Environmental Systems Research (Nov 2020)
Present and future suitability of the Lake Tana Biosphere Reserve in Ethiopia for the Nile monitor (Varanus niloticus) using the MaxEnt model
Abstract
Abstract Introduction The Nile monitor (Varanus niloticus) is the largest lizard native to Sub-Saharan Africa along the Nile River. The species inhabits a wide variety of habitats including woodlands, grasslands, mangroves, and swamps. Although the practice is not common in the Lake Tana Biosphere Reserve, the species is being hunted in Sahelian Africa for its leather, food, and pet trade. Consequently, the species is listed under the Convention on International Trade in Endangered Species. Methodology Data collection was based on onsite GIS aided presence recording. Each record of the species was first vetted for data quality. A multicollinearity analysis was conducted before fitting the MaxEnt model to the 19 bioclimatic variables. Since it provides good coverage for Africa, the Hadley Global Environment Model 2-Atmosphere Ocean (HadGEM2-AO) model was used for extracting future climate scenarios. The implementation of change factor was to correct the modeled mean climate from the climate models. The jackknife test was selected to measure the contribution of each environmental predictor variable. Area under the curve of the receiver operating characteristic was used to evaluate the performance of MaxEnt model. Results On average 2750 individuals of Nile monitor were recorded within the Lake Tana Biosphere Reserve. Mean annual temperature, precipitation and temperature were the most important predictors that limit the potential distribution of Nile monitor in the area. Most of the suitable habitats of Nile monitor were mainly predicted in the northern parts of Lake Tana. The ecological niche model produced an average AUC of 0.85. Notable records of the species were found in the vicinity of the lake and the nearby wetlands. Future projection of potential suitable areas revealed that the currently available suitable area to Nile monitor will decline in both 2050 and 2070 under both RCP 6.5 and RCP 8.5, of which the decline in suitable area under the business as usual scenario is the greatest. Conclusion The potential distribution map for Nile monitor in the Lake Tana Biosphere Reserve can help in planning land use management around its existing habitat range, discover new populations or set priorities to restore its natural habitat for more effective conservation. Extensive reductions in the amount of suitable areas under future climate scenarios suggest that the species may become threatened in future if effective conservation measures are not implemented.
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