Extending the stress‐gradient hypothesis – is competition among animals less common in harsh environments?

BackgroundThe association between the couple relationship and the mothers’ and fathers’ psychological adjustment to the transition to parenthood has been examined in the literature. However, the direction of effects between these variables has not been extensively explored. This study aimed to assess the direction of effects between mothers’ and fathers’ positive and negative interactions and anxiety and depression symptoms trajectories over the transition to parenthood. MethodsA sample of 129 couples (N = 258) completed self-report measures of positive and negative interactions, anxiety and depression symptoms at each trimester of pregnancy, at childbirth, and at 3- and 30-months postpartum. Dyadic growth curve models were performed using multilevel modeling. ResultsWhereas anxiety and depression showed no moderation effect on positive and negative interactions over time, negative interaction moderated depression from 3- to 30-months postpartum. Mothers and fathers with high negative interaction scores experienced a steeper increase in depression from 3- to 30-months postpartum. Additionally, gender moderated the effect of positive interaction on anxiety from 3- to 30-months postpartum. Fathers with low positive interaction scores experienced an increase in anxiety, whereas fathers with high positive interaction scores and mothers with high or low positive interaction scores did not experience changes in anxiety from 3- to 30-months postpartum. LimitationsDespite the longitudinal aspect of the models, a possible causal relationship need to be taken with caution. ConclusionsOur results suggest that mothers’ and fathers’ positive and negative interactions affect their anxiety and depression symptoms trajectories: negative interaction raises mothers’ and fathers’ depression symptoms and positive interaction prevents the increase of fathers’ anxiety symptoms over the postpartum period.

Primary hepatocellular carcinoma (HCC) is highly prevalent in China. Although hepatitis B virus (HBV) and aflatoxin B1 (AFB1) are considered the major risk factors, among the high-risk cohorts only a small fraction develops liver cancer. Therefore, we investigated if organochlorine pesticides (OCPs) exposure contributed to HCC risk in the Xiamen population. The questionnaire database was built from 346 HCC cases and 961 healthy controls during 2007-2009. The serum levels of α-, β-, γ-, δ-HCH, p, p'-DDT, p, p'-DDE, o, p'-DDT and p, p'-DDD were measured by gas chromatography-tandem mass spectrometer and statistical analysis was done using SPSS16. Significantly, we observed p, p'-DDT, p, p'-DDE, and at first time β-HCH displayed quartile dose-dependent HCC risk trends; p, p'-DDT showed positive (i.e., synergistic) interactions with HBV, diabetes mellitus, AFB1 and polycyclic aromatic hydrocarbon (PAH) exposure, but negative (i.e., antagonistic) interaction with heavy drinking; p, p'-DDE had positive interaction with PAH but negative interaction with HBV and p, p'-DDT; and β-HCH was positively interacted with p, p'-DDT but negatively interacted with heavy drinking and diabetes. p, p'-DDT, p, p'-DDE and β-HCH were independent HCC risk factors. Because of their synergistic interactions with other factors, the high level exposure combined with common AFB1 and HBV exposure in the investigated area may greatly enhance the risk of HCC.

ObjectiveTo understand whether 15‐year‐old adolescents' reports of positive and negative interactions in their romantic relationships are associated with their depressive symptoms and externalizing behavior.BackgroundTo ensure that relationship education programs comprehensively address adolescent romantic development, there is a need for research focused on relationship dynamics during adolescence. In particular, there is a paucity of research on the associations between romantic relationship quality and adolescent adjustment.MethodData were from adolescents in romantic relationships during the fourth wave of the NICHD Study of Early Child Care and Youth Development (N = 205). Adolescents reported the positive and negative interactions in their romantic relationships, depressive symptoms, and externalizing behavior.ResultsNegative interactions were positively associated with depressive symptoms and externalizing behavior. Positive interactions were not associated with adolescent adjustment but did moderate the associations between negative interactions and depressive symptoms. Specifically, and unexpectedly, positive interactions exacerbated the association between high (+1 SD) negative interactions and depressive symptoms.ConclusionAdolescents in romantic relationships may be at risk for depressive symptoms and externalizing behavior when they experience negative interactions with romantic partners. They do not, however, appear to benefit from positive interactions.ImplicationsA primary goal of adolescent‐specific relationship education should be to minimize negative interactions between romantic partners.

When immigrant minority individuals engage in frequent and positive social contact with majority culture members, their emotions become a better fit with the majority norm; the increased fit is called emotional acculturation. In the current research, we test the prediction that high-quality interactions with majority others, in which minorities feel accepted, increase the likelihood of emotional fit. We also explore whether this prediction holds true for both positive and negative interactions with majority. To test this prediction, we conducted a 7-day daily diary study with minority students in Belgian middle schools (N = 117). Each day, participants reported one positive and one negative interaction at school. They subsequently evaluated each interaction (e.g., felt accepted), assessed their relationship with the interaction partner (e.g., our relationship is important to me), and rated their emotions. Analyses focused on the interactions with Belgian majority interaction partners. Emotional acculturation was computed for positive and negative interactions separately, by calculating the fit between the emotional pattern of the minority student and the average emotional pattern of a sample of majority participants (N = 106) who also took part in the daily diary. As predicted, we found higher emotional fit in positive interactions when immigrant minorities felt accepted by the interaction partner. In contrast to this finding for positive interactions, emotional fit for negative interactions was higher when minorities felt excluded by the interaction partner. Further analyses on the negative interactions suggested that minority adolescents felt more negative autonomy-promoting emotions (e.g., anger and frustration) when they perceived being excluded. Given that Belgian majority youth feel more autonomy-promoting emotions generally, minorities’ fit with majority patterns was higher. The results confirm our hypothesis that minorities’ fit with majority emotions is contingent on the quality of their interactions with majority, even if in negative interactions, high-quality interactions produced less rather than more emotional fit. Our findings suggest that emotional acculturation is not just a ‘skill’ that minority individuals acquire, but also a response to the ways in which interactions with majority others develop. Inclusive interactions, especially when they are positive, appear to align immigrant minority individuals with the majority norm.

Plant facilitation is now recognized as an important process in severe environments. However, there is still no agreement on how facilitation changes as conditions become increasingly severe. The classic stress gradient hypothesis (SGH) predicts a monotonic increase in facilitation, which rises in frequency as conditions approach the extreme end of the environmental gradient. However, few studies have evaluated the validity of the SGH at the community level, the level at which it was formulated. Moreover, few studies have tested the SGH at either extreme of the gradient, and very few have excluded the effect of livestock on community response to stress. In line with the SGH, we hypothesized that several spatial pattern summary statistics would change monotonically from the least to the most arid sites, indicating increasingly aggregated patterns. In this study, we performed an evaluation of the SGH both within communities of shrub species and across a large portion of the Atacama Desert, and we isolated the abiotic component of the SGH. Our environmental gradient covered an extreme aridity gradient (< 20-130 mm annual precipitation). To perform point pattern analysis, we established 13 sites with environmental conditions representing four distinct levels of this gradient. Further, we conducted species co-occurrence analyses at 19 sites along the gradient. Both sets of analyses showed stronger positive spatial associations among plants at the most extreme end of the gradient. This was true regardless of whether we included all individuals, only small individuals located around large ones, or individuals in species pairs. Moreover, species tended to show greater co-occurrence as environmental severity increased. This increase in aggregation in the plant community seems to correlate with an increase in the strength of positive interspecific interactions, rather than greater clustering within each species. These monotonic increases in species co-occurrence and spatial association in more severe environments are consistent with some of the predictions of SGH, and collectively these results suggest that as the climate becomes more arid, positive species pairs interactions tend to be prevalent in the community.

Contents: 1 Introduction: 2 Direct mechanisms for facilitation: 2.1 Water relations: hydraulic lift.- 2.2 Water relations: canopy interception.- 2.3 Shade.- 2.4 Water relations: soil moisture.- 2.5 Nutrients.- 2.6 Wind.- 2.7 Soil oxygenation.- 2.8 Substrate.- 2.9 Disturbance.- 2.10 Population size and positive density dependence.- 2.11 Seed shadows.- 2.12 Communication.- 2.13 Conclusion.- 3 Indirect interactions: 3.1 Herbivore-mediated facilitation.- 3.2 Other herbivore-mediated positive effects.- 3.3 Reproductive feedback, pollinators, and population size.- 3.4 Dispersers.- 3.5 Mycorrhizae.- 3.6 Plant-soil microbe feedbacks.- 3.7 Positive interactions among competing plants.- 3.8 Conclusion.- 4 Interaction between competition and facilitation: 4.1 Competition, facilitation and abiotic stress.- 4.2 Spatial scales, time scales and the balance of facilitation and competition on stress gradients.- 4.3 Facilitation and stress: importance versus intensity.-4.4 Facilitation and life history stage.- 4.5 Competitive advantages provided by benefactors.- 4.6 Indirect effects and the balance of competition and facilitation.- 4.7 Pollution and shifts in facilitation and competition.- 4.8 Conclusion.- 5 Species-specific positive interactions: 5.1 Are beneficiary species non-randomly associated with potential benefactors? .-5.2 What Mechanisms cause species-specific facilitation?.- 6 Positive interactions and community organization: 6.1 Positive interactions and the expansion of niche space.- 6.2 Positive interactions and the role of diversity in community function.- 6.3 Positive interactions and spatial scale.- 6.4 Positive interactions and stability in plant.- 6.5 Facilitation and productivity.- 6.6 Positive interactions and exotic invasion.- 6.7 Facilitation and conservation.- 6.8 Facilitation and evolution in plant communities.- 6.9 Replacing the notion of individualistic communities with the 'integrated community.- 6.10 Conclusions.- References.- Index

ABSTRACTThe current study aimed to examine the associations between teacher presence and social scaffolding and preschool children’s peer interactions. Using a time sampling method, peer interactions of 22 four- and five-year-old preschoolers (12 girls; Mage = 52.95 months) and teacher behavior were observed on two different days during various classroom activities in seven public preschool classrooms. Eco-behavioral analyses revealed that (a) teacher presence was negatively associated with positive peer interactions; (b) teacher absence was positively associated with negative peer interactions; (c) positive change of peer interactions was more likely to occur when the teacher was present; (d) children showed more positive peer interactions during child-directed activities than during adult-directed activities or daily routines and transitions; and (e) teacher’s social scaffolding was positively associated with children’s positive peer interactions although it occurred only for 3.61% of the intervals during which the teacher was in close proximity to children. In addition, although the likelihood for children’s positive interaction was over 2 times higher in child-directed activities in comparison to adult-directed activities, teacher presence still seems very important for inhibiting negative peer interactions.

Theories to explain the diversity of species have required that individual species occupy unique niches and/or vary in their response to environmental factors. Positive interactions within a species, although common in communities, have not been thought to maintain species diversity because in non-spatial models the more abundant species always outcompetes the rarer species. Here, we show, using a stochastic spatial model, that positive intraspecific interactions such as those caused by positive frequency dependence and/or priority effects, can maintain species diversity if interactions between individuals are primarily local and the habitat contains areas that cannot be colonized by any species, such as boulders or other physical obstructions. When intraspecific interactions are primarily neutral, species diversity will eventually erode to a single species. When the landscape is homogeneous (i.e. does not contain areas that cannot be colonized by any species), the presence of strong intraspecific interactions will not maintain diversity.

Summary 1. An unresolved question in plant ecology is how the balance between positive and negative interactions changes with environmental conditions. Recently, the debate has been expanded by Brooker &amp; Kikvidze (2008), reintroducing the importance, rather than the intensity, of interactions as the appropriate concept for empirical studies. Importance is the difference in performance with interactions relative to all affecting factors. 2. Positive interactions among plants (facilitation) are common in nature. However, the advocated importance indices fail to address facilitation and can thus not be applied to studying shifts in the balance between positive and negative interactions. The deficiencies of the current importance indices are both conceptual as well as mathematical. In particular, their maximum performance estimator is based on the assumption that it can only be attained in the absence of neighbours. 3. We suggest two major improvements. First, we use the target’s overall maximum performance as a surrogate for the plant optimum, i.e. we allow the possibility of higher performance with neighbours (i.e. facilitation). Second, we propose an alternative approach to treat the factors affecting measured performance. The new index is limited in its range [−1, 1], is symmetrical for competition and facilitation, and it preserves the intuitive nature of the original index by Brooker &amp; Kikvidze (2008). 4. Synthesis. The concept of interaction importance is useful for studying interactions along environmental gradients. In contrast to previous indices, our index accommodates facilitative interactions and thus offers a significant conceptual and methodological advancement. We advocate its use in future empirical studies.

Positive interactions are sensitive to human activities, necessitating synthetic approaches to elucidate broad patterns and predict future changes if these interactions are altered or lost. General understanding of freshwater positive interactions has been far outpaced by knowledge of these important relationships in terrestrial and marine ecosystems. We conducted a global meta-analysis to evaluate the magnitude of positive interactions across freshwater habitats. In 340 studies, we found substantial positive effects, with facilitators increasing beneficiaries by, on average, 81% across all taxa and response variables. Mollusks in particular were commonly studied as both facilitators and beneficiaries. Amphibians were one group benefiting the most from positive interactions, yet few studies investigated amphibians. Invasive facilitators had stronger positive effects on beneficiaries than non-invasive facilitators. We compared positive effects between high- and low-stress conditions and found no difference in the magnitude of benefit in the subset of studies that manipulated stressors. Future areas of research include understudied facilitators and beneficiaries, the stress gradient hypothesis, patterns across space or time and the influence of declining taxa whose elimination would jeopardise fragile positive interaction networks. Freshwater positive interactions occur among a wide range of taxa, influence populations, communities and ecosystem processes and deserve further exploration.

This meta-analysis examines patterns of sex differences in teacher-initiated teacher–student interactions. While extensive research has examined factors that influence student evaluations of effective and ineffective teachers, this study examines whether teacher-initiated interactions with students, such as praising or blaming, vary as a function of student sex. After a careful examination of 127 empirical studies, 32 studies were retained for the meta-analysis. The studies were coded for positive, negative, and total interactions. The results suggest that teachers initiate more overall interactions and more negative interactions, but not more positive interactions, with male students than with female students.

Interspecies interactions have a profound influence on spatial distribution of coexisting microbial species. We explored whether spatial variance of species distribution (SVSD) predicts the degree of interspecies interactions within a microbial metacommunity. Simulations were used to determine the relationships from random, lake, soil, and biofilm metacommunity datasets (1,000 times). All of the bacterial datasets showed a negative correlation between the habitat breadth (inverse to SVSD) and the numbers of total, positive, and negative interspecies interactions (P < 0.05); the only exception was the relationship between habitat breadth and negative interactions in the biofilm dataset. The random dataset had no significant relationships (P > 0.05). We repeated the simulations to determine the degree of correlation and reproducibility (100 times). Habitat breadth was negatively correlated with the total and positive interactions in all of the real datasets (P < 0.05), and the negative relationships persisted across repetitions. Despite variability in the slope of total interactions, the slope values of positive interactions were similar for the real datasets (- 19.9, - 19.2, and - 25.8 for lake, soil, and biofilm, respectively). In conclusion, our results demonstrate the patterns of species interaction-distribution and show that interspecies interactions are positively correlated with the SVSD.

Positive and negative interactions in the behavioural expression of d 1 and D 2 receptor stimulation in a model of parkinsonism: Role of priming

The relationship between niche and distribution, and especially the role of biotic interactions in shaping species' geographic distributions, has gained increasing interest in the last two decades. Most ecological research has focused on negative species interactions, especially competition, predation and parasitism. Yet the relevance of positive interactions – mutualisms and commensalisms – have been brought to the fore in recent years by an increasing number of empirical studies exploring their impact on range limits. Based on a review of 73 studies from a Web of Science search, we found strong evidence that positive interactions can influence the extent of species' geographic or ecological ranges through a diversity of mechanisms. More specifically, we found that while obligate interactions, and especially obligate mutualisms, tend to constrain the ranges of one or both partners, facultative positive interactions tend to widen ranges. Nonetheless, there was more variation in effects of facultative interactions on range limits, pointing to important context‐dependencies. Therefore, we propose that conceptual development in this field will come from studying ecological interactions in the context of networks of many species across environmental gradients, since pairwise interactions alone might overlook the indirect and environmentally‐contingent effects that species have on each other in communities of many interacting species. Finally, our study also revealed key data gaps that limit our current understanding of the pervasiveness of effects that positive interactions have on species' ranges, highlighting potential avenues for future theoretical and experimental work.

Neuroticism modulates the effects of intranasal vasopressin treatment on the neural response to positive and negative social interactions