The question of group-living in animals has attracted a lot of research attention. Today, we have a nuanced understanding of ultimate explanations and proximate mechanisms for group-living, as well as the genetic basis for seemingly puzzling aspects of sociality such as altruism. However, our current view of sociality has been obtained almost entirely in an intraspecific context, i.e. based on groups consisting of individuals of a single species. On the other hand, heterospecific sociality, i.e. groups formed by individuals of multiple species, has been largely ignored in group-living theory and empirical research. This is despite the fact that heterospecific sociality is widely prevalent in nature and is known to occur in many different contexts, in a variety of taxa and in both marine and terrestrial habitats. My dissertation focuses on one of the best-known examples of heterospecific sociality, namely heterospecific foraging associations of terrestrial insectivorous birds (commonly called mixed-species flocks; flocks hereon). Flocks are found all over the world, in a variety of habitats, and include a unique suite of species in each area. Although flocks are the best-studied among different types of heterospecific associations known, most of the research has been descriptive. In other words, while we have descriptions of the richness, size and composition of flocks from many areas, we know little about why and how flocks form. Therefore, one broad objective of this dissertation was to better understand the causes of flock formation. Birds are thought to join flocks either to obtain direct foraging benefits or better protection from predators. I used different approaches to understand which of these two reasons is likely to be more important. Additionally, to situate heterospecific sociality within sociality in general, I also examined whether the mechanisms underlying flocks are similar to single-species groups or unique to a mixed-species condition. In other words, are flocks a different route to obtain the same benefits as single-species groups, or a route to obtain benefits that conspecifics cannot provide? In the previous section, I described why understanding flocks is important from the point of view of sociality. Flocks are also important for the consequences they might have on community organization. While each flock is a collection of interacting individuals of different species, populations of species are linked in a network of interactions across multiple flocks in an area. The theoretical framework guiding our understanding of community organization is currently dominated by the idea of interspecific competition. Mutualisms or positive interactions, if any, are only expected to occur between members of different trophic levels. Only recently has the need to incorporate positive interactions between members of the same trophic level into ecological theory been emphasized. Flocks and other heterospecific associations present an important example of within-trophic level positive interactions. Therefore, the second broad objective of this dissertation was to examine the consequences of flock formation on community organization. The objectives described above were addressed using multiple approaches in this dissertation. “Why” questions in ecology and evolution are generally tackled using manipulative experiments. Given that experiments are neither feasible nor ethical in the case of multispecies flocks in the wild, I addressed the “why” question by focusing on “who” instead. To understand “why” flocks form, I examined what kinds of species participate in flocks, who associates with whom, and who provides and who receives the benefits. This dissertation uses a combination of methods and data, including questions addressed at a global scale using descriptive information on flocks available from across the world. For other questions that were based on entirely new approaches developed in this dissertation, data were collected in a field site in the Western Ghats. In general, given the two broad objectives of this dissertation, the approaches I used were drawn from both behavioural and community ecology. The dissertation is organized in the following way: Chapter 1: General Introduction The first chapter provides the background to the two broad objectives of this thesis, namely understanding the causes and consequences of heterospecific foraging associations in terrestrial bird communities. Chapter 2 (published in The American Naturalist) Based on a global dataset (55 presence-absence matrices from 24 locations in multiple continents) on the composition of flocks, I asked if flocks largely consist of ecologically similar or dissimilar species. Using null models and randomization tests followed by meta-analysis, I found that the association strength of species in flocks was strongly related to similarity in body size and foraging behaviour, and higher for congeneric compared with non-congeneric species pairs. In other words, flocks seem to consist largely of similar species. Extending group-living and social information use theory to a heterospecific context, I discuss potential behavioral mechanisms leading to positive interactions among similar species in flocks as well as ways in which competition costs are reduced. These findings highlight the need to consider positive interactions along with competition when seeking to explain community organisation. Chapter 3 (published in Animal Behaviour) Two kinds of participants are recognized in flocks: those that join other species (‘followers’) and are therefore likely to be the recipients of the benefits of flock participation and those that are joined (‘leaders’). Through comparative analyses, using a large sample of flocks from around the world, I found (1) ‘followers’ tend to be smaller, more insectivorous, and feed in higher strata than matched species that participate in flocks to a lesser extent and (2) ‘leaders’ tend to be cooperative breeders (which are known to have well-developed anti-predatory systems) more often than matched species that are not known to lead flocks. Furthermore, meta-analyses of published results from across the world showed that bird species in terrestrial mixed-species flocks increased foraging rates and reduced vigilance compared to when they were solitary or in conspecific groups. Moreover, the increase in foraging rates was seen only in the case of flock followers and not flock leaders. These findings suggest a role for predation in the evolution of mixed-species flocking. Species that are vulnerable to predation follow species whose vigilance they can exploit. By doing so, they are able to reduce their own vigilance and forage at higher rates. Chapter 4 (to be submitted to Behavioural Ecology and Sociobiology) In this study, conducted in a tropical evergreen forest in the Western Ghats of India, I used intraflock association patterns to generate a community-wide assessment of benefits of flock participation for different species. I assumed that individuals needed to be physically proximate to particular heterospecific individuals within flocks to obtain any direct foraging benefit (flushed prey, kleptoparasitism, copying foraging locations). Alternatively, for all anti-predation benefits, physical proximity to particular heterospecifics is not required, i.e. just being in the flock vicinity will suffice. Therefore, I used the choice of locations within flocks to infer whether individual species are obtaining direct foraging or antipredation benefits. A small subset of the bird community (5/29 species), composed of all members of the sallying guild, showed non-random physical proximity to heterospecifics within flocks. All preferred associates were from non-sallying guilds, suggesting that the sallying species were likely obtaining direct foraging benefits, either in the form of flushed or snatched prey. The majority of species (24/29) chose locations randomly with respect to heterospecifics within flocks, and thus were likely obtaining anti-predation benefits. In summary, my study indicates that direct foraging benefits are important for only a small proportion of species in flocks and therefore that predation is likely to be the main driver of flocking. Chapter 5 (to be submitted to Oecologia) Two types of species – intraspecifically gregarious and sallying species – are thought to play important roles in flocks because studies have shown they attract other flock participants. However, it is not clear why these types of species are attractive, i.e. are they cues for flocks or do they directly provide benefits to other species? It is also not known whether these types are essential for flock formation. In this study, in a tropical evergreen forest in the Western Ghats of India, I used a novel approach to address these questions. Flocks contain anywhere between two and tens of species. My approach focused on the simplest, i.e. two-species, flocks. In two-species flocks, attraction between species must be based on direct benefit to at least one of the species. Therefore, only species combinations that result in benefit to at least one species will occur as two species flocks. Further, by examining leading and following behaviour in these combinations, I could also determine the direction of benefit-flow. Finally, given that all flocks pass through a two-species step, examining which two-species combinations are joined by other species helped understand species roles in flock formation. I found that intraspecifically gregarious species, but not sallying species, were disproportionately represented in two-species flocks, always provided the benefits when present, and that flocks containing them were joined significantly more often. Therefore, intraspecifically gregarious species, but not sallying species, play a role in providing flock benefits and flock formation. Moreover, given that most (7/8) intraspecifically gregarious species in my study site played these roles, the intraspecifically gregarious species guild can be considered an example of a within-trophic level “keystone”. Chapter 6 (“in press” in Oikos) There is a growing recognition of the need to integrate non-trophic interactions into ecological networks for a better understanding of whole-community organization. To achieve this, the first step is to build networks of individual non-trophic interactions. In this study, I analyzed the network of interdependencies among bird species that participated in flocks in an evergreen forest site in the Western Ghats, India. I found that flock networks contain a small core of highly important species that other species are strongly dependent on, a pattern seen in many other biological networks. Further, I found that structural importance of species in the network was strongly correlated to functional importance of species at the individual flock level. Finally, comparisons with flock networks from other Asian forests showed that the same taxonomic groups were important in general, suggesting that species importance was an intrinsic trait and not dependent on local ecological conditions. Hence, given a list of species in an area, it may be possible to predict which ones are likely to be important. Chapter 7: Conclusions In this section, I provide a summary of the main findings of this dissertation, discuss the main conclusions with regard to each of the two broad objectives and finally suggest future lines of investigation to further understand the causes and consequences of flock formation and heterospecific sociality in general. In summary, the work presented in this dissertation provides a picture of how and why flocks form and their likely consequences for community organization. The main driver of flock formation seems to be protection from predators, although a few species do obtain direct foraging benefits. Additionally, given that I found flocks to largely be groupings of similar species, the mechanisms through which benefits are obtained are likely to be similar to those in single-species groups. In other words, flocks are possibly a way for species that are unable to group with conspecifics, to obtain group-living benefits. My finding, that flocks largely consisted of similar species, also questions the stereotyping of interactions between similar species in communities as competitive. Other results from this study demonstrate the importance of intraspecifically gregarious species in flocks. Such species are the main providers of benefits to other flock participants and seem essential for flock formation. Finally, network analysis showed that a small core of species, mainly including species known to provide benefits at the individual flock level, are disproportionately important in the emergent community-level network of interdependencies. Such species are possibly one of the first examples of within-trophic level “keystones” discovered. Apart from the findings, this study also provides a set of new approaches and analytical frameworks that can be used to examine other multispecies foraging groups and heterospecific foraging associations in other contexts.

Release and combustion of a spray cloud in an atmosphere is a phenomenon encountered in a wide range of applications. For solution of a set of problems which is connected with ecology, theory of combustion and explosion, engine design, fire safety, etc. the knowledge of spray combustion behaviour is required. To investigate the influence of a variety in density and transport coefficients and flame front structure, combustion of pure gas cloud is studied numerically. Combustion of a small-scale spherical pocket of fuel droplets in a calm environment may be considered as a model enabling the transient combustion process to be studied conveniently in one-dimensional geometry. Apart from pure academic interest, such a study provides useful estimations of burning spray cloud characteristics which can be applied for the analysis of more complicated situations. An analytical approach is used to find quasi-steady state distributions of gas temperature and fuel mass fraction for both pure evaporating and burning clouds. This approach is quite fruitful, it gives important qualitative analytical relationships, which help to comprehend the complex process of evaporation or combustion of spray the cloud. Numerical method is used to solve the problem of spray cloud combustion using more common unsteady statement. Two types of ignition are used at the centre or from penphery of cloud. Two types of flames (premixed and diffusion flames) are observed in the numerical simulations. Distributions of all components and temperature are obtained at different moments of time for both types of ignition. The diffusion burning time and total evaporation time are estimated using numerical results.

An Fourier Series solution is presented that describes the simultaneous, one-dimensional, vertical flow of heat and ground water in homogeneous, porous media beneath streams. Use of this analytical solution provides an indirect method of determining vertical flow rates and the effective vertical hydraulic connection between sediments and overlying streams. The method consists of varying the Darcy velocity in the solution until the temperature profiles predicted by the solution match those measured in the field. The method was applied at three field sites in Central Massachusetts. At the first site, which is underlain by lacustrine clay, the vertical flow rate through the clay was determined to be less than 5x10⁻⁷ cm/s and the vertical hydraulic conductivity was less than 0.08 cm/s. The vertical flow rate through mixed sand and gravel underlying the second site equaled 7.5x10⁻⁶ cm/s and vertical hydraulic conductivities of sediments underlying the site ranged from 3.8x10⁻⁴ to 3.1x10⁻³ cm/s. The vertical flow rate through mixed sand and gravel underlying the third site ranged from 3x10⁻⁵ to 7x10⁻⁵ cm/s and vertical hydraulic conductivities of sediments underlying the site ranged from 1x10⁻³ to 4x10⁻³ cm/s. The simultaneous flow of heat and ground water in sediments beneath streams may be more complex than that assumed for the Fourier Series solution. The additional complexity may be partially attributable to two factors: the presence of horizontal ground-water flow, and the presence of thermal conditions near the stream that differ from conditions in the stream itself. The effects of that these two factors have on thermal regimes in sediments beneath streams were investigated using numerical simulations. Results indicate, for example, that under conditions of no horizontal ground-water flow, thermal conditions near the stream can affect temperatures in sediments beneath the stream as far as 900 cm from the stream bank. For horizontal flow rates greater than about 1x10⁻⁴ cm/s, thermal conditions near the stream can affect temperatures in sediments beneath the stream as far as 1500 cm from the stream bank. The method of determining flow rates and hydraulic connection has been applied to stream-aquifer systems. However, the method also may have application in other hydrologic settings. Two such applications might be to determine flow rates to and from lakes and rates of recharge to aquifers.

This research describes a two-dimensional modelling effort of heat and mass transport in simplified intrusive models of sills and their feeder dykes. These simplified models resembled a complex intrusive system such as the Great Dyke of Zimbabwe. This study investigated the impact of variable geometry to transport processes in two ways. First the time evolution of heat and mass transport during cooling was investigated. Then emphasis was placed on the application of convective scavenging as a mechanism that leads to the formation of minerals of economic interest, in particular the Platinum Group Elements (PGEs). The Navier-Stokes equations employed generated regions of high shear within the magma where we expected enhanced collisions between the immiscible sulphide liquid particles and PGEs. These collisions scavenge PGEs from the primary melt, aggregate and concentrate it to form PGEs enrichment in zero shear zones. The PGEs scavenge; concentrate and 'glue' in zero shear zones in the early history of convection because of viscosity and dispersive pressure (Bagnold effect). The effect of increasing the geometry size enhances scavenging, creates bigger zero shear zones with dilute concentrate of PGEs but you get high shear near the roots of the dyke/sill where the concentration will not be dilute. The time evolution calculations show that increasing the size of the magma chamber results in stronger initial convection currents for large magma models than for small ones. However, convection takes, approximately the same time to cease for both models. The research concludes that the time evolution for convective heat transfer is dependent on the viscosity rather than on geometry size. However, conductive heat transfer to the e-folding temperature was almost six times as long for the large model (M4) than the small one (M2). Variable viscosity as a physical property was applied to models 2 and 4 only. Video animations that simulate the cooling process for these models are enclosed in a CD at the back of this thesis. These simulations provide information with regard to the emplacement history and distribution of PGEs ore bodies. This will assist the reserve estimation and the location of economic minerals.

No description available.

Rising temperatures associated with climate change will alter the fundamental physiological processes of most ectothermic species. Drastic changes in catabolic and anabolic reaction rates exert strong effects on growth, reproduction, and consumption rates that cascade up through all levels of the biological hierarchy. This dissertation determined how climate warming might alter the important relationship between plants and insect herbivores, as mediated through changes in herbivore physiology. Consumption and fitness increased with temperature for almost all consumers. However, all consumers also exhibited a critical temperature, beyond which consumption declined rapidly through metabolism continued to increase. This mismatch in metabolic demands and energy intake reduced consumer fitness at high temperatures. Furthermore, increased metabolic nitrogen demand can induce nitrogen limitation in insect herbivores at high temperatures. These basic physiological changes can modify the way herbivores interact with plants in a number of ways. For example, the Japanese beetle, Popillia japonica, altered its feeding behavior on numerous host plant species, depending on host plant quality. Unfortunately, the effects of temperature on plant-herbivore interactions will be difficult to predict, as there was no predictable relationship between consumption and temperature across numerous plant-herbivore pairs. Finally, rising temperatures disrupt insect herbivore control of plant fitness, thereby altering one of the most important components of plant-herbivore interactions. Thus, climate change will fundamentally change the nature of plant-herbivore interactions in the future.

Estuaries are dynamic on many spatial and temporal scales. Distinguishing effects of unpredictable events from cyclical patterns can be challenging but important to predict the influence of press and pulse drivers in the face of climate change. Diatom assemblages respond rapidly to changing environmental conditions and characterize change on multiple time scales. The goals of this research were to 1) characterize diatom assemblages in the Charlotte Harbor watershed, their relationships with water quality parameters, and how they change in response to climate; and 2) use assemblages in sediment cores to interpret past climate changes and tropical cyclone activity. Diatom assemblages had strong relationships with salinity and nutrient concentrations, and a quantitative tool was developed to reconstruct past values of these parameters. Assemblages were stable between the wet and dry seasons, and were more similar to each other than to assemblages found following a tropical cyclone. Diatom assemblages following the storm showed a decrease in dispersion among sites, a pattern that was consistent on different spatial scales but may depend on hydrological management regimes. Analysis of sediment cores from two southwest Florida estuaries showed that locally-developed diatom inference models can be applied with caution on regional scales. Large-scale climate changes were suggested by environmental reconstructions in both estuaries, but with slightly different temporal pacing. Estimates of salinity and nutrient concentrations suggested that major hydrological patterns changed at approximately 5.5 and 3 kyrs BP. A highly temporally-resolved sediment core from Charlotte Harbor provided evidence for past changes that correspond with known climate records. Diatom assemblages had significant relationships with the three-year average index values of the Atlantic Multidecadal Oscillation and the El Niño Southern Oscillation. Assemblages that predicted low salinity and high total phosphorus also had the lowest dispersion and corresponded with some major storms in the known record, which together may provide a proxy for evidence of severe storms in the paleoecological record.

The thesis explores the U.S. early warning system in the context of three separate but interlocking components: emergency management; special needs populations, in this case represented by the Deaf and hard of hearing community; and disaster education. Of importance is the need to bring further understanding to the relevancy of each and how the interrelationship among all three reflects a microcosm illustrative of the larger early warning paradigm and its challenges. Meeting those challenges requires implementation of innovative interventions and evidence-based approaches for adapting to the changing urban and rural demographics, climatological and technological environments. Severe weather and tornado hazard early warning is the embodiment of an integration of multiple systems requiring complex coordination of functions consisting of forecasting, detection, analysis, message development and dissemination, message reception, and action. This culminates in individual decision making for taking self-protection measures. The thesis methodological framework consisted of a mixed method approach. Data collection utilised a survey questionnaire instrument, individual interviews and focus groups. The research questioned if current warning processes within the U.S. tornado early warning system positively integrate with emergency management practices and effectively influence protective actions of the special needs population. Results indicate the emergency management system continues to be institutionally focused and operationally centric. Emergency managers recognise the need to become more of an integrated component between the warning mechanism and the communities they represent. Data indicate the Deaf and hard of hearing population remains underserved and generally ill-prepared for severe weather events. Disaster education programmes addressing their particular needs are scarce and current warning notification processes are often inadequate. Although tornado early warning detection and notification times are increasing, questions remain on how to more effectively encourage individuals to better heed warning messages.

No description available.

Thesis advisor: Heather C. Olins / This study creates a protocol to investigate microplastics in local freshwater wetlands surrounding Boston College. This study also investigated potential plastic-degrading bacteria in the sediment of local freshwater wetlands. A list of potential plastic-degrading bacterial species and genera were compiled from the literature. Using these compiled lists, we searched for these potential plastic-degrading organisms in our metagenomics and 16S datasets. Looking for potential correlations between abiotic factors and the abundance of potential plastic-degrading bacteria, for both data sets, it was found that sandy sediment had a higher abundance of potential plastic-degrading bacteria than non-sandy sediment. Finally, our list of plastic-degrading bacterial species was cross-referenced with a previously compiled list of potential pathogens. Of the 26 taxa in our sites that were identified as potential plastic-degrading bacteria, 57.69% of those taxa are also potentially pathogenic to humans. / Thesis (BS) — Boston College, 2020. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Earth and Environmental Sciences.