Combined Grazing and Drought Stress Alter the Outcome of Nurse: Beneficiary Interactions in a Semi-arid Ecosystem

Positive interspecific plant–plant interactions in (semi-)arid ecosystems are crucial for supporting ecosystem diversity and stability, but how interactions respond to grazing combined with temporal variation in drought is poorly understood. In a semi-arid area in south-eastern Spain (Murcia region), we planted 1280 saplings of the palatable shrub Anthyllis cytisoides (beneficiary) under the canopy of the unpalatable shrub Artemisia herba-alba (nurse) or in open microsites between shrub patches. We applied four grazing treatments (no grazing, low goat grazing pressure, high goat grazing pressure and rabbit grazing) and two watering treatments. Sapling height and survival were followed for two consecutive years, during which one extreme drought event occurred. We analysed how grazing, watering and their combination affected nurse effects throughout the course of the study. Grazing and the drought event, but not watering, significantly altered the nurse effects. Under ungrazed conditions prior to the extreme drought event, nurse effects on sapling survival were neutral, whereas they were positive at rabbit-grazed plots. At low goat grazing, sapling growth was higher under nurse shrubs than in open microsites. However, after the extreme drought event, sapling survival was higher in open microsites at ungrazed plots, whereas at rabbit-grazed plots, nurse effects shifted from positive to neutral. Our findings highlight the importance of rabbit grazing in determining the direction of plant–plant interactions in arid ecosystems. Moreover, our findings support the idea that positive plant–plant interactions may wane under the combination of high grazing and drought stress.This study has been supported by a NWO—ALW Open Program Grant (Netherlands Science Foundation— Earth and Life Sciences, project number 820.01.020), the projects CASCADE (Grant Agreement 283068) funded by the Seventh Framework Programme FP7/2007e2013 and FEEDBACK (Grant #CGL2011-30515- C02-01) and DRYEX (Grant #CGL2014-59074-R) funded by the Spanish Ministry of Economy and Competitiveness

Non-Standard Errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty: Non-standard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for better reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants

Binding the Smart City Human-Digital System with Communicative Processes

This chapter will explore the dynamics of power underpinning ethical issues within smart cities via a new paradigm derived from Systems Theory. The smart city is an expression of technology as a socio-technical system. The vision of the smart city contains a deep fusion of many different technical systems into a single integrated “ambient intelligence”. ETICA Project, 2010, p. 102). Citizens of the smart city will not experience a succession of different technologies, but a single intelligent and responsive environment through which they move. Analysis of such an environment requires a framework which transcends traditional ontologically-based models in order to accommodate this deep fusion. This chapter will outline a framework based on Latour’s Actor-Network Theory and Luhmann’s treatment of society as an autopoetic system. We shall use this framework to map the influence of relevant factors on ethical issues, irrespective of their composition or type. For example, under this treatment, both human praxis and technical design can be viewed as comparable tools of domination. This chapter will provide a framework for the analysis of relations between any elements of the smart city, ranging from top-level urban management processes down to individual device operations. While we will illustrate the use of this schema through examination of ethical issues arising from power dynamics within the smart city, it is intended that this example will demonstrate the wider utility of the model in general

Non-standard errors

In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence generating process (EGP). We claim that EGP variation across researchers adds uncertainty: Non-standard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for better reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants

Employee well-being, firm leverage and bankruptcy risk

Employees of liquidating firms are likely to lose income and non-pecuniary benefits of working for the firm, which makes bankruptcy costly for employees. This paper examines whether firms take these costs into account when deciding on the optimal amount of leverage. We find that firms with leading track records in employee well-being significantly reduce the probability of bankruptcy by operating with lower debt ratios. Moreover, we observe that firms with better employee track records have better credit ratings, even when we control for differences in firm leverage

Asymptotic evaluation of blocking probabilities in a hierarchical cellular mobile network.

This paper investigates blocking probabilities obtained from multidimensional truncated Poisson distributions. For blocking probabilities typically arising in layered cellular mobile communications networks, the large deviations results of Gazdzicki et al. [9] are extended to state spaces determined by multiple constraints. The results yield asymptotically exact expressions that provide an accurate approximation of probabilities up to 1%, which considerably extends the applicability of large deviations results and enables efficient approximation of blocking probabilities for realistic mobile communications networks.</jats:p

Interspecific facilitation and critical transitions in arid ecosystems

<p>Climate change and intensified land-use impose severe stress on arid ecosystems, resulting in relatively rapid degradation which is difficult to reverse. To prevent such critical transitions it is crucial to detect early warning signals. Increased patchiness' smaller and fewer vegetated patches is thought to be such a signal, but the underlying mechanisms are still poorly understood. Facilitation between plants is known to be an important mechanism driving the patchiness of the vegetation, but we lack understanding of how interactions between plants change in response to combined effects of drought and consumer pressure the main stressors in many arid ecosystems. Over the last decade numerous experimental studies have tested how intensity of facilitation between plants changes with increasing stress. The most recent synthesis predicts a decline in facilitation intensity at the severe end of a drought stress gradient. Adding consumer pressure may result in even earlier and faster declines in facilitation intensity. So far, studies on critical transitions and plantplant interactions have developed separately. The relationship between stress and facilitation intensity has been overlooked in critical transition theory, while facilitation intensity may determine the position of a critical transition threshold. In this study, we incorporate experimental studies on the relation between stress and facilitation intensity into the critical transition framework, to improve our ability to predict critical transitions. Moreover, we propose that a decline in facilitation intensity at the severe end of a stress gradient may occur prior to a critical transition. Inclusion of consumer pressure will speed up this process, leading to earlier and faster degradation. In-field monitoring of seedlingfacilitator associations and declines in facilitator recruitment can indicate declines in facilitation intensity and may thus provide additional early warning signals for imminent critical transitions, besides increased patchiness.</p>