate the effects of rodent herbivory and granivory on populations of Tragopogon dubius, a Eurasian aster that typically occurs at low abundance across North America.
Vegetation surveys encompassing 20 000 km2 of west‐central Montana grasslands established that T. dubius is regionally well distributed, occurring in 81% of 16 grasslands sampled. However, it consistently occurred at low local abundance, averaging < 0.5% cover in 1 m2 plots.
In large rodent exclosures, T. dubius attained population densities that averaged over five times higher than in paired rodent‐access control plots at 11 grassland sites spread over 750 km2. This pattern was six times stronger in older compared with newer rodent exclosures, indicating enclosed populations were still increasing. Floral herbivory, which reduces or prevents reproduction in this biennial plant, decreased by 99% in rodent exclosures compared with control plots. Additionally, seedling establishment was nearly eight times higher in seed‐addition subplots within versus outside of rodent exclosures.
Synthesis. Our findings illustrate how biotic resistance from granivory and florivory of native generalist rodents can provide an important ecosystem service by strongly limiting the local abundance of a widely distributed exotic weed.
Which traits determine shifts in the abundance of tree species in a fire‐prone savanna?
Authors: Higgins Steven I. , Bond William J. , Combrink Henri , Craine Joseph M. , February Edmund C. , Govender Navashni , Lannas Kathryn , Moncreiff Glenn , Trollope Winston S. W. 
Published: May 2013

Summary

Fire is a process that shapes the structure and composition of vegetation in many regions. Species in these regions have presumably evolved life‐history strategies that allow success in fire‐prone environments.

In this study, we examine the extent to which the ecological success of savanna trees is determined by traits that enhance the capacity to tolerate fire and/or traits indicative of an ecophysiological capacity for rapid growth. We define ecological success as the relative change in stem density over the course of a long‐term (circa 40 year) fire experiment conducted in the Kruger National Park, South Africa.

We first examine the extent to which differences in the capacity of trees to tolerate fire can be explained by allometries describing bark traits and tree size. We then examine whether these differences in fire tolerance traits can explain observed shifts in abundance.

We show that species differ in their topkill responses (probability of above‐ground mortality) and that these differences are explained in part by differences in bark moisture content and the allometry between height and diameter. Contrary to previous studies, we find no evidence that bark thickness is important in explaining susceptibility to topkill.

Synthesis. Fire tolerance traits did explain a significant component of the variance in observed shifts in the abundance of tree species. However, traits related to the carbon economy of photosynthesis were also important.
One‐sided competition for light promotes coexistence of forest trees that share the same adult height
Authors: Kohyama Takashi S. , Takada Takenori 
Published: May 2013

Summary
Coexistence of tree species is usually explained in relation to horizontal heterogeneity of forests caused by disturbance. In contrast, it remains unknown whether one‐sided competition for light in vertically structured forests contributes to stable coexistence of tree species that share the same adult height, even without horizontal heterogeneity. And if so, it is needed to specify the conditions of stable coexistence in terms of demographic and allometric traits between species. To answer these questions, we employ a theoretical model that describes dynamics of tree populations in forests of which vertical structure is expediently divided by height classes.
We carry out analytical examination for a forest with two height classes where tree populations are adult in canopy and juvenile in understorey. Demographic processes in the canopy are regulated by foliage density in the canopy, whereas juvenile survival is suppressed by overall foliage density in both classes.
A between‐species difference in juvenile/adult ratio of foliage density is required for coexistence equilibrium of two species to exist. The difference in juvenile/adult ratio in equilibrium is determined by demographic and allometric parameters of species.
Trade‐offs between demographic parameters are necessary for a coexistence equilibrium which is either stable or unstable. A species with high fecundity and/or shade‐free juvenile survival can stably coexist with a species with high shade‐free growth rate and/or adult survival, whereas it cannot stably coexist with a species with high shade tolerance in growth rate and/or in adult survival. Difference in shade tolerance in juvenile survival does not contribute to stable coexistence. Height‐foliage allometry contributes only additionally to enhance coexistence equilibrium.
When we divide forests into three height classes, up to three species can coexist, by means of demographic trade‐offs that bring about interspecific differentiation in vertical foliage distribution. We show all possible cases of coexistence among canopy (C), subcanopy (S) and understorey (U) species in terms of maximum adult height as follows: CCC, CCS, CCU, CSS and CSU.
Synthesis. Our theoretical model shows that demographic trade‐offs among tree species with identical demographic responses to shade promotes stable coexistence through vertical foliage partitioning. This mechanism works independently of the coexistence mechanism through horizontal partitioning of patch mosaic, which is associated with interspecific difference in shade tolerance.
Methicillin‐Resistant Staphylococcal Contamination of Clothing Worn by Personnel in a Veterinary Teaching Hospital
Authors: Singh Ameet , Walker Meagan , Rousseau Joyce , Monteith Gabrielle J. , Weese Jeffrey Scott 
Published: May 2013

AbstractObjectiveTo determine the methicillin‐resistant Staphylococcus aureus (MRSA) and methicillin‐resistant Staphylococcus pseudintermedius (MRSP) contamination rate of white coats (WC) and surgical scrubs (SS) worn by personnel at the Ontario Veterinary College Health Sciences Centre (OVCHSC) and to identify risk factors associated with clothing contamination.Study DesignCross‐sectional study.Sample PopulationPersonnel including clinical faculty, house officers, technicians, and veterinary students working at the OVCHSC.MethodsElectrostatic cloths were used to sample WC and SS of hospital personnel. Samples were tested for MRSA and MRSP and isolates were typed. Participants completed a self‐administered questionnaire and data was evaluated for risk factors.ResultsOf 114 specimens, MRS were isolated from 20 (17.5%), MRSA from 4 (3.5%), and MRSP from 16 (14.0%). Technicians were 9.5× (OR = 0.95, 95% CI: 1.2–∞, P = .03) more likely than students to have clothing contaminated with MRSA. No risk factors were identified for MRSP or for overall MRS contamination.ConclusionsStandard hospital clothing was found to have a high prevalence of MRS contamination in a veterinary teaching hospital and could be a source of hospital‐acquired infections.
Are Toleration and Respect Compatible?
Authors: Carter Ian 
Published: May 2013

AbstractToleration and respect are often thought of as compatible, and indeed complementary, liberal democratic ideals. However, it has sometimes been said that toleration is disrespectful, because it necessarily involves a negative evaluation of the object of toleration. This article shows how toleration and respect are compatible as long as ‘respect’ is taken to mean (what some moral philosophers have called) recognition respect, as opposed to appraisal respect. But it also argues that recognition respect itself rules out certain kinds of evaluation of persons, and with these, certain bases for toleration: if recognition respect is really distinct from appraisal respect, and if the fundamental rights assigned to people on the basis of recognition respect are to be equal rights, then recognition respect must itself involve a refusal to evaluate certain basic agential capacities of persons when deliberating about how to treat them. Even where ‘respect’ means recognition respect, then, there is some truth both in the thesis that toleration and respect are compatible, and in the thesis that they are incompatible. The different truths in these two theses help to shed light on the nature of toleration considered specifically as a liberal democratic virtue. This point can be illustrated by showing how the foregoing analysis provides a plausible solution to the so‐called ‘paradox of the tolerant racist’.
To confront or not to confront: non‐targets' evaluations of and responses to racist comments
Authors: Dickter Cheryl L. , Newton Virginia A. 
Published: May 2013

AbstractThe current studies explore situational and individual factors affecting non‐target perceivers' reactions and behavior following a racist comment, focusing on verbal confronting behavior. Two studies were conducted in which participants reported about recent situations in which they witnessed a racist comment that was not directed specifically at their own racial group. Results indicated that only one third of participants directly confronted the commenter. Strength of verbal confrontation was predicted by affective reactions and judgments of the offensiveness of the prejudicial comment. Analyses also revealed that strength of confrontation for females was predicted by the experience of negative emotions, but that males confronted more with stronger ratings of the offensiveness of the racist remarks. Implications for theory and policy are discussed.
Conformity and counter‐conformity to anti‐discrimination norms: the moderating effect of attitude toward foreigners and perceived in‐group threat
Authors: Falomir‐Pichastor Juan Manuel , Chatard Armand , Selimbegovic Leila , Konan Paul N'Dri , Mugny Gabriel 
Published: May 2013

AbstractTwo studies examined the influence of an anti‐discrimination norm on Swiss nationals' discrimination against foreigners as a function of initial attitude (pro‐foreigner vs. anti‐foreigner) and in‐group threat (i.e., whether or not foreigners are perceived as taking nationals' jobs). Results showed that anti‐foreigners decreased their level of discrimination (i.e., a conformity effect) when threat was low, but did not change (Study 1) or increased discrimination (i.e., a counter‐conformity effect) when threat was high (Study 2). No significant effects were observed for pro‐foreigners. It is argued that conformity to anti‐discrimination norms increases as the individual–norm discrepancy increases, insofar as the social context provides legitimacy to this norm (i.e., low in‐group threat conditions).
A time to make (and lose) friends: effects of soccer tournaments on German adolescents' attitudes toward foreigners
Authors: Gniewosz Burkhard , Noack Peter , Kessler Thomas , Eckstein Katharina 
Published: May 2013

AbstractThe present research examined the effects of one's national sports team defeats in international competitions on adolescents' out‐group attitudes and the moderation of these effects by in‐group identification. We conducted two longitudinal studies surveying German adolescents (Soccer World Championship 2006 and European Championship 2008). Both studies showed deterioration in adolescents' evaluations of people from the countries whose soccer teams defeated the German team (Italy and Spain). There was no generalization to other national groups. The deterioration in out‐group evaluations was shown to be more pronounced for adolescents reporting a high in‐group identification. The results are discussed in terms of macro‐societal effects on adolescents' attitude development and the function that intergroup bias serves for social identity.
Discontinuous gas exchange exhibition is a heritable trait in speckled cockroaches Nauphoeta cinerea
Authors: Schimpf N. G. , Matthews P. G. D. , White C. R. 
Published: May 2013

AbstractThe regulation of insect respiratory gas exchange has long been an area of interest. In particular, the reason why insects from at least five orders exhibit patterns of gas exchange that include regular periods of spiracular closure has been the source of much controversy. Three adaptive hypotheses propose that these discontinuous gas‐exchange cycles (DGCs) evolved to either limit water loss across respiratory surfaces, facilitate gas exchange in underground environments or to limit oxidative damage. It is possible that DGCs evolved independently multiple times and for different reasons, but for DGCs to be a plausible target for natural selection, they must be heritable and confer a fitness benefit. In a previous study of cockroaches Nauphoeta cinerea, we demonstrated that DGCs are repeatable and extend survival under food and water restriction. Here, we show for the first time that DGCs are heritable, suggesting that they are a plausible target for natural selection.
Genetic drift or natural selection? Hybridization and asymmetric mitochondrial introgression in twoCaribbean lizards (Anolis pulchellusandAnolis krugi)
Authors: Jezkova T. , Leal M. , Rodríguez‐Robles J. A. 
Published: May 2013

AbstractHybridization and gene introgression can occur frequently between closely related taxa, but appear to be rare phenomena among members of the species‐rich West Indian radiation ofAnolislizards. We investigated the pattern and possible mechanism of introgression between two sister species from Puerto Rico,Anolis pulchellusandAnolis krugi,using mitochondrial (ND2) and nuclear (DNAH3,NKTR)DNAsequences. Our findings demonstrated extensive introgression ofA. krugimtDNA(k‐mtDNA) into the genome ofA. pulchellusin western Puerto Rico, to the extent thatk‐mtDNAhas mostly or completely replaced the native mtDNAofA. pulchelluson this part of the island. We proposed two not mutually exclusive scenarios to account for the interspecific matings betweenA. pulchellusandA. krugi. We inferred that hybridization events occurred independently in several populations, and determined thatk‐mtDNAhaplotypes harboured in individuals ofA. pulchelluscan be assigned to four of the five major mtDNAclades ofA. krugi. Further, the spatial distribution ofk‐mtDNAclades in the two species is largely congruent. Based on this evidence, we concluded that natural selection was the probable driving mechanism for the extensivek‐mtDNAintrogression intoA. pulchellus. Our two nuclear data sets yielded different results.DNAH3 showed reciprocal monophyly ofA. pulchellusandA. krugi, indicating no effect of hybridization on this marker. In contrast, the two species shared nineNKTRalleles, probably due to incomplete lineage sorting. Our study system will provide an excellent opportunity to experimentally assess the behavioural and ecological mechanisms that can lead to hybridization in closely related taxa.