Doctor of Philosophy / Department of Psychological Sciences / Lester C. Loschky / Political videos are created as persuasive media, and at a basic level that persuasion would require that the videos guide viewer attention to the relevant persuasive content. Recent work has shown that filmmakers have techniques that allow them to guide where viewers look, and this guidance occurs even when viewers have very different understandings of the film. The current research tested if these attentional effects carry over to political videos, or if the top-down factors of attitude congruence and social vigilantism, belief superiority and the tendency to impress one’s “superior” beliefs on others (O'Dea, Bueno, & Saucier, 2018; Saucier & Webster, 2010; Saucier, Webster, Hoffman, & Strain, 2014), will break the ability of videos to guide viewers’ attention. Attentional selection was measured through participants’ eye movements, and memory encoding was measured through recall and recognition for both verbal and visual information. Three overarching competing hypotheses predicted different relationships between attitude congruence, social vigilantism, and visual attention and memory. The Tyranny of Film Hypothesis predicted that the videos would guide viewer attention, regardless of attitude congruence. This would result in similar eye-movements and memory for all participants. The Selective Exposure Hypothesis predicted that participants would avoid processing attitude-incongruent information. As a result, viewers’ visual attention would be directed away from attitude-incongruent information, and subsequent memory would be worse. Lastly, the Social Vigilantism Hypothesis predicted that people high in Social Vigilantism would engage more with attitude-incongruent information. Two experiments tested these hypotheses. The first was the Memory experiment (conducted online), and the second was the Eye movement experiment. In each experiment, participants watched a series of political advertisement and debate videos, and attitudes were measured to identify which information in the videos was attitude-congruent and incongruent. The Memory experiment showed some support for the Social Vigilantism Hypothesis, with People high in Social Vigilantism having better memory for attitude-incongruent information on certain memory measures. Conversely, the Eye movement experiment consistently showed strong stimulus driven effects in support of the Tyranny of Film, but also weaker attitude and social vigilantism effects that were independent of attitude congruence. Altogether, these results show dynamic video stimuli features are the best predictors of viewer attention and memory, but viewer attitude and social vigilantism have subtle top-down effects. The support for different hypotheses between the two experiments indicates the strength of top-down effects may depend on the format of the viewing experience, and specifically how much control the viewer has over the experience.

Climate change and exotic plant invasions are significant anthropogenic threats to desert community structure and resilience . In the Mojave Desert, the invasive grass red brome (Bromusrubens L) is increasing fire frequency and extent in response to climatic factors. The resilience of this ecosystem will be affected by how plant and animal communities respond to fire. To better understand these dynamics, we studied the environmental factors underlying changes in invasive grass fire regimes in the Mojave Desert and its structural and functional effects on plant and animal communities. Following fire, reestablishment of native vegetation can be preempted by repeated burning associated with the abundant exotic grass red brome. Red brome density is correlated with various climate and landscape variables, but to establish causality, we experimentally assessed germination and growth of red brome. Red brome responded positively to fall precipitation, finer-textured soils, fertile-islands soils, and soils from burned landscapes. Red brome germination is maximized in wet fall periods when adequate water and optimal temperatures overlap . To evaluate landscape responses of pre- and post-fire plant communities and the potential for repeated burning we analyzed vegetation greenness (NDVI) data from 1985-2011 in response to temperature and precipitation. Landscape analysis indicated that the dominance of exotic grasses increases on post-fire landscapes. Following wet fall and winter seasons, high red brome productivity increases fire potential. Without mitigation, the establishment of an invasive-plant-driven fire regime is likely and may drive state transitions from arid shrublands to arid annual grasslands. Potential revegetation of post-fire landscapes will depend at least in part upon the physiological response of surviving vegetation to post-fire landscapes. Plant physiological responses to post-fire landscapes were generally neutral or positive, suggesting that revegetation of post-fire landscapes is not precluded by resource loss associated with fire and may even be enhanced by post-fire conditions. This will likely translate to increased reproductive potential of surviving plants. Alterations to small mammal populations will likely play a role in the reestablishment of vegetation (both native and exotics) as small mammals have strong top-down effects in arid ecosystems. Diversity and species richness responded negatively to burned landscapes as Merriam's kangaroo rat (Dipodomys merriami) increased in abundance while other species practically disappeared from burned landscapes. Merriam's kangaroo rat affects propagule sources through direct consumption, and seed dispersal. Increases in abundance and dominance of Merriam's kangaroo rat will likely alter plant recruitment.

Trophic downgrading of ecosystems necessitates a functional understanding of trophic cascades. Identifying the presence of cascades, and the mechanisms through which they occur, is particularly important for seagrass meadows, which are among the most threatened ecosystems on Earth. Shark Bay, Western Australia provides a model system to investigate the potential importance of top-down effects in a relatively pristine seagrass ecosystem. The role of megagrazers in the Shark Bay system has been previously investigated, but the role of macrograzers (i.e., teleosts), and their importance relative to megagrazers, remains unknown. The objective of my dissertation was to elucidate the importance of teleost macrograzers in transmitting top-down effects in seagrass ecosystems. Seagrasses and macroalgae were the main food of the abundant teleost Pelates octolineatus, but stable isotopic values suggested that algae may contribute a larger portion of assimilated food than suggested by gut contents. Pelates octolineatus is at risk from numerous predators, with pied cormorants (Phalacrocorax varius) taking the majority of tethered P. octolineatus. Using a combination of fish trapping and unbaited underwater video surveillance, I found that the relative abundance of P. octolineatus was greater in interior areas of seagrass banks during the cold season, and that the mean length of P. octolineatus was greater in these areas compared to along edges of banks. Finally, I used seagrass transplants and exclosure experiments to determine the relative effect of megagrazers and macrograzers on the establishment and persistence of three species of seagrasses in interior microhabitats. Teleost grazing had the largest impact on seagrass species with the highest nutrient content, and these impacts were primarily observed during the warm season. My findings are consistent with predictions of a behaviorally-mediated trophic cascade initiated by tiger sharks (Galeocerdo cuvier) and transmitted through herbivorous fishes and their predators.