• Direct Observation of Hillslope Scale StorAge Selection Functions in Experimental Hydrologic Systems: Geomorphologic Structure and Preferential Discharge of Old Water

      Kim, M.; Volkmann, T.H.M.; Wang, Y.; Meira Neto, A.A.; Matos, K.; Harman, C.J.; Troch, P.A.; Biosphere 2, University of Arizona; Department of Environmental Science, University of Arizona; Department of Hydrology and Atmospheric Sciences, University of Arizona (John Wiley and Sons Inc, 2022)
      Spatially integrated water transport dynamics at the hillslope scale have rarely been observed directly, and underlying physical mechanisms of those dynamics are poorly understood. We present time-variable transit time distributions and StorAge Selection (SAS) functions for a 28 days tracer experiment conducted at the Landscape Evolution Observatory, Biosphere 2, the University of Arizona, AZ, USA. The observed form of the SAS functions is concave, meaning that older water in the hillslope was preferentially discharged than younger water. The concavity is, in part, explained by the relative importance of advective and diffusive water dynamics and by the geomorphologic structure of the hillslopes. A simple numerical examination illustrates that, for straight plan-shaped hillslopes, the saturated zone SAS function is concave when the hillslope Péclet (Pe) number is large (and thus when the advective water dynamics are more pronounced). We also investigated the effect of hillslope planform geometry on the saturated zone SAS function using a model and found that the more convergent the plan shape is, the more concave the SAS function is. A numerical examination indicates that the unsaturated zone SAS function is concave for straight and convergent hillslopes when the soil thickness is uniform. The concavity of those subcomponent SAS functions signifies that the hillslope scale SAS function is concave for straight or convergent plan shape hillslopes when the hillslope Pe number is high. © 2022. American Geophysical Union. All Rights Reserved.
    • Drought, pollen and nectar availability, and pollination success

      Waser, Nickolas M.; Price, Mary V.; Univ Arizona, Sch Nat Resources & Environm; Rocky Mountain Biological Laboratory; P. O. Box 519 Crested Butte Colorado 81224 USA; Rocky Mountain Biological Laboratory; P. O. Box 519 Crested Butte Colorado 81224 USA (WILEY-BLACKWELL, 2016-06)
      Pollination success of animal-pollinated flowers depends on rate of pollinator visits and on pollen deposition per visit, both of which should vary with the pollen and nectar "neighborhoods" of a plant, i.e., with pollen and nectar availability in nearby plants. One determinant of these neighborhoods is per-flower production of pollen and nectar, which is likely to respond to environmental influences. In this study, we explored environmental effects on pollen and nectar production and on pollination success in order to follow up a surprising result from a previous study: flowers of Ipomopsis aggregata received less pollen in years of high visitation by their hummingbird pollinators. A new analysis of the earlier data indicated that high bird visitation corresponded to drought years. We hypothesized that drought might contribute to the enigmatic prior result if it decreases both nectar and pollen production: in dry years, low nectar availability could cause hummingbirds to visit flowers at a higher rate, and low pollen availability could cause them to deposit less pollen per visit. A greenhouse experiment demonstrated that drought does reduce both pollen and nectar production by I. aggregata flowers. This result was corroborated across 6 yr of variable precipitation and soil moisture in four unmanipulated field populations. In addition, experimental removal of pollen from flowers reduced the pollen received by nearby flowers. We conclude that there is much to learn about how abiotic and biotic environmental drivers jointly affect pollen and nectar production and availability, and how this contributes to pollen and nectar neighborhoods and thus influences pollination success.
    • Incidental Emotions and Cooperation in a Public Goods Game

      Nguyen, Y.; Noussair, C.N.; Department of Economics, University of Arizona (Frontiers Media S.A., 2022)
      The study reported here considers the relationship between emotional state and cooperation. An experiment is conducted in which the emotions of fear, happiness, and disgust are induced using 360-degree videos, shown in virtual reality. There is also a control condition in which a neutral state is induced. Under the Fear, Happiness, and Disgust conditions, the cooperation level is lower than under the Neutral condition. Furthermore, cooperation declines over time in the three emotion conditions, while it does not under Neutral. The findings suggest that emotions are associated with the dynamic pattern of declining cooperation over time. Copyright © 2022 Nguyen and Noussair.
    • Positive Emotion and Honesty

      Medai, E.; Noussair, C.N.; Eller College of Management, University of Arizona (Frontiers Media S.A., 2021)
      We report an experiment that considers the impact of emotional state on honesty. Using the die-rolling task created by Fischbacher and Föllmi-Heusi to detect the level of dishonesty in a sample of individuals, we study the effects of induced happiness on the incidence of self-interested lying. The experiment uses 360-degree videos to induce emotional state. We find that people behave more honestly in a state of happiness than they do in a neutral state. © Copyright © 2021 Medai and Noussair.
    • Reference Point Heterogeneity.

      Terzi, Ayse; Koedijk, Kees; Noussair, Charles N; Pownall, Rachel; Univ Arizona, Dept Econ; Univ Arizona, Ecol Sci Lab (FRONTIERS MEDIA SA, 2016-09-12)
      It is well-established that, when confronted with a decision to be taken under risk, individuals use reference payoff levels as important inputs. The purpose of this paper is to study which reference points characterize decisions in a setting in which there are several plausible reference levels of payoff. We report an experiment, in which we investigate which of four potential reference points: (1) a population average payoff level, (2) the announced expected payoff of peers in a similar decision situation, (3) a historical average level of earnings that others have received in the same task, and (4) an announced anticipated individual payoff level, best describes decisions in a decontextualized risky decision making task. We find heterogeneity among individuals in the reference points they employ. The population average payoff level is the modal reference point, followed by experimenter's stated expectation of a participant's individual earnings, followed in turn by the average earnings of other participants in previous sessions of the same experiment. A sizeable share of individuals show multiple reference points simultaneously. The reference point that best fits the choices of the individual is not affected by a shock to her income.
    • Social Identity and Group Emotion: Media Effects and Support for Military Intervention

      Bradshaw, Seth; Kenski, Kate; Univ Arizona (USC ANNENBERG PRESS, 2019)
      This study examines how news coverage of terrorist threats affects emotions that then shape support for antiterrorism policies, presidential approval, and attitudes toward Muslims. Using a national sample, news stories were experimentally manipulated to emphasize terrorist threats (high/low) and depictions of U.S. military strength (high/low). Results show that group-based anger-when people thought about themselves as Americans-mediated the relationships between threat coverage and antiterrorism policies, whereas group-based fear did not. On the other hand, group-based fear mediated the relationship between threat coverage and negative attitudes toward Muslims, whereas group-based anger did not. When people thought about themselves as individuals, neither anger nor fear mediated these relationships.
    • Transit time distributions and StorAge Selection functions in a sloping soil lysimeter with time-varying flow paths: Direct observation of internal and external transport variability

      Kim, Minseok; Pangle, Luke A.; Cardoso, Charléne; Lora, Marco; Volkmann, Till H. M.; Wang, Yadi; Harman, Ciaran J.; Troch, Peter A.; Univ Arizona, Biosphere2; Univ Arizona, Dept Soil Water & Environm Sci; et al. (AMER GEOPHYSICAL UNION, 2016-09)
      Transit times through hydrologic systems vary in time, but the nature of that variability is not well understood. Transit times variability was investigated in a 1 m(3) sloping lysimeter, representing a simplified model of a hillslope receiving periodic rainfall events for 28 days. Tracer tests were conducted using an experimental protocol that allows time-variable transit time distributions (TTDs) to be calculated from data. Observed TTDs varied with the storage state of the system, and the history of inflows and outflows. We propose that the observed time variability of the TTDs can be decomposed into two parts: internal variability associated with changes in the arrangement of, and partitioning between, flow pathways; and external variability driven by fluctuations in the flow rate along all flow pathways. These concepts can be defined quantitatively in terms of rank StorAge Selection (rSAS) functions, which is a theory describing lumped transport dynamics. Internal variability is associated with temporal variability in the rSAS function, while external is not. The rSAS function variability was characterized by an inverse storage effect, whereby younger water is released in greater proportion under wetter conditions than drier. We hypothesize that this effect is caused by the rapid mobilization of water in the unsaturated zone by the rising water table. Common approximations used to model transport dynamics that neglect internal variability were unable to reproduce the observed breakthrough curves accurately. This suggests that internal variability can play an important role in hydrologic transport dynamics, with implications for field data interpretation and modeling.