Publications

Research manuscripts from students and faculty in the Center for Environmental Studies.  Student co-authors are indicated with (§) for undergraduates and () for graduates.

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McGarvey DJ, Faris SE. 2019An Arts-based approach to Science Communication Training. Scientia https://doi.org/10.26320/SCIENTIA311.

Undergraduate Author(s)
Rapid growth in the number and diversity of digital media outlets is creating novel opportunities to increase public engagement with science. Dr Daniel J. McGarvey and Sarah E. Faris, working at Virginia Commonwealth University, have developed an interdisciplinary training program that teaches STEM graduate students to use digital media to effectively communicate scientific topics to general audiences.
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Woods‡ T, McGarvey DJ2018Assessing the relative influences of abiotic and biotic factors on American eel Anguilla rostrata distribution using hydrologic, physical habitat, and functional trait data Ecography 41:1-13. https://doi.org/10.1111/ecog.03782.

Graduate Author(s)
Species’ distributions are influenced by abiotic and biotic factors but direct comparison of their relative importance is difficult, particularly when working with complex, multi‐species datasets. Here, we compare the relative effects of hydrology, physical habitat, and co‐occurring fish functional traits on the contemporary (1950–1990) distribution of the American eel Anguilla rostrata in six Mid‐Atlantic (USA) rivers. To do so, we implement a null model approach that compares conditions at sites of known American eel presence to a random sample of sites throughout a broader landscape, allowing us to identify variables that may have the strongest influences on American eel distribution. Results suggest that, within this subset of the American eel's geographic range, the functional characteristics of locally co‐occurring fishes and habitat fragmentation by dams may have the strongest influences on American eel distribution, compared to other predictor variables included in the analysis. Given the widespread distribution and complex biology of this species, we caution that our results may not apply to all American eel subpopulations or life stages. Nonetheless, the observed importance of co‐occurring fish functional traits may inform American eel conservation and, more generally, provide a means to incorporate biotic influences in research on species’ distributions.
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Haber Lisa T2018Forest Structural Complexity and Net Primary Production Resilience Across a Gradient of Disturbance in a Great Lakes Ecosystem MS Thesis https://scholarscompass.vcu.edu/etd/5277/.

Graduate Author(s)
Forests are an important component of the global carbon (C) cycle and contribute to climate change mitigation through atmospheric C uptake and storage in biomass and soils. However, the forest C sink is susceptible to disturbance, which modifies physical and biological structure and limits spatial extent of forests. Unlike severe, stand-replacing disturbances that reset forest successional trajectories and may simplify ecosystem structure, moderate severity disturbances may instead introduce complexity in ways that sustain net primary production (NPP), leading to the phenomenon of “NPP resilience.” In this study, we examined the linkage between disturbance severity and ecosystem biological and physical structural change, and implications for NPP within an experimentally disturbed forest in northern Michigan, USA. We computed spatially resolved and spatially agnostic metrics of forest biological and physical structure before and 10 years after disturbance across a continuum of severity. We found that while biological structure did not change in response to disturbance, three of four physical structural measures increased or were unimodally related to disturbance severity. Physical structural shifts mediated by disturbance were not found to directly influence processes coupled with NPP. However, decadal changes in the spatial aggregation index of Clark and Evans, though not a function of disturbance severity, were found to predict canopy light uptake, leaf physiological variability, and relative NPP within plots. We conclude that ecosystem structural shifts across disturbance severity continua are variable and differ in their relationship to NPP resilience.
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Kramer GR, Andersen DE, Buehler DA, Wood PB, Peterson SM, Lehman JA, Aldinger KR, Bulluck LP, Harding S, Jones JA, Loegering JP, Smalling C, Vallender R, Streby HM.2018Population trends in Vermivora warblers are linked to strong migratory connectivity Proceedings of the National Academy of Sciences 14:E3192-E3200. https://doi.org/10.1073/pnas.1718985115.

Migratory species can experience limiting factors at different locations and during different periods of their annual cycle. In migratory birds, these factors may even occur in different hemispheres. Therefore, identifying the distribution of populations throughout their annual cycle (i.e., migratory connectivity) can reveal the complex ecological and evolutionary relationships that link species and ecosystems across the globe and illuminate where and how limiting factors influence population trends. A growing body of literature continues to identify species that exhibit weak connectivity wherein individuals from distinct breeding areas co-occur during the nonbreeding period. A detailed account of a broadly distributed species exhibiting strong migratory connectivity in which nonbreeding isolation of populations is associated with differential population trends remains undescribed. Here, we present a range-wide assessment of the nonbreeding distribution and migratory connectivity of two broadly dispersed Nearctic-Neotropical migratory songbirds. We used geolocators to track the movements of 70 Vermivora warblers from sites spanning their breeding distribution in eastern North America and identified links between breeding populations and nonbreeding areas. Unlike blue-winged warblers (Vermivora cyanoptera), breeding populations of golden-winged warblers (Vermivora chrysoptera) exhibited strong migratory connectivity, which was associated with historical trends in breeding populations: stable for populations that winter in Central America and declining for those that winter in northern South America.
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DeSaix MG2018Migratory patterns and population genetic structure in a declining wetland-dependent songbird MS Thesis https://scholarscompass.vcu.edu/etd/5432/.

Graduate Author(s)
Understanding migratory connectivity is essential for assessing the drivers behind population dynamics and for implementing effective management in migratory species. Genetic markers provide a means to describe migratory connectivity, as well as incorporate population genetic analyses, however genetic markers can be uninformative for species with weak genetic structure. In this study, we evaluate range-wide population genetic structure and migratory connectivity in the prothonotary warbler, Protonotaria citrea, a wetland-dependent neotropical migratory songbird, using high-resolution genetic markers. We reveal regional genetic structure between sampling sites in the Mississippi River Valley and the Atlantic Seaboard with overall weak genetic differentiation among populations (FST = 0.0051). By ranking loci by FST and using subsets of the most differentiated genetic markers (200 – 3000), we identify a maximum assignment accuracy (89.7% to site, 94.3% to region) using 600 single nucleotide polymorphisms. We assign samples from unknown origin nonbreeding sites to a breeding region, illustrating weak migratory connectivity between prothonotary warbler breeding and nonbreeding grounds. Our results highlight the importance of using high-resolution markers in studies of migratory connectivity with species exhibiting weak genetic structure. Using similar techniques, studies may begin to describe population genetic structure that was previously undocumented, allowing us to infer the migratory patterns of an increasing number of species.
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Fernandez L, Mukherjee M, Scott T2018The effect of conservation policy and varied open space on residential property values: A dynamic hedonic analysis Land User and Policy 73:480-487. https://doi.org/10.1016/j.landusepol.2017.12.058.

We investigate open space value in an ideal setting for a natural experiment between Riverside County, with an open space conservation policy, and neighboring San Bernardino County without the policy. With spatial econometrics, time series and spatial data, this study accounts for both spatial and temporal variation of open space values. The novelty of our paper is that we combine an investigation of the effect of open space proximity on residential property value with an analysis of the effect of endangered species habitat preservation policy distinguishing between types of open space (wild habitat for endangered species versus developed parks) in a two county study. We find that proximity to open space has a positive and statistically significant influence on increased value of residential real estate, with some distinction among type of open space between the counties. Conservation policy for open space with wild habitats contributes to increased value of this amenity in Riverside County.
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Miles LS, Johnson JC, Dyer RJ, Verrelli BC2018Urbanization as a facilitator of gene flow in a human health pest. Molecular Ecology https://doi.org/10.1111/mec.14783.

Graduate Author(s)
Urban fragmentation can reduce gene flow that isolates populations, reduces genetic diversity and increases population differentiation, all of which have negative conservation implications. Alternatively, gene flow may actually be increased among urban areas consistent with an urban facilitation model. In fact, urban adapter pests are able to thrive in the urban environment and may be experiencing human‐mediated transport. Here, we used social network theory with a population genetic approach to investigate the impact of urbanization on genetic connectivity in the Western black widow spider, as an urban pest model of human health concern. We collected genomewide SNP variation from mitochondrial and nuclear ddRAD sequence datasets from 210 individuals sampled from 11 urban and 10 non‐urban locales across its distribution of the Western U.S. From urban and non‐urban contrasts of population, phylogenetic, and network analyses, urban locales have higher within‐population genetic diversity, lower between‐population genetic differentiation, and higher estimates of genetic connectivity. Social network analyses show that urban locales not only have more connections, but can act as hubs that drive connectivity among non‐urban locales, which show signatures of historical isolation. These results are consistent with an urban facilitation model of gene flow, and demonstrate the importance of sampling multiple cities and markers to identify the role that urbanization has had on larger spatial scales. As the urban landscape continues to grow, this approach will help determine what factors influence the spread and adaptation of pests, like the venomous black widow spider, in building policies for human and biodiversity health.
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Djukic I, et al.2018Early stage litter decomposition across biomes Science of the Total Environment 628-629:1369-1394. https://doi.org/10.1016/j.scitotenv.2018.01.012.

Undergraduate Author(s)
Through litter decomposition enormous amounts of carbon is emitted to the atmosphere. Numerous large-scale decomposition experiments have been conducted focusing on this fundamental soil process in order to understand the controls on the terrestrial carbon transfer to the atmosphere. However, previous studies were mostly based on site-specific litter and methodologies, adding major uncertainty to syntheses, comparisons and meta-analyses across different experiments and sites. In the Tea Composition Initiative, the potential litter decomposition is investigated by using standardized substrates (Rooibos and Green tea) for comparison of litter mass loss at 336 sites (ranging from -9 to +26 degrees C MAT and from 60 to 3113 mm MAP) across different ecosystems. In this study we tested the effect of climate (temperature and moisture), litter type and land-use on early stage decomposition (3 months) across nine biomes. We show that litter quality was the predominant controlling factor in early stage litter decomposition, which explained about 65% of the variability in litter decomposition at a global scale. The effect of climate, on the other hand, was not litter specific and explained <0.5% of the variation for Green tea and 5% for Rooibos tea, and was of significance only under unfavorable decomposition conditions (i.e. xeric versus mesic environments). When the data were aggregated at the biome scale, climate played a significant role on decomposition of both litter types (explaining 64% of the variation for Green tea and 72% for Rooibos tea). No significant effect of land-use on early stage litter decomposition was noted within the temperate biome. Our results indicate that multiple drivers are affecting early stage litter mass loss with litter quality being dominant. In order to be able to quantify the relative importance of the different drivers over time, long-term studies combined with experimental trials are needed.
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Najjar RG, Herrmann M, Alexander R, Boyer EW, Burdige DJ, Butman D, Cai WJ, Canuel EA, Chen RF, Friedrichs MAM, Feagin RA, Griffith PC, Hinson AL, Holmquist JR, Hu X, Kemp WR, Kroeger KD, Mannino A, McCallister, SL, et al.2018Carbon budget of tidal wetlands, estuaries, and shelf waters of eastern North America Global Biogeochemical Cycles 32:389-416. https://doi.org/10.1002/2017GB005790.

Carbon cycling in the coastal zone affects global carbon budgets and is critical for understanding the urgent issues of hypoxia, acidification, and tidal wetland loss. However, there are no regional carbon budgets spanning the three main ecosystems in coastal waters: tidal wetlands, estuaries, and shelf waters. Here we construct such a budget for eastern North America using historical data, empirical models, remote sensing algorithms, and process‐based models. Considering the net fluxes of total carbon at the domain boundaries, 59 ± 12% (± 2 standard errors) of the carbon entering is from rivers and 41 ± 12% is from the atmosphere, while 80 ± 9% of the carbon leaving is exported to the open ocean and 20 ± 9% is buried. Net lateral carbon transfers between the three main ecosystem types are comparable to fluxes at the domain boundaries. Each ecosystem type contributes substantially to exchange with the atmosphere, with CO2uptake split evenly between tidal wetlands and shelf waters, and estuarine CO2outgassing offsetting half of the uptake. Similarly, burial is about equal in tidal wetlands and shelf waters, while estuaries play a smaller but still substantial role. The importance of tidal wetlands and estuaries in the overall budget is remarkable given that they, respectively, make up only 2.4 and 8.9% of the study domain area. This study shows that coastal carbon budgets should explicitly include tidal wetlands, estuaries, shelf waters, and the linkages between them; ignoring any of them may produce a biased picture of coastal carbon cycling.
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Leach TH, Winslow LA, Acker FW, Bloomfield JA, Boylen CW, Bukaveckas PA, Charles DF, Daniels RA, Diriscoll CT, Eichler LW, et al.2018Long-term dataset on aquatic responses to concurrent climate change and recovery from acidification Scientific Data 5:180059. https://doi.org/10.1038/sdata.2018.59.

Concurrent regional and global environmental changes are affecting freshwater ecosystems. Decadal-scale data on lake ecosystems that can describe processes affected by these changes are important as multiple stressors often interact to alter the trajectory of key ecological phenomena in complex ways. Due to the practical challenges associated with long-term data collections, the majority of existing long-term data sets focus on only a small number of lakes or few response variables. Here we present physical, chemical, and biological data from 28 lakes in the Adirondack Mountains of northern New York State. These data span the period from 1994-2012 and harmonize multiple open and as-yet unpublished data sources. The dataset creation is reproducible and transparent; R code and all original files used to create the dataset are provided in an appendix. This dataset will be useful for examining ecological change in lakes undergoing multiple stressors.

 

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