Research projects
Using Big Data to understand spatial and geographic patterns in ecological processes
Large, spatially extensive, and publicly available ecological datasets are becoming more readily available and offer an opportunity to evaluate the generality or context-dependence of fundamental ecological principles or processes. Using a number of large datasets, particularly from distributed experiments or monitoring studies (such as the Nutrient Network and the National Ecological Observatory Network) I evaluate ecological relationships or processes across systems and geography. This includes diversity-invasibility or diversity-ecosystem function relationships, species area relationships, and the relative roles of environmental filtering vs species interactions in driving community assembly. In particular I am interested in latitudinal patterns in the drivers of community structure and how those can produce large scale patterns such as the Latitudinal Diversity Gradient and how the strengths of different processes may differ between habitat types (e.g., terrestrial vs aquatic systems).
Large, spatially extensive, and publicly available ecological datasets are becoming more readily available and offer an opportunity to evaluate the generality or context-dependence of fundamental ecological principles or processes. Using a number of large datasets, particularly from distributed experiments or monitoring studies (such as the Nutrient Network and the National Ecological Observatory Network) I evaluate ecological relationships or processes across systems and geography. This includes diversity-invasibility or diversity-ecosystem function relationships, species area relationships, and the relative roles of environmental filtering vs species interactions in driving community assembly. In particular I am interested in latitudinal patterns in the drivers of community structure and how those can produce large scale patterns such as the Latitudinal Diversity Gradient and how the strengths of different processes may differ between habitat types (e.g., terrestrial vs aquatic systems).
Predicting spread and impacts of an incipient invasion in Upper Midwest lakes
Nitellopsis obtusa (starry stonewort; SSW) is an invasive freshwater macroalga that has been recently identified in lakes of Minnesota. The alga is in the family Characeae and is a close relative to native Chara and Nitella species, which occupy similar habitats. Unlike native charophytes, N. obtusa can grow in dense mats up to 2m tall having significant nuisance effects on recreational activities. The effects of N. obtusa on native communities (including plants, fish, and invertebrates) are less certain. Relatedly, there is little information on the dynamics of N. obtusa invasions, how spread is influenced by native communities, whether N. obtusa or native species modify the environment in ways that can facilitate or inhibit expansion, or how invasions may be influenced by climate change.
I am studying starry stonewort invasions using a variety of both ecological and social science methods. I am using publicly available data on lake characteristics to develop regional scale habitat suitability models to predict potential invasion risks for starry stonewort. In addition, I have established long-term monitoring stations and protocols to evaluate spread dynamics and the role of competition with native communities. I am also working with collaborators to study stakeholder opinions and preferences around invasions and different control strategies and how to develop the most effective management approaches.
Starry stonewort has also recently been identified in wild rice beds in Leech Lake, MN which could present a significant risk to future wild rice populations. This has led to collaborations with the Leech Lake Band of Ojibwe to establish monitoring protocols, study potential competition between starry stonewort and wild rice, and evaluate the effectiveness of different removal techniques.
Nitellopsis obtusa (starry stonewort; SSW) is an invasive freshwater macroalga that has been recently identified in lakes of Minnesota. The alga is in the family Characeae and is a close relative to native Chara and Nitella species, which occupy similar habitats. Unlike native charophytes, N. obtusa can grow in dense mats up to 2m tall having significant nuisance effects on recreational activities. The effects of N. obtusa on native communities (including plants, fish, and invertebrates) are less certain. Relatedly, there is little information on the dynamics of N. obtusa invasions, how spread is influenced by native communities, whether N. obtusa or native species modify the environment in ways that can facilitate or inhibit expansion, or how invasions may be influenced by climate change.
I am studying starry stonewort invasions using a variety of both ecological and social science methods. I am using publicly available data on lake characteristics to develop regional scale habitat suitability models to predict potential invasion risks for starry stonewort. In addition, I have established long-term monitoring stations and protocols to evaluate spread dynamics and the role of competition with native communities. I am also working with collaborators to study stakeholder opinions and preferences around invasions and different control strategies and how to develop the most effective management approaches.
Starry stonewort has also recently been identified in wild rice beds in Leech Lake, MN which could present a significant risk to future wild rice populations. This has led to collaborations with the Leech Lake Band of Ojibwe to establish monitoring protocols, study potential competition between starry stonewort and wild rice, and evaluate the effectiveness of different removal techniques.
Consequences of displacement of a foundation species by an invasive competitor
The displacement of native species is the most noticeable result of the spread of invasive species; however, the broader community and ecosystem consequences of invasions are less well understood. Even when native and invasive species are ecologically similar, the cascading impacts of a shift in a foundational species can be complex and far-reaching. I have been collaborating with Demian Wilette (LMU), Peggy Fong (UCLA), and Anna Toline (NPS) on an effort to monitor the impacts of an incipient invasion of the seagrass Halophila stipulacea in the Caribbean. Native seagrasses, are important foundational species supporting a complex community but are being displaced by the recently arrived H. stipulacea. We have initiated an effort to monitor the extent of the invasion by assembling an online database of sightings in the region. At Virgin Islands National Park we are monitoring the invasion at a finer spatial scale. There we are measuring the growth of invasive populations and spread to new locations, as well as evaluating the potential community level implications of this shift by studying the ways native and invasive seagrasses are utilized by different members of the community. These efforts will hopefully inform a number of management issues including a comparison of natural and anthropogenic long-distance dispersal processes, prediction of local and regional spread, and decisions about the allocation of management resources.
The displacement of native species is the most noticeable result of the spread of invasive species; however, the broader community and ecosystem consequences of invasions are less well understood. Even when native and invasive species are ecologically similar, the cascading impacts of a shift in a foundational species can be complex and far-reaching. I have been collaborating with Demian Wilette (LMU), Peggy Fong (UCLA), and Anna Toline (NPS) on an effort to monitor the impacts of an incipient invasion of the seagrass Halophila stipulacea in the Caribbean. Native seagrasses, are important foundational species supporting a complex community but are being displaced by the recently arrived H. stipulacea. We have initiated an effort to monitor the extent of the invasion by assembling an online database of sightings in the region. At Virgin Islands National Park we are monitoring the invasion at a finer spatial scale. There we are measuring the growth of invasive populations and spread to new locations, as well as evaluating the potential community level implications of this shift by studying the ways native and invasive seagrasses are utilized by different members of the community. These efforts will hopefully inform a number of management issues including a comparison of natural and anthropogenic long-distance dispersal processes, prediction of local and regional spread, and decisions about the allocation of management resources.
Catastrophic community shifts and resilience in tropical reef ecosystems
In the past few decades many coral reefs across the globe have experienced catastrophic losses of coral and have transitioned to communities dominated by various algal species. Because of the rapidity and extent of these transitions, coral reefs have been used as classic examples of alternate stable states or regime shifts, though this remains contentious. In collaboration with Peggy Fong (UCLA), Tyler Smith (University of the Virgin Islands), and Peter Glynn (University of Miami), I have conducted empirical work quantifying the structure and dynamics of tropical reef communities in Panama and French Polynesia. In particular I have focused on the environmental and ecological factors that control algal populations. This work has included long-term monitoring of benthic and fish communities, manipulative experiments to evaluate the influence of anthropogenic stresses, and numerous small-scale studies of algal population dynamics under different environmental conditions. This work showed that while a variety of anthropogenic stresses can push reefs toward greater algal abundances, the effects are strongly context dependent and there are numerous mechanisms that confer significant resilience to the coral-dominated community.
To develop a more synthetic understanding of the system that could incorporate the complex interactions between processes, I developed a cellular automaton model of the benthic community. Using that model, I have been able to study the dynamics of major community shifts and the role of positive feedback processes in those transitions. This approach links local-scale understanding of specific reef processes to the patterns identified at larger spatial and temporal scales. It also provides a way to evaluate the impacts of external stresses on reefs with different resilience mechanisms. On a theoretical level, by evaluating the model I have been able to evaluate the role of competition and positive-feedbacks in determines in producing phase shift or alternate stable state dynamics.
In the past few decades many coral reefs across the globe have experienced catastrophic losses of coral and have transitioned to communities dominated by various algal species. Because of the rapidity and extent of these transitions, coral reefs have been used as classic examples of alternate stable states or regime shifts, though this remains contentious. In collaboration with Peggy Fong (UCLA), Tyler Smith (University of the Virgin Islands), and Peter Glynn (University of Miami), I have conducted empirical work quantifying the structure and dynamics of tropical reef communities in Panama and French Polynesia. In particular I have focused on the environmental and ecological factors that control algal populations. This work has included long-term monitoring of benthic and fish communities, manipulative experiments to evaluate the influence of anthropogenic stresses, and numerous small-scale studies of algal population dynamics under different environmental conditions. This work showed that while a variety of anthropogenic stresses can push reefs toward greater algal abundances, the effects are strongly context dependent and there are numerous mechanisms that confer significant resilience to the coral-dominated community.
To develop a more synthetic understanding of the system that could incorporate the complex interactions between processes, I developed a cellular automaton model of the benthic community. Using that model, I have been able to study the dynamics of major community shifts and the role of positive feedback processes in those transitions. This approach links local-scale understanding of specific reef processes to the patterns identified at larger spatial and temporal scales. It also provides a way to evaluate the impacts of external stresses on reefs with different resilience mechanisms. On a theoretical level, by evaluating the model I have been able to evaluate the role of competition and positive-feedbacks in determines in producing phase shift or alternate stable state dynamics.
Development of spatially explicit modeling frameworks for analysis of ecological dynamics in complex landscapes
Spatial and geographic features play an important role in the dynamics of ecosystems – altitudinal or latitudinal clines, dispersal barriers, and environmental variability. Yet much ecological theory is still based on the assumption of homogeneous environments and specific landscape level information is rarely applied in management and policy-making. I develop models that explicitly consider the influence on ecological dynamics of heterogeneous environments, feedbacks between populations and their environment, and interspecies interactions. While incorporating complexity into models can be difficult, using spatial structure as an organizing principle for interactions between system components can reduce conceptual and computational challenges, allowing more realistic models to still remain tractable. Working in collaboration with James Forester (University of Minnesota), Nick Jordan (University of Minnesota), Adam Davis (USDA-ARS/University of Illinois), and Natalie West (USDA-ARS), I have developed a spatially explicit model of potential spread of a candidate biofuel crop Miscanthus × giganteus. Using the model I can evaluate invasion risks at different locations and under different management strategies in order to identify best management practices for biofuel production. By exploring different parameter space with the model I also consider more generally how landscape characteristics interact with invader traits to influence invasion dynamics.
I have subsequently expanded and generalized the Miscanthus framework for application in a variety of other contexts. The structure is flexible enough to include multiple species and stage classes, a variety of ecological processes (e.g., growth, dispersal, competition), evolutionary mechanisms (e.g., mutation, selection) or economic concerns (agricultural yields, ecosystem services, costs of eradicating escapes) relevant to regulation of agricultural or natural systems. Current applications have spanned a broad range of topics including modeling movement in multi-trophic systems in African savannahs, evaluating the role of phenotypic plasticity in dispersal traits on plant invasion dynamics, and the design of sustainable agroecosystems that optimize the production of multiple ecosystem services.
Spatial and geographic features play an important role in the dynamics of ecosystems – altitudinal or latitudinal clines, dispersal barriers, and environmental variability. Yet much ecological theory is still based on the assumption of homogeneous environments and specific landscape level information is rarely applied in management and policy-making. I develop models that explicitly consider the influence on ecological dynamics of heterogeneous environments, feedbacks between populations and their environment, and interspecies interactions. While incorporating complexity into models can be difficult, using spatial structure as an organizing principle for interactions between system components can reduce conceptual and computational challenges, allowing more realistic models to still remain tractable. Working in collaboration with James Forester (University of Minnesota), Nick Jordan (University of Minnesota), Adam Davis (USDA-ARS/University of Illinois), and Natalie West (USDA-ARS), I have developed a spatially explicit model of potential spread of a candidate biofuel crop Miscanthus × giganteus. Using the model I can evaluate invasion risks at different locations and under different management strategies in order to identify best management practices for biofuel production. By exploring different parameter space with the model I also consider more generally how landscape characteristics interact with invader traits to influence invasion dynamics.
I have subsequently expanded and generalized the Miscanthus framework for application in a variety of other contexts. The structure is flexible enough to include multiple species and stage classes, a variety of ecological processes (e.g., growth, dispersal, competition), evolutionary mechanisms (e.g., mutation, selection) or economic concerns (agricultural yields, ecosystem services, costs of eradicating escapes) relevant to regulation of agricultural or natural systems. Current applications have spanned a broad range of topics including modeling movement in multi-trophic systems in African savannahs, evaluating the role of phenotypic plasticity in dispersal traits on plant invasion dynamics, and the design of sustainable agroecosystems that optimize the production of multiple ecosystem services.
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