Browsing by Author "Brown, Bryan L."
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- Abundance Trends and Drivers of Change in Freshwater Fish Communities of the New River BasinSleezer, Logan J. (Virginia Tech, 2020-06-25)Habitat destruction/alteration and non-native species are widely considered the two most serious threats to biodiversity within freshwater ecosystems, which are among the most threatened in the world. I examined the effects of these factors, specifically focusing on land use and non-native species as drivers of abundance patterns of native fishes in the highly invaded and anthropogenically impacted New River basin (NRB) in the Appalachian region of the United States. In chapter 2, I examine current native and non-native species abundance patterns related to the highly variable land-use mosaic present across the NRB, with specific focus on the species-specific effects of intensive land-use practices (agriculture and urbanization) at varying spatial extents (upstream watershed, upstream riparian, and local riparian). In chapter 3, I investigate historical context of basin-wide and site-level abundance spread and decline of natives and non-natives in the upper and middle New River basin (UMNR) over the past 60+ years. Finally, in chapter 4, I partition the variation in native species abundance explained separately by land use and non-native species to determine which factor might be most influential in describing abundance distributions of UMNR native fishes over the past 20+ years. My results indicate widely varying responses of native species to various combinations of intensive land use and non-native species across contributing watersheds and widespread biotic homogenization and native species declines over the past 60+ years. These declines include reductions in unique communities and endemic species provided little consideration or protection under current conservation law. I suggest potential avenues for improvement of conservation actions to help preserve these unique species and communities based on their responses to various land-use and non-native species stressors. My study framework should be broadly applicable to other drainages and should provide opportunities for early identification of potential native species declines and the stressors that may be contributing to them.
- Benthic macroinvertebrate community structure responses to multiple stressors in mining-influenced streams of central Appalachia USADrover, Damion R. (Virginia Tech, 2018-06-25)Headwaters are crucial linkages between upland ecosystems and navigable waterways, serving as important sources of water, sediment, energy, nutrients and invertebrate prey for downstream ecosystems. Surface coal mining in central Appalachia impacts headwaters by burying streams and introducing pollutants to remaining streams including excessive sediments, trace elements, and salinity. Benthic macroinvertebrates are widely used as indicators of biological conditions of streams and are frequently sampled using semi-quantitative methods that preclude calculations of areal densities. Studies of central Appalachian mining impacts in non-acidic streams often focus on biotic effects of salinity, but other types of pollution and habitat alteration can potentially affect benthic macroinvertebrate community (BMC) structure and perhaps related functions of headwater streams. Objectives were: 1) use quantitative sampling and enumeration to determine how density, richness, and composition of BMCs in non-acidic central Appalachian headwaters respond to elevated salinity caused by coal surface mining, and 2) determine if BMC structural differences among study streams may be attributed to habitat and water-quality effects in addition to elevated salinity. I analyzed BMC structure, specific conductance (SC, surrogate measure of salinity), and habitat-feature data collected from 15 streams, each visited multiple times during 2013-2014. BMC structure changed across seasonal samples. Total benthic macroinvertebrate densities did not appear to be impacted by SC during any months, but reduced densities of SC-sensitive taxa were offset by increased densities of SC-tolerant taxa in high-SC streams. Total richness also declined with increasing SC, whereas BMCs in high-SC streams were simplified and dominated by a few SC-tolerant taxa. Taxonomic replacement was detected in high-SC streams for groups of benthic macroinvertebrates that did not exhibit density or richness response, showing that taxonomic replacement could be a valuable tool for detecting BMC changes that are not evident from analyses using conventional metrics. Specific conductance, water-column selenium concentration, large-cobble-to-fines ratio of stream substrate, and relative bed stability were associated with changes in BMC structure. These results suggest multiple stressors are influencing BMCs in mining-influenced Appalachian streams. These findings can inform future management of headwater streams influenced by mining in central Appalachia.
- Characterization and Assessment of Transportation Diversity: Impacts on Mobility and Resilience Planning in Urban CommunitiesRahimi Golkhandan, Armin (Virginia Tech, 2020-06-25)A transportation system is a critical infrastructure that is key for mobility in any community. Natural hazards can cause failure in transportation infrastructure and impede its routine performance. Ecological systems are resilient systems that are very similar to transportation systems. Diversity is a fundamental factor in ecological resilience, and it is recognized as an important property of transportation resilience. However, quantifying transportation diversity remains challenging, which makes it difficult to understand the influence of diversity on transportation performance and resilience. Consequently, three studies are undertaken to remedy this circumstance. The first study develops a novel approach – inspired by biodiversity in ecological stability theory – to characterize and measure transportation diversity by its richness (availability) and evenness (distribution). This transportation diversity approach is then applied to New York City (NYC) at the zip code level using the GIS data of transportation modes. The results demonstrate the variation of transportation diversity across the city. The characterized inherent and augmented complementarities start to uncover the dynamics of modal compensation and to demonstrate how transportation diversity contributes to this phenomenon. Moreover, the NYC zip codes with low transportation diversity are mainly in hurricane evacuation zones that are more vulnerable. Consequently, low transportation diversity in these areas could affect their post-disaster mobility. In the second study, the influence of transportation diversity on post-disaster mobility is examined by investigating the patterns of mobility in New York City one month before and after Hurricane Sandy using Twitter data. To characterize pre- and post-Sandy mobility patterns, the locations that individuals visited frequently were identified and travel distance, the radius of gyration, and mobility entropy were measured. Individuals were grouped according to the transportation diversity of their frequently visited locations. The findings reveal that individuals that lived in or visited zip codes with higher transportation diversity mostly experienced less disturbance in their mobility patterns after Sandy and the recovery of their mobility patterns was faster. The results confirm that transportation diversity affects the resilience of individual post-disaster mobility. The approach used in this study is one of the first to examine the root causes of changes in mobility patterns after extreme events by linking transportation infrastructure diversity to post-disaster mobility. Finally, the third study employs the transportation diversity approach to investigate modal accessibility and social exclusion. Transportation infrastructure is a sociotechnical system and transport equity is crucial for access to opportunities and services such as jobs and infrastructure. The social exclusion caused by transport inequity could be intensified after natural disasters that can cause failure in a transportation system. One approach to determine transport equity is access to transportation modes. Common catchment area approaches to assess the equity of access to transportation modes cannot differentiate between the equity of access to modes in sub-regions of an area. The transportation diversity approach overcomes this shortcoming, and it is applied to all transportation modes in NYC zip codes to measure the equity of access. Zip codes were grouped in quartiles based on their transportation diversity. Using the American Community Survey data, a set of important socioeconomic and transport usage factors were compared in the quartile groups. The results indicated the relationship between transportation diversity and income, vehicle ownership, commute time, and commute mode. This relationship highlighted that social exclusion is linked with transport inequity. The results also revealed that the inequity of the transport system in zip codes with low transportation diversity affects poor individuals more than non-poor and the zip codes with a majority of black and Hispanic populations are impacted more. Further consideration of the impacts of Hurricanes Irene and Sandy in NYC shows that people in areas with a lower transportation diversity were affected more and the transport inequity in these areas made it difficult to cope with these disasters and caused post-disaster social exclusion. Therefore, enhancing transportation diversity should support transport equity and reduce social exclusion under normal situations and during extreme events. Together, these three studies illustrate the influence of transportation diversity on the resilience of this infrastructure. They highlight the importance of the provision and distribution of all transportation modes, their influence on mobility during normal situations and extreme events and their contribution toward mitigating social exclusion. Finally, these studies suggest that transportation diversity can contribute to more targeted and equitable transportation and community resilience planning, which should help decision-makers allocate scarce resources more effectively.
- The cyanobacterium Gloeotrichia echinulata increases the stability and network complexity of phytoplankton communitiesCarey, Cayelan C.; Brown, Bryan L.; Cottingham, Kathryn L. (Wiley-Blackwell, 2017-07-07)Changes in the abundance of a taxon can have large effects on communities, particularly if that taxon is a strong interactor. These changes may arise as a consequence of environmental change, recruitment from dormant stages, or quirks of population dynamics, and have effects that ripple through a community interaction network. We hypothesized that cyanobacteria, which are increasing in many freshwater lakes globally, may be strong interactors because they can exert large and persistent effects on the biomass and composition of other phytoplankton. To test this hypothesis, we evaluated how the phytoplankton community responded to different densities of Gloeotrichia echinulata, a large colonial cyanobacterium increasingly observed in low‐nutrient lakes in northeastern North America, in an in situ mesocosm experiment. We observed that many phytoplankton taxa, especially diatoms and green algae, responded primarily to increased nutrient availability (a result of Gloeotrichia's nitrogen fixation and translocation of phosphorus from the sediments), while a few taxa (two euglenophytes, one dinoflagellate, and one cyanobacterium) responded to both the direct and indirect effects of Gloeotrichia. Surprisingly, Gloeotrichia reduced the compositional variability of the phytoplankton community relative to the non‐Gloeotrichia control treatment; there was no effect on the aggregate temporal variability of total non‐Gloeotrichia biovolume. Moreover, experimentally increased densities of Gloeotrichia coincided with increasing complexity of the phytoplankton community in network analyses of taxon co‐occurrences, as indicated by significantly greater network density and transitivity and shorter path lengths. Taken together, these findings suggest that Gloeotrichia may be a strongly interacting species in low‐nutrient lakes, with the potential to increase the resilience of phytoplankton communities to future disturbance by increasing compositional stability and network complexity.
- The dilution effect in a freshwater mutualism: Impacts of introduced host species on native symbiontsCreed, Robert P.; Bailey, Gretchen L.; Skelton, James; Brown, Bryan L. (Wiley, 2022-01-18)The dilution effect was originally proposed to describe the negative effect of increased host diversity on parasite or pathogen abundance; with greater host diversity, parasite or pathogen levels per host are predicted to be lower due to a higher probability of dispersing parasites or pathogens encountering noncompetent hosts. Dilution effects could occur in many mutualisms if dispersing symbionts encounter hosts that vary in their competence. Introduced, non-native hosts can change the community competence of a local group of host species. Crayfish introductions are occurring world-wide and these introductions are likely disrupting native crayfish-symbiont systems. Branchiobdellidan symbionts declined on native Cambarus crayfish co-occurring with non-native Faxonius crayfish in the New River watershed, USA. We performed an experiment investigating the effect of host density (1 vs. 2 native hosts) and host diversity (1 native host and 1 introduced host) on branchiobdellidan abundance. The introduced Faxonius cristavarius is a noncompetent host for these worms. Six C. ingens were stocked on a Cambarus chasmodactylus in each treatment and worm numbers were followed over 34 days. Worm numbers decreased over time on C. chasmodactylus alone and in the treatment in which a C. chasmodactylus was paired with an F. cristavarius. Worm numbers remained highest in the 2 C. chasmodactylus treatment. There was no effect of host diversity on worm reproduction. Crayfish invasions may have negative effects on mutualistic symbionts depending on the competence of introduced hosts. Loss of native symbionts is one of the potential hidden, negative effects of invasions on native freshwater diversity.
- Disentangling structural and functional responses of native versus alien communities by canonical ordination analyses and variation partitioning with multiple matricesSirbu, Ioan; Benedek, Ana-Maria; Brown, Bryan L.; Sirbu, Monica (Nature Portfolio, 2022-07-27)Freshwaters are under accelerated human pressure, and mollusk communities are among its most sensitive, threatened, and valuable components. To the best of our knowledge, the overall effects of damming, environment, space, time, and invasive alien mollusk species, on structural and functional responses of native mollusk communities were not yet compared. Using historical information and recent data from a river, we aimed to investigate and disentangle these effects and evaluate the differences in structural and functional responses of natives and alien invasives to the same predictors. Variation partitioning showed that alien species were as important predictors as were environmental factors and time in explaining species composition of native freshwater mollusk communities. Aliens were more independent of environmental conditions than natives and responded to different drivers, partially explaining their invasion success. The increased abundance of some alien gastropods was positively related to taxonomic diversity, while certain alien bivalves were negatively associated with the functional diversity of native communities. We introduce a cumulative variation partitioning with multiple response (native and alien) and predictor matrices, along with a diagram to show their relations, advocating for a conceptual shift in future community ecology, from "variables to matrices" and from "multivariate analyses to multi-matrix statistical modeling".
- Disentangling the influence of dispersal on community assembly and stabilityCathey, Sara Elizabeth (Virginia Tech, 2023-01-31)With the introduction of metacommunity theory, the field of community ecology expanded its scope to include patterns and processes beyond the scale of local communities. Dispersal, or the movement of organisms between sites, can play an influential role in generating patterns of community assembly and stability. However, little is known about the role of dispersal in structuring and stabilizing freshwater communities. For my dissertation, I conducted a literature review of dispersal in stream metapopulations and metacommunities. Our current knowledge of the movement of freshwater taxa is limited due to difficulties in accurately monitoring dispersal. We have inferred the role of dispersal based primarily on organismal-based and graph-based proxies, although the body of work in modeling and experimental research is growing. Future research should incorporate innovative methods to directly monitor dispersal at finer spatial and temporal scales. To address this knowledge gap, we experimentally manipulated dispersal mode (aerial and drift) alongside the magnitude of dispersal (network location as a proxy) to investigate the role of these components of dispersal in community assembly and multiple metrics of stability. The results of my experiment suggest both factors may play a role in community assembly and stability patterns in stream metacommunities. Lastly, I conducted a mesocosm experiment with zooplankton mesocosms to investigate if biodiversity can generate asynchronous patterns of community dynamics that contribute to stability. There was a positive biodiversity-asynchrony relationship that, in turn, generated higher levels of stability. This effect was strongest in communities connected via dispersal. Overall, my dissertation demonstrates that dispersal plays a role in the assembly and stability of freshwater communities.
- Dispersal in Stream Networks: Meta-populations and Meta-communitiesCathey, Sara; Brown, Bryan L. (Elsevier, 2022-05-23)Meta-approaches to understanding diversity, including meta-populations and meta-communities, have created a paradigm shift in ecological research, including in stream ecosystems. Both of these frameworks emphasize the major role that organismal dispersal plays in generating and maintaining biodiversity patterns because dispersal links processes at local scales to processes at larger spatial scales. Fundamental to the application of meta-approaches is an understanding of dispersal. Ecologists working in stream systems use various methods to measure or estimate the dispersal of aquatic organisms. More direct measures include mark-recapture techniques and the use of various nets and traps. Due to the difficulty of directly monitoring the dispersal of aquatic organisms, particularly smaller taxa, organismal-based dispersal proxies such as traits-based approaches and population genetics can be used to infer dispersal patterns. Graph-based proxies that rely on the spatial distribution of sampling sites can also be used to infer dispersal in stream networks. While experimental approaches—including the direct manipulation of dispersal—have been employed less often than observational approaches, they have been able to mechanistically link dispersal rates and patterns to patterns in observed biodiversity. Likewise, theoretical approaches that include mathematical and simulation modeling have been able to conduct in silico experiments to test scenarios that are impractical or impossible to conduct in real-world systems. Here we provide a brief introduction to these techniques, highlight some of the insights that they have enabled, and discuss their importance in bringing meta-approaches to the study of stream ecosystems. In this chapter, we provide an introduction to the study of dispersal from the perspective of its importance for meta-approaches in stream ecology that briefly touches on the conceptual importance of studying dispersal and on the techniques used to measure or estimate dispersal. In reviewing literature to include in this article, we chose to focus on fine-scale work performed at a maximum scale of a few adjacent watersheds because these studies best illustrate the approaches and techniques for the study of dispersal. However, a considerable amount of work also exists that applies meta-population and meta-community theory to large-scale biogeographic biodiversity patterns. Thus, our work here is not meant to be an exhaustive review of the literature on dispersal in stream networks, but to serve as an introduction to the various techniques used to understand the dispersal of stream organisms. Additionally, while the focus of this article is mainly dispersal in stream meta-populations and meta-communities, these are relatively new fields of study. Multiple foundational papers on dispersal in stream networks that we included here do not directly address meta-population or meta-communities. These older works are, however, crucial for an introduction to the topic, and the study of dispersal would be much diminished without the groundwork that these works provided.
- Diversity Patterns Associated with Varying Dispersal Capabilities as a Function of Spatial and Local Environmental Variables in Small Wetlands in Forested EcosystemsTornwall, Brett M.; Pitt, Amber L.; Brown, Bryan L.; Hawley-Howard, Joanna; Baldwin, Robert F. (MDPI, 2020-10-29)The diversity of species on a landscape is a function of the relative contribution of diversity at local sites and species turnover between sites. Diversity partitioning refers to the relative contributions of alpha (local) and beta (species turnover) diversity to gamma (regional/landscape) diversity and can be influenced by the relationship between dispersal capability as well as spatial and local environmental variables. Ecological theory predicts that variation in the distribution of organisms that are strong dispersers will be less influenced by spatial properties such as topography and connectivity of a region and more associated with the local environment. In contrast, the distribution of organisms with limited dispersal capabilities is often dictated by their limited dispersal capabilities. Small and ephemeral wetlands are centers of biodiversity in forested ecosystems. We sampled 41 small and ephemeral wetlands in forested ecosystems six times over a two-year period to determine if three different taxonomic groups differ in patterns of biodiversity on the landscape and/or demonstrate contrasting relationships with local environmental and spatial variables. We focused on aquatic macroinvertebrates (aerial active dispersers consisting predominantly of the class Insecta), amphibians (terrestrial active dispersers), and zooplankton (passive dispersers). We hypothesized that increasing active dispersal capabilities would lead to decreased beta diversity and more influence of local environmental variables on community structure with less influence of spatial variables. Our results revealed that amphibians had very high beta diversity and low alpha diversity when compared to the other two groups. Additionally, aquatic macroinvertebrate community variation was best explained by local environmental variables, whereas amphibian community variation was best explained by spatial variables. Zooplankton did not display any significant relationships to the spatial or local environmental variables that we measured. Our results suggest that amphibians may be particularly vulnerable to losses of wetland habitat in forested ecosystems as they have high beta diversity. Consequently, the loss of individual small wetlands potentially results in local extirpations of amphibian species in forested ecosystems.
- Does Stream Size Really Explain Biodiversity Patterns in Lotic Systems? A Call for Mechanistic ExplanationsVander Vorste, Ross; McElmurray, Philip; Bell, Spencer; Eliason, Kevin M.; Brown, Bryan L. (MDPI, 2017-07-08)Understanding drivers of biodiversity is a long-standing goal of basic and applied ecological research. In riverine systems, there remains a critical need to identify these drivers as efforts to manage and protect rivers grow increasingly desperate in the face of global change. We explored one commonly cited potential driver of riverine biodiversity, stream size (e.g., stream order, watershed area, width), using a systematic literature review paired with an analysis of broad-scale macroinvertebrate and fish communities. Of the 165 papers reviewed, we found mostly positive, but no universal, relationship between biodiversity and stream size despite inconsistent use of over 30 measures of stream size. One-third of studies failed to report explanatory mechanisms driving biodiversity–stream size relationships. Across over 4000 macroinvertebrate and fish samples from 1st–8th order streams in the contiguous USA, our analysis showed biodiversity (Shannon diversity, functional diversity, beta diversity) generally increased with measures of stream size. However, because of inconsistent and generally weak relationships between biodiversity and stream size across organismal groups, we emphasize the need to look beyond simple physical stream size measures to understand and predict riverine biodiversity, and strongly suggest that studies search for more mechanistic explanations of biodiversity patterns in lotic systems.
- Ectosymbionts alter spontaneous responses to the Earth’s magnetic field in a crustaceanLandler, Lukas; Skelton, James; Painter, Michael Scott; Youmans, Paul W.; Muheim, Rachel; Creed, Robert P.; Brown, Bryan L.; Phillips, John B. (Nature Publishing Group, 2019-02-28)Magnetic sensing is used to structure every-day, non-migratory behaviours in many animals. We show that crayfish exhibit robust spontaneous magnetic alignment responses. These magnetic behaviours are altered by interactions with Branchiobdellidan worms, which are obligate ectosymbionts. Branchiobdellidan worms have previously been shown to have positive effects on host growth when present at moderate densities, and negative effects at relatively high densities. Here we show that crayfish with moderate densities of symbionts aligned bimodally along the magnetic northeast-southwest axis, similar to passive magnetic alignment responses observed across a range of stationary vertebrates. In contrast, crayfish with high symbiont densities failed to exhibit consistent alignment relative to the magnetic field. Crayfish without symbionts shifted exhibited quadramodal magnetic alignment and were more active. These behavioural changes suggest a change in the organization of spatial behaviour with increasing ectosymbiont densities. We propose that the increased activity and a switch to quadramodal magnetic alignment may be associated with the use of systematic search strategies. Such a strategy could increase contact-rates with conspecifics in order to replenish the beneficial ectosymbionts that only disperse between hosts during direct contact. Our results demonstrate that crayfish perceive and respond to magnetic fields, and that symbionts influence magnetically structured spatial behaviour of their hosts.
- Effects of Freshwater Salinization and Associated Base Cations on Bacterial Ecology and Water QualityDeVilbiss, Stephen Edward (Virginia Tech, 2021-01-05)Anthropogenic freshwater salinization, which is caused by numerous human activities including agriculture, urbanization, and deicing, impacts an estimated 37% of the contiguous drainage area in the United States. High salt concentrations in brackish and marine environments (~1,500 – 60,000 µS cm-1) influence aquatic bacteria. Less is known about the effects of freshwater salt concentrations (≤ 1,500 µS cm-1) on bacterial ecology, despite the pervasiveness of freshwater salinization. Bacteria perform many fundamental ecosystem processes (e.g. biogeochemical cycling) and serve as indicators of human health risk from exposure to waterborne pathogens. Thus, to understand how salt pollution affects freshwater ecosystems, there is a critical need to understand how freshwater salinization is impacting bacterial ecology. Using a series of controlled mesocosm experiments, my objectives were to determine how (1) survival of fecal indicator bacteria (FIB), (2) the diversity of native freshwater bacterial communities, and (3) bacterial respiration and nutrient uptake rates responded across a freshwater salinity gradient of different salt profiles. Survival rates (t90) of Escherichia coli, the EPA recommended freshwater FIB, increased by over 200% as salinity increased from 30 to 1,500 µS cm-1. Survival rates were also significantly higher in water with elevated Mg2+ relative to other base cations, suggesting that different salt sources and ion profiles can have varied effects in FIB survival. Thus, freshwater salinization could cause accumulating concentrations of FIB even without increased loading, increasing the risk of bacterial impairment. Diversity of native bacterial communities also varied across a freshwater salinity gradient, with a general increase in species richness as salinity reached 1,500 µS cm-1. Community variability (β-diversity) was greatest at intermediate salinities of 125 – 350 µS cm-1 and decreased towards the upper and lower extremes (30 and 1,500 µS cm-1, respectively). These diversity patterns suggest that osmotic stress is an environmental filter, but filtering strength is lowest at intermediate salinities causing a change from more deterministic to more stochastic assembly mechanisms. Different salt types also produced distinct bacterial community structures. Lastly, bacterial respiration doubled as salinity increased to 350 – 800 µS cm-1, revealing a subsidy-stress response of bacterial respiration across a freshwater salinity gradient. Corresponding changes in nitrogen and phosphorus uptake increased N:P ratios in ambient water, especially in mesocosms with elevated Ca2+, which could affect nutrient limitation in salinized streams enriched with Ca2+. Bacterial community structure based on Bray-Curtis dissimilarity was not correlated to pairwise changes in respiration rates but was linked to net nitrogen and phosphorus uptake after five days. Collectively, these results establish that freshwater salinization alters bacterial ecology at the individual population, whole community, and ecosystem process scales. Further, different salt types (e.g., CaCl2, MgCl2, NaCl, KCl, sea salt) had varying effects on bacteria at all levels and should be considered when predicting the effects of salinization on freshwater ecosystems. Developing more nuanced salt management plans that consider not only amount, but different types, of salts in freshwaters could help improve our ability to predict human health risk from waterborne pathogens and mitigate/ reduce salinity-induced impacts to freshwater ecosystem processes and services.
- The Effects of Hypoxia on Zooplankton Communities in Lakes and ReservoirsDoubek, Jonathan Patrick (Virginia Tech, 2018-06-19)Global change is altering the community composition, variability, and behavior of organisms in a diverse suite of ecosystems. Because of climate change and eutrophication, freshwater lakes and reservoirs are experiencing an increase in low dissolved oxygen concentrations (hypoxia) in their bottom waters (hypolimnion), which can disrupt ecological communities. Zooplankton, important aquatic organisms for regulating water quality and food webs, are one group of organisms affected by hypoxia since zooplankton need oxygen to respire. My research shows that hypoxia may disrupt zooplankton behavior and increase the variability of zooplankton communities. Zooplankton ubiquitously exhibit diel vertical migration, where the majority of the population resides in the hypolimnion during the daytime to escape predation from fish and damage from ultraviolet radiation. At night, many zooplankton ascend to the surface waters to feed on phytoplankton, when there is decreased risk of predation and radiation. My results from intensive 24-hour sampling campaigns suggest that hypolimnetic hypoxia may alter zooplankton migration, biomass, and behavior, which may in turn exacerbate water quality degradation due to the critical role zooplankton play in freshwater ecosystems. In addition, field surveys in four reservoirs over three years revealed that hypoxia may increase the variability of zooplankton communities compared to oxic conditions. Consequently, as lakes and reservoirs experience increased extent and duration of hypoxia in the future, it is critical to understand how more variable zooplankton communities alter freshwater ecosystem functioning.
- Experimental logging alters the abundance and community composition of ovipositing mosquitoes in the southern AppalachiansHopkins, M. Camille; Thomason, Courtney A.; Brown, Bryan L.; Kirkpatrick, Laila T.; Paulson, Sally L.; Hawley, Dana M. (2018-08)1. The loss of intact forest via logging can influence vector-borne disease dynamics in part by altering the abundance or diversity of mosquito species. Using an experimental field approach, we characterised how two types of logging (clearcut and repeat-entry shelterwood) affected temperate forest mosquito abundance and diversity in southwestern Virginia. 2.From May to September in 2008-2010, infusion-baited gravid traps were used to collect ovipositing female mosquitoes across experimental forest plots that varied in logging treatment. Of the 29680 collected adult female mosquitoes, the three dominant taxa captured were Aedes triseriatus (55%), Aedes japonicus (21%), and Culex pipiens/restuans (20%). 3. Logging treatment had a significant effect on the overall number of female mosquitoes caught per trap night, with lower average abundance of females on both logged treatments relative to two types of unlogged, control plots. When the three most abundant mosquito species were examined separately, logging treatment significantly influenced the abundance of both Aedes species, but did not significantly affect C. pipiens/restuans abundance. 4. Logging treatment did not influence the richness or diversity of mosquito species captured in gravid traps. However, logging treatment significantly altered the multivariate community composition of captured mosquitoes, an effect probably mediated by differential species-specific impacts of logging on abundance. 5. Overall, the results of the present study suggest that the risk of arboviruses transmitted by container-breeding Aedes species may be lower following a logging event in Appalachian forests because of reduced A. japonicus and A. triseriatus abundance with logging.
- A framework for understanding how biodiversity patterns unfold across multiple spatial scales in urban ecosystemsSwan, Christopher M.; Brown, Bryan L.; Borowy, Dorothy; Cavender-Bares, Jeannine; Jeliazkov, Alienor; Knapp, Sonja; Lososova, Zdenka; Padulles Cubino, Josep; Pavoine, Sandrine; Ricotta, Carlo; Sol, Daniel (2021-07)Whether cities are more or less diverse than surrounding environments, and the extent to which non-native species in cities impact regional species pools, remain two fundamental yet unanswered questions in urban ecology. Here we offer a unifying framework for understanding the mechanisms that generate biodiversity patterns across taxonomic groups and spatial scales in urban systems. One commonality between existing frameworks is the collective recognition that species co-occurrence locally is not simply a function of natural colonization and extinction processes. Instead, it is largely a consequence of human actions that are governed by a myriad of social processes occurring across groups, institutions, and stakeholders. Rather than challenging these frameworks, we expand upon them to explicitly consider how human and non-human mechanisms interact to control urban biodiversity and influence species composition over space and time. We present a comprehensive theory of the processes that drive biodiversity within cities, between cities and surrounding non-urbanized areas and across cities, using the general perspective of metacommunity ecology. Armed with this approach, we embrace the fact that humans substantially influence beta-diversity by creating a variety of different habitats in urban areas, and by influencing dispersal processes and rates, and suggest ways how these influences can be accommodated to existing metacommunity paradigms. Since patterns in urban biodiversity have been extensively described at the local or regional scale, we argue that the basic premises of the theory can be validated by studying the beta-diversity across spatial scales within and across urban areas. By explicitly integrating the myriad of processes that drive native and non-native urban species co-occurrence, the proposed theory not only helps reconcile contrasting views on whether urban ecosystems are biodiversity hotspots or biodiversity sinks, but also provides a mechanistic understanding to better predict when and why alternative biodiversity patterns might emerge.
- Getting out of the water and into the air: Understanding aerosolization of the bacterium Pseudomonas syringae from aquatic environmentsPietsch, Renee (Virginia Tech, 2016-05-04)Aquatic environments contain a great diversity of microorganisms, some of which may be aerosolized and transported long distances through the atmosphere. The bacterium Pseudomonas syringae can be found in aquatic environments and in the atmosphere and may express an ice nucleation protein (bacteria expressing the protein are Ice+ and bacteria not expressing the protein are Ice-). Ice+ bacteria may be involved in cloud formation and precipitation processes due to their ability to freeze water at warmer temperatures. Freshwater aerosolization processes are not well understood, particularly the role the Ice+ phenotype may play. Water samples were collected from Claytor Lake, Virginia, USA and screened for Ice+ P. syringae. Results indicated that between 6% and 15% of Pseudomonas colonies assayed were Ice+. Preliminary phylogenetic analysis of cts (citrate synthase) sequences from strains of P. syringae showed a surprising diversity of phylogenetic subgroups present in the lake. A Collison nebulizer was used to aerosolize an Ice+ and an Ice- strain of P. syringae under artificial laboratory conditions. The aerosolization of P. syringae was not influenced by water temperature between 5° and 30°C. In general, the culturability (viability) of P. syringae in aerosols increased with temperature between 5 and 30°C. The Ice+ strain was aerosolized in greater numbers than the Ice- strain at all temperatures studied, suggesting a possible connection between the Ice+ phenotype and aerosol production. A quantitative empirical assessment of aerosolized droplets was generated using a laboratory flume and high-speed video. Droplet diameter and initial velocity upon leaving the water surface were examined at four wind speeds (3.5, 4.0, 4.5, and 5.0 m/s), and the results showed that droplet diameter and velocity had a gamma distribution and droplet mass flux increased exponentially with wind speed. An estimate of the potential amount of bacteria capable of aerosolizing was made for each wind speed. An interdisciplinary unit for advanced high school students has been developed presenting biological aerosolization and ice nucleation. This interdisciplinary work combines modeling and experimental approaches across biology and engineering interfaces, with the goal of increasing our understanding of microbial aerosols from aquatic environments that may impact our planet's water cycle.
- Host specificity and microhabitat preference of symbiotic copepods (Cyclopoida: Clausiididae) associated with ghost shrimps (Decapoda: Callichiridae, Callianideidae)Sepahvand, Vahid; Brown, Bryan L.; Gholamifard, Ali (2020-09-03)We examined the host specificity of two ectosymbiotic Clausidium Kossman, 1874 copepods (Cyclopoida: Clausiididae) on two co-occurrence species of host ghost shrimps. Our results revealed that both species of symbiotic copepod demonstrated extremely high host specificity. Moreover, within a single host shrimp species, each symbiont species displayed strong spatial patterns in microhabitat selection on their hosts' bodies.Clausidium persiaensisSepahvand & Kihara, 2017, was only found on the hostCallianidea typaMilne Edwards, 1837 and almost exclusively within the host shrimp gill chamber, whileC. iranensisSepahvand, Kihara, & Boxshall, 2019 was only found on the hostNeocallichirus jousseaumei(Nobili, 1904) and showed extremely strong preferences for the chelae and anterior walking legs. We also found that while the number of symbionts tends to increase with the host size, the two host species differed in the degree of symbiont infestation, with largeC. typahosting approximately 7x as many symbionts as the similarly sizedN. jousseaumeia. The mechanisms resulting in the observed differences in infestation levels and microhabitat preferences of clausidium copepods among their hosts, including differences in physiology, burrowing pattern, and host grooming behavior should be further investigated.
- Improving the Utility of Artificial Shelters for Monitoring Eastern Hellbender Salamanders (Cryptobranchus alleganiensis alleganiensis)Button, Sky Terryn Christopher (Virginia Tech, 2019-06-20)Artificial shelters show great promise as novel, non-invasive tools for studying hellbenders, but their use thus far has faced several challenges. During initial trials in multiple river networks, artificial shelters routinely became blocked by sediment and dislodged during high stream discharge events, and were rarely used by hellbenders. We sought to determine whether these complications could be overcome via alternative shelter design, placement, and maintenance. Between 2013 and 2018, we deployed 438 artificial shelters of two different designs across ten stream reaches and three rivers in the upper Tennessee River Basin. We assessed evidence for several hypotheses, postulating broadly that the availability, stability, and use of artificial shelters by hellbenders would depend on how shelters were constructed, deployed, and/or maintained. We found that maintaining shelters at least once every 40 days limited sediment blockage, and building ~ 40 kg shelters with 3-4 cm thick walls and recessed lids improved their stability during high discharge events. Additionally, we found that hellbenders most frequently occupied and nested in artificial shelters when they were deployed in deeper (~50+ cm) portions of reaches with high adult hellbender densities. Our results suggest that artificial shelters can serve as effective tools for studying hellbenders when designed, deployed, and maintained with these advancements, but also highlight some limitations of their use.
- Influence of landscape-variation in geochemistry on taxonomic and functional composition of microbial mat communities in the McMurdo Dry Valleys, AntarcticaRisteca, Paul Joseph (Virginia Tech, 2023-06-08)Microbial communities play critical roles in biogeochemical cycles of aquatic and terrestrial ecosystems, but studies of soil microbial communities have been limited by the diversity and complexity found in most ecosystems. Here we report on work investigating the functional diversity of microbial mat and underlying soil communities in the McMurdo Dry Valleys of Antarctica across a gradient of phosphorus availability on glacial tills of distinct age and mineral composition in Taylor Valley, Antarctica. Microbial mat and soil DNA were extracted and sequenced on an Illumina NextSeq500 in a 150 bp paired end format. Raw sequences were uploaded to the MG-RAST server for processing and annotation. Community taxonomic and functional annotation were determined using the RefSeq and SEED Subsystem databases, respectively. The results revealed significant variation in microbial mat community taxonomic composition between the two tills, strongly associated with visual assessment of mat morphology, e.g., "black" and "orange" mats, and soil N:P ratios. The underlying soil microbial communities did not exhibit significant differences in diversity between the two tills, but community composition varied significantly across gradients of soil chemistry, particularly extractable-phosphate content even within tills. The relative abundance of biogeochemistry-relevant pathways determined from the SEED database varied amongst soil microbial communities between the two tills. For example, microbial mat communities exhibited significant variation in the relative abundance of key nitrogen and phosphorus metabolism associated genes strongly associated with the underlying soil N:P. These results suggest that spatial variation in geochemistry influences the distribution and activity of microbial mats, but that the microbial mats themselves also exert a significant homogenizing effect on the underlying soil communities and some of the key biogeochemical processes they facilitate.
- Investigating Historical and Contemporary Land Cover Effects on Macroinvertebrate Communities and Water Quality of Virginia Piedmont StreamsAmos, Katlyn L. (Virginia Tech, 2014-09-17)I investigated the relationships between historical and contemporary land cover and macroinvertebrate communities, water quality, and nutrient levels in 10 streams in a historically agricultural region of the Virginia Piedmont. Historical (1963) and contemporary (2011) impervious surface, open area, and forested cover were evaluated using aerial photos and GIS data. Macroinvertebrates were collected in the fall of 2012 and spring of 2013. Water quality parameters (temperature, conductivity, alkalinity, hardness, and DO) and nutrient concentrations (NH3+NH4, PO4-P, NO3-N, Cl, and SO4) were measured at each site. Overall, forest cover decreased by 6.29%, open area decreased by 1.46%, and impervious surface increased by 4.83% from 1963 to 2011. Macroinvertebrate communities were explored using Principal Coordinates Analysis and were found to be significantly related to 2011 percent impervious surface. Water quality parameters were not significantly related to contemporary or historical land cover. Nitrate was negatively related with 2011 forest cover and positively related with 2011 open area; chloride was positively related with 2011 impervious surface and negatively related with 2011 open area. For the 10 watersheds included in this study, contemporary land cover is a better predictor of macroinvertebrate assemblages and nutrient concentrations than historical land cover.