This paper studies mutual funds' use of social media (Twitter) as a new marketing instrument and its effects on the behavior of mutual fund investors. Using hand-collected data from Twitter regarding 175 mutual fund families, I find that mutual fund families are more likely to introduce Twitter when they have star funds in the family and when they are introducing new funds. The average inception size of new funds after a family joined Twitter is significantly larger than before joining Twitter. Moreover, mutual fund families using Twitter receive higher subsequent flows relative to other similar non-Twitter families. These incremental flows disappear six months after the introduction of Twitter. The higher flows are not entirely driven by the flows to the newly launched funds, as pre-existing funds also experience higher flows after introducing Twitter. The flow effect is especially pronounced for young funds within a family. Overall, the evidence suggests that mutual funds strategically use the introduction of Twitter to capture investors' attention and attract flows.

The Neogene (~23.0 – 2.6 million years ago) is the current climate analogue used in predictive scenario modeling, as it is characterized as having similar biota, geography, and environments when compared to present-day. Parameters that cannot be directly measured from the past can be estimated by stable isotope analysis measurements from proxies. Unlike most marine proxies, shark teeth provide ‘snapshots’ of environmental conditions during formation. Shark teeth can be used to calculate sea temperatures the teeth formed in after measuring δ18O of phosphate (PO4) and carbonate (CO3) within the enameloid and using δ18O of seawater (δ18Osw) estimates. Here, we model δ18OPO4 and δ18OCO3 from published linear regression equations to assess the fidelity of local T and δ18Osw being recorded in modern shark teeth. We also developed a Bayesian regression model to estimate the probability of T and δ18Osw for basins using δ18OPO4 of fossilized Neogene shark teeth from our collection and published datasets. Modern empirical δ18O and predictive δ18O* values indicate that carbonate (mean = 27.4 ± 1.5‰) is not a reliable recorder and therefore should not be considered as a paleothermometer until further constrained, but phosphate (mean = 23.5 ± 0.7‰) δ18OPO4 values were similar between taxa at localities and suggest a latitudinal temperature gradient. Variation within and between taxa may be due to species specific migration and mesothermy. Neogene T and δ18Osw estimates reflect a warmer climate, and salinity and temperature differences between the Miocene and Pliocene epochs.

Shark teeth are abundant in the fossil record and serve as ancient data buoys, recording physiological information, ecological interactions, and paleo-oceanographic conditions. A tool often used in paleobiological studies to access this recorded information is stable isotope analysis. Fossil shark teeth are well suited for stable isotope analysis because their enameloid is primarily fluorapatite, Ca5(PO4)3F, which is resistant to diagenetic alteration due to its high chemical stability. Although often used in paleoecological studies of mammals, carbonate carbon isotope compositions (δ13CCO3) in shark enameloid have remained enigmatic. Here, we investigate multiple stable isotope systems (δ13Corg, δ13CCO3, δ18OCO3, δ18OPO4) within modern shark teeth to determine relationships between the different systems and build an interpretative framework for future fossil studies. Interestingly, there is no correlation between δ18OPO4 and δ18OCO3 values in modern shark teeth, which contrasts with mammalian studies to date and suggests this metric is not an appropriate test for diagenetic alteration in fossil shark teeth. Organic carbon isotope composition (δ13Corg) measured from collagen in tooth dentine ranges from -16.0‰ to -10.8‰. Surprisingly, the δ13CCO3 values we measured are much higher, ranging from -6.0‰ to 10.3‰, and there is no direct relationship between δ13Corg and δ13CCO3 values in shark teeth. Instead, we found the fractionation (ε) between δ13Corg and δ13CCO3 values to correspond with δ18OCO3 values but not δ18OPO4 values. It is possible that the source of carbon in shark enameloid is partitioned between dietary carbon and dissolved inorganic carbon (DIC), similar to fish otoliths. We applied the fractionation factor from modern teeth to carbonate isotope composition of fossil shark teeth to predict organic carbon isotope values. The ability to estimate δ13Corg values in fossils will provide better insight into carbon cycling and food web dynamics of ancient marine ecosystems.

Precipitation is a key driver of ecosystem development, and terrestrial ecosystems are experiencing important changes in the amount and seasonality of precipitation, which is expected to go on well into the next century. Precipitation affects soil moisture, and there is still uncertainty about how changing soil moisture regimes will affect carbon and nitrogen cycling, and how these climate change impacts will interact with changing plant species diversity to affect the dynamics of soil organic matter. We studied carbon and nitrogen cycling in two Mediterranean systems, a natural precipitation gradient of California grasslands, and a precipitation manipulation experiment. The precipitation gradient focuses on three sites across California that experience precipitation ranging from low (~300 mm precipitation/year) to a wet precipitation regime (~2160 mm precipitation/year). The precipitation manipulation experiment is set up in a random block design at the wettest site in the gradient. It has three treatments: ambient precipitation, additional precipitation in the winter, and additional precipitation in the spring. We collected samples from across the natural precipitation gradient to 1m and also at the precipitation experiment to 3m after 20 years of manipulation. This sampling design addresses key questions regarding how changes in the amount and seasonality of precipitation affect soil organic matter stability and turnover of soils below and above 1 meter. At the precipitation gradient, we determined changes in total elemental concentrations of soil carbon and nitrogen, stable isotope composition (δ13C, δ15N), and composition of soil organic matter (SOM) as measured through Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS) to 1m soil depth. We measured carbon persistence in soil organic matter (SOM) based on beta (β), a parameter based on the slope of carbon isotope composition across depth and proxy for turnover. Further, we examined the relationship between δ15N and C:N values to infer SOM’s degree of microbial processing. As expected, we measured the greatest carbon stock at the surface of our wettest site, but carbon stocks in subsoils converged at the wet and dry sites. Soils at depth (>30cm) at the wettest site had the lowest C:N ratio and highest δ15N values with the greatest proportion of simple plant-derived organic matter, as determined DRIFTS. These results suggest differing stabilization mechanisms of organic matter at depth across our study sites. We infer that the greatest stability was conferred by associations with reactive minerals at depth in our wettest site. In contrast, organic matter at our driest site was subject to the most microbial processing. Results from this study demonstrate that precipitation patterns have important implications for deep soil carbon storage and composition, suggesting the vulnerability of deep SOM to climate change induced alterations in precipitation patterns. At the precipitation experiment, we found that the winter precipitation addition resulted in the largest cumulative (0-300cm) C stock. However, we found evidence for vertical translocation of carbon to deep soil layers, specifically of plant-derived carbon, with both winter and spring additions of precipitation. Winter addition of precipitation also resulted in the highest subsoil carbon stock compared to the ambient and spring treatments. Overall, added winter precipitation led to the best conditions for carbon accumulation since the added precipitation coincides with lower temperatures and improved growing conditions at our field site. When we zoomed into surface soils at the precipitation experiment, we found greater surface carbon stocks with winter addition of precipitation. We also found weakened associations with short-range order iron and aluminum oxides in the winter and spring treatments. However, we did see significant and positive associations in only the winter treatment between short range order oxides and complex plant matter and microbially associated OM. The conclusions of this study suggest that over decadal time scales, changing precipitation amount and seasonality could affect SOM accumulation and persistence in grassland ecosystems.

Sharks and their relatives have been successful predators for over 400 million years, playing critical ecological roles in marine environments. Their recent, dramatic population decline—largely due to climate change—poses a serious threat to ecosystem stability. Their fossil record provides a valuable system to document how sharks have coped, survived, or declined in response to major climatic changes over geological time. Insights from these records are vital to inform current conservation practices. This dissertation investigates how major climatic events influenced the temperature, salinity, and dietary preferences of sharks that lived during the Eocene Epoch (54–33.9 Ma) in Antarctica, a region that underwent significant environmental shifts as the global climate cooled at the Epoch's end. The study develops a new protocol to isolate silver phosphate for geochemical analysis, enabling temperature and salinity estimations from bones and teeth, including various shark tooth sizes. Temperature and salinity preferences were inferred for both pelagic and benthic shark taxa (n = 16) across the Eocene. The study also examines geochemical and morphological metrics of Eocene sand tiger sharks and compares them with the critically endangered modern species Carcharias taurus. By addressing a longstanding analytical variability enigma affecting temperature and salinity estimates derived from shark teeth, we found that pelagic and benthic Eocene sharks generally preferred similar conditions, with only cooler-adapted species continuing in the fossil record likely surviving climate change. Additionally, our results suggest that fossil sand tiger sharks serve as valuable analogs for the extant C. taurus in terms of habitat and dietary preferences. Altogether, this study underscores the significant impact of climate on sharks and highlights how their fossil record can illuminate aspects of modern shark ecology.