Habitat use and foraging ecology of a batoid community in Shark Bay, Western Australia

Worldwide declines in populations of large elasmobranchs and the potential cascading effects on marine ecosystems have garnered considerable attention. Far less appreciated are the potential ecological impacts of changes in abundances of small to medium bodied elasmobranchs mesopredators. Crucial to elucidating the role of these elasmobranchs is an understanding of their habitat use and foraging ecology in pristine conditions. I investigated the trophic interactions and factors driving spatiotemporal variation in abundances of elasmobranch mesopredators in the relatively pristine ecosystem of Shark Bay, Australia. First, I describe the species composition and seasonal habitat use patterns of elasmobranch mesopredator on the sandflats of Shark Bay. Juvenile batoids dominated this diverse community and were extremely abundant in nearshore microhabitats during the warm season. Stomach content analysis and stable isotopic analysis revealed that there is a large degree of dietary overlap between common batoid species. Crustaceans, which tend to be found in seagrass habitats, dominated diets. Despite isotopic differences between many species, overlap in isotopic niche space was high and there was some degree of individual specialization. I then, investigated the importance of abiotic (temperature and water depth) and biotic (prey and predator abundance) factors in shaping batoid habitat use. Batoids were most abundant and tended to rest in shallow nearshore waters when temperatures were high. This pattern coincides with periods of large shark abundance suggesting batoids were seeking refuge from predators rather than selecting optimal temperatures. Finally, I used acoustic telemetry to examine batoid residency and diel use of the sandflats. Individual batoids were present on the sandflats during both the warm and cold seasons and throughout the diel cycle, suggesting lower sandflat densities during the cold season were a result of habitat shifts rather than migration out of Shark Bay. Combined, habitat use and dietary results suggest that batoids have the potential to seasonally impact sandflat dynamics through their presence, although foraging may be limited on the sandflats. Interestingly, my results suggest that elasmobranch mesopredators in pristine ecosystems probably are not regulated by food supply and their habitat use patterns and perhaps ecosystem impacts may be influenced by their predators.

Endocrine regulation of dynamic communication signals in gymnotiform fish

Communication signals are shaped by the opposing selection pressures imposed by predators and mates. A dynamic signal might serve as an adaptive compromise between an inconspicuous signal that evades predators and an extravagant signal preferred by females. Such a signal has been described in the gymnotiform electric fish, Brachyhypopomus gauderio, which produces a sexually dimorphic electric organ discharge (EOD). The EOD varies on a circadian rhythm and in response to social cues. This signal plasticity is mediated by the slow action of androgens and rapid action of melanocortins. My dissertation research tested the hypotheses that (1) signal plasticity is related to sociality levels in gymnotiform species, and (2) differences in signal plasticity are regulated by differential sensitivity to androgen and melanocortin hormones. To assess the breadth of dynamic signaling within the order Gymnotiformes, I sampled 13 species from the five gymnotiform families. I recorded EODs to observe spontaneous signal oscillations after which I injected melanocortin hormones, saline control, or presented the fish with a conspecific. I showed that through the co-option of the ancient melanocortin pathway, gymnotiforms dynamically regulate EOD amplitude, spectral frequency, both, or neither. To investigate whether observed EOD plasticities are related to species-specific sociality I tested four species; two territorial, highly aggressive species, Gymnotus carapo and Apteronotus leptorhynchus, a highly gregarious species, Eigenmannia cf. virescens , and an intermediate short-lived species with a fluid social system, Brachyhypopomus gauderio. I examined the relationship between the androgens testosterone and 11-ketotestosterone, the melanocortin α-MSH, and their roles in regulating EOD waveform. I implanted all fish with androgen and blank silicone implants, and injected with α-MSH before and at the peak of implant effect. I found that waveforms of the most territorial and aggressive species were insensitive to hormone treatments; maintaining a static, stereotyped signal that preserves encoding of individual identity. Species with a fluid social system were most responsive to hormone treatments, exhibiting signals that reflect immediate condition and reproductive state. In conclusion, variation in gymnotiform signal plasticity is hormonally regulated and seems to reflect species-specific sociality.

Social and environmental regulation of signal plasticity and signal reliability in the electric fish Brachyhypopomus gauderio

The balance between the costs and benefits of conspicuous signals ensures that the expression of those signals is related to the quality of the bearer. Plastic signals could enable males to maximize conspicuous traits to impress mates and competitors, but reduce the expression of those traits to minimize signaling costs, potentially compromising the information conveyed by the signals. ^ I investigated the effect of signal enhancement on the information coded by the biphasic electric signal pulse of the gymnotiform fish Brachyhypopomus gauderio. Increases in population density drive males to enhance the amplitude of their signals. I found that signal amplitude enhancement improves the information about the signaler's size. Furthermore, I found that the elongation of the signal's second phase conveys information about androgen levels in both sexes, gonad size in males and estrogen levels in females. Androgens link the duration of the signal's second phase to other androgen-mediated traits making the signal an honest indicator of reproductive state and aggressive motivation. ^ Signal amplitude enhancement facilitates the assessment of the signaler's resource holding potential, important for male-male interactions, while signal duration provides information about aggressive motivation to same-sex competitors and reproductive state to the opposite sex. Moreover, I found that female signals also change in accordance to the social environment. Females also increase the amplitude of their signal when population density increases and elongate the duration of their signal's second phase when the sex ratio becomes female-biased. Indicating that some degree of sexual selection operates in females. ^ I studied whether male B. gauderio use signal plasticity to reduce the cost of reproductive signaling when energy is limited. Surprisingly, I found that food limitation promotes the investment in reproduction manifested as signal enhancement and elevated androgen levels. The short lifespan and single breeding season of B. gauderio diminishes the advantage of energy savings and gives priority to sustaining reproduction. I conclude that the electric signal of B. gauderio provides reliable information about the signaler, the quality of this information is reinforced rather than degraded with signal enhancement.^

Strategic Directions of Hotel Industry Expectations

A factor analysis is presented which indicates that among 20 potential strategic issues reated by hotl industry executives three fundamental strategic directions exist. The author summarizes an empiracle study that queried these individuals' beliefs regarding strategic issues they rated at most important.

Race, Class and the Promise of the Public University

Commencement address by Professor Thomas Breslin at Florida International University dissects in a few words both the promise of a public university system and the threats to that system embedded in racial and class privilege.

The Politics of Ahmadinejad and Chavez: A Misplaced Comparison

This piece illustrates that comparing the political and economic impact of Hugo Chavez and Mahmoud Ahmadinejad on their respective countries based solely on generalizations regarding similarities in foreign policy discourse is an unwarranted analytical jump. To identify the essential difference between the two administrations, the article pays attention to the different domestic politics in each country. Ahmadinejad’s populism seems to fit best within neoliberal populism. In stark contrast, Chavista socialism can be understood as a “heterodox” or “alternative” economic policy.

How Commerce Trumped Art at Miramax

Louis Proyect documents the role of corporate decision-making and profit in the undermining of ostensibly "independent" cinema. He focues on Miramax and its history of tampering with the work of writers and directors.

Transnational Capital and the Politics of Global Supply Chains

In the latest phase of globalization, transnational corporations based in the U.S. have worked closely with U.S. foreign policymakers to secure favorable foreign direct investment provisions within U.S. domestic legislation and within U.S. trade agreements. These interactions between transnational firms and the U.S. state have provided many of the preconditions for an expansion of foreign direct investment connected to capital liberalization and the growth of global supply chains from the 1980s to the present. This relationship is best conceptualized as representing a “transnational interest bloc,” whose policy objectives are incorporated within investment provisions in US-backed trade and investment agreements.

The Occupy Movement: Two Steps Forward, One Step Back

The op-ed evaluates the successes and limitations of the Occupy Movement in the United States. Ronald W. Cox argues that the Movement was inspirational in directing media focus to the trends of growing inequality and the privileges and power of the one percent. The critique of establishment parties and progressive organizations was a key part of the Occupiers efforts to rethink the meaning of social change. The limitations of the Movement became evident, however, in its extremely decentralized structures that emphasized consensus over majoritarian decision-making, and in its refusal to acknowledge and hold accountable its own leaders.

Climate Change and the Color Line

Climate change is estimated to be responsible for 400,000 deaths per year, mostly because of hunger and communicable diseases affecting children in the Global South. Using the sociology of W.E.B. Du Bois, I attempt to demonstrate how and why climate change occurs along the color line. I conclude by arguing why it is important to think about climate change as a human rights issue.

The Corporatization of Higher Education

This essay reviews recent books and articles that examine the politics and economics of the restructuring of public universities in the United States. The author weaves the arguments together to point to several prominent trends: increased corporatization of university governance and increased dependence on the market for resources previously provided by the state, reduction of full-time faculty in favor of instructors and adjuncts, dramatic growth of administrative personnel, and mounting student debt. The history of these developments is explored by examining the roots of the political attacks on the public university.

The Relevance of Marxist Academics

This commentary examines the relationship between a Marxist scholar and the institutional and societal environment of the university. The focus is on how a Marxist academic navigates the social, economic and political aspects of the university while attempting to maintain a commitment to class analysis and Marxism as political practice.

Factors influencing movements and foraging ecology of American alligators (Alligator mississippiensis) in a dynamic subtropical coastal ecosystem

Top predators can have large effects on community and population dynamics but we still know relatively little about their roles in ecosystems and which biotic and abiotic factors potentially affect their behavioral patterns. Understanding the roles played by top predators is a pressing issue because many top predator populations around the world are declining rapidly yet we do not fully understand what the consequences of their potential extirpation could be for ecosystem structure and function. In addition, individual behavioral specialization is commonplace across many taxa, but studies of its prevalence, causes, and consequences in top predator populations are lacking. In this dissertation I investigated the movement, feeding patterns, and drivers and implications of individual specialization in an American alligator (Alligator mississippiensis ) population inhabiting a dynamic subtropical estuary. I found that alligator movement and feeding behaviors in this population were largely regulated by a combination of biotic and abiotic factors that varied seasonally. I also found that the population consisted of individuals that displayed an extremely wide range of movement and feeding behaviors, indicating that individual specialization is potentially an important determinant of the varied roles of alligators in ecosystems. Ultimately, I found that assuming top predator populations consist of individuals that all behave in similar ways in terms of their feeding, movements, and potential roles in ecosystems is likely incorrect. As climate change and ecosystem restoration and conservation activities continue to affect top predator populations worldwide, individuals will likely respond in different and possibly unexpected ways.

Social Capital and International Migration from Latin America

We combine data from the Latin American Migration Project and the Mexican Migration Project to estimate models predicting the likelihood of taking of first and later trips to the United States from five nations: Mexico, the Dominican Republic, Costa Rica, Nicaragua, and Peru. The models test specific hypotheses about the effects of social capital on international migration and how these effects vary with respect to contextual factors. Our findings confirm the ubiquity of migrant networks and the universality of social capital effects throughout Latin America. They also reveal how the sizes of these effects are not uniform across settings. Social capital operates more powerfully on first as opposed to later trips and interacts with the cost of migration. In addition, effects are somewhat different when considering individual social capital (measuring strong ties) and community social capital (measuring weak ties). On first trips, the effect of strong ties in promoting migration increases with distance whereas the effect of weak ties decreases with distance. On later trips, the direction of effects for both individual and community social capital is negative for long distances but positive for short distances.

Intergenerational associations between a consensual childhood sexual experience and adult substance abuse among Latina mothers and daughters

Purpose: Early onset of sexual activity has been linked to later substance abuse. Our study aimed to further describe the associations between Latina mothers’ and daughters’ early sexual activity and adult substance abuse. Methods: A survey was conducted with 92 Latina mother–daughter dyads whose members never experienced sexual abuse. Childhood sexual experience was defined as the occurrence of a consensual sexual encounter at the age of 15 years or younger. Substance abusers were identified by the extent of substance use during the 12 months prior to the interview. Path analysis was used to fit our conceptual models to the data. Main findings: Daughters’ current, adult substance abuse was associated independently with: their own childhood sexual experience (odds ratio [OR] = 6.0) and mothers’ current, adult substance abuse (OR = 2.0). Compared with daughters who first experienced sex after the age of 19, the odds of using substances were 17.7 times higher among daughters who had childhood sexual experience and 3.8 times higher among daughters who first experienced sex between the age of 16–19 years. Explicitly, sexual experiences between the ages of 16–19 years were also risk factors for later adult substance abuse. Mothers’ childhood sexual experience (OR = 7.3) was a strong predictor for daughters’ childhood sexual experience. Conclusions: Our study supported a link between mother and daughter childhood sexual experience among Latinas, and indicated it is a correlate of adult substance abuse. Family based substance abuse prevention efforts and future longitudinal studies should consider maternal childhood sexual experience as a potential indication of risk for Latina daughters.