The Nile monitor lizard [Varanus niloticus (Linnaeus, 1766)] is a generalist carnivore, native to Sub-Saharan Africa and the Nile River but now established in North America as a result of the pet trade. Once introduced, they are a potential invasive threat to native wildlife. Here, I create ensemble species distribution models (SDMs) to predict the global distribution of this generalist carnivore given current and future climate conditions. I then quantify the monitor's potential effects on 85 food webs representing >900 different species within the projected regions based on stomach content data. Climate, vegetation, and elevation data are used for 507 georeferenced observation points from the Nile monitor's native range to produce current and future (2070) ensemble SDMs. Explanatory variables are evaluated as ten alternative models organized in three subsets according to model assumptions. The true skill statistic (TSS), sensitivity, and specificity were used to assess model performance, and the best subset was averaged to represent an ensemble model. Food web impacts after the generalist predator's addition are determined by changes in nine metrics of food web structure. The most predictive (TSS scores ?0.87) ensemble SDM was based on the MARS and FDA algorithms using elevation and climate for current and future conditions. This model shows that, if introduced, Nile monitors will likely spread into many regions in the Americas, the Caribbean, Madagascar, Southeast Asia, and Australia. Assuming unabated carbon emissions by 2070, climate change will enhance that potential range. Adding Nile monitors to food webs generally increases overall trophic links, connectance, link density, and fraction of intermediate taxa, with decreases in the fraction of top and basal taxa. These results are consistent with a generalist predator that affects many species and is likely to affect food web stability. The potential Nile monitor range is vast and encompasses multiple biodiversity hotspots. Given many strong food web interactions by this generalist predator, vulnerable regions should actively prohibit/regulate Nile monitors as pets, enforce those restrictions, and promote exotic pet amnesty programs. Southern US states should especially act soon to prevent spread of the Nile monitor to the Neotropics from its current introduced population in Florida and as released pets.
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Master of Science (M.S.)
College of Sciences
Length of Campus-only Access
Masters Thesis (Open Access)
Bevan, Hannah, "From Pet to Pest? The Potential Global Range and Food Web Effects of a Generalist Carnivore" (2016). Electronic Theses and Dissertations, 2004-2019. 5295.