1,721,106 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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Foraging behavior, body condition, and neonicotinoid pesticide exposure reveal effects of habitat types on breeding Tricolored Blackbirds (Agelaius tricolor)
Get PDFAnthropogenic land-use change and agricultural intensification have caused extensive ecological change on a global scale, especially during the last 50 years. This has coincided with large declines in avian abundance, especially among farmland-associated and grassland birds. There is increasing awareness of the negative ecological and environmental effects of the widespread use of pesticides and other anthropogenic chemicals across entire landscapes. Neonicotinoid insecticides in particular are associated with population declines in insectivorous birds due to pesticide-mediated reductions in food supply, and may exasperate declines in species that are of conservation concern. The direct and indirect effects of agricultural land-use change are complex, may be synergistic with other threats, and it is often difficult to untangle their individual contributions to biodiversity loss. As a discipline, conservation physiology aims to unmask effects that are not otherwise apparent with traditional methods used in applied conservation biology. For addressing questions of how species respond to anthropogenic land-use change, measures of individual body condition and behavior may be more sensitive for assessing habitat quality than are broad metrics of population size or species’ presence. In this dissertation, I test the impacts of neonicotinoid pesticides and available foraging habitat, by combining movement behavior, individual health measures, and pesticide exposure, in the Tricolored Blackbird (Agelaius tricolor). Chapter 1 establishes pesticide exposure in Tricolored Blackbirds as directly quantified from salvaged carcasses. Chapter 2 investigates how habitat characteristics influence Tricolored Blackbird health and body condition. Chapter 3 evaluates how Tricolored Blackbird foraging behavior was related to suitable foraging habitat availability. Historically, Tricolored Blackbirds were associated with wetland and grassland habitats throughout their range in California and adjacent states. In recent years, Tricolored Blackbirds have become increasingly associated with agricultural habitats for both foraging and nesting and form breeding colonies within a diverse range of landscape matrices. For this reason, Tricolored Blackbirds are an excellent study system for exploring questions about how species respond to anthropogenic habitat changes. This species is known to forage extensively in some crops such as rice and alfalfa, while other crops such as walnuts and almonds do not provide suitable foraging habitat for breeding birds. Previous research and anecdotal observations indicate the Tricolored Blackbird reproductive success is closely tied to the abundance of suitable insect prey in habitats surrounding breeding colonies. While adult Tricolored Blackbirds are granivorous to some extent, females need to consume insect prey during the egg-laying stage of reproduction and nestlings are obligately insectivorous. To assess pesticide exposure levels in Tricolored Blackbirds in Chapter 1, carcasses were opportunistically salvaged from breeding colony locations during banding and other monitoring efforts throughout the species range. A liquid chromatography-mass spectrometry (LC-HRMS) assay was used to detect neonicotinoid insecticides and other compounds in adult liver tissue and whole-carcass homogenates of nestlings. Contrary to expectations, the results show that Tricolored Blackbirds showed little pesticide residue as directly measured from salvaged carcasses of both adults and nestlings. Only two out of the 85 samples showed detectable levels of any target compound. Specifically, one adult male and one nestling showed exposure to clothianidin, and both were salvaged from breeding colonies near or in dairies in Kern County. Birds may be coming into contact with our target compounds at a frequency that was not captured by our salvage sampling method. Environmental exposure may be higher at other times of the year outside the Tricolored Blackbird breeding season. This study only targeted neonicotinoid insecticides (and sulfoxaflor, a sulfoximine systemic insecticide), so further evaluation of exposure to other classes of pesticides is also necessary. Additional research is needed to understand if and how insecticide use on the landscape affects the insect prey base of Tricolored Blackbirds, and to better understand the observed neonicotinoid exposure in dairy-associated breeding colonies.In Chapter 2, I tested how the amount of natural and agricultural foraging habitats surrounding Tricolored Blackbird breeding colonies affected bird health and condition. Assessments of habitat quality have frequently been done via simple abundance or occupancy measures, however, it is useful to establish a mechanistic relationship with habitat quality. Physiological indicators may show signs of poor or decreasing habitat quality before changes in population size are detected at a larger scale, which can provide key insights for how individuals respond to habitat availability in agricultural landscapes. Specifically, I quantified body mass, composite fat score, average hematocrit, the ratio of heterophils to lymphocytes (H-L ratio), estimated total white blood cells (WBC), and severity of Knemidokoptes spp. scaly-leg mite infestations that are frequently observed in Tricolored Blackbirds. Day of year, colony stage, and nest substrate explained much of the variation in individual bird health and condition metrics analyzed, with significant differences between males and females. Foraging habitat characteristics did not have significant overall effects on the health and condition measures used here. I found that birds nesting in freshwater emergent vegetation showed lower H-L ratios than did birds nesting in upland/terrestrial vegetation. Because higher H-L ratios are broadly correlated with higher glucocorticoid levels and can be used as a proxy measure of stress in wild animals, the results suggest that birds nesting in upland/terrestrial vegetation are in a heightened state of physiological stress compared to birds nesting in freshwater emergent vegetation. Birds sampled from colony locations with a greater proportion of suitable foraging habitat had significantly lower severity of foot mite infestations. While it is not currently known where or how Tricolored Blackbirds contract and/or spread these mites, these results indicate that habitat may play a role in their epidemiology. These results highlight the importance of conservation physiology in showing how individuals and populations are impacted by landscape characteristics beyond what can be shown by studies using only information on presence/absence or abundance of birds. While population presence (such as Tricolored Blackbird colony settlement) is an important metric, it is also important to understand the relative value of different habitat characteristics for individual bird health and condition.Chapter 3 added to the results presented in Chapter 2 by exploring how the availability of suitable foraging habitat influenced foraging behavior of breeding Tricolored Blackbirds. Habitat quality is a central concept in ecological theory and also plays a valuable role in applied conservation management of threatened species. Foraging behavior and foraging bout length have been shown to correlate with food abundance or availability, and provide proxies for assessing food availability on a broad spatial scale. Recent advancements in tracking technology have provided powerful tools for understanding species’ responses to environmental change and other stressors through detailed tracking of foraging behavior and other movement patterns. The mechanisms by which agricultural intensification have caused population declines are complex with habitat loss and degradation, pesticide exposure, direct mortality, and other disturbances often acting synergistically on both individuals and populations. Tricolored Blackbirds have become increasingly associated with agricultural habitats in recent decades, and this species is sensitive to reproductive failure if there is not sufficient insect prey available across the foraging landscape. I aimed to test the effects of the proportions of natural and agricultural foraging habitats surrounding Tricolored Blackbird breeding colonies on individual bird foraging behavior. Specifically, I used automated radio telemetry to passively monitor presence-absence of tagged birds at Tricolored Blackbird breeding colonies to infer foraging bout lengths. I found that birds nesting in colonies surrounded by a higher proportion of suitable foraging habitat took significantly shorter foraging bouts than birds nesting in colonies surrounded by a lower proportion of suitable foraging habitat. Similarly, birds nesting in freshwater emergent vegetation took significantly shorter foraging bouts than birds nesting in upland/terrestrial vegetation. These foraging bout lengths would have allowed approximately 13.8 foraging bouts per hour for females during the nestling stage with 94% habitat suitable within 5 km of the colony (the highest values observed in my study) compared to approximately 9.5 foraging bouts per hour when only 44% of habitat within 5 km was suitable. This shows that habitat characteristics within and adjacent to the colony have a large influence on bird foraging bout length and presumed adult energy expenditure during the reproductive cycle, which strengthens the case for conservation actions that seek to enhance the habitats around Tricolored Blackbird breeding colonies
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Urbanization Impacts Individual Variation in Coyote Diet and Hormone Metabolite Concentrations
No full textAs cities expand globally, the effect of urbanization on wildlife populations has become a central focus in ecology and evolutionary biology. Numerous studies have demonstrated that urban animals differ morphologically, physiologically, and behaviorally from nonurban conspecifics. These differences emerge, in part, from phenotypic variation among individuals, yet most studies have focused on population-level patterns rather than individual-level processes. Although individual variation is the target of natural selection and a key determinant of adaptive potential, little is known about how urbanization shapes intraspecific variation. I investigated how environmental attributes within San Francisco, California, influence individual variation in diet and endocrine function in a population of coyotes (Canis latrans).In Chapter 1, I examined how within-city landscape heterogeneity shaped dietary variation at the individual and territory levels. With DNA metabarcoding of fecal samples and individual genotyping, I quantified diet composition and individual niche differentiation across coyote territories. I found that diet composition varied significantly among territories and among individuals within territories. The greatest proportion of territory-level variation in diet was explained by impervious surface cover. Coyotes in highly urbanized territories consumed more anthropogenic food, whereas those in greener areas consumed less anthropogenic food and had stronger among-individual dietary differences. The quantity of non-native, human-commensal rodents in the diet was positively correlated with the number of restaurants and other food services in a territory. My results suggest that urbanization facilitates dietary diversification by structuring access to different food resources. In Chapter 2, I tested whether urbanization was associated with individual dietary specialization by comparing dietary niche width and among-individual dietary differentiation between an urban and nonurban population of coyotes. I predicted that heterogeneity in urban environments is associated with variation in diets among individuals that forage in different neighborhoods. To test these predictions, I analyzed stable isotopes in coyote vibrissae. I found that urban coyotes had narrower dietary niches, more consistent diets, and greater among individual dietary variation than nonurban coyotes, indicating stronger individual specialization. Within the urban population, diet variation was primarily associated with differences in anthropogenic food consumption, which was correlated with percentage of impervious surface cover. Overall, my results suggest that urbanization facilitates within-population dietary niche diversity by creating spatial variation in foraging opportunities. In Chapter 3, I integrated endocrine, dietary, and genetic analyses to explore the environmental and biological correlates of hormone production in urban coyotes and quantify among-individual variation in mean hormone metabolite concentrations and variability. I found that stress (glucocorticoids, GC) and thyroid (triiodothyronine, T3; thyroxine, T4) hormone metabolite concentrations were correlated with urbanization and diet. Impervious surface cover was associated with increased glucocorticoid metabolite concentrations and anthropogenic food was associated with decreased glucocorticoid metabolite concentrations. Glucocorticoid metabolites were also higher in breeding individuals and in males at the onset of the breeding season. Thyroid hormone metabolite concentrations increased with impervious surface cover and anthropogenic food consumption. Glucocorticoid metabolite concentrations showed moderate among-individual variation, whereas individual differences in thyroid hormone metabolite levels were weak. My results suggest that land cover, diet, and life history may influence both physiological stress and metabolism of coyotes. Consumption of human food may help individuals mitigate some of the stress associated with urban development and allow for increased energy expenditure. The observed within-individual variation in hormone metabolite concentrations, particularly for T3 and T4, highlights the flexibility of individuals’ physiological responses to their environments and the importance of endocrine plasticity for urban tolerance.In Chapter 4, I focused on the evolutionary relevance of behavioral shifts in urban environments. I synthesized evidence on behavior-led evolution in cities, arguing that behavioral plasticity in urban animals, for instance shifts in habitat use, migration patterns, or courtship, can serve as precursors for evolution. I examined case studies of how behavioral shifts may facilitate population divergence at multiple spatial extents via movement, phenological, and mate-choice mechanisms. I emphasized the relevance of incorporating behavioral plasticity into studies of urban evolution and highlighted the opportunity cities provide to study mechanisms of rapid evolutionary change. Overall, this dissertation demonstrates that urbanization can facilitate within-population heterogeneity in diet and physiology and examines mechanisms of intraspecific variation. 
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Climate Change, Predator-Prey Interactions, and Population Dynamics of the Ranchman’s Tiger Moth (Arctia virginalis)
Get PDFIn my dissertation, I examined how a changing environment affects Ranchman’s tiger moth (Arctia virginalis) population dynamics via predator-prey and host-pathogen interactions. I also examined the complex ways in which biotic drivers of population dynamics interact with climate forcing.In Chapter 1, I examined how body size mediates the effect of warming on the interaction between Arctia virginalis and an ant predator (Formica lasioides). I also developed a general framework for understanding warming effects on stage or size-dependent predator-prey interactions. Specifically, I showed through experiments and modelling that A. virginalis is only vulnerable to predation by F. lasioides when small. This window of vulnerability narrows as the development rate of A. virginalis increases with warming. However, the attack rate of F. lasioides also increases with warming and overcompensates for the decreasing window of prey vulnerability. We therefore project warming to favor the predator in this case, in contrast to the results of previous related work in other systems.
In Chapter 2, I expanded upon Chapter 1 by examining the effects of warming on predator-prey interactions in multi-predator communities. In Chapter 1, I showed that asymmetries in predator-prey thermal response rates can result in changing interactions, constituting an important indirect effect of warming. In demographic models using simulated and empirically informed parameters from a natural community of ant predators, I showed that greater predator diversity paired with sufficient thermal niche diversity attenuates these indirect effects of warming, leaving only direct, physiological effects. This result depends on predator diversity and thermal niche diversity and complementarity, which has significant implications for how we might expect warming to affect predator-prey interactions in different communities dependent on traits of the community thermal niche.
In Chapter 3, I examined viral disease as a mechanism for delayed density-dependent dynamics in A. virginalis populations and the role of ultraviolet radiation in reducing viral infection through attenuating virions persisting in the environment. I censused 18 populations across 9° of latitude and a gradient of ultraviolet radiation intensity for two years and measured viral infection rate, severity, and survival of lab-reared caterpillars. I found that caterpillar density in the previous year led to a higher infection rate and severity and lower survival and that ultraviolet radiation led to lower infection severity and higher survival. This suggested that virus is the main mechanism for cyclic dynamics in this species, which has been proposed theoretically but rarely shown empirically. I also found a population-level effect of ultraviolet radiation on viral infection severity, which had not been shown previously.
In Chapter 4, I analyzed long-term A. virginalis census data, finding that changing precipitation patterns due to changes in large-scale climate led to qualitative changes in population dynamics. Using change-point analysis and state-space models, I showed that caterpillar dynamics transitioned from short to long-period dynamics concurrent with a change in precipitation dynamics. Using deterministic simulations, I showed that shifting dynamics were likely due to resonance: precipitation patterns interfered with cycles initially and later amplified cycles
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Abundance of the Monarch Butterfly (Danaus plexippus) in the Eastern United States
Get PDFThe abundances of many migratory species, including the monarch butterfly (Danaus plexippus), have drastically declined. The breeding and nonbreeding ranges of migratory species are often separated by long distances, and climate, vegetation, and human activities in the two ranges can be considerably different. Attempts to determine the mechanisms of changes in the abundances of migratory species often do not consider spatial patterns of abundances and environmental attributes in the breeding and nonbreeding ranges. However, identifying these spatial patterns may increase understanding of the population dynamics of migratory species. Variation in spatial patterns of abundances and the environmental factors that affect abundances may be correlated and spatially clustered. Here, I tested which factors were associated with D. plexippus abundance and spatial clustering of abundance within three regions occupied by the eastern population of the monarch butterfly in the United States. The variables included in the best supported model of D. plexippus abundance were temperature, water availability, land use, and purchases of glyphosate (a commonly used herbicide). However, the relative strength of these factors among the three regions was similar, and no single variable had a substantial effect on abundance. There was a clear spatial pattern in D. plexippus abundance across the eastern United States, and the spatial clustering of abundance was most strongly correlated with the spatial clustering of water availability. This research suggests that incorporating spatial clustering into analyses of abundance can increase understanding of the factors shaping migratory populations
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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