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Browsing by Author "Verhoeven, Michael"

Now showing 1 - 3 of 3
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    Community assembly, invasion, and management of aquatic plant communities
    (2022-12) Verhoeven, Michael
    Determining what mechanisms drive native species declines and what governs their recovery is foundational to understanding community change, and successfully applying this knowledge to limit further losses or restore degraded ecosystems. Efforts to reduce invasive plant populations are often considered critical for halting degradation of native plant communities and fostering their subsequent recovery or restoration. To assess whether management of two invasive plants—Eurasian watermilfoil (Myriophyllum spicatum) and curlyleaf pondweed (Potamogeton crispus)—is likely to foster recovery of native aquatic plant communities, I integrate experimental and observational methods to study community assembly processes in aquatic plants. Chapter 1 builds the foundation for subsequent studies by constructing an observational monitoring database, compiled from more than 500,000 plant observations collected by disparate sources over a 19-year period. In Chapter 2, I use niche models to unpack how patterns of dominance seen in P. crispus and M. spicatum have likely arisen through different mechanisms, predicting direct competition with native species is less likely for P. crispus than M. spicatum. The aquatic plants database is used in Chapter 3 to assess invader control for boosting native plant communities in real-world management projects, with a focus on comparing the two invaders to test predictions from niche models. I show that limitations of monitoring data constrain estimation of causal effects of management. This limits the generalizability of the findings, highlighting the need for more strategic allocation of aquatic plant monitoring efforts and improved tracking of management interventions. In Chapter 4 I synthesize results of a 4-year, in-lake field experiment and the 19-year, statewide observational data, using community assembly theory to ascribe changes in plant communities to three major mechanisms (invader competition, environmental conditions, and regional species pools) and assess the scales at which these mechanisms shape aquatic plant communities. The results highlight complexity and interactivity of community assembly in this system, with mixed evidence for each mechanism and strong differences across scales. This research demonstrates that contrary to common dogma in aquatic plant management, invaders’ relationships with recipient communities are nuanced, and that invader control alone is insufficient to achieve restoration.
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    Complete data and code to generate datasets in: Occurrence and environmental data for aquatic plants of Minnesota from 1999-2018
    (2024-07-15) Verhoeven, Michael; Larkin, Daniel J.; michael.verhoeven.mrv@gmail.com; Verhoeven, Michael; Minnesota Aquatic Invasive Species Research Center (MAISRC); Fisheries Systems Ecology Lab
    A dataset (and multi-scale aggregations thereof) of point-level occurrences, relative abundances, and associated environmental data for macrophytes (freshwater plants) across Minnesota. The data encompass 3,194 surveys of 1,520 lakes and ponds performed over a 19-year timespan. A total of 372,091 points were sampled, across which 231 taxa were recorded. Macrophyte occurrence data and depth, as well as point-level relative-plant-abundance measures for a subset of surveys, were collated, cleaned, and joined to geospatial data and Secchi-depth measurements of water clarity, enabling light availability, a primary control on aquatic plant growth, to be estimated.
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    Cost-Effective Roadside Revegetation Methods to Support Insect Pollinators
    (Minnesota Department of Transportation, 2022-08) Mitchell, Timothy; Verhoeven, Michael; Darst, Ashley; Evans, Elaine; Cariveau, Dan; Snell-Rood, Emilie
    Roadsides contain promising habitat for insect pollinators, yet roadside restorations can be expensive and are rarely evaluated for effectiveness. Where do we establish pollinator-friendly revegetation to maximize benefits? How effective are current revegetation practices at providing habitat for pollinators? We address these questions with two studies. Chapter 2 examines the impact of roadside-adjacent habitat that has been identified as pollinator-friendly for bumble bees. We use pollinator habitat maps to examine associations between the amount of nearby pollinator-friendly habitat and bumble bees (abundance and richness). We also regroup land covers to more specifically align with bumble bee habitat needs and compare the ability of both land cover categorizations to predict bumble bee metrics. This study can help refine predictors in mapping efforts to prioritize locations for pollinator habitat enhancements. Chapters 3 and 4 combine detailed insect and floral surveys of sites with known revegetation history to test efficacy of current revegetation methods for providing habitat for insect pollinators. We show which plants establish after seeding and how communities change as they age. We find that native flowering plants are more likely to establish in roadsides when they are planted, but native and non-native seeded sites converge in the plant community through time. Bumble bee and butterfly abundance and diversity is tied to flowering plant abundance and diversity, regardless of their status as native plants. This work identifies where pollinator-friendly restorations should be implemented and how current seeding practices could be modified to improve benefits to pollinators while reducing costs.