Potential distribution and the habitat suitability of the African mustard (Brassica tournefortii) in Tunisia in the context of climate change

The global warming resulting from anthropogenic activities is considered a major threat for the biodiversity in arid and semi-arid regions worldwide. North African countries in western Mediterranean basin, including Tunisia, are expected to experience strong rainfall drop and temperature increase in the next few decades, interrogating the geographical distribution of many plant species in the context of future climate change. Here, ecologically based quantitative climatic envelope model was developed using Maximum Entropy (MaxEnt) to predict current and future distribution of Brassica tournefortii in Tunisia. The data inputs were composed of the species occurrence data and nineteen climatic layers varied over time in line with the predictions created from the global warming scenarios (RCP 4.5 and RCP 6.0) by 2050 and 2070. Using nine uncorrelated variables fitting very well our MaxEnt model, results revealed that the distribution of B. tournefortii was mainly influenced by precipitation-related variables, which contributed with 79.58% in the model, whereas a small contribution was attributed to temperature-related variables (18.20%). Moreover, a noticeable reduction in the current species' range was recorded, compared with that observed during Last Glacial Maximum (LGM). However, the results suggested a small increase in the areas of very highly, highly, and moderately suitable habitats for the species (0.2, 0.28, and 2.41%, respectively) by 2070 under RCP 6.0. Importantly, we found that the habitat suitability of the species, when applying a climate envelope model, was optimal both along the coastal and the dry South-Western zones of the study area. Overall, the results indicated that B. tournefortii exhibits a great tolerance to severe abiotic constraints of southern Tunisia and seemed to be able to survive under future environmental conditions of its adaptation range. These findings can be used to design reasonable exploitation strategies in order to benefit from the ecological and economical values of B. tournefortii.