• Shyam Thomas

    Postdoc Researcher, Ryerson University, Toronto

     

    Landscape Ecology - Ecological Modeling - Environmental Conservation

  • About Me

    I am a broadly trained ecologist with a long-standing interest in natural history & conservation. I acquired a BS in Botany & Zoology from St Xavier's college Mumbai (India) and an MS in Plant Ecology from Oklahoma State University under the mentorship of Michael Palmer. After a short stint as Information Officer at the Bombay Natural History Society, I returned to the US to pursue PhD in landscape ecology and modeling in Kirk Moloney's lab at Iowa State University.

     

    After my PhD, I was a postdoc in Matt Daugherty's lab at the University of California Riverside. With Matt and collaborators from USDA, I worked on developing spatiotemporal models aimed at understanding the landscape-level dynamics of a recent insect invasion. Currently, I am a postdoc in Stephanie Melles lab at Ryerson University, Toronto where I am developing geospatial visualization tools and spatial models that improve on our current understanding of mercury contamination in sport fishes. Overall, I consider myself as a spatial ecologist with a bias for conservation-oriented research, irrespective of the system or taxa.

  • Fish Mercury Pollution in Inland Lakes of Ontario

    Mercury in fish is a major environmental concern as it poses a serious health hazard through food consumption. Organic methylmercury found in fish bioaccumulates, such that larger individuals tend to have higher amounts of mercury. Not surprisingly, fish mercury levels are typically predicted as a function of body size. However, several other factors like ambient temperature, precipitation, water chemistry, proximity to pollution sources, trophic position within the aquatic food chain, species richness and composition can further modulate mercury bioaccumulation in fishes. Spatiotemporal variations in mercury bioaccumulation are thus expected. The current project at Ryerson university in collaboration with Ontario Ministry of Environment & Climate Change focuses on understanding these spatiotemporal variations and developing spatially augmented models of fish mercury and body size by incorporating lake-specific covariates, landscape conditions, and broad-scale latitudinal variation.

     

    As part of this project, I work with a large Ontario-wide sport fish monitoring database spanning 45 years (1970-2015). And during the initial phase of this project, I developed an interactive geospatial web application using R shiny and leaflet packages to visualize large amounts of fish mercury data in an efficient manner. An early version of the web app can be found below:

  • Past Research Projects

    Inferring stages of invasion from spatiotemporal patterns of occurrence

    Biological invasions are characterized by dynamic spatiotemporal patterns and associated processes that are most evident at the landscape level. However, landscape-level distribution patterns of invasive species are rarely leveraged to comprehensively understand the process of invasion. Here I address the potential of spatiotemporal distribution patterns in understanding the process of invasion by considering a stage-based approach for an invasive insect. In short, the recent invasion of Asian Citrus Psyllid (ACP is a highly destructive insect pest with a history of invasion in Florida) in South California and the associated spatiotemporal patterns were analyzed to characterize three key stages of invasion .

     

    As part of this (postdoc) research, I worked with a large monitoring database of ACP collected across urban South California. The extensively collected spatiotemporal data on ACP invasion since 2008 provides a unique opportunity to understand an active ongoing invasion process, and characterize key stages of invasion - introduction, establishment, spread, and impact. Using a suite of spatiotemporal analyses and habitat suitability models, the study addresses three key questions: (i) Do major roads serve as long-distance dispersal corridors of ACP introduction in an urban landscape?, (ii) Can habitat suitability models based on presence and abundance information capture ACP's establishment and impact risks, respectively?, and finally (iii) Do the locations predicted as high establishment and high impact risk overlap?

    Effects of aboveground herbivory on plants with stored belowground biomass

    Herbivory is perhaps the most ubiquitous of all ecological interactions with a long history of empirical and theoretical studies. One aspect of herbivory that continues to puzzle researchers is - how sessile plants defend and sustain repeated (often severe) damage caused by herbivores? Tolerance is a well-recognized defense mechanism wherein plants are able to maintain fitness after damage by regrowth, adaptive allocation of resources or through enhanced reproduction. Allocation of biomass to roots in response to aboveground defoliation damage is thus considered common among perennials with large perennating rootstocks.

     

    As part of my PhD research, I developed a theoretical model that explored how temperate perennials with strong seasonality in growth and long-term stored biomass tolerate periodic herbivory by specialist insect folivores. The study addresses how three key plant traits - spring growth from rootstock, post-herbivory regrowth, and eventual allocation of biomass to roots, together affect plant tolerance response and folivore population dynamics. Results from the coupled plant-insect population model indicate that allocation to belowground storage is indeed a critical factor in determining plant's tolerance response, and it also affects folivore population dynamics (Thomas et al. 2017). From an applied perspective, findings suggest that invasive perennials with efficient storage allocation are weakly impacted by defoliating insects, which questions the effectiveness of conventional biocontrol programs.

    Species distribution models: hierarchical effects of land-use & propagule pressure

    Study of species distribution is one of the oldest and central premises in ecology that strives to explain biodiversity patterns in space and time. Earlier, biogeographical studies considered mostly factors such as climate that operate at large spatial scales. Species distributions are now increasingly viewed as an 'emergent' outcome of multiple factors (biotic and abiotic) operating hierarchically in space. Not surprisingly, species distribution models (aka habitat suitability / niche models) now explicitly incorporate ecological factors in a hierarchical framework, wherein effects of various factors are scale dependent (highlighted in above figure).

     

    My PhD dissertation project explored the spatial distribution of an invasive wetland plant - purple loosestrife (inset picture above) by taking a hierarchical approach. My research highlighted that loosestrife invasion across an urban landscape is a complex process wherein three key spatially nested ecological factors - availability of suitable habitat (i.e. wetlands), its spatial neighborhood, and propagule pressure, together explain loosestrife distribution. Predictive invasive species models based on surrounding land-use conditions and propagule pressure further vindicated the significance of incorporating fine-scale processes such as dispersal, since models that included propagule pressure as the eventual nested factor yielded accurate predictions and also minimized the area predicted as high risk of invasion.

    Community ecology & conservation of grassland ecosystems

    Grasslands are interesting ecosystems in that they are largely maintained by a suite of natural disturbances like fire & grazing. Not surprisingly, grasslands have provided a 'natural' platform to study and understand how various disturbances, both natural & anthropogenic, modulate ecological systems. Given the increasing trend in anthropogenic modifications of natural habitats and disturbance-driven establishment of exotic species, understanding the 'ecology of disturbances' is today all the more significant. And, grassland systems continue to provide an ideal ecological setting for this purpose.

     

    My masters research project explored how species diversity and composition respond to disturbances in an Oklahoman tallgrass prairie grassland, through a long-term experimental mowing study. The study highlighted the usefulness of mowing as a restoration tool as it enhances species richness by creating microsites or gaps with high light availability. The study also revealed the confounding effects invasive plant species can have on grassland conservation as disturbances that enhance plant diversity can also facilitate establishment by invasive plants (Dee et al. 2016). Alongside, I also reviewed the literature on the lesser known montane shola-grasslands of Western Ghats, India in an effort to compare the community ecology and conservation lessors learnt and gaps that needs to be filled (Thomas & Palmer 2007).

  • Publications

    (click on journal thumbnails for pdf copy)

    Thomas, S.M. Simmons, G.S., Daugherty, M.P. (2017) Spatiotemporal distribution of an invasive insect in an urban landscape: introduction, establishment and impact Landscape Ecology (in press)

    Bayles, B.R., Thomas, S.M., Simmons, G.S., Grafton-Cardwell, E.E., & Daugherty, M.P. 2017. Spatiotemporal dynamics of the Southern California Asian citrus psyllid (Diaphorina citri) invasion PLoS ONE 12: e0173226

    Thomas, S.M., Abbott, K.C. & Moloney, K.A. 2017. Effects of aboveground herbivory on plants with long-term belowground biomass storage Theoretical Ecology 10: 35-50

    Dee J.R., Thomas, S.M., Thompson S.D. & Palmer M.W. 2016. Long-term late season mowing maintains diversity in a southern US tallgrass prairie invaded by Bothrichloa ischaemum. Applied Vegetation Science 19: 442-453

    Thomas, S.M. & Moloney, K.A. 2015. Combining the effects of surrounding land-use and propagule pressure to predict the distribution of an invasive plant. Biological Invasions17: 477-495

    Thomas, S.M. & Moloney, K.A. 2013. Hierarchical factors impacting the distribution of an invasive species: landscape context and propagule pressure. Landscape Ecology 28: 81-93

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    Always keen to hear from folks with similar interests.

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