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, we create ensemble species distribution models (SDMs) to predict the global distribution of this generalist carnivore given current and future climate conditions. We then quantify the monitor’s effect on ≥87 food webs within the projected regions through species addition based on stomach content data. 507 georeferenced observation points were used from the Nile monitor’s native range as well as climate, vegetation, and elevation data for those points to produce current and future (2070) ensemble SDMs. Explanatory variables are evaluated as alternative models, using the true skill statistic (TSS), sensitivity, and specificity to assess model performance. Ten modeling algorithms (in three subsets for optimal pseudo-absence performance) are used to analyze alternative models. Food web impacts after Nile monitor addition are determined by changes in food web connectance, link density, and prey:predator metrics that indicate overall robustness.
Results/Conclusions
The most predictive (TSS scores ≥0.87) ensemble SDM was based on elevation and climate for current and future conditions. If introduced, this projection shows that Nile monitors will likely invade many regions in the Americas, the Caribbean, Madagascar, Southeast Asia, and Australia. Assuming unabated carbon emissions, climate change will enhance its potential range by 2070. Food web analyses in both native and invasive ranges show minor increases in overall connectance and link density due to the Nile monitor, with decreases in prey:predator (some <1 consistent with food web instability); further analyses of food webs will relate changes in these metrics to food web stability and invasive status of the generalist carnivore. The potential Nile monitor range is vast and encompasses multiple biodiversity hotspots. If this large generalist carnivore is invasive, vulnerable regions should actively prohibit/regulate Nile monitors as pets, enforce those restrictions, and promote exotic pet amnesty programs. US states bordering Mexico should especially act soon to prevent introduction to the Neotropics.